Essay on neurones
HOW DOES THE STRUCTURE OF NEURONES REFLECT THEIR FUNCTION
The neuron or nerve cell is the structural unit of the nervous system. It is able to transmit messages between the central nervous system (CNS) and all parts of the body. There are two basic types of neuron namely - the sensory neuron (afferent) and the motor neuron (efferent) (Bear et al., 3rd edition).
The sensory neurons (Fig. 1-1) are capable of transmitting the sensation of pain and consist of three major portions which are the dendritic zone, the axon and the cell body. The dendritic zone is the most distal segment of the sensory neuron and is composed of an arborization of free nerve endings. These free nerve endings respond to stimulation produced in the tissues in which they lie, provoking an impulse that is transmitted centrally along the axon. The axon is a long cylinder of neural cytoplasm encased in a thin sheath, the nerve membrane. At its central end, there is an arborization similiar to that seen in the dendritic zone. However, the arborization form synapses with various nuclei in the CNS to distribute incoming (sensory) impulses to their appropriate sites within the CNS. The axoplasm, a gelatinous substance, is separated from extracellular fluids by a continuous nerve membrane. Some of this membranes are covered by myelin. Nerve cells have a cell body and a nucleus like all other cells but nerve cells have an axonal process from which the cell body may be some distance from the axon.
The cell body, is the third part of the neuron, located at a distance from the axon, or the main pathway of impulse transmission in the nerve. The cell body is therefore not involved in the process of impulse transmission. Its primary function is to provide the vital metabolic support for the entire neuron.
The motor neurons are nerve cells that conduct impulses from the CNS peripherally. They are structurally different from the sensory neurons in that their cell body is interposed between the axon and the
The neuron or nerve cell is the structural unit of the nervous system. It is able to transmit messages between the central nervous system (CNS) and all parts of the body. There are two basic types of neuron namely - the sensory neuron (afferent) and the motor neuron (efferent) (Bear et al., 3rd edition).
The sensory neurons (Fig. 1-1) are capable of transmitting the sensation of pain and consist of three major portions which are the dendritic zone, the axon and the cell body. The dendritic zone is the most distal segment of the sensory neuron and is composed of an arborization of free nerve endings. These free nerve endings respond to stimulation produced in the tissues in which they lie, provoking an impulse that is transmitted centrally along the axon. The axon is a long cylinder of neural cytoplasm encased in a thin sheath, the nerve membrane. At its central end, there is an arborization similiar to that seen in the dendritic zone. However, the arborization form synapses with various nuclei in the CNS to distribute incoming (sensory) impulses to their appropriate sites within the CNS. The axoplasm, a gelatinous substance, is separated from extracellular fluids by a continuous nerve membrane. Some of this membranes are covered by myelin. Nerve cells have a cell body and a nucleus like all other cells but nerve cells have an axonal process from which the cell body may be some distance from the axon.
The cell body, is the third part of the neuron, located at a distance from the axon, or the main pathway of impulse transmission in the nerve. The cell body is therefore not involved in the process of impulse transmission. Its primary function is to provide the vital metabolic support for the entire neuron.
The motor neurons are nerve cells that conduct impulses from the CNS peripherally. They are structurally different from the sensory neurons in that their cell body is interposed between the axon and the
References: 1) Malamed SF: Handbook of Local Anaesthesia, ed 3, St Louis, 1990, Mosby – Year Book. 2) Chiu SY Ritchie JM: On the physiological role of internodal potassium channels and the security of conduction in myelinated nerve fibers, Proc R Soc Lond [Biol] 220:415-422, 1984. 3) Courtney KR, Strichartz GR: Structural elements which determine local anaesthetic activity. In Strichartz GR, editor: Local Anaesthetics, New York, 1987 Springer-Verlag New York Inc. 4) Hille B: Ionic channels in nerve membranes,Prog Biohys Mol Biol 21:1-32, 1970. 5) Singer SJ, Nicholson GL: The fluid mosaic model of the structure of cell membranes, Science 175:720731, 1972.