Spinal Cord and Reflex Action

Spinal Cord

Spinal cord ( 42 to 45 cm long ) extends from the medulla oblongata and is continuous to the level of second lumbar vertebra.

It conducts impulses to and from the brain and controls most of the reflex activities and provides a Reflexes categorised into simple or unconditioned and conditioned reflexes. Simple or unconditioned reflexes are inborn , unlearned response to a stimulus or any change in the environment . Whereas , conditioned reflexes are not inborn but are acquired on past experiences , training or learning. Conditioned reflexes were first demonstrated by Ivan Pavlov .

Inhibition of Reflex Action

In infants, the act of micturition and defecation are carried out by reflex action and there is no voluntary control over these processes . As the child grows , the sensory nerve tracts of the spinal cord become fully developed , the impulses from the bladder and rectum reach the brain and can be controlled . Hence , now the act of micturition and means of communication between spinal nerves and the brain.

It is formed of two types of neural tissue : internal grey matter and outer white matter . The area within the vertebral column below the second lumbar vertebra contains spinal nerves that are collectively called , the cauda equina . The spinal cord ends as the conus medullaris from which a fine connective tissue filament called filum terminale arises that anchors spinal cord within the vertebral column .

Functions

Spinal cord performs two main functions

( i ) The stimuli are passed from and to the brain through the spinal cord .

( ii ) It is the centre of spinal reflex action .

REFLEX ACTION

Reflex action ( Marshal Hall , 1833 ) is an immediate involuntary action of any organ or part of the body in response to a particular stimulus .

The nervous pathway taken by nerve impulses in a reflex action is called reflex arc .

The components that mediate a reflex , usually includes a receptor , afferent pathway , integrating centre , efferent pathway and effector.

Manish Mevada

M.Sc, M.Phil, B.Ed