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What is a neuron?
Neuron or nerve cell is the basic structural unit of the nervous system. Like all other cells, the neuron has a cell membrane, cytoplasm and nucleus. All neurons have three different parts – dendrites, cell body and axon. The neuron structure is specially adapted to carry messages over large distances in the body quickly in the form of electrical signals.
Analyse the diagram below and write a short note on parts of neurons
The main parts of Neurons are dendrite, dendrone, axon, axonite,schwann cell and synaptic knob
Dendrite
- Branches of Dendron.
- Part that receives impulses from adjacent neuron.
Dendron
- Short filament from the cell body.
- Carries impulses from dendrites to the cell body
Schwann cell
- Encircles the axon.
- Schwann cell Encircles the axon.
Axon
- Longest filament from the cell body.
- Carries impulses from the cell body to outside.
Axonite
- Branches of axon.
- Carries impulses to the synaptic knob.
Synaptic knob
- Tip of axonite.
- Secretes neurotransmitter.
Make a short note about the function of myelin sheath
Axons of most of the neurons are repeatedly encircled by myelin, a membrane containing lipid. This is called myelin sheath.The major functions of the myelin sheath are to provide nutrients and oxygen to the axon, accelerate impulses, act as an electric insulator and protect the axon from external shocks.
Distinguish Schwann cells and oligodendrocytes
Myelin sheath in the nerves is formed of Schwann cells. Myelin sheath in the brain and the spinal cord is formed of specialized cells called oligodendrocytes. Oligodendrocytes and Schwann cells provide protection to neurons. An oligodendrocyte constructs myelin sheath by covering the different axons simultaneously or by covering the different parts of the same axon repeatedly. Myelin sheath made up of Schwann cells are seen in the axons in nerves. A Schwann cell encircles the axon repeatedly.
Distinguish white matter and grey matter
The myelin sheath has a shiny white colour. The part of the brain and the spinal cord where myelinated nerve cells are present in abundance is called white matter and the part where non-myelinated nerves cells are present is called grey matter.
Write a short note on Classification of Neurons
On the basis of the direction of impulse, neurons can be classified into sensory neurons and motor neurons. Sensory neurons carry impulses to the brain and spinal cord.The sensory neurons convert signals from the external environment into corresponding internal stimuli.They are pseudounipolar in structure.
Motor neurons carry impulses from the brain and spinal cord to various parts of the body.These are multi polar and are located in the central nervous system extending their axons outside the central nervous system. This is the most common type of neuron and transmits information from the brain to the muscles of the body.
Analyse the diagram below and make a short note about it
Synapse is the junction between two neurons or a neuron and a muscle cell or a neuron and a glandular cell. When electric impulses from the axon reach the synaptic knob, certain chemical substances are secreted from there to the synaptic cleft. These chemical substances are called neurotransmitters. They stimulate the adjacent dendrite or cell and new electric impulses are generated. Acetylcholine and dopamine are examples of neurotransmitters. Synapse helps to regulate the speed and direction of impulses.
Distinguish chemical synapse and Electrical synapse
In chemical synapses, the action potential affects other neurons through a gap present between two neurons known as the synapse. The action potential is carried along the axon to a postsynaptic ending that initiates the release of chemical messengers known as neurotransmitters. These neurotransmitters excite the action potential.
When two neurons are connected by a gap junction, it results in an electrical synapse. These gaps include ion channels that help in the direct transmission of a positive electrical signal. These are much faster than chemical synapses.
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