Unit 8- Nervous Coordination

Question 1

What is a neurone and what does it do?

Answer 1

A neurone is one nerve cell. Neurones carry electrical impulses called action potentials.

Question 2

Structure of a neurone

Question 3

Role of the dendrites?

Answer 3

Where the action potential starts. Intermediate neurone synapse here. Carry action potentials to the cell body.

Question 4

Role of the cell body?

Answer 4

Contains the cell’s organelles. Neurotransmitters are made here.

Question 5

Role of the axon?

Answer 5

Long fibre which carries action potentials away from the cell body to the terminal.

Question 6

Role of the Myelin Sheath?

Answer 6

Made of Schwann cells, with membranes rich in myelin. Speeds up the conduction of the action potential.

Question 7

Role of the node of Ranvier?

Answer 7

Gaps between Schwann cells where there is no Myelin Sheath.

Question 8

Role of the axon terminal?

Answer 8

The end of the axon. Effectors synapse here.

Question 9

How is a resting potential maintained?

Answer 9

The sodium potassium pump actively transports 3 sodium ions out of the neurone and 2 potassium ions into the neurone.
The membrane is more permeable to potassium ions than sodium ions.
There is a higher concentration of potassium ions inside and higher concentration of sodium ions outside the neurone.
The membrane is polarised, there is more positive charge outside the cell than inside creating a resting potential of about -70mV.

Question 10

Action potential graph

Question 11

Steps of the formation of an action potential?

Answer 11

When the neurone is stimulated the voltage gated sodium ion channels open.
Sodium ions diffuse into the axon down their concentration gradient causing depolarisation.
More voltage gated sodium ion channels open and if threshold is reached, the neurone depolarises to about +40mV.
The sodium ion channels then close preventing sodium ions entering the axon and potassium ion channels open.
Potassium ions diffuse out causing the neurone to become too negative. This is called hyperpolarisation.
Potassium ion channels close and the sodium potassium pump returns the neurone back to resting potential.

Question 12

What is the refractory period?

Answer 12

The time during which no new action potentials can be generated. This is due to the sodium ion channels staying closed, so no more sodium ions can diffuse in.

Question 13

Where is the refractory period on the graph?

Answer 13

Over the whole thing

Question 14

What are the 3 reasons why refractory periods are important?

Answer 14

1. So action potentials move in one direction
2. Produces discrete impulses (separate)
3. Limits the maximum frequency of action potentials

Question 15

What is the all or nothing principle?

Answer 15

An action potential is only produced if the threshold is reached. All - if threshold is reached you get an action potential which is always the same size or nothing - if threshold is not reached there will be no action potential.

Question 16

How does the brain stimulate the strength of a stimulus?

Answer 16

The stronger the stimulus the greater the frequency of action potentials.

Question 17

Propagation of an action potential on an Unmyelinated neurone?

Answer 17

1. An action potential occurs at a section of the axon membrane
2. The membrane adjacently in front of the action potential detects the depolarisation and adjacent voltage gated sodium ion channels open, also forming an action potential.
3. The action potential moves forward. The refractory period behind the action potential prevents the impulse being conducted backwards.

Question 18

Propagation of an action potential along a myelinated neurone?

Answer 18

1. The myelin insulates the axon (preventing ion movements)
2. Depolarisations only take place at the nodes of Ranvier so the action potentials ‘jump’ from node to node. This is known as saltatory conduction.
3. Therefore there are less depolarisations along the whole length of the axon membrane.

Question 19

What are 3 ways you can speed up the conduction of action potnetials?

Answer 19

1. Myelination allows saltatory conduction
2. A higher temperature increases the kinetic energy of ions so they diffuse faster through the membrane
3. A greater axon diameter reduces resistance to ion flow.

Question 20

Diagram of a pre-synaptic and post-synaptic neurone?

Question 21

Role of the synaptic vesicle?

Answer 21

Contains neurotransmitters

Question 22

Role of the calcium ion channel?

Answer 22

Takes Ca2+ into the presynaptic neurone which causes the synaptic vesicle to fuse with the presynaptic membrane

Question 23

Role of the mitochondria?

