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Introduction:A. The nervous system is composed of neurons

and neuroglia.1. Neurons transmit nerve impulses to other

neurons.2. Nerves are made up of bundles of nerve

fibers or axons.3. Neuroglia aid and protect components

of the nervous system.

Chapter 9Nervous System

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2 divisions:

central nervous system (CNS),

the brain and spinal cord

peripheral nervous system (PNS), made up of peripheral nerves that connect the CNS to the rest of the body.

(Think pair share: come up with 3 main roles neurons can play)

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Nervous System Functions:

sensory, integrative, and motor.

(think pair share: 3 types of sensory input and 3 types of motor responses)

1. Motor functions

somatic nervous system: conscious control

autonomic nervous system: Unconscious control

Sympathetic: Fight or flight

Parasympathetic: at rest

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Supporting cellsA. Neuroglial Cells

1. fill spaces, support neurons, provide structural frameworks, produce myelin, and carry on phagocytosis.

4 in the CNS and 1 in the PNS.

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Schwann Cell

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Microglial cells - phagocytosis

Oligodendrocytes – form myelin

Astrocytes – provide nutrients, aid metabolism, structural supportrespond to brain injury by filling in spaces.

Ependymal cells – line ventricles, form choroid plexuses

Schwann cells – form myelin in PNS

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Classification of Neuronsgrouped two ways:

1- structural differences(bipolar, unipolar, and multipolarneurons),

2- functional differences(sensory neurons, interneurons, and motorneurons).

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Structural

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Structural classification1. Bipolar neurons – Sensory neurons: eyes, nose,

ears

2. Unipolar neurons - in ganglia outside the CNS- sensory neurons

3. Multipolar neurons - brain and spinal cord- interneurons- motor neurons

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4. Sensory (afferent ) neurons usually unipolar, some are bipolar.conduct impulse from body to CNS

5. Interneurons - multipolarconduct impulse between neurons

6. Motor (efferent) neurons - multipolarConduct impulse from CNS to body

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Neuron StructureNerve fibers = one axon, many dendrites.

dendritescarry impulses toward the cell body.

axonstransmit the impulse away from the cell body

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Larger axons are enclosed bysheaths of myelin provided bySchwann cells = myelinated.

Nodes of Ranvier = gaps in the myelin sheath between Schwann cells

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White matter in the CNS is due tomyelin sheaths in this area.

gray matter is unmyelinated nerve tissuein the CNS

The smallest axons lack a myelinsheath and are unmyelinated fibers.

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Nerve Impulse physiology

1- cells keep positive charge outside, negative charge inside = membrane potential. controlling ion concentrations.

2- Sodium/Potassium pumps create concentration gradient for Na+ and K+ ions.

cause membrane potential.

depolarization (flow of + ions into cell) caused by stimulation to neuron.

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Summation: = depolarizations pile up on each other.

(Like 2 small waves becoming a larger one)

Threshold: the amount of stimulation needed to cause an action potential to fire.

Action Potential: Rapid depolarization of cell membrane caused by the opening of Na+ channels.

(Nerve Impulse)

Nerve Impulse: rippling of action potentials down an axon. 22

Nerve Impulse

Conduction speed1. Unmyelinated fibers = slow

Conduct impulses over entire membrane.

2. Myelinated fibers = fast conduct impulses from node to node

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The Synapse• The junction (space) between two neurons.

• way of controlling impulse transmission

• Where many drugs take action

• Where neurotransmitters released

Synaptic Transmission

process where impulse in presynaptic neurontransmitted across synapse to postsynaptic neuron.

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Figure 9.13

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Synaptic Transmission

1- impulse reaches synaptic knob (end of axon)

2- synaptic vesicles release neurotransmitter to synaptic cleft. (synapse)

3- Neurotransmitters bind to specific receptors on postsynaptic neuron (dendrite)

4- if Threshold stimulus is reached, action potential triggered

5- Nerve impulse travels to cell body and down axon

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NeurotransmittersAt least 50 kinds

Most made in synaptic knobs stored in synaptic vesicles.

Ex: Acetylcholine =neurotransmitter that controls skeletal muscle actions.

