Ch. 13 Central Nervous SystemLindsey Bily

Anatomy & Physiology

Austin High School

The Central Nervous System Consists of the brain and

spinal cord. Processes all of the

information received from the body and outside world.

Coverings of the Brain and Spinal Cord The brain and spinal cord are very delicate and so

vital. They are well protected. Outer covering: bone (cranial bones and vertebrae) Inner covering: membranes called meninges which

have 3 layers… Dura mater: strong white fibrous tissue (outer) Arachnoid membrane: delicate cobweb layer (middle) Pia mater: transparent and sticks to the surface of the

brain and spinal cord and contains blood vessels (innermost)

Meninges

Meningitis Inflammation of the meninges. Usually involves the arachnoid layer and the pia

mater. Most often caused by bacteria, but can also be viral,

fungal, or due to tumors. Symptoms are fever and severe headaches as well as

neck stiffness and pain. Can be fatal. Spinal meningitis only occurs in the spinal cord.

Cerebrospinal Fluid Cerebrospinal fluid (CSF)

cushions and bathes the brain and spinal cord.

Found in the subarachnoid space around the CNS and within cavities or canals within the CNS.

Ventricles: large fluid filled spaces within the brain. There are 4.

Cerbrospinal Fluid Formed by separation of fluid from blood in

ventricles. Circulates through the ventricles and into the

central canal and subarachnoid spaces. Absorbed back into the blood The average adult has 140 mL in the CNS.

Hydrocephalus Condition that interferes with the circulation

of CSF. Usually a tumor has blocked off flow. Blood clots or hemorrhage may occur. In an infant, the head may swell since the

cranium is not fused. A tube may be inserted to drain the fluid, but

it can lead to brain damage, coma, or death.

Hydrocephalus

Hydrocephaly normal

Spinal Cord About 18 inches long and extends from the

foramen magnum in the skull to the first lumbar vertebra.

The spinal cavity includes the cord, meninges, CSF, adipose tissue, and blood vessels.

Provides conduction routes to and from the brain and serves as an integrator, or reflex center or spinal reflexes.

Functions of the Spinal Cord Ascending tracts: conduct sensory impulses up the cord to the

brain. Descending tracts: conduct motor impulses from the brain

down the spinal cord. All of the axons from any tract originate from neuron cell

bodies located in the same area of the CNS and they terminate in the same structure elsewhere in the CNS and they serve one general function. EX: All of the axons in the spinothalamic tract originate from neuron

cell bodies located in the spinal cord and terminating in the thalamus. All of the axons transmit impulses that produce sensations of crude touch, pain and temperature.

Spinal Cord

Human cadaver

Brain One of the largest organs in the adult. Weighs about 3

pounds. Attains its full size by age 18, but grows rapidly only until

about age 9. There are six major divisions of the brain that you need to

know…. Medulla oblongata Pons Midbrain Cerebellum Diencephalon cerebrum

Brainstem

Divisions of the Brain

(cerebrum)

Structure of the Brainstem Three divisions make up the brainstem (pons,

medulla oblongata, midbrain)

Medulla Oblongata Attaches to the spinal cord. About an inch in length. Has cardiac, respiratory and vasomotor control

centers (vital centers). Also controls non-vital reflexes such as vomiting,

coughing, sneezing, hiccupping and swallowing. An injury or disease of the medulla is often fatal

(blows to the base of the skull or bulbar poliomyelitis cause death because they interrupt impulse conduction)

Pons Just above the medulla oblongata. Has an arching, bridgelike appearance. Contains control centers for reflexes mediated by the 5th, 6th,

7th, & 8th cranial nerves. (More on that in later chapters)

Midbrain Forms the midsection of the brain. Lies above the pons and below the cerebrum. Contains auditory and visual centers as well as muscle

control.

Cerebellum 2nd largest part of

the brain Has a distinctive

pattern similar to a leaf.

