Anatomy Exam 3 Study Guide

Chapter 15, Brain and Cranial Nerves General Information

• Brain composed of four major regions: cerebrum, diancephalon, brainstem, and cerebellum

• Size doe not equal intelligence, though – it’s all about the WIRING • Better wiring, higher intelligence – neuronal pools* • Wiring simply refers to neuronal pool and circuits. • Men have larger brains than women do

Brain Development and Tissue Organization

• Anterior and rostral are synonymous – means towards the nose (front) • Posterior and caudal are synonymous – means towards the tail (back) • Elevation referred to as a gyrus • Depression called a sulcus, • Fissure is a really deep depression. • 4 major regions: cerebrum, diancephalon, brainstem, cerebellum

Structure of the brain

• Look at just the cerebrum (pink portion), have five distinct regions • Frontal, parietal, occipital, temporal, and insula lobes

• Diancephalon: region around the structures that make up the third ventricle • Hypothalamus, thalamus, epithalamus

• Brain stem • Midbrain region: pons, medulla oblongata, spinal cord • Little brain, or cerebellum • Lessencephaly: born without gyrus and sulcus, smooth brain

• Very flat, no extra area, these individuals usually are severely mentally retarded and suffer from seizures

• Longevity depends on the amount of smooth brain they have. Embryonic Development of the Brain

• Brain looks like a mushroom with a cap and a stem, cerebellum too. • Brain begins growing from the cranial (superior) part of the neural tube

• Undergoes disproportionate growth rates in different regions • Embryonic and fetal periods the telencephalon has rapid growth and envelops

diencephalon • Surface becomes folded, especially in the telencephalon, leading to

formation of gyrus and sulcus. • Together, the bends creases and folds in the telencephalon are necessary to

fit the massive amounts of brain tissue within the confines of the cranial cavity.

• Restricted by membranous skull • Observe 2 main flexures that bend brain toward brain stem

• Midbrain & cervical • Convolutions form

• Creases & folds Organization of Neural Tissue Areas

• Mantel of grey matter in the brain: cell body location, on outside in the brain, medulla, cerebellum

• Deep brain matter • White brain matter: myelinated axons are present in the neurons. • Gray matter: houses motor neuron and internueron cell bodies, dendrites,

telodendria, and unmyelinated axons. o External layer of grey matter is called the cerebral cortex: covers the

entire surface of most of the adult brain. • White matter: derives its color from the myelin in the myelinated axons.

o Within the masses of white matter, the brain contains discrete, internal gray matter called cerebral nuclei

§ Oval, spherical shaped clusters of neuron cell bodies. § Remember: ganglion is a cluster of cell bodies in the PNS

Support and Protection of the Brain

• Endothelium: simple squamous cells that make up the capillaries • Cranium: provides rigid support • Meninges: protective CT membranes that surround, support, stabilize, and

partition parts of the brain. • 3 connective tissue layers that separate the soft tissue of the brain from the

bones of the cranium • They also enclose and protect blood vessels that supply the brain • They also contain and circulate CSD • Some parts of the cranial meninges form some of the veins that drain

blood from the brain. • CSF: cushioning fluid in the brain • Blood brain barrier: prevents harmful materials from leaving the bloodstream.

Cranial Meninges

• Inner-most layer: Pia mater o Thin, areolar layer o Highly vascularized o Tightly adheres to the brain, following every contour of the surface

• Middle layer: arachnoid mater, lies underneath the dura mater and external to the pia mater

o Arachnoid refers to the fact that it resembles a spider web § Delicate web of collagen and elastic fibers known as arachnoid

trabeculae

o Subarachnoid space is deep to the arachnoid mater § Arachnoid trabeculae (filled with CSF) extend through this space

from the arachnoid mater to the underlying pia mater. § Brown and spongy

• Outermost layer: Dura mater o Subdural space: POTENTIAL space between the overlying dura mater and

the arachnoid mater § If blood or fluid accumulates here it becomes a space and a subdural

hematoma can form. o Dura mater is the external, tough, dense irregular CT with two fibrous layers

§ Periosteal layer: more superficial layer, forms the periosteum on the internal surface of the cranial bones

§ Meningeal layer: lies deep to the periosteal layer • Fused to the periosteal layer except in specific areas where the

two layers separate to form the dural venous sinuses: large veins that simply function to drain blood from the brain and transport this blood to the internal jugular veins that help drain blood circulation of the head.

o Meningeal layer of the dura mater extends as flat partitions known as septa

into the cranial cavity in four locations. These double layers of dura mater = cranial dura septa. • Separate specific parts of the brainand provide stabilization and support to

the entire brain. • Falx cerebri: largest if the four dural septa, located in the midsagittal

plane, projects into the longitudinal fissure between left and right cerebral hemispheres.

• Tentorium cerebelli: separates the occipital and parietal, horizontally oriented fold of a dura mater.

• Falx cerebelli: divides the cerebellum into the left and right halves • Arachnoid granulation (villa)

Brain Ventricles

• Ventricles are simply fluid filled cavities within the brain • Remnants from the embryonic cavities, like from the lumen of the neural

tube. • Continuous with one another as well as with the central canal of the spinal cord

they connect with. • Four ventricles in the brain

• 2 lateral ventricles in the cerebrum • Lateral ventricles communicate with the third ventricle through

and opening called the intervertebral foramen. • Third ventricle in the diancephalon

• The cerebral aqueduct (narrow canal) connects the third and fourth ventricles.

• Fourth ventricle located between the ponds/medulla and cerebellum

• They all drain into the third and fourth ventricles • Lined by ependymal cells that create CSF

• Means that all the ventricles contain CSF • Connect with the subarachnoid space

Cerebrospinal Fluid

• Buoyancy: Brain wouldn’t be able to hold its own weight without the CSF • Would simply sink through the foramen magnum

• Protection: CSF provides a liquid cushion to protect delicate neural structures from sudden movements.

• When you try to walk quickly in a swimming pool, your movements are slowed as the water acts as a movement buffer.

• CSF helps to slow movements of the brain if the skull and or body move suddenly/forcefully.

• When changes occur, brain can go into shock • Stability: The CSF optimizes the environment

• Transports nutrients and chemicals to the brain • Removes waste products from the brain • Protects nervous tissue from chemical fluctuations that would disrupt

neuron function • Waste products and excess CSF transported into venous circulation

• Eventually filtered from the blood and secreted in urine. CSF Formation

• Formed in the choroid plexus, which hangs from the roof of ventricles. • Choroid plexus is made of a layer of ependymal cells and the capillaries

that lie within the pia mater. • CSF is produced by secretion of a fluid from the ependymal cells that originate

from the blood plasma. • Similar to blood plasma, but different in ion concentrations.

• Choroid plexus is found especially in the lateral and fourth ventricles. CSF Circulation

• CSF circulates through and eventually leaves the ventricles, entering the subarachnoid space.

• There is often excess CSF as the volume ranges from 100 mL to 160 mL • This is removed from the subarachnoid space so the fluid will not accumulate and

compress and damage nervous tissue. • Arachnoid villa: fingerlike extensions of arachnoid mater that project into the

dural venous sinuses • Excess CSF move across the arachnoid villi to return to the blood within

the dural venous sinuses. • Cells overlap and when pressure builds, it releases fluid into circulation by

opening the flaps!

CSF Circulation Steps • CSF produced by choroid plexus in ventricles • CSF flows from third ventricle through cerebral aqueduct to fourth ventricle • CSF from fourth ventricle flows into subarachnoid space by passing through some

aperatures, and into the central canal of the spinal cord. • As the CSF moves through subarachnoid space, it removes waste products and

provides buoyancy to support the brain. • Excess CSF flows into arachnoid villi, then drains into the dural venous sinuses.

• When the pressure exerted on the arachnoid villi is greater than that of blood pressure, the arachnoid villi extending into the dural venous sinuses provide a conduit for a one-way flow of excess CSF to be returned into the blood within the dural venous sinuses.

