14.1Coordination and Response
Coordination and response — Cambridge IGCSE Biology 0610 Revision Notes & Topical Questions
10 min read 14 parts Lesson 1 of 5 5 quizzes
Lesson summary
Coordination, the nervous system and homeostasis — IGCSE BIOLOGY notes: The mammalian nervous system; Types of neurone; Voluntary and reflex responses; The synapse.Two parts of the nervous system.Central nervous system (CNS) — the brain and spinal cord.Peripheral nervous system (…
- Nerve impulses
- Parts of a neurone
- Voluntary action
- Reflex action
- One-way transmission
- Peripheral nervous system (PNS) — all the nerves in the body
Part 1 of 5The mammalian nervous system
The mammalian nervous system
Two parts
Two parts of the nervous system.
- Central nervous system (CNS) — the brain and spinal cord.
- Peripheral nervous system (PNS) — all the nerves in the body.
Role
- Role to make sense of the surroundings, respond to them, and coordinate and regulate body functions.
Nerve impulses
- Nerve impulses electrical signals passing along nerve cells called neurones.
- A bundle of neurones is a nerve.
Part 2 of 5Types of neurone
| Neurone | Function | Features |
|---|---|---|
| Sensory | Carries impulses from receptors/sense organs to the CNS | Long; cell body branching off the middle of the axon |
| Relay (intermediate) | Connects sensory and motor neurones inside the CNS | Short; small cell body at one end with many dendrites |
| Motor | Carries impulses from the CNS to effectors (muscles or glands) | Long; large cell body at one end with long dendrites |
- Parts of a neurone.
- Dendrites — short, branched extensions that carry impulses towards the cell body.
- Axon — a longer extension that carries impulses away from the cell body.
- A fatty sheath insulates the axon, with small uninsulated nodes along it, so the impulse jumps from node to node and travels faster.
Part 3 of 5Voluntary and reflex responses
Voluntary action
- Voluntary action a conscious decision starting in the brain, e.g. picking up a cup.
Reflex action
- Reflex action a means of automatically and rapidly integrating and coordinating stimuli with the responses of effectors.
- (muscles and glands)
- Reflexes are automatic, fast and protective.
- They do not involve the brain as coordinator, so the person is aware only after the response.
1
A stimulus (e.g. a hot object or a pin) is detected by a receptor in the skin.
2
An impulse travels along a sensory neurone to the spinal cord.
3
The impulse passes across a synapse to a relay neurone in the spinal cord.
4
It passes to a motor neurone.
5
The motor neurone carries the impulse to an effector (muscle).
6
The muscle contracts and the hand or foot is withdrawn (response).
Part 4 of 5The synapse
- Synapse
- the junction between two neurones; there is a gap between them, so impulses cross chemically.
- Synapses let the nervous system work as a connected network and direct impulses to the correct route.
1
An impulse arrives at the end of the axon.
2
Vesicles release neurotransmitter into the synaptic gap.
3
The neurotransmitter diffuses across the gap.
4
It binds to receptor proteins on the membrane of the next neurone.
5
An impulse is started in the next neurone.
One-way transmission
- One-way transmission synapses ensure impulses travel in one direction only.
Drugs
- Drugs many act at synapses, e.g. heroin, because transmission here is chemical.
Part 5 of 5More from the specification
More from the specification
Nervous coordination contrasting with auxin
- Nervous coordination contrasting with auxin rapid saltatory conduction along myelinated axons coordinates reflex responses, unlike slow hormonal transport of auxin in plants.
Reflex Arc and Direction of Impulse
- In a reflex arc, receptor stimulation initiates electrical impulses passing sequentially through sensory neurones, relay neurones in the central nervous system,
- and motor neurones to effectors.
The Pupil Light Reflex
- Radical changes in ambient light intensity trigger involuntary antagonistic contractions of circular and radial iris muscles, constricting or dilating the pupil to protect the retina and optimize vision.
Negative Feedback Control Mechanisms
- Endocrine and neural regulatory loops continuously monitor internal physiological variables, initiating corrective responses whenever levels deviate from set point values.
Retina
- Layer of the eye containing light receptors.
Pupil reflex
- Change in pupil diameter in response to light intensity.
Ciliary muscle
- Muscle that changes the tension on the lens.
Suspensory ligaments
- Fibres that connect the ciliary muscle to the lens.
Negative feedback
- A mechanism in which a change from the set point triggers a response that returns the factor to the set point.
Radial muscle
- Iris muscle that widens the pupil when it contracts.
Circular muscle
- Iris muscle that narrows the pupil when it contracts.
Glucose
- A simple sugar; the unit that starch, glycogen and cellulose are built from.
Growth
- A permanent increase in size and dry mass.
Hormone
- A chemical substance produced by a gland and carried by the blood that alters the activity of specific target organs.
Glycogen
- The polysaccharide in which glucose is stored in animals.
Key terms
| Term | Meaning |
|---|---|
| Reflex action | A means of automatically and rapidly integrating and coordinating stimuli with the responses of effectors. |
| Synapse | A junction between two neurones where an impulse passes by neurotransmitter diffusing across a gap. |
| Neurone | A nerve cell that carries electrical impulses. |
Avoid these mistakes
Avoid these mistakes
Reflexes go through the brain — a reflex arc passes through the spinal cord without the brain coordinating.
Impulses cross a synapse electrically — a chemical neurotransmitter crosses the gap.
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