Neurons And Synaptic Transmission Flashcards
(26 cards)
What is the function of neurons?
- 100 billion neurons in the human system
- 80% of which are located in the brain
- by transmitting signals electrically and chemically, these neurons provide the nervous system with its primary means of communication
What are the three types of neurons?
Sensory neurons
Relay neurons
Motor neurons
What is the structure of a neuron?
- Cell body (or soma), includes nucleus (which contains genetic material of the cell)
- Branchlike structures called dendrites protrude from the cell body. These carry nerve impulses from neighbouring neurons towards the cell body
- The axon carries the impulses away from the cell body down the length of the neuron (its covered in a fatty layer of myelin sheath that protects the axon and speeds up electrical transmission of the impulse)
- Myelin sheath is segmented by gaps called nodes of Ranvier (speed up the transmission of the impulse by forcing it to ‘jump’ across the gaps along the axon)
- At the end of the axon are terminal buttons that communicate with the next neuron in the chain across a gap known as the synapse
Describe the location of neurons
- The cell bodies of motor neurons may be in the CNS but they have long axons which form part of the PNS
- Sensory neurons are located outside of the CNS, in the PNS in clusters known as ganglia
- Relay neurons make up 97% of all neurons and most are found within the brain and the visual system
Describe electrical transmission - the firing of a neuron
- When a neuron is in a resting state the inside of the cell is negatively charged compared to the outside
- When a neuron is activated by a stimulus, the i side of the cell becomes positively charged for a split second causing an action potential to occur.
- This creates an electrical impulse that travels down the axon and towards the end of the neuron
Explain chemical transmission
- Neurons communicate with eachother within groups known as neural networks
- Each neuron is seperated by an extremely tiny gap called the synapse
- Signals within neurons are transmitted electrically
- However, signals between neurons are transmitted chemically across the synapse
- When the electrical impulse reached the end of the neuron (the presynaptic terminal) it triggers the release of neurotransmitter from tiny sacs called synaptic vesicles
What are neurotransmitters?
- Chemicals that diffuse across the synapse to the next neuron in the chain
What happens once a neurotransmitter crosses the gap?
It is taken up by a postsynaptic receptor site on the dendrites of the next neuron.
Here the chemical message is converted back into an electrical impulse and the process of transmission begins again in this other neuron.
What is the primary function of neurons?
To communicate with each other within groups known as neural networks.
What separates neurons from each other?
An extremely tiny gap called the synapse.
How are signals transmitted within neurons?
Electrically.
How are signals transmitted between neurons?
Chemically across the synapse.
What triggers the release of neurotransmitters?
The arrival of an electrical impulse at the presynaptic terminal.
What are the tiny sacs that contain neurotransmitters called?
Synaptic vesicles.
Where do neurotransmitters bind after crossing the synapse?
To postsynaptic receptor sites on the dendrites of the next neuron.
What is the direction of neurotransmitter travel?
One-way, from presynaptic neuron to postsynaptic neuron.
What is an example of a neurotransmitter that causes muscle contraction?
Acetylcholine (ACh).
What types of effects can neurotransmitters have on neighboring neurons?
Excitatory or inhibitory.
What effect does serotonin have on the receiving neuron?
Inhibition, making the neuron more negatively charged.
What effect does adrenaline have on the postsynaptic neuron?
Excitation, increasing its positive charge.
What process decides whether a postsynaptic neuron will fire?
Summation of excitatory and inhibitory influences.
What happens if the net effect on a postsynaptic neuron is inhibitory?
The postsynaptic neuron is less likely to fire.
What is the threshold in the context of neuron firing?
The level of excitatory input required to trigger an action potential.
Fill in the blank: Neurotransmitters are chemicals that diffuse across the _______.
synapse.
