I. General functions

A. Receive stimuli from environment and respond to them

B. Provide ability to think, reason, remember, etc.

C. Controls and coordinates body movements

II. Divisions of nervous system

A. Central Nervous System (CNS): consists of brain and spinal cord. structural and functional center of entire nervous system.

B. Peripheral Nervous System (PNS): nerves in periphery. cranial nerves, spinal nerves.

1. Afferent (sensory) nervous system: incoming pathways

2. Efferent (motor) nervous system: outgoing pathways

a. Somatic Nervous System: skeletal muscles

b. Autonomic Nervous System (ANS): smooth muscles, cardiac muscles, glands

1. Sympathetic Division: fight-or-flight.

2. Parasympathetic Division: rest-and-repair.

III. Nervous tissue

A. Two Types of Cells

1. Neuroglia

a. astrocytes (star-shaped). form tight sheaths around brain's capillaries.

b. microglia: engulf, destroy microbes, cellular debris.

c. ependymal cells: form sheaths that line fluid filled cavities in brain, spinal cord. produce fluid.

d. oligodendrocytes: produce myelin sheath around nerve fibers.

e. Schwann cells: only in PNS. functional equivalent of oligodendrocytes. gaps between adjacent Schwann cells are called nodes of Ranvier.

2. Neurons: nerve cells

a. Structure

1. cell body: contains nucleus, cytoplasm, organelles, Nissl bodies.

2. dendrites: branches extending from cell body. conduct impulses to cell body of neuron.

3. axon: single process extending from cell body. conducts impulses away from cell body.

b. Structural classification

1. multipolar: one axon, several dendrites.

2. bipolar: one axon, one dendrite.

3. unipolar: axon and dendrite fused together close to cell body.

c. Functional classification

1. afferent neurons (sensory): nerve impulses to spinal cord, brain

2. efferent neurons (motor): nerve impulses away from brain, spinal cord toward muscles, glands.

3. interneurons: conduct impulses from afferent neurons or toward motor neurons. lie in CNS.

B. Terms to Know

1. White matter: bundles of myelinated fibers.

2. Gray matter: cell bodies, unmyelinated fibers

3. Tract: bundle of axons within CNS

4. Nerves: cordlike bundles of myelinated axons.

5. Nerve Trunk: a group of several nerves

IV. Membrane potential

A. Membrane potential: difference in electrical charge across cell membrane.

B. Resting membrane potential: membrane potential maintained by nonconducting neuron's membrane.

V. Nerve Impulse

A. Action Potential

1. Stimulation: stimulus applied. some sodium channels at point of stimulation open.

2. Depolarization: sodium ions diffuse in as a result of stimulation. If threshold potential is reached, impulse will continue.

3. All-or-none: if threshold potential surpassed, full action potential always reached.

4. Polarization: membrane potential moves back toward resting potential. potassium channels open once sodium moves in. restores original excess of positive ions outside polarization.

5. Hyperpolarization: more potassium rush out of cell, hyperpolarizing cell until sodium-potassium pump returns ions to resting state.

B. Refractory period: brief period during which area of membrane resists restimulation.

1. absolute refractory period: after threshold potential is reached, will not respond to any stimulus, no matter how great the impulse.

2. relative refractory period: after absolute refractory period; membrane repolarizing, will respond only to very strong stimuli. therefore, magnitude of stimulus determines frequency of impulses.

C. Conduction of action potential

1. next segment of membrane triggered to open due to reverse in polarity. triggers sodium channels in next segment to open. moves action potential from one point to next along membrane.

2. saltatory conduction: action potential conduction from one node to next.

VI. Synapse: place where impulses transmitted from one neuron to another.

A. Structure

1. Synaptic knob: tiny bulge at end of terminal branch of axon. contains small vesicles with neurotransmitter.

2. Synaptic cleft: space between synaptic knob and plasma membrane of post-synaptic knob.

3. Postsynaptic neuron membrane: protein molecules embedded in it opposite pre-synaptic knob. receptors for neurotransmitters.

