Class 10th Science Reflex Actions Working of Neuron Chapter 7 Control Coordination NCERT

Control and Coordination: The Nervous System and Reflex Actions

All living organisms respond to stimuli in their environment. In animals, the nervous system and the endocrine system work together to detect, process, and respond to changes in the external and internal environment. This chapter in CBSE Class 10 Science focuses on the structure and functioning of the nervous system, the mechanism of reflex actions, the structure and function of the human brain, and the role of hormones in coordination. Understanding control and coordination explains how we react to a hot stove instantly, how our body maintains a steady internal temperature, and how hormones regulate growth, metabolism, and reproduction.

A neuron (nerve cell) is the structural and functional unit of the nervous system. It consists of three main parts: the cell body (cyton, containing the nucleus and organelles), dendrites (branch-like extensions that receive signals from other neurons or sensory receptors), and the axon (a long fibre that carries electrical impulses away from the cell body toward the next neuron or effector organ). The axon is covered by a myelin sheath (made of Schwann cells) that insulates the fibre and speeds up impulse conduction. Nerve impulses are electrochemical signals. At rest, the inside of the neuron is negatively charged compared to the outside (resting potential, about −70 mV). When stimulated, sodium ions rush in, reversing the polarity to about +40 mV (depolarisation). This wave of depolarisation travels along the axon. The junction between two neurons (or between a neuron and a muscle) is called a synapse. The impulse triggers the release of chemical messengers called neurotransmitters (such as acetylcholine) from the synaptic vesicles of the presynaptic neuron into the synaptic cleft. These chemicals bind to receptors on the postsynaptic membrane, generating a new impulse in the next neuron. This process ensures one-way transmission of signals.

A reflex action is an automatic, rapid, involuntary response to a stimulus that does not involve conscious thought. When you accidentally touch a hot object, your hand is pulled away almost instantly — you jerk your hand back before you even feel the pain. This is because the signal takes a shortcut called the reflex arc. The reflex arc path: sensory receptor (in the skin) → sensory neuron → spinal cord (interneuron in the grey matter) → motor neuron → effector muscle (the arm muscle contracts to pull the hand away). The brain receives the signal and registers pain only after the reflex action has already occurred, which is why you feel pain after withdrawing your hand. This process is faster than if the signal had to travel all the way to the brain and back — it saves vital milliseconds that could prevent injury. The reflex arc involves only the spinal cord, not the brain. The human brain is the control centre of the nervous system, protected inside the skull by three layers of membranes called meninges and cushioned by cerebrospinal fluid. The brain is divided into three main parts: the forebrain (cerebrum, the largest part responsible for conscious thought, memory, language, reasoning, sensory perception, and voluntary movement), the midbrain (controls reflex movements of the head and eyes in response to visual and auditory stimuli), and the hindbrain (cerebellum for coordination of balance and fine motor skills, medulla oblongata for involuntary functions like heartbeat, breathing, blood pressure, and vomiting). The peripheral nervous system consists of nerves that connect the brain and spinal cord to all parts of the body. The somatic nervous system controls voluntary actions (walking, writing), and the autonomic nervous system controls involuntary functions (heartbeat, digestion, salivation) — further divided into the sympathetic (fight-or-flight response) and parasympathetic (rest-and-digest) divisions.

• A neuron consists of dendrites (receive signals), cell body (nucleus), and axon (carries impulses away); synapses use neurotransmitters for chemical transmission between neurons.
• The reflex arc: receptor → sensory neuron → spinal cord → motor neuron → effector — faster than involving the brain because it takes a spinal shortcut.
• Reflex actions are automatic and involuntary; the brain perceives pain after the reflex movement has already occurred.
• Brain parts: cerebrum (conscious thought, memory, voluntary action), cerebellum (balance and coordination), medulla (heartbeat, breathing, involuntary functions).
• The autonomic nervous system controls involuntary functions — sympathetic (fight-or-flight) and parasympathetic (rest-and-digest) divisions.