Coordination and Nervous System

Coordination and Nervous System

🟢 Lite — Quick Review (1h–1d)

Rapid summary for last-minute revision before your exam.

Coordination is the process by which body systems work together to produce a proper response to a stimulus. In animals, it is carried out by the nervous system (rapid, electrical impulses along neurones) and the endocrine system (slower, chemical messages via hormones in the blood). A stimulus is detected by a receptor, the signal travels through sensory (afferent), relay (interneurone), and motor (efferent) neurones, and a response is produced by an effector (muscle or gland) — this chain is the reflex arc. The central nervous system (CNS) comprises the brain and spinal cord; the peripheral nervous system (PNS) carries impulses to and from it. NABTEB focus: name the five components of a reflex arc in correct order, distinguish voluntary from involuntary actions, and identify the role of acetylcholine at the synapse.

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🟡 Standard — Regular Study (2d–2mo)

Standard content for students with a few days to months.

Types of Coordination

Two systems coordinate responses in mammals. The nervous system uses electrical impulses transmitted along neurones, producing fast, short-lived responses. The endocrine system uses hormones released by ductless glands into the bloodstream, producing slower but longer-lasting effects on target organs.

Structure of a Neurone

A typical neurone has dendrites (receive impulses), a cell body containing the nucleus, and a long axon that conducts impulses away. Many vertebrate axons are wrapped in a myelin sheath (formed by Schwann cells), with gaps called Nodes of Ranvier that allow saltatory conduction — faster impulse travel.

Reflex Arc

A reflex is a rapid, involuntary response. The pathway is:

Component	Role
Receptor	Detects the stimulus (e.g. skin in a pin prick)
Sensory neurone	Carries impulse to the CNS
Relay (intermediate) neurone	In the spinal cord, links sensory to motor
Motor neurone	Carries impulse to the effector
Effector	Muscle or gland that produces the response

Synaptic Transmission

At the synapse, the electrical impulse reaches the synaptic knob. Ca²⁺ ions enter, prompting vesicles to release neurotransmitters (e.g. acetylcholine) into the synaptic cleft. These bind to receptors on the post-synaptic membrane, generating a new impulse in the next neurone. The neurotransmitter is then broken down by enzymes (e.g. acetylcholinesterase) to stop the signal.

Divisions of the Nervous System

The CNS (brain + spinal cord) integrates information. The PNS includes cranial and spinal nerves, split into the somatic system (voluntary, controls skeletal muscle) and the autonomic system (involuntary). The autonomic system is antagonistic: the sympathetic branch accelerates heart rate and dilates pupils (fight-or-flight), while the parasympathetic branch slows heart rate and constricts pupils (rest-and-digest).

Sense Organs

• Eye: photoreceptors — rods (dim light, black-and-white) and cones (colour, bright light) in the retina.
• Ear: cochlea detects sound; semicircular canals detect balance.
• Skin: receptors for touch, pressure, temperature, and pain.
• Tongue: taste buds detect chemicals in food.
• Nose: olfactory receptors detect smell.

Common Exam Traps

• Confusing afferent (sensory) with efferent (motor).
• Forgetting that reflex arcs in the knee-jerk test pass through the spinal cord, not the brain — this is why the response is faster than conscious action.
• Calling the cerebellum the “thinking” region; it actually coordinates balance and posture. Voluntary thought is in the cerebrum.

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🔴 Extended — Deep Study (3mo+)

Comprehensive coverage for students on a longer study timeline.

Membrane Potentials in Detail

A neurone at rest maintains a resting potential of about –70 mV (inside negative relative to outside), set up by the sodium–potassium (Na⁺/K⁺) pump, which moves 3 Na⁺ out for every 2 K⁺ in using ATP. When stimulated, voltage-gated Na⁺ channels open, Na⁺ rushes in, and the membrane depolarises (inside becomes positive — the action potential, ≈ +30 mV). Na⁺ channels then inactivate; K⁺ channels open, K⁺ flows out, and the membrane repolarises. The refractory period that follows prevents the impulse from travelling backwards and limits maximum firing frequency. This all-or-nothing principle means stimulus strength is coded by frequency, not size, of impulses.

Endocrine Coordination in Depth

Unlike nerves, hormones travel in the blood and affect only cells with matching receptors. Key glands and hormones NABTEB often tests:

• Adrenal medulla → adrenaline: increases heart rate, blood pressure, blood glucose, and pupil dilation (sympathetic-mimicking).
• Pancreas (islets of Langerhans): insulin (β-cells) lowers blood glucose by promoting glycogen storage; glucagon (α-cells) raises it by stimulating glycogen breakdown — a classic antagonistic pair.
• Pituitary: “master gland” controlling many others; releases ADH (anti-diuretic hormone) which controls water reabsorption in kidney tubules.
• Thyroid → thyroxine: regulates metabolic rate.

Autonomic Antagonism in Action

During exercise, the sympathetic system increases heart rate and dilates bronchi; at rest, the parasympathetic (vagus nerve) slows the heart and constricts bronchi. The same dual control applies to gut motility, pupil size, and bladder sphincters.

Practice Prompts

1. A man accidentally touches a hot object and withdraws his hand. Trace the impulse along the reflex arc, naming each neurone type and the effector involved. Explain why this response is faster than consciously moving the hand away.
2. Compare the speed, duration, and mode of transmission of nervous and hormonal coordination. Give one named example of a hormone and describe its effect on its target organ.

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