Neural Control and Coordination
The neural system coordinates and integrates functions as well as metabolicand homeostatic activities of all the organs.
The human neural system is divided into two parts: Central neural system (CNS) and peripheral neural system (PNS).
CNS comprises of brain and spinal cord.
Brain is divided into three major parts: forebrain, midbrain and hindbrain.
• Forebrain consists of cerebrum, thalamus, and hypothalamus. Cerebrum is divided into two hemispheres longitudinally, which are connected by a corpus callosum.
• Midbrain has four swellings called corpora quadrigemina on its dorsal surface.
• Hindbrain consists of cerebellum, pons, and medulla.
PNS includes all the nerves of the body associated with the CNS.
PNS is divided into two divisions, namely; Somaticneural system and autonomic neural system.
The autonomic neural system is further classified into sympathetic and parasympathetic neural system.
The nerve fibres of the PNS are of two types, namely; Afferent and efferent nerves.
Neurons are the functional units of neural system.It consists of three major parts, i.e., cell body (cyton), dendrites and axon.
• The cell body contains the cytoplasm having typical cell organelles, nucleus and Nissl’s granules.
• Dendritesarise from the cell body.
• Axon also arises from the cell body. Its branch ends have synaptic knobs.
Most neurons can be anatomically characterised as:Unipolar, bipolar and multipolar.
The two types of axons are:
• Myelinated axons: They possess an extra sheath of myelin secreted by Schwann cells. The gaps between two myelin sheaths are called Nodes of Ranvier.
• Non-myelinated axons: They lack sheath of myelin and are commonly found in autonomous and somatic neural systems.
Nerve impulse generation and conduction is an electrochemical change that moves in one direction along the length of a nerve fibre.
When a neuron is not conducting any impulse, the potential difference at this stage is called the resting potential.
Generation of the nerve impulse involves depolarisation and the potential difference at this stage is called action potential or nerve impulse.
The nerve impulse is conducted along the axon membrane in the form of a wave of depolarisation and repolarisation.
Nerve impulse is transmitted through a synapse, which can be electrical synapse or chemical synapse (neurotransmitters).
A synapse is formed by the membranes of a pre-synaptic neuron and a post-synaptic neuron which may or may not be separated by synaptic cleft.
The process of involuntary response to the peripheral nervous stimulation is called reflex action. The path taken by an impulse in the reflex action is called reflex arc.
Stimulus is received by sense organs. Sense organs are eyes, ears, nose and tongue.