Tiêu đề SP-2_Ch-8-Neural Control and Coordination.pdf ✅

40 Neural Control and Coordination NEET Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 HUMAN NEURAL SYSTEM The nervous system consists of two main parts : (A) Central nervous system : It consists of brain and spinal cord. The brain is lodged in the skull while spinal cord is enclosed by the vertebral column. (B) Peripheral nervous system : The nerves arising from the central nervous system, constitute the peripheral nervous system. The nerves originating from the brain and spinal cord and are known as cranial nerves and spinal nerves respectively. It is further differentiated into somatic neural system and autonomic nervous system. Visceral nervous system is that part of the peripheral nervous system that comprises the whole complex of nerves, fibres, ganglia and plexuses by which impulses travel from the central nervous system to the viscera and from the viscera to the central nervous system. Types of Nerve Fibres of the PNS The nerve fibres of the PNS are of two types : (a) Afferent fibres : The afferent nerve fibres transmit impulses from tissues/organs to the CNS. The afferent nerve fibres are also called the sensory nerve fibres. The function of these nerve fibres is to carry the sensory information from various tissues/organs of the body towards the CNS so that the CNS can accordingly respond and control the body. (b) Efferent fibres : The efferent nerve fibres transmit the regulatory impulses from the CNS to the concerned peripheral tissues/organs. The efferent nerve fibres are also called the motor nerve fibres. The function of these nerve fibres is to carry the regulatory information from CNS to the concerned peripheral tissue/organ through which the response of the body is shown. Type of Nerves based on their Function (a) Sensory nerves: Some cranial nerves contain only sensory (afferent) nerve fibres, and are thus called sensory nerves. First (olfactory nerve), second (optic nerve) and eighth (auditory nerve) cranial nerves are sensory. (b) Motor nerves: Some cranial nerves contain only motor (efferent) nerve fibres, and are thus called motor nerves. Third (occulomotor nerve), fourth (trochlear nerve), sixth (abducens nerve), eleventh (accessory spinal nerve) and twelfth (hypoglossal nerve) cranial nerves are motor in function. (c) Mixed nerves: The remaining cranial nerves contain both sensory and motor nerve fibres and are referred to as mixed nerves. Fifth (trigeminal nerve), seventh (facial nerve), ninth (glossopharyngeal nerve) and tenth (vagus nerve) cranial nerves are mixed in nature. Each spinal nerve contains both afferent and efferent nerve fibres and is thus mixed in nature. NEURON AS STRUCTURAL AND FUNCTIONAL UNIT OF NEURAL SYSTEM Nerve cells also called neurons are structural as well as functional unit of neural system. On an average, the human brain is made up of more than 100 billion (1010) neurons. Similarly, other parts of the neural system, whether of CNS or of PNS, are structurally made up of a large number of neurons. These neurons are further interlinked with each other or are linked with other cells of the body forming complex nerve connections for the exchange of neural informations. Neurons are called the functional units of the neural system because the various functions of the neural systems are basically the functions of the neurons. Structure of a Neuron A neuron is a microscopic structure composed of three major parts: (a) Cell body or soma (b) Dendrites (c) Axon