Serotonin deficits associated with depression (SSRI-medications Zoloft, Paxil, Prozac) Serotonin reuptake inhibitors

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Nerve Pathwaysroutes nerve impulses travelsimplest is a reflex arc.

Reflex Arcssensory receptor - sensory neuron – interneuron(in spinal cord ) - motor neuron - effector.

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Reflexes

automatic, subconscious response to stimuli

Maintain homeostasis (heart rate, blood pressure, etc.)

responses = vomiting, sneezing, swallowing, etc.

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knee-jerk reflex (patellar tendon reflex) sprain protectionmonosynaptic reflex (no interneuron).

withdrawal reflexInjury protectionsensory neurons, interneurons, motor neurons.

At the same time, antagonistic extensormuscles inhibited.

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MeningesMembranes that surround the brain and spinal cordbetween bone and soft tissues.

1- Dura mater: outermost, is made of tough, white, dense connective tissue, contains many blood vessels.

forms the inner periosteum of skull bones.In some areas, forms partitions between lobes of the brainin others, forms dural sinuses.

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arachnoid mater,

Middle membrane, thin & lacks blood vessels.

does not follow convolutions of brain.

subarachnoid space: between arachnoid and pia maters contains cerebrospinal fluid.

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Pia Matter: Innermost

is thin and contains many blood vessels and nerves.

is attached to the surface of the brain and spinal cord and follows their contours.

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Spinal Cord

extends to the level of the intervertebral disk between the first and second lumbar vertebrae.

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Structure of the Spinal Cord31 segments, each gives rise to a pair of spinal nerves.

cervical enlargement gives riseto nerves leading to the upperlimbs,

lumbar enlargement gives rise to thoseinnervating the lower limbs.

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3. Two deep longitudinal grooves (anterior median fissure and posterior median sulcus) divide the cord into right and left halves.

4. White matter, made up of bundlesof myelinated nerve fibers (nervetracts), surrounds a butterfly-shaped core of gray matterhousing interneurons.

5. A central canal containscerebrospinal fluid.

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Functions of the Spinal Cordtwo major functions:

transmit impulses to and from the brain house spinal reflexes.

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BrainA. The brain is the largest, most complex

portion of the nervous system, containing 100 billion multipolar neurons.

B. can be divided into the cerebrum (largest portion and associated with higher mental functions), the diencephalon (processes sensory input), the cerebellum (coordinates muscular activity), and the brain stem (coordinates and regulates visceral activities).

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Cerebrum1. largest portion of the mature brain, consistingof two cerebral hemispheres.

2. A deep ridge of nerve fibers called thecorpus callosum connects thehemispheres.

3. The surface of the brain is marked byconvolutions, sulci, and fissures.

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4. The lobes are named according to the bones they underlie and include the frontallobe, parietal lobe, temporal lobe, occipital lobe, and the insula.

5. A thin layer of gray matter, thecerebral cortex, lies on theoutside of the cerebrum andcontains 75% of the cell bodies inthe nervous system.

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6. Beneath the cortex lies a mass of white matter made up of myelinated nerve fibers connecting the cell bodies of the cortex with the rest of the nervous system.

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Functions of the Cerebrum

1. provides higher brain functions, such as interpretation of sensory input, initiating voluntary muscular movements, memory, and integrating information for reasoning.

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Hemisphere Dominance

a. Both cerebral hemispheres function inreceiving and analyzing sensory inputand sending motor impulses to theopposite side of the body.

b. Most people exhibit hemispheredominance for the language-relatedactivities of speech, writing, andreading.

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c. The left hemisphere is dominant in 90% of the population, although some individuals have the right hemisphere as dominant, and others show equal dominance in both hemispheres.

d. The non-dominant hemispherespecializes in nonverbal functions andcontrols emotions and intuitivethinking.

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Diencephalon

1. The diencephalon lies above thebrain stem and contains thethalamus and hypothalamus.

2. The thalamus functions in sortingand directing sensory informationarriving from other parts of thenervous system, performing theservices of both messenger andeditor.

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3. The hypothalamus maintains homeostasis by: regulating heart rate and arterial blood pressure, body temperature, water and electrolyte balance, hunger and body weight, movements and secretions of the digestive tract, growth and reproduction, and sleep and wakefulness.

