KA4 The cells of the nervous system Flashcards
What do neurones do?
Neurones receive and transmit electrical impulses, and provide the body with a rapid means of communication and control
What are the 3 types of neurones?
Sensory, inter and motor
What 3 structures do each neuron have?
Dendrites, a cell body and an axon
D—C—A
What is the function of the myelin sheath?
The layer of fatty material that insulates an axon and increases the speed of impulse conduction
When does myelination continue from?
Myelination continues from birth to adolescence
Responses to stimuli in the first two years of life are not as rapid or co-ordinated as those of an older child or adult
What causes the myelin sheath to break down?
Certain diseases cause the myelin sheath to break down, causing a loss of coordination in the sufferer
What is the function of glial cells?
Glial cells produce the myelin sheath and support neurons
Where do neurons connect with other neurons?
At a synaptic cleft
What is the transmission at a synapse?
Neurotransmitters are stored in vesicles in the axon endings of the presynaptic neuron
The neurotransmitters are released into the synaptic cleft on arrival of an impulse
They diffuses across the cleft and bind to receptors on the membrane of the postsynpatic neuron.
Why must neurotransmitters be rapidly removed after the impulse has been transmitted?
They must be removed by enzymes or reuptake as soon as the impulse has been transmitted to prevent continuous stimulation of post synaptic neurone
How is acetylcholine removed?
It is broken down by an enzyme
Acetylcholine—enzyme—non active products
How is noradrenaline broken down?
It is directly reabsorbed
What determines whether a signal is excitatory or inhibitory?
Receptors
What does excitatory mean?
Excitatory signals increase the chance of the impulse being transmitted
What does inhibitory mean?
Inhibitory signals reduce the chance of the impulse being transmitted
What does noradrenaline do?
It is sympathetic
It increases activity in heart and lungs
It decreases activity in digestive system
What does acetylcholine do?
It is parasympathetic
It slows activity in heart and lungs
It increases activity in digestive system
What is a threshold?
For a nerve impulse to be transmitted, a minimum number of neurotransmitter molecules must attach to receptors in order to reach the threshold on the post synaptic membrane
What happens if the threshold is not met?
The stimulus is too weak and is filtered out by synapse.
What is a summation?
A series of weak stimuli added together can release enough neurotransmitter to fire a nerve impulse.
Convergent neural pathways can do this
What are endorphins?
Endorphins are neurotransmitters that stimulate neurons involved in reducing the intensity of pain
What do endorphins increase in respond to?
Stress
Severe injury
Prolonged and continuous exercise
Certain foods eg chocolate
What are increased levels of endorphins linked to?
Feelings of pleasure obtained from activities such as eating, sex and prolonged exercise
What is the function of dopamine?
Dopamine is a neurotransmitter that incudes feelings of pleasure and reinforces particular behaviour by activating the reward pathway
