- 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.
- 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.