Chapter 18 of Class 11 Biology is Neural Control and Coordination. It covers the human nervous system, the structure and function of neurons, nerve impulse transmission, and the reflex arc. These Class 11 Biology Chapter 18 solutions are also useful as quick revision notes before exams.
Neuron Structure
A neuron has three parts: cell body (soma), dendrites (receive signals), and axon (transmits signals, may be myelinated for faster conduction).
Nerve Impulse (Action Potential)
A neuron at rest has a resting potential (~−70mV, inside negative relative to outside, maintained by Na⁺-K⁺ pump). On stimulation, depolarization occurs (Na⁺ rushes in, inside becomes positive), followed by repolarization (K⁺ rushes out, restoring negative internal potential). This all-or-none electrical signal is the action potential, propagated along the axon.
Synaptic Transmission
At a chemical synapse, the electrical impulse triggers release of neurotransmitters (e.g. acetylcholine) from the presynaptic neuron, which diffuse across the synaptic cleft and bind receptors on the postsynaptic neuron, propagating (or inhibiting) the signal.
Central Nervous System (CNS)
Brain (forebrain: cerebrum for higher functions; midbrain; hindbrain: cerebellum for coordination/balance, medulla for vital involuntary functions) and spinal cord (reflex centre, connects brain to peripheral nerves).
Peripheral Nervous System (PNS)
Somatic (voluntary, controls skeletal muscles) and autonomic (involuntary, controls internal organs; sympathetic “fight or flight” vs parasympathetic “rest and digest”).
Reflex Action
A rapid, involuntary, automatic response to a stimulus, bypassing conscious brain processing, mediated via a reflex arc: receptor → sensory neuron → spinal cord (relay) → motor neuron → effector. Faster than voluntary responses because it doesn’t require signal travel to/from the brain.
Class 11 Biology Chapter 18 – Notes and Extra Questions
Along with these NCERT Solutions, students can also use the Class 11 Biology Chapter 18 Extra Questions and Class 11 Biology Chapter 18 Revision Notes for quick revision and extra practice.
