� Introduction� Functions of nervous system

� Parts of nervous system� Neurons� Neuroglia (glial cells)� Peripheral nerves� Autonomic Nervous System (ANS)� Applied Anatomy

Central Nervous System

� Chief controlling & coordinating system of the body

� Controls all activities of body

Functions of nervous system

� Sensory – monitors internal & external environment through presence of receptors

� Integration – interpretation of sensory information (information processing); complex (higher order) functions

� Motor – response to information processed through stimulation of effectors

� muscle contraction

� glandular secretion

Sensory neurons

� Carries impulses from receptors e.g pain receptors in skin to the CNS( brain or spinal cord

From periphery (skin, mucous membranes, muscles, tendons, joints & special sense organs)

To CNS

Relay neuron

� Carries impulses from sensory nerves to motor nerves

Motor neuron

� Carries impulses from CNS to effector e.g. muscle to bring about movement or gland to bring about secretion of hormone e.gADH

To periphery (muscles & glands)

From CNS

Central nervous system (CNS)� Brain

� Spinal cord

Peripheral nervous system (PNS)� All the neural tissue outside CNS

� Afferent division (sensory input)

� Efferent division (motor output)� Somatic nervous system

� Autonomic nervous system

Brain

Spinal cord

Periperalnerves

Cell types of Nervous system

� Neurons - For processing, transfer, and storage of information

� Neuroglia – For support, regulation & protection of neurons

Neurons

� Neurons perform all of the communication, information processing, and control functions of the nervous system.

Structure of a Neuron

� Cell body – has a central nucleus & cytoplasm with nissl granules

� Cell processes or neurites, of 2 types:1. Dendrites –

freely branched & shorter

2. Axon – single long process

� Terminal branches of axon called axon terminal or telodendria

� Cell bodies for nuclei in CNS & ganglia in PNS

� Axons form tracts in CNS & nerves in PNS

� Most axons of the nervous system are surrounded by a myelin sheath (myelinatedaxons)

� Presence of myelin speeds up transmission of action potentials along the axon

� Myelin will get laid down in segments (internodes) along the axon, leaving unmyelinated gaps called nodes of Ranvier

� white matter - groupings of myelinated axons

� Gray matter - groups of neuron cell bodies, dendrites & synapses

Four functions of neurons

1. Dendrites and cell body -Receive and integrate inputs

2. Axon hillock and initial segment - Generate action potentials

3. Axon -Conducts action potential

4. Terminals -Synaptic transmission

Sensory neuron

Interneuron Motor neuron

Classification of neurons

Structural classification based on number of processes coming off of the cell body:

� Unipolar – eg: mesencephalic nucleus

� Pesudo-unipolar – eg: sensory ganglia

� Bipolar – eg: spiral & vestibular ganglia

� Multipolar

� Two processes coming off cell body – one dendrite & one axon

� Only found in eye, ear & nose

� Single process coming off cell body, giving rise to dendrites (at one end) & axon (making up rest of process)

� Multiple dendrites & single axon

� Most common type

Classification based on length of axon:

� Golgi type I – long axon

� Golgi type II – short or no axon

Synapse

� Junction between neurons

� Impulses are transmitted across a synapse by specific neurotransmitters

Eg: acetylcholine, noradrenalin, dopamine, serotonin, etc.

� Common types:Axo-dendriticSomato-somaticSomato-dendritic

Neuroglia (glial cells)

� CNS neuroglia:

• Astrocytes

• Oligodendrocytes

• Microglia

• Ependymal cells

� PNS neuroglia:

• Schwann cells (neurolemmocytes)

• Satellite cells

� Star-shaped

� Supportive framework for neurons

� Create “blood-brain barrier”

� Secrete chemicals for embryological neuron formation

� Stimulate formation of scar tissue secondary to CNS injury

Oligodendrocytes� Create myelin

sheath around axons of neurons in CNS

Microglia� “Brain macrophages”

� Phagocytize cellular wastes & pathogens

Ependymal cells� Line ventricles of brain &

central canal of spinal cord

� Produce, monitor & help circulate CSF (cerebrospinal fluid)

Satellite cells

� Support groups of cell bodies of neurons within ganglia of the PNS

Schwann cells

� Surround all axons of neurons in the PNS creating a neurilemmaaround them. Neurilemma allows for potential regeneration of damaged axons

� Creates myelin sheatharound most axons of PNS

Peripheral nerves

� Solid white cords composed of bundles (fasciculi) of nerve fibres

� Each nerve fibre is an axon with its coverings

Coverings of Nerve

Epineurium – dense connective tissue covering a nerve trunk

Perineurium – ensheathseach fasciculi

Endoneurium – lose connective tissue covering each nerve fibre

Spinal nerves

� 31 pairs spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal nerve.

