Presentation on theme: "Nervous System Physiology"— Presentation transcript:
1Nervous System Physiology ByDr. SHAHAB SHAIKHPhD MD MBBSLecture – 2: Spinal Cord Reflexes••••••••••••••••••••••••••••••••••Faculty of MedicineAl Maarefa Colleges of Science & Technology
2SPINAL CORD It is the elongated part of the Central nervous system Begins as Continuation of Medulla Oblongata at Foramen Magnum and extends up to upper border of L2 vertebraIt contains white matter on the outside mainly and grey matter in the central regionMany Interneurons in the grey matter of spinal cord are Centers for spinal reflexesFunction:Conduit for Information passage To & fro BrainCenter for some reflexes
4Reflexes in the body may be … Reflex : It is an automatic response to a stimuli that occurs without conscious effortReflexes in the body may be …Simple or BasicConditioned or AcquiredReflexes Important in maintaining homeotsasisExamplesReflexes carry out the automatic actions of swallowing, sneezing, coughing, vomiting.Reflexes maintain balance and posture; e.g., spinal reflexes control trunk and limb muscles.Brain reflexes involve reflex center in brainstem; e.g., reflexes for eye movement.
5Components of reflex arc are: SPINAL REFLEXReflex : It is an automatic response to a stimuli that occurs without conscious effortComponents of reflex arc are:Sensory ReceptorAfferent pathwayCenterEfferent pathwayEffector organ
6Receptor responds to the stimulus and produces action potential (AP) REFLEXReceptor responds to the stimulus and produces action potential (AP)↓AP is taken by afferent pathway to the integrating center (usually CNS)Integrating center processes all the information and makes the decision about the responseInstruction from integrated center are sent via efferent pathway to the Effector organ (muscle or gland)
7Classification of reflexes Monosynaptic reflexAlso called as stretch reflex or tendon jerke.g. Bicep jerk ,triceps jerk, knee jerk, ankle jerkPolysynaptic reflexe.g. Withdrawal reflex, Abdominal reflex, Plantar reflexVisceral reflexe.g. Micturation, defecation reflexJendressik Phenomenon
8Stretch Reflex [monosynaptic] Sudden stretch to a muscle leads to contraction of that muscle is known as stretch reflex.Stretch Reflex is a basic spinal reflex. Example Knee jerkThe 5 components of Stretch ReflexSensory receptor – Muscle Spindle in skeletal muscleAfferent pathway – 1a fibersCenter – spinal cordEfferent fibers – α-motor neuronEffector organ – skeletal muscle contraction
9Types of muscle fibers Extrafusal muscle fibers Takes part in muscle contractionSupplied by α - motor neuronIntrafusal muscle fibersAlso called as Muscle SpindleReceptors for stretch reflexsupplied by γ - motor neuron
10Muscle spindle These are the receptors of the muscles Consist of two types of fibersNuclear bag fiberNuclear chain fiberSensory innervations of muscle spindleIa – nuclear bag & nuclear chain fibersII – nuclear chain fibersMotor supply – γ motor neuronDetect both dynamic and static changes in muscles
16Polysynaptic ReflexIn polysynaptic reflex, there are many synapses between inter-neurons in the reflex pathwayEg. Withdrawal reflex:When a person touches a hot stove or pin prick, a withdrawal reflex occurs from the painful stimulusReceptor- pain and Temperature Receptors stimulatedAfferent impulse travels via Sensory nervesEfferent fibers to Biceps to contract ( flexion of arm ) and inhibitory neuron stimulated to inhibit contraction of Triceps.This type of connection causing stimulation of nerve supply to one muscle and simultaneous inhibition of the nerve to its Antagonistic muscle is known as RECIPROCAL INNERVATION.
18Poly synaptic reflex Important Afferent neuron stimulate also interneuron that carry signals to the Brain ( Ascending tracts in the spinal cord )Therefore Brain can modify the with drawl reflex. How?By sending impulses via descending pathways to the efferent motor neuron supplying the involved muscles and prevent contracting of biceps inspite of painful stimulus e.g. pin prick
26Golgi Tendon OrgansGolgi tendon organ is present in the tendon and is Composed of Nerve fiber endings that wind between collagen fibers inside connective tissue capsule that make up the tendon.
27Golgi Tendon ReflexIf muscle is stretched by striking the tendon Free nerve endings are pinched in the tendon and they fireActivation of Golgi tendon organs Inhibits alpha motor neurons and decreases muscle contraction
32Clinical Importance of reflexes To test the integrity of reflex arc.Localization of neurological lesion.Deep tendon reflexes are absent in lower motor neuron lesion.They become exaggerated in upper motor neuron lesions.Pendular jerks are observed in cerebellar lesions.Identifying the type of lesion.Monitoring the progress of neurological deficit.
33ReferencesHuman physiology by Lauralee Sherwood, 8th editionText Book Of Physiology by Guyton & Hall, 11th edition