Nervous System Organization

Nervous System Nervous System OrganizationOrganization

Dr. Carmen E. Dr. Carmen E. RexachRexachPhysiologyPhysiology

MtSACMtSAC Biology Dept. Biology Dept.

Organization of nervous system

CNS PNS

Sensory(afferent)

Motor(efferent)

autonomicsomatic

sympatheticparasympathetic

Single neuronpathway

Two neuronpathway

CNS

Functions Integrates information from PNS Processes information Cognition, learning, memory Plans and executes voluntary

movements Components

Brain Cerebrum Diencephalon Midbrain and Hindbrain

Spinal cord Ascending and descending tracts

Brain

Cerebrum Cerebral cortex

frontal, parietal, temporal, occipital lobes Cerebral lateralization

Decussation of pyramids split brain procedures of the corpus callosum in epilepsy

Major landmarks of CNS

Cerebrum Only structure of the telencephalon. Largest portion of brain (80% mass). Responsible for higher mental

functions. Corpus callosum:

Major tract of axons that functionally interconnects right and left cerebral hemispheres.

Cerebral cortex Convolutions

Elevated folds: gyri Depressed groves: sulci

Frontal lobe Anterior portion of each cerebral hemisphere. Precentral gyri

Contains upper motor neurons. Involved in motor control.

Body regions with the greatest amount of motor innervation are represented by largest areas of motor cortex.

Cerebral Cortex Parietal lobe:

Primary area responsible for perception of somatesthetic sensation.

Body regions with highest densities of receptors are represented by largest areas of sensory cortex.

Temporal lobe: Contain auditory centers that receive sensory

fibers from cochlea. Interpretation and association of auditory and

visual information.

Cerebral Cortex

Occipital Lobe: Primary area responsible for vision and

coordination of eye movements. Insula:

Implicated in memory encoding. Integration of sensory information with

visceral responses. Coordinated cardiovascular response to

stress.

Basal ganglia Masses of gray matter

composed of neuronal cell bodies located deep within white matter.

nuclei around thalamus that help plan voluntary movement Corpus striatum = largest

part of basal ganglia caudate nucleus putamen globus pallidus

Basal ganglia diseases

Parkinsons Cause: lesions in

substantia nigra Results: loss of

dopaminergicneurotransmitters

Symptoms: tremor, rigidity, bradykinesia

Basal ganglia diseases

Huntingtons chorea Cause: genetic

disorder causing loss of striatopallidal and striatonigral neurons

Result: loss of GABA (inhibitory)

Symptoms: progressive dementia and bizarre involuntary movements

Cerebral Lateralization Cerebral dominance:

Specialization of one hemisphere.

Left hemisphere: More adept in language

and analytical abilities. Damage:

Severe speech problems.

Right hemisphere: Most adept at

visuospatial tasks. Damage:

Difficulty finding way around house.

Emotion and Motivation Important in the neural basis of emotional

states are hypothalamus and limbic system. Limbic system:

Group of forebrain nuclei and fiber tracts that form a ring around the brain stem. Center for basic emotional drives.

Closed circuit (Papez circuit): Fornix connects hippocampus to

hypothalamus, which projects to the thalamus which sends fibers back to limbic system.

Limbic system: functions Controls emotional behavior, such as:

aggression fear feeding sex goal directed behavior

Papez circuit Emotions and their expression governed by a

circuit of four structures interconnected by nerve fibers, not by a single structure

Four structures: hypothalamus, anterior thalamic nucleus, cingulate gyrus, and hippocampus

Memory

Several different systems of information storage

declarative memory ability to remember facts short and long term memory medial temporal lobe consolidates short term

into long term protein synthesis consolidates memory other structural changes in neurons and synapses

formation of new synapses growth of dendritic spines

Neuronal Stem Cells in Learning and Memory

Neural stem cells: Cells that both renew themselves through

mitosis and produce differentiated neurons and neuroglia.

Hippocampus has been shown to contain stem cells (required for long-term memory).

Neurogenesis = Production of new neurons Indirect evidence that links neurogenesis

in hippocampus with learning and memory.

Diencephalon Thalamus & epithalamus

(pineal gland) relay center for sensory

information alertness and arousal

from sleep Hypothalamus &

pituitary gland hunger, thirst centers body temperature

regulation visceral responses to

emotional state

Midbrain Corpora quadrigemina:

Superior colliculi: Involved in visual reflexes.

Inferior colliculi: Relay centers for auditory information.

Cerebral peduncles: Composed of ascending and descending fiber

tracts. Substantia nigra:

Required for motor coordination. Red nucleus:

Maintains connections with cerebrum and cerebellum.

Involved in motor coordination.

Hindbrain Metencephalon

Pons apneustic and pneumotactic centers

Cerebellum coordination

Myelencephalon medulla oblongata

Myelencephalon:Medulla oblongata

Pyramids regulation of breathing

respiratory center regulation of cardiovascular responses

vasomotor center -- enervation of blood vessels

cardiac control center RAS

reticular activation system nonspecific arousal of the cerebral cortex

Spinal cord tracts Ascending

sensory from proprioceptors, cutaneous, visual receptors

decussation of pyramids Descending

Corticospinal Extrapyramidal

Corticospinal (pyramidal) tract

No synapse from cortex to spinal cord

Most of the nuclei in the precentral gyrus

Action: fine muscle control

Lateral decussates in the medulla 80-90% of the tract

Anterior decussates in the spine

Extrapyramidal tract Many synapses = more difficult to

diagnose location of stroke Action: Gross motor control and

involuntary muscle excitation Originates in the midbrain and brainstem back circuits up to cortex and nuclei Influence: trunk, neck, upper part of

limbs Ex) Reticulospinal tract

major descending pathway

Cranial and Spinal Nerves

Cranial nerves: 2 pairs arise from neuron cell bodies in

forebrain. 10 pairs arise from the midbrain and hindbrain. Most are mixed nerves containing both sensory

and motor fibers. Spinal nerves:

31 pairs grouped into 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and l coccygeal.

