M5C13

Question 1

What is the resting potential of a neuron and how is it maintained?

Answer 1

Resting potential is -70mV. It is maintained by the sodium-potassium pump which actively transports 3 Na⁺ out and 2 K⁺ in creating a charge difference across the membrane.

Question 2

What happens during depolarisation?

Answer 2

Voltage-gated Na⁺ channels open Na⁺ rushes in down electrochemical gradient, increasing + charge inside axon.

Question 3

What is hyperpolarisation?

Answer 3

After the action potential diffusion of K+ out causes inside to become more negative than resting potential.

Question 4

Describe repolarisation in a neuron.

Answer 4

Once membrane potential reaches +40mv, VG Na⁺ channels close, VG K⁺ channels open and K+ ions diffuse out - inside of axon goes from + to -.

Question 5

What is the ‘All or Nothing’ principle in neural transmission?

Answer 5

An action potential only occurs if the threshold is reached. Below -55mV = no action potential; above = full action potential.
-AP size remians the same despite size of stimulus.

Question 6

What is the role of the Pacinian corpuscle?

Answer 6

It detects pressure. Pressure deforms the membrane opens stretch-mediated Na⁺ channels, which cause the inside of the axon to become depolarised.

Question 7

What is the refractory period and its significance?

Answer 7

It’s a short period after an action potential where the neuron can’t be re-stimulated. It ensures one-way transmission and limits action potential frequency

Question 8

How does myelination affect the speed of nerve impulses?

Answer 8

Myelinated axons allow saltatory conduction (jumping between nodes of Ranvier) which is much faster than continuous conduction in unmyelinated axons.

Question 9

What is saltatory conduction?

Answer 9

It’s the jumping of action potentials from node to node where the whole axon isn’t depolarised in myelinated neurons increasing transmission speed.
-Requires less ATP
-Faster in neurones with a wider axon = less resistance.

Question 10

What are the advantages of myelination?

Answer 10

Faster transmission of nerve impulses, energy efficiency (less ATP needed)

Question 11

What happens at a synapse when an action potential arrives?

Answer 11

It triggers the opening of Ca²⁺ channels in the pre-synaptic membrane, Ca²⁺ enters and causes vesicles to move to and fuse with pre-p membrane.

Question 12

What does acetylcholine do at the synapse?

Answer 12

It binds to receptors on the post-synaptic membrane causing Na⁺ channels to open and trigger a new action potential in the next neuron.

Question 13

How is acetylcholine removed from the synapse?

Answer 13

It’s broken down by acetylcholinesterase in the synaptic cleft. The products are reabsorbed into the pre-synaptic neuron and recycled.
-Hydrolyses acetylcholine into chlorine and ethanoic acid.

Question 14

Why is neurotransmitter removal from the synapse important?

Answer 14

It prevents continuous stimulation of the post-synaptic neuron and allows the synapse to reset.

Question 15

What are the three main functions of synapses?

Answer 15

1. Ensure transmission takes place in one direction only
2. Allow summation (temporal or spatial)
3. Filter out low-level stimuli by requiring a threshold potential.

Question 16

What is temporal summation?

Answer 16

When a single pre-synaptic neuron releases neurotransmitter multiple times over a short period, combining to reach the threshold in the post-synaptic neuron.

Question 17

What is spatial summation?

Answer 17

When multiple pre-synaptic neurons release neurotransmitters at the same time to reach threshold in a single post-synaptic neuron.

Question 18

What is the purpose of inhibitory synapses?

Answer 18

They reduce the likelihood of an action potential by opening Cl⁻ or K⁺ channels causing hyperpolarisation of the post-synaptic membrane.

Question 19

How does GABA function at inhibitory synapses?

Answer 19

GABA binds to receptors causing Cl⁻ ions to enter and K⁺ ions to leave the post-synaptic neuron. This hyperpolarises the post-synaptic neurone = less likely an AP is generated.

Question 20

How is the nervous system organized?

Answer 20

CNS: Brain and spinal cord
PNS: Somatic (voluntary) and Autonomic (involuntary)
Autonomic: Sympathetic (fight/flight) and Parasympathetic (rest/digest)

Question 21

What is the role of the cerebrum?

