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A Level - Biology > 15: Nervous coordination and muscles > Flashcards

15: Nervous coordination and muscles Flashcards

1
Q

What are the two main forms of coordination in animals?

A

Nervous system

Hormonal system

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2
Q

What are the features of the nervous system?

A 
Communication by nerve impulses
Transmission by neurones
Very rapid transmission
Travel to specific parts of the body
Response is localised
Response is rapid and short-lived
Effect is temporary and reversible
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3
Q

How is communication done in the nervous system?

A

Nerve impulses

Transmission by neurones

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4
Q

What are the features of the hormonal system?

A 
Communication by hormones
Transmission by blood system
Transmission is slow
Hormones travelled all parts of body, only target cells respond
Response is widespread
Response is slow
Response is often long-lasting
Effect could be permanent and irreversible
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5
Q

What are hormones transported in?

A

Blood plasma

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6
Q

Why do hormones only affect target cells?

A

Specific receptor on membrane and the change in conc of hormones stimulate them

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7
Q

What is a neurone?

A

Nerve cells specialised to carrying nerve impulses from one part of the body to another

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8
Q

What is the composition of a neurone?

A

Cell body
Dendrons
Axon
Schwaan cells

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9
Q

What is a cell body in a neurone?

A

Cell which produces proteins and neurotransmitters

Contain a nucleus and a lot of RER

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10
Q

What is a dendron in a neurone?

A

Extensions of cell body which divide into dendrites

Carries nerve impulses to cell body

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11
Q

What is an axon in a neurone?

A

Single long fibre that carries nerve impulses away from the cell body

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12
Q

What is a Schwaan cell in neurones?

A

Surround the axon and provide electrical insulation
Membrane forms myelin sheath
Removes cell debris by phagocytosis

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13
Q

What is a myelin sheath?

A

Forms a covering to axon made of Schwaan cell membrane

Rich in myelin lipid

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14
Q

What are neurones with myelin called?

A

Myelinated neurone

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15
Q

What are nodes of Ranvier in a neurone?

A

Constrictions between Schwann cells where there is no myelin sheath

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16
Q

How close are nodes of Ranvier?

A

2-3 um long

Occur 1-3 mm in humans

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17
Q

What are the types of neurones?

A

Sensory neurones
Motor neurones
Intermediate or relay neurone

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18
Q

What is the function of a sensory neurone?

A

Transmit nerve impulses from a receptor to an intermediate or motor neurone

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19
Q

What is the structure of a sensory neurone?

A

One dendron that is often very long

One axon to transport away and towards from cell body

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20
Q

What is the function of a motor neurone?

A

Transmit nerve impulses from an intermediate or relay neurone to an effector

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21
Q

What is the structure of a motor neurone?

A

Long axon and many short dendrites

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22
Q

What is a intermediate/relay neurone?

A

Transmit impulses between neurones

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23
Q

What is the structure of an intermediate/relay neurone?

A

Numerous dendrons and dendrites

Small and thin axons

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24
Q

What is the definition of a nerve impulse?

A

Self-propagating wave of electrical activity that travels along the axon membrane

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25
Q

What are the two states of electrical activity on the axon membrane?

A

Resting potential

Action potential

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26
Q

How can Na+ and K+ cross the axon membrane?

A

Phospholipid bilayer prevents diffusion
Channel proteins allow them to move by facilitated diffusion
Sodium-potassium pump by active transport

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27
Q

How are Na+ and K+ transported at an axon using a pump?

A

Potassium ions are transported into the axon

Sodium ions are transported out of the axon

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28
Q

What are the types of protein channels found on an axon?

A

Leak - open all the time

Voltage-gated - open when depolarised

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29
Q

What is the resting potential value?

A

-50 to -90 mV but usually -65 mV in humans

Negatively charged relative to outside

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30
Q

When is the axon membrane polarised?

A

When it is at the resting potential

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31
Q

What occurs to form the resting potential?

