14.1 Coordination and response
- Syllabus
- 0610–2026–2027
- Topic
- 14.1
- Level
- —
Learning objectives
14.1.1Electrical impulses travel along• State that electrical impulses travel along neurones14.1.2Mammalian nervous system• Describe the mammalian nervous system in terms of: (a) the central nervous system (CNS) consisting of the brain and the spinal cord (b) the peripheral nervous system (PNS) consisting of the nerves outside of the brain and spinal cord14.1.3Role of the nervous system• Describe the role of the nervous system as coordination and regulation of body functions14.1.4Sensory, relay and motor neurones• Identify in diagrams and images sensory, relay and motor neurones14.1.5Simple reflex arc in terms• Describe a simple reflex arc in terms of: receptor, sensory neurone, relay neurone, motor neurone and effector14.1.6Reflex action as a means• Describe a reflex action as a means of automatically and rapidly integrating and coordinating stimuli with the responses of effectors (muscles and glands)14.1.7Synapse as a junction between two• Describe a synapse as a junction between two neurones14.1.8Structure of a synapse• Describe the structure of a synapse, including the presence of vesicles containing neurotransmitter molecules, the synaptic gap and receptor proteins14.1.9Events at a synapse• Describe the events at a synapse as: (a) an impulse stimulates the release of neurotransmitter molecules from vesicles into the synaptic gap (b) the neurotransmitter molecules diffuse across the gap (c) neurotransmitter molecules bind with receptor proteins on the next neurone (d) an impulse is then stimulated in the next neurone14.1.10Synapses ensure that impulses travel• State that synapses ensure that impulses travel in one direction only
State how nerve signals travel
Electrical impulses travel along neurones.
A neurone is a nerve cell specialised to carry these electrical signals from one part of the nervous system to another.
The signal along a neurone is an electrical impulse; neurotransmitter molecules carry the signal across a synaptic gap, not along the neurone.
Describe the mammalian nervous system
The mammalian nervous system has a central nervous system and a peripheral nervous system.
| Division | What it consists of |
|---|---|
| central nervous system (CNS) | brain and spinal cord |
| peripheral nervous system (PNS) | nerves outside the brain and spinal cord |
The spinal cord belongs to the CNS; nerves entering or leaving it belong to the PNS.
Describe the role of the nervous system
The nervous system coordinates and regulates body functions.
| Job | Meaning |
|---|---|
| receive information | receptors detect changes inside or outside the body |
| coordinate | the CNS integrates information and organises an appropriate response |
| regulate | impulses control effectors so body functions change when required |
Coordination links information to a response; regulation adjusts body functions. The nervous system does more than detect a stimulus.
Identify sensory, relay and motor neurones
Identify a neurone in a diagram by the direction and connections of its pathway, not only by its shape.
| Neurone | Direction of impulse | Diagram cue |
|---|---|---|
| sensory | receptor → CNS | enters the brain or spinal cord from a receptor |
| relay | within the CNS | links neurones inside the brain or spinal cord |
| motor | CNS → effector | leaves the brain or spinal cord for a muscle or gland |
Sensory neurones carry impulses towards the CNS; motor neurones carry them from the CNS. A relay neurone lies within the CNS.
Describe a simple reflex arc
A simple reflex arc is the pathway followed from detection of a stimulus to the action of an effector.
| Order | Component | Job |
|---|---|---|
| 1 | receptor | detects the stimulus |
| 2 | sensory neurone | carries an impulse to the CNS |
| 3 | relay neurone | passes the impulse within the CNS |
| 4 | motor neurone | carries an impulse away from the CNS |
| 5 | effector | produces the response |
receptor → sensory neurone → relay neurone → motor neurone → effector
A receptor detects the stimulus; an effector carries out the response. They are not types of neurone.
Describe a reflex action
A reflex action automatically and rapidly coordinates a stimulus with the response of an effector.
| Feature | Meaning |
|---|---|
| automatic | occurs without conscious decision |
| rapid | the response follows the stimulus quickly |
| integrated and coordinated | nervous-system input is linked to a suitable output |
| effector response | a muscle contracts or a gland secretes |
A reflex action is the automatic response; a reflex arc is the nervous pathway that produces it. Effectors can be muscles or glands.
Define a synapse
A synapse is a junction between two neurones.
The two neurones do not form one continuous cell: a small synaptic gap separates them, so the signal must cross the junction.
The synapse is the whole junction between neurones; the synaptic gap is only the space within that junction.
Describe the structure of a synapse
A synapse has different structures on the sending and receiving sides of a synaptic gap.
| Part | Position or contents |
|---|---|
| vesicles | in the end of the first neurone; contain neurotransmitter molecules |
| synaptic gap | small space between the two neurones |
| receptor proteins | in the membrane of the next neurone |
Vesicles contain neurotransmitter molecules; receptor proteins are on the next neurone and do not fill the gap.
Describe transmission across a synapse
Transmission across a synapse converts an arriving electrical impulse into a chemical signal and then stimulates a new electrical impulse.
| Order | Event |
|---|---|
| 1 | an impulse stimulates vesicles to release neurotransmitter molecules into the synaptic gap |
| 2 | neurotransmitter molecules diffuse across the gap |
| 3 | the molecules bind to receptor proteins on the next neurone |
| 4 | an impulse is stimulated in the next neurone |
Neurotransmitter diffuses only across the gap; the impulses travel along the neurones on either side.
State why synaptic transmission is one-way
Synapses ensure that impulses travel in one direction only.
| First neurone | Next neurone |
|---|---|
| has vesicles that release neurotransmitter | has receptor proteins that bind the neurotransmitter |
Because release machinery and matching receptors are on opposite sides, the signal passes from the first neurone to the next, not backwards across that synapse.
The one-way rule refers to transmission across a synapse; it is not caused by neurotransmitter diffusing in only one physical direction.