Answer 21

Coordinates voluntary responses receives sensory input.

Question 22

What does the cerebellum control?

Answer 22

Coordinates movement and balance

Question 23

What functions does the medulla oblongata serve?

Answer 23

Controls non-skeletal muscle activity like breathing rate and heart rate

Question 24

What is the hypothalamus responsible for?

Answer 24

Homeostasis regulation e.g. temperature

Question 25

What is the reflex arc and why is it important?

Answer 25

A rapid involuntary response to a stimulus. Helps protect the body from harm by bypassing the brain for faster reaction.

Question 26

How does the knee jerk reflex work?

Answer 26

Tapping below the kneecap stretches the tendon → triggers sensory neuron → motor neuron → contracts quadriceps causing leg extension.

Question 27

How does the blinking reflex work?

Answer 27

Stimulus (e.g. bright light) → sensory neuron → relay neuron in brain → motor neuron → blink

Question 28

What are skeletal muscles and their characteristics?

Answer 28

Attached to bones - voluntary control

Question 29

What are cardiac muscles and their characteristics?

Answer 29

Found in the heart - involuntary

Question 30

What are smooth muscles and their characteristics?

Answer 30

Found in hollow organs e.g. intestines

Question 31

How is heart rate controlled by the autonomic nervous system?

Answer 31

Via the medulla oblongata: Sympathetic nervous system increases heart rate by sending signals via the SAN to the accelerator nerve; Parasympathetic nervous system decreases heart rate by sending signals via the SAN to the Vagus nerve.

Question 32

What do chemoreceptors monitor and where are they located?

Answer 32

Monitor CO₂, found in the aorta and carotid arteries.

Question 33

How do chemoreceptors influence heart rate when CO₂ levels increase?

Answer 33

Increased CO₂ → decreased blood pH → chemoreceptors detect change → Medulla sends impulses via sympathetic neurons to increase heart rate.

Question 34

What happens when CO₂ levels return to normal?

Answer 34

Impulses sent via parasympathetic neurons to decrease heart rate.

Question 35

What do baroreceptors detect and where are they found?

Answer 35

Detect changes in blood pressure. Found in the aortic and carotid arteries.

Question 36

What happens when blood pressure increases?

Answer 36

Baroreceptors detect stretch → medulla sends parasympathetic impulses to SAN → Heart rate decreases to reduce pressure

Question 37

What happens when blood pressure decreases?

Answer 37

Baroreceptors send impulses to increase heart rate via sympathetic nervous system

Question 38

What is the neuromuscular junction?

Answer 38

A synapse between a motor neuron and muscle fiber where acetylcholine is released to trigger contraction.

Question 39

What events occur at the neuromuscular junction to cause muscle contraction?

Answer 39

Action potential → Ca²⁺ channels open → Ca²⁺ enters → Vesicles release acetylcholine → binds to receptors → Na⁺ channels open → depolarization → muscle action potential

Question 40

What role does the sarcoplasmic reticulum play in muscle contraction?

Answer 40

Releases Ca²⁺ ions when depolarized → Ca²⁺ binds to troponin → tropomyosin moves → exposes myosin binding sites on actin

Question 41

How does the sliding filament theory explain muscle contraction?

Answer 41

1. Myosin binds actin; 2. Power stroke uses ATP; 3. ATP binds to detach myosin; 4. ATP hydrolyzed to recock myosin; 5. Cycle repeats

Question 42

What changes occur in the sarcomere during contraction?

Answer 42

Z-lines move closer; I-band and H-zone narrow; A-band remains constant; Overall sarcomere shortens

Question 43

Why is ATP essential for muscle contraction?

Answer 43

Powers myosin head movement; Allows detachment of myosin; Re-cocks myosin head; Pumps Ca²⁺ back into sarcoplasmic reticulum

Question 44

What is phosphocreatine and its function?

Answer 44

A high-energy compound in muscles that regenerates ATP quickly from ADP used during short bursts of intense activity.