P&A Unit 4

Nervous System

I. Intro – 2 parts to Nervous System

• A. Central Nervous System – CNS– Brain and spinal cord

• B. Peripheral Nervous System – PNS– All the nerves that connect to CNS and other body

parts

II. Nervous Tissue

• A. Neurons– 1. Def: Nerve cell – structural and functional unit of the

nervous system• B. Neuron Structure– 1. cell body

• Main portion of neuron• Contains neurofibrils• Conatains NISSIL BODIES

– Make protein

• Contains nucleus– Mature neurons cannot reproduce– DESTROY THEM AND THEY ARE GONE!!

– 2. dendrites• Short, highly branched parts off of cell body• Each neuron may have many• F: main RECEPTIVE surface of neuron

– Communicates with other neurons– **BRINGS IMPULSES IN

– 3. axon• An extension of the cell body which sends impulses AWAY from

the neuron• Schwaan cells

– Cells which surround axon– Make up myelin (lipoprotein) sheath

» MS – makes impulse travel very quickly– A). Not all axons are myelinated

» GRAY MATTER• Def: group of cells in NS which are unmyelinated

» WHITE MATTER• Def: group of cells in NS which ARE myelinated

• Nodes of Ranvier– Def: narrow gaps in myelin sheath b/n axon cells

III. Nerve Impulse Conduction

• A. Nerve impulse– Def: the propagation (increase/transmission) of

electrical charges along nerve cells• B. Process of Conduction– 1. nerve fiber develops resting potential

• Def: state in which a net POSITIVE charge is on the OUTSIDE of the cell membrane = POLARIZED

• Cause: Na+ and K+ are key ions– 3 Na+ ions diffuse outside the nerve fiber – low to high conc.– 2 K+ ions diffuse inside the nerve fiber – low to high– What is the charge? POSITIVE on OUTSIDE = resting potential

– 2. Threshold stimulus is received• Minimal stimulus needed for a nerve to fire• Will be reached if a nerve is stimulated by:

– Nearby nerve stimulus– Changes in light, temperature, pressure

• Resting potential decreases – net positive charge on outside of membrane decreases

• How?– Sodium/Potassium pump = active transport– Na+ channels open and Na+ starts flowing inside (L to H) cell

membrane = DEPOLARIZED

• If stimuli are strong enough, THRESHOLD STIMULUS is reached

• 3. Shortly after, K+ diffuses outside of cell (L to H) causing the cell to be REPOLARIZED

• 4. Action potential occurs– Def: rapid depolarization and repolarization of a nerve cell

• Lasts 1/1000 of a second

– Causes electric current to flow to next area of nerve cell• 5. Wave of APs continue through nerve = IMPULSE• 6. refractory period

– Time when nerve is repolarizing and will not respond to another stimulus

– http://people.eku.edu/ritchisong/301notes2.htm

• C. Impulse conduction– 1. unmyelinated fibers• Impulses travel slowly

– 2. myelinated fibers• Impulses travel quickly• Jump from N of R to N of R

• D. all or none response– Nerve fiber ALWAYS responds completely when TS is

reached– Impulse always travels through entire nerve

• E. Synapse– Def: the junction where 2 neurons meet and interact

• Sending neuron: PRESYNAPTIC NEURON• Receiving neuron: POSTSYNAPTIC NEURON

– Synaptic cleft: space b/n pre and post neurons• ** impulses jump this gap when traveling

• F. Neurotransmitters– 1. def: chemical substance released by presynaptic neuron

which may cause impulses to be conducted to postsynaptic neuron• ** if enough NT is released, TS in postsynaptic is reached and

impulse travels

– 2. Types• A. excitatory NT

– Cause impulse to quickly be transferred to postsynaptic neuron– Allows ions to quickly diffuse through membrane

• B. inhibitory NT– Cause impulse to die– TS is raised because ions can’t diffuse

• Examples– Excitatory• Acetylcholine• Dopamine

– Inhibitory• GABA – gamma amino butyric acid

– Mood, control many other excitatory NT

• Serotonin– Slow the brain down, reduce stress, relax, effect mood

V. Types of Neurons/nerves

– A. Multipolar neurons – many nerve fibers• Many dendrites/ 1 axon• Located: brain and spinal cord

– B. bipolar neurons – 2 nerve fibers• 1 axon/ 1 dendrite• Located: eyes, nose, ears

– C. unipolar neuron – 1 nerve fiber, splits into A and D• 1 dendrite/ 1 axon• Axon connected to brain/ spinal cord• Dendrite connected to peripheral body part