B. Synaptic transmission: neurotransmitters bring about response in postsynaptic neuron. some cause depolarization, some cause hyperpolarization.

1. Calcium diffuses into knob

2. Triggers movement of vesicles to membrane. releases neurotransmitters.

3. Neurotransmitters diffuse across narrow synaptic cleft, contact postsynaptic neuron's plasma membrane. bind to receptor molecules.

4. Ion channels open, producing postsynaptic potential. if threshold potential is reached, impulse begins.

5. Neurotransmitter action quickly terminated.

VII. Neurotransmitters

A. Acetylcholine (ACh). junctions with motor effectors; parts of brain.

B. Amines: serotonin, histamine, dopamine, epinephrine, norepinephrine. found in brain; affect learning, emotions, motor control.

C. Amino Acids: found in brain, spinal cord.

D. Neuropeptides: enkephalins, endorphins. pain-relieving effects.

VIII. Nerve Pathways

A. Reflex arcs

1. Semicircular pattern of neurons. an impulse conduction route to and from the CNS. One direction only.

2. Three neuron arc (most common)

a. sensory (afferent) neuron

b. interneuron

c. motor (efferent) neuron

B. Path of a reflex

1. sensory receptor in PNS (to dendrites)

2. afferent neuron (through cell body, across synapse)

3. CNS (interneuron) (dendrites, through cell body and axon, across synapse)

4. efferent neuron (dendrites of motor neuron through body, across neuron to:)

5. effector (muscle tissue or glandular tissue)

C. Reflex: nerve impulse passing over reflex arc.

1. somatic reflexes: contractions of skeletal muscles.

2. autonomic reflexes: contractions of smooth or cardiac muscles or secretion of glands.

D. Reflex behavior

1. knee jerk (patellar reflex): extension of lower leg in response to tapping patellar tendon.

2. ankle jerk (Achilles reflex): extension (plantarflexion) of foot in response to tapping Achilles tendon.

3. Babinski reflex: extension of big toe. normal in infants.

4. corneal reflex: blinking in response to touching cornea.

5. abdominal reflex: drawing in of abdominal wall in response to stroking side of abdomen.

IX. Coverings of CNS

A. Bone

B. Meninges: a tough membrane which contains fluids. surround brain and spinal cord.

1. dura mater: strong white fibrous tissue. (serves as inner periosteum of cranial bones)

2. arachnoid: delicate, cobwebby layer

3. pia mater: adheres to outer surface of brain, spinal cord; contains blood vessels

C. Spaces

1. epidural: between bone and dura. contains fat, connective tissue.

2. subdural: between dura and arachnoid. contains lubricating serous fluid

3. subarachnoid: between arachnoid and pia. contains CSF: cerebrospinal fluid: clear, colorless fluid that provides supportive, protective cushioning. reservoir of circulatory fluid the brain monitors for changes in internal environment. (CSF fluid also found in the cerebral ventricles: fluid filled spaces inside the brain)

X. Spinal cord

A. Structure

1. Location: inside vertebral column from occipital bone to bottom of first lumbar vertebra, within spinal cavity

2. Gray matter: "H" shaped core (composed of dendrites and neuron cell bodies. 2 bulges (cervical, lumbar regions); 2 deep grooves: anterior median fissure, posterior median sulcus.

3. White matter: outer portion which contains spinal tracts. spinal tracts provide 2-way conducting paths to and from the brain

a. Ascending: carries impulses up.

b. Descending: carries impulses down.

c. Each tract serves a function, transmitting pain, touch, temp., impulses

B. Function

1. Integrator: Center of reflex activity

a. Withdrawal reflex

b. Jerk reflex

2. Two way conduction route: carries impulses to and from brain.

XI. Brain

A. Brain Stem: performs sensory, motor, reflex functions.

1. Medulla oblongata: attaches to spinal cord.

a. Structure: composed of white matter and reticular formation. contains cardiac, respiratory, vasomotor control centers.

b. Functions: vital reflexes (cardiac, vasomotor, respiratory); nonvital reflexes: vomiting, coughing, sneezing, hiccuping, swallowing

2. Pons: above medulla

a. Structure: white matter and reticular formation.

b. Functions: regulation of respiration, reflexes of 5th-8th cranial nerves

3. Midbrain: midsection of brain.

a. Structure: white matter, reticular formation. cerebral peduncles.

b. Functions: reflex for cranial nerves (pupillary, reflexes, eye movements). some auditory centers here.

