21. NEURAL CONTROL AND CO-ORDINATION
It includes cranial nerves and spinal nerves.Nerve fibres of PNS are 2 types:
- Afferent (sensory) fibres: Carry impulses from sense organs to CNS.
- Efferent (motor) fibres: Carry impulses from CNS to muscles and glands.
- Somatic neural system: Relays impulses from the CNS to skeletal muscles.
- Autonomic neural system (ANS): Transmits impulses from CNS to involuntary organs & smooth muscles. It includes sympathetic & parasympathetic nerves. Sympathetic system prepares body to cope with emergencies, stresses & dangers. It increases heartbeat, breathing rate, constricts arteries and elevates BP. Parasympathetic system returns the body to a resting state after stressful situations and slows down heartbeat, dilates arteries, lowers BP etc.
It is the rapid, involuntary and unconscious actions of body in response to a stimulus. E.g.
- Withdrawal of the hand when it touches a hot object.
- Touching lips of a nursing baby evokes sucking reflex.
- Closing of the eyelids when light falls on them.
- Knee jerk phenomenon.
- If a child sees or smells a food unknown to him, he does not salivate. But if he sees or smells that food every time before tasting it, he salivates (conditioned reflex).
- A receptor organ: It receives the stimulus.
- Sensory (afferent) neuron: It transmits impulses from sense organ to CNS.
- Intermediate (connector) neuron: It connects sensory and motor neurons.
- Motor (efferent/effector/excitor) neuron: It conducts impulse from the CNS to effector organ.
- An effector organ (muscle/gland): It responds to impulse.
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