Co-ordination and response Flashcards
What is a voluntary action
A voluntary action involves a conscious decision made within the cerebral hemispheres of the brain Relatively slow response The same stimulus can provide a variety of different responses Many voluntary actions are learnt
What does the nervous system allow us to do
It allows us to make sense of our surroundings and respond to them and to co-ordinate and regulate body functions
What are neurones
Nerve cells found in the nervous system
Hundreds of neurones make up one nerve
What are receptors
They are found in sense organs
They respond to changes in the environment (stimuli)
What is an effector
Parts of the body that respond to a stimulus
e.g. muscles and glands
What are the three different types of neurone and what are their functions
Sensory - Carry nerve impulses from sense organs to the central nervous system
Relay - Found in the central nervous system and connect sensory and motor neurones
Motor - Carry nerve impulses from the central nervous system to effectors
Why can a nerve impulse only travel in one direction along the reflex arc?
Because the neurotransmitter is present on the only one side of the synapse Drugs act as synapses
What does the human nervous system contain
Central nervous system - brain and spinal cord
Peripheral nervous system - all of the nerves in the body
What is an involuntary action
An involuntary action only involves the spinal cord and other parts of the brain Faster response The same stimulus produces the same response; it is automatic Many involuntary actions are instinctive
What is a synapse?
A tiny gap between two neurones
Describe what happens when a nerve impulse arrives at the end of a sensory neurone
Vesicles containing neurotransmitters move to the cell membrane of the sensory neurone The vesicles burst open and empty the neurotransmitter into the synaptic cleft The neurotransmitter diffuses across the cleft The neurotransmitter molecules slot into their receptors on the membrane of the relay neurone This sets off a nerve impulse in the relay neurone
How are neurones adapted
They have a long axon to carry impulses over long distances
The axon is insulated by a fatty (myelin) sheath, increases the speed of nerve impulse
What do dendrites do
Dendrons are tiny branches at the end of neurones which break up in dendrites which recieve incoming nerve impulses
What is a nerve impulse
An electrical signal that passes along a nerve impulse
What is a sense organs
Groups of receptor cells responding to specific stimuli; light, touch, sound, tempurature and chemicals
What does the iris do
Controls how much light enters the pupil
What does the lens do
Focuses light on the retina
What do the pupil do
A hole in the iris that allows light to pass through to the lens
What does the cornea do
Refracts light
What does the retina do
Contains light receptors, some sensitive to light of different colours
What does the fovea do
Where light is focused when you look directly on an object; geatest concentration of receptors is here
What does the blind spot do
No receptors here; so light falling onto this area is not seen
What does the optic nerve do
Carries nerve impulses to the brain
What happens when light enters the eye
Light enters the eye through the cornea
Light is refracted as it passes through the cornea and the lens
Light is focused onto the recpetor cells in the retina
This sets off nerve impulses that travel along the optic nerve to the brain
Why do the muscles in the iris contract making the diameter of the pupil smaller in bright light
The bright light may damage the retina
What happens when bright light falls on the retina
Impulses pass alomng sensory neurones to the brain, and then along motor neurones to the muscles in the iris
Circular muscles in the iris contract, the diameter of the pupil is decreased, reduces amount of light able to pass through the pupil
What happens when dim light falls on the retina
Radial muscles in the iris contract, this widens the pupil allowing more light to pass through
What are the radial and circular muscles in the eyes
Antagnostic, they have opposite effects
What do the suspensory ligaments do
They hold the lens in place
How does an eye focus on a close object
The lens needs to be wide and thick, so it refracts more strognly
To achieve this, the suspensory ligaments must be loose
the ciliary muscles must contract