B. Diencephalon

1. Hypothalamus: Posterior to the pituitary gland.

a. Structure: 2 pairs of neuron cell body clusters.

b. Functions: Exerts control over most of internal organs.

1. regulator and coordinator of autonomic activities.

2. link between cerebral cortex, lower autonomic centers.

3. maintaining water balance.

4. secrete releasing factors that affect pituitary.

5. maintain waking state.

6. part of mechanism for appetite regulation.

7. maintenance of body temperature.

2. Thalamus

a. Structure: mass of gray matter.

b. Functions:

1. sensation of conscious recognition of temperature, touch.

2. plays part in mechanism responsible for emotions.

3. plays part in arousal, alerting mechanism.

3. Pineal Body seems to be involved in regulating biological clock.

C. Cerebrum: largest

1. Structure: made of ridges (gyri), grooves (fissures, sulcus) cerebral cortex: gray matter 2-4 mm thick surface of cerebrum.

a. deep fissures divide into 4 lobes

1. longitudinal fissure: divides brain into right and left cerebral hemispheres.

2. central sulcus: between frontal and parietal

3. lateral fissure: between temporal and frontal/parietal

4. parietooccipital fissure: separates occipital from parietal lobes.

b. five major lobes

1. Temporal: hearing, smell, taste

2. Occipital: vision

3. Parietal: wide variety: heat, cold, pain, touch, pressure

4. Frontal: voluntary movements, personality, some memory, speech

5. Insula (hidden in lateral fissure)

c. corpus callosum: connect regions in each hemisphere

2. Functions: functional areas of cortex

a. sensory: postcentral gyrus: general somatic sensory area (touch, pressure, temperature, body position)

b. motor: precentral gyrus: general somatic motor area

c. integration

1. consciousness: functions as arousal system.

2. language: speech center part of frontal, parietal, temporal lobes.

3. emotions: limbic system.

4. memory: especially temporal, parietal, occipital lobes.

D. Cerebellum

1. Structure: gray matter makes up outer portion, white matter inside ("arbor vitae").

2. Functions:

a. produce skilled movement by coordination of activities of groups of muscles.

b. helps control posture.

c. controls skeletal muscles to maintain equilibrium

XII. PNS

A. Cranial nerves

sensory motor both

I. Olfactory: smell information.

II. Optic: visual information.

III. Oculomotor: external eye muscles (except superior oblique, lateral rectus).

IV. Trochlear: superior oblique in eye.

V. Trigeminal: sensations from skin, mucosa in head, teeth; chewing.

VI. Abducens: lateral rectus muscle of eye.

VII. Facial: facial expression, secretion of saliva, tears. taste.

VIII. Vestibulocochlear: equilibrium; hearing.

IX. Glossopharyngeal: sensations of tongue, swallowing.

X. Vagus: controls muscles in swallowing, controls heart rate, visceral activity.

XI. Accessory: shoulder movements, turning of head, voice production.

XII. Hypoglossal: muscles of tongue.

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B. Spinal nerves

1. Structure

a. 31 pairs of nerves attach to level of vertebral column. all contain sensory (dorsal) root and motor (ventral) root fibers

great sciatic nerve: largest nerve in body. runs down back of thigh, supplies skin of leg, posterior thigh muscles, leg and foot muscles.

2. Function of Spinal Nerves

a. Conduct impulses between spinal cord and body

XIII. ANS

A. Functions of sympathetic division: maintains normal functioning of autonomic effectors.

B. Functions of parasympathetic division: rest and repair.

C. Autonomic neurotransmitters

1. Norepinephrine

2. Acetylcholine

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