Nerve Cell Physiology Obert Tada Dept of Livestock & Wildlife Management

Content Introduction Structure of types of neurones Membrane excitation & generation of action potentials.

Introduction

The Vertebrate Nervous System Nervous tissue senses stimuli and transmits signals from one part of the animal to another. A neuron is a cell specialized to conduct electrochemical impulses called nerve impulses or action potentials. Consists of  Cell body  Dendrites, extensions that conduct impulses to the cell body  Axons, extensions that transmit impulses away from the cell body What does it look like?

Neuron

All neurons outside the CNS conduct impulses along hair- like cytoplasmic extensions, the nerve fibers or axons. The axons connecting spinal cord to the foot can be as much as 1m long. Axons grow out of the cell body, which houses the nucleus as well as other organelles such as the ER. Nerve impulses are generated in short, branched fibers (dendrites) and also in the cell body. The impulses are then conducted along the axon. Neuron cont’d

Many axons are covered with a glistening fatty sheath, the myelin sheath (greatly-expanded plasma membrane of an accessory cell, the Schwann cell). Schwann cells are spaced at regular intervals along the axon. Their plasma membrane is wrapped around and around the axon forming the myelin sheath. Where the sheath of one Schwann cell meets that of the next, the axon is unprotected. This region, the node of Ranvier, plays an important part in the propagation of the nerve impulse. Neuron cont’d

Type of Neurons There are three major classes of neurons. A.Sensory neurons B.Interneurons C.Motor neurons

Sensory Neurons These run from the various types of stimulus receptors to the CNS (brain & spinal cord).  e.g. touch, odour, taste, sound, visiontouchodourtastesoundvision The cell bodies of the sensory neurons leading to the spinal cord are located in clusters, called ganglia, next to the spinal cord. The axons usually terminate at interneurons.

Interneurons These are found exclusively within the spinal cord and brain. They are stimulated by signals reaching them from:  sensory neurons  other interneurons or  both. Interneurons are also called association neurons. It is estimated that the human brain contains 100 billion (10 11 ) interneurons averaging 1000 synapses on each; that is, some connections.

Motor neurons These transmit impulses from the CNS to the muscles and glands that carry out the response.musclesglands Most motor neurons are stimulated by interneurons, although some are stimulated directly by sensory neurons. Diagram….

Organization of Neurons