✨Module 5: Neuronal communication Flashcards
Nervous transmission, synapses, brain, muscles, sliding filament model (80 cards)
1
Q
Dendrites conduct impulse …
Axons conduct impulse …
A
Towards the cell body.
Away from the cell body.
2
Q
Explain why the cell body in a neurone is important.
A
In their cytoplasm, there are lots of ER and mitochondria that produce neurotransmitters.
3
Q
State the order of transmission of an impulse around the body.
A
- Stimulus
- Receptor
- Integrating centre
- Effector
- Response
4
Q
What is the integrating centre?
A
Region in the brain, usually the hypothalamus, that signals part of the body to respond to stimuli.
5
Q
What is an effector?
A
Organ or cell that acts in response to a stimulus, like muscle or gland like the pancreas.
6
Q
What is the myelin sheath?
A
Made up of Schwann cells wrapped around the axon several times and is an electrical insulator. Allows electrical impulses to jump between the nodes of Ranvier on the axon. Travels down the axon faster than unmyelinated neurone.
7
Q
What is an energy transducer? Give an example.
A
A cell that converts energy from one form to another. Sensory receptor cells respond to stimuli like light and convert this to nervous impulses (generator potential) in sensory neurones. E.g. rod cell in eye respond to light and produces a GP.
8
Q
Facts about the 3 neurones?
A
Sensory - carry impulses from sensory organs to CNS, 1 short dendron, cell body in middle, 1 short axon.
Relay - carry impulses within CNS and connect sensory and motor neurones, nonmyelinated sheath.
Motor - carry impulses from CNS to effectors, 1 long axon, short dendrites, cell body at the end.
9
Q
Thermoreceptors detect …
Photoreceptors detect …
Mechanoreceptors detect …
Proprioceptors detect …
Chemoreceptors detect …
Nociceptors detect …
A
Change in thermal energy e.g.. in tongue.
Change in light energy.
Change in kinetic energy e.g. Pacinian corpuscle detects pressure.
Stretch in muscles.
Change in chemical energy e.g. in nose.
10
Q
Define stimulus.
A
A change in an organism’s environment that causes a response.
11
Q
MS is an autoimmune disease so …
A
Immune system mistakenly attacks healthy body tissue, leading to damaged myelin sheath and then axons, so impulse cannot reach the CNS/brain.
12
Q
Explain how Pacinian corpuscles are a transducer. What is their structure like?
A
Sensory receptors that only detect mechanical pressure so are mechanoreceptors. E.g. convert mechanical energy like touch into an electrical impulse.
Found on the skin in fingers and soles of feet.
They contain a sensory nerve ending, which is wrapped with connective tissue called lamellae.
13
Q
Explain what happens when a Pacinian corpuscle is stimulated.
A
- At resting potential, stretch-mediated Na channels in sensory neurone membrane are too narrow to allow Na to pass through. When pressure is applied, corpuscle changes shape and lamellae deform.
- The stretched membrane causes the stretch-mediated Na channels to open. Na+ diffuse into cell down a conc gradient, so more positive inside. Membrane becomes depolarised.
- This results in a generator potential as the pd in and out the membrane change. If it reaches threshold/becomes depolarised enough, it triggers an ACTION potential along the rest of the neurone to CNS.
14
Q
How do plants respond to stimuli?
A
Instead of producing nerve impulses, their receptor cells produce chemicals.
15
Q
What is pd in millivolts (mV) across the membrane when a neurone is polarised?
A
-70mV. This is at the RESTING POTENTIAL. Positively charged on outside and negative on the inside. Different charges mean there’s a pd/voltage across the membrane at its resting potential. It is maintained by sodium-potassium pumps and potassium ion channels in its membrane.
16
Q
What is the threshold potential in mV?
A
-55mV
17
Q
Pd across membrane when membrane of neurone is depolarised?
A
+30mV
18
Q
Explain what happens to sodium and potassium ions across a neurone cell membrane at the resting potential.
A
- Sodium-potassium pumps (by active transport) move 3 sodium ions out of the neurone for every 2 K+ ions moved in. ATP needed to do this.
- When the cell is at rest, most K+ channels are open, so they allow facilitated diffusion of K+ out of the neurone, down their conc gradient. Therefore the membrane is permeable to K+, so some diffuse back through the potassium ion channels.
- The sodium ion channels are closed at rest. So the membrane isn’t permeable to sodium so they can’t diffuse back in. This creates a Na+ electrochemical gradient as there’s more positive Na+ outside the cell than inside.
19
Q
A stronger stimulus means …
A
More frequent action potentials are generated. Change in voltage is the same.
