The Nervous SystemDR MWAIHOJO JUSTINMD, BMH

•Detects and responds to changes inside and outside the body.

•Provide immediate response to stimuli.•It consist of the brain, spinal cord and

peripheral nerves.

Basic Functions1.1. Sensory input Sensory input – gather information2.2. IntegrationIntegration – process and interpret

sensory input3.3. Motor output Motor output – response by muscles and

glands

OrganizationFor descriptive purposes the parts of the nervous system For descriptive purposes the parts of the nervous system

can grouped as followscan grouped as followsA.A. Central Nervous System (CNS)Central Nervous System (CNS)

▫Brain & spinal cord▫Integrative and control centers

B.B. Peripheral Nervous System (PNS)Peripheral Nervous System (PNS)▫Nerves (spinal nerves, cranial nerves)▫Communication lines between CNS and rest of body▫Two Divisions:Two Divisions:

1.1. Sensory (afferent) DivisionSensory (afferent) Division: Sensory receptors CNS2.2. Motor (efferent) DivisionMotor (efferent) Division: CNS effectors (muscles

& glands)

Motor Division• Somatic nervous systemSomatic nervous system (voluntary) –

control skeletal muscles• Autonomic nervous systemAutonomic nervous system (ANS)

(involuntary) – regulate smooth muscles, cardiac, glands▫Subdivisions: sympatheticsympathetic &

parasympatheticparasympathetic

Nervous System•Master controlling and communicating

system

Nervous TissueNervous Tissue1.1. NeuronsNeurons (nerve cells) - transmit message

Anatomy:▫ Cell bodyCell body – contains nucleus; metabolic center▫ DendriteDendrite – fiber that conveys messages toward

cell body▫ AxonAxon – conduct nerve impulses away from the

cell body▫ Axon terminalsAxon terminals – end of axon; contain

neurotransmitters & release them▫ Synaptic cleft/synapseSynaptic cleft/synapse – gap between neurons

Nervous TissueNervous Tissue2. Supporting cells (NeurogliaNeuroglia)CNSCNS: : astrocytes, microglia, ependymal cells, astrocytes, microglia, ependymal cells,

oligodendrocytesoligodendrocytes barrier between capillaries and neurons protect neurons immune/defense line brain and spinal cord cavities wrap nerve fibers produces myelin sheaths (covering)

PNSPNS: Schwann cells, satellite cells: Schwann cells, satellite cells surround large neurons protect & cushion

• MyelinMyelin:: whitish, fatty material that covers nerve fibers to speed up nerve impulses

• Schwann cellsSchwann cells:: surround axons and form myelin sheath

• Myelin sheathMyelin sheath:: tight coil of wrapped membranes• Nodes of RanvierNodes of Ranvier: gaps between Schwann cells

• GangliaGanglia: collections of cell bodies• Bundles of nerve fibers = tractstracts (CNS) or

nervesnerves (PNS)• White matterWhite matter: dense collections of myelinated

fibers• Gray matterGray matter: unmyelinated fibers & cell bodies

Classification of Neurons

1. Functional Classification: direction nerve impulse is traveling

Sensory neurons

Motor neurons Interneurons

carry impulses from sensory receptors to

CNS

carry impulses from CNS to muscles &

glands

connect sensory & motor neurons

Vision, hearing, equilibrium, taste, smell,

pain, pressure, heat

2. Structural Classification: # processes extending from cell body

Multipolar Bipolar Unipolar1 axon, several

dendrites1 axon, 1 dendrite 1 process

Most common (99%) Rare

Short with 2 branches

(sensory, CNS)Eg. Motor neurons,

interneuronsEg. retina, nose,

ear Eg. PNS ganglia

Nerve Impulses

Neuron Function1.1. IrritabilityIrritability: ability to respond to stimulus

& convert to nerve impulse2.2. ConductivityConductivity: transmit impulse to other

neurons, muscles, or glands

Exciting a Neuron:•Cell membrane at rest = polarizedpolarized

▫Na+ outside cell, K+ inside cell▫Inside is (-) compared to outside

•Stimulus excited neuron (Na+ rushes in) becomes depolarizeddepolarized

•Depolarization activates neuron to transmit an action potential action potential (nerve impulse)▫All-or-none response▫Impulse conducts down entire axon

