Somatosensory & Motor Pathways (Reflexes) by Dr Chiranjeevi Student Copy.pptx

Somatosensory & Motor Pathways (Reflexes) Dr Chiranjeevi Endukuru Lecturer in Medical Sciences (Physiology) [email protected] Reflexes - Dr Chiranjeevi 1 A Reflex A reflex is an inborn, involuntary, sudden, rapid and stereotyped response to...

Somatosensory & Motor Pathways (Reflexes) Dr Chiranjeevi Endukuru Lecturer in Medical Sciences (Physiology) [email protected] Reflexes - Dr Chiranjeevi 1 A Reflex A reflex is an inborn, involuntary, sudden, rapid and stereotyped response to the stimulus. A reflex is a survival mechanism It play a critical role in the coordination of body movement and protection by withdrawal. The pathway for a reflex activity is called reflex arc Reflexes - Dr Chiranjeevi 2 A Reflex Arc It forms the functional unit of nervous system for a reflex and consists of 5 components Reflexes - Dr Chiranjeevi 3 Somatosensory & Motor Pathways Reflexes - Dr Chiranjeevi 4 Somatosensory & Motor Pathways Reflexes - Dr Chiranjeevi 5 Somatosensory & Motor Pathways Reflexes - Dr Chiranjeevi 6 Classification of reflexes Depending upon the number of synapses Monosynaptic vs. Polysynaptic reflexes Depending upon the location of an integrating centre Cortical reflexes vs. Cerebellar reflexes vs. Midbrain reflexes vs. Medullary reflexes vs. Spinal reflexes Physiological classification Flexor reflexes vs. Extensor reflexes Inborn versus acquired reflexes Clinical classification Somatic reflex vs. visceral (autonomic) reflex vs. Pathologic reflex Reflexes - Dr Chiranjeevi 7 Classification of reflexes Reflexes - Dr Chiranjeevi 8 Classification of reflexes Some autonomic reflexes may be processed at the level of the spinal cord. These include the micturition reflex (urination) and the defecation reflex. Although these reflexes are subject to influence from higher nervous centers, they may occur without input from the brain. Reflexes - Dr Chiranjeevi 9  Spinal Somatic Reflexes and Stretch Receptors Four common spinal reflexes, which involve skeletal muscle as the effector, include the stretch reflex, the Golgi tendon reflex, the with-drawal (flexor) reflex, and the crossed-extensor reflex. These reflexes can be initiated by proprioceptors or pain receptors (nociceptors). Those reflexes involving proprioceptors include stretch reflexes and Golgi tendon reflexes. Proprioceptor resides in a joint, muscle, or tendon. These sensory receptors specifically detect any change to that Reflexes - Dr Chiranjeevi 10 structure.  Stretch Reflex – Monosynaptic Reflex Reflexes - Dr Chiranjeevi 11 Stretch Reflex – Monosynaptic Reflex Stretch Reflex - Summary Reflexes - Dr Chiranjeevi 12 Functions of stretch reflex Role in maintaining muscle tone. The muscle tone refers to partial state of contraction of the muscle under resting condition. It is the function of stretch reflex, which is under the influence of discharge from the gamma motor neuron. Role in maintaining posture Role in control of voluntary movement A stretch reflex helps the motor command system in performing voluntary movements. Reflexes - Dr Chiranjeevi 13  Golgi-tendon Reflex or Inverse stretch reflex Relaxation of the muscle in – Di-or-poly synaptic response to a strong reflex stretch is called inverse stretch reflex. This is also known as autogenic inhibition, prevents rupture of muscle. Receptors are Golgi tendon organs (GTO) The stimulus for inverse Reflexes - Dr Chiranjeevi 14 stretch reflex is a stronger  Inverse Stretch Reflex - Summary Reflexes - Dr Chiranjeevi 15 Flexor withdrawl & Crossed Extensor Reflex Withdrawal reflex is a protective reflex and it is an example of polysynaptic spinal reflex. The receptors are nociceptors that are present in the skin, muscle, tendon, or joints. Noxious or painful stimulation of skin, subcutaneous tissue or muscle elicits this reflex. The afferents are called flexor reflex afferents (FRA). This includes type III and IV somatic afferents. The afferents, after entering the spinal cord divides into branches to terminate on Reflexes - Dr Chiranjeevi 16  Summary of Flexor withdrawl & Crossed extensor Reflex or Polysynaptic or Protective Reflex Reflexes - Dr Chiranjeevi 17 Sensory-Motor Integration Sensory Input can be integrated at many points in CNS Complexity of integration increases with ascent through CNS Spinal cord Lower brain stem Cerebellum Thalamus Cerebral cortex (primary sensory cortex) Reflexes - Dr Chiranjeevi 18 Integration of somatic reflexes Three levels of the nervous system control movement: (1) the spinal cord, which integrates spinal reflexes and contains central pattern generators; (2) the brain stem and cerebellum, which control pos-tural reflexes and hand and eye movements; and (3) the cerebral cortex and basal ganglia, which are responsible for voluntary movements. The thalamus relays and modifies signals as they pass from the spinal cord, basal ganglia, and cerebellum to the cerebral cortex Reflexes - Dr Chiranjeevi 19 Summary Definition of a Reflex Reflex arc and its components Stretch reflex and its function Inverse stretch reflex and its function Flexor withdrawl reflex and its function Sensory – Motor integration Supra-spinal control of reflexes Reflexes - Dr Chiranjeevi 20 THANKS! Reflexes - Dr Chiranjeevi Do you have any questions? Please contact me at: [email protected] 21