A

Na+ actively transported out, K+ in
More Na+ (3) out and 2 K+ in, therefore causes relative negative charge on inside
K+ diffuses out of axon, Na+ not allowed to diffuse in as channels are closed

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32
Q

What is a voltage-gated channel?

A

Channels in axon membrane which open/close based on voltage across membrane

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33
Q

What is the change in membrane potential which forms an action potential?

A

-65 mV to +40 mV

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34
Q

What is the action potential?

A

Inside of axon membrane becomes + charge

Caused by a large enough stimulus is detected by a receptor

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35
Q

What is depolarisation?

A

When a part of the membrane becomes +vely charged

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36
Q

What causes an action potential?

A

Stimulus of a large enough size causes action potential if reversal of charge reaches threshold value

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37
Q

What are the stages in the formation of an action potential?

A 
Resting potential
Rising phase
Overshoot phase
Falling phase
Undershoot phase
Recovery
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38
Q

What occurs in the stages of an action potential?

A

Resting
Rising - energy from stimulus opens Na+ voltage-gated channels, Na+ diffuses in and only depolarises if large enough stimulus
Overshoot - Na+ channels open, causes even greater +ve charge
Falling - after +40mV Na+ voltage-gated channels close and K+ voltage-gated channels open, K+ leaves axon and repolarises membrane
Undershoot - K+ voltage and leak channels open to remove K+ and all others close, hyperpolarisation as more -ve than resting
Recovery - K+ voltage close and Na+/K+ pump removes Na+ and K+ in causes resting potential to be reached

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39
Q

Where does an action potential form?

A

Particular point on the axon membrane not the whole membrane

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40
Q

How is the resting and action potential maintained?

A

Action potential - passive

Resting potential - active

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41
Q

What are the features of an action potential?

A

Moves rapidly along axon
Size of action potential remains constant
Part of axon which is depolarised, acts as a stimulus for depolarisation of next region of axon
Action potential is travelling wave of depolarisation

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42
Q

What are the stages of the passage of an action potential along an unmyelinated neurone?

A

Stimulus causes Na+ into axon causing depolarisation
Localised electrical current causes Na+ voltage-gated channels open further along axon, causing depolarisation further along
Behind depolarisation Na+ voltage close and K+ open, K+ move down electrochemical gradient
Repolarised membrane follows area of depolarised

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43
Q

How does a myelin sheath work?

A

Acts an electrical insulator

Prevents action potentials from forming

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44
Q

What is saltatory conduction?

A

Process whereby localised currents form between adjacent nodes and action potentials jump from node to node to Ranvier

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45
Q

Where can an action potential occur along a myelinated axon?

A

Only at the nodes of Ranvier

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46
Q

Does an action potential travel faster in an unmyelinated and myelinated axon?

A

Myelinated axon

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47
Q

Why do myelinated axons conduct impulses faster than unmyelinated?

A

Depolarisation only at nodes of myelinated
Saltatory conduction - jumps from node to node
Myelinated - impulse does not travel along whole length

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48
Q

Why can destruction of the myelin sheath cause problems with muscle control?

A

Action potential moves slower

Causes delays in muscle contractions

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49
Q

How does the size of the action potential change along the neurone?

A

Remains the same size throughout

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50
Q

Why does reploarisation occur behind the depolarisation in the axon?

A

Outward movement of K+ ions meaning it returns to relative -ve charge
Caused as K+ voltage open and Na+ close

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51
Q

What actually travels between adjacent nodes of Ranvier in myelinated neurons?

A

Current move from one to another

Causes voltage-gated channels to open/close

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52
Q

Define nerve impulse

A

Transmission of an action potential along the axon

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53
Q

What are the main factors which affect the speed at which an action potential travels?

A

Myelin sheath
Diameter of the axon
Temperature

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54
Q

What is the range for how fast an action potential travels?

A

0.5 ms-1 to 120 ms-1

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55
Q

How does the diameter of the axon affect the speed of action potentials?