– D. Nerve types• Nerves: group of neurons held together by connective

tissue• 1. sensory nerves

– Send messages to brain/SC

• 2. motor nerves– Send messages to muscles/glands

• 3. mixed nerves– Send messages to both

• 4. interneurons– Connect nerves in brain/SC

VI. Nerve pathways

• A. reflex arc– 1. def: the simplest pathway an impulse may take• ** never reaches the brain• Process:

– 1. Sensory receptor at end of sensory nerve fiber takes in stimulation

– 2. SNF takes it to reflex processing center in Spinal Cord– 3. interneurons communicate in SC– 4. motor neuron carries response to effector– 5. effector does action – muscle, gland etc

• B. reflex behavior– 1. def: automatic unconscious responses to changes

occurring within or outside the body– 2. controls:

• Heart rate• Breathing rate• Blood pressure• Digestion• Sneezing• Coughing• Vomiting

– 3. example: knee jerk• A. sensory receptor sense touch to petallar ligament• B. sensory nerve fiber dendrite takes in info• C. impulse sent to SC where sensory axon meets an

interneuron which connects to motor neuron dendrite• D. motor axon carries impulse to effector in quad• E. quad flexes

– 4. withdrawal reflex• Person touches something hot, pulls away body part• P. 214

VII. Impulse processing

• A. convergence– 1. def: neuron impluses from 2 or more axons

converge on 1 neuron• Allows NS to bring different information together

• B. divergence– 1. def: impulses leaving 1 axon pass into several

other neurons• Allows impulse effect to be amplified• Ex: send message to all motor neurons in muscle so all

contract

VIII. Coverings of CNS

• A. Intro– 1. brain lies in: cranial cavity– 2. SC lies in: vertebral canal– 3. both surrounded by membranes called

MENINGES• Between bone and nerve tissue

• B. meninges– 3 layers• Dura mater• Arachnoid mater• Pia mater

– 1. dura mater• Outermost• Tough, white connective tissue• Many vessels & nerves• May extend into lobes of brain

– 2. arachnoid mater• Thin, weblike• Middle layer• No blood vessels

– ** Cerebrospinal fluid between arachnoid and pia mater – CSF

– 3. pia mater• Thin• Innermost• Many vessels to nourish brain and SC

VIII. Spinal Cord

• A. Intro– Cord begins at foramen magnum and end at intervertebral

disk b/n 1st and 2nd lumber vertebrae• B. structure– 1. 31 segments, each with a pair of nerves that branches off

peripherally• Spinal nerves

– 8 cervical– 12 thoracic– 5 lumbar– 5 sacral– 1 coccygeal– CAUDA EQUINA – last group of nerves, taillike

2. Cross Section

– 3. Functions of SC• 1. to conduct nerve impulses to and from Brain

– Involves only white matter– A. ascending tract

» Carry impulses TO brain– B. descending tract

» Carry impulses FROM brain to muscles/glands

• 2. to be the center of the reflex arc– Involves grey matter

IX. Brain

• A. Intro– 100 billion multipolar neurons– 3 major portions:

• 1. cerebrum– Largest– Nerve centers for sensory and motor functions– Memory and reasoning centers here

• 2. cerebellum– Posterior/dorsal region– Coordinates complex skeletal voluntary muscle movements– Maintains posture– Position of body parts

• 3. brain stem– Connects nerve pathways that connect many nerves between SC and brain– Regulate many organ activities

• B. Cerebrum– 1. Structure

• A. cerebral hemispheres (2)– 2 equal halves of cerebrum

• B. corpus callosum– Bridge of nerve fibers that connects cerebral hemisheres

» Allows R and L sides to communicate

• C. convolutions– Ridges of cerebrum

• D. sulcus– Groves b/w convolutions

• E. fissures– DEEP groves b/n parts of the brain

• F. frontal lobe• G. parietal lobe• H. occipital lobe• I. Temporal lobe• J. cerebral cortex

– Thin layer of grey matter over cerebrum– Covers convolutions, sucli, and fissures– Contains nearly 75% of all neuron cell bodies– Just beneath is a mass of White Matter that makes up

cerebrum

• 2. functions– A. frontal lobe• 1. motor speech area – Broca’s Area

– Moves mouth, tongue, pharynx, larynx

• 2. frontal eye field– Controls voluntary movements of eyes and eyelids

• 3. Concentration, planning, problem solving area• 4. emotions and reasoning• 5. motor areas which control voluntary muscles

– B. parietal lobe• Sensory areas involved with sensations of skin• Understanding speech, using words

