The Nervous System (Ch. 9)

Chapters 9 and 10

Terminology

Neurology: branch of science that deals with the functioning & disorders of the nervous system

Plasticity: can change based on experience Cranial nerves: emerge from brain Spinal nerves: emerge from spinal cord Nerve: bundle of axons Ganglia: cluster of cell bodies Neuron: basic functioning unit of the nervous system Neuroglia: smaller, support structures for neurons;

higher in number than the 100 billion neurons in brain and 100 million neurons in spinal cord

The Nervous System

Two divisions: Central & Peripheral

Central or CNS- brain and spinal cord

Peripheral or PNS- nerves connecting CNS to muscles and organs

• SNS: somatic

• ANS: autonomic

– Sympathetic & parasympathetic

Central Nervous System

Peripheral Nervous System

Functions of Nervous System

3 functions Sensory: detect stimuli Integrative: analyzes and stores information Motor: responds to information

Nervous Pathway

Receptor

Control Center

(CNS)

Effector

Sensory neuron=

Afferent neuron

Motor neuron=

Efferent neuron

*Remember a receptor perceives a stimulus

*Effectors are usually muscles and glands.

Basic Neuron Parts

Neuron Parts

3 basic parts: Cell body: integrates stimuli Dendrites: receive impulse and send to cell

bodyMany per neuron

Axon: send impulse away from cell body onto another neuron or effector

one per neuron

More neuron parts to know

Look on p. 216, figure 9.4 Schwann Cells: cells surrounding the axon Neurolemma: cell membrane on Schwann cells Nodes of Ranvier: indentations between Schwann cells Myelin: lipid substance that occupies Schwann cells;

insulates impulse traveling on axon this substance is the reason why CNS repair is usually

not possible Synaptic end bulbs: enlarged part of axon terminal that

secretes neurotransmitters Synapse = space between neurons

More neuron parts to know

Neurons can be…

Myelinated Myelin is present Comprises white matter in brain and spinal

cord Functions in nerve impulse conduction

Unmyelinated Myelin is absent Comprises gray matter in the brain and spinal

cord Functions in nerve impulse integration

Organization

Tracts Bundle of axons in CNS 2 types

Ascending: carry impulses from spinal cord UP to brain

Descending: carry impulse from brain DOWN to spinal cord

Works sort of like a 2 way street.

Nervous Impulses

Action potential = how neurons communicate with one another Created by Sodium (Na+) and Potassium (K+) ions

Polarized membranes: charges are opposite so potential energy results

Resting membranes: charges are alike so no energy results = resting period

Threshold: level that must be reached in order to send an impulse All-or-none principle

Anesthesia: blocks the Na+ and K+ channels so pain signals do not reach the CNS

Central Nervous System

Brain and Spinal Cord

SpinalCord

Brain

Neurotransmitters

Acetylcholine: excitatory (muscle contraction) Norepinephrine: awakening from sleep; resting Epinephrine: fight or flight Dopamine: regulates muscle tone Serotonin: sensory perception (eg. happiness) Endorphins: pain relief

*See Table 9.2 on p. 226

Spinal Cord

Located in vertebral canal Covered in meninges (layers of connective tissue)

3 layers with CSF (cerebrospinal fluid) Dura mater (outer) = dense, tough, fibrous Arachnoid mater (middle) = spider-web Pia mater (inner) = thin Epidural space between vertebrae & dura mater

• Space for administering epidurals Subarachnoid space between arachnoid & pia mater

• Space where spinal tap/lumbar puncture is performed 16-18 inches long Extends from foramen magnum to L2 (then cauda equina

emerges)

Spinal Cord

Reflexes

Fast, automatic responses Follow a pathway called the reflex arc Somatic reflexes

Involve skeletal muscle Ex: patellar reflex (“knee jerk”), withdrawal

reflex Autonomic reflexes

Involve smooth and cardiac muscle Ex: swallowing, urinating, defecating

Spinal Nerves

31 pairs Cervical – 8

C1-C8

Thoracic – 12T1-T12

Lumbar – 5L1-L5

Sacral – 5S1-S5

Coccygeal - 1

D

E

R

M

A

T

O

M

E

S

Brain

One of the largest organs Contains 100 billion neurons and 1 trillion neuroglia Weighs ~ 3 pounds Covered by same 3 meninges layers + CSF 4 major parts:

Brain stem, diencephalon, cerebrum, cerebellum Requires 20% of body’s oxygen

Low O2 = unconsciousness, brain damage

Requires normal glucose levels Low glucose = confusion, dizziness, convulsions

Cerebrospinal Fluid (CSF)

Clear Colorless 80-150 mL Delivers nutrients to brain and spinal cord Removes wastes & toxins from brain and spinal cord Lubrication Can be tested through lumbar puncture/spinal tap Hydrocephalus (water head) can result from too much CSF Made in ventricles on brain

Brain Stem

Consists of 3 parts: Medulla (continuous with spinal cord)

