Biopsychology : neurons and synaptic transmission Flashcards
Define neuron
The basic building blocks of the nervous system - neurons are the nerve cells that process and transmit messages through electrical and chemical signals
Define sensory neurons
They carry messages from the PNS (peripheral nervous system) to the CNS. They have long dendrites and short axons
Define relay neuron
They connect the sensory neurons to the motor or other relay neurons. They have short dendrites and shirt axons
Define motor neuron
They connect the CNS to effectors such as muscles and glands. They have short dendrites and long axons
How many neurons are there in the human nervous system?
100 billion neurons
80% are located in the brain
How do the neurons provide the nervous system with its primary means of communication?
By transmitting signals electrically and chemically
What are the size variations of a neuron?
From less than a millimetre to a metre long
Explain the structure of cell body in neuron?
Cell body / soma - includes nucleus (which contains genetic material of the cell.
from cell body
What do dendrites do?
They carry nerve impulses from neighbouring neurons toward the cell body
What does the axon do?
Carries the impulses away from the cell body down the length of the neuron
What is the axon covered in and what does it do?
A fatty layer of myelin sheath - protects axon and speeds up electrical transmission of the impulse
What are nodes of ranvier
They separate the myelin sheath which speeds up the transmission of the impulse by forcing it to ‘jump’ across the gaps along the axon
What is at the end of the axon and what do they do?
Terminal buttons : communicate with the next neuron in the chain across a gap, the synapse
Where would the cell bodies of motor neurons be found?
In the CNS but they have long axons which form part of the PNS
Where are sensory neurons located ?
Outside of the CNS , in the PNS in clusters known as ganglia
Where are relay neurons found?
Within the brain and the visual system - they make up 97% of all neurons
What happens when a neuron is in resting state ?
The inside of the cell is negatively charge pd compared to the outside
What happens when a neuron is activated by a stimulus?
The inside of the cell becomes positively charged for a split second causing action potential to occur. This creates an electrical impulse that travels down the axon toward the end of the neuron
What are the groups that neurons communicate within called?
Neural networks
What are each neurons separated by?
Synapses
How are signals within neurons transmitted?
Electrically
How are signals between neurons transmitted between neurons?
Chemically accross the synapse
What happens when the electrical impulse reaches the end of the neuron (the presynaptic terminal)?
It triggers the release of neurotransmitter from tiny sacs called synaptic vesicles
What are neurotransmitters?
Chemicals which 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 post synaptic receptor site on the dendrites of the next neuron (axons take signals to the synapse, dendrites take signals away)
Chemical message is converted back into an electrical impulse and the process of transmission begins again in the other neuron
What is the direction of a neurotransmitter?
Only one way because they are released from the presynaptic neuron terminal and received by the post synaptic neuron (at the receptor sites)
What does each neurotransmitter have?
It’s own specific molecular structure that fits perfectly into a postsynaptjc receptor site - similar to lock and key
What else do neurotransmitters have?
Specialist functions
Eg : acetylcholine is found at each point where a motor neuron meets a muscle and upon release, it will cause muscles to contract
What does neurotransmitters either have?
An excitatory or inhibitory effect on the neighbouring neuron
Eg: serotonin causes inhibition in the receiving neuron - resulting in the neuron becoming more negatively charged and less likely to fire
What is summation?
Whether a postsynaptic neuron fires
What happens in summation?
The excitatory and inhibitory influences are summed - if the net effect on the postsynaptic neuron is inhibitory , then the postsynaptic neuron is less likely to fire
Once the electrical impulse is created, it travels down the neuron
So , the action potential of the postsynaptic neuron is only triggered if the sum of the excitatory and inhibitory signals at any one time reaches the threshold
Define synaptic transmission
Process which neighbouring neurons communicate with each other by sending chemical messages across the gap that separates them
Define neurotransmitter
Brain chemicals released from synaptic vesicles which relay signals across the synapse from one neuron to another
They can be broadly divided into those that perform an inhibitory function and those which perform an excitably function
Define excitation
When a neurotransmitter eg adrenaline increases the positive charge of postsynaptic neuron # increases likelihood that the postsynaptic neuron will pass on the electrical impulse
Define inhibition
When a neurotransmitter such as serotonin increases the negative charge of the postsynaptic neuron - decreasing the likelihood that the postsynaptic neuron will pass on the electrical impulse
