Neural Control and CoordinationNEET Zoology · Class 11 · NCERT Chapter 18

You can expect 2 to 3 questions from Neural Control and Coordination in NEET 2027. The most reliable scoring topics are: parts of a neuron and their functions, the resting potential value, ion movements during an action potential, saltatory conduction, neurotransmitter release at the chemical synapse, the parts of the brain with their functions, and the components of a reflex arc.

Resting potential is the voltage difference across the neuron membrane when the neuron is not firing. The inside of the cell is about negative 70 mV compared to the outside. This is maintained by the Na+/K+ pump (3 Na+ out, 2 K+ in) and selective ion channels. Action potential is a sudden, brief reversal of this voltage triggered by a stimulus. The inside becomes positive (around +30 mV) due to sudden Na+ influx (depolarisation), and then returns to negative due to K+ efflux (repolarisation). It is an "all or none" event.

In a myelinated axon, the myelin sheath insulates most of the axon. Only the small gaps called nodes of Ranvier are exposed to the extracellular fluid. The action potential jumps from one node to the next instead of moving smoothly down the whole axon. This jumping is called saltatory conduction. It is much faster (up to 120 metres per second) than the continuous conduction in unmyelinated axons (about 1 metre per second), and uses less energy because Na+/K+ pumping happens only at the nodes.

An electrical synapse has membranes of pre- and post-synaptic neurons in direct contact via gap junctions. Ion flow passes the signal directly. Transmission is very fast but not selective. Found in some heart muscle and embryonic tissue. A chemical synapse has a tiny gap called the synaptic cleft between the two neurons. The pre-synaptic neuron releases a neurotransmitter (like acetylcholine) into the cleft. The neurotransmitter binds to receptors on the post-synaptic neuron and opens ion channels. Most synapses in the human nervous system are chemical. Chemical synapses are slower but allow integration of many signals.

The brain has three regions. The forebrain includes the cerebrum (largest part, voluntary actions, memory, intelligence), thalamus (relay station for sensory input), and hypothalamus (controls body temperature, hunger, thirst, links to the endocrine system through the pituitary). The midbrain contains the corpora quadrigemina and helps with visual and auditory reflexes. The hindbrain has the pons, cerebellum (precision and balance of voluntary movement), and medulla oblongata (controls breathing, heart rate, gastric secretion).

Both are parts of the autonomic nervous system. The sympathetic system prepares the body for "fight or flight": speeds up the heart, dilates pupils, dilates the bronchioles, releases glucose from the liver, slows digestion. The parasympathetic system prepares the body for "rest and digest": slows the heart, constricts pupils, speeds up digestion. Their effects are opposite, but both systems are active at the same time, just at different levels.

A reflex arc has five parts in order: (1) Receptor (sense organ that detects stimulus). (2) Afferent (sensory) neuron carrying signal toward the CNS. (3) Centre, usually the spinal cord (in the grey matter, but sometimes the brain stem). (4) Efferent (motor) neuron carrying signal away from the CNS to the muscle or gland. (5) Effector (muscle or gland that responds). The classic example is the knee jerk reflex (monosynaptic, no interneuron) or the withdrawal reflex when you touch a hot object.