Controls vital signs

Pons (bulges anteriorly)Regulates rhythmic respiration

MidbrainPerceives auditory & visual reflexes

Diencephalon

Consists of 2 parts Thalamus

Principle relay station for sensory impulsescognition

HypothalamusControls homeostatic activitiesControls ANS, pituitary gland, body temperature,

emotions, behaviors, eating & drinking (satiety center), circadian rhythms (sleep-wake cycle)

Cerebellum

2nd largest portion of the brain Consists of 2 hemispheres connected by arbor

vitae Controls coordinated movements, posture,

balance Protected by occipital bone

Cerebrum

Largest portion of the brain Consists of 2 hemispheres connected by corpus

callosum Folds = gyri & grooves = sulci Controls coordinated movement, senses memory,

judgement, intelligence

Corpus Callosum

Major (but not only) pathway between sides

Connects comparable structures on each side

Permits data received on one side to be processed in both hemispheres

Aids motor coordination of left and right side

Corpus Callosum

Medial surface of right hemisphere

Electroencephalogram (EEG)graphical reading of brain waves to determine normal function

Cranial Nerves – 12 pairs

I. Olfactory: smell II. Optic: sight III. Oculomotor: eye movement IV. Trochlear: eye movement & proprioception V. Trigeminal: chewing, touch, pain VI. Abducens: eye movement VII. Facial: facial expression VIII. Vestibulocochlear: hearing & equilibrium IX. Glossopharyngeal: taste, swallowing X. Vagus: swallowing, coughing XI. Spinal Accessory: head & shoulder movement XII. Hypoglossal: tongue movement

*TABLE 9.6 on p. 246*

12 Cranial Nerves

Cranial nerves continued

You must know these nerves IN ORDER It will be beneficial to know them before

dissection as you will have to label them on the brain.

Remember: Oh, Oh, Oh, That Trashy And Fat Vain Girl’s Van Almost Hydroplaned OR make up your own study device

Diseases/Disorders

Parkinson’s: dopamine is slow or no longer released; causes tremors & possible muscle rigidity

Multiple Sclerosis: chronic myelin degeneration Alzheimer’s: causes disabling senile dementia Meningitis: inflammation of meninges

Viral & bacterial Cerebrovascular Accident (CVA) = stroke

3rd leading cause of death in the US

Brain scan of stroke patient

Broca’s Area speech

Peripheral Nervous System

2 subdivisions Autonomic Nervous

system (ANS) Somatic Nervous

system (SNS)

SpinalCord

Brain

Nerves

Somatic Nervous System (SNS) Utilizes sensory

and motor neurons

Produces voluntary and conscious movements

Muscle

MotorNeuron Interneuron

Skin receptors

SensoryNeuron

Brain

Autonomic Nervous System (ANS)

Controls involuntary functions heartbeat blood pressure respiration perspiration digestion

Can be influenced by thought and emotion Two divisions:

sympathetic parasympathetic

Sympathetic & Parasympathetic (Have opposing effects on the body)

Sympathetic Neurons synapse with

MANY other neurons = widespread bodily responses

Most neurons are adrenergic (cause long-lasting responses)

Parasympathetic Neurons synapse with

FEW other neurons = local bodily responses

Most neurons are cholinergic (cause short-lasting responses)

Sympathetic division = Thoracolumbar division

“ Fight or flight” response

Release adrenaline (epinephrine) and noradrenaline (norepinephrine)

Impulses come from thoracic and lumbar spinal nerves

Increases heart rate and blood pressure

Increases blood flow to skeletal muscles

Inhibits digestive functions

CENTRAL NERVOUS SYSTEMBrain

Spinalcord

SYMPATHETIC

Dilates pupil

Stimulates salivation

Relaxes bronchi

Accelerates heartbeat

Inhibits activity

Stimulates glucose

Secretion of adrenaline,nonadrenaline

Relaxes bladder

Stimulates ejaculationin male

Sympatheticganglia

Salivaryglands

Lungs

Heart

Stomach

Pancreas

Liver

Adrenalgland

Kidney

Parasympathetic division = Craniosacral division

“ Rest and digest” response

Calms body to conserve and maintain energy

Lowers heartbeat, breathing rate, blood pressure

Impulses come from cranial nerves and sacral spinal nerves

SLUDD Salivation Lacrimation Urination Defecation digestion

CENTRAL NERVOUS SYSTEMBrain

PARASYMPATHETIC

Spinalcord

Stimulates salivation

Constricts bronchi

Slows heartbeat

Stimulates activity

Contracts bladder

Stimulates erectionof sex organs

Stimulates gallbladder

Gallbladder

Contracts pupil

Summary of autonomic differences

Sympatheticdivision (arousing)

Parasympatheticdivision (calming)

Pupils dilate EYES Pupils constrict

Decreases SALIVATION Increases

Perspires SKIN Dries

Increases RESPIRATION Decreases

Accelerates HEART Slows

Inhibits DIGESTION Activates

Secrete stresshormones

ADRENALGLANDS

Decrease secretionof stress hormones

Paradoxical Fear – p. 251

Parasympathetic division overrides the sympathetic division

Caused during extremely stressful situations and the body realizes there is no way out/no way to win