20
Q
At resting potential which channels are open?
A
Sodium/potassium pump is always active, some K+ ion channels are open, Na+ channel CLOSED.
So sodium/potassium pump and potassium ion channels create and maintain resting potential, but not Na+ ion channels.
21
Q
What is an action potential?
A
Rapid change in voltage across AXON cell membrane that send an electrical impulse along axon.
Action potentials don’t overlap and are unidirectional as they have a refractory period - ion channels are recovering and can’t be made to open. No more Na+ can diffuse into neurone to fire another action potential.
22
Q
Explain what happens in a change in pd action potential graph.
A
- Resting potential.
- At the threshold of -55mV, stimulus triggers some voltage gated Na+ channels to open, so membrane more permeable to Na+. Na+ diffuse down electrochemical gradient into axon, making the inside less negative.
- DEPOLARISATION - more voltage gated Na+ channels open (positive feedback).
- REPOLARISATION - when peak pd reaches +30mV, voltage gated Na+ channels close and voltage gated K+ channels open. Membrane now more permeable to K+, so more K+ diffuse out of axon down the electrochemical gradient. (negative feedback) Inside of axon now becomes more negative.
- HYPERPOLARISATION - K+ channels are slow to close so lots of K+ ions diffuse out of axon. Inside axon becomes more negative than resting potential.
- REPOLARISED - Na+ channels are closed (so no more movement by facilitated diffusion), some K+ is opened and closed. The sodium/potassium pump causes Na+ to move out and K+ in, so the membrane returns to resting potential. Until membrane is excited by another stimulus.
23
Q
Explain what the refractory period is.
A
Time delay between one action potential and the next, occurs immediately after an action potential. Ion channels are recovering and can’t be made to open. Na+ channels are closed (so sodium can’t go into axon) during repolarisation. It makes sure action potentials don’t overlap and travel in one direction. It prevents another AP from being generated.
During this phase, Na+ channels are closed and K+ channels are open, sodium/potassium pump continues to work to ensure ions are correctly redistributed and resting potential is restored before another AP is generated.
24
Q
Absolute refractory period.
Relative refractory period.
A
Na+ channels are inactivated - ensures AP’S are unidirectional.
Na+ channels can open again if the stimulus is strong enough.
25
Explain what happens during a wave of depolarisation.
When an action potential happens, some Na+ that has entered the neurone diffuse sideways. This causes voltage gated Na+ channels in the next region to open and Na+ diffuse into that part. The electrical impulse propagates along the neurone.
26
What is saltatory conduction?
Action potential jumps from node to node due to myelin sheath. The neurones cytoplasm conducts enough electrical charge to depolarise the next node, rather than propagating continuously along the entire length of the axon.
Myelinated - some neurones have a myelin sheath surrounding the AXON that is an electrical insulator. Depolarisation only happens at nodes of Ranvier so much quicker conduction than non-myelinated.
27
Advantages of saltatory conduction?
=> Requires less energy as the action potential is regenerated only at the nodes of Ranvier, rather than along the entire length of the axon.
=> Increased speed.
28
Myelin sheath in CNS is formed from ...
Cells called oligodendrocytes.
29
Describe 2 factors that effect the speed of an action potential.
1. Bigger axon diameter - quicker conduction of action potentials as there's less resistance to flow of ions in cytoplasm.
2. Higher temperature - ions diffuse faster so faster impulse transmitted. Higher than 40 degrees C denatures the proteins (like Na+/K+ pump) and speed decreases.
30
What is a synapse?
The junction between 2 neurones. Impulses are transmitted across the synapse using neurotransmitters.
31
What is the synaptic cleft?
Gap that separates the axon of one neurone from the dendrite is the next neurone.
32
Presynaptic neurone is where …
Postsynaptic neurone is where …
Impulse has arrived.
Neurone that receives the neurotransmitter.
33
What is the synaptic knob?
Swollen end of presynaptic neurone that contains mitochondria and ER to manufacture neurotransmitters.
34
What is the role of synaptic vesicles?
They fuse with the presynaptic membrane and release their neurotransmitters into the synaptic cleft.
35
What are the neurotransmitter receptors?
Neurotransmitters bind to these in the postsynaptic membrane.
36
What are the two types of neurotransmitters and explain the difference.
Excitatory - result in depolarisation of postsynaptic neurone. If threshold is reached in postsynaptic membrane, action potential is triggered. E.g acetylcholine.
Inhibitory - result in hyperpolarisation of postsynaptic membrane. Prevents action potential being triggered. E.g GABA found in some synapses in the brain.