Blood-Brain Barrier

• Protective mechanism o Isolates brain from general circulation o Maintains stable environment

• Hypothalamus and vomiting center do NOT have a blood brain barrier • Easy access to neural tissue

• Nervous tissue is protected from general circulation from the brain blood barrier • Regulates what substances can enter the interstitial fluid of the brain. • Keeps neuron in the brain from being exposed to some normal substances, drugs,

waste product, and variations in levels of normal substances that could adversely affect brain function.

• Capillary endothelial cells contribute to blood brain barrier • The continuous basement membrane of the endothelial cells create tight

junctions between adjacent endothelial cells • This reduces capillary permeability and prevents materials from

diffusing across the capillary wall • Fused basement membranes make a thick basal lamina • Astrocytes have perivascular feet – act as gatekeepers that permit materials to

pass to the neurons after they leave the capillaries. • Selective, rather than an absolute barrier

• Small, nonpolar, lipid soluble • Observe select regions where the blood-brain barrier is absent allowing easy

access to neural tissue

Cerebrum

• Cerebrum is the location of conscious thought processes and the origin of all complex and intellectual functions.

• Identified as the two large hemispheres on the superior aspect of the brain. • Center of intelligence, reasoning, sensory perception, thought, memory,

judgment, etc.

• Cerebrum is composed of two halves called the left and right cerebral hemispheres.

• Longitudinal fissure extends along the midsagittal plane and separates the two hemispheres.

• Two regions are distinct except at a few location where bundles of axons (tracts) form white matter region that allow for communication between them.

• Largest of these white matter tracts is the corpus callosum • In most cases, it is difficult to assign precise function to a specific regions of the

cerebral cortex. • With a few exceptions, both cerebral hemisphere receive their sensory

information from and project motor commands to the OPPOSITE SITE OF THE BODY.

• Right cerebral hemisphere controls the left side of the body and vice versa. • Both hemispheres receive sensory information from and project motor

commands to the OPPOSITE SIDE OF THE BODY IT COMES IN ON • Appear as anatomic mirror images, but display some functional differences

(hemispheric lateralization) • Portions of brain responsible for speech and understanding are located in

the left hemisphere • Differences primary affect higher order functinos.

Primary Somatosensory Cortices

• Motor and sensory humunculi: body maps, illustrate the topography of the primary motor cortex and the primary somatosensory motor cortex. • Figure of the body depicts nerve distributions • The size and location of each body region indicates relative innervation

• Motor homunculus: innervation of the primary motor cortex (frontal lobe) to

various body part. • Hand muscles much larger area of the cortex than trunk

• More motor activity is denoted to the hand in humans than other animals because our hands are adapted for fine, precise movements needed to manipulate the environment

• Many motor units are devoted to muscles that move the hand and fingers.

• Sensory homunculus: traced on the postcentral gyrus (pariental lobe), similar to motor humunculus.

• Surface area of somatosensory cortex devoted to a body region indicates the amount of sensory information collected at that region.

• Lips, fingers, gentials occupy larger protions than the trunk with fewer receptors.

Central White Matter

• Lies deep to the grey matter of the cerebral cortex and is composed of primarily myelinated axons.

• Remember: cerebral cortex is the outer layer of the cerebrum composed of folded grey matter.

• Most of these axons are grouped into bundles called tracts with different classifications

• Association tracts: connectdifferentregionsofthecerebralcortexwithintheSAMEHEMISPHERE.

• Commisural tracts: extendBETWEENthehemispheresthroughaxonalbridgescalledcommissures.

• Corpus callosum and anterior/posterior commissures • Projection tracts: connect cortex to caudal brain & spinal cord •

Cerebral Nuclei • Found deep within the central white matter • These are paired, irregular masses of GREY MATTER • These have other brain functions, but above states are the MOTOR

ACTIVITIES* • Caudate nucleus: C shaped, enlarged head, slender arching tail

• Neurons in this nucleus stimulate appropriate muscles to produce pattern and rhythm of arm and leg movements associated with walking.

• Amygdaloid body: expanded region at the tail of the caudate nucleus • Expression of emotions, control of behavioral activities, moods

• Putamen & Globulus pallidus: two masses of grey matter between the insula and lateral wall of diancephalon.

• Combine to form a larger body called the lentiform nucleus • Putamen: controls muscle mvoement at subconscous level • Globulus: excites and inhibits activity of the thalamus to control and

adjust muscle tone. • Claustrum: thin sliver of grey matter formed by a layer of neurons internal to the

insula. • Processes visual information at a subconscious level • Information about body position*

Diancephalon

• The “in-between brain” • Location: third ventricle • Septum pellucidum: veil between the left and right ventricle • Composed of: hypothalamus, thalamus, epithalamus. • Functions

• Relay and switching centers for some sensory and motor pathways • Control of visceral activities

Epithalamus

• Pineal gland: produces melatonin which affects the circadian rhythm (body’s day-night cycles).

• Epithalamus moves anteriorly to find the habenular nuclei • Habenular nuclei: relay signals from the limbic system to the midbrain.

• Part of the emotional and visceral response to odors • Food poisoning leads to nauseous feeling when smelling that same

food again Thalamus

• Location: roof and sides of the third ventricle, forms the superior lateral walls. • Each part of the thalamus is a GRAY MATTER mass composed of thalamic

nuclei that are organized by function • Axons from these nuclei project into the cerebral cortex in specific regions • Sensory impulses from all the conscious senses (NOT OLFACTION*)

converge on the thalamus and synapse in at least one of its nuclei. • Neurons coming from the thalamus go to specific locations in the central

cortex. • They carry sensory information (i.e. go to sensory locations EXCEPT

OLFACTION which goes directly to primary olfactory cortex) • Example: thalamus lets the cerebrum know that a nerve impulse it

received came from the eye, indicating the information is visual. • Filters about 95% or more of sensory information out • Recreational drugs dampen the thalamus, causing brain overload, and stories

are made up (tripping) • Even if the connection at the sensory organ was unaffected, if the wiring in

the brain is mixed up you would sense the wrong thing. Hypothalamus

• Location: basement, anterior inferior walls of the third ventricle • Functions of hypothalamus controlled by many specific nuclei. • The hypothalamus is the HOMEOSTATIC CONTROL CENTER of the body

• Master control of autonomic nervous system • Master control of endocrine system • Regulation of body temperature • Control of emotional behavior • Control of food intake • Control of water intake • Regulation of sleep-wake (circadian rhythm)

Brain Stem

• Midbrain, pons and medulla • Connection between cerebellum, cerebrum and spinal cord • Contains autonomic and reflex center i.e. the brain stem

Midbrain (Mesencephalon) • Superior part of the brain stem • Cerebral peduncles: motor tracts, motor axons descend from primary motor

cortex through these peduncles to the spinal cord. • Pyramidal motor tracts: direct motor pathway involved with major voluntary

movements • Periaqueductal grey matter: can be a modulator of pain

o Involved with development of aggressive behaviors • Tectal plate: inferior and superior colliculus (double butt)

o Inferior colliculi: auditory reflex center, controls turning of head and eyes in the direction of a sound.

o Superior colliculi: visual reflex center that coordinates eye and head movement – visually tracking moving objects

• Pigmented nuclei o Substantia nigra: inhibitory to motor output

§ Black in appearance due to presence of melanin § Relay inhibitory signals to cerebral nuclei to regulate the motor

output to SkM. § House clusters of neurons that produce NT Dopamine

• Affects brain processes that control voluntary movement, emotional response, pleasure and pain.

§ Decay leads to Parkinson's disease o Red nuclei: red because IRON is housed within the neuron cell bodies,

also blood vessel density. § Associated with crawling in babies § Associated with arm swinging when walking in adults

• Reticular formation happens later Pons

• House sensory and motor tracts that connect to the brain and spinal cord • House autonomic nuclei in respiratory center – VITAL, works along side medulla

• Regulates skeletal muscle breathing, medulla dictates the rate and depth of the breathing and pons modifies it.

