Neurons, synaptic transmission and neurotransmitters Flashcards
What is a neuron?
A neuron is a nerve cell that processes and transmitts chemical and electrical signals
What are 3 the types of neurons?
- Sensory
- Motor
- Relay
What is the function of sensory neurons?
They carry messages from sensory receptors along nerves in the PNS to the CNS
What is the function of motor neurons?
They carry messages from the CNS, along the PNS to effectors in the body (e.g muscles and glands)
What is the function of relay neurons?
They connect sensory and motor neurons together allowing them to communicate
Name the structures found in a neuron
- Soma (cell body)
- Dendrites
- Axon
- Myelin sheath
- Nodes of Ranvier
- Terminal buttons
Describe the soma of a neuron
- Cell body
- Contains the nucleus, DNA, ribosomes and mitochondria
Describe the dentrites of a neuron
- Branch-like structures that stick out from the soma
- Carries impulses from neighbouring neurons to soma
Describe the axon of a neuron
- Tube-like structure
- Carries impulses away from the cell body
Describe the myelin sheath of a neuron
- Fatty layer that covers the axon
- Both protects the axon and speeds up electrical transmission of an impulse
Describe the Nodes of Ranvier
- Gaps in the myelin sheath
- Allows the increase in speed of impulses across a neuron as impulses ‘jump’ across these gaps
Describe the terminal buttons of a neuron
- Small, bulbous endings of axons
- They contain synaptic vesicles filled with neurotransmitters
What is a synapse?
The space between the axon terminal of a neuron and the dendrite of a neighbouring neuron
What is depolarisation?
- When a neuron is in a resting state the inside of the cell is negatively charged relative to the outside of the cell
- When a neuron is activated by a stimulus the inside of the cell becomes positively charged for a split second
- This rapid switch from negative to positive creates an action potential
What is meant by an action potential?
An electrical impulse
Summarise the process of synaptic transmission
- An AP moves down the axon terminal towards the terminal buttons of the presynaptic neuron
- Vesicles containing neurotransmitters are released and fuse with the presynaptic membrane
- The neurotransmitters are released from vesicles and diffuse across the synaptic cleft
- The neurotransmitters attach to receptors on the postsynaptic neuron
- When detected, the neurotransmitter molecule is absorbed by the postsynaptic neuron and is converted back into an electrical signal which may fire another AP
What happens to neurotransmitters that remain in the synaptic cleft?
They are reabsorbed by the presynaptic neuron (re-uptake) or destroyed by enzymes
What is a neurotransmitter?
A chemical messenger that carries signals between nerve cells
What are 3 examples of neurotransmitters?
- Dopamine
- Serotonin
- Acetylcholine
What are the two types of neurotransmitters?
- Excitatory
- Inhibitory
What is an excitatory neurotransmitter?
Neurotransmitters that stimulate an action potential in the postsynaptic neuron
- They increase the neurons positive charge making it more likely to ‘fire’ an AP
What is an inhibitory neurotransmitter?
Neurotransmitters that inhibit an action potential in the postsynaptic neuron
- They increase the neurons negative charge making it less liekly to ‘fire’ an AP
What is summation?
- The excitatory and inhibitory influences are summed
- If the net effect is excitatory then it is more likely to fire
- If the net effect is inhibitory then it is less likely to fire
