Presentation on theme: "Organization of Somatic Nervous system Spinal nerve and Reflex arc. Dr"— Presentation transcript:
1 Organization of Somatic Nervous system Spinal nerve and Reflex arc. Dr Organization of Somatic Nervous system Spinal nerve and Reflex arc Dr. Qazi Imtiaz RasoolWhere nerve impulses convert to neurotransmittersTransmission of impulses Inhibition of impulses Integration of impulses Modification of impulses Learning and memory
2 OBJECTIVES Recall various components of somatic nervous system. Explain structure of typical spinal nerve.Describe reflex arc.Identify clinical application.
4 Somatic nervous system (SNS) All parts of the nervous system outside of the brain and spinal cordSomatic System: Links spinal cord with body and sense organs; controls voluntary behaviorAutonomic System: Serves internal organs and glands; controls automatic functions such as heart rate and blood pressureEnteric System
5 Functional Classification BRAINSPINAL CORD(CNS)AFFERENTNERVESEFFERENTNERVESPNSThe ANS is one of the most sophisticated control systems known to man. It is primarily involved in maintaining the homeostatic state of the organism while allowing adaptation to changes in conditions, sometimes even severe changes.Contrary to the somatic division of the CNS is it a totally unconscious activity. It also involves a sophisticated interplay of chemical and neural signals (see previous lecture).EXTERO-RECEPTORSINTERO-RECEPTORSSOMATICAUTONOMICEFFECTORORGANSSKELETALMUSCLESSMOOTH ANDCARDIAC MUSCLESAND GLANDS
6 Spinal NerveEach side of spine Dorsal and ventral roots joinTo form a spinal nerveMixed NervesCarry both afferent (sensory)and efferent (motor) fibersTwo branches of spinal nervesVentral rootContains axons of motor neuronsDorsal root1. Contains axons of sensory neurons2. Dorsal root ganglia
7 Peripheral Distribution of Spinal nerve Nerves Spinal nervesForm lateral to intervertebral foramenWhere dorsal and ventral roots uniteThen branch and form pathways to destinationMotor nervesfirst branchWhite ramus Carries visceral motor fibers to sympathetic ganglion of autonomic nervous systemGray ramus Unmyelinated nerves , Return from sympathetic ganglion to rejoin spinal nerve• Spinal nerve are the path of communication between the spinal cord and the specific region of the bodyCervical and thoracic spinal nerves arise and leave at corresponding vertebra .• Because the spinal cord are shorter than vertebra column, nerve that arise from lumbar, sacral and coccyx region of spinal cord do not leave the vertebra column at the same level where they exit the cord.• The root of these spinal nerves angle inferiorly in the vertebral canal from the end of spinal cord like wisps of hair.
10 Spinal Nerves . Based on vertebrae where spinal nerves originate Positions of spinal segment and vertebrae change with ageCervical nervesAre named for inferior vertebraAll other nervesAre named for superior vertebra
12 Nerve structure Nerves are only in the periphery Cable-like organs in PNS = cranial and spinal nervesConsists of ,000 of myelinated + unmyelinated axons (nerve fibers)+ connective tissue + blood vesselsSupport Cells of the PNSSatellite cells ---Protect neuron cell bodiesSchwann cells---Form myelin sheath
13 Presynaptic terminals. terminal (bouton / button) Morphology of neuron1.membrane2.perikaryonCell body (soma)3.nucleusTwo partsDendritesTerminal branches (telodendria)End in knobs called axon terminals (aka synaptic terminals, end bulbs, boutons, synaptic knobs)ProcessesAxonPresynaptic terminals.terminal (bouton / button)
14 AXON 1.Plasmalemma--axolemma 2.Cytoplasm--axoplasm (mitochondria,microtubues,Neurofilaments,)3, Axon hillock;Origin4. No rough ER--No protein synthesisOften branch sparsely, forming collaterals.Each collateral may split into telodendria which end in a synaptic knob, which contains synaptic vesicles – membranous bags of NTsrefer to the end points of an axon responsible for releasing chemicals to communicate with other neuronsSurrounded by a myelin sheath, a wrapping of lipid which:Protects the axon and electrically isolates itIncreases the rate of AP transmissionThe myelin sheath is made by ________ in the CNS and by _________ in the PNS.This wrapping is never complete. Interspersed along the axon are gaps where there is no myelin – these are nodes of Ranvier.In the PNS, the exterior of the Schwann cell surrounding an axon is the neurilemmaIn life: soft, elastic, homogeneous (jelly)Unspecialized cytoplasm (neuroplasm) = axoplasm5. Axon terminal6. Chromatophilic-----no Nissl body
15 FUNCTIONAL PARTS OF AXON 1. ProcessesIntegration zone2.Axon hillock1ST portion of the axon plus the region of the cell body fro m which the axon leavesNeuron’s trigger zone3.Nerve fiberSingle, elongated tubular extensionthat conducts AP away from the cellConducting zone of the neuron4..CollateralsSide branches of axon5.Axon terminalsRelease chemical messengers other cells with which they come into closeOutput zone of the neuron
16 is an involuntary, immediate, automatic and REFLEX = reflectionis an involuntary, immediate, automatic andstereotyped response to a specific sensory stimulation.
