The spinal cord is located within the vertebral column and consist of the following: The grey matter forms the central part of the spinal cord. It consists of nerve¬cell bodies and intermediate nerve fibres.
The white matter of the spinal cord carries sensory nerve fibers while the ventral root carries motor nerve fibers.
Simple and Conditioned Reflex Actions
Simple Reflex Action
A simple reflex action is an automatic response to a stimulus. The route that is followed by impulses during a reflex action is called a reflex arc.
A reflex action follows the following sequence:
- A receptor is stimulated and an impulse is transmitted along a sensory nerve fibre to the spinal cord.
- The impulse is picked up by an intermediate neurone within the CNS.
- The intermediate nerve fibre transmits the impulse to a motor nerve fibre which is connected to an effector.
- The effector responds.
Examples of reflex action include:
- Pulling the hand away from a hot object.
- The knee jerk.
Conditioned Reflexes
- These are learned responses.
- When two or more stimuli are presented to an animal at the same time and repeatedly, the animal eventually responds to either stimulus.
- For example, if a hungry animal is presented with food, it will respond by salivating.
- If a bell is rung at the same time as the food is presented to the animal, the animal will learn to associate the sound of the bell with food.
- Eventually, the animal can be made to salivate at the sound of the bell alone.
- This response is called conditioned reflex and is one of the ways by which animals learn.