Nervous Coordination and muscles Flashcards
1
Q
How is a Resting Potential maintained?
A
- The negative resting membrane potential is created and maintained by increasing the concentration of positive ions outside the cell relative to inside the cell.
- The negative charge within the cell is created by the cell membrane being more permeable to potassium ion movement than sodium ion movement - potassium diffuses out of the cell at a much faster rate than sodium leaks in.
- Because more cations are leaving the cell than are entering, this causes the interior of the cell to be negatively charged relative to the outside of the cell.
2
Q
What is membrane potential?
A
The difference in total charge between the inside and outside of the cell is called the membrane potential.
3
Q
What is resting potential?
A
A neuron at rest is negatively charged: the inside of a cell is approximately 70 millivolts more negative than the outside.
4
Q
How is an Action Potential generated?
A
- The soma end of the axon becomes depolarized
- A nerve impulse is caused by energy from a stimulus causing sodium voltage-gated ion channels to open, which causes sodium ions to flow in down their electrochemical gradient, this alters the p.d across the membrane
- This causes more sodium ion channels to open and more sodium ions to diffuse at that location - causing the membrane to depolarise causing the inside to be net positive and the outside to net negative
- This causes nearby sodium ion channels to open causing the depolarisation to move along the membrane - this is an action potential
5
Q
How is the resting potential restored after an action potential is generated?
A
- Voltage-gated sodium channels close and voltage gates potassium channels open, this allows rapid flow of K+ ions out of the cell
- The outward diffusion causes a temporary overshoot of the electrical gradient - hyperpolarisation.
- Potassium ion channels close and sodium-potassium pumps cause sodium ions to move out and potassium moving in - the resting potential reached (repolarisation)
6
Q
Refractory Period:
A
Once an action potential has been created in any region of an axon, sodium ion channels close preventing the inward movement of sodium ions and a further action potential cannot be created.
7
Q
Why is the refractory period important?
A
- Impulse is unidirectional - prevent impulses going in both directions
- Discrete impulses are sent, one doesn’t run into the other
- In certain time periods, the number of impulses are limited in a certain number
8
Q
Why do Myelinated sheaths lead to faster impulses?
A
- Acts as an electrical insulator, preventing action potentials from forming.
- This means action potentials occur at the nodes of Ranvier (which are breaks in the myelinated sheaths)
- This allows Action Potentials to effectively jump from one node to another - Saltatory conduction
- Action potential passes along faster in a myelinated neurone than in an unmeylinated neurone - depolarisation has to occur along the whole axon
9
Q
How does a synapse work:
A
- An action potential arrives at the synaptic Knob. Depolarisation of the synaptic knob leads to opening CA2+ channels and CA diffuses into the synaptic knob
- Vesicles containing neurotransmitters move towards and fuse with the pre-synaptic membrane.
- Neurotransmitter is released to the synaptic cleft
- Neurotransmitters diffuse, down a concentration gradient, across the synaptic cleft, to the post-synaptic membrane, neurotransmitter binds to complementary of shapes to receptors on the surface of the post-synaptic membrane,
- NA+ ion channels of the postsynaptic membrane open and Na+ diffuses in; if enough neurotransmitter, then enough Na+ diffuses in, above the threshold and the post-synaptic neuron becomes depolarised
- The neurotransmitter is degraded and released from the receptor; the Na+ channels close and the post-synaptic neurone can re-establish resting potential; the neurotransmitter is transported back into the presynaptic neurone.
10
Q
Spatial summation:
A
many different pre-synaptic neurones attaching to one synapse and one post-synaptic neurone, so multiple quantities of neurotransmitters are being released so they can reach the threshold
11
Q
Temporal summation:
A
only one neuron releases neurotransmitters repeatedly over a short period of time to add up to enough to exceed the threshold value.
12
Q
Inhibition:
A
Inhibitory synapses cause chloride ions to move into the postsynaptic neurone and potassium ions to move out
13
Q
How do inhibitory synapses work?
A
- The pre-synaptic neurone releases a neurotransmitter that binds to chloride ion protein channels on the postsynaptic neurone.
- The neurotransmitter causes the chloride ions protein channels to open
- Chloride ions move into post-synaptic neurone by facilitated diffusion.
