Components of Nervous Co-Ordination

NERVOUS CO-ORDINATION:


This type of co-ordination involves specialized cells or neurons linked together directly or via the central nervous system, to form a network that connects the cell organs which receive stimuli (receptors) and those which carry out actions or responses (effectors). The neuron has the ability to generate and conduct impulses which travel across the synapse and pass from the receptors to the effectors, brings about nervous co-ordination. The elements of the nervous system which helps co-ordination are:

• Receptors

• Neurons

• Effectors

The neuron fibers and cell bodies can be excited by slight electric shocks, mechanical, chemical, light and temperature stimuli. Receptors detect changes in the external and internal environment of the animal. The receptor may be a cell, or neuron ending or a receptor organ. Receptors are classified as follows:

Chemoreceptors:

These are for smell, taste and for blood Carbon dioxide, oxygen, glucose, amino acids and fatty acids.

Mechanoreceptors:

These detect stimuli of touch, pressure, hearing and equilibrium.

(E.g. free nerve endings + expanded tip endings + Stray endings)

Photoreceptors: 

These (electromagnetic receptors) respond to stimuli of light for example in eyes, rods and cones.

Thermoreceptors:

These are free nerve endings. These show response to cold and warmth.

Nocireceptors:

(Undifferentiated endings) which produces the sensation of pain.

Structure of five different types of sensory receptors in brain

Each type of principal type of sensation that we can experience_ pain, touches, sight, sound and so forth are called Modalities of sensation. Yet despite the fact that we experience these different modalities of sensation; nerve fibers transmit only impulses. How is it that different nerve fibers transmit different modalities of sensation? The answer to this question is:

Each nerve tract terminates at a specific point in the CNS; and the type of sensation is determined by the point in the nervous system to which the fiber leads. So touch stimulus is carried by the nerve impulse in the ‘touch’ area of the brain. Similarly fibers from the eyes (retina) terminate in the visual cortex of the brain.

There are numerous receptors which respond to mechanical conditions of internal organs. Examples are the receptors of the stomach wall which may be concerned with arousal of ‘hunger’; stretch receptors in the carotid and aortic arteries of tetrapods have important roles in regulation of blood pressure; endings with similar properties are found in branchial vessels of fishes.

Neurons:

"The structural and functional unit of the nervous system in all animals including man is the neuron”. This is a highly specialized cell which contains the typical organelles found in most eukaryotic cells. This cell is particularly adapted for communication because of its wire like projection; the dendrites which are often further branched and carry impulses towards the central cell body. The cell body is the thicker region of the neuron containing the nucleus and most of the cytoplasm. The axon is the projection, generally very long, that carries impulses away from the cell body. Usually a neuron has a single axon. A fatty substance covering the axon is the myelin sheath along with short regions of exposed axons is called Nodes of Ranvier. Many axons and even dendrites combine to form a single nerve. 

'The chief structural and functional units of the nervous system are neurons, but there are other cells, in higher animals, and in humans called neuroglia, which make up as much as half of the nervous system. Neuroglia plays a vital role in the nutrition of neurons and their protection from the myelin sheath. There are three functional types of neurons:

• Sensory
• Associative (intermediate/relay)
• Motor

The neuron has protoplasmic processes arising from its cell body containing a nucleus and various organelle embedded in the cytoplasm. There are two main types of cytoplasmic processes or fibers. One which carries impulse towards cell body is called Dendron, if it is a single fiber, but if smaller fibers _they are called dendrites (singular: dendrite). The processes conducting impulses away from the cell body are termed axons: These may be more than a meter long in some neurons. Nissl's granules which are groups of ribosomes associated with rough E.R and Golgi apparatus are present in the cell body. Microtubules, neurofibrils, rough endoplasmic recticulum and mitochondria are present throughout the axoplasm of neuron.

The cell body or soma is the main nutritional part of the cell and is concerned with the biosynthesis of the materials necessary for the growth and maintenance of the neuron. If the cell body of the neuron remains intact, it can regenerate axonal and dendrite fibers; but neurons once mature, do not divide any further.

Effectors:

These are the structures which respond when they are stimulated by impulses coming via motor neuron. The principal effectors is glands, which respond by secreting; and muscles which respond by contracting. Flow of information through the nervous system is explained with the help of a reflex arc.

Effectors in Human Body

Reflex Arc:

Flow of impulse through the nervous system involving receptors, neurons and effectors will be quite clear if we study an example of a reflex arc. Reflex arc is the pathway of passage of an impulse during a reflex action. Reflex action is a form of involuntary action. The direction of stimulus is from receptors to the sensory neuron to associative (Association / relay) neuron and then through the motor neuron to the effectors. 

Autonomic Reflex:

Any of a large number of normal reflexes governing and regulating the functions of the viscera.

Autonomic reflexes control such activities of the body as blood pressure, heart rate, peristalsis, sweating, and urination.

Autonomic Reflex

Somatic Reflex:

An involuntary control system characterized by a control loop which includes skeletal muscles.

Somatic Reflex