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A Level Biology Year 1 > Chapter 15 - Nervous coordination and muscles > Flashcards

Chapter 15 - Nervous coordination and muscles Flashcards

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1
Q

Characteristics of the nervous system

A

Nerve cells transmit electrical impulses along their length
Impulse stimulates the secretion of neurotransmitters onto target cells
Short-lived, affect a small area

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2
Q

Characteristics of the hormonal system

A

Hormones transported in blood plasma to target cells

Slow, widespread, long-lasting effect

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3
Q

What is the cell body?

A

Contains organelles, produces neurotransmitters

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4
Q

What are dendrons?

A

Extensions of cell body
Divide into dendrites
Carry impulse TO cell body

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5
Q

What is an axon?

A

A long fibre that carries impulses FROM the cell body

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6
Q

Function of Schwann cells

A

Electrical insulation

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7
Q

Function of myelin sheath

A

Covers the axon

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8
Q

What are the nodes of Ranvier?

A

No myelin sheath

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9
Q

How is a resting potential established?

A

The phospholipid bilayer prevents Na+ and K+ ions passing through by simple diffusion
Channel proteins form a sodium-potassium pump - they actively transport sodium ions out of the axon and potassium ions in

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10
Q

How is the membrane polarised?

A

Na+ transported out
K+ transported in
3 Na+ out for every 2 K+ in
An electrochemical gradient is established - there are more Na+ ions in the tissue fluid around the axon and more K+ ions in the cytoplasm
Na+ diffuse back in and K+ diffuse out
The Na+ gates are closed but the K+ gates are open

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11
Q

How is the membrane depolarised and repolarised?

A

Some K+ gates are open but the Na+ gates are closed
The stimulus causes some Na+ gates to open so Na+ ions can diffuse into the axon
As more diffuse into the axon, more voltage gates open
At a limit, the gates close and the K+ gates open
This means K+ can diffuse out of the axon and causes more K+ gates to open - the membrane is repolarised
This action causes a temporary overshoot where the inside of the axon is more negative than the outside so the K+ gates close and Na+ is pumped in

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12
Q

Which three factors affect the speed of an impulse?

A

Temperature, diameter of the axon, myelin sheath

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13
Q

How does the myelin sheath impact the speed of the impulse?

A

Saltatory conduction (impulse jumps between nodes of Ranvier)

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14
Q

How does temperature impact the speed of an impulse?

A

Rate of diffusion of ions

Enzymes

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15
Q

How does the diameter of the axon impact the speed of an impulse?

A

Big diameter = less leakage = faster

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16
Q

What is the all-or-nothing principle?

A

Above the threshold value, an action potential is triggered

Below the threshold value, no action potential is triggered

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17
Q

What is the refractory period?

A

When an action potential is generated, there is a time delay when Na+ ions can’t enter the axon because the gates are closed

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18
Q

What are the three purposes served by the refractory period?

A

Limits the number of action potentials
Produced discrete impulses
Action potentials only go in one direction

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19
Q

How does an action potential pass alone the neurone?

A

Saltatory conduction

‘Jumps’ between unmyelinated nodes of Ranvier

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20
Q

How is the axon depolarised?

A

Sudden influx of Na+ ions

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21
Q

In what direction will muscles work?

A

They can only pull, not push

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22
Q

Why do skeletal muscles only work in antagonistic pairs?

A

The pairs work in opposite directions - when one is relaxed, the other contracts

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23
Q

Where will myofibrils be darker in colour?

A

Where the actin and myosin filaments overlap

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24
Q

What changes happen to the sarcomere when the muscle contracts?

