ReviewSheetPhysiology2[1] - Reflexes and Spinal cord...

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Reflexes and Spinal cord function (Physiology Col. Book Plates 26-27,29-30, 82, 84-86,95) Structure of spinal cord -Cervical, Thoracic, Lumbar, Sacral, Coccygeal Segments -Dorsal/Posterior Horn (sensory), Middle Zone/Interneurons (association), Ventral horn (motor nuclei) Gray matter vs. white matter -Gray matters function is to route sensory or motor stimuli to interneurons of CNS to create response to stimulus. Process info originating in sensory organs or other gray matter regions, contains sensory and motor neurons that come in through dorsal root and can be sent up to brain or use interneuron to sent inhibitory or stimulatory signal through ventral root. These connect at sensory ganglia. -White matter is tissue made up of axons that pass between gray matter. White matter transmits info quickly through axons, can be thought of as wiring. Spinal cord and reflex functions (what is a spinal reflex? -Spinal reflexes are those associated with spinal cord control of trunk and limb muscles. Somatic reflexes involve skeletal muscles and motor fxns, while autonomic reflexes regulate internal environment by affecting exocrine glands, heart and visceral muscle. -Spinal reflexes are important for 1) defending against noxious stimuli 2) maintaining postural body support Reflex arc - parts of reflex arc : 1) Sensory receptor, to detect stimulus 2) Afferent nerve, which conveys sensory signal to spinal cord or brain 3) Synaptic center, to integrate and analyze sensory input and produce motor output commands 4) Efferent nerve, to conduct motor output to the periphery 5) Motor Effector, to carry out response Spinal shock; variation in animal species in duration of spinal shock; reason: Spinal reflexes can occur independently, without brain control as seen in spinal transected animals and quadriplegic humans. For varying durations after spinal transaction, spinal reflexes do not occur. This period of spinal shock is shorter in lower animals and long in higher animals because a higher animal’s brain exerts more control over its spinal cord, compared to a lower animal. The gradual increase in motor control during development is known as encephalization. Monosynaptic vs. Polysynaptic reflexes: -A monosynaptic reflex, like the stretch reflex , is the simplest reflex because there is only one synapse in the path of its arc (the monosynaptic reflex arc). Large skeletal muscles involved in body support and limb movements contain muscle spindles, which act as sensory organs detecting change in muscle length -A polysynaptic reflex arc contains one or more interneurons and higher number of synaptic connections. The knee jerk reflex contains both mono and polysynaptic reflexes.
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This is because the stretch reflex that occurs when your patellar tendon is hit causes thigh extensor muscles in hamstrings, yet in order to extend the flexor muscles in your thighs must be inhibited. This is the result of an extra synapse diverging from the afferent nerve to an inhibitory interneuron causes this reflex to be polysynaptic. Knee jerk reflex:
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This note was uploaded on 04/16/2008 for the course MCB 240 taught by Professor Meissami during the Spring '08 term at University of Illinois at Urbana–Champaign.

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ReviewSheetPhysiology2[1] - Reflexes and Spinal cord...

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