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Note on Spinal cord and Reflex actions

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Spinal cord:

It is the long cylindrical part of CNS. It is present in the neural canal of the vertebral column. It is the center of all reflex actions. Grey matter, which has a pinkish-grey color in the living brain, contains the cell bodies, dendrites and axon terminals of neurons, so it is where all synapses are. White matter is made of axons connecting different parts of grey matter to each other. In spinal cord grey matter is inside and white matter is outside. Major functions of spinal cord are:

  1. It acts as the main center for reflex actions.
  2. It acts as a link between spinal nerves and brain. Thus it participates in conscious actions.

Reflex actions:

It is defined as an involuntary action performed by muscles under the direction of the spinal cord in response to the stimulus. The best example of the reflex action is pulling of hand when we touch hot or very cold objects and contraction of the pupil when the light is shown in the eye.

Reflex arc:

The path which is followed by impulses during the reflex action is called the reflex arc. It consists of an afferent (or sensory) nerve, usually one or more interneurons within the central nervous system, and an efferent (motor, secretory, or secretomotor) nerve.

  • Spinal cord is the long cylindrical part of Central Nervous System.
  • Spinal cord acts as the main center for reflex actions.
  • Spinal cord acts as a link between spinal nerves and brain. Thus it participates in conscious actions.
  • Reflex actions is defined as an involuntary action performed by muscles under the direction of spinal cord in response to the stimulus.
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Very Short Questions

The immediate and automated response shown to a stimulus without the involvement of brain is called reflex action. When we touch something very hot, we jerk our hand away. This is an example of reflex action.

The path followed by nerve impulses during the process of reflex action is called reflex arc.

When a pin is suddenly pricked in foot, the stimulus is transferred by the following ways:
i. Receptor: tip of nerve of skin of foot.
ii. Sensory nerve: to carry the message from receptor to spinal cord.
iii. Intermediate nerve: to send the stimulus from top to bottom of the spinal cord.
iv. Motor nerve: to carry the stimulus from spinal cord to muscle.
v. Effector: to receive the stimulus in the muscle. Thus the pin is suddenly pricked in the foot, the stimulus transfers to the spinal cord through the nerves of skin. After that the spinal cord sends message to muscle of leg to withdraw the leg immediately.

Reflex action involves sensory neuron, spinal cord and motor neuron only. So, when we touch something hot, the impulse passes from the hand to spinal cord and back to muscles. As brain is not involved during the action, impulses each the brain and we feel pain after sometime.

A man jumped with fear because of reflex action when his bare foot touched the cold object on the ground. During this, the nerves in the skin transmitted the information to spinal cord through sensory nerve, from when an instruction is sent to the muscle through motor nerve.

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  • Spinal cord is the ling cylindrical part of ______.

    RNA


    DNA


    CNS


    BNS


  • Spinal cord is the center of all ______.

    cell bodies


    Grey matter


    reflex actions


    brain


  • The path which is followed by impulses during reflex action is called ______.

    White matter


    reflex arc


    None of these


    Grey matter


  • ______ is made of axons connecting different parts of grey matter to each other

    reflex arc


    reflex actions


    white matter


    all of these


  • Grey matter, which has a pinkish-grey color is present in the  ______.

     living brain
    White matter
    cell
    body
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kaushal

what happens if spinal cord is injured?


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