Importance of neural system in humans
This is in continuation to the last article focusing on neural system and mechanisms of neural coordination in a human body. In today’s article we will discuss Human neural system and neurons. Human neural system • The human neural system is divided into two parts: (i) The central neural system (CNS) (ii) The peripheral neural […]
This is in continuation to the last article focusing on neural system and mechanisms of neural coordination in a human body. In today’s article we will discuss Human neural system and neurons.
Human neural system
• The human neural system is divided into two parts:
(i) The central neural system (CNS)
(ii) The peripheral neural system (PNS)
• The CNS includes the brain and the spinal cord, and is the site of information processing and control.
• The PNS comprises all the nerves of the body associated with the CNS (brain and spinal cord).
• The nerve fibres of the PNS are of two types —
— Afferent fibres
— Efferent fibres
• The afferent nerve fibres transmit impulses from tissues/organs to the CNS.
• The efferent fibres transmit regulatory impulses from the CNS to the concerned peripheral tissues/organs.
Peripheral Neural System (PNS)
The PNS is divided into two divisions:
— Somatic neural system
— Autonomic neural system
• The somatic neural system relays impulses from the CNS to skeletal muscles.
• The autonomic neural system transmits impulses from the CNS to the involuntary organs and smooth muscles of the body.
• The autonomic neural system is further classified into —
— Sympathetic neural system and
— Parasympathetic neural system
• Visceral nervous system is the part of the peripheral nervous system that comprises the whole complex of nerves, fibres, ganglia, and plexuses by which impulses travel from the central nervous system to the viscera and from the viscera to the central nervous system.
Neuron
• Neuron is structural and functional unit of neural system.
• A neuron is a microscopic structure composed of three major parts, namely cell body, dendrites and axon.
• The cell body contains cytoplasm with typical cell organelles and certain granular bodies called Nissl’s granules.
• Short fibres which branch repeatedly and project out of the cell body also contain Nissl’s granules and are called dendrites.
• These fibres transmit impulses towards the cell body.
• The axon is a long fibre, the distal end of which is branched. Each branch terminates as a bulb-like structure called synaptic knob which possess synaptic vesicles containing chemicals called neurotransmitters.
• The axons transmit nerve impulses away from the cell body to a synapse or to a neuro-muscular junction.
• Based on the number of axon and dendrites, the neurons are divided into three types, i.e., multipolar (with one axon and two or more dendrites; found in the cerebral cortex), bipolar (with one axon and one dendrite, found in the retina of eye) and unipolar (cell body with one axon only; found usually in the embryonic stage).
• There are two types of axons, namely myelinated and nonmyelinated.
• The myelinated nerve fibres are enveloped with Schwann cells, which form a myelin sheath around the axon.
• The gaps between two adjacent myelin sheaths are called nodes of Ranvier.
• Myelinated nerve fibres are found in spinal and cranial nerves.
• Unmyelinated nerve fibre is enclosed by a Schwann cell that does not form a myelin sheath around the axon, and is commonly found in autonomous and the somatic neural systems.
To be continued…
