Neural Control and Coordination CBSE Class 11th Biology Full Chapter in 5 Mins Rapid Revision

Neural Control and Coordination: The Human Nervous System at Work

Coordination is the process by which different organs and systems of the body work together in a harmonious manner. In animals, the nervous system and the endocrine system together achieve this coordination. This chapter in CBSE Class 11 Biology provides a comprehensive study of the neural (nervous) system, starting with the structure and function of neurons and neuroglia, the mechanism of nerve impulse conduction, the architecture of the human brain and spinal cord, the peripheral nervous system, and the various reflex arcs and sensory organs.

The human nervous system is divided into two main parts. The central nervous system (CNS) consists of the brain (protected by the skull) and the spinal cord (protected by the vertebral column), both surrounded by three layers of meninges (dura mater, arachnoid mater, pia mater) and bathed in cerebrospinal fluid that cushions shock and provides nutrition. The peripheral nervous system (PNS) consists of 12 pairs of cranial nerves (emerging from the brain) and 31 pairs of spinal nerves (emerging from the spinal cord). The PNS is further divided into the somatic nervous system (controls voluntary actions — skeletal muscle movement — with myelinated efferent neurons) and the autonomic nervous system (controls involuntary functions — heartbeat, breathing, digestion, peristalsis, gland secretion — with two antagonistic divisions: the sympathetic "fight-or-flight" system and the parasympathetic "rest-and-digest" system). Sympathetic activation increases heart rate, dilates pupils, inhibits digestion, and prepares the body for stress. Parasympathetic activation slows the heart, constricts pupils, stimulates digestion, and promotes relaxed states. The autonomic system uses two-neuron chains: preganglionic neurons (whose cell bodies are in the CNS) synapse with postganglionic neurons (whose cell bodies are in autonomic ganglia outside the CNS), which then innervate the target organs. The sympathetic ganglia form the chain-like sympathetic trunk alongside the spinal cord, while parasympathetic ganglia are located near or within the target organs.

Transmission of nerve impulses is an electrochemical process. At rest, the axonal membrane is polarised — the interior is negatively charged at about −70 mV (resting potential) compared to the exterior, maintained by the sodium-potassium pump (actively pumps 3 Na⁺ out for every 2 K⁺ in, using ATP). When a stimulus reaches a threshold level, voltage-gated sodium channels open, Na⁺ rushes in, and the interior potential rises to about +40 mV (depolarisation). Sodium channels then inactivate, voltage-gated potassium channels open, K⁺ rushes out, and the membrane repolarises (returns to negative). There is a brief hyperpolarisation phase (more negative than resting) before the sodium-potassium pump restores the original distribution. This action potential travels along the axon in both myelinated and unmyelinated fibres. In myelinated axons (with myelin sheaths produced by Schwann cells in the PNS and oligodendrocytes in the CNS), the impulse jumps between Nodes of Ranvier (the gaps between myelin sheaths) — this is called saltatory conduction, which is much faster (up to 100 m/s) than the slower continuous conduction in unmyelinated fibres (about 1 m/s). At the synapse, the action potential triggers the opening of voltage-gated calcium channels, Ca²⁺ enters the presynaptic terminal, and synaptic vesicles fuse with the membrane, releasing neurotransmitters (such as acetylcholine, dopamine, serotonin, GABA, glutamate) into the synaptic cleft. These chemicals bind to receptors on the postsynaptic membrane, causing ion channels to open and generating either an excitatory postsynaptic potential (EPSP, which brings the postsynaptic neuron closer to threshold) or an inhibitory postsynaptic potential (IPSP, which moves it farther from threshold). The neurotransmitter is then either degraded by enzymes (e.g., acetylcholinesterase breaks down acetylcholine) or taken back up into the presynaptic terminal to be recycled — this prevents continuous stimulation. The human brain, weighing about 1.3-1.4 kg, is the most complex organ, containing approximately 86 billion neurons. The cerebrum (forebrain) has two hemispheres connected by the corpus callosum, divided into lobes — frontal (motor control, reasoning, planning, personality), parietal (touch, pain, temperature, spatial orientation), temporal (hearing, language comprehension, memory), and occipital (vision). The cerebellum (hindbrain) coordinates fine motor movements and balance. The medulla oblongata controls vital involuntary functions like heart rate, breathing rate, blood pressure, and reflex centres for coughing, sneezing, swallowing, and vomiting.

• Nervous system divisions: CNS (brain + spinal cord, protected by meninges and CSF) and PNS (cranial + spinal nerves); PNS has somatic (voluntary) and autonomic (involuntary) branches.
• Autonomic nervous system: sympathetic (fight-or-flight, NE neurotransmitter) and parasympathetic (rest-and-digest, ACh neurotransmitter) have antagonistic effects on most organs.
• Nerve impulse: resting potential −70 mV → depolarisation to +40 mV (Na⁺ in) → repolarisation (K⁺ out) — the action potential propagates along the axon.
• Saltatory conduction in myelinated axons: impulse jumps between Nodes of Ranvier, 50× faster than unmyelinated fibres.
• Synaptic transmission: Ca²⁺ entry → vesicle fusion → neurotransmitter release → receptor binding → EPSP (excitatory) or IPSP (inhibitory) → neurotransmitter cleared by enzymes or reuptake.