•K+ diffuses out repolarizationrepolarization of membrane•Na+/K+ ion concentrations restored by

sodium-potassium pumpsodium-potassium pump (uses ATP)

Resting membrane potential (-70mV)

Gated Ion Channels (Na+ and K+)

Depolarization

• Saltatory conductionSaltatory conduction: electrical signal jumps from node to node along myelinated axon (30x faster!)

Multiple Sclerosis (MS)•Autoimmune disease•Myelin sheaths destroyed reduced to

hardened lesions (scleroses)•Blindness, muscle weakness, speech

disturbance, urinary incontinence•Treatment: interferons, glatiramer (hold

off attacks)

Nerve Conduction• Action potential

reaches axon terminal vesicles release neurotransmittersneurotransmitters (NT) (NT) into synaptic cleftsynaptic cleft

• NT diffuse across synapse bind to receptors of next neuron

• Transmission of a nerve impulse = electrochemical eventelectrochemical event

Neurotransmitters• 50+ identified• ExcitatoryExcitatory: cause depolarization• InhibitoryInhibitory: reduce ability to cause action

potential• Eg. acetylcholine, serotonin, endorphins

NeurotransmittersNeurotransmitt

erAction Affected by:

Acetylcholine muscle contraction botulism, curare (paralytic), nicotine

Dopamine “feeling good” cocaine, amphetamines

Serotonin sleep, appetite, nausea, mood, migraines

Prozac, LSD, ecstasy

Endorphins inhibit pain morphine, heroin, methadone

GABA main inhibitory NT alcohol, Valium, barbiturates

Reflexes•Rapid, predictable, involuntary responses to

stimuli

1.Somatic Reflexes: stimulate skeletal muscles▫ Eg. jerking away hand from hot object

2.Autonomic Reflexes: regulate smooth muscles, heart, glands▫ Eg. salivation, digestion, blood pressure,

sweating

Reflex Arc (neural pathway)Five elements:1. Receptor – reacts to stimulus2. Sensory neuron3. CNS integration center4. Motor neuron5. Effector organ – muscle or gland

Reflex ActivitiesPatellar (Knee-jerk)

Reflex Pupillary Reflex

Patellar (Knee-jerk) Reflex Pupillary Reflex

• Stretch reflex• Tapping patellar

ligament causes quadriceps to contract knee extends

• Help maintain muscle tone, posture, & balance

• Optic nerve brain stem muscles constrict pupil

• Useful for checking brain stem function and drug use

Flexor (withdrawal) reflex:painful stimulus withdrawal of threatened body part▫Pin prick

Plantar reflex:draw object down sole of foot curling of toes▫Babinski’s sign: check to see

if motor cortex or corticospinal tract is damaged

Voluntary Reactions•More neurons and synapses are involved longer response times

Reflex = Involuntary Reaction Voluntary Reaction

CNS•THE HUMAN BRAIN

4 Major Regions1. Cerebral

Hemispheres2. Diencephalon3. Brain stem4. Cerebellum

1. Cerebral Hemispheres (Cerebrum)L & R hemispheresCorpus callosum: large fiber tract;

connects 2 hemispheresLobes: major regions (named for cranial

bones) ParietalParietal, frontalfrontal, occipitaloccipital, temporaltemporal

Gyri (gyrus) = elevated ridges of tissueSulci (sulcus) = shallow groovesFissures = deeper grooves, separate large

regions of brain• Motor & sensory function: opposite

hemispheres• Responsible for:

▫ reasoning, thought, memory, speaking, sensesation, sight, hearing, voluntary body movement

▫ reasoning, thought, memory, speaking, sensstion, sight, hearing, voluntary body movement

Cerebral Cortex•Grey matter•“Executive suite” conscious mind

2. Diencephalon (interbrain)

3 main structures:1.Thalamus: relay station for incoming info2.Hypothalamus:

A. Autonomic control center (heart rate, BP, digestion)

B. Emotional response (limbic system)C. Body temperature regulationD. Regulate food intakeE. Sleep-wake cyclesF. Control endocrine system pituitary gland at

base3.Epithalamus: pineal gland (sleep-wake cycle)

Diencephalon

3. Brain Stem

•Programmed, automatic behaviors for survival•3 regions:

1. Midbrain: vision, hearing, reflex2. Pons: breathing3. Medulla oblongata: heart rate, BP,

breathing, swallowing, vomiting, coughing, sneezing

Brain Stem

4. Cerebellum•Balance, equilibrium, timing of skeletal

muscle activity. Responsible for:▫coordination of muscles, balance, posture,

& muscle tone

Protection of CNS•Meninges: connective tissue covering

CNS structures▫Dura mater (leathery outer), arachnoid

mater (web-like middle), pia mater (surface of brain)

▫Meningitis: inflammation of meninges; bacterial or viral infection

▫Lumbar (spinal) tap – test for infection, tumors, multiple sclerosis

CSFCerebrospinal fluid (CSF): watery cushion to

protect NS from trauma .Circulates continuouslycontains: glucose, proteins,lactic acid, urea,

cations, anions, WBC .app 150mls in adultProduced in choroid plexusFUNCTION• Serves as shock absorber to protect brain and

spinal• Carries nurients to parts of brain and spinal cord• helps remove metabolic products & wastes

after circulation, absorbed into the blood vessels of the dura mater.

Hydrocephalus occurs when this balance is disrupted. Although there are many factors that can disrupt this balance, the most common is a blockage, or obstruc tion, somewhere along the circulatory pathway of CSF. The obstruction may develop from a variety of causes, such as brain tumors, cysts, scarring and infection.

Treatment for Meningitis•Bacterial antibiotics•Herpes meningitis antiviral meds•IV fluids•Prevention: vaccines for bacterial

infections (HiB)

Traumatic Brain Injuries

• Concussion• Contusion• Subdural or subarachnoid

hemorrhage• Contrecoup injury

Cerebrovascular Accidents (CVAs)

• Ischemia• Thrombus• Embolism• Arteriosclerosis• Stroke

Degenerative brain diseases

• Alzheimer’s• Down’s • Parkinson’s• Huntington’s Chorea• MS• Epilepsy• Schizophrenia

The peripheral nervous system

▫Nerves (spinal nerves, cranial nerves)

▫Two Divisions:Two Divisions:1.1. Sensory (afferent) DivisionSensory (afferent) Division: Sensory

receptors CNS2.2. Motor (efferent) DivisionMotor (efferent) Division: CNS

effectors (muscles & glands)

Motor Division• Somatic nervous systemSomatic nervous system (voluntary) –

control skeletal muscles• Autonomic nervous systemAutonomic nervous system (ANS)

(involuntary) – regulate smooth muscles, cardiac, glands▫Subdivisions: sympatheticsympathetic &

parasympatheticparasympathetic

On Old Olympus Towering Tops A Fat Voracious German Viewed A Hop

1. Olfactory- smell2. Optic- vision3. Oculomotor- 4 of the 6 extrinsic eye muscles 4. Trochlear- extrinsic eye muscles5. Trigeminal- sensory fibers to the face and motor fibers to the

chewing muscles6. Abducens- controls eye muscles that turn the eye laterally7. Facial- facial expression8. Vestibulocochlear- hearing and balance9. Glosopharyngeal- tongue and pharynx10.Vagus- from medulla- acetylcholine slows heart & breathing11.Accessory- accessory part of vagus nerve12.Hypoglossal- moves muscles under tongue

Olfactory

Optic

Oculomotor

Trochlear

Trigeminal

Abducens

VestibulocochlearGlossopharyngeal

VagusAccessory Hypoglossal

Facial

13-71

Points to Remember•Cranial nerves are part of the peripheral

nervous system.•Carry sensory or motor information or a

combination and function in parasympathetic nervous system.

