Chapter 6- Neurons And Synapses

Question 1

What are the two systems in the body that are used for internal communication ?

Answer 1

Endocrine system

Nervous system

Question 2

What does the endocrine system consist of?

Answer 2

Glands that release hormones

Question 3

What does the nervous system consist of?

Answer 3

Nerve cells called neurons

Question 4

Explain the parts of a neuron

Answer 4

1) have a cell body with cytoplasm and a nucleus
2) dendrites
3) axons
4) skeletal muscle

Question 5

What are the functions of dendrites?

Answer 5

Short branches nerve fibres, used to transmit impulses between neurone in one part of the brain or spinal cord

Question 6

What are axons? /functions

Answer 6

Are elongated nerve fibres, they transmit impulses from tips of toes or the fingers to the spinal cord

Question 7

What does the myelination of nerve fibres allow for?

Answer 7

Saltatory conduction

Question 8

What is saltatory conduction?

Answer 8

There is gap between the myelin deposited by adjacent Schwann cells and these are called the node of ranvier- in myelinated nerve fibres the nerve impulse can jump from one node of ranvier to the next

Question 9

Why do neurons pump sodium and potassium ions across there membranes?

Answer 9

To generate a resting potential

Question 10

What is a resting potential

Answer 10

A neuron that is not transmitting a signal has a potential difference or voltage across its membrane that is called a resting potential

Question 11

What is the resting potential due to?

Answer 11

An imbalance of positive and negative charges across the membrane

Question 12

explain the process of a resting potential

Answer 12

1) sodium potassium pumps transfer (Na+) and potassium (K+) ions across the membrane - sodium pumped in, potassium pumped out- number of ions pumped are unequal 3:2
2) membrane is 50 times more permeable to potassium so it leaks back in quicker then sodium and the result is a concentration gradient steeper than the potassium gradient

Question 13

What does an action potential consist of?

Answer 13

Depolarisation and repolarisation of the neuron

Question 14

What is an action potential?

Answer 14

An action potential is a rapid change in membrane potential, consisting of two phases-

1) depolarisation- a change from negative to positive
2) repolarisation- opposite

Question 15

What is depolarisation due to in an action potential due to?

Answer 15

Is due to the opening of sodium channels in the membrane allowing sodium ions to diffuse into the neuron down the concentration gradient- reverses the charge imbalance

Question 16

What is repolarisation due to in an action potential due to?

Answer 16

Happens rapidly after repolarisation and is due to the closing of sodium channels and opening of potassium channels - this allows potassium to diffuse out of the neuron- which makes inside of cell negative again and make sit go back to resting potential

Question 17

What is a nerve impulse?

Answer 17

Is an action potential that starts at one end of a neuron and is then propagated along the axon to the other end of a neuron

Question 18

How does the propagation of thre action potential begin?

Answer 18

Because the ion movements that depolarise one part of the neuron triggers depolarisation in the neighbouring part of the neuron

Question 19

Why do nerve impulses only happen in one direction in humans?

Answer 19

Because an impulse can only be initiated at one terminal of a neuron and can only be passed on to another neuron or deifferent cell types at the other terminal

Question 20

What is the propagation of an action potential due to?

Answer 20

Movement of sodium ions - leads to reduced sodium conc outside axon and increased inside- the depolarised part of the axon therefore has different sodium ion concentrations to the neighbouring part of the axon that has not yet depolarised - result is sodium ions diffuse between these regions both inside and out

Question 21

What do local currents do?

Answer 21

Reduce the concentration gradient in the part of the neuron that has not yet been depolarised - makes resting potentials rise - Sodium gates are voltage- gated and open when a membrane potential of -50mV has been reached (resting is -70mV) - opening of sodium gates causes depolarisation

Question 22

What are synapses?

Answer 22

Junctions between neurons and between neurons and receptors or effector cells

Question 23

What is a neurotransmitter?

Answer 23

Chemicals that are used to send signals across synapses

Question 24

What happens when pre-synaptic neurons are depolarised X?

Answer 24

They release a neurotransmitter into the synapse

Question 25

Explain the 9 step synaptic transmission

Answer 25

1) nerve impulse is propagated along pre-synaptic neuron until it reaches end of the neuron
2) depolarisation of pre-synaptic membrane causes calcium ions to diffuse through channels into neuron
3) influx of calcium causes vesicles containing neurotransmitter to move to the pre-synaptic membrane and fuse with it
4) neurotransmitter is released by exocytosis
5) neurotransmitter diffuses along synapse and binds to receptors on post synoatic membrane
6) binding of neurotransmitter causes adjacent sodium ions channels to open
7) sodium ions diffuse down conc gradient
8) action potential is triggered in post synoatic membrane
9) neurotransmitter is rapidly broken Down
8

Question 26

What is acetylcholine ?

Answer 26

Is used as the neurotransmitter in many synapses

Question 27

When is a nerve impulse only initiated?

Answer 27

If the threshold potential is reached

Question 28

Why is an actio potential only initiated if the threshold potential is reached?

Answer 28

Because only at this potential do voltage gated sodium Open, causing depolarisation

Question 29

What do neutrons do?

Answer 29

Transmit electrical impulses