17 Classification CLINICAL PHYSIOLOGICAL NUMBER OF SYNAPSES SITE ANATOMICALDEVELOPMENTFUNCTIONALON PURPOSESRESPONSE IS CONFINEDDEPENDING ON THE PART INVOLVEDCHARACTER OF THE RESPONSEOTHER REFLEXES1. CLINICALSUPERFICAL REFLEX2. DEEP REFLEX3. VISERAL REFLEX4. PATHOLOGICAL REFLEX2.PHYSIOLOGICAL1. FLEXORS REFLEXES2. EXTENSORS REFLEXES3.ANATOMICAL/ACCORDING TO DESTINATION OF INTERNEURON IN THE SPINAL CORD1.segmental reflex2.Intrasegmental reflex -3.Intersegmental reflex-4. Supra-segmental reflexAccording to the Location of the Receptor(1) Superficial Reflexes :The receptor is in the skin ( cutaneous receptor)(2) Deep reflexes : The receptor is located in muscle or tendona) Stretch Reflexes (Tendon jerks)b) Inverse Stretch Reflex ( Golgi Tendon Organ)5.NUMBER OF SYNAPSES MONOSYNAPTIC QUICKER2 .POLYSYNAPTIC SLOWER3. A SYNAPTIC REFLEX( AXON REFLEX)6.DEVELOPMENTINBORN (INTRINSIC) REFLEX –unlearned, unpremeditated, and involuntary;LEARNED (ACQUIRED) REFLEX –7.FUNCTIONAL. Motor reflexes2. Sensory reflexes8.ON PURPOSESPROTECTIVE OR FLEXOR REFLEXES2.ANTIGRAVITY REFLEXES3. RIGHTENING REFLEXES4. CONDITIONAL REFLEXES5. LOCOMOTOR REFLEXES9.RESPONSE IS CONFINED TO ONE MUSCLE R MORE1.SIMPLE RFEFLEXES2. CO-ORDINATEDE REFLEXES3. CONVULSIVE REFLEXES10.DEPENDING ON SITE OF PROCESSING SITESPINAL REFLEXES2. BIULBAR REFLEXES3. CORTICAL REFLEXES4. MESENCEPHALIC REFLEXESDI-ENCEPHALIC REFLEXES11.CHARACTER OF THE RESPONSE1.MOTOR REFLEXES2. SECERTORY REFLEXES3.VASOMOTOR REFLEXESPRESENTATION REFLEXESCROSSED FLEXION REFLEXESCROSSED EXTENSION REFLEXESWALKING REFLEXESHOPPING REFLEXESGALLOPING REFLEXES.
18 SIGNIFICANCE HOMEOSTASIS (autonomic reflexes) TONE DURING RESTING STATETONE DURING TENSE MOTOR ACTIVITY3. POSTURE4. EQUILIBRIM5. EXECUTION OF MOVEMENTS6. SMOOTHNESSDAMPNESS during resting , walking, running, statesROLE AS PROPRIOCEPTOR( unconcouscious+ concious kinaesthetic sensations)Reflexes maintain homeotasis–heart rate, breathing rate, bp, digestion.b. Reflexes also carry out the automatic actions ofswallowing, sneezing, coughing, vomiting.
19 R-SIM Reflex arc pathway receptor neuron receives the stimuli2. Ssensory neuron passes the impulse on3. Iinterneuron at the spinal cord processes4. Mmotor neuron acts
23 Simplified reflex arc stimulus sensory neurone receptor spinal cord of central nervous system
24 Simplified reflex arc stimulus sensory neurone receptor spinal cord of central nervous systemrelay neurone
25 Simplified reflex arc stimulus sensory neurone receptor spinal cord of central nervous systemrelay neuronemotor neurone
26 Simplified reflex arc stimulus sensory neurone receptor spinal cord of central nervous systemrelay neuroneeffectormotor neurone
27 Simplified reflex arc stimulus sensory neurone receptor spinal cord of central nervous systemrelay neuroneeffectorresponsemotor neurone
28 Spinal ReflexesSomatic reflexes mediated by the spinal cord are called spinal reflexesThese reflexes may occur without the involvement of higher brain centersAdditionally, the brain can facilitate or inhibit them
29 R 3 Inputs to Alpha Motor Neurons DRG(1) Afferent (sensory) neuron(2) Uppermotorneurons(3) Spinal interneuron
36 SPINAL SHOCKSpinal 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.
37 Shingles ( of the herpes family) In dorsal root ganglia and cranial nerves Initial infection: chicken pox virusPeripheral NeuropathyRegional loss of sensory or motor functionDue to trauma or compression R metabolic causes