� Formation: each spinal nerve is formed by union of anterior and posterior roots at intervertebralforamen � The anterior root contains motor

fibers for skeletal muscles. Those from T1 to L2 contain sympathetic fibers; S2 to S4 also contain parasympathetic fibers

� The posterior root contains sensory fibers whose cell bodies are in the spinal ganglion.

Posterior root

Anterior root

� Dorsal root characterised by presence of spinal or dorsal root ganglion (collections of cell bodies of unipolar sensory neurons forming dorsal roots)

� Dorsal & ventral roots unite to form a spinal nerve

� Spinal nerve divides into ventral & dorsal ramus

� Ventral ramus: largest , innervates anterolateral body wall and limbs

� Dorsal ramus: innervates the back of the trunk

� Communicating branch: connect the spinal nerve to the sympathetic trunk

� Meningeal branch: re-enters vertebral canal through intervertebral foramen to duramater

Nerve plexuses

� Formed by ventral rami

� Supply limbs

� Against each plexus spinal cord is enlarged to form� Cervical enlargement for

brachial plexus

� Lumbar enlargement for lumbosacral plexus

Cervical Plexus

� Formed by ventral rami of spinal nerves C1-C4

� Motor: Innervates muscles of the neck (SCM, trapezius), laryngeal muscles

� Sensory: Skin of upper chest, shoulder, neck, and ear

� Phrenic nerve� From C3-C5 (cervical and

brachial plexuses)� Innervates diaphragm

Brachial Plexus� Formed by ventral rami of spinal

nerves C5-T1� Five ventral rami form three

trunks that separate into six divisions then form cords that give rise to: (RTDC)

� Branches/nerves� Axillary� Radial� Musculocutaneous� Ulnar� Median

Blood supply – vasa nervorum

Nerve supply – nervi nervorum

Mylinated nerve fibres� They form the bulk of

the somatic nerves� Structurally consists of

following parts-1.Axis cylinder2. myelin sheath, nodes of ranvier, Schmidt Lantermann(oblique clefts in mylein sheath)3.Neurolemmal sheath4.Endoneurium

Formation of myelin sheath

Non-Mylinated nerve fibres� It comprise the smaller

axons of the CNS,postganglionicautonomic fibres,sensory fibres(c-fibres of skin, muscle and viscera),olfactory nerve.

� It consists of agroup of small axons(0.12 to 2micron) that have invaginated seaperatelya single Schwann cell.

Classification of pheriperalnerves� According to their

function-GSE,SVE,GVE,GVA,SVA,GSA,SSA

Classification of pheriperalnerves� According to their size and speed of conduction

the nerve fibres are divided into three catogoriesnamely A,B and C

Neurobiotaxis

� It is process in which the cell bodies of the motor and connector neuron move,as a result of some attractive force,towards their chief source of stimulation

� Postulated by Kappers in 1907

Autonomic Nervous System (ANS)

The ANS consists of motor neurons that: � Innervate smooth and cardiac muscle and

glands

� Make adjustments to ensure optimal support for body activities

� Operate via subconscious control

� Have viscera as most of their effectors

� Most visceral organs are innervated by both sympathetic and parasympatheticfibers

� This results in dynamic antagonisms that precisely control visceral activity

� Sympathetic fibers increase heart and respiratory rates, and inhibit digestion and elimination

� Parasympathetic fibers decrease heart and respiratory rates, and allow for digestion and the discarding of wastes

� Axon of 1st (preganglionic) neuron leaves CNS to synapse with the 2nd (ganglionic) neuron

� Axon of 2nd (ganglionic) neuron extends to the organ it serves

Divisions of the autonomic nervous system

� Parasympathetic division� Sympathetic division

� Also called craniosacral system because all its preganglionic neurons are in brain stem or sacral levels of spinal cord