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Brain Stem

1. consists of the midbrain, pons, and medulla oblongata. lies at the base of the cerebrum, and connects the brain to the spinal cord.

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Midbraina. located between

the diencephalon and pons,contains bundles of myelinatednerve fibers that convey impulsesto and from higher parts of thebrain, and masses of gray matterthat serve as reflex centers.

b. contains centers forauditory and visual reflexes.

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Pons

a. lies between the midbrain and medulla oblongata, transmits impulses between the brain and spinal cord, and contains centers that regulate the rate and depth of breathing.

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Medulla Oblongata

a. transmits all ascending and descending impulses between the brain and spinal cord.

b. Functions include:heart rate control, bloodpressure control, worksalong with the pons to controlthe rate and depth of breathingand is associated with coughing,sneezing, swallowing, and vomiting

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Cerebellum

1. The cerebellum is made up oftwo hemispheres connectedby a vermis.

2. The cerebellum functions tointegrate sensory informationabout the position of body partsand coordinates skeletal muscleactivity and maintains posture.

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Peripheral Nervous SystemA. The peripheral nervous system (PNS)

consists of the cranial and spinal nervesthat arise from the central nervoussystem and travel to the remainder ofthe body.

B. The PNS is made up of the somaticnervous system that oversees voluntaryactivities, and the autonomic nervoussystem that controls involuntaryactivities.

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C. Cranial Nerves1. Twelve pairs of cranial nerves

arise from the underside of thebrain, most of which are mixednerves.

2. The 12 pairs are designated bynumber and name and include theolfactory, optic, oculomotor,trochlear, trigenimal, abducens,facial, vestibulocochlear,glossopharyngeal, vagus,accessory, and hypoglossalnerves.

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3.Refer to Figure 9.31 and Table 9.6 for cranial nervenumber, name, type, and function.

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D. Spinal Nerves1. Thirty-one pairs of mixed nerves

make up the spinal nerves.2. Spinal nerves are grouped

according to the level from whichthey arise and are numbered insequence, beginning with those inthe cervical region.

3. Each spinal nerve arises from tworoots: a dorsal, or sensory, root,and a ventral, or motor, root.

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4. The main branches of somespinal nerves form plexuses.

5. Cervical Plexusesa. The cervical plexuses lie

on either side of the neckand supply muscles andskin of the neck.

6. Brachial Plexusesa. The brachial plexuses arise

from lower cervical andupper thoracic nerves andlead to the upper limbs.

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7. Lumbrosacral Plexuses

a. The lumbrosacral plexusesarise from the lower spinalcord and lead to the lowerabdomen, externalgenitalia, buttocks, andlegs.

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Autonomic Nervous SystemA. maintains homeostasis of visceral activities

without conscious effort.

B. General Characteristics

1. two divisions: sympathetic and parasympathetic divisions, exert opposing effects on target organs.

parasympathetic operates under normalconditions.

sympathetic operates under conditions of stress or emergency.

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Autonomic Nerve Fibers

motor pathways include two fibers:

preganglionic fiber that leaves the CNSpostganglionic fiber that innervates the

effector.

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Sympathetic Division

Fibers arise from the thoracic and lumbar regions of the spinal cord, and synapse in paravertebral ganglia close to the vertebral column. Postganglionic axons lead to an effector organ.

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Parasympathetic Division

Fibers arise from the brainstemand sacral region of the spinal cord, and synapse in ganglia close to the effector organ.

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Autonomic Neurotransmitters

Preganglionic fibers of both sympathetic andparasympathetic divisions release acetylcholine.

Parasympathetic postganglionic fibers are cholinergic fibers and release acetylcholine.

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Sympathetic postganglionic fibers are adrenergic and release norepinephrine.

The effects of these two divisions, based on the effects of releasing different neurotransmitters to the effector, are generally antagonistic.

Determine what action some of your organs would have if they were sympathetically stimulated verses parasympathetically stimulated. (Ex. What happens in the pancreas? Blood vessels? Intestines?)

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Control of Autonomic Activity

largely controlled by reflex centers in the brain and spinal cord.

The limbic system and cerebral cortex alter the reactions of the autonomic nervous system through emotional influence.

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