Pack 19 Flashcards
1
Q
Give an example of hormonal communication?
A
Blood glucose concentration.
2
Q
What chemical is used to stimulate target cells in the nervous system?
A
Neurotransmitters.
3
Q
Describe the difference in how communication occurs in the hormonal and nervous system.
A
- Chemicals called hormones.
* Action potentials/nerve impulses and neurotransmitters
4
Q
What carries the “signal” in both the hormonal and the nervous system?
A
- Blood system.
* Neurones.
5
Q
Which transmission is more rapid, hormonal or nervous?
A
Nervous
6
Q
Describe three differences in the RESPONSE to the hormonal system and the nervous system.
A
- Hormonal response - widespread, slow, long-lasting
* Nervous Response - localised, rapid, short-lived.
7
Q
Where do hormones travel compared to nerve impulses? Therefore how is the response to hormones specific?
A
• All parts of the body (but only target cells respond). Nerve impulses travel to specific locations.
8
Q
What is a neurone?
A
• A specialised cell adapted to rapidly carrying electrochemical changes called nerve impulse from one part of the body to another.
9
Q
Describe the structure of a motor neurone. (6)
A
- A call body - containing all the usual organelles.
- Dendrons - extensions of the cell body which subdivide into dendrites.
- An axon - a single long fibre that carries the nerve impulse away from the cell body.
- Schwann cells - surround the axon - electrical insulation. Carry out phagocytosis. They wrap themselves around the axon many times - layers of their membranes.
- Myelin sheath - forms covering of the axon - made up of Schwann cell membranes.
- Nodes of Ranvier - gapes between Schwann cells. 2-3μm. very 1-3mm in humans
10
Q
What do dendrons and dendrites do?
A
Carry the nerve impulse towards the cell body.
11
Q
What are neurones with a myelin sheath called?
A
Myelinated Nerone.
12
Q
What is the role of Schwann cells? (3)
A
- Protect the axon providing electrical insulation.
- Carry out phagocytosis (removal of cell debris)
- Nerve regeneration.
- Form myelin sheath.
13
Q
Name the three types of neurone.
A
- Sensory
- Motor
- Intermediate
14
Q
What is the role of a sensory neurone?
A
Transmit nerve impulses from a receptor to an intermediate or motor neurone.
15
Q
Describe the basic structure of a sensory neurone.
A
• One long dendron that carries the impulse towards the cell body and an axon that carries it away.
16
Q
What is the role of a motor neurone?
A
• Transmit nerve impulses from n intermediate neurone to an effector, gland or muscle. Long axon short dendrites.
17
Q
What is the role of an Intermediate neurone/relay neurone?
A
• Transmit impulses between neurones e.g. from sensory to motor. They have numerous short processes.
18
Q
Define nerve impulse.
A
A self-propagating wave of electrical activity that travels along the axon membrane.
19
Q
What are the two states of a neurone membrane. In terms of nerve impulse.
A
- Resting potential
* Action potential.
20
Q
Give three ways in which the movement of ions across the axon plasma membrane is controlled.
A
- Phospholipid bilayer prevents sodium and potassium ions diffusing across it.
- Cannel proteins - some are gated ie. can be opened and closed - facilitated diffusion. Some remain open all the time.
- Carrier proteins - active transport. Na+/K+ pump.
21
Q
By what process do ions move through channel proteins?
A
Facilitated diffusion.
22
Q
By what process do ions move through carrier proteins such as the sodium-potassium pump?
A
Active transport.
23
Q
Why does the cell body of a motor neurone contain a large rough endoplasmic reticulum.
A
Production of neurotransmitters (proteins)
24
Q
What is the resting potential of humans usually? Which side of the membrane is negatively charged?
A
65mV - meaning the inside of the axon is negatively charged.
25
During resting potential (65mV) what is the neurone membrane said to be?
Polarised
26
Describe how a resting potential is achieved. (4)
* 3Na+ ions actively transported OUT and 2K+ ions IN TO the axon by the Na+/K+ pump.