○ Cranial nerves III,VII, IX and X○ In lateral horn of gray matter from S2-S4

� Acetylcholine is neurotransmitter at end organ as well as at preganglionic synapse: “cholinergic”

Parasympathetic Nervous System

� Concerned with keeping body energy use low

� Involves the D activities – digestion, defecation, and diuresis

� Its activity is illustrated in a person who relaxes after a meal� Blood pressure, heart rate, and respiratory rates

are low

� Gastrointestinal tract activity is high

� The skin is warm and the pupils are constricted

� Cranial outflow� III - pupils constrict� VII - tears, nasal mucus, saliva� IX – parotid salivary gland� X (Vagus n) – visceral organs of thorax & abdomen:

○ Stimulates digestive glands○ Increases motility of smooth muscle of digestive

tract○ Decreases heart rate○ Causes bronchial constriction

� Sacral outflow (S2-4): form pelvic splanchnicnerves� Supply 2nd half of large intestine� Supply all the pelvic (genitourinary) organs

Sympathetic Nervous System� Also called thoracolumbar system: all its neurons

are in lateral horn of gray matter from T1-L2

� Lead to every part of the body (unlike parasymp.) � When nervous, you sweat; when afraid, hair stands on

end; when excited blood pressure rises (vasoconstriction): due to sympathetic activity

� Also causes: dry mouth, pupils to dilate, increased heart & respiratory rates to increase O2 to skeletal muscles, and liver to release glucose

� Norepinephrine (noradrenaline) is neurotransmitter released by most postganglionic fibers (acetylcholine in preganglionic): “adrenergic”

� The sympathetic division is the “fight, fright or flight” system

� Involves E activities – exercise, excitement, emergency, and embarrassment

� Promotes adjustments during exercise –blood flow to organs is reduced, flow to muscles is increased

� Preganglionic axons exit spinal cord through ventral root & enter spinal nerve

� Exit spinal nerve via communicating ramus

� Enter sympathetic trunk or chain where postganglionic neurons are

� Has three options…

1. Synapse on postganglionic neuron in chain ganglion then return to spinal nerve & follow its branch to the skin

Synapse in chain ganglia at same level or different level

2. Ascend or descend within sympathetic trunk, synapse with a posganglionic neuron within a chain ganglion, & return to spinal nerve at that level & follow branches to skin

Synapse in chain ganglia at same level or different level

3. Enter sympathetic chain, pass through without synapsing, form a splanchnic nerve that passes toward thoracic or abdominal organs

� These synapse in prevertebral ganglion in front of aorta� Postganglionic axons follow arteries to organs

Applied Anatomy

� Nerve injury

� Neuropathy

� Dementia

� Infections of brain

� Parkinson’s diseases

� Cerebral stroke

� Tumors of CNS

Nerve injury

� Neurapraxia-spontaneous recovery

� Axonotmesis-Walleriandegeneration

� Neurotmesis-complete nerve division

Neuropathy

� Peripheral neuropathy is damage to nerves of the peripheral nervous system, which may be caused either by diseases of or trauma to the nerve or the side effects of systemic illness

� Polyneuropathy and mononeuropathy

Dementia

Dementia (taken from Latin, originally meaning "madness", is a serious loss of global cognitiveability in a previously unimpaired person, beyond what might be expected from normal aging

Alzheimers disease

Infections of brain

� Brain abscess (or cerebral abscess) is an abscess caused by inflammation and collection of infected material, coming from local (ear infection, dental abscess, infection of paranasal sinuses, infection of the mastoid air cells of the temporal bone, epidural abscess) or remote (lung, heart, kidneyetc.) infectious sources, within the brain tissue.

� Meningitis

Parkinson’s diseases

� Parkinson's disease (PD also known as idiopathic or primary parkinsonism, hypokinetic rigid syndrome/HRS, or paralysis agitans) is a degenerativedisorder of the central nervous system

Cerebral stroke

� A stroke, sometimes referred to by the older term cerebrovascularaccident (CVA), is the rapid loss of brain function due to disturbance in the blood supply to the brain.

Tumors of CNS

� A brain tumor, or tumour, is an intracranial solid neoplasm, a tumor(defined as an abnormal growth of cells) within the brain or the central spinal canal.

Thank You

�����������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������