• Houses CN V, VI, VIII. Medulla

• Called medulla until you hit the foramen magnum, then it is the spinal cord. • First bumps are called pyramids

• Where pyramidal motor tracts run through • Axons cross to the opposite side of the brain, forming an X: decussation

of pyramids • Crossover causes each cerebral hemisphere to control opposite side of the

body. • Second bumps are called olives, lateral to the pyramids

• Contain olivary nuclei that relay sensory information to the cerebellum.

• Takes information from joints (the amount of bend) and integrates it into a 3D plane

• Additional nuclei with various functions • Autonomic nuclei: regulate functions vital for life.

• Group together to form centers in the medulla. • Cardiac center, vasomotor center, medullary respiratory center

• Vomiting center: in the hypothalamus – remember: there is no brain blood barrier, so it can monitor blood circulation!

Cerebellum

• Has left and right hemispheres, each hemisphere has 2 lobes. • Three regions: outer grey matter cortex, internal white matter, deepest gray

matter. • White matter = arbor vitae

• Same composition as the brain • All fibers are ipsilateral (on the same side and do not cross) • Main function of Cerebellum: coordinates and “fine tunes” motor movements of

skeletal muscles • Also ensures that the correct pattern is initiated for smooth, coordinated

movements • Cerebellum STORES MEMORIES of previously learned movement

patterns – SUBCONSCIOUS, INDIRECT function • Cerebrum initiates a movement, then sends a rough draft over to the

cerebellum for fine tuning. • Also regulates the body’s position, able to balance because cerebellum maps out a

muscle tone plan to keep body upright • Primary motor cortex does not correct you when you trip while walking

• Cerebellum has to help maintain balance Limbic System

• Process and experience EMOTIONS, reticular formation also involved. • Made of many cerebral structures that COLLABORATIVELY work together to

process and experience emotions • Collective name for structures associated with motivation, emotion, memory with

emotional association • Memory in terms of emotional response – helps to encode emotion into

memories • Cingulate gyrus, fornix, olfactory nerve, etc. but depends on textbook • Tends to retain a memory if it is emotional – enhances memory pathway

Chapter 16, Spinal Cord and Spinal Nerves

General Information

• Vital link between the brain and the rest of the body • Functional independence from the brain

• Serve as a pathway for sensory and motor impulses • Responsible for reflexes aka the quickest reactions to a stimulus

Gross Anatomy of Spinal Cord

• 42-45 cm in length • Extends inferiorly from the brain through the foramen magnum and through the

vertebral canal • Ends at L1 vertebrae • Cervical, thoracic, lumbar, sacral, coccygeal regions

• Regions of the spinal cord do not match up directly with the vertebrae • lumbar part of the spinal cord is closer to the inferior thoracic

vertebrae than lumbar • Relatively cylindrical, but also flattened both front and back • Cervical enlargement: neurons that innervate upper limbs • Lumbosacral enlargements: innervates the lower limbs • Conus medullaris

• tapered inferior end of spinal cord • marks “official” end of spinal cord proper • Beginning of L1 vertebrae

• Cauda equina • Group of axons • Project inferiorly from the spinal cord • Exit vertebrae they are associated with

• Filum terminale • Within the cauda equina • Thin strand of pia mater • Helps anchor conus medullaris to coccyx • Tether that helps prevent movement along the denticulate ligaments

• Denticulate ligaments • triangular extensions of pia mater, suspend & anchor SC laterally to dura

mater • 31 prs spinal nerves

• Connect CNS to muscles, receptors, glands Spinal Cord Meninges

• Spinal cord meninges: protect and encapsulate the spinal cord – continuous with the cranial meninges!

• Epidural space: between dura mater and periosteum, covers inner walls of vertebra

• Filled with areolar CT, adipose CT, and blood vessels • Deep to the epidural space is the dura mater, the most external meninges

• Spinal dura mater only has one meningeal layer, NO PERIOSTEAL LAYER.

• Subdural space: separate dura mater from arachnoid mater • Only a potential space

• Subarachnoid space: deep to the arachnoid mater, real space filled with CSF • Pia mater: deep to subarachnoid space, delicate innermost meningeal layer

• Elastic and collagen fibers • Directly adheres to spinal cord • Supports blood vessels supplying the spinal cord

• Denticulate ligaments: paired, lateral triangular extensions of pia mater that attach to the dura mater

• Suspend and anchor spinal cord LATERALLY to the dura mater Sectional Anatomy of the Spinal Cord

• Between left and right communication occurs through the grey commissure of the grey matter

• Inner grey matter region: dominated by dendrites and cell bodies of neurons and glial cells and unmyelinated axons, centrally located

• Anterior, posterior and lateral horns • Gray commissure: surrounds central canal, COMMUNICATION

ROUTE between left and right sides of grey mater. • Outer white matter: myelinated axons, externally located/

• Anterior, posterior and lateral funiculi • Axons organized into tracts

• Conduct sensory impulses (ascending) or motor commands (descending)

• Each funiculi contains both sensory and motor axons Location and Distribution of Gray Matter

• Anterior horn: cell bodies of SOMATIC MOTOR NEURONS • Lateral horn: cell bodies of AUTONOMIC MOTOR NEURONS • Posterior horn: AXONS of SENSORY NEURONS, cell bodies of

INTERNEURONS • CELL BODIES OF SENSORY NEURONS are actually found in the

POSTERIOR ROOT GANGLION • Within the horns of gray matter there are groups of neuron cell bodies known as

nuclei • Posterior horn – SENSORY NUCLEI

• SOMATIC sensory nuclei: receive information from sensroy receptors (pain, pressure, skin, touch)

• VISCERAL sensory nuclei: receive information from sensroy receptors like stretch receptors in smooth muscle in walls of viscera

• Anterior and later horns – MOTOR NUCLEI • SOMATIC motor nuclei: innervate skeletal muscle • AUTONOMIC motor nuclei: innervate smooth muscle, glands, cardiac

muscle

Location and Distribution of White Matter • Anterior, Posterior, Later funiculi

• Axons within white matter organized into tracts. • Remember, no cell bodies in white matter, just axons!

• Individual tracts wither conduct sensory impulses (ascending) or motor commands (descending)

• Each funiculus contains both ascending and descending tracts • No mixed tracts or funiculi

Spinal Nerves

• Spinal nerves: connect the CNS to muscles, glands and receptors. • Spinal nerve is formed from thousands of motor and sensory axons joining

together • Spinal nerve is wrapped by epi, peri, or endoneurium

• Motor axons in a spinal nerve originate from the SPINAL CORD • Anterior rootlets: arise from anterior aspect of spinal cord and merge to form a

single anterior root • Anterior root: carries MOTOR AXONS ONLY

• Motor axons arise from cell bodies in the lateral and anterior HORNS of spinal cord

• Posterior rootlets: arise from posterior aspect of spinal cord and merge to form a single posterior root

• Posterior root: carries SENSORY AXONS ONLY • Cell bodies of sensory neurons houses in the posterior root ganglion

• Each anterior and posterior root mere within the intervertebral foramen to form a spinal nerve.

• Thus, a spinal nerve contains both motor axons and sensory axons • Compare a spinal nerve to a cable made of many wires – the wires within the

nerve are the motor and sensory axons • The spinal nerves exit the vertebrae of the same number EXCEPT!!! For

C8, where the nerve leaves between C8 and T1. • The spinal nerve below C8 exit BELOW the vertebra of the same number,

spinal nerves above C8 exit ABOVE the vertebra of the same number • Anterior and posterior roots of are much longer in lumbar and sacral region

• Spinal cord is shorter than the vertebral canal • Roots of the lumbar and sacral nerves travel INFERIORLY to

reach respective intervertebral foramina to merge and become a spinal nerve

Spinal Nerve Distribution

• Once spinal nerve leave the intervertebral foramina it splits off into branches called rami

• Posterior ramus: smaller, innervates deep muscles of the back and the skin of the back

• Anterior ramus: larger of the two main branches • Splits into many other branches that innervate the anterior and lateral

portions of the trunk, upper and lower limbs

• Anterior rami go on and form nerve plexuses • Dermatomes: specific segment of the skin supplied by a single spinal nerve

• All spinal nerves EXCEPT C1 innervate a segment of the skin, so each is associated with a dermatome as well

• Skin of the body can be divided into sensory segments that make up a dermatome map!