A

The I-band becomes narrower
The sarcomere shortens
The H-zone becomes narrower

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25
What is myosin?
Made of the tail (fibrous proteins) and the head (bulbous structures)
26
What is actin?
A long, helical strand of protein
27
What is tropomyosin?
Wound around actin to block binding sites
28
What is the sliding filament theory of muscle contraction?
The layers of actin and myosin slide past each other to contract the muscle
29
How are muscles stimulated to contract?
An action potential reaches neuromuscular junctions Ca2+ protein channels open and Ca2+ diffuses into synaptic knob Ca2+ causes vesicles to release acetylcholine into the cleft Acetylcholine diffuses across the cleft and binds with receptors on neighbouring muscles, depolarising them
30
How do muscles relax?
Hydrolysis of ATP provides the energy to actively transport Ca2+ into the endoplasmic reticulum This makes tropomyosin block the binding sites again Myosin can't attach so muscles relax
31
What is energy needed for during muscle contraction?
Movement of myosin heads | Active transport of Ca2+
32
How is energy provided for muscle contraction?
ATP -> ADP
33
What does phosphocreatine do?
Acts as a source of phosphate Phosphate + ADP -> ATP Demand for oxygen outweighs supply - another way to form ATP must be used
34
How is the phosphate supply regenerated?
When muscle relaxes
35
How do muscles contract?
Action potential travels through T-tubules into endoplasmic reticulum Endoplasmic reticulum has actively transported Ca2+ from muscle so has low Ca2+ concentration Protein channels open, Ca2+ diffuses in down concentration gradient Causes tropomyosin to move from binding sites Myosin head and associated ADP bind to actin Myosin heads change shape, releasing ADP and pulling actin along ATP attaches to myosin head Myosin head detaches Ca2+ activates ATPase (ATP - ADP) Energy released use to move myosin head to original position Myosin head reattaches to actin
36
Why will two actin filaments move in opposite directions?
The myosin heads are joined tail to tail so the movement of one set of heads is in the opposite direction to the other
37
Why does the sarcomere shorten when a muscle contracts?
Because the actin is moving in opposite directions, they are pulled towards each other
38
What are the three types of muscle?
Cardiac, smooth and skeletal
39
Where is cardiac muscle found?
In the heart
40
Where is smooth muscle found?
The walls of blood vessels and gut
41
Where is skeletal muscle found?
Attached to bone, acts under voluntary control
42
What are the 'monomers' of muscles called?
Myofibrils
43
Why is it advantageous that muscle cells merge together?
There are no points of weakness
44
What is sarcoplasm?
Cytoplasm found in myofibrils
45
Characteristics of actin
Thinner, twisted strands
46
Characteristics of myosin
Thicker, bulbous heads project to side
47
Why do myofibrils appear striped?
Alternating light and dark coloured bands
48
What are the light bands called?
I bands (isotropic bands)
49
What are the dark bands called?
A bands (anisotropic bands)
50
Why do I bands appear lighter and A bands appear darker?
The thick and thin filaments overlap in the I band
51
What is at the centre of each A band?
A lighter coloured zone called the H-zone
52
What is at the centre of each I band?
The Z-line
53
What is the sarcomere?
The distance between adjacent z-lines
54
What are slow twitch fibres?
Endurance
55
Wha are the two types of muscle tissue?
Fast-twitch and slow-twitch fibres
56
Adaptations of slow-twitch fibres
Lots of myoglobin Blood vessels for oxygen Mitochondria for ATP
57
What are fast-twitch fibres?
Intense, short exercise
58
Adaptations of fast-twitch fibres
Lots of myosin Lots of glycogen Lots of enzymes for anaerobic respiration Phosphocreatine
59
What is a neuromuscular junction?
The point that a motor neurone meets a muscle fibre
60
What happens when a nerve impulse is received at a neuromuscular junction?
Synaptic vesicles fuse with presynaptic membrane Acetylcholine released and diffuses to postsynaptic membrane Increased permeability to Na+ - enters rapidly Membrane depolarised
61
How is a neuromuscular junction 'reset'?
Acetylcholine broken down by acetylcholinerase Choline and ethnic acid diffuse back to neurone Mitochondria provide energy to reform acetylcholine
62
Similarities between neuromuscular junction and synapse
Both have neurotransmitters moved by diffusion Receptors that cause influx of Na+ Sodium-potassium pump
