3.4 The cells of the nervous system and neurotransmitters at synapses

Question 1

State 3 characteristics of neurons

Answer 1

They have a nucleus, cytoplasm and cell
membrane (cell body)
They have fibres called axons which carry nerve impulses away from the cell body
The have fibres called dendrites which carry nerve impulses towards the body.

Question 2

Describe the sensory neuron

Answer 2

Has dendrites in contact with sense organ receptors.
dendrites merge to form a myelinated dendron which carries impulses to the cell body.
Has a short axon which forms connections with inter
neuron.

Question 3

Describe the inter neuron.

Answer 3

Connects sensory neurons to motor neurons.
Very short and contained inside the CNS.
Many dendrites which form many complex connections.

Question 4

describe the motor neuron

Answer 4

Short dendrites which receive impulses from inter neuron.
Long myelinated axon which carries nerve impulses to effectors.

Question 5

what is the purpose of the myelin sheath?

Answer 5

Axons have myelin sheaths around them which insulate them and increase the speed of electrical impulse conduction. Produced by glial cells.

Question 6

what is myelination?

Answer 6

myelination is the development of myelin sheaths and continues from birth until adolescence. response to stimuli in the first 2 years of life are not as rapid or coordinated as an adult child.

Question 7

how do neurons connect with one and other and also muscle fibres.

Answer 7

Via the space between the axon ending of one neuron and the dendrite of another is called the synapse (synaptic cleft)

Question 8

How do electrical impulses cross between neurons?

Answer 8

Nerve impulses travel along the presynaptic neuron.
Vesicles containing the neurotransmitter move towards and fuse with the presynaptic membrane.
Neurotransmitter is released into the synaptic cleft and diffuses across it.
Neurotransmitter then binds to receptors on the membrane of the postsynaptic neuron,
If enough neurotransmitters bind, an impulse travels along postsynaptic neuron

Question 9

Why and how are the neurotransmitters removed from the synapse after the impulse is transmitted?

Answer 9

To prevent continuous stimulation of the postsynaptic neuron.
By the reuptake of the neurotransmitter by the presynaptic neuron.

Question 10

What is an excitatory signal?

Answer 10

causes an increase in action e.g., causes muscle to contract

Question 11

what is an inhibitory signal?

Answer 11

One which causes a decrease in action e.g., slowing of heart rate.

Question 12

what is an inhibitory signal?

Answer 12

One which causes a decrease in action e.g., slowing of heart rate.