- The binding of neurotransmitters causes the opening of nearby potassium protein channels
- Potassium ions move out of the post-synaptic neurone into the synapse
- The combined effect of negatively charged chloride ions moving in and positively charged potassium ions moving out is to make the inside the postsynaptic membrane more negative and the outside more positive
- The membrane potential increases this is called hyperpolarisation
14
Q
Cholinergic synapse:
A
Neurotransmitter - acetylcholine
Enzyme - acetylcholinesterase breaks down acetylcholine into choline and acetate
15
Q
What are the 3 main types of muscles?
A
1cardiac muscles - found exclusively in the heart,
-smooth muscle - found in the walls of blood vessels and gut (both not in conscious control)
-skeletal muscle - makes up the bulk of body molecules in vertebrates, is attached to bone and acts under voluntary, conscious control.
16
Q
What are myofibrils?
A
Individual muscles comprise millions of muscle fibres
17
Q
What is in large concentration in the sarcoplasm?
A
sarcoplasm is a large concentration of mitochondria and endoplasmic reticulum.
18
Q
What are myofibrils made out of ?
A
two types of protein filament: Actin - which is thinner and consists of two strands twisted around one another. Myosin - which is thicker and consists of long rod-shaped tails with bulbous heads that project to the side.
19
Q
What are the characteristics of Actin?
A
which is thinner and consists of two strands twisted around one another. (little balls)
20
Q
What are the characteristics of Myosin?
A
which is thicker and consists of long rod-shaped tails with bulbous heads that project to the side.
21
Q
Why do myofibrils appear stripped?
A
- appear stripped due to their alternating light-coloured (I[sotropic] bands) and dark-coloured (A[nistropic] bands).
22
Q
What is in the centre of each A band?
A
- is a lighter-coloured region called the H-zone.
23
Q
What is in the centre of each I band?
A
Z-line.
24
Q
What is the distance between the adjacent Z lines called?
A
sarcomere.
25
What are some characteristics of slow-twitch fibres?
- contract more slowly
- Provide less powerful contractions but work over time = adopted to endurance with
- Adapted for aerobic respiration by having a large store of myoglobin which stores oxygen and rich supply of vessels, large number of mitochondria for ATP - avoid buildup of lactic acid
26
What are some characteristics of fast-twitch fibres?
- contract more rapidly and produce powerful contractions but only for a short period = adapted to intense exercise like weightlifting
- Are adapted for intense activity: thicker and more numerous myosin filaments, high conc of glycogen, high conc of enzymes used in anaerobic respiration,
store of phosphocreatine which can rapidly convert ATP from ADP in anaerobic conditions - provide energy for contraction
27
Skeletal muscles act in _________ when one contacts the other relaxes
antagonistic pairs
28
What happens when a muscle contracts?
more overlap of action did myosin
I band becomes narrower
The Z line moves closer together
H-zone becomes narrower
A band remains the same width
29
How does the sliding filament mechanism of muscle work?
- bulbous head of the myosin filaments form cross-bridges with actin by attaching to binding sites - pulling on actin filaments
- Using ATP as a source of energy to detach
30
What happens in muscle stimulation?
- An action potential reaches neuromuscular junctions, causing calcium ion protein channels to open - calcium ions diffuse into the synaptic knob
-The calcium ions cause the synaptic vesicles to fuse with the presynaptic membrane and release their acetylcholine into the synaptic cleft
-Acetylcholine diffuses across the synaptic cleft and binds with receptors on the muscle cell-surface membrane, causing it to depolarise.
31
What is muscle contraction?
-The action potential travels into T tubules
-Calcium ions are released from sarcoplasmic reticulum into sarcoplasm.
-Calcium ions cause tropomyosin molecules that were blocking actin binding sites to pull away allowing myosin binding sites to be accessible
-ADP and Pi molecules are attached to myosin heads mean they can bind to actin filaments and form actinmyosin cross-bridge
-Once attached to the actin filament, myosin heads change their angle, pulling the actin filament along as they do so (powerstroke) and releasing a molecule of ADP and Pi
- An ATP molecule attaches to each myosin head, causing it to change shape slightly and become detached from actin filaments
- The calcium ions then activates enzyme ATPase (found in sarcoplasm), hydrolyses ATP to ADP - provides energy for myosin head to return its original position
- Myosin head, once more with an attached ADP + pi molecule, then attaches itself further along the actin filaments and the cycle is repeated as long as the calcium ion concentration remains high and ATP is present
- When nervous stimulation stops, calcium ions are actively transported back into sarcoplasmic reticulum, causing tropomyosin to move back
32
What is the role of phosphocreatine?