Has numerous grooves (sulci) and raised areas (gyri).

Functions of the Cerebellum Performs 3 general functions that control the

skeletal muscles. 1. Acts with the cerebral cortex to produce skilled

movements by coordinating the activities of groups of muscles.

Helps control posture. Makes movements smooth, steady and efficient instead of jerky, trembling, and awkward.

Controls skeletal muscles to maintain balance.

Functions of the Cerebellum Impulses from the cerebrum start motor

action, but also travel to the cerebellum. The cerebellum compares the motor commands of the cerebrum to the information coming from receptors in the muscle.

It compares the intended movement with the actual movement.

Cerebellar Disease Abscess, hemorrhage, tumors or trauma to the

cerebellum cause certain symptoms. Ataxia (muscle incoordination), hypotonia,

tremors, disturbances of gait and balance.

Diencephalon Literally means

“between brain”. Contains the

thalamus and hypothalamus, optic chiasma, pineal body, and other small structures.

Thalamus Dumbbell shaped mass of gray matter made

up of many nuclei (cell bodies and unmyelinated axons)

Large numbers of axons conduct impulses into the thalamus from the spinal cord, brainstem, cerebellum, cerebral nuclei and various parts of the cerebrum.

Major relay station for sensory impulses on their way to the cerebral cortex.

Thalamus

Thalamus1. Once certain sensory impulses get to the thalamus,

we become conscious of the crude, less critical sensations of pain, temperature and touch.

2. Plays a part in emotions. Associates sensory impulses with feelings of pleasantness and unpleasantness.

3. Plays a part in the arousal or alerting mechanism.

4. Plays a part in mechanisms that produce complex reflex movements.

Hypothalamus

Hypothalamus Lies beneath the thalamus. “hypo” means low. Weighs about 7 grams, but it is super important

for survival and the enjoyment of life. Functions as the link between the body and the

mind (soma and psyche). Links the nervous system to the endocrine

system.

Hypothalamus Functions Regulator and coordinator of autonomic activities, “Mind Body Link”: It is the major relay station between the cerebral

cortex and the lower autonomic centers; crucial part of the route by which emotions can express themselves in bodily functions.

Synthesizes hormones secreted by the posterior pituitary gland and plays an essential role in maintaining water balance because it makes a hormone that is involved in amount of urine excreted.

Some neurons function as endocrine glands. The axons secrete releasing hormones which cause the anterior pituitary to release certain hormones.

Plays a crucial role in the arousal mechanism. Sleepiness disorders can be due to problems with the hypothalamus.

Involved in the mechanism regulating appetite. Involved in the mechanism regulating body temperature. It has neurons

whose fibers connect with autonomic centers for vasoconstriction, dilation, sweating and somatic centers for shivering.

Pineal Body (Gland) Named so

because it resembles a tiny pine cone.

Involved in regulating the biological clock.

Produces melatonin

Structure of the Cerebrum Cerebrum is the largest and uppermost division of

the brain and has two halves… left and right cerebral hemispheres.

The surface of the cerebrum is 2-4mm thick and is gray matter. Called the cerebral cortex.

Five lobes: Frontal lobe Parietal lobe Temporal lobe Occipital lobe insula

Cerebral Lobes

The insula lobe is not visible. You have to separate the temporal and frontal lobes to see it.

Cerebrum Mostly white matter, but

areas of gray matter embedded are called cerebral nuclei.

The corpus callosum connects the left and right hemispheres.

Parkinson Disease Normally neurons from the midbrain lead to the

cerebral nuclei and secrete dopamine. Dopamine inhibits the excitatory effects of

acetylcholine. In Parkinson disease, these neurons degenerate, so

you don’t have the dopamine. The cerebral nuclei produce excess signals that

affect the voluntary muscles. Overstimulation of the postural muscles of the neck,

trunk, and upper limbs produces tremors and abnormal gait.

