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OBJECTIVES
1. Recall various components of somatic nervous system.
2. Explain structure of typical spinal nerve.
3. Describe reflex arc.
4. Identify clinical application.
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
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
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
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.