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Organization of Somatic Nervous system Spinal nerve and Reflex arc Dr. Qazi Imtiaz Rasool.

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Presentation on theme: "Organization of Somatic Nervous system Spinal nerve and Reflex arc Dr. Qazi Imtiaz Rasool."— Presentation transcript:

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2 Organization of Somatic Nervous system Spinal nerve and Reflex arc Dr. Qazi Imtiaz Rasool

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

4 Nervous System Nervous System 1.CNS 2.PNS 1.CNS 2.PNS 1. SOMATIC 2. AUTONOMIC 1. Brain 2. Spinal Cord

5 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

6 Functional Classification BRAIN SPINAL CORD (CNS) PNS AFFERENT NERVES EFFERENT NERVES EXTERO- RECEPTORS INTERO- RECEPTORS SOMATICAUTONOMIC EFFECTOR ORGANS SKELETAL MUSCLES SMOOTH AND CARDIAC MUSCLES AND GLANDS

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8 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

9 DRG Afferent fiber Efferent fiber

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11 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

12 Peripheral Nerves 1.Epineurium wraps entire nerve 2.Perineurium wraps fascicles of tracts 3.Endoneurium wraps individual axons

13 Nerve structure 1. Nerves are only in the periphery 2. Cable-like organs in PNS = cranial and spinal nerves 3. Consists of ,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

14 Morphology of neuron Two parts Cell body (soma) Processes Dendrites Axon 1.membrane 2.perikaryon 3.nucleus Presynaptic terminals. terminal (bouton / button)

15 AXON 1.Plasmalemma--axolemma 2.Cytoplasm--axoplasm 3, Axon hillock; 3, Axon hillock;Origin No protein synthesis 4. No rough ER--No protein synthesis 5. Axon terminal 5. Axon terminal ( mitochondria,microtubues, Neurofilaments,) 6. Chromatophilic----- no Nissl body

16 FUNCTIONAL PARTS OF AXON 1. Processes 1. Processes Integration zone 2.Axon hillock 1 ST portion of the axon plus the region of the cell body fro m which the axon leaves 1 ST portion of the axon plus the region of the cell body fro m which the axon leaves Neuron’s trigger zone 3. Nerve fiber 3. Nerve fiber Single, elongated tubular extension Single, elongated tubular extension that conducts AP away from the cell that conducts AP away from the cell Conducting zone of the neuron Conducting zone of the neuron 4..Collaterals 4..Collaterals Side branches of axon Side branches of axon 5.Axon terminals 5.Axon terminals Release chemical messengers other cells with which they come into close Release chemical messengers other cells with which they come into close Output zone of the neuron Output zone of the neuron

17 REFLEX = reflection is an involuntary, immediate, automatic and stereotyped response to a specific sensory stimulation.

18 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

19 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)

20 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

21 Simplified reflex arc stimulus

22 receptor Simplified reflex arc

23 stimulus receptor sensory neurone Simplified reflex arc

24 stimulus receptor sensory neurone spinal cord of central nervous system Simplified reflex arc

25 stimulus receptor sensory neurone spinal cord of central nervous system relay neurone Simplified reflex arc

26 stimulus receptor sensory neurone spinal cord of central nervous system relay neurone motor neurone Simplified reflex arc

27 stimulus receptor sensory neurone spinal cord of central nervous system relay neurone motor neurone effector Simplified reflex arc

28 stimulus receptor sensory neurone spinal cord of central nervous system relay neurone motor neurone effector response Simplified reflex arc

29 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

30 R 3 Inputs to Alpha Motor Neurons 29 (3) Spinal interneuron DRG (1) Afferent (sensory) neuron (2) Upper motor neurons

31 Monosynaptic Reflexes

32 Stimulus Biceps (flexor) contracts Hand withdrawn Triceps (extensor) relaxes Ascending pathway to brain Response Integrating center (spinal cord) Thermal pain receptor in finger Efferent pathway Effector organs = Inhibitory interneuron = Excitatory interneuron = Synapse = Inhibits = Stimulates Afferent Pathway

33 Efferent pathway Afferent pathway Efferent pathway Flexor muscle contracts Extensor muscle relaxes Flexor muscle relaxes Extensor muscle contracts Stimulus Response Pain receptor in heel Injured extremity (effector organ) Integrating center (spinal cord) Opposite extremity (effector organ) Response

34 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

35 UMN v LMN Cortex UMN LMN Muscle Spasticity Flaccidity

36 Reflex testing 0 = ABSENT 1+ = HYPOREFLEXIA 2+ = NORMAL 3+ = HYPERREFLEXIA 4+ = HYPERREFLEXIA & CLONUS

37 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.

38 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


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