Samacheer Kalvi 10th Science Chapter 15 Short Answer Questions — Nervous System with Answers

The nervous system is the control and communication system of the body. It receives information from the environment (external and internal), processes it, and coordinates responses.

Divisions:

A. Central Nervous System (CNS):

• Brain (protected by skull)
• Spinal cord (protected by vertebral column)

B. Peripheral Nervous System (PNS):

• Somatic nervous system: Controls voluntary movements; carries sensory signals from skin/sense organs
• Autonomic nervous system (ANS): Controls involuntary functions (heart rate, digestion, glands)
• Sympathetic division: "Fight or flight" — prepares for emergencies
• Parasympathetic division: "Rest and digest" — normal functions

A reflex arc is the neural pathway for a reflex action.

Components of a reflex arc: 1. Receptor — sense organ that detects stimulus (e.g., skin pain receptor) 2. Afferent (sensory) neuron — carries impulse from receptor to spinal cord 3. Nerve centre (interneuron in spinal cord) — processes the signal 4. Efferent (motor) neuron — carries impulse from spinal cord to effector 5. Effector — muscle or gland that responds (e.g., arm muscle withdraws)

Example — Withdrawal reflex: Hot object → pain receptor in finger → sensory neuron → spinal cord → motor neuron → arm muscle → hand withdraws

Significance: Reflex actions are fast because the signal bypasses the brain; the response occurs before the brain consciously perceives the pain. This protects the body quickly.

Memory trick: Cerebrum = Conscious; Cerebellum = Coordination/Balance; Medulla = Mandatory life functions

A synapse is the junction between two neurons (or between a neuron and a muscle/gland). There is a tiny gap called the synaptic cleft.

Types:

• Chemical synapse (most common): Uses neurotransmitters to transfer signal
• Electrical synapse: Direct electrical coupling (rare in vertebrates)

Transmission across a chemical synapse: 1. Nerve impulse reaches the axon terminal (presynaptic knob) 2. The impulse triggers release of neurotransmitters (e.g., acetylcholine, dopamine) stored in synaptic vesicles 3. Neurotransmitters diffuse across the synaptic cleft 4. They bind to receptor proteins on the postsynaptic membrane (next neuron or effector) 5. This generates a new impulse in the next neuron (or causes muscle to contract / gland to secrete) 6. Neurotransmitters are then broken down by enzymes or reabsorbed

Significance: Synapses ensure one-way transmission of impulses. They allow integration and modulation of nerve signals.

Example: When you face danger (sympathetic): heart races, pupils dilate, digestion stops, muscles get more blood. After the danger passes (parasympathetic): body returns to normal.

The spinal cord is a cylindrical structure inside the vertebral column, extending from the medulla oblongata to the lumbar region.

Functions: 1. Reflex centre: Coordinates simple reflex actions (like withdrawal, knee-jerk) without involving the brain — making responses faster 2. Conduction pathway: Carries sensory impulses from the body up to the brain (ascending tracts) and carries motor commands from the brain down to the body (descending tracts) 3. Integration: Receives and integrates information at the spinal level

Structure:

• Grey matter (H-shaped inner region) — contains nerve cell bodies and interneurons
• White matter (outer region) — contains myelinated nerve fibres (ascending and descending tracts)
• Central canal — contains cerebrospinal fluid (CSF)