- (stored in muscles) assists this process by providing phosphate to regenerate ATP from ADP
33
What is the role of ATP in muscle contraction?
-To break actinomysoin bridges (detach or attach myosin and actin)
- To bend the myosin head so that action filaments are moved inwards
- For active transport of calcium ions back into sarcoplasmic reticulum when nerve stimulation stops
34
What is the role of glycogen granules in skeletal muscles?
- As a store of glucose that can be hydrolysed to glucose
- The glucose is used as a respiratory substrate to provide the ATP needed
35
What is the role of calcium ions in the contraction of a myofibril?
-When an action potential reaches the muscle fibre, calcium ions are released from the sarcoplasmic reticulum and diffuse into the myofibrils
- The calcium ions bind to tropomyosin, causing it to move and expose the binding sites on the actin filament
- With these sites now accessible, the myosin heads attach to actin, forming actinomyosin cross bridges
36
What is the neuromuscular junction?
Connects a neurone to a muscle allowing muscles to contract when it receives an impulse through the neuromuscular junction
37
How do neuromuscular junctions work?
- An action potential reaches the presynaptic membrane of the motor neurone
-Calcium ion channels open and calcium ions diffuse into the presynaptic neurone.
- This influx of calcium ions triggers vesicles containing the neurotransmitter acetylcholine to fuse with the pres-synaptic membrane, releasing ACH into the neuromuscular junction
- The ACH diffuses across the junction and binds to receptor proteins on the sarcolemma, the muscle fibres surface membrane
This binding causes sodium ion channels in the sarcolemma to open, allowing sodium ions to diffuse in
- This depolarises the membrane and creates an action potential that moves down the T-tubules towards the centre of the muscle fibre
- These action potentials prompt the opening of voltage-gates calcium ion channels in the membranes of the sarcoplasmic reticulum situated near the T-tubules
- As a result, calcium ions diffuse out of the sarcoplasmic reticulum and into the sarcoplasm around the myofibrils
38
Sacromere:
functional unit of myofibril defined as the region between 2 z lines. It contains overlapping actin and myosin filaments.
39
Sarcolemma
plasma membrane of muscle fibre - conducts electrical impulses to trigger contract and maintain ion balance
40
Sarcoplasmic reticulum
a specialised form of smooth endoplasmic reticulum that surrounds myofibrils - stores and releases calcium ions
41
Sarcoplasm
cytoplasm of muscle containing organelles, enzymes and myoglobin needed for energy production
42
Neuromuscular Junction are only _______ whereas Cholinergic synapses could be excitatory or __________
a. excitatory
b. inhibitory
43
Is neuromuscular the end point for an action potential?
true
44
Cholinergic synapse causes a new action potential is generated in the next neurone
yes
45
Why is phosphocreatine important?
Phosphocreatine can be stored in muscles - used to generate ATP
46
How does phosphocreatine form ATP ?
Phosphocreatine is hydrolysed(releases energy) by creatine kinase to release phosphate and can form ATP from ADP released from myosin heads
47
Describe how sarcolemma is depolarised ?
neurotransmitters diffuse down synaptic cleft, this causes na+ ion channels to open and na+ to move in to sarcoplasm causing it to be depolarised - down a concentration gradient
48
How does depolarisation spread to sarcoplasmic reticulum?
- Action potential is transmitted through the sarcolemma to sarcoplasmic reticulum
49
How are calcium ions released from the sarcoplasmic reticulum?
- T-tubules are connected to sarcoplasmic reticulum
- calcium ion channels open and calcium ions diffuse down a conc gradient from sarcoplasmic reticulum
50
How is the binding of calcium ions similar to non-competitive enzyme inhibition?
- in both cases, a susbstance binds to binding site and alters tertiary structure
51
What is the role of tropomyosin in muscular contraction?
- tropomyosin covers myosin binding sites on actin when not contacting
- calcium ions cause topomoysin to reveal binding sites
52
What causes the release of myosin heads from actin?
- binding of atp - causes myosin to detacg
53
What is the importance of the enzyme ATPase for muscular contraction?
enabling mysoin heads to re-attach to any actin further along filaments
