Nervous Coordination

Question 1

What are the conditions of a neurone’s resting state?

Answer 1

It is positively charged on the outside and negatively charged on the inside, as there are more positive ions on the outside

Question 2

How is the resting potential maintained?

Answer 2

• The sodium-potassium pump moves sodium ions out the neurone, but as the membrane is not permeable to sodium, it doesn’t diffuse back in
• This creates a sodium ion electrochemical gradient, as it is more positive on the outside then the inside
• The sodium-potassium pumps also move potassium ions into the neurone, the membrane is permeable to potassium ions so potassium ions diffuse back out through potassium ion channels
• Resulting in the outside of the cell being positively charged compared to the inside

Question 3

What happens during the stimulation of cell membranes?

Answer 3

• Na⁺ ion channels in the cell membrane open
• Na⁺ ions flood into the neurone
• PD changes to be more positive on the inside

Question 4

What happens during depolarisation?

Answer 4

• If PD is above threshold value, then the membrane becomes depolarised
• More Na⁺ ion channels open and a sharp increase in PD occurs

Question 5

What happens during repolarisation?

Answer 5

• Na⁺ ion channels close and K⁺ ion channels open

- Na⁺ ions are transported back out of the neurone so PD is more negative

Question 6

What happens during hyperpolarisation?

Answer 6

• PD becomes slightly more negative than the resting potential
• It prevents the neurone from being re-stimulated instantly

Question 7

Why can’t neurone cell membranes get excited after an action potential?

Answer 7

• Due to the fact that the ion channels are recovering and can’t be opened. The period when both sodium and potassium ion channels are closed, it is called the refractory period

Question 8

How do action potentials have an all or nothing nature?

Answer 8

• Once the threshold is reached, an action potential will fire with the same change in voltage
• If the threshold is not reached, an action potential will not fire

Question 9

How do action potentials move along a neurone?

Answer 9

• Some sodium ions that enter diffuse sideways
• This causes sodium ion channels in the next region to open and sodium ions to diffuse into that region
• This causes a wave of depolarisation to travel across the neurone

Question 10

How does myelination affect the speed of conduction of action potentials?

Answer 10

• Depolarisation only happens at the nodes of Ranvier
• The neurone’s cytoplasm conducts enough electrical charge to depolarise the next node, in a process called sultatory conduction
• If unmyelinated, the action potential travels across the whole membrane and is slower than sultatory conduction

Question 11

How does axon diameter affect the speed of conduction of action potentials?

Answer 11

• The bigger the diameter, the quicker the speed of conduction because their is less resistance to the flow of ions
• Depolarisation is able to reach other parts of the neurone quicker

Question 12

How does temperature affect the speed of conduction of action potentials?

Answer 12

• As temperature increases, the speed of conduction increases because ions diffuse faster
• After 40℃, the proteins start to denature and the speed decreases

Question 13

What is a synapse?

Answer 13

• A junction between a pre-synaptic and post-synaptic neurone / effector cell

Question 14

What happens when an action potential reaches the end of a neurone?

Answer 14

• When an action potential reaches the end of a neurone, it causes neurotransmitters to be released into the synaptic cleft and diffuse to the post-synaptic membrane and bind to specific receptors
• Once the bind, they can trigger an action potential causing either muscle contraction of the secretion of a hormone
• Neurotransmitters are removed from the cleft so the response is not continuous

Question 15

Why are impulses unidirectional?

Answer 15

• The travel in one direction as the receptors are only found on the post-synaptic membrane

Question 16

How are nerve impulses transmitted across a cholinergic synapse?

Answer 16

• An action potential arrives at the synaptic knob of the presynaptic neurone, which stimulates voltage-gated calcium ion channels to open
• Calcium ions then diffuse into the synaptic knob, causing the synaptic vesicles to move to and fuse with the presynaptic membrane
• ## The vesicles release acetylcholine (ACh) into the synaptic cleft called exocytosis and diffuse across to bind to specific cholinergic receptors on the postsynaptic

Question 17

How are nerve impulses transmitted across a cholinergic synapse?