•Cranial nerves I, II and VIII are purely sensory.

•Cranial nerves III, IV, VI, XI and XII are motor (although also function for proprioception).

Spinal Nerves- There are 31 pairs of nerves exiting the spinal column:

8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal.

• They innervate the body in sections • Each nerve has a dorsal (sensory) and ventral root

(motor) that attach to the spinal cord at the rootlets.• Each spinal nerve also has dorsal and ventral ramus

that carries motor and sensory nerves. • The ventral ramus connects to rami commicantes

that connect to symphathetic chain ganglia. The dorsal rami supplies the posterior parts of the body and ventral rami supplies the lateral and anterior sides of the body.

• A. Innervation of the back- the nerves follow a neat and simple pattern.

B. Innervation of the anterior thoracic an abdominal wall- supply intercostals muscles, skin or anterior and lateral thorax and abdomen.

C. Introduction to nerve plexuses- these are networks of nerve clusters formed by ventral rami from different spinal nerves. Plexuses serve the limbs and are designed to prevent paralysis of a limb muscle by the distruction of just one spinal nerve.

1. The cervical plexus and innervation of the neck- formed by C1-C4 nerves, most branches are cutaneous nerves and anterior neck muscles and diaphragm.

2. The brachial plexus and innervation of the upper limb- formed by C5-C8 nerves, it supplies the upper limbs. The plexus’ extremely complex lies between the cervical and axillary regions. Roots run deep of the sternocleidomastoid, they unite to form trunks which divide into anterior and posterior divisions that break into lateral, medial, and posterior cords that divide into the terminal branches

(around axilla) that innervate the arm The nerves of the arms are: axillary nerve, musculocutaneous nerve, median nerve, ulnar nerve, and radial nerves.

3. The lumbar plexus and innervation of the lower limb- formed by L1-L4 nerves the main branches innervate the anterior thigh via the femoral nerve. Medial thigh and adductor muscles are innervated by the obturator nerve.

4. The sacral plexus and innervation on the lower limb- formed by L4-S4 nerves, its many branches innervate the buttock, lower limb, pelvis, and perineum. The largest branch is the sciatic nerve that supplies lateral and posterior limb regions. It branches into the tibial and fibial nerve.

5. Innervation of joints of the body- As a health professional you need to know the nerves that innervate the joints. Use Hilton’s Law: any nerve that innerates a muscle producing movement at a joint also innervates the joint itself and the skin over it. Example: Knee joint is surrounded by anterior and posterior thigh muscles that are innervated by femoral, obturator, and branches of the sciatic nerves.

6. Innervation of the skin: dermatomes- each spinal nerves innervates a skin zone

•A map of referred pain: these are skin or body regions that present pain when there is visceral pain. The organ and site of referred pain are innervated by the same nerve.

÷’s of PNS•Somatic

control skeletal muscle (bones, skin that a person can control)

Voluntary control

•Autonomic control the muscles of the glands and internal

organs which we can’t control Involuntary Autonomic-automatic

Sub÷’s of Autonomic NS

•Sympathetic prepares body for stress {fight or flight}

Norepinephrine

•Parasympathetic brings things back to normal {calms} acetylcholine

• VI. The sympathetic division- This division innervates more organs and is more complex than the parasympathetic.

• A. basic organization- The sympathetic system innervates the integument: its glands and the arrector pili in addition to internal organs and blood vessels. There is also more glanglia due to the preganglionic and postganglionic cell bodies.