37
Explain how an impulse is transmitted across a synapse.
1. AP arrives at end of presynaptic neurone.
2. Depolarisation of presynaptic membrane causes voltage gated calcium ion channels to open, so calcium ions diffuse into presynaptic knob.
3. This influx of Ca2+ causes the cytoskeleton to move the synaptic vesicles to fuse with presynaptic membrane. So acetylcholine is released by exocytosis.
4. Acetylcholine diffuse down their conc gradient across the synaptic cleft.
5. Neurotransmitter binds to complementary cholinergic receptors on the postsynaptic membrane, causing voltage gated Na+ channels to open.
6. This causes depolarisation of post-synaptic membrane which may initiate an action potential if the threshold is reached.
38
What happens to the neurotransmitter/ACH that has been released into the synaptic cleft?
Acetylcholinesterase (ACHe) enzyme converts acetylcholine into choline and ethanoic acid, which diffuse back across synaptic cleft into presynaptic knob by endocytosis.
ATP released by mitochondria is used to recombine choline and ethanoic acid into acetylcholine. This is stored in synaptic vesicles for future use. Sodium ion channels close in the absence of acetylcholine in the receptor sites.
39
Give a benefit of recycling the neurotransmitter from the synaptic cleft.
The breakdown of acetylcholine prevents it from continuously generating an action potential in postsynaptic neurone.
40
Where are cholinergic synapses found?
In CNS and at neuromuscular junctions (where motor neurone meets muscle).
41
How do synapses ensure impulses are unidirectional?
Neurotransmitter receptors are only present on postsynaptic membrane.
Also only presynaptic neurones contain vesicles of acetylcholine.
42
Difference between synapse convergence and divergence.
Divergence - one presynaptic neurone to several postsynaptic neurones, resulting in a stimulus creating a number of different responses.
Convergence - several presynaptic neurones to 1 post synaptic neurone. Stimuli from different receptors interact to produce a single result.
43
What is temporal summation?
When a single presynaptic neurone releases neurotransmitters as a result of high frequency of action potentials/nerve impulses over a SHORT period. This builds up in the synapse until the quantity is sufficient to trigger an action potential.
44
What is spatial summation?
When lots of presynaptic neurones connect to 1 postsynaptic neurone. Each releases neurotransmitter which builds up to a high enough level in the synapse to trigger an action potential.
45
What is the ‘all or nothing’ law?
If stimulus isn’t strong enough, threshold isn’t reached so no AP.
46
The human nervous system consists of ...
=> Central nervous system - brain and spinal cord. We find relay neurones here.
=> Peripheral nervous system - all the nerves that connect the CNS to rest of body. These are sensory and motor neurones.
47
Explain the difference between the somatic and autonomic nervous system.
Somatic - under conscious control. Consists of sensory/motor/relay neurones. Carries impulses to skeletal muscles.
Autonomic - without conscious control, heart rate, peristalsis. carries impulses to glands, smooth muscle and cardiac muscle. It's divided into:
=> Sympathetic - controls fight or flight by controlling the release of adrenaline. Heart rate increases so more blood supply to respiring muscles so muscles will have more glucose and oxygen for respiration. Neurotransmitter is noradrenaline.
=> Parasympathetic - controls the relax and digest system. Neurotransmitter is acetylcholine.
48
Examples of sympathetic and parasympathetic stimulation?
Sympathetic - saliva production reduced, decreased urine secretion, peristalsis reduced.
Parasympathetic - saliva production increased, increased urine secretion, digestion increased.
49
Function of cerebrum.
Involved in conscious activities like vision, speech, memory. The cerebral hemispheres are joined together by nerve fibres called corpus callosum.
Has a thin outer layer called cerebral cortex that is highly folded to increase SA for lots of neurones to allow more complex behaviours. Beneath the cerebral cortex is 'white matter' which has lots of myelinated axons of neurones.
50
Function of hypothalamus.
Middle lower part of brain. Above pituitary gland. Involved in autonomic nervous system by controlling temperature and water balance, blood glucose conc.
Involved in homeostasis/releases hormones by monitoring the blood than flows through it, or stimulates pituitary gland to release hormones.
51
Function of pituitary gland.
Stores and releases hormones directly into bloodstream that regulate body functions. Below the hypothalamus. Divided into:
Anterior pituitary (front) : produces and release certain hormones like FSH in reproduction.
Posterior pituitary (back) - stores and releases hormones produced by the hypothalamus (e.g. ADH).
52
Function of cerebellum.
Below cerebrum and controls muscle coordination and balance, posture. This is voluntary.
