synaptic transmission

Question 1

what is a synapse?

Answer 1

an extremely tiny gaps which separates each neuron from the next

Question 2

how are signals transmitted within and between neurons?

Answer 2

• signals within neurons are transmitted electrically
• signals between neurons are transmitted chemically

Question 3

what happens when the electrical impulse reaches the end of the neuron?

Answer 3

when the electrical impulse reaches the end of the neuron (the presynaptic terminal) it triggers the release of neurotransmitters from tiny sacs called synaptic vesicles

Question 4

what is synaptic transmission?

Answer 4

the process by which neighbouring neurons communicate with each other by sending chemical messages across the gap (the synapse) that separates them

Question 5

what happens once a neurotransmitter crosses the gap?

Answer 5

• it is taken up a postsynaptic receptor site on the dendrites of the next neuron
• the chemical message is converted back into an electrical impulse
• process of transmission begins again within this neuron

Question 6

what is the difference between where axons and dendrites take signals?

Answer 6

• axons take signals to the synapse
• dendrites take signals away from the synapse

Question 7

why can the direction of travel only be one-way?

Answer 7

because neurotransmitters are released from the presynaptic neuron terminal and received by the postsynaptic neuron at the receptor sites

Question 8

what are neurotransmitters?

Answer 8

they are brain chemicals released from synaptic vesicles that relay signals across the synapse from one neuron to another
- they can broadly be excitatory or inhibitory

Question 9

what is excitation?

Answer 9

when a neurotransmitter, such as adrenaline, increases the positive charge of the postsynaptic neuron
- this increases the likelihood that the postsynaptic neuron will pass on the electrical impulse

Question 10

what is inhibition?

Answer 10

when a neurotransmitter, such as serotonin, increases the negative charge of the postsynaptic neuron
- this decreases the likelihood that the postsynaptic neuron will pass on the electrical impulse

Question 11

what is summation?

Answer 11

the process which decides whether a postsynaptic neuron is fired or not

Question 12

describe the process of summation

Answer 12

• the excitatory and inhibitory influences are summed
  > if the net effect on the postsynaptic neuron is inhibitory/excitatory then the postsynaptic neuron is more/less likely to fire
• when the electrical impulse is created, when the inside of the postsynaptic neuron momentarily becomes positively charged, it travels down the neuron

Question 13

when is the action potential of the postsynaptic neuron only triggered?

Answer 13

if the sum of the excitatory and inhibitory signals at any one time reaches the threshold

Question 14

describe the reflex arc using the knee-jerk reflex as an example

Answer 14

• a stimulus, such as a hammer, hits the knee
• this is detected by sense organs in the PNS
• a message is conveyed along a sensory neuron
• the message reaches the CNS, where it connects with a relay neuron
• this then transfers the message to a motor neuron
• this then carries the message to an effector, such as a muscle, which causes the muscle to contract and, hence, causes the knee to move or jerk