The Nervous System

Nervous System: Control and coordination system of body. Responds to stimuli, maintains homeostasis.

Components: (1) Central Nervous System (CNS) - brain and spinal cord, (2) Peripheral Nervous System (PNS) - nerves outside CNS.

Functions: (1) Receives sensory input, (2) Processes information, (3) Generates responses, (4) Controls voluntary and involuntary actions.

Neurons: Basic functional units. Specialized cells that transmit electrical impulses.

Nerves: Bundles of axons. Carry impulses between CNS and body parts.

Diagram Importance: Overview diagram of human nervous system showing CNS and PNS is essential.

Neuron: Structural and functional unit of nervous system. Specialized for impulse transmission.

Parts: (1) Dendrites - receive impulses, (2) Cell body (cyton) - contains nucleus, (3) Axon - conducts impulses away, (4) Axon terminals - pass impulses to next neuron, (5) Myelin sheath - insulating layer, speeds conduction.

Types: (1) Sensory neurons - carry impulses from receptors to CNS, (2) Motor neurons - carry impulses from CNS to effectors, (3) Interneurons - connect neurons within CNS.

Synapse: Junction between two neurons. Impulse transmission via neurotransmitters (acetylcholine).

Impulse Transmission: Electrical (along neuron) and chemical (across synapse).

Diagram Importance: Detailed labeled diagram of neuron showing all parts is crucial for ICSE.

Brain: Control center. Located in cranium. Weight: 1.3-1.4 kg.

Parts: (1) Cerebrum (largest part) - controls voluntary actions, intelligence, memory, (2) Cerebellum - maintains balance and coordination, (3) Medulla oblongata - controls involuntary actions (breathing, heartbeat).

Protection: (1) Cranium (skull), (2) Meninges (membranes), (3) Cerebrospinal fluid (CSF) - shock absorber.

Functions: Cerebrum - thinking, learning; Cerebellum - posture, balance; Medulla - vital functions.

Diagram Importance: Labeled diagram of human brain showing cerebrum, cerebellum, medulla is frequently asked.

Spinal Cord: Cylindrical structure. Extends from medulla to lumbar region. Length: 45 cm.

Structure: (1) Grey matter (inner) - neuron cell bodies, (2) White matter (outer) - myelinated axons, (3) Central canal - contains CSF.

Functions: (1) Reflex actions, (2) Conducts impulses between brain and body, (3) Controls simple movements.

Protection: Vertebral column, meninges, CSF.

Diagram Importance: Cross-section of spinal cord showing grey and white matter is important.

Peripheral Nervous System: Nerves outside CNS. Connects CNS to body parts.

Cranial Nerves: 12 pairs. Originate from brain. Example: Optic nerve (vision), Auditory nerve (hearing).

Spinal Nerves: 31 pairs. Originate from spinal cord. Mixed nerves (sensory and motor).

Somatic Nervous System: Controls voluntary actions (skeletal muscles).

Autonomic Nervous System: Controls involuntary actions (smooth muscles, glands). Divisions: Sympathetic (fight or flight), Parasympathetic (rest and digest).

Difference: Somatic - voluntary, conscious; Autonomic - involuntary, subconscious.

Reflex Action: Automatic, rapid response to stimulus. Protects body from harm.

Reflex Arc: Pathway of impulse. Receptor → Sensory neuron → CNS → Motor neuron → Effector.

Components: (1) Receptor - detects stimulus, (2) Sensory neuron - carries impulse to CNS, (3) Interneuron - processes in CNS, (4) Motor neuron - carries impulse to effector, (5) Effector - muscle or gland that responds.

Types: Simple reflex (knee jerk), Conditioned reflex (salivation at bell).

Importance: Quick response without conscious thought. Saves time and energy.

Diagram Importance: Diagram of reflex arc showing all components and direction of impulse is crucial.

Coordination: Integration of sensory input and motor output.

Nervous Coordination: Fast, short-term. Uses electrical impulses.

Chemical Coordination: Slower, long-term. Uses hormones (endocrine system).

Integration: Brain integrates information from various senses to produce coordinated response.

Feedback Mechanism: Response modifies stimulus. Example: Body temperature regulation.

Meningitis: Inflammation of meninges. Causes: viral or bacterial infection. Symptoms: headache, fever, stiff neck.

Polio: Viral infection affecting motor neurons. Causes paralysis. Prevented by vaccination.

Alzheimer's Disease: Degeneration of brain cells. Causes memory loss, dementia.

Parkinson's Disease: Degeneration of dopamine-producing neurons. Causes tremors, rigidity.

Epilepsy: Abnormal electrical activity in brain. Causes seizures.

Stroke: Interruption of blood supply to brain. Causes paralysis or death.

Prevention: Healthy lifestyle, vaccination, avoid head injuries, regular exercise.