Definition of nerve cell

What is Nerve Cell ?

• Nervous system is made up of specific type of cells which are called nerve cells. These cells are completely different from other body cells in structure and function. Nerve cell is the basic and smallest unit of our nervous system. These cells are also called neurons.
• “Nerve cells are specialized cells which convert different stimuli into electrical impulse. Itreceives information, converts it into electrochemical form, and carries it to different cells of our body. It receives information from sense organs and other nerve cells, carries it to Central Nervous System (Brain and Spinal Cord) and then carries the information back to related organs, muscles, glands. This way, Nervous system connects different parts of body with brain and spinal cord and conducts information among them.”

Types of Nerve Cells

Neurons areofthree types onthe basis of functions.

1. Sensory Nerves: Nerves that receive nerve impulse from the receptor cells found in different sense organs of our body that receive sensory information from external environment and carry it to central nervous system i.e. brain and spinal cord. If a person looks at an object, the function of carrying information of that object to brain is done by sensory nerves. These nerves are also called afferent neurons.
2. Motor Nerves: Nerves that carry instructions, information and decisions received from brain and spinal cord to appropriate places: to organs, muscles, glands are called motor nerves for e.g. if a person looks at an object and then the brain’s decision to touch that object is carried to muscles of hands by motor nerves. These types of nerves are also called efferent nerves.
3. Association Nerves: These nerves are found only in brain and spinal cord and establish association or connection between sensory and motor nerves.
   These three types of nerves work in a synchronized manner so that a person can respond to a stimulus.

Structure of Nerve Cell

• Human nervous system is made up of 12 billion nerve cells. These cells differ from each other in shape, size, chemical composition and function. Despite these differences, the following three main components are found in all nerve cells. These are Soma, Dendrites, and Axon.
• Soma: Soma is the main part of nerve cell. It contains nucleus and other structures. The genetic material of a nerve cell is being stored in nucleus which enables reproduction and protein synthesis in a cell. Somais responsible formaintaining life of a nerve cell and keeps it healthy and alive. Ifsoma is damaged then the nerve cell stops functioning. Another function of soma is to receive the nerve impulse through dendrite and transmit it further.
• Dendrites: Dendrites are branches that originate from soma. These are the receiving ends of a neuron. Its function is to receive neural signals from the nearby nerve cells or directly from the sense organs. Dendrites contain special receptors that gets activated when they receive any electrochemical or biochemical signals.
• Axon: An elongated structure which is attached to soma is called axon. It receives information from soma and sends it to other nerve cells and muscles. Axon carries information through its entire length. Its length varies from many feet in spinal cord to less than one millimeter in brain. The axon, in the end is divided into many small branches which are called terminal buttons. These buttons send information from one neuron to another neuron, gland or muscles. Usually, a neuron conducts information in one direction only that is from dendrite to soma to axon and lastly to terminal buttons. It means that information is received in a neuron from the dendrite end only.
• The axon is covered in most neurons by a covering called myelin sheath. This sheath is not found through the axon in continuity but is separated by small ridges type spaces. These spaces are called Nodes of Ranvier. Both myelin sheath and nodes of Ranvier help in increasing the speed of information flow.

Function of Nerve Cell

• Nerve cell conducts information in our body. This information flows in the form of nerve impulse in nervous system. Nerve impulse means an electrical current passing through axon for a very short duration. This is called spike. When stimulus energy reaches receptors, then some electrical changes takes place in nerve potential. When the stimulus intensity or energy is very less, then the resulting electrical changes are weak and cannot produce nerve impulse. If the stimulus energy is strong above a certain level, then it generates electrical impulse which is then taken to central nervous system. It means that the strength of nerve impulse is not dependent on the strength of stimulus. Nerve fibers work on the principle of ‘All or None law’. Nerve fibers will either respond fully or will not respond at all. The strength of nerve impulse does not increase or decrease with stimulus intensity.
• Synapse: Information flows in the form of nerve impulse in nervous system. One neuron can carry information only through the length of its axon. But when information is to be sent to distant body parts then so many neurons participate in this process. One neuron sends information to another neuron, which sends information to other neuron and so on. One neuron is not physically attached to other neurons rather they are separated by a small space in between both the neurons. This space is called synapse.
• Information is passed through the synapse by a specific process. The nature of nerve impulse conduction is electrochemical in axon. But the nature of synaptic transmission is chemical. These chemicals are known as neurotransmitters.

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Important Points of Human Behavior :- 

1. “Inthis chapter, the relation of human behavior and biology is described.”
2. The cell is the basic unit of human body. Many cells form tissue, many tissue to organ, many organs to organ systems are formed. These organ systems perform specific functions of our body. Nerve cell is the basic and smallest unit of nervous system. It is also called neuron.
3. Nerve cells are of three types on the basis of functions: Sensory, motor and association neurons.
4. Nerve cells perform the function of transmitting information in our body.
5. Nervous system is of two types: Central Nervous System and Peripheral Nervous System.
6. Central Nervous system consists of brain and spinal cord.
7. Peripheral nervous system is divided in two parts somatic nervous system and autonomic nervous system.

Human Behavior Questions and Answers

1. Which part of nerve cell contains nucleus?
A Axon
B. Soma
C. Myelin Sheath
D. Nodes of Ranvier

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2. Which part of nerve cell increases the speed of nerve conduction?
A Myelin Sheath
B. Dendrites
C. Thalamus
D. Pons

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“3. Which part of brain controls activities like eating, drinking, sleeping, temperature regulation and sexual arousal?”
A Pons
B. Cerebellum
C. Hypothalamus
D. Thalamus

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4. How many pairs of cranial nerves are there in human brain?
A. 6
B. 10
C. 12
D. 31

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