neurons & synaptic transmission

Question 1

what are neurons?

Answer 1

The basic building blocks of the nervous system, neurons are nerve cells that process and transmit messages through electrical and chemical signals.

Question 2

what are sensory neurons?

Answer 2

These carry messages from the PNS (peripheral nervous system) to the CNS (central nervous system). They have long dendrites and short axons.

Question 3

what are relay neurons?

Answer 3

These connect the sensory neurons to the motor or other relay neurons. They have short dendrites and short axons.

Question 4

what are motor neurons?

Answer 4

These connect the CNS to effectors such as muscles and glands. They have short dendrites and long axons.

Question 5

what is the structure of a neuron?

Answer 5

Neurons vary in size from less than a millimetre to up to a metre long, but all share the same basic structure.

Question 6

what is the cell body of a neuron?

Answer 6

The cell body includes a nucleus, which contains the 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.

Question 7

what is the axon of a neuron?

Answer 7

The axon carries the impulses away from the cell body down the length of the neuron.
The axon is covered in a fatty layer of myelin sheath that protects the axon and speeds up electrical transmission of the impulse.

Question 8

what is the myelin sheath & nodes of Ranvier?

Answer 8

If the myelin sheath was continuous this would have the reverse effect and slow down the electrical impulse. Thus, the myelin sheath is segmented by gaps called nodes of Ranvier. These speed up the transmission of the impulse by forcing it to “jump’ across the gaps along the axon.

Question 9

what are terminal buttons?

Answer 9

Finally, 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.

Question 10

what are neurons located?

Answer 10

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.

Question 11

electrical transmission - the firing of a neuron

Answer 11

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 inside 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 towards the end of the neuron.

Question 12

what is synaptic transmission?

Answer 12

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

Question 13

what are neurotransmitters?

Answer 13

Brain chemicals released from synaptic vesicles that relay signals across the synapse from one neuron to another.
Neurotransmitters can be broadly divided into those that perform an excitatory function and those that perform an inhibitory function.

Question 14

what is excitation?

Answer 14

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 15

what is inhibition?

Answer 15

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 16

what is chemical transmission?

Answer 16

Neurons communicate with each other within groups known as neural axon
networks. Each neuron is separated from the next by an extremely tiny gap called the synapse. Signals within synaptic vesicle
neurons are transmitted electrically.
However, signals between neurons
presynaptic nerve terminal neurotransmitter are transmitted chemically across the synapse.
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.

Question 17

what happens to neurotransmitters?

Answer 17

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.

Question 18

why can neurotransmitters only travel one way?

Answer 18

the direction of travel can only be one-way. This is because neurotransmitters are released from the presynaptic neuron terminal and received by the postsynaptic neuron at the receptor sites.

Question 19

is serotonin excitatory or inhibitory?

Answer 19

the neurotransmitter serotonin causes inhibition in the receiving neuron, resulting in the neuron becoming more negatively charged and less likely to fire.

Question 20

is adrenaline excitatory or inhibitory?

Answer 20

causes excitation of the postsynaptic neuron by increasing its positive charge and making it more likely to fire.

Question 21

what is summation?

Answer 21

Whether a postsynaptic neuron fires is decided by the process of 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. If the net effect is excitatory it is more likely to fire. Once the electrical impulse is created it travels down the neuron.