Answer 23

Provides the energy/ATP for the re-uptake and reformation of neurotransmitter

Question 24

Role of the synaptic cleft?

Answer 24

Space between neurones which neurotransmitter diffuses across

Question 25

Role of the neurotransmitter receptor?

Answer 25

Neurotransmitter binds to these, to either cause or inhibit action potentials in post synaptic neurone

Question 26

Role of the neurotransmitter re-uptake pump?

Answer 26

Allows neurotransmitter to be reabsorbed back into the presynaptic neurone by active transport preventing further action potentials.

Question 27

Steps of the transmission of an impulse across a Cholinergic synapse?

Answer 27

1. an action potential depolarises the pre-synaptic membrane, voltage gated calcium ion channels open and calcium ions diffuse in 2. calcium ions cause synaptic vesicles to fuse with the pre-synaptic membrane and release Acetylcholine into the synaptic cleft 3. acetylcholine diffuses across the synaptic cleft and binds to receptors on the post-synaptic membrane 4. sodium ion channels open and sodium ions diffuse into the post-synaptic neurone, depolarising the post-synaptic membrane causing an action potential (if the threshold is reached) 5. acetylcholinesterase hydrolyse the acetylcholine. the sodium ion channels close and no more action potentials are generated 6. the products of hydrolysis are taken back into the pre-synaptic neurone via active transport using the neurotransmitter re-uptake pump.

Question 28

What can summation be used for?

Answer 28

To increase the neurotransmitter in the synaptic cleft to increase the depolarisation of the post-synaptic membrane, so threshold is reached.

Question 29

What is spatial summation?

Answer 29

More than one pre-synaptic neurone connected to one post-synaptic neurone.

Question 30

What is temporal summation?

Answer 30

Repeated action potentials arrive in short time from one presynaptic neurone to provide enough neurotransmitter to reach threshold in the post synaptic neurone.

Question 31

Synapses have unidirectionality, what is this?

Answer 31

Action potentials travel in one direction across the synapse, from pre-synaptic neurone to post-synaptic neurone.

Question 32

Explain how synapses have unidirectionality?

Answer 32

-Neurotransmitter only released from/store in the presynaptic neurone -Receptors only on post-synaptic membrane

Question 33

Describe the effect of chloride ion channels opening and explain how this leads to synapse inhibition?

Answer 33

Chloride ions diffuse in and make the post-synaptic membrane more negative (hyper polarised). More sodium ions need to diffuse in to reach threshold for an action potential.

Question 34

Diagram of a neuromuscular junction?

Question 35

Describe how the action potential crosses the neuromuscular junction?

Answer 35

1. nerve impulses depolarise the presynaptic membrane and calcium ion channels open 2. calcium ions diffuse into the presynaptic neurone causing synaptic vesicles to fuse with the presynaptic membrane 3. acetylcholine is released into the synaptic cleft and diffuses across 4. acetylcholine binds receptors on sarcolemma 5. sodium ion channels open and sodium ions diffuse into muscle fibre causing depolarisation of the sarcolemma

Question 36

Similarity between a neuromuscular junction and a cholinergic synapse?

Answer 36

Both use acetylcholine as the neurotransmitter which is broken down by acetylcholinesterase

Question 37

Differences between a neuromuscular junction and a cholinergic synapse?

Answer 37

Cholinergic synapse: -neurone to neurone -can be excitatory or inhibitory -no cleft in post synaptic membrane -less ACh receptos on post synaptic membrane Neuromuscular junction: -neurone to muscle fibre -only excitatory -contains clefts in muscle fibre membrane which store acetylcholinesterase -more ACh receptors on muscle fibre

Question 38

Definition of a motor unit?

Answer 38

All the neuromuscular junctions from a single motor neurone. When a motor unit is activated, all of the connected muscle fibres contract at the same time.

Question 39

Defintion of an electrochemical gradient?

Answer 39

A concentration gradient of ions. The amount of diffusion depends not only on the concentration of ions but also the difference in electrical charge (how positive or negative it is).