Organization of Somatic Nervous system

Spinal nerve and Reflex arc

Dr. Qazi Imtiaz Rasool

OBJECTIVES

1. Recall various components of somatic nervous system.

2. Explain structure of typical spinal nerve.

3. Describe reflex arc.

4. Identify clinical application.

Nervous System

1.CNS 2.PNS

1. SOMATIC 2. AUTONOMIC

1. Brain 2. Spinal Cord

Somatic nervous system (SNS)

All parts of the nervous system outside of the brain and spinal cord

1. Somatic System: Links spinal cord with body and sense organs; controls voluntary behavior

2. Autonomic System: Serves internal organs and glands; controls automatic functions such as heart rate and blood pressure

3. Enteric System

Functional ClassificationBRAIN

SPINAL CORD(CNS)

PNSAFFERENT

NERVES

EFFERENT

NERVES

EXTERO-RECEPTORS

INTERO-RECEPTORS

SOMATIC AUTONOMIC

EFFECTORORGANS

SKELETALMUSCLES

SMOOTH AND CARDIAC MUSCLES AND GLANDS

Nerves Spinal nerves

1. Form lateral to intervertebral foramen

2. Where dorsal and ventral roots unite

3. Then branch and form pathways to destination

1. Motor nerves

first branch

1. White ramus Carries visceral motor fibers to sympathetic

ganglion of autonomic nervous system

2. Gray ramus Unmyelinated nerves , Return from

sympathetic ganglion to rejoin spinal nerve

Peripheral Distribution of Spinal nerve

DRG

Afferent fiber

Efferent fiber

Spinal Nerves.

1. Based on vertebrae where spinal nerves originate

2. Positions of spinal segment and vertebrae change with age

1. Cervical nerves

Are named for inferior vertebra

2. All other nerves

Are named for superior vertebra

Peripheral Nerves

1.Epineurium wraps entire nerve

2.Perineurium wraps fascicles of tracts

3.Endoneurium wraps individual axons

Nerve structure

1. Nerves are only in the periphery

2. Cable-like organs in PNS = cranial and spinal nerves

3. Consists of 100-100,000 of myelinated + unmyelinated axons (nerve fibers)+ connective tissue + blood vessels

4. Support Cells of the PNS

Satellite cells ---Protect neuron cell bodies

Schwann cells---Form myelin sheath

Morphology of neuron

Two parts

Cell body (soma)

Processes

Dendrites

Axon

1.membrane

2.perikaryon

3.nucleus

Presynaptic terminals.terminal (bouton / button)

AXON

1.Plasmalemma--axolemma

2.Cytoplasm--axoplasm

3, Axon hillock;Origin

4. No rough ER--No protein synthesis

5. Axon terminal

(mitochondria,microtubues,Neurofilaments,)

6. Chromatophilic-----no Nissl body

FUNCTIONAL PARTS OF AXON 1. Processes

Integration zone

2.Axon hillock 1ST portion of the axon plus the region of

the cell body fro m which the axon leaves

Neuron’s trigger zone

3.Nerve fiber

Single, elongated tubular extension that conducts AP away from the cell

Conducting zone of the neuron

4..Collaterals Side branches of axon

5.Axon terminals Release chemical messengers other cells

with which they come into close Output zone of the neuron

REFLEX = reflection

is an involuntary, immediate, automatic and

stereotyped response to a specific sensory stimulation.

Classification

1. CLINICAL

2. PHYSIOLOGICAL

3. NUMBER OF SYNAPSES

4. SITE

5. ANATOMICAL

6. DEVELOPMENT

7. FUNCTIONAL

8. ON PURPOSES

9. RESPONSE IS CONFINED

10. DEPENDING ON THE PART INVOLVED

11. CHARACTER OF THE RESPONSE

12. OTHER REFLEXES

SIGNIFICANCE HOMEOSTASIS (autonomic reflexes)

1. TONE DURING RESTING STATE

2. TONE DURING TENSE MOTOR ACTIVITY

3. POSTURE

4. EQUILIBRIM

5. EXECUTION OF MOVEMENTS

6. SMOOTHNESS

7. DAMPNESS during resting , walking, running, states

8. ROLE AS PROPRIOCEPTOR( unconcouscious+ concious

kinaesthetic sensations)

R-SIM Reflex arc pathway 1. R

receptor neuron receives the stimuli

2. S

sensory neuron passes the impulse on

3. I

interneuron at the spinal cord processes

4. M

motor neuron acts

Simplified reflex arc

stimulus

stimulus

receptor

Simplified reflex arc

stimulus

receptor

sensory neurone

Simplified reflex arc

stimulus

receptor

sensory neurone

spinal cord of central nervous system

Simplified reflex arc

stimulus

receptor

sensory neurone

spinal cord of central nervous system

relay neurone

Simplified reflex arc

stimulus

receptor

sensory neurone

spinal cord of central nervous system

relay neurone

motor neurone

Simplified reflex arc

stimulus

receptor

sensory neurone

spinal cord of central nervous system

relay neurone

motor neurone

effector

Simplified reflex arc

stimulus

receptor

sensory neurone

spinal cord of central nervous system

relay neurone

motor neurone

effectorresponse

Simplified reflex arc

Spinal Reflexes

1. Somatic reflexes mediated by the spinal cord are called spinal reflexes

2. These reflexes may occur without the involvement of higher brain centers

3. Additionally, the brain can facilitate or inhibit them

R 3 Inputs to Alpha

Motor Neurons

29

(3 )Spinal interneuron

DRG(1) Afferent

(sensory) neuron

(2) Upper motor

neurons

Monosynaptic Reflexes

Stimulus

Biceps(flexor)contracts

Handwithdrawn

Triceps(extensor)relaxes

Ascending pathwayto brain

Response

Integrating center(spinal cord)

Thermalpain receptor

in finger

Efferent pathway

Effectororgans

= Inhibitory interneuron= Excitatory interneuron= Synapse= Inhibits= Stimulates

AfferentPathway

Efferent pathway

Afferentpathway Efferent

pathway

Flexormusclecontracts

Extensormusclerelaxes

Flexormusclerelaxes

Extensormusclecontracts

Stimulus

Response

Painreceptorin heel

Injuredextremity(effectororgan)

Integrating center(spinal cord)

Oppositeextremity(effectororgan)

Response

UMN lesions

1. Weakness, paralysis

2. Spasticity

3. tendon reflexes

4. +ve Babinski sign

5. Little,if muscle

atrophy

6. No fasiculation

LMN lesions

1. weakness, paralysis

2. flaccidity, hypotonia

3. tendon reflexes

4. -ve Babinski sign

5. Muscle atrophy

6. Fasiculation of muscle

UMN v LMNCortex

UMN

LMN

Muscle

SpasticityFlaccidity

Reflex testing

0 = ABSENT

1+ = HYPOREFLEXIA

2+ = NORMAL

3+ = HYPERREFLEXIA

4+ = HYPERREFLEXIA & CLONUS

SPINAL SHOCK

Spinal shock is a state of transient physiological (rather than anatomical) reflex depression of cord function below the level of injury with associated loss of all sensorimotor functions.

An initial increase in blood pressure is noted due to the release of catecholamines, followed by hypotension.

Shingles ( of the herpes family) In dorsal root ganglia and cranial nerves

Initial infection: chicken pox virus

Peripheral Neuropathy

Regional loss of sensory or motor

function

Due to trauma or compression R

metabolic causes