• Maps follow a segmental pattern along the body • Dermatomes indicate potential damage to one of more spinal nerves • Dermatomes are involved in visceral pain where pain in an organ is

mistakenly referred to a dermatome • A good example is the appendix – innervated from axons of T10,

so appendicitis causes referred visceral pain in the umbilical region rather than abdominopelvic region where the appendix actually is!

Nerve Plexuses

• Nerve plexus: network of interweaving anterior rami of spinal nerves, form on the right and left side of the body.

• Split into multiple “named” nerves that innervate various body structures • Principal plexuses: cervical, brachial, lumbar, sacral • Organization: axons from each anterior ramus extend to the body structures

through seceral different branches. • Each terminal branch of the plexus has axons from several different spinal

nerves • Most of the named nerves from a plexus are composed of axons from

multiple spinal nerves • Therefore, damage to a single segment of the spinal cord DOES

NOT RESULT IN COMPLETE INNERVATION! • Most thoracic spinal nerves + S5-Co1 don’t form plexuses – instead form the

intercostal nerves! Reflexes

• Reflex: rapid, automatic involuntary reactions of muscles or glands to a stimulus • Similar properties of all reflexes:

• STIMULUS required for a response to be initiated • FEW NEURONS INVOLVED & MINIMAL SYNAPTIC DELAY for a

rapid response • PREPROGRAMMED RESPONSE happens the same way every single

time • INVOLUNTARY RESPONSE does not require any intent or pre-

awareness of the activity • NOT SUPPRESSED • Basically, awareness of the stimulus occurs after the action of the

reflex has already occurred • This corrects or avoids a potentially dangerous situation

• Survival mechanism: can quickly respond to a stimulus that may be detrimental to us without having to wait for the brain to process the info!

Components of a Reflex Arc

1. Stimulus activates sensory receptor with internal or external stimuli 2. Nerve impulse travels through sensory neuron to the CNS from the receptor in

the spinal cord 3. Information from nerve impulse is processed in the integration center by

interneurons 1. More complex reflexes: use a number of interneurons within CNS to

integrate and process incoming sensory info and transmit info to motor neuron

2. Simplest reflexes: do not use any interneurons 1. Instead, the sensory neuron DIRECTLY SYNAPSES on a motor

neuron on the anterior gray horn of the spinal cord (SENSORY AREA)

4. Motor neuron transmits nerve impulse through anterior root & spinal nerve to effector

1. Effector: peripheral target organ that responds to the impulse from motor neuron

2. Effector responds to nerve impulse from motor neuron 5. Effector responds to the nerve impulse from motor neuron

1. Response is to either counteract or remove original stimulus! Examples of Spinal Reflexes

• Ipsilateral: sensory receptor and effector are on the SAME SIDE of the spinal cord

• Ex) Muscles in left arm contract to pull left hand away from hot object • Contralateral: sensory receptor transmits impulse that crosses over the spinal

cord to activate effector on OPPOSITE site • Ex) step on a sharp object with left foot, contract muscles in right leg to

maintain balance as you withdraw left leg from damaging object • Monosynaptic: simplest of all reflexes

• Sensory axons synapse directly with the motor neurons whose axons project to the effector

• Very minor synaptic delay • Ex) Knee Jerk reflex

• Polysynaptic: many synapses with interneurons within the reflex arc • More prolonged delay between stimulus and response • Ex) crossed-extensor reflex – supports postural activity like in

aforementioned example with foot. • Ex) Withdrawal (flexor) reflex: touching something really hot

Reflex Testing

• Reflexes are an important diagnostic tool

• Used to test integrity of NS • can also be used to test specific muscle groups or specific spinal nerves or

segments of the spinal cord • Toes will curl in plantar flexion on lateral side of bottom of the foot • If they splay it’s the Babinski sign

• Indicative of upper motor neuron issues • Young babies whose neural system is still maturing shows Babinski

• Once toes start to curl the nervous system is mature

Chapter 17, Pathways and Integrative Functions General characteristics of NS pathways

• CNS communicates with peripheral body structures through pathways o Can either conduct sensory or motor information

§ Ascending pathway: carries sensory information • Info ascends through spinal cord to brain

§ Descending pathway: carries motor commands • Info descends through spinal cord to muscles/glands

• Pathway made up of a tract and a nucleus o Tracts: bundles of axons that travel together in the CNS

§ Tracts may work with multiple nuclei groups in CNS o Nucleus: collection of neuron cell bodies in the CNS

• Decussate: pathways cross over from one side of the body to the other at some point in their travels

o Means that left side of the brain processes information from the right side of the body

• Somatotophy: receptors in the body regions correspond to specific functional areas in the cerebral cortex (through axons)

o Pathways that connect primary motor cortex to specific region of the body show somatotophy

• All pathways have paired tracts o Pathway on left side of CNS has matching pathway on right side of CNS o Both left and right tracts are needed to innervate both left and right sides

of the body • Most pathways have 2 or 3 neurons that work together

o Sensory: primary neuron, secondary neurons, tertiary neurons o Motor pathways: upper motor neuron, lower motor neuron

Sensory Pathways

• Utilize a 2 or 3 neuron chain to transmit stimulus information • Ascending pathways: conduct information about limb position, sensation of

touch, temperature, pressure and pain to the brain. o Somatosensory: process stimuli received from receptors within skin,

muscles, joints o Viscerosensory: processes stimuli received from viscera

• Process o Sensory receptor detects stimuli o Sensory receptor conducts nerve impulse to CNS o Sensory pathway centers within spinal cord or brainstem o Sensory pathway processes and filters incoming sensory information o Centers determine if info is sent to cerebrum or terminated o Not all incoming impulses reach cerebral cortex and our conscious

awareness • Three major types of somatosensory pathways

o Posterior funiculus-medial lemniscal o Anterolateral o Spinocerebellar

Functional Anatomy of Somatosensory Pathways

• Series of two or three neurons to transit stimulus information from body periphery to the brain

o Ascending pathway, so start at the sensory receptor! • Primary neuron: first neuron in chain,

o Dendrites in this neuron are part of the sensory neuron that detects a stimulus

o Cell bodies in PRG o Axons extend to secondary neuron & synapses

• Secondary neuron: second neuron in chain and is an interneuron o Axons project into thalamus for conscious sensations

§ Axons that project into thalamus synapse with tertiary neuron o Axons project into cerebellum & synapses for unconscious proprioception

• Tertiary neuron: interneuron as well o Cell body resides within the thalamus itself o Thalamus is the central processing center for almost all sensory

information* Somatosensory Pathway: Posterior Funiculus-Medial Lemniscal Pathway

• Project through spinal cord, brainstem, and diencephalon before terminating in the cerebral cortex

• Name is derived from two components o Tracts within the spinal cord (funiculi) o Tracts within brain stem (medial lemnicus)

• Conducts sensory information about limb position, discriminative touch, precise pressure, vibration sensation

• Process: o Primary neuron starts the chain and synapse within posterior funiculi on

the secondary neuron cell bodies o Secondary neurons project axons to relay incoming information into the

thalamus

§ Within thalamus, ascending sensory info is sorted according to region of body involved (somatotopy)

o Synapse in the thalamus & Directs to somatosensory cortex § Tertiary neuron is in the region of the cortex that processes § Flows through medial lemniscus to the somatosensory cortex!

o Decussation occurs after secondary neuron axons exit specific nuclei and before they enter medial lemniscus

Somatosensory Pathway: Anterolateral Pathway

• Located in anterior and lateral white funiculi • Axons project from primary neurons enter at the spinal cord and synapse on

secondary neurons within the posterior horns • Axons entering these pathways conduct stimuli related to crude touch, pressure,

pain, and temperature • Axons of secondary neurons cross over to opposite side of spinal cord before

ascending towards the brain o Decussates through the white commissure

• Secondary neurons synapses in the thalamus • Axons of tertiary neurons conduct stimulus information to appropriate region of

somatosensory cortex. Somatosensory Pathway: Spinocerebellar Pathway

• Conducts prioreceptive information to cerebellum for processing to coordinate body movements

