3.4 Cells Of The Nervous System And Neurotransmitters At Synapses Flashcards
What are neurons composed of?
- Dendrites
- A Cell Body
- Axons
What direction do nerve impulses travel?
Dendrite to Cell Body to Axon
What is the cell body?
- Contains a nucleus and cytoplasm
- Cytoplasm contains a mitochondria to provide energy for impulses and ribosomes which synthesise proteins for the synthesis of neurotransmitters
What is the dendrite?
Receives nerve impulses and carries them towards the cell body
What is the axon?
Carries nerve impulses away from the cell body
What is the myelin sheath?
A layer of fatty material that surrounds the axon that insulates the axon and increases the speed of nerve impulses
What is myelination?
Myelination is not complete at birth and it continues until adolescene
What diseases destroy the myelin sheath causing a loss of coordination?
- Polio
- Multiple Sclerosis (MS)
What do glial cells do?
- Physically support neurons
- Produce the myelin sheath
What is the area called between an axon of one neuron and the dendrite of another?
A synapse
What is the synaptic cleft?
The space that separates the plasma membranes of each neuron
What is the presynaptic cleft?
The neuron before the synaptic cleft
What is the postsynaptic cleft?
The neuron after the synaptic cleft
What are neurotransmitters?
Chemicals that pass messages across synaptic clefts
What are two examples of neurotransmitters?
- Acetylcholine
- Noradrenaline
What is stimulated when a nerve impulse passes through a neuron and reaches the axon?
Many vesicles containing neurotransmitters
When do neurotransmitters within the vesicles get released into the synaptic cleft?
When the vesicles move to and fuse with the membrane at the surface of the axon terminal
What happens after neurotransmitters diffuse across the synaptic cleft?
They bind to receptor molecules on the dendrites of the next neuron, transmitting the impulse to the next neuron
Why should neurotransmitters be rapidly removed as soon as the impulse has been transmitted?
To prevent continuous stimulation of the postsynaptic neuron so that the membrane is sensitive to the next stimulus
How can neurotransmitters be removed from the synaptic cleft?
- Enzymes
- Reuptake
What is excitatory signal?
Causes an increase in action
What is inhibitory signal?
Causes a decrease in action
What is summation?
The cumulative effect of many weak stimuli
What are endorphins?
Neurotransmitters that stimulate neurons involved in reducing the intensity of pain
What does endorphin production increase in response to?
- Severe Injury
- Prolonged and continuous exercise
- Physical and emotional stress
- Chocolate and chilli peppers
What does increased levels of endorphins bring about in the body?
- Europhic feelings
- Regulation of appetite
- Release of sex hormones
What is dopamine?
A neurotransmitter which induces the feeling of pleasure
What is dopamine involved in?
Reinforcing particular behaviour by activating the reward pathway in the brain when an individual engages in a behaviour that is beneficial to them
What are agonists?
Chemicals that bind to and stimulate specific receptors on postsynaptic neurons
What does an agonist do?
Mimic the action of natural neurotransmitters at the synapse and so normal cell responses occur
What are antagonists?
Chemicals that bind to and block specific receptors on postsynaptic neurons
What do antagonists prevent?
The normal neurotransmitter from acting by blocking the receptor sites
What do antagonists do?
Greatly reduce or stop the normal transmission of nerve impulses
What do inhibitors do to neurotransmitters?
Degrade neurotransmitters by inhibiting the enzymes
What do recreational drugs do?
Act as agonists and antagonists and therefore effect neurotransmission at a synapse
What can the use of recreational drugs lead to?
- Person feeling happier
- Poorer at carrying out complex mental tasks
- Misinterprets enviromental stimuli
- Stay awake for longer
What do antagonists cause an increase in?
The number and sensitivity of neurotransmitter receptors
What do agonists cause a decrease in?
The number and sensitivity of neurotransmitter receptors