A

Greater the diameter the faster the conductance speed

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56
Q

Why does the diameter of the axon affect the speed of action potentials?

A

Faster conductance

Due to less leakage of ions from a large axon so membrane potential is easier to maintain

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57
Q

Why do larger diameters cause less leakage?

A

Ions collide with the axon less and hence less leak

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58
Q

How does the temperature the speed of action potentials?

A

The higher the temp the faster the nerve impulse

Over a certain temp it slows/stops it

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59
Q

Why does the temperature affect the speed of action potentials?

A

Increasing temp increases rate of diffusion of ions and respiration enzymes act faster so energy more available for active transport
Over certain temp denatures enzymes for respiration and channel proteins, impulses stop

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60
Q

Which type of animal’s speed of conduction will be most affected by changes of temp?

A

Ectothermic (cold-blooded) animals

Temperature varies massively and can also affect muscle contractions

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61
Q

What does the all-or-nothing response mean?

A

Any impulse above the threshold value causes an action potential of the same size
Below causes no response

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62
Q

What occurs if the stimulus is below the threshold value?

A

Does never generate an action potential part

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63
Q

How can an organism perceive the size of a stimulus?

A

Number of impulses in a given time

Different neurones with different threshold values

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64
Q

How does the number of impulses change based on the size of the stimulus?

A

Larger the stimulus the more impulses generated in a given time

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65
Q

What is the refractory period?

A

Period after the depolarisation where sodium voltage-gated channels are closed so cannot move into membrane
Hence membrane cannot have another action potential generated across it

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66
Q

What are the main purposes of the refractory period?

A

Ensures action potentials only propagate in one direction
Produces discrete impulses
Limits number of action potentials

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67
Q

Why does the refractory period mean action potentials can only move in one direction?

A

Region behind is in refractory period

Na+ cannot move in so doesn’t move in both directions

68
Q

Why does the refractory period mean only discrete impulses are made?

A

Time difference between the impulses due to the refractory period
Hence discrete impulses formed

69
Q

Why does the refractory period mean it limits the number of action potentials?

A

Separated action potentials means limited number which can pass in a certain time
Limits strength of stimulus that can be detected

70
Q

What is a synapse?

A

Point where one neurone communicates with another or an effector

71
Q

What do synapses transmit?

A

Information not impulses

72
Q

What is a neurotransmitter?

A

Chemicals are used to transmit information from one neurone to another

73
Q

What is the synaptic cleft?

A

Small gap which separates the neurones

20-30 nm wide

74
Q

What is the presynaptic neurone?

A

Neurone which releases the neurotransmitter

75
Q

What is the presynaptic knob?

A

Swollen portion of the presynaptic neurone

Contains many mitochondria and ER

76
Q

What is the function of the presynaptic knob?

A

Required for manufacture and storage of the neurotransmitter

77
Q

What is the neurotransmitter stored in when in the presynaptic knob?

A

Synaptic vesicles

78
Q

How is a synapse unidirectional?

A

Synapses only pass info in one direction

79
Q

What is summation?

A

Processes used to ensure that sufficient neurotransmitter is released to cause a new action potential in the postsynaptic neurone

80
Q

What are the two types of summation?

A

Spatial summation

Temporal summation

81
Q

What is spatial summation?

A

Many presynaptic neurones release neurotransmitter simultaneously
Together release enough and can form a new action potential

82
Q

What is temporal summation?

A

Single presynaptic neurone releases neurotransmitters many times in a very short period of time
If conc is larger than threshold it causes a new action potential

83
Q

What is an inhibitory synapse?

A

Type of synapse that makes it less likely a new action potential will be created on the postsynaptic neurone

84
Q

How does an inhibitory synapse work?

A

Releases neurotransmitter that binds to Cl- protein channel on postsynaptic neurone, opening them and causing Cl- to diffuse into it
Also causes opening of K+ channels which move out of neurone into synapse
Makes inside of postsynaptic membrane more -ve and outside more +ve, called hyperpolarisation
Requires more Na+

85
Q

What is the membrane potential changed to in hyperpolarisation?