53
Function of medulla oblongata.
Used in autonomic control such as heart rate, peristalsis. Found at base of brain and joins the spinal cord. The medulla contains 3 centres:
Cardiac centre - controls heart rate.
Vasomotor centre - controls blood pressure by controlling the contraction of smooth muscles in arteriole walls.
Respiratory centre - controls breathing rate
54
Define a reflex action.
INVOLUNTARY response to certain stimuli. Mostly go to spinal cord, sometimes to the unconscious part of brain like the medulla. It's a very fast response.
55
Why is moving hand away an example of a reflex action?
Rapid and automatic. It doesn't go to cerebrum so it's speedier.
56
The medulla is made up of what 2 parts?
Acceleratory centre - causes heart to speed up by sending impulses through sympathetic nervous system by the accelerator nerve.
Inhibitory centre - causes heart to slow down by sending impulses through parasympathetic nervous system along the vagus nerve.
Both centres are connected to the SAN by their nerves. These make up the autonomic nervous system.
57
What are chemoreceptors?
Detect changes in level of particular chemicals like CO2 in blood. They are found in aorta, carotid artery and medulla.
58
What are baroreceptors?
Detect blood pressure. They are present in aorta, vena cava and carotid arteries.
59
Why does high CO2 lead to low pH?
Carbonic acid is formed when CO2 reacts with water in the blood.
60
What happens during increased CO2 concentration in blood/decreased pressure in blood?
=> Increased stimulation of chemoreceptors and pressure receptors in aorta and carotid arteries (supply the head with oxygenated blood).
=> These receptors release nerve impulses that are sent to acceleratory and inhibitory centres.
=> Acceleratory centre in medulla sends impulses along the sympathetic neurones to the SAN.
=> Noradrenaline is secreted at the synapse with the SAN and it causes SAN to increase the frequency of the electrical waves across the atria and ventricles. This results in an increased heart rate.
Stress leads to release of adrenaline/noradrenaline, which increases the frequency of impulses from SAN.
61
What happens in decreased CO2 concentration in blood/increase in blood pressure?
=> Decreased stimulation of chemoreceptors/baroreceptors.
=> Reduction of nerve impulses to medulla oblongata, so reduces frequency of impulses sent to SAN by sympathetic pathway, heart rate decreases back to normal.
=> Inhibitory centre in medulla sends impulses along the parasympathetic neurones to the SAN.
=> Acetylcholine is secreted at the synapse with the SAN. This neurotransmitter causes the SAN to reduce the frequency of the electrical waves that it produces. This reduces the elevated heart rate towards the resting rate.
62
how does the body know whether to increase or decrease heart rate?
Lower frequency impulses activate the inhibitory centre to slow down the heart rate.
Higher frequency impulses activate the acceleratory centre to speed up the heart rate.
63
Define gland.
Group of cells that produces and releases one or more substances through secretion.
64
Which hormones increase heart rate?
Adrenaline, noradrenaline, thyroxine.
65
Which hormone decreases heart rate?
Acetylcholine in the parasympathetic nerves.
66
PAG: Investigating the effect of caffeine on human heart rate.
1. Use heart rate monitor to see the heart rates at rest.
2. Ask each individual to drink 200ml of caffeine and wait 15 minutes. Then record heart rate at rest.
3. Repeat the heart rate measurements every 15 minutes for 2 hours to show the duration for which caffeine has an effect on heart rate.
4. Present results on graph or table.
67
Skeletal muscle.
- Striated muscle
- Voluntary
- Regularly arranged so muscle contracts in 1 direction
- Rapid contraction
68
Cardiac muscle.
- Striated and myogenic
- Involuntary
- Cardiac muscle fibres are connected to each other via specialised connections called intercalated discs, resulting in simultaneous contraction.
- Fibres are branched and uninucleated.
- Lots of mitochondria in muscle fibres for produce ATP for contraction of heart.
69
Smooth muscle.
- Non-striated
- Involuntary
- No regular arrangement so cells can contract in different directions.
- Slow contraction speed
- Fibres are spindle shaped and uninucleated.
70
Structure of myofibrils.
- Cell surface membrane = sarcolemma.
- Cytoplasm = sarcoplasm.
- Endoplasmic reticulum = sarcoplasmic reticulum.
Sarcoplasm contains mitochondria to produce ATP.
The membranes of the SR contain protein pumps that transport calcium ions into the lumen of the SR. Myofibrils are in the sarcoplasm and made up of:
=> Thick filaments called myosin
=> Thin filaments called actin
Parts of myofibril:
=> H band has only myosin filaments found in centre of dark band. When muscle contracts, H zone decreases.