• Composed of anterior and posterior spinocerebellar tracts o Major routes for regulating posture and balance and skilled movements

• Only have primary and secondary neurons, NO TERTIARY NEURONS. • Pathway ends at the cerebellum • Important as it is responsible for transmitting postural input to the cerebellum • Cerebellum relies on this pathway to bring sensory information it needs to have

skilled motor movements. Motor Pathways

• Formed from the cerebral nuclei, cerebellum, descending tracts, and motor neurons

• Beings in primary motor cortex in the brain to contract skeletal muscles • Comprised of at least 2 motor neurons that are involved in VOLUNTARY

movement o Upper motor neuron

§ Housed with cerebral cortex § Serve to excite/inhibit motor neuron § Everything arises from the upper motor neuron

o Lower motor neuron

§ ALWAYS EXCITATORY § This is what actually synapses or forms a NmJ with SkM

Functional Anatomy of Motor Pathways

• Direct Pathways (Pyramidal Pathways) o Corticobular: assist with forming cranial nerves, help speak,

superficial muscles of neck and back, facial muscles etc. o Corticospinal: control voltunary motor activity

• Indirect Pathway o Lateral pathway

§ Rubrospinal o Medial pathway (GENERALITY)

§ Reticulospinal, tectospinal, vestibulospinal Direct Pathways

• Originate in the pyramidal cells in primary motor cortex • Internal capsule: descend through this, looks like a bottle neck

• It’s like going from a 4 lane to a 2 lane highway à less space • Flows around or through basal nuclei, lots of info that flows through there • On separate tracts, but lots of space from cerebral cortex, but everything

now gets squeezes up into a smaller space. • After descending through internal capsule, enters cerebral peduncles in midbrain

and form 3 descending motor tracts… • Corticobulbar: assist with forming cranial nerves, helps speak, superficial

muscles of neck and back, facial muscles, etc. • Corticospinal: control voluntary motor activity

• Anterior: axial muscles • Decussates in spinal cord

• Lateral: limbs, skilled movement (moving around and stuff) ß what everyone thinks of

• Decussates in the medulla Indirect Pathways

• More complex, circuitous route • Not direct or easy to follow as we’ve seen in sensory ones or direct

pathways • Important to us, but work at the SUBCONSCIOUS level

• Motor commands at subconscious level • Modify/help control pattern of somatic motor activity

• This basically means that: primary motor cortex says MOVE LEFT LEG, but the actual motion of the leg isn't the only thing that happens…

• Who controls trunk stability? • Who controls motion of arms? • These pathways maintain these other motions for you!

• They can do this by altering motor sensitivity • OR through activation of feedback loops

• Work in the background, modifying the voluntary muscle movement.

• Grouped according to primary function • Lateral pathway: help regulate and control PRECISE/DISCRETE

movements • Rubrospinal

• Medial pathways: regulates TONE and GROSS MOVEMENTS of everything else besides the limbs

• Reiculospinal, tectospinal, vestibulspinal Role of Cerebral Nuclei

• Be aware there are multiple things that are going on when you are using voluntary movement

• Receive impulses form entire cerebral cortex and limbic system • Output mostly to PRIMARY motor cortex • Only work on pyramidal cells in the upper motor cortex • Patterned background movements needed for conscious motor activity, help

establish the PATTERN • Individuals have a GAIT – this is part of this grouping

Role of Cerebellum

• Sensory information in from the joints • Receives plans for movement and follows activity to make sure it is carried out

correctly • Error correcting signal: corrects any disparity between intending and actual

movement • Regaining balance: cerebellum makes the correction there

• NORMAL PATTERN IS NOT WORKING, HOW DO WE REESTABLISH PATTERN?

• Works subconsciously • Actually exerts effect indirectly by effecting excitability of the motor

neuron • We can influence how information is moved, and that is what cerebellum

really does Hemispheric/Cerebral Lateralization

• Hemispheres specialized for specific tasks o Categorical and representational hemispheres

§ Cognitive locatization: not anatomic elements, all in regards to psychological aspects

• Petalias: left and right hemispheres aren’t really asymmetrical o This is the shape asymmetry between the frontal and occipital lobe o If youre right handed, there is a right frontal petalias and a left occipital

petalias (projection of one side over another

• Higher order processing involved now o Left hemisphere is often referred to as CATEGORICAL

§ Categorization, symbols, language centers, sequential and analytical reasoning, partition info into smaller fragments for your analysis)

o Right hemisphere is Representational § involved with visuospatial & analysis of those relationships,

imagination and insights, music and art, sounds smells and tastes • Both sides communicate with each other but there is specialization of tasks in

each hemisphere!

Consciousness • Being aware of sensations occurring around you • Involves voluntary control of motor activities and those required for higher

mental processing • Reticular formation: gray matter, loosely organized core

o Midbrain, pons, diencephalon, spinal cord o NOT LIMITED, in several parts of brain

• Functional brain center: motor and sensory components • Sensory components: alerts cerebrum of incoming sensory information

o If we didn't’t have this RAS (reticular activating system), your brain wouldn't just naturally fall asleep!

o We need something to tell our brains to stay awake or else we would just be always falling asleep

Chapter 18, Autonomic Nervous System of the Motor NS

Autonomic Nervous System

• Processes regulated below conscious level • Work reflexively and without our awareness • Works constantly with somatic to regulate body organs and maintain homeostasis

Comparison of Somatic and Autonomic NS FEATURE SOMATIC AUTONOMIC Type of control Voluntary control (from

cerebrum) Reflexive control (brainstem and SC)

Involuntary control

Number of neurons in pathway

One neuron in pathway Somatic motor neuron axon extends from CNS to effector

Two neurons in pathway Pre-ganglionic neuron has pre-ganglionic axon that projects to ganglionic neuron Ganglionic neuron has post-ganglionic axon that

projects to effector Sensory Input Special senses

Skin Proprioreceptors

Visceral Senses Somatic Senses

Ganglia associated with sensory neurons

PRG PRG

Ganglia associated with motor neurons

Automatic ganglia, intramural ganglia Sympathetic trunk ganglia

Effector organs SkM Cardiac, Smooth, Glands Neurotransmitter released ACh Pre-ganglionic release ACh

Post-ganglionic release ACh or NE

Axon properties Thicker diameter Myelinated FAST conduction

Preganglionic: thin, myelinated Postganglionic: thin, Unmyelinated SLOW conduction

• Effectors

o Somatic: Skeletal muscle § Response: only excitatory

o Autonomic: Cardiac, Smooth, Glands § Response to effector: either excitation or inhibition

• Efferent Pathway o Somatic: motor, see one motor neuron that innervates skeletal muscle o Autonomic: two neuron chain/sequence

§ First tier = preganglionic motor neuron (autonomic denotation), synapses within autonomic ganglion

§ Then we have the post ganglion motor neuron – • Axon innervates the target (smooth muscle)

§ Remember ganglion is a collection of cell bodies. § Cell bodies of the postganglionic neuron is in the autonomic

ganglion. • Target Organ Response to NT – release of Ach

o Autonomic § Pre-ganglionic neuron always released Ach § Post-ganglionic neuron releases ACH or NE. § Can be excitatory or inhibitory, depends on what effector organ Is

and what the pathway is representing. o Somatic: o

Components of Autonomic NS

• Preganglionic neuron: released Ach, myelinated, large diameter

• Faster than the postganglionic neuron due to myelination and larger diameter

• Myelination and size of axon increases speed • Postganglionic neuron: varied NTs, unmyelinated, smaller diameter

Divisions of Autonomic NS -- Perform dramatically different functions

• Parasympathetic – “brake” • Rest and digest response • Main job: bring body back to homeostasis • Setlles you down, gets you back to homeostasis, relaxing

• Sympathetic – “gas” • Emergency responses, fight or flight response • Gas: revs entire system up, gets body ready for any challenges, activates

system to get ready to do something Anatomic Difference between Parasympathetic and Sympathetic

• Autonomic ganglion where synapse occurs located in different areas in sympathetic and parasympathetic

• Preganglionic differences • Sympathetic: lots of branches on presynaptic side, • Parasympathetic: longer axon!

