For those writing CIE IGCSE examinations, this section covers both the CORE and SUPPLEMENTARY components (TOPIC 14.1) of the 0610 syllabus (accurate in 2017). Please note that these revision notes SHOULD NOT be used as a substitute for comprehensively studying the course, but are advised to be used as revision tools to help with concepts and ‘cramming’. As always – enjoy the resource, study hard and all the best!
Coordination & Response (CORE & SUPPLEMENT) – 14.1 Nervous Control in Humans
Coordination is the “way in which receptors pick up stimuli and then pass information on to effectors”.
Stimuli (singular: stimulus) are “changes in an organism’s environment, that are sensed by receptors”.
Most animals have two ways of sending information from receptors to effectors.
- NERVES (fastest way)
- HORMONES (slower, by means of chemicals; part of the endocrine system)
A Nerve Impulse is “electrical signal that passes along nerve cells called neurones”.
Neurones have a nucleus, cytoplasm and cell membrane.
- They also have Nerve Fibres (made of long thin fibres of cytoplasm which stretch out from the cell membrane) which enable them to carry messages very quickly.
- The axon is the longest nerve fibre (can be more than 1m long).
- Dendrons or Dendrites are shorter nerve fibres (which pick up signals from other neurones and pass them to the cell body and along the axon).
- Myelineated Neurones are wrapped in myelin (a layer of fat and protein), which insulates the nerve fibres, enabling them to carry impulses much faster.
All mammals and many other animals have both a CNS and a Peripheral Nervous System. The human nervous system is made up of neurones and consists of:
- THE CENTRAL NERVOUS SYSTEM (CNS)
- made up of brain and spinal cord
- coordinates messages travelling through the Nervous System
- THE PERIPHERAL NERVOUS SYSTEM
- made up of nerves and receptors
- COORDINATION & REGULATION OF BODY FUNCTIONS
When a receptor detects a stimulus, it sends an electrical impulse to the brain/ spinal cord >> The brain/ spinal cord receives the impulse and sends it on along the appropriate nerve fibres to the appropriate effector.
A Reflex Action is “a means of automatically and rapidly integrating and coordinating stimuli with the responses of effectors (muscles and glands)”.
Reflexes (Reflex Arcs or Actions) are involuntary actions, which allow rapid response (as opposed to Voluntary Actions, which are under conscious control). They are very useful because the message gets from the receptor to effector as quickly as possible.
Example: A hand touching a hot plate >> Impulse picked up by a sensory receptor in your finger >> Travels to the spinal cord, along the axon from the receptor cell (or sensory neurone) >> In the spinal cord, the neurone passes an impulse to a motor neurone (relay neurones) >> Relay neurones pass the impulse on to the brain and to an effector – arm muscles contracts and hand pulled away.
A simple Reflex Arc (the pathway which the nerve impulse passes) looks something like this:
RECEPTOR >> SENSORY NEURONE >> RELAY NEURONE >> MOTOR NEURONES >> EFFECTOR
A Synapse is “a junction between two neurones”.
A Synapse contains a neurotransmitter, containing vesicles; a synaptic cleft and neurotransmitter receptor molecules.
In a reflex arc, the synapses ensure that impulses travel in one direction only.
An impulse triggers the release of a neurotransmitter from vesicles into the synaptic gap. The neurotransmitter diffuses across to bind with receptor molecules, in the membrane of the neurone after the synaptic gap, causing the impulse to continue.
Many drugs (e.g. heroin) act upon synapses.