– C. occipital lobe• Visual area• Combines visual images from L and R eyes• Recognition

– D. temporal lobe• Interpretation of sensory experiences• Memory of visual and audio patterns

– E. general interpretive area• Overlaps all lobes• Primary in complex thought and processing

– F. hemisphere dominance• L= verbal, analytical, computational, detailed• R= musical, visual, creative,

• C. cerebrospinal fluid – CSF– 1. structure

• A clear liquid that is secreted by CHOROID PLEXUS in pia mater– Tiny flowerlike masses

• Circulates around the brain and down central canal of SC – eventually reaches blood to deliver wastes etc

– 2. function• Surrounds brain and SC for support/protection• Provide path to blood for waste• ** always stays at same pressure b/c it is continually made and

reabsorbed– ** it not, pressure on the brain

• D. cerebellum– 1. located below occipital lobe– 2. mostly white matter– 3. covered by CEREBELLAR CORTEX – grey matter– 4. involved in:

• Planning• Personality• Intelligence• Interprets desired movements and causes body to do them

– 5. damage = :• Tremors• Loss of muscle tone• Uncoordinated walk• Loss of equilibrium

• E. brain stem– Def: bundle of nerve tissue that connects cerebrum to

spinal cord• Several masses of grey matter

– 1. Parts:• A. diencephalon

– b/w cerebral hemispheres– 1) infundibulum here

» A piece which hangs down and attaches to pituitary gland– 2) thalamus here

» Receives all sensory impulses and relays them to appropriate region of cortex for interpretation

– 3) hypothalamus here» Regulates heart rate, blood pressure, body temp, hunger,

release of hormones, regulates sleep– 4)limbic system here

» Combination of many areas» Involved in emotional expression» Fear, anger, pleasure, sorrow» Recognizes things that threaten life – “fight or flight”

• B. midbrain– Below diencephalon– Much grey matter as a reflex center– Visual reflex = eyeballs move when head moves– Auditory reflex = ears move close to sound

• C. pons– Below midbrain – round bulge– Relay impulses all over brain– Ex: relays breathing rhythms to medulla oblongata

• D. medulla oblongata– Extends from pons– Controls:

» Cardiac center: speed or lower heart rate» Vasomotor center: constrict/dilate blood vessels» Respiratory center: rate/rhythm of breathing

X. Peripheral Nervous System - PNS

• A. def: nerves that branch out from the brain and SC– SOMATIC NS: consists of cranial and spinal nerves

that connect to skin and skeletal muscle– AUTONOMIC NS: nerves that connect to

organs/glands

• B. Cranial nerves – 12 pair– * go in order from front to back– 1. olfactory nerves (I)

• Sensory nerves• Transmit smell impulses

– 2. optic nerves (II)• Sensory nerves• Transmit vision impulses

– 3. oculomotor(III)• Mostly motor nerves• Transmit impulses to: adjust lens, adjust pupil, move eyelid, move

eye

– 4. trochlear (IV)• Mostly motor nerves• Transmit eye movement impulses

– 5. trigeminal (V)• Mixed• Sensory:

– Transmit impulses from: tear glands, scalp, forehead, upper eyelids, teeth, lips, skin of face

• Motor:– Transmit impulses of chewing

– 6. Abducens (VI)• Mostly motor• Transmit impulses of eye movement

– 7. facial (VII)• Mixed• Sensory:

– Transmit impulses of tongue/taste

• Motor:– Facial expression, tear glands, salivary glands

– 8. vestibulocochlear (VIII)• Sensory nerves• Transmit impulses for equilibrium and hearing

– 9. glossopharyngeal (IX)• Mixed• Sensory:

– Pharynx, tonsils, tongue, neck artery

• Motor:– Swallowing, salivary

– 10. vagus (X)• Mixed• Sensory:

– Pharynx, larynx, esophagus, organs

• Motor:– Speech, swallowing, heart, glands

– 11. accessory (XI)• Mostly motor• Pharynx, larynx, neck, back

– 12. hypoglossal (XII)• Mostly motor• Muscles that move tongue

• D. Spinal Nerves– 31 pair– Communicate impulses from spinal cord and arms,

legs, neck, trunk

• D. Autonomic Nervous System– Regulates heart rate, BP, breathing rate, body temp– Respond to emotional stress and strenuous physical

activity– 1. sympathetic division

• Prepares body for emergency situations• Initiates activation and secretion of adrenaline

– 2. Parasympathetic division• Active during ordinary conditions• Restores body back to normal after stress

XI. Clinical Terms