• Postganglionic differences • Sympathetic: longer • Para: shorter

Parasympathetic NS

• Motor neurons housed within brain stem nuclei where they come from sacral region of SC

• Because preganglionic neurons originate from 1 or the 2 areas – known as the craniosacral division

• “Rest and digest” • Most active when body is processing nutrients, when we need to conserve

energy/replace energy, • Main goal is to return body back to homeostasis! • Actions discrete and localized

• Fairly long preganglionic neuron Sympathetic NS

• Branching element of preganglionic neurons and what happens in post ganglionic neurons

• Thoracolumbar division: preganglionic originates in thoracic and lumbar regions in spinal cord

• Can activate single effector or many effectors together (mass activation)

• Mass activation = crisis management • Being scared, your body has been challenged – do we fight or flight? We

need to activate a lot of different things • More nerve plexus with sympathetic than parasympathetic

Other features of Autonomic Nervous System

• Brachioplexus designed the way it is allows it to have/gives us SAFETY DURING DAMAGE – options, we have alternative plans

• Lose section of nerve, we wont lose complete paralysis of a muscle • We don’t want that here – we want to retain characteristics of para. and sympa.

because they have antagonistic effects • Body uses those two to hit the levels it wants to obtain • No interaction to maintain antagonistic effects

• Communication is between neurons and effectors by NT • Dual innervation

• Antagonistic: body can utilizes the “brake and the gas” • Cooperative effects: para and sympa both initiate a different

response/have different effects, but that response works together to provide cohesive single distinctive response!

Chapter19–Senses,General&Special

GeneralInformation

• Wearecontinuouslyexposedtostimulifrommanydifferentsourceso Stimulireferstochangesintheexternalorinternalenvironment

• Ourconsciousawarenessofincomingsensoryinformationiscalledsensationo Yetweareonlyconsciouslyawareofasmallfractionofthestimuliwe

senseo Interpretationisperception:colors,intensityoflight

• StimuliaredetectedbyR’s,whicharedividedinto2classes:o Generalsenses

§ Temperature,pain,touch,stretch&pressureo Specialsenses

§ Gustation,olfaction,vision,equilibriumandauditionPropertiesofreceptors

• AllsensoryR’sserveastransducerso Transformsthestimulusenergyintoanerveimpulse

§ Convertsoneformofenergyintoanother• Stimulusenergytransduced/changedtoelectrical

energythatoursystemcommunicateswith• Actionpotentials&stuffflowsalongsensoryneuron

• PatternofnerveimpulsesconductedtotheCNSconveysinformationaboutthestimulus

o Interpretationo Importance

• Howdoweascertaininformationaboutthestimulus?o AllitisPATTERN

§ Helpswithinterpretationaswellasimportant§ BismoreimportantthanA–greaterfrequencyofnerve

impulses,itismoreimportantReceptors

• Structuresthatdetectstimulio Rangeincomplexity

• MonitorbothexternalandinternalenvironmentalconditionsandthenconductinformationaboutthosestimulitotheCNS

• Receptivefieldso EntireareathroughwhichsensitiveendsoftheRcellaredistributedo Observearelationshipbetweensizeofthereceptivefieldandour

abilitytoIDtheexactlocationofastimulus§ Small�preciselocation§ Asking–who’sthemostsensitive?1or2?1is!

o Receptivefieldsmalleràpreciselocationàmostsensitiveo Smallreceptivefieldsonhands,biggeronesonupperback,trunketc.

• TonicReceptorso Respondcontinuouslytostimuliataconstantrateo Examples:balancereceptorswithintheinnerear

• PhasicReceptorso Reactandthenadapt

§ Adaptation:reductionofsensitivityofphasicreceptortoacontinuouslyappliedstimulus

o Youknowitsthere,butnoticeitbecauseitscontinuouslyrunninginthebackgroundàknowwhenitchanges

o NotcontinuouslybombardedbysensoryinformationClassificationofReceptors

• GeneralR’saredistributedthroughouttheskin&organs,whereasspecialsenseR’sarehousedwithincomplexorgansinthehead

• ReceptorDistributiono Generalsenses

§ SomaticR’s–bodywall§ VisceralR’s–wallsofviscera

o Specialsenses§ Locationrestrictedtosenseorgansinhead

• StimulusOrigino Exteroceptors-sensitivetostimulithatariseoutsidebody(touch,

pressure,temperature,painalongwithspecialsenses)

o Interoceptors-sensitivetostimulithatariseinsidebody,internalviscera&bldvessels(chemicalchanges,stretching,temperature);unawareofworkings

o Proprioceptors-respondtointernalstimulifromskeletalmuscle,joints,tendons,ligaments&CTofboneandmuscles

ModalityofStimulus

• Chemoreceptors-chemicalsinsolution• Thermoreceptors-temperature• Photoreceptors-lightenergy• Mechanoreceptors-mechanicalforce• Baroreceptors–pressurewithinbodystructure• Nociceptors-potentiallydamagingstimulithatresultinpain

Pain

• Verysignificantproblem–hardtomanage• Phantompain:painassociatedwithbodypartremoved/amputated

• Howcanthisevenoccur?Painfrompartofbodythatisn’teventhere?Takeawaysensoryreceptor,shouldtakeawayusbeingabletosensethatarea,right?

• HOWEVER:thenervepathwayisstillintact!• Remember,thisisthefirstorderneuronàsecondaryà

tertiaryneuron• Thethirdorderneuroncontactsthethalamus,whichendsup

establishingconnectionwithsomatosensory,creatingthesensorypathway(primaryneurontosecondarytotertiary)

• Ifpathwayisstimulated/activated,thingsareMAPPEDOUT,thephantompainstillabletooccur!

• Referredpain:CNSmisinterpretingINCOMINGinformation• Whenimpulsesfromthevisceraareperceivedascomingfroma

dermatomeofskin–it’sbecausetheyusethesameASCENDINGTRACTwithinthespinalcord.

• Thiscausesthesystemtoincorrectlylocalizethesource!• Example:Appendix&bellybuttonpain• Example:heartattack&leftarmdiscrepancy

• Sympatheticinnervationforheart(involuntary,autonomicnervous)isthroughT1–T5finalsegment.

• T1–t5usesthesameascendingpathwayasdermatomeregion!Thiscausesmis-localization.Reallycomingfromtheheart,butthepathwaymakesitseemslikeitscomingfromthearmbecauseweareUTILIZINGTHESAMEASCENDINGPATHWAY*

GeneralSenses

• R’sforgeneralsensesareusuallysimpleinconstruction

• TactileR’so MostnumeroustypeofRo TypicallymechanoR’sthatreacttotouch,pressure&vibrationstimulio Locatedindermis&subcutaneouslayer

SimpleR’sofGeneralSensation

• Widelydistributedreceptors–dermis/subcutaneous/surfaceofintegument• Unencapsulated:noconnectivetissuestructurearoundit

• Freenerveendings–haveareceptivefield,temperaturereceptoraswellaspainreceptor.

• Roothairplexus:sensoryneuronaroundrootofhair,dealswithdisplacementofhair(contraction,hairmovesifwindblowsoverit)

• Merklecells/tactilecells:sensorycellattachedtosensoryneuronbasically,veryimportantfortextureandshaperecognition*

• Encapsulated:CTstructurearoundit,havecapsuleorlayersofCTfibers(fluidfilled,respondtopressure,lamellatedhasthis)

• Ruffinicorpuscle:pressure,distortionofyourskin*STRETCHRECEPTOR–stretch/distortionofskinitself

• Lamellatedcorpuscle:DEEPPRESSUREandDEEPVIBRATIONS• Tactile/Meissnercorpuscle:discriminativetouch,LIGHTER

PRESSURE,FINETOUCH,textureaswell*• NumberofdendritesfoundwithinacapsuleofCT.

