§ All animals are capable of corresponding to their surroundings. They gather stimuli from the environment by sensory receptors and the motor effectors react to it.
§ Most invertebrates and vertebrates process and integrate the information from the receptors and issue the instructions to the motor effectors. This process is done by the nervous system. It connects the receptors and effectors by the large network of nerve cells.
§ These nerve cells are called as “Neurons”.
§ The nervous system is principally consisting of Neurons and Glial cells.
Neurons
§ Consists of large cell body with cytoplasmic extensions.
§ Cell body is large containing the nucleus.
§ Other organelles such as mitochondria, ER, Golgi apparatus, microfilaments are present in the cell body.
§ Also Nissel bodies which are groups of ribosome are present in the cell body.
§ Two types of cytoplasmic extensions; Dendrites and Axon.
Dendrites | Axon |
· One or more can be extend from the cell body | · Single Axon extends from the cell body |
· Can branch forming dentritic spines. | · Branches only at the terminal end. |
· Schwann cells are not present. Myelin sheath is not present. | · Schwann cells are present. Myelin sheath is present. |
· Radius tapers. | · Constant radius |
· Short | · Much longer |
· Transmit signals into the cell body. | · Transmit signals away from the cell body. |
§ Neurons communicate with other cells via synapses.Synaptic Bulbs at the Axon terminal ends are important to form these synapses.
Structure of Synapses
Structural classes of neurons
§ Bipolar neuron: One dendrite and one axon attached to the cell body.
§ Pseudounipolar neuron: One extension from the cell body. That is an axon.
§ Multipolar neuron: Many dendrites and one axon.
Functional types of neurons
§ Sensory neurons: Transmit massages from the receptors.
§ Motor neurons: Transmit massages to the motor effectors.
§ Intermediate neurons: Connect sensory and motor neurons.
Glial cells
§ Non-neuronal, supporting cells.
§ Support neurons both structurally and functionally.
§ Large numbers of different types are present.
§ Ex: Schwann cells
Mainly Nervous system can be divided in to two sections as Central Nervous System and Peripheral Nervous System.
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