UNIT 13: COORDINATION AND RESPONSE
Stimuli: a change in an organism’s body surroundings
that can be detected by its sense organs or receptors and
the effectors response
o Nerves: fast method of sending information
o Hormones: slower but important and diffuse into
the blood plasma (long lasting, each hormone has
one or more target organs, require less energy)
Central nervous system (CNS) consists of brain and
spinal cord
Peripheral nervous system consists of nerves and
receptors
Neurones: nerves cell
specialised for rapid transfer of
electrical impulses, make up nervous system
Long, thin fibers of cytoplasm to carry messages quickly
Dendrites pick up impulses from other neurones nearby
Impulse: electrical signal that sweeps along a neurone
Myelin: fatty substance surrounds the axon of many
neurones, enabling the nerve impulses to travel faster
Make sure the impulses don’t scatter
Increase the time needed to respond to a stimuli
Insulates the nerve fibers
Reflex arc: the arrangement of neurones along which an
impulse passes during a reflex action
1. An impulse is picked up by receptor
2. Impulse travels to the spinal cord along the axon from the sensory neurone
3. In the spinal cord, the impulse is relayed to several neurones by relay
neurone
4. Relay neurone passes the impulse to the brain
5. Simultaneously, the impulses are passed to
effector by motor neurone for suitable action
Reflex action: a means of automatically and rapidly
integrating and coordinating stimuli with the responses of
effectors (muscles and glands)
Involuntary action: an action taken automatically
without conscious thought
Voluntary action: an action taken as the result of
conscious decision, slower, not inherited
, UNIT 13: COORDINATION AND RESPONSE
Synapse: a junction between 2 nerve cells, consisting of a minute gap across which
impulses pass by diffusion of neurotransmitter
Synaptic cleft: a tiny gap between 2 neurones
An impulse triggers the release of a neurotransmitter from vesicles into the
synaptic gap
Neurotransmitter diffuses across, attaches to the receptor molecules in cell
membrane of relay neurones because shape is complementary
The binding triggers a nerve impulse in the relay neurone
Ensure that impulses travel in
one direction only
Many drugs, e.g. heroin act
upon synapses
Sense organ: a group of receptor
cells that respond to specific stimuli
(light, sound, touch, temperature,
chemical)
Cornea: refracts light
Lens: focuses light onto retina
Optic nerve: carries impulses to brain
Blind spot: optic nerves leave eye (no receptor cells)
Retina: consists of fovea and blind spot, receptor cells that is sensitive to light,
protected by the rest of the eye and focused light into
Choroid: absorbs light after it has been through the retina so it does not get
scattered the inside of the eye and rich in blood vessels to nourish eye
Iris: coloured part of the eye which controls amount of light allowed through to
the retina and lens
o Pupil: in the middle of the iris and can adjust in size -> iris reflex
Dim light Bright light
Circular muscle relaxes, radial muscle Radial muscle relaxes, circular muscles
contracts contracts
Pupil dilates to allow more light into the Pupil constricts, less light can pass
eye through to avoid damaging the retina
Antagonistic action of circular and radial muscles in the iris
Rod cells Cone cells
Greater sensitivity for night Function in bright light
vision
Only see black and white Sensitive to red, green,
blue light
Show less detailed image Detailed image
Further out on the retina, Fovea contains almost
less tightly packed entirely cones tightly
Stimuli: a change in an organism’s body surroundings
that can be detected by its sense organs or receptors and
the effectors response
o Nerves: fast method of sending information
o Hormones: slower but important and diffuse into
the blood plasma (long lasting, each hormone has
one or more target organs, require less energy)
Central nervous system (CNS) consists of brain and
spinal cord
Peripheral nervous system consists of nerves and
receptors
Neurones: nerves cell
specialised for rapid transfer of
electrical impulses, make up nervous system
Long, thin fibers of cytoplasm to carry messages quickly
Dendrites pick up impulses from other neurones nearby
Impulse: electrical signal that sweeps along a neurone
Myelin: fatty substance surrounds the axon of many
neurones, enabling the nerve impulses to travel faster
Make sure the impulses don’t scatter
Increase the time needed to respond to a stimuli
Insulates the nerve fibers
Reflex arc: the arrangement of neurones along which an
impulse passes during a reflex action
1. An impulse is picked up by receptor
2. Impulse travels to the spinal cord along the axon from the sensory neurone
3. In the spinal cord, the impulse is relayed to several neurones by relay
neurone
4. Relay neurone passes the impulse to the brain
5. Simultaneously, the impulses are passed to
effector by motor neurone for suitable action
Reflex action: a means of automatically and rapidly
integrating and coordinating stimuli with the responses of
effectors (muscles and glands)
Involuntary action: an action taken automatically
without conscious thought
Voluntary action: an action taken as the result of
conscious decision, slower, not inherited
, UNIT 13: COORDINATION AND RESPONSE
Synapse: a junction between 2 nerve cells, consisting of a minute gap across which
impulses pass by diffusion of neurotransmitter
Synaptic cleft: a tiny gap between 2 neurones
An impulse triggers the release of a neurotransmitter from vesicles into the
synaptic gap
Neurotransmitter diffuses across, attaches to the receptor molecules in cell
membrane of relay neurones because shape is complementary
The binding triggers a nerve impulse in the relay neurone
Ensure that impulses travel in
one direction only
Many drugs, e.g. heroin act
upon synapses
Sense organ: a group of receptor
cells that respond to specific stimuli
(light, sound, touch, temperature,
chemical)
Cornea: refracts light
Lens: focuses light onto retina
Optic nerve: carries impulses to brain
Blind spot: optic nerves leave eye (no receptor cells)
Retina: consists of fovea and blind spot, receptor cells that is sensitive to light,
protected by the rest of the eye and focused light into
Choroid: absorbs light after it has been through the retina so it does not get
scattered the inside of the eye and rich in blood vessels to nourish eye
Iris: coloured part of the eye which controls amount of light allowed through to
the retina and lens
o Pupil: in the middle of the iris and can adjust in size -> iris reflex
Dim light Bright light
Circular muscle relaxes, radial muscle Radial muscle relaxes, circular muscles
contracts contracts
Pupil dilates to allow more light into the Pupil constricts, less light can pass
eye through to avoid damaging the retina
Antagonistic action of circular and radial muscles in the iris
Rod cells Cone cells
Greater sensitivity for night Function in bright light
vision
Only see black and white Sensitive to red, green,
blue light
Show less detailed image Detailed image
Further out on the retina, Fovea contains almost
less tightly packed entirely cones tightly
