Reflex arc(Neurology)

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1. Reflex Arc Presented by : Gajraj Singh Bika

2. What is reflex Arc? A reflex arc is a neural pathway that controls a reflex . In vertebrates, most sensory neurons do not pass directly into the brain, but synapse in the spinal cord . A neural pathway that controls an action reflex. In higher animals, most sensory neurons do not pass directly into the brain, but synapse in the spinal cord. This characteristic allows reflex actions to occur relatively quickly by activating spinal motor neurons without the delay of routing signals through the brain, although the brain will receive sensory input while the reflex action occurs. There are two types of reflex arcs: autonomic reflex arc and somatic reflex arc.

3. Parts of Reflex Arc 1. Receptor – detects the stimulus. a) Description: the receptor end of a particular dendrite or a specialized receptor cell in a sensory organ. b) function: sensitive to a specific type of internal or external change . 2. sensory neuron – conveys the sensory info. to brain or spinal cord. a. Description: Dendrite, cell body, and axon of a sensory neuron. b. Function: transmit nerve impulses from the receptor into the brain or spinal cord.

4. 3. Interneuron: relay neurons. a. Description: dendrite, cell body, and axon of a neuron within the brain or spinal cord. b. function: serves as processing center , conducts nerve impulses from the sensory neuron to a motor neuron. 4. Motor neuron: conduct motor output to the periphery. a. Description: Dendrite, cell body, and axon of a motor neuron. b. function: transmits nerve impulse from the brain or spinal cord out to an effecter.

5. 5. Effecter: a. Description: a muscle or gland. b. function: Response to stimulation by the motor neuron and produces the reflex or behavioral action.

6. alpha motor neuron : These are large, lower motor neurons of the brainstem and spinal cord. They innervate the extrafusal muscle fibers of skeletal muscle and are directly responsible for initiating their contraction. Alpha motor neurons are distinct from gamma motor neurons that innervate the intrafusal muscle fibers of muscle spindles.

7. Spinal reflexes include the stretch reflex, the Golgi tendon reflex, the crossed extensor reflex, and the withdrawal reflex. Stretch Reflex : The stretch reflex is a muscle contraction in response to stretching within the muscle. This reflex has the shortest latency of all spinal reflexes. It is a monosynaptic reflex that provides automatic regulation of skeletal muscle length .

8. Golgi Tendon Reflex : The Golgi tendon reflex is a normal component of the reflex arc of the peripheral nervous system. The tendon reflex operates as a feedback mechanism to control muscle tension by causing muscle relaxation before muscle force becomes so great that tendons might be torn.

9. Crossed Extensor Reflex : The crossed extensor reflex is a withdrawal reflex. The reflex occurs when the flexors in the withdrawing limb contract and the extensors relax, while in the other limb, the opposite occurs. An example of this is when a person steps on a nail, the leg that is stepping on the nail pulls away, while the other leg takes the weight of the whole body.

10. Withdrawal Reflex : The withdrawal reflex is a spinal reflex intended to protect the body from damaging stimuli. It is polysynaptic, and causes the stimulation of sensory, association, and motor neurons.