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 Nervous System 1.CNS 2.PNS 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
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
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
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; 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
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
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 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 effector response 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
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