Answer 17

• An action potential arrives at the synaptic knob of the presynaptic neurone, which stimulates voltage-gated calcium ion channels to open
• Calcium ions then diffuse into the synaptic knob, causing the synaptic vesicles to move to and fuse with the presynaptic membrane
• The vesicles release acetylcholine (ACh) into the synaptic cleft called exocytosis and diffuse across to bind to specific cholinergic receptors on the postsynaptic membrane
• This causes sodium ion channels to open and release sodium ions into the postsynaptic knob causing depolarisation
• An action potential is generated if the threshold is reached
• ACh is removed from the synaptic cleft so the response does not keep happening. It is broken down by the enzyme acetylcholinesterase (AChE) and the products are reabsorbed by the pres-synaptic neurone

Question 18

What is a neurotransmitter?

Answer 18

• A chemical that allows an action potential to be transmitted across a synapse

Question 19

What do excitatory neurotransmitters do?

Answer 19

• They depolarise the postsynaptic membrane, making it fire an action potential if the threshold is reached

Question 20

What do inhibitory neurotransmitters do?

Answer 20

• They hyperpolarise the postsynaptic membrane, preventing it from firing an action potential

Question 21

What is spatial summation?

Answer 21

• When many neurones connect to one neurone
• The small amount of neurotransmitters released could be enough to trigger an action potential
• But if some of neurones release an inhibitory neurotransmitter then the total effect might result in no action potential

Question 22

What is temporal summation?

Answer 22

• When 2 or more nerve impulses arrive in quick succession from the same presynaptic neurone
• Therefore an action potential is more likely as more neurotransmitters are released into the synaptic cleft

Question 23

What is a neuromuscular junction?

Answer 23

• A synapse between a motor neurone and a muscle cell

- They use ACh which bind to nicotinic cholinergic receptors

Question 24

What are the differences between cholinergic synapses and neuromuscular synapses?

Answer 24

• The postsynaptic membrane has loads of folds that form clefts, which stores AChE
• The postsynaptic membrane has more receptors
• ACh is always excitatory, an action potential will normally trigger a response

Question 25

How do excitatory drugs affect synaptic transmission?

Answer 25

• Some drugs have the shape of the neurotransmitter so mimic their action to receptors so more receptors are activated eg, Nicotine
• Some drugs inhibit the enzyme that breaks down neurotransmitters, so more neurotransmitters are in the synaptic cleft binding to receptors eg, Nerve gases
• Some drugs stimulate the release of neurotransmitters from the presynaptic neurone so more receptors are activated eg, Amphetamines

Question 26

How do inhibitory drugs affect synaptic transmission?

Answer 26

• Some drugs block receptors so they can’t be activated, so fewer receptors are activated resulting in muscle failure/being paralysed eg, Curare
• Some drugs inhibit the release of neurotransmitters from the presynaptic neurone so fewer receptors are activated eg, Alcohol

Question 27

What are sensory neurones?

Answer 27

Neurones that carry nervous impulses from receptors to the CNS

Question 28

What are motor neurones?

Answer 28

Neurones that carry impulses from the CNS to the effector

Question 29

What are relay neurones?

Answer 29

• Intermediate neurones

- Receive impulses from the sensory neurone to the motor neurone

Question 30

What are dendrites?

Answer 30

Carry nervous impulse to the cell body

Question 31

What are axons?

Answer 31

Carry nervous impulses away from the cell body

Question 32

What are the nodes of Ranvier?

Answer 32

The gaps between the Schwann cells

Question 33

How does temperature affect the rate of transmission?

Answer 33

• It increases kinetic energy

- So ions move more quickly across the membrane

Question 34

What happens at a neuromuscular junction?

Answer 34

• An action potential arrives at the synaptic knob at the end of the motor neurone
• It depolarises the membrane of the synaptic knob causing Ca²⁺ ion channel to open + Ca²⁺ ions to diffuse in
• The conc starts to increase causing the vesicles to fuse with the presynaptic membrane and ACh is released (exocytosis)
• ACh binds to receptors on the postsynaptic membrane opening Na⁺ ion channels + they diffuse in and depolarise the membrane
• If threshold is reached and action potential is generated

Question 35

How is ACh removed from the synaptic cleft?

Answer 35

• AChE breaks down ACh

- The products are reabsorbed by the presynaptic neurone and reused to synthesise more ACh

Question 36

What is ACh?

Answer 36

Acetylcholine

Question 37

What is AChE?

Answer 37

Acetylcholinesterase

Question 38

Why is it important that ACh is removed?

Answer 38

• To stop any further action potential from being continuously generated in the postsynaptic cell

Question 39

What is a cholinergic synapse?

Answer 39

• A synapse between 2 neurones