BIO 02 - Neurons and synaptic transmission

Question 1

What is a neuron?

Answer 1

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

Question 2

What is a sensory neuron?

Answer 2

• These carry message from the PNS (peripheral nervous system) to the CNS
• They have long dendrites and short axons

Question 3

What is a relay neuron?

Answer 3

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

Question 4

What is a motor neuron?

Answer 4

• These connect the CNS (central nervous system) to effectors such as muscles and glands
• They have short dendrites and long axons

Question 5

What is synaptic transmission?

Answer 5

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

Question 6

What is a neurotransmitter?

Answer 6

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

Question 7

What is excitation?

Answer 7

• When a neurotransmitter, such as adrenaline or dopamine, increases the positive charge of the postsynaptic neuron
• This increases the likelihood that the postsynaptic neuron will pass on the electrical impulse

Question 8

What is inhibition?

Answer 8

• When a neurotransmitter, such as serotonin or GABA, increases the negative charge of the postsynaptic neuron
• This decreases the likelihood that the postsynaptic neuron will pass on the electrical impulse

Question 9

What is summation?

Answer 9

• This process decides whether a postsynaptic neuron fires
• The excitatory and inhibitory influences are summed: if the net effect on the postsynaptic neuron is inhibitory then the postsynaptic neurons 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
• Therefore, the action potential of the post synaptic neuron is only triggered if the sum of the excitatory and inhibitory signals at any one time reaches the threshold

Question 10

What is action potential?

Answer 10

When a neuron is activated by a stimulus the neuron ‘fires’ and creates an impulse

Question 11

What structures are present in all neurones?

Answer 11

• Cell body (or soma)
• Dendrites
• Axon
• Mylein sheath
• Synapse

Question 12

What is the cell body of a neuron?

Answer 12

It is like a regular animal cell with a nucleus, which contains the genetic material of the cell, and cytoplasm

Question 13

What is a dendrite?

Answer 13

They are branch-like structures that protrude from the cell body, and they receive the electrical nerve impulses from neighbouring neurons and carry it towards the cell body

Question 14

What is an axon?

Answer 14

They send electrical impulses away to the next neuron (away from the cell body down the length of the neuron)

Question 15

What is the mylein sheath?

Answer 15

• A fatty multilayer wrapping covers the axon region in some neurons such as the sensory and motor neuron
• It acts as an insulator
• The periodic gap in the insulating sheath called the Nodes of Ranvier, speeds up the transmission of nerve impulses by forcing it to ‘jump’ across the gaps along the axon

Question 16

What is the synapse?

Answer 16

Terminal buttons that communicate with the next neuron in the chain across a gap

Question 17

What is the strucure and function of sensory neurons?

Answer 17

• They are nerve cells that are responsible for converting a specific stimulus from the internal and external environment into the internal electrical impulses within the nervous system
• It then transmits the impulses to the central nervous system
• Structurally, they have long dendrites and short axons
• The distinctive feature is that their cell bodies are bulging out of the neuron
• They are located outside the CNS in the PNS in clusters known as ganglia

Question 18

What is the strucure and function of relay neurons?

Answer 18

• They link sensory and motor neurons so that the impulse moves uninterruptedly
• They make up 97% of all neurons and most are found within the brain and the visual system
• They are present in the brain and spinal cord regions of our body and do not contain myelin sheath

Question 19

What is the strucure and function of motor neurons?

Answer 19

• They take care of our motor skills
• They transmit messages from the central nervous system to effector organs
• Effector organs are any muscle, organ, gland etc that can produce a response to a detected stimulus from a nerve
• Structurally, they have short dendrites and long axons
• These long axons branch repeatedly in the muscle
• The cell bodies of motor neurons may be in the CNS but they have long axons which form part of the PNS

Question 20

Describe the process of synaptic transmission.

Answer 20

• Neurons must transmit information both within the neuron and from one neuron to the next
• The dendrites receive the information and pass it along to the axon. Once the signal arrives at the axon, it is passed down its length as an electrical signal, this is known as an action potential
• Once the action potential arrives at the axon terminal, it needs to be transferred to another neuron or muscle tissue
• Consequently, it must cross a gap between the presynaptic neuron and post synaptic neuron which is called the synaptic gap
• In the axon terminal there are a number of sacs called synaptic vesicle
• These contain hundreds of chemical messengers called neurotransmitters. Once the action potential reaches the synaptic vesicles it causes them to release their neurotransmitters
• The neurotransmitters diffuse across the gap and bind to a receptor cell on the post synaptic neuron or effector.