Basic Neural Mechanism
While a neuron is the structural and func¬tional unit of nervous system, the structural and functional unit of basic neural mechanism is a reflex.
Reflexes : A reflex is an involuntary auto-matic response brought about by a sensory stimulus. It represents the first order of nervous activity in the body. The reflexes are mediated through neuron pathways i.e., neurons ar¬ranged in a system of relays, called reflex arcs.
A reflex arc usually consists of a chain of three neurons (see p. 5) : (i) afferent or sensory neurons bring information from sense organs e.g., receptors in the skin to the spinal cord or brainstem;(ii) internuncial neu¬rons or interneurons are interposed and transmit nerve impulses from sensory to motor neurons, and also connect different groups of neurons within CNS; (iii) efferent or motor neurons convey nerve impulses form CNS to the effector organs e.g., muscle fibres. In a simplified system a stimulus applied to a receptor gives rise to a nervous impulse which is eventually carried to the muscle and causes it to contract. In spinal cord reflexes play an im¬portant role in maintaining muscle tone, which is the basis for body posture.
Examples : Knee jerk: When a sharp tap is given to the tendon of quadriceps femoris muscle just below the patella, the muscle reneurons within CNS; (iii) efferent or motor neurons convey nerve impulses form CNS to the effector organs e.g., muscle fibres. In a simplified system a stimulus applied to a receptor gives rise to a nervous impulse which is eventually carried to the muscle and causes it to contract. In spinal cord reflexes play an important role in maintaining muscle tone, which is the basis for body posture.
Examples : Knee jerk: When a sharp tap is given to the tendon of quadriceps femoris muscle just below the patella, the muscle responds by contracting so that the knee is suddenly extended. (Note : This is a monosynaptic reflex arc; in this case the internuncial neuron is absent).
2. Pupillary light reflex : consists of con¬striction of pupil of the eyes when light is shone into it.
sponds by contracting so that the knee is suddenly extended. (Note : This is a monosynaptic reflex arc; in this case the internuncial neuron is absent).
2. Pupillary light reflex : consists of con¬striction of pupil of the eyes when light is shone into it.
Tags: CNS, Neuron, reflex arc
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