63
Differences between neuromuscular junction and synapse
Neuromuscular junction links muscles to neurones, synapses link neurones to neurones The action potential ends at a neuromuscular junction but can continue after a synapse Neuromuscular junction only involves motor neurones
64
What is a cholinergic response?
Neurotransmitter is acetylcholine
65
What are the two components making up acetylcholine?
Ethnic acid and choline
66
How does an impulse cross a synapse?
Action potential reaches presynaptic neurone Ca2+ channels open, Ca2+ enters presynaptic knob by facilitated diffusion This causes vesicles to fuse with membrane, releasing acetylcholine into cleft Acetylcholine diffuses across cleft to Na+ channels, increasing their permeability to Na+ Influx of Na+ by diffusion This generates new action potential Acetylcholinesterase hydrolyses acetylcholine into ethnic acid + choline which diffuse back to presynaptic neurone ATP used to reform acetylcholine which is stored in vesicles
67
Why is information transferred discretely across a synapse?
Acetylcholinesterase hydrolyses acetylcholine into ethanoic acid + choline This prevents it from continuously generating new action potentials
68
What are synapses?
Points where neurones communicate either with other neurones or effectors
69
How is information passed across a synapse?
Neurotransmitters diffuse across
70
What is the gap between neurones called?
The synaptic cleft
71
What is the neurone before the synapse called?
The presynaptic neurone
72
What is the neurone after the synapse called?
The postsynaptic neurone
73
Where are neurotransmitters released from?
The presynaptic knob
74
How is the presynaptic knob adapted for its function?
Possesses many mitochondria and lots of endoplasmic reticulum for the production of neurotransmitters
75
What are neurotransmitters stored in?
Vesicles
76
Why are synapses unidirectional?
Information can only pass from the presynaptic neurone to the post
77
What are the two types of summation?
Spatial and temporal
78
What is spatial summation?
Many presynaptic neurones together release enough neurotransmitter to reach over the threshold value of the postsynaptic neurone and trigger an action potential
79
What is temporal summation?
A single presynaptic neurone releases neurotransmitter many times over a short period exceed the threshold value of the postsynaptic neurone
80
How do inhibitory synapses work?
Presynaptic neurone releases a neurotransmitter that binds to Cl- channels on postsynaptic neurone This causes channels to open Cl- moves in by facilitated diffusion K+ channels open K+ moves out of postsynaptic neurone into synapse Inside of postsynaptic membrane is more negative and outside is more positive This is hyper polarisation - a larger influx of Na+ is needed to create a new action potential so it is less likely
81
What are the two functions of synapses?
Allows a single impulse to initiate new impulses in numerous neurones Allows a number of impulses to be combined at a synapse
82
What are excitatory synapses?
Synapses that produce a new action potential when neurotransmitters bind with receptors in the postsynaptic neurone
83
How does an impulse pass along an axon?
The action potential acts as a travelling wave of depolarisation
84
How does an action potential pass along a myelinated axon?
Action potentials jump between nodes of Ranvier - saltatory conduction
85
Why is the moment of an action potential along a myelinated axon faster than an unmyelinated one?
In an unmyelinated axon, depolarisation has to occur across the whole length of the axon, which is time consuming
86
How does an action potential pass along an unmyelinated axon?
Resting potential: higher concentration of positive ions on outside compared with inside of membrane - membrane is polarised Stimulus causes sudden influx of Na+ which reverses the charge on the axon membrane causing it to depolarise This is the action potential The influx of Na+ causes Na+ channels to open further along the axon causing depolarisation Beyond this region, Na+ channels close and K+ voltage gates open K+ begins to diffuse out of membrane The depolarisation occurs along the axon The outward movement of K+ has meant that the original area of depolarisation has repolarised Repolarisation means Na+ is actively transported out, returning the axon to its resting potential
87
Charge of resting potential
65mv

A Level Biology Year 1 (21 decks)

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