Neurons and Synaptic Transmission Flashcards
What is a motor neuron?
neurons that form synapses with muscles and control their contractions
What is a neurotransmitter?
chemical substances that play an important part in the workings of the nervous system by transmitting nerve impulses across a synapse
What is a relay neuron?
neurons that allow sensory and motor neurons to communicate with each other
What is the most common type of neuron in the CNS?
relay neurons
What is a sensory neuron?
neurons that carry nerve impulses from sensory receptors to the spinal cord and the brain
What is a synapse?
the conjunction of the end of the axon of a neuron and the dendrite/cell body of another
What is synaptic transmission?
refers to the process by which a nerve impulse passes across the synaptic cleft from one neuron (the presynaptic neuron) to another (the postsynaptic neuron)
What cells are the brain made up of?
glial cells and astrocytes
What are amongst the cells in the brain?
neurons
How many neurons does the average human brain have? (+ how many are connected to these)
100 billion neurons and each neuron is connected to 1,000 other neurons
Where do the dendrites of neurons receive information from?
sensory receptors or other neurons
What happens to the information after the dendrites of neurons receive it?
the information is then passed down to the cell body and on to the axon
What happens when the information has reached the axon?
it travels down the axon in the form of an electrical signal known as an action potential
What are neurons?
cells that are specialised to carry neural information throughout the body
What are the 3 types of neurons?
- sensory neurons
- moor neurons
- relay neurons
What are the 3 key features of a neuron?
- cell body
- dendrites
- axon
What is the job of dendrites?
to receive signals from other neurons or from snesory receptors
What are dendrites connected to?
the cell body
What is the cell body?
the control centre of the neuron
From the cell body, where is the impulse carried?
along the axon, where it terminates at the axon terminal
What is the myelin sheath?
an insulating layer that forms around the axon
How long is a neuron?
can vary from a few millimetres up to one metre
Give 3 examples of sensory receptors?
receptors for vision, taste and touch
Where are sensory receptors found? (+3 examples)
in various parts of the body; e.g., skin, tongue, eyes
How do sensory neurons cause an organism to react?
sensory neurons convert information from the sensory receptors into neural impulses which then reach the brain, and are translated into sensations of, e.g. pain/visual input/heat, so the organism can act accordingly.
Not all sensory information travels as far as the brain, with some neurons terminating in the …..
spinal cord
Why does some sensory information terminate at the spinal cord, and not travel as far as the brain?
because this allows reflex actions to occur quickly without the delay of sending impulses to the brain
What is another name for relay neurons?
interneurons
Where are relay neurons located?
ONLY within the brain and spinal cord
What is a motor neuron?
neurons that conduct signals from the CNS to effector organs; e.g. muscles
Where are motor neurons located?
cell bodies may be in the CNS but they have long axons which form part of the PNS.
What do motor neurons form and control?
form synapses with muscles and controls their contractions
What happens when a motor neuron is stimulated?
the motor neuron releases neurotransmitters that bind to receptors on the muscle and triggers a response which leads to muscle movement
How does a muscle move?
the motor neuron releases neurotransmitters that bind to receptors on the muscle and triggers a response that leads to muscle movement
How does a muscle contract?
when the axon of a motor neuron fires, the muscle with which it has formed synapses with contracts
What does the strength of the muscle contraction depend on?
depends on the rate of firing of the axons of motor neurons that control it
What causes a muscle to relax?
as a result of inhibition of the motor neuron
Outline the process of synaptic transmission
- an electrical impulse travels down the length of the axon
- a nerve impulse/action potential reaches the end of the neuron
- electrical current changes the ions in the axon causing synaptic vesicles to release neurotransmitters from the presynaptic neuron into synaptic gap
- neurotransmitters move across the synaptic gap and bind to receptors on postsynaptic neuron
- once enough neurotransmitters are bound, the sign is passed on to the receiving neuron
- enzymes are released to breakdown the neurotransmitters
- neurotransmitters returns to presynaptic neuron (re-uptake)
How long does the process of synaptic transmission take?
only a fraction of a second
What happens after the neurotransmitters return to the presynaptic neuron?
neurotransmitter is stored and made available for later release
How quickly the presynaptic neuron takes back the neurotransmitter from the synaptic cleft determines…
how prolonged the effects of the neurotransmitter will be; i.e. the quicker it is taken back, the shorter the effects on the postsynaptic neuron
How do some antidepressants prolong the action of the neurotransmitter?
by inhibiting the re-uptake of the neurotransmitters by the presynaptic neuron
How can neurotransmitters be ‘turned off’?
through the action of enzymes produced by the body, which make the neurotransmitters ineffective
When can neurotransmitters be ‘turned off’?
after they have been stimulated by the postsynaptic neuron
Neurotransmitters can be classified as either…
inhibitory or excitatory
Give 2 examples of excitatory neurotransmitters
- acetylcholine
2. noradrenaline
What are excitatory neurotransmitters?
‘ON SWITCHES’ - neurotransmitters that increase the likelihood that an excitatory signal is sent to the postsynaptic cell, which is then more likely to fire
What are inhibitory neurotransmitters?
generally responsible for;
- calming the mind and body
- inducing sleep
- filtering out unnecessary excitatory signals
Give 2 examples of inhibitory neurotransmitters
- serotonin
2. GABA
An excitatory neurotransmitter binding with a postsynaptic receptor causes…
an electrical change in the membrane of that cell, resulting in an excitatory post-synaptic potential (EPSP), meaning that the postsynaptic cell is more likely to fire
An inhibitory neurotransmitter binding with a postsynaptic receptor results in…
an inhibitory postsynaptic potential (IPSP), making it less likely that the cell will fire
The likelihood of a cell firing is determined by…
the summation of the EPSPs and IPSPs
Can a nerve cell receive both EPSPs and IPSPs at the same time?
YES
Name two ways in which the strength of the EPSP can be increased
- spatial summation
2. temporal summation
How does spatial summation increase the strength of the EPSP?
a large number of EPSPs are generated in many different synapses on the postsynaptic neuron at the same time
How does temporal summation increase the strength of the EPSP?
a large number of EPSPs are generated at the same synapse by a series of high-frequency action potentials on the presynaptic neuron
If excitatory synapses are more active, ….
the cell fires at a high rate
If inhibitory synapses are more active, …
the cell fires at a much lower rate, if at all