=> I band has actin filaments
=>A band has areas where only myosin filaments are present and areas where myosin and actin filaments overlap.
=> M line is attachment for myosin filaments
=> Z line is attachment for actin filaments. found as centre of each light band. The distance between adjacent Z lines is called a sarcomere. when muscle contracts, sarcomere shortens.
=> Sarcomere is the section of myofibril between two Z lines.
Light bands - region where actin and myosin filaments don't overlap. Known as I bands.
Dark bands - presence of thick myosin filaments overlapping with actin. Known as A band.
71
Myosin structure
Myosin filaments have globular heads that are hinged which allows they to move back and forwards. On the head is the binding site for actin and ATP.
ATP is required to break the actin-myosin bridges. Move vesicles to reabsorb Ca2+ back into sarcoplasmic reticulum.
72
Actin structure.
Actin filaments have binding sites for myosin heads: actin-myosin binding sites.
In relaxation, these sites are blocked by presence of tropomyosin protein which is held in place by troponin. So actin can't bind to myosin and filaments can't slide past each other.
73
Sliding filament model for muscular contraction.
During contraction, myosin filaments pull actin filaments inwards towards centre of sarcomere. Results in:
A band doesnt change
I band gets narrower
Z lines move closer together, shortening the sarcomere
H zone disappears
=> Dark band stays same as the myosin filaments haven't shortened.
74
Transmission along a neuromuscular junction.
1. Neuromuscular junctions are located between a neurone and muscle cell. Striated muscle contracts when it receives an impulse from motor neurone.
2. When an impulse travelling along the axon of a motor neurone arrives at the presynaptic membrane, the action potential causes calcium ions to diffuse into the presynaptic neurone.
3. This stimulates vesicles containing acetylcholine to fuse with the presynaptic membrane.
4. ACh diffuses across the synaptic cleft and binds to receptor proteins on the sarcolemma.
5. This stimulates Na+ ion channels in the sarcolemma to open, allowing sodium ions to diffuse in, resulting in depolarisation.
6. Action potential passes down the T-tubules towards the centre of the muscle fibre.
7. These action potentials cause voltage-gated calcium ion channel proteins in the membranes of the sarcoplasmic reticulum (which lie very close to the T-tubules) to open.
8. Calcium ions diffuse out of the sarcoplasmic reticulum and into the sarcoplasm surrounding the myofibrils.
9. Ca2+ ions bind to troponin molecules, stimulating them to change shape.
10. Myosin-binding sites are exposed to the actin molecules. The process of muscle contraction can now begin.
75
How is muscular contraction stopped?
ACHe enzyme present in the synaptic cleft breaks down the acetylcholine into choline and something else. Ca2+ are also pumped back into the SR once the sarcolemma, T tubules and SR are no longer polarised.
76
Why does muscular contraction require ATP?
Energy is required for movement of myosin heads
Required to break actin-myosin bridge
ATP is also needed for active transport of Ca2+ back into sarcoplasmic reticulum to reset myosin head.
ATP is needed to break bond/cross-bridge between actin and myosin (1); if no ATP available actin
remains bonded to myosin (1); filaments remain in contracted state / filaments can’t slide back to
original position.
ATP binding allows myosin to detach from actin and ATP hydrolysis allows the myosin heads to return to their original shape.
77
Compare cholinergic synapse and neuromuscular junction.
Cholinergic - acetylcholine is neurotransmitter, found between neurones, can be excitatory or inhibitory, stimulated by AP on presynaptic membrane.
Neuromuscular - acetylcholine is neurotransmitter, found between motor neurone and muscle, only excitatory, stimulated by AP on presynaptic membrane.
78
Why is it beneficial that sprinters have high levels of creatine phosphate?
During a sprint, muscles work so hard oxygen cannot be replaced as quickly as it is used up. Aerobic respiration alone can’t be used/anaerobic respiration required (1); creatine phosphate is a source of phosphate (1); the more creatine phosphate, the more ADP can be phosphorylated (1); muscles can perform at maximum rate for longer.
79
What is creatine phosphate?
Stored in muscle and used to phosphorylate ADP to ATP. Makes ATP rapidly but creatine phosphate is used up quickly. When muscle is relaxed, creatine phosphate is replenished using phosphate from ATP.
80
: Muscles do not contract as much (1); as fewer calcium ions released into
sarcoplasm/from sarcoplasmic reticulum (1); fewer calcium ions bind to troponin (1); less troponin
moves/pulls tropomyosin.
