Nervous Coordination in Mammals

Nervous system involves five main components: These are

1. Stimulus: A change in the external or internal environment e.g. touch, pain, smell and sound.
2. Receptor: A structure which detects the change in the environment e.g. eyes, ears, nose, skin and tongue (sense organs).
3. Coordinator: An organ which receives message from receptor and use the message to coordinate the activities in the body e.g. brain, spinal cord, and messages received (impulses).
4. Effectors: An organ which is controlled by the brain or spinal cord to bring about appropriate response e.g. muscles and glands.
5. Responses: A body activity provoked by a stimulus e.g. pulling away a hand when accidentally one touches a hot object.

Nervous system is made up of interconnected nerve cells or neurones.

1. Excitability– highly capable of responding to stimuli.
2. Conductivity- capable of conducting massage along it.

1. Receive stimuli.
2. Convert stimuli into the form of electrical impulses.
3. Transmit the impulses over a considerable distance.

Based on their function and structure there are three types of neurones; which are

1. sensory neurones, intermediate neurones (interneurones)
2. motor neurones.

Sensory neurones (Afferent neurones)

Sensory and intermediate neurones are also known as afferent neurones. These are neurones with long dendrites and short axon. The cell body and dendrites of the sensory neurones mostly lie outside the brain and spinal cord. Sensory neurones transmit nerve impulses from sensory receptors to the CNS for the interpretation.

Interneurones (Intermediate neurones)

These are also known as connector neurones or relay neurones. They are much smaller nerve cells with many interconnections. Interneurones have short dendrites and short or long axons. They lie entirely within the CNS (brain and spinal cord). They transmit nerve impulses within the CNS; that is, they relay information between sensory and motor neurones. The sensory neurones and intermediate neurones both carry impulses towards the CNS.

Motor neurones (Efferent neurones)

Motor neurone have short dendrites and long axons; their dendrites and cell bodies are located in the CNS; and the axon is outside the CNS. Motor neurones transmit nerve impulses from the CNS to the effector organs such as muscles or glands, which eventually respond to the stimulus. Axon always transmits impulses away from the cell body while dendron carries impulses towards the cell body.

Neurones can also be classified on the basis of the number of their dendrites arising from the soma (cell body). In this classification, there are three main types of neurones. These include unipolar, bipolar and multipolar neurones. Unipolar neurones have a single short dendrite terminating onto bush-like tufts or dendrites. These are found in the granular layer of the cerebellum. Bipolar neurones are sensory neurones that have two processes coming from the cell body; one dendron and one axon. Bipolar sensory neurones are found in the retina of the eye, ganglia of the vestibulocochlear nerve and the olfactory epithelium. Multipolar neurones have three or more processes coming from the cell body. They possess one axon and two or more dendrites. Multipolar neurones form the major part of the CNS. They include interneurones and motor neurones.