SpecialSenses–Gustation

• CHEMORECEPTORS–respondtochemicalsinaqueoussolution• SALIVAinoralcavitytokeepenvironmentmoistsofoodcandissolve

withinsaliva&sensorystructurecanrespond• Medianfortastechemicals!

• Eatsomethingdry–does’treallyhavemuchtasteinyourmouth.• Massecationofasaltine,chewandmixsalivawithcracker–>has

sometasteassociatedwithit• Foodchemicalsaredissolved,cannowsensethem!

• Gustatoryreceptors(sensoryreceptorsfortaste)housedwithinatastebud• Tastebudslocatedinoralcavityontongue

• Papillae:elevationsontongue,epitheliumandCTmakethemup• Notethattheyarealsofoundonwallsoforalcavityaswell!

TasteBuds

• Comprisedofsupportingcells(protect&insulatetastecell),gustatory/tastecell(Rcell–neuroepithelialcelltype;short-lived;gustatoryhairs/microvillicontainsensitiveportion–Rmembranes)andbasalcells(stemcellpopulation)

• Vallatepapillae:ontheSIDE&househousetheMOSTtastebuds

• Surfaceofepitheliumwearsawayquickly,that’swhytheyarehousedonthesides–crevices

• Filiformpapillae:Mechanicalmanipulation(spikesonthem)aswellastexturedetection

• Fungiformpapillae:Havesometastebuds.• Foliatepapillae:onlyimportanttoyouasababy,onlyhousetastebudsin

infancyandearlychildhooddevelopmentTastebuds:Embeddedintotheepithelium

• Supportcells:protectandsupport• Gustatoryhairs:microvilli,receptorsfoundforfoodmoleculesarehere*

• foodmoleculesyoucansenseactivatethereceptorsbindingtothegustatoryhairsyoucanseeonthetastepore

GustatoryDiscrimination

• Sensoryreceptorsongustatoryhairsareactivatedandrespondtothese5elements.

• Tastesensationsaregroupedinto5basicqualities:o Sweet:elicitedbyorganicsubstances

§ Sugars,alcohols,aminoacids§ Respondtoleadsaltsaswell*--Whychildrenliketoeatlead

basedpaint–tasteslikecandytochildreninoldhomes!o Sour:acid,especiallyH+o Salty:metalions&inorganicsalts

§ Mostsensitivetosodiumchlorideo Bitter:alkaloidsaswellastoxinsorpoisonso Umami:aminoacidsglutamateandaspartate

• ObservevariationinthresholdrequiredtostimulateR’so Moresensitivetosour&bitterstimuli

• Combinationsoftastemodalitiesallowsustoperceivewidevarietyoftastes–besttasterswillbethroughNOSEactually!

• GoesthroughcranialnerveVII(facial)andIX(vassopharyngeal)• Thresholdcountsfor80%oftaste,senseofrequiredtostimulateisvariety• Senseofsmell–youcansenseagreatervarietyofscentsorodormolecules

thanfoodmolecules!

SpecialSenses–Olfaction• Tasteandolfactioncanbelinked• Sensoryorganforsmell=olfactoryepithelium

• Superiorportioninthenasalcavitybelowthecribiformplate• Sensorystructuresgothrougholfactoryforamina,theneuronsrun

throughthis• Detectsodorants• Chemoreceptors(chemicalsdissolveinMUCUSLAYER)

• Dryenvironment=nopotentsmellsincomparisontosteamyshowerinmen’slockerroom…..Verymoistandsmellsdisgusting,easiertosenseinmoistenvironment!

• Olfactorycells=receptorcellsandADAPTQUICKLY• Smellconsistencychanges–madeawareofthis.

• PseudostratifiedEpithelium• Supportingcells:(sustainandsupport),• Olfactoryreceptorcells:

• unique:actuallyBIPOLARNEURONS*• REPLACETHEMSELVESANDTURNOVERWHENNEURONS

CANTREALLYDOTHATMANYPLACES• Olfactoryhairsextenddownintomucuslayerinreceptorcells,

variousodorantsfoundonthesehairswithinthemucuslayer• Basalcells:replacethebipolarcellsmaybe,notexactlysurehowthis

entireprocesswouldoccur.• Bipolarneuronsactivatedasodorantbindstohair–goesthrough

olfactorybulb,sentalongolfactorytract.• Remember,OLFACTIONISTHEONLYSENSETHATDOESNOT

RUNTHROUGHTHETHALAMUS!Allotherdo,notolfaction.SpecialSenses–Vision

• Isourdominantsenseandassistsusinformingspecificdetailedvisualimagesofobjectsinourenvironment

AccessoryStructuresoftheEye• Providesuperficialcoveringoveranteriorexposedsurface,preventforeign

objects(pollen,dust)fromcomingintocontactwitheyeandkeeptheexposedsurfacemoist,cleanandlubricated

• eyebrows,eyelids,conjunctiva,lacrimalapparatusandextrinsiceyemuscles• Eyebrows:rowofthick,shorthairs,keepssweatoutofeye• Eyelashes:preventforeignobjectsfromcomingintocontactwithanterior

surfaceofeyeo Squintingbringseyelashestogethertofilteroutdust,debris,etc.

• Eyelids:movableanteriorprotectivecoveringoversurfaceofeyeo Akapalpebrae

§ Superior(larger)&inferior(smaller)

Conjunctiva• Foundin2locations• Specializedstratifiedsquamousepitheliumthatformscontinuousliningover

whitepartoftheeyeandinnersurfaceofeyelids.• Externalanteriorsurfaceofeye

• Whiteoftheeyehastheocularconjunctiveandpalpebralconjunctiveisontheinsideoftheupperandlowereyelids

• Gobletcells:mucinproducing,glycoproteinreleasedandloveswater

• basicallyjoinswithwatertoformmucustolubricateeyeandkeepeyemoist.

• Conjunctivitisisinflammationofeitherconjunctiva.LacrimalApparatus

• Lacrimalapparatus:Lacrimalgland+lacrimalducts• LacrimalGland:producessecretion(tears)

• Collects&goesthroughlacrimalpumpductàlacrimalcaniliculiàlacrimalsac

• Collectsexcessintonasalcavity.• LacrimalglandsactuallylocatedLATERALLYontheside,totheedge,not

acrosstheentirearea• Releasetearsontosides,contouredsurfaceofeyebringsfluidsfrom

outeredgetotheinneredge• Actuallypullingtearsacrosseyewhenyoublink• Architectureofeyelidsandsurfaceofeyecausesthiscentrality.

• Lacrimalcaruncle:grittystuffineyeswhenyouwakeup,modifiedsweatglandthatproducesgrittytypeofmateiralthatisbasicallyathicksecretoryproductduringthenightwhilesleeping

ExtrinsicEyeMuscles

• Responsibleforthemovementofeyeballinanyway• Superior/inferiorrectus

o Elevates/depresseseyeo Rollseyesuperiorly/inferiorly

• Medial/lateralrectuso Moveseyelateral/medial

• Superior/InferiorObliqueo Elevates/depresseseyeo Turnseyelaterally

EyeStructure

• EyeballsareNOTperfectlyspherical• Weneedmovability–somethingarounditthatallowsmuscletomovesince

itsrecededintotheskull.• Thebesttohelpthisisuniversalpackingmaterialknownasorbital

fat(adiposetissue)• Cushionforlateralandposteriorsidesofeye,protection,flexible

supportformovingeyefast,vasculaturecanalsorunthroughthere!• Inferiorofeyeishollow+lens