Mixed nerve that separates near the attachment of the nerve to spinal cord.

Produces 2 roots to each nerve. Dorsal root composed of sensory fibers. Ventral root composed of motor fibers.

Electroencephalograms (EEG)

Records electrical activity of neurons = brain waves Determined by # of neurons firing together Four frequency classes

Alpha waves (8-13 Hz) idling brain = relaxed, calm, wakeful

Beta waves (14-25 Hz) Higher frequency, not regular Concentrating on something

Theta waves (4-7 Hz) Irregular, common in children

Delta waves (4 Hz or

EEG

Change with age, stimuli, brain disease

Aids in diagnosis and localization of lesions, tumors, infarcts, epileptic lesions

Absence of brain waves = brain death

Peripheral nervous system

Sensory receptors Somatic motor neurons Autonomic motor neurons

Sensory (afferent) Sense environmental stimuli and

transduce signal Transmit information to CNS

Somatic (efferent) Innervate skeletal

muscle fibers One neuron

pathway Nerve cell bodies in

CNS Axons leave either

through ventral root or cranial nerve

Autonomic nervous system Innervates organs not usually under

voluntary control Two neuron pathways

Pre-ganglionic neurons in CNS Post-ganglionic neurons in PNS

Sympathetic = fight or flight Parasympathetic = rest or repose Synapse on autonomic effectors

Cardiac muscle Smooth muscle Glands

Characteristics of Autonomic Neurons

Preganglionic autonomic fibers originate in midbrain, hindbrain, and upper thoracic to 4th sacral levels of the spinal cord.

Autonomic ganglia are located in the head, neck, and abdomen.

Presynaptic neuron is myelinated and postsynaptic neuron is unmyelinated.

Autonomic nerves release NT that may be stimulatory or inhibitory.

Autonomic ganglia Located in head, neck, abdomen Sympathetic chain ganglia

CNS PNS

preganglionic postganglionic

Sympathetic division Synapse close to the CNS & far away from

effector organ Travel within spinal nerves Mass activation due to convergence &

divergence Sympathoadrenal system: converge on

adrenal medulla

preganglionicpostganglionic

AChNE

Sympathetic Division

Parasympathetic division

Terminal ganglia -- close to effector organ Fibers outside of spinal nerves (usually) No stimulation to: cutaneous blood vessels,

blood vessels in skeletal muscle, sweat glands, arrector pili muscles

ACh

ACh

preganglionicpostganglionic

ParasympatheticDivision

Cranial nerves and Parasympathetic Division

4 of the 12 pairs of cranial nerves (III, VII, X, XI) contain preganglionic parasympathetic fibers.

III, VII, XI synapse in ganglia located in the head. X synapses in terminal ganglia located in widespread

regions of the body. Vagus (X):

Innervates heart, lungs esophagus, stomach, pancreas, liver, small intestine and upper half of the large intestine.

Preganglionic fibers from the sacral level innervate the lower half of large intestine, the rectum, urinary and reproductive systems.

Functions of the ANS Sympathetic = fight or flight

Increased HR Bronchiole dilation Increase blood glucose, etc.

Parasympathetic = rest and repose Decrease HR Incr digestion Dilation visceral bv

Neurotransmitters Adrenergic: release norepinephrine

(NE) Adrenal medulla

85% epinephrine 15% norepinephrine

Cholinergic: release acetylcholine (ACh)

catecholamines

Adrenergic receptors Beta adrenergic receptors:

Produce their effects by stimulating production of cAMP.

NE binds to receptor. G-protein dissociates into subunit or

complex. Depending upon tissue, either subunit or

complex produces the effects. Alpha subunit activates adenylate cyclase, producing

cAMP. cAMP activates protein kinase, opening ion channels.

Adrenergic receptors

Alpha1 adrenergic receptors: Produce their effects by the production of

Ca2+ Epi binds to receptor. Ca2+ binds to calmodulin Calmodulin activates protein kinase, modifying

enzyme action Alpha2 adrenergic receptors:

Located on presynaptic terminal Decreases release of NE

Negative feedback control Located on postsynaptic membrane

When activated, produces vasoconstriction

Response to adrenergic stimulation

Excitatory and inhibitory effects. Responses due to different membrane

receptor proteins.1) 1 : constricts visceral smooth muscles.2) 2 : contraction of smooth muscle. 3) 1 : increases HR and force of contraction.4) 2 : relaxes bronchial smooth muscles.5) 3: adipose tissue, function unknown.

Cholinergic stimulation All somatic motor neurons, all preganglionic

and most postganglionic parasympathetic neurons are cholinergic. Release ACh as NT. Somatic motor neurons and all preganglionic

autonomic neurons are excitatory. Postganglionic axons, may be excitatory or

inhibitory. Two types of receptors

Muscarinic receptors Nicotinic receptors