Neurons + synaptic transmission

Question 1

What are neurons?

Answer 1

Cells that are specialised to carry neural information around the body. Typically consist of a cell body, dendrites and an axon.

Question 2

Journey of impulse

Answer 2

dendrites
cell body
axon +myelin sheath

Question 3

Journey of electrical impulse

Answer 3

At one end of the neuron- dendrites receive signals from other neurons and sensory receptors.
Connected to the cell body, the control centre of the neuron.
From the cell body, the impulse is carried up the axon and it reaches the axon terminal.
The myelin sheath surrounds the axon and allows the nerve impulses to transmit more rapidly. (If damaged the impulse slows).

Question 4

Purpose of neurons

Answer 4

Neurons are for communicating messages around the nervous system.
They transmit signals electrically (within cells) and chemically (between cells).

Question 5

Electrical transmission

Answer 5

Action potential- when the charge within a cell changes. This causes an electrical impulse to travel along the axon.

Question 6

Chemical transmission

Answer 6

Allows neurons to communicate with each other by releasing neurotransmitters (chemical) into the synaptic cleft between them.

Question 7

Sensory neuron: features

Answer 7

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CELL BODY/ SOMA: the ‘brain’ of the cell. Contains the nucleus of the cell + genetic information.

AXON: the main component that carries impulses AWAY from the soma. Covered in segments of myelin sheath.

MYELIN SHEATH: a spiral of fatty tissue that protect and insulate the axon (speeds up electrical transmission).

NODES OF RANVIER: the gaps between myelin sheath that force an impulse to ‘jump’ the gaps, therefore speeding up.

DENDRITES: branches that protrude from the soma. Carry nerve impulses from neighbouring neurons TOWARDS the soma.

TERMINAL BUTTONS: at the end of the axon/ dendrites and communicate with the next neuron in the chain across the synapse.

Question 8

Sensory neuron

Answer 8

These carry messages from the PNS to the CNS. They have long dendrites and short axons.

Question 9

Relay neuron

Answer 9

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

Question 10

Motor neuron

Answer 10

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

Question 11

Neurotransmitter

Answer 11

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

Question 12

Outline how excitation and inhibition are involved in synaptic transmission.

Answer 12

Neurotransmitters can be excitatory or inhibitory. Excitation occurs when a neurotransmitter increases the positive charge of the postsynaptic neuron, which increases the likelihood that the neuron will fire an electrical impulse.
Inhibition occurs when a neurotransmitter increases the negative charge of the postsynaptic neuron which limits a neuron firing.
These charges are summed (summation) and the net effect is either excitatory (more likely to fire) or inhibitory (less likely to fire).

Question 13

Process of synaptic transmission.

Answer 13

1. Electrical impulse travels along presynaptic neuron and reaches the synaptic terminal.
2. Triggers movement of vesicles towards synaptic cleft.
3. Impulse reaches end of neuron and triggers release of neurotransmitters-diffusion.
4. neutransmitters taken up by postsynaptic receptor sites (dendrites)