TunicsoftheEye

• Fibrous:outermostlayeroftheeyeo Sclera:outermostlayerhere,whiteofeyes

§ Dissectingeyesinlab:pretttttyyytoughlayer

§ Protectandassistwithshapeofeyeball§ Attachmentsiteforextrinsiceyemuscles§ Attachdirectlytocornea

o Cornea:transparent,bulgesanteriorly§ AVASCULAR*§ Notjustasinglelayerstructure,butrathermanylayeredwith

outerandepithelium,cantreplaceinnerlayerthough*§ Reliesonlacrimalsecretionsfornutrientdeliveryandremoval

ofwasteduetoAvascularity§ Also,beyondreachofimmunesystemduetoAvascularity–

caneasilytransplantcorneas!!!o Limbus:corneal/scleraljunction,continuitybetweenthetwo

structures• VascularTunic:middlelayer

o Bloodvesselsandlymphatics+intrinsiceyemusclesduetovasculature

o Choroid:highlyvacularized,suppliesnutrientstovasrioustunics,coloredsoitabsorbsanyrefractedlightineyesinterior

o Ciliarybody:madeof2things…§ Ciliarymuscle(4layersofsmoothmuscle,organizedintoa

ring• Attachedtociliaryprocesses[comingoffofthese=CT

bundlesthatattachtothelens,helppositionandshapethelens])

• Ciliarymuscleofcil.Bodytocontractàpullonprocessesàpullonmusclesthatpositionthelens

o Iris:sizeofpupil(howmuchlightcanenterintoeyeitself!)• Retina:innermostlayer

o Pigmentedlayerlaysnexttochoroid+retinawithreceptorcells*(rods&cones,sensoryorgansforlight)

o Placewhereeverythingattachesto,whitestructure=retina,easytodetachanywhereexceptopticdisk,whichiswherenerveexitsfromtheeye

o Foveacentralis:reallyjustanindentation,representsSHARPESTVISIONAREA*--wherewehavethesharpestvision

§ Lightrefractedthroughcornea&humors&lensandisfocusedinthisarearighthere,mainlymadeupofCONES*

OrganizationofNeuralRetina

• Choroidthenpigmentedlayer(photoreceptorcellshaveintimaterelationship)

o GoesthroughmanylayerstoreachphotoRcellsandthenthesignalistransducedtheoppositeway,

• PhotoRcellso Transducelightenergy

§ Rods• Moreabundant• Dim-light,peripheralvision

§ Cones• Bright-light• High-acuitycolorvision

§ Greateracuitywithcolorsbecauseoneononerelationship,severalrodstakesinmanythingsandconvergesononereceptorgivingbettervisionindark

o Horizontalcells(interneurons)assistcones§ Helpwithsensitivitytocontrast

• Bipolarcells:placeofconvergenceofinfofromphotoRcells• Ganglioncells

o Amacrinecells:assistwithprocessing/integratingvisualinfoo axonsformopticnerve(placeofneuronalconvergence)

• Alreadyhaveprocessingofinformationintheretina

Lens• Biconvex,transparent,flexiblestructure

o Flexibilityisimportantbecauseitallowschangingshapetofocuslightrightonretina(notinfrontorbehind)

• Canchangeshapeforprecisefocusingoflightonretina• Ciliarymusclespullonciliarymusclestoligamentsandthenchangeslens

shape• Comprisedofpreciselyarrangedcellsthathavelosttheirorganelles

o Filledwithaprotein,crystallin§ Crystallin-structuralproteinthatiswatersoluble,comesin

contactwithwaterandbecomestransparent,waterwasremovedfromlensincoweye(whyitwascloudy)

o Lightisrefractedinmanymediumsthrougheye

CavitiesoftheEye• Cavity(anteriorandposterior)alldependentoninfrontorbehindLENS• Anteriorcavityissplitintoanteriorandposteriorchamber(delineatedby

IRIS)• Aqueoushumor:bringsnutrientstostructures

o Continuallyrenewed*,producedbyciliarybodies• Vitreoushumor:istransparentsolightcanmovethroughit(transmits

light)supportseye,holdsretinaagainstchoroidandlensupright(suspensoryligamentsarenotrobust)

o Lastsalifetime*• Displacedretinahasdisassociatedfromchoroid

EquilibriumandHearing

• Middleear:distinguishingcharacteristics,withintympaniccavitycontainsauditoryossicles;boundbytympanicmembrane

• Includessenseofhearingandequilibrium• Vestibularapparatusisvestibulesandsemicircularcanals• CNVIIIvestibulocochlearandVII(facial)

Outer/ExternalEar

• Pinna,orauricleo Elasticcartilagecoveredwiththinskino Function

§ directsoundwavesintoexternalacousticmeatuso Pinna=soundwavecollectormadeofelasticcartilage

• Externalacousticmeatuso Madeofelasticcartilage&carvedtemporalboneo Linedwithhairs,ceruminousglands

§ Cerumenisearwax§ Preventsbugs,§ Keepstympanicmembranepliableandmoist

• Tympanicmembraneo Thin,translucentCTmembraneo Mucosaoninnerlining

§ Externalface–skin§ Internalface–mucosa

o Vibratewhensoundwavesstrikeit,transferssoundenergytoossicles

MiddleEar• Air-filled,mucosalinedcavitylaterallyflankedbyeardrum,mediallybythe

bodywallandobservetwo“openings”:o Ovalwindowo Roundwindow

• Housesopeningfortheauditorytubeo Linksmiddleeartonasopharynx

• Auditoryossicleso Smallestbonesinhumanbodies,heldinplacebyligamentsandmini

synovialjointso Malleus,incus,stapeso Suspendedbyligaments,connectedmymini-synovialjointso Transmitvibratorymotionfromeardrumtoovalwindow

§ Amplifiessoundo 2SkM

§ Stapedius&tensortympani• Contractwithloudsound,preventsamplifyingby

stoppingvibrations• Auditorytube:linkstonasopharynx,allowsadjustmentinpressurewithin

innerear

Inner/InternalEar

• Locatedwithinpetrousregionoftemporalboneo Bonylabyrinth

§ systemoftorturouschannelsthroughbone,filledwithperilymph

§ similartoCSF• foundfloatingwithincontoursofthisfluid-filledcavityisthemembranous

labyrintho Fluidfilledmembranousstructuresfloatwithin(membranous

labyrinth)o Continuousseriesofmembranoussacs&ducts

§ Filledwithendolymph-likeintercellularfluid• containssensorystructuresforequilibriumandhearing

• Bonylabyrinthstructurally&functionallypartitionedinto3distinctregions: o vestibuleo semicircularcanalso cochlea

StructuresandMechanismofEquilibrium

• Allusehaircells,ciliaconnectedtosensoryneuron(mechanicalmechanismthatinitiatesanerveimpulse)

o Movetowards(depolarization)oraway(hyperpolarization)fromkinocilium

o Asfluidflowswithinvestibulethingstumblearoundwithin• Macula

o SensoryRforstaticequilibrium§ Linearaccelerationforces

o Foundonwallof:§ Utricle-horizontal§ Saccule–vertical

• Gravityactivatessaccule• Cristaampullaris

o SensoryRfordynamicequilibrium§ Rotary/angularmovement

o Foundinampullaofsemicircularcanals• Bonylabyrinthmovesbutfluidmovesindifferentdirectionswhichis

detectedandgivessenseofdirectionalityaswellasrateofmovement

StructuresforHearing• Hearingstructuresarehousedwithinthecochlea

o a“snail-shaped”spiralchamberinboneofinnerearo Observeaspongyboneaxiscalledthemodiolus(withbonyshelves

forsupportofsensoryorgan-spirallamina)

• Thicksensoryepitheliumwitho Haircells&supportingcellsrestingonabasilarmembrane–Spiral

organo Distortioniscausedbypressurewavesinfluidasconsequenceof

soundwavesarrivingatthetympanicmembrane

SoundWaveInterpretation• Frequency

o Numberofsoundwavesthatmovepastapointduringaspecificamountoftime

§ Hertz(Hz)• Wavelength

o Distancebetween2consecutivecrests(ortroughs)§ Constantforaparticulartone§ Shorterwavelength,higherfrequency

o Human§ 20to20,000Hz

• 1500-4000Hz,greatestsensitivity• Pitch

o Differentsoundfrequencies• Amplitude

o Heightofwave,relatestointensity,orloudness(subjectiveinterpretationofsoundintensity)

§ Decibels(dB)