A

-65 mV to -80 mV

86
Q

What do the structure of synapse allow?

A

Single impulse along one neurone can initiate many different neurones at a synapse, one neurone can make many responses
Number of impulses combined at a synapse so many can make one response

87
Q

Where is the neurotransmitter produced?

A

Only in presynaptic neurone

88
Q

How does a synapse work?

A

Acton potential causes Ca2+ gated channels to open in presynaptic neurone
Ca2+ diffuse into neurone and cause synaptic vesicles to fuse with presynaptic membrane
Releases neurotransmitter into cleft which diffuses and binds to specific receptor proteins on postsynaptic neurone
Leads to Na+ protein channels opening and Na+ diffuses into postsynaptic neurone causing an action potential to form

89
Q

What is an excitatory synapse?

A

Synapses which produce new action potentials in synapses next to it

90
Q

What is a cholinergic synapse?

A

One where the neurotransmitter used is acetylcholine

91
Q

What is acetylcholine?

A

Neurotransmitter

Made of acetyl (ethanoic acid) and choline

92
Q

Where are cholinergic synapses common?

A

Vertebrates

Found in CNS and at the neuromuscular junction

93
Q

What is the abbreviation of acetylcholine?

A

ACh

94
Q

How is transmission done at a cholinergic synapse?

A

Action potential opens Ca2+ in presynaptic neurone which enter by facilitated diffusion
Ca2+ cause synaptic vesicles to fuse with presynaptic membrane, releasing ACh
ACh diffuse across cleft and binds to receptor sites on Na+ protein channels in postsynaptic membrane
Na+ diffuse down conc gradient into postsynaptic neurone and creates a new action potential in it

95
Q

How is acetylcholine recycled?

A

Acetylcholinesterase hydrolyses ACh to acetyl and choline
Diffuse into presynaptic neurone into synaptic vesicles
ATP from mitochondria used to recombine them

96
Q

What does the breakdown of ACh prevent?

A

Prevents from continuously generating a new potential in the postsynaptic neurone
As Na+ channel proteins are allowed to close
Means discrete transfer can occur

97
Q

Why are there many mitochondria in the presynaptic neurone?

A

Produce ATP for recombining ACh

98
Q

What are the three types of muscle?

A

Cardiac
Smooth
Skeletal

99
Q

What occurs when acetylcholinesterase is inhibited?

A

Causes constant muscle stimulation as it continually binds and leaves Na+ protein channels open

100
Q

What is cardiac muscle?

A

Muscles only found in the heart

Involuntary/unconscious control

101
Q

What is smooth muscle?

A

Walls which decrease in diameter when they contract
Found in walls of blood vessels and gut
Involuntary/unconscious

102
Q

What is skeletal muscle?

A

Muscle attached to the bone either directly or by tendons

Acts under voluntary control, conscious

103
Q

What is the prefix used for muscle cells?

A

Sarco-

104
Q

What is a muscle made of?

A

Millions of tiny muscle fibres called myofibrils

105
Q

Why are myofibrils grouped together?

A

Lined up parallel as it maximises its collective strength

106
Q

Why could the muscle not be made of individual cells joined up end to end?

A

Junction between cells would be a point of weakness

107
Q

What is a muscle fibre?

A

Separate cells which have fused together to form longer

Share nuceli, sarcoplasm etcl.

108
Q

What is the name of the cytoplasm in muscle fibres?

A

Sarcoplasm

109
Q

What is the name of the endoplasmic reticulum in muscle fibres?

A

Sarcoplasmic reticulum

110
Q

What is found in the sarcoplasm in high conc?

A

Mitochondria

Sarcoplasmic reticulum

111
Q

What is body movement caused by?

A

Contraction of skeletal muscle

112
Q

What is a muscle split into?

A 
Muscle
Bundle of muscle fibres
Muscle fibres
Myofibrils
Sarcomere
113
Q

What is the sarcomere?

A