* Outward movement of sodium ions is greater than the inward movement of potassium so more Na+ in the tissue fluid than the axon and more potassium ions in the cytoplasm.
* Electrochemical gradient.
* Most of the potassium channels are open and most of the sodium ones are closed.
27
What is an action potential? What causes an action potential?
* The temporary reversal of charges either side of the axon membrane.
* A stimulus of sufficient size is detected by a receptor.
28
What happens to the membrane potential during an action potential?
• The membrane potential difference changes from around -65mV (negative inside) to +40mV (+ve inside).
29
What is the part of the axon said to be during the temporary reversal of charges?
Depolarised.
30
Why does depolarisation occur? (1)
Channels in the axon membrane change shape and hence open or close, depending on the voltage across the membrane.
31
What are the channels that change shape due to voltage called?
voltage-gated
32
Describe the sequence of events of the depolarisation of the membrane of the axon. (7)
1. at resting potential some K+ voltage gated channels are open (permanently). Na+ ones are closed.
2. Energy of the stimulus causes some Na+ voltage-gated to open therefore Na+ diffuse in along the electrochemical gradient.
3. This causes a reverse in the potential across the membrane.
4. As Na+ diffuse in more Na+ channels open so even more Na+ diffuse in.
5. Once the action potential is around +40mV the voltage gates on the Na+ channels close and K+ ones open.
6. With K+ now open the electrical gradient preventing further outward movement of K+ is now reversed, more K+ open. More K+ diffuse out. Repolarisation.
7. Outwards diffusion of K+ causes temporary overshoot of potential = hyper polarisation. The K+ ion gates now closed the pump restores resting potential.
33
What happens to an action potential once it has been created?
It moves rapidly along the axon.
34
How can an action potential be described in terms of depolarisation? What is the stimulus for each next portion of the axon?
* A traveling wave of depolarisation.
| * The depolarisation of the previous region.
35
Why can an action potential be likened to a Mexican wave?
• Nothing actually moves all along the axon - each action potential causes the next section to depolarise. Like the passage of a Mexican wave.
36
Describe the passage of an action potential along an unmyelinated axon. (5)
1. Resting potential - polarised.
2. Stimulus causes sudden influx of Na+ - reversal of charge of membrane - depolarised.
3. Localised electrical currents established bu influx of Na+ cause opening of Na+ V- gated channels a little further along - depolarisation in this region.Behind this new region the Na+ gates close and K+ ones open. K+ begin to leave.
4. Propagated in the same way along the axon - membrane behind the action potential is repolarised.
5. Repolarisation allows Na+ to be actively transported back out - ready for new action potential.
37
Does the size of the action potential change along the axon?
No
38
What does the myelin sheath do in terms of action potentials?
Prevents them from forming at this part of the axon membrane.
39
Where can action potentials occur on myelinated axons?
The nodes of Ranvier
40
What is the effect of myelination on the passage of an action potential? What is this type of conduction called?
* Localised circuits arise between adjacent nodes of the Ranvier
* Saltatory conduction
* passes faster than an unmyelinated axon
41
Why does an action potential pass faster along a myelinated axon?
• Depolarisation of the membrane only has to occur at each node rather than along the entire length of the axon membrane.
42
What is the transmission of an action potential along the axon known as?
Nerve impulse
43
Which three factors affect the speed at which an action potential travels?
* Myelination
* Diameter of axon
* Temperature
44
Why does myelination affect the speed at which an action potential travels?
* Insulator
* Action potentials can't form between nodes.
* Saltatory conduction.
* 30ms⁻¹ to 90ms⁻¹
45
Why does the diameter of the axon affect the speed at which an action potential travels?
Greater the diameter the greater the conductance. Due to less leakage of ions from a large axon (leakage makes membrane potentials harder to maintain)
46
Why does the temperature of the axon affect the speed at which an action potential travels? (4)
* Affects rate of diffusion of ions therefore the higher the temperature the faster the nerve impulse.
* Energy for active transport comes from respiration.
* Respiration controlled by enzymes
* Enzymes function more rapidly at higher temps until a point.
* At high temps enzymes and membrane will denature therefore no action potential.
47
Describe the all-or-nothing principle. (3)
* There is a certain level of a stimulus known as the threshold value which triggers an action potential.
* Below this value, any stimulus, whatever size, no action potential is generated.
* Any stimulus, whatever size, above this value will generated an action potential of the same size.
48
Why can't the strength of a stimulus be detected using one action potential?
All action potentials are roughly the same size. Only threshold value has to be crossed.
49
How can an organism perceive the size of a stimulus through nerve impulses?
* The frequency of impulses. Larger stimulus higher frequency.
* Different neurones with different threshold values. the brain interprets the number and type of neurones that pass impulses as a result of a given stimulus.
50
What is the refectory period?
The period after an action potential has been created in one specific region of the axon when inward movement of Na+ can't happen because voltage -gated channels are shut. Therefore no action potential can be created.
51
Why can't an action potential be created during the refectory period?
• Na+ voltage-gated channels are closed.
52
What are the three purposes of the refectory period?
* It ensures that action potentials are propagated in one direction only.
* Produces discrete impulses.
* It limits the number of action potentials in a given time.
53
What is the significance of limiting the number of action potentials that can be propagated in a given time due to the refectory period?
• Limits the strength of stimulus that can be detected.
54
What is the significance of producing discrete impulses?
Ensures action potentials are separated from one another.
55
Why can is it that action potentials are propagated in one direction only? Why is this important? (3)
* refectory period
* The region behind the action potential is repolarising so can't depolarise.
* So impulses don't spread out in both direction, act like valves.
56
What is a synapse?
Where one neurone communicates with another or an effector.
57
how do synapses transmit information from one neurone to another?
Neurotransmitters.
58
What is the gap between neurones called?
Synaptic cleft
59
What is the neurone that releases the neurotransmitter called? What is the swollen end of this neurone known as?
* Presynaptic neurone
| * Synaptic knob
60
Which organelles are found in large quantities/size in the synaptic know? Why?
Mitochondria and endoplasmic reticulum - manufacture of neurotransmitters/formation of vesicles
61
What are neurotransmitters stored in in the synaptic knob?
Synaptic vesicles
62
Why can synapses only pass information on one direction? (2)
* Only the presynaptic nurse contains nueronetransmitter.
| * Only the post synaptic membrane contains receptor binding sites.
63
Why might low frequency action potentials not lead to the formation of an action potential in the postsynaptic neurone?
• Not sufficient neurotransmitters is released to produce an excitatory post synaptic potential.
64
Name the two types of summation and how they work in producing a new action potential.
* Spatial - a number of different presynaptic neurones synapse with one postsynaptic neurone - together they release enough neurotransmitter to exceed the threshold value and trigger an action potential
* temporal - A single presynaptic neurone releases neurotransmitter many times over a short period. If the conc. exceed the threshold value a new action potential is produced in the postsynaptic neurone.
65
What is the name of a synapse that makes it less likely a new action potential will be produced?
Inhibitory synapse
66
How do inhibitory synapses function? (8) (2 effects)
* Presynaptic neurone releases a neurotransmitter that binds to chloride ion channels on the postsynaptic neurone.
* neurotransmitter causes Cl⁻ channels to open.
* Cl⁻ move into the postsynaptic neurone by facilitated diffusion
* Binding of neurotransmitter causes the opening of nearby K+ channels.
* K+ move out of postsynaptic neurone into synapse.
* Combined effect makes the inside of the postsynaptic neurone more negative.
* Membrane potential increases to as much as -80mV - hyper-polarisation.
* Less likely a new action potential will be created because a larger influx of Na+ is needed to produce one.
67
What are the function of synapses? (2)
* Single impulse along one neurone can initiate new impulses in a number of different neurones. Single stimulus can produce multiple responses.
* A number of impulses can be combined at a synapse. Nerve impulses from receptors reacting to different stimuli to contribute to a single response (summation).
68
What are synapses they produce new action potentials in the postsynaptic neurone called?
Excitatory synapses.
69
What is a cholinergic synapse.
The neurotransmitter is acetylcholine.
70
What is acetylcholine made up of?
* Acetyl (ethanoic acid)
| * choline.
71
Where do cholinergic synapses often occur?
In vertebrates, CNS and at neuromuscular junctions.
72
Describe transmission across a cholinergic synapse in 7 steps.
1. Arrival of action potential at the presynaptic neurone causes Ca²⁺ protein channels to open and Ca²⁺ to enter by facilitated diffusion.
2. Influx of Ca²⁺ causes synaptic vesicles to fuse with the presynaptic membrane - releasing acetylcholine into the cleft.
3. ACh diffuses across the cleft quickly and binds to the receptor sites on Na⁺ channels in the postsynaptic neurone membrane.
4. Causes Na⁺ channels to open allowing Na⁺ to diffuse in rapidly along conc. grad.
5. Generates a new action potential.
6. Acetylcholinesterase hydrolyses ACh into its components which diffuse back across the cleft - recycling. This also prevents it from continuously generating new action potentials. Discrete transfer.
7. ATP used to recombine choline and acetyl. Stored in synaptic vesicles. Na+ channels close.
73
Why is the synaptic cleft narrow?
So neurotransmitter diffuses across quickly
74
What is the purpose of acetylcholinesterase working rapidly? (2)
* Recycling of choline and ethanoic acid.
| * Prevents action potentials being continuously sent.
75
What are the three types of muscle found in the body? Where are they found? Which I under conscious control?
* Cardiac - heart only
* Smooth - walls of blood vessels and gut.
* Skeletal muscle - attached to bone.
Skeletal is under voluntary conscious control.
76
How much force does each myofibril produce relatively.
Very little. But together they can produce large forces.
77
How are myofibrils arranged? Where are they found?
Parallel to each other . Many are found in one muscle fibre.
78
How are the the bundles of muscle fibres arranged?
Parallel to each other in groups forming whole muscles.
79
What would be the problem if muscle fibres were made up of individual muscle cells joined end to end?
Where adjacent cells would join would be a weakness. Would reduce the overall strength.
80
What is the structure of a muscle fibre (single fibre)? What problem does this overcome? How is this created?
Several cells are fused together into a fibre. They share they same sarcoplasm and nuclei.
81
What is the cytoplasm of muscle cells called?
Sarcoplasm
82
What organelles are there a large amount of in muscle fibres?
Mitochondria and endoplasmic reticulum
83
Describe the gross and microscopic structure of a muscle.
* Whole muscle contains many
* Bundles of muscle fibres, contain
* many muscle fibres.
* Contain many Myofibrils. made up of actin and myosin
84
What is the structure of a myofibril?
Hexagonal arrangement of thick and thin filaments. The thick filaments are made up of many myosin molecules. The thin filaments are made up of actin molecules.
85
What types of protein filament make up myofibrils? What is the structure of each protein?
Actin - thinner, two strands twisted around one another.
| Myosin - thicker, long rod shaped with bulbous heads that project to the side.
86
Why do myofibrils paper striped?
The alternating light and dark patterns (where myosin and actin filaments overlap)
87
What are the light bands in a myosin filament called? What causes them to be light?
* Isotropic bands (I bands)
| * Thick and thin filaments do not overlap.
88
What are the dark bands in a myosin filament called? What causes them to be dark?
* Anisotropic bands (A bands)
| * Thick and thin filaments overlap.
89
What is the name of the lighter-coloured region at the centre of the A-band? Why is it lighter?
* H-zone
| * Only the myosin filaments are found here. It is in-between actin filaments.
90
What is the name of the line at the centre of each I band called?
z-line
91
Other than actin and myosin, what is an important protein found in muscle? Where does it form?
* Tropomyosin
| * Forms fibrous strands around actin.
92
What is an individual unit of a myofibril called? (Z line to Z line)
Sarcomere
93
What are the two types of muscle fibre?
* Slow-twitch
| * Fast-twitch
94
Give 3 differences between how fast-twitch and slow-twitch muscle fibres act.
```
Slow-Twitch:
• contract more slowly
• Less powerful contractions.
• Over a longer period of time
Fast-Twitch:
• contract more rapidly
• more powerful contractions.
• Over a shorter period of time
```
95
Give an example of a type of exercise fast-twitch and slow-twitch muscle fibres would be used in.
* Slow-Twitch - marathon
| * Fast - weight lifting
96
Which muscles are fast-twitch and slow-twitch muscle fibres more common in and why?
* Slow-Twitch - e.g. calf, to maintain upright position.
| * Fast - biceps - short bursts of intense activity
97
What type of respiration are fast-twitch and slow-twitch muscle fibres adapted to? Why?
* Slow-Twitch - aerobic - so lactic acid doesn't build up over long periods of time
* Fast - anaerobic
98
Give three ways in which slow-twitch fibres are adapted to their function.
* A large store myoglobin (a bright red molecule that stores oxygen)
* Rich blood supply to deliver oxygen and glucose for aerobic respiration.
* Numerous mitochondria to produce ATP
99
What is myoglobin?
A molecule that stores oxygen in slow-twitch muscle fibres.
100
Give four ways in which fast-twitch fibres are adapted to their function.
* Thicker and more numerous myosin filaments.
* High concentration of glycogen.
* High concentration of enzymes involved in anaerobic respiration.
* Store of phosphocreatine - molecule that can rapidly generate ATP from ADP in anaerobic conditions.
101
What is phosphocreatine?
A molecule that can rapidly generate ATP from ADP in anaerobic conditions.
102
What is a neuromuscular junction?
The pain where a motor neurone meets a skeletal muscle fibre.
103
What would happen if there were only one neuromuscular junction along a muscle fibre?
It would take time for a wave of contraction to travel across the muscle in which can all the fibres would not contract simultaneously and movement would be slow.
104
What are all the muscles fibres supplied by a single motor neurone called?
A motor unit
105
What is the advantage of having separate motor units in muscles each supplied by a different motor neurone?
* Gives control over the force required.
* Greater force required - more motor units stimulated.
* Less force required - less units stimulated.
106
What happens when a nerve impulse arrives at the neuromuscular junction? (not including muscle contraction details) (transmission across synapse) (5 steps)
* Synaptic vesicles fuse with the presynaptic membrane.
* Release acetylcholine which diffuses to the post synaptic membrane (muscle fibre membrane)
* Bind to sodium ion channels causing Na+ iones to diffuse rapidly into the muscle fibre.
* Depolarising the membrane.
* Leads to muscle contraction
* Acetylcholine broken down by acetylcholinesterase.
107
What provides the energy to recombine ethnic acid and choline
ATP
108
What are the similarities between a neuromuscular junction and a cholinergic synapse? (4)
* Both have neurotransmitters transported by diffusion
* Have receptors, that on binding of the neurotransmitter cause an influx of na+ ions.
* Use Na+/K+ pump to depolarise the axon.
* Use enzymes to breakdown the neurotransmitter.
109
What are the differences between a neuromuscular junction and a cholinergic synapse? (5)
* Neuromuscular junction is only excitatory. Cholinergic synapse may be excitatory or inhibitory.
* Neuromuscular junction links neurone to muscles. Cholinergic synapse links neurone to neurone or neurone to other effector organs
* Neuromuscular junction - only motor neurones. Cholinergic synapse - motor sensory or intermediate.
* Neuromuscular junction - action potential ends here. Cholinergic synapse - new one may be created.
* Acetylcholine binds to muscle fibre membrane rather than post-synaptic neurone membrane.
110
Explain how the contraction of skeletal muscles brings about movement.
* Attached to bones which are incompressible.
* Muscle exerts a force, via tendons an the bone moves rather than changing shape.
* Different parts of the skeleton move relative to each other around joints.
111
How do two muscles work together to move a limb for example? Why is it like this?
* Antagonistically
| * Muscles can only pull not push
112
How does skeletal muscle occur?
IN antagonistic pairs. When one is contracted the other is relaxed
113
What is the process involving actin and myosin sliding past one another called?
The sliding filament mechanism
114
According to the sliding filament mechanism will there be more or less overlap of the thick and thin filament in a contracted muscle than in a relaxed one?
More
115
What changes occur to the sarcomere when a muscle contracts? (3) What does not change, why? (1)
* I-band becomes narrower
* Z-lines move closer together - the sarcomere shortens
* The H-zone becomes narrower.
• A-band stays the same size - because the A-band corresponds to the myosin filaments and these have not shortened.
116
How do we know the filaments themselves do not shorten during muscle contraction?
the A-band stays the same size.
117
What are the two types of protein that myosin is made up of?
* A fibrous protein arranged into a filament made up of several hundred molecules.
* A globular protein formed into two bulbous structures at one end (the head)
118
What type of protein is actin and how are its molecules arranged?
* Globular
| * Long chains that are twisted around one another to form a helix
119
What structure does tropomyosin form and where?
• Long thin threads wound around actin.
120
How does the shape of myosin support the sliding filament mechanism?
• Bulbous head form cross bridges with actin filaments
121
How does myosin form cross bridges with actin filaments?
• Attach themselves to binding sites on actin and then flex in unison fallen the actin along the myosin.
122
What causes myosin heads to return to their original angle?
Hydrolysis of ATP
123
Describe how muscle is stimulated in 3 steps.
* Action potential arrives at neuromuscular junctions simultaneously causing calcium ion protein channels to open and calcium ions to diffuse in.
* Calcium ions cause synaptic vesicles to fuse with the presynaptic membrane and release ACh.
* ACh diffuses across cleft and binds to receptors on the muscle cell surface membrane. => depolarisation
124
How does the action potential travel deep into the muscle fibre?
A system of tubules (T-tubules) that are extensions of the CSM and branch throughout the sarcoplasm.
125
Describe how Ca²⁺ are released into the sarcoplasm one an action potential has travelled down the T-tubules. (3)
* Tubules are in contact with the sarcoplasmic reticulum which has actively transported Ca²⁺ ions in leaving a very low conc. in the sarcoplasm
* Action potential opens calcium ion protein channels o the endoplasmic reticulum so Ca²⁺ diffuse into the sarcoplasm (conc. gradient)
126
How is a low Ca²⁺ conc. achieved in the sarcoplasm.
Actively transported into the sarcoplasmic reticulum
127
What effect do Ca²⁺ ions have once they have diffused into the sarcoplasm?
They cause tropomyosin molecules that were blocking the binding site on the actin filament to pull away. So now myosin can bind
128
Why doesn't myosin bind to actin when the muscle is not being stimulated?
• Tropomyosin blocks the binding site.
129
Describe how muscle contracts. (From once tropomyosin has changed shape due to Ca²⁺) (6)
1. Myosin head attaches to binding site on the actin.
2. head of myosin changes angle moving the actin filament along.
3. ADP is released
4. ATP molecule fixes to myosin head, causing it to detach from actin filament.
5. Hydrolysis of ATP to ADP by ATPase provides energy for myosin to resume its normal position
6. head of myosin reattaches to a binding site further along. Cycle is repeated
130
When can myosin head bind to actin binding site?
When it is attached to an ADP molecule. (When tropomyosin changes shape also)
131
When does the cycle of sliding filaments repeat until?
• Until the Calcium ion concentration drops (it is actively transported back into the sarcoplasmic reticulum)
132
What effect does the movement of myosin heads have on actin filaments?
They are pulled closer together.
133
Describe muscle relaxation in 4 steps.
* When nervous stimulation ceases, Ca²⁺ are actively transported back into the sarcoplasmic reticulum using ATP
* Allows tropomyosin to block the actin filament again.
* Myosin heads are now unable to bind to actin filaments and contraction ceases.
* Antagonistic muscles can pull actin filaments out from between myosin.
134
What is the energy released from the hydrolysis of ATP used for in muscle contraction? (2)
* The movement of myosin heads.
| * The reabsorption of calcium ions into the sarcoplasmic reticulum
135
How is the phosphocreatine store replenished during relaxation?
Using phosphate from ATP