Functions of the Cerebral Cortex Certain areas of the cortex engage in

predominately one function. However, this can vary from person to person and at different times in an individual when the brain is damaged. (cerebral plasticity)

The function of each region depends on the structures that is communicates with.

No part of the brain functions alone and they work together to function normally.

Sensory Functions of the Cortex The cortex integrates separate bits of sensory

information into whole perceptions. For example, that someone put an ice cube in your

hand. You would see it and sense something cold touching your hand. You would also know it was an ice cube because you would perceive a total impression compounded of many sensations such as temperature, shape, size, color, weight, texture, and movement and position of your hand and arm.

Fig. 13-17 Primary somatic sensory (A) and motor (B) areas of the cortex. The

body parts illustrated here show which parts of the body are "mapped" to specific areas of each cortical area. The exaggerated face indicates that

more cortical area is devoted to processing information to/from the many receptors and motor units of the face than for the leg or arm, for

example.

Integrative Functions of the Cortex Consciousness Use of language Emotions Memory

Consciousness The state of awareness of one’s self, one’s environment, and

other beings. Very little is known about the neural mechanisms that produce

consciousness. Depends on excitation of cortical neurons by impulses

conducted to them by a network of neurons known as the reticular activating system.

The reticular activating system lies in the brainstem and receives impulses from the spinal cord and relays them to the thalamus then to all parts of the cortex.

If the neurons are not excited, you are unconscious. Drugs that depress the activating system decrease your alertness

and put you to sleep (barbiturates). Drugs such as amphetamines stimulate the center.

Consciousness We exhibit certain levels of consciousness at

different times. Sometimes we are relaxed and nonattentive,

sometimes we are alert and attentive. During sleep, we cycle from Slow Wave Sleep

(SWS) and Rapid Eye Movement (REM) sleep. SWS has slow frequency, high voltage brain waves

and it’s dreamless. REM has dreams.

States of Consciousness Anesthesia: reversible lack of awareness. Coma: state of unconsciousness, lasting more than 6

hours in which a person cannot be awakened, fails to respond normally to painful stimuli, light or sound, lacks a normal sleep-wake cycle and does not initiate voluntary actions.

Meditation: waking state but the person is highly relaxed but also highly alert. Takes training and practice.

Language Ability to speak and write words and to

understand spoken and written words. Language centers are located in the frontal,

parietal, and temporal lobes almost exclusively on the left side of the brain.

Lesions in speech centers give rise to language defects (aphasias)

Emotions Controlled by the limbic system (emotional brain) in

the cerebrum. Allows us to feel many emotions– anger, fear, sexual

feelings, pleasure, sorrow, etc. However, other parts of the cortex control the

normal expression of these emotions. Limbic activity without modulation by the cortex

may bring on attacks of abnormal, uncontrollable rage.

Limbic SystemLimbic System is also

involved in learning and memory. We are able to recognize other’s feelings and associate emotions with memories.

Memory Short-term memory: storage of information

for a few seconds or minutes. Short term memories can be consolidated and stored as long term memories days, months or weeks later.

Temporal, parietal, and occipital lobes are involved.

Left and Right Brain Left: talking, speaking, language, hand

movements (skilled and gesturing). Right: Perception of non-speech sounds.

Melodies, coughing, crying, laughing. Better at tactual perception and visualizing spatial relationships.

Both sides of the brain communicate with each other via the corpus callosum to perform a task however.

Diseases Stroke: hemorrhage or clot in the brain causes destruction of

motor neurons in the cerebrum. May see paralysis. Cerebral palsy: Damage to motor control areas of the brain

that is present at birth or occurs shortly after. May be caused by prenatal infection, disease of the mother, lack of oxygen to the brain.

Dementia: Degeneration of the neurons in the brain. Affects memory, attention span, intellectual capacity, personality and motor control.

Seizures: sudden bursts of abnormal neuron activity that result in temporary changes in brain function.