Neurones and Synaptic Transmission Flashcards
How many neurones are in the human nervous system? How many of those are located in the brain?
100 billion
80%
What is the purpose of a neurone? What does this provide the nervous system?
Transmit signals electrically and chemically which provides nervous system its primary means of communication
Name the three types of neurones
Sensory
Relay
Motor
Describe the function of a sensory neurone and its structure
Carry messages from PNS to CNS
Long dendrites and short axons
Describe the function of a relay neurone and its structure
Connect sensory neurons to motor or other relay neurones
Short dendrites and short axons
Describe the function of a motor neurone and its structure
Connect CNS to effectors
Short dendrites and long axons
How does the size of neurones vary?
Less than a mm to a metre
Name the seven basic structures of a neurone
Cell body Nucleus Dendrites Axon Myelin sheath Nodes of Ranvier Terminal buttons
Describe the structure of dendrites and their function
Branch like structures that protrude from the cell body Carry nerve impulses from neighbouring neurones towards cell body
Describe the function of an axon
Carries impulses away from cell body down neurone
What is the myelin sheath and two of their functions?
Fatty layer that covers the axon
Protection and speeds up electrical transmission of impulse
What are the nodes of Ranvier and their function?
Gaps in the myelin sheath
To speed up transmission by forcing it to ‘jump’ across gaps along the axon
Where are terminal buttons on a neurone and what is their function?
End of an axon
Communicate with next neurone in chain across a gap (synapse)
Describe the process of firing a neuron (3)
When a neuron is in a resting state the inside of the nerve cell is negatively charged compared to the outside
When neuron activated by a stimulus, inside of cell becomes positively charged for a split second causing an action potential to occur
Creates an electrical impulse than travels down the axon towards end of neuron
Define neurotransmitter
Brain chemicals released from synaptic vesicles relay signals across synapse from one neuron to another
Define synaptic transmission
Process by which neighbouring neurons communicate with each other by sending chemical messages across the synapse
Describe the process of electrical transmission (6)
Electrical impulse reaches presynaptic terminal
Triggers release of neurotransmitters from the synaptic vesicles
Neurotransmitter crosses the synapse
Taken up by postsynaptic receptor site on next neuron
Chemical message converted back to electrical impulse
Process of electrical transmission can begin
How do the type of signals vary depending on where they are happening in the neuron?
Inside = electrical Between = chemically
What two effects can neurotransmitters have?
Excitatory and inhibitory
Describe the excitatory effect of a neurotransmitter
Binds with postsynaptic receptor
causes electrical change in the membrane of that cell
results in excitatory post-synaptic potentional postsynaptic cell is more likely to fire
Describe the inhibitory effect of a neurotransmitter
Binds with postsynaptic receptor causes
electrical change in the membrane of that cell
results in inhibitory post-synaptic potential
postsynaptic cell is more less to fire
Describe the effect of summation
Excitatory and inhibitory influences summed
Must reach a certain threshold for the action potential for the post synaptic neuron to be triggered
If net effect of neurotransmitter is inhibitory then post synaptic neuron is less likely to fire, excitatory net effect, more likely to
Describe the reflex arc
E.g. Knee-jerk reflex
Stimulus detected by sense organs in PNS
Conveys message along a sensory neuron
Message reaches CNS where it connects with a relay neuron
Transfers message to motor neuron
Carries message to effector which brings about the response
