the cells of the nervous system and neurotransmitters at synapses Flashcards
Describe the structure and function of neurons
Neurons receive and transmit electrical impulses in the nervous system. A neuron consists of a cell body, axons and many dendrites.
Dendrites are stimulated by sense organs or other neurons to carry impulses towards the cell body.
The axon ends in many divisions called axon terminals.
The axon carries impulses in one direction from the dendrites to the axon terminals.
The cell body controls the cell’s metabolism.
State the function of the myelin sheath
Axons are surrounded by a myelin sheath which insulates the axon and increases the speed of impulse conduction
Explain the process of myelination
Myelination is the development of myelin around the axon fibres. It begins in the foetus and continues into 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
describe what happens when the myelin sheath is destroyed
a loss of coordination
State the function of glial cells
Glial cells produce the myelin sheath and support neurons
Describe the difference between a synapse and a synaptic cleft
the junction between neurons is called a synapse. The gap between one neuron and the next is called the synaptic cleft
Explain what neurotransmitters are and how they work
Neurotransmitters relay impulses across the synaptic cleft. Neurotransmitters are stored in vesicles in the axon endings of the presynaptic neuron. They are released into the cleft on arrival of an impulse. They diffuse across the cleft and bind to receptors on the membrane of the postsynaptic neuron.
Explain how neurotransmitters are removed from the synaptic cleft
This is to stop continuous stimulation of the postsynaptic neuron. Removal is achieved in two different ways; enzyme degradation or reuptake of neurotransmitters by the presynaptic neuron.
State what receptors on the postsynaptic neuron determine
Receptors determine whether the signal is excitatory or inhibitory
Describe how the threshold for an impulse is reached
A minimum number of neurotransmitter molecules must attach to receptors in order to reach the threshold on the postsynaptic membrane to transmit the impulse.
Explain what summation is
summation of a series of weak stimuli can release enough neurotransmitter to trigger an impulse. Convergent neural pathways can release enough neurotransmitter molecules to reach threshold and trigger an impulse.
State the role of endorphins
Endorphins are neurotransmitters that stimulate neurons involved in reducing the intensity of pain. Increased levels of endorphins are also linked to the feelings of pleasure obtained from activities such as eating, sex and prolonged exercise. Endorphin production increases in response to severe injury, prolonged and continuous exercise, stress and certain foods.
Describe the role of dopamine
Dopamine is a neurotransmitter that induces feelings of pleasure and reinforces particular behaviour by activating the reward pathway in the brain. The reward pathway involves neurons which secrete or respond to dopamine. The reward pathway is activated when an individual engages in a behaviour that is beneficial to them, for example eating when hungry.
Explain how Antagonists work
Antagonists are chemicals that bind to specific receptors blocking the action of a
neurotransmitter at a synapse.
explain how agonists work
Agonists are chemicals that bind to and stimulate specific receptors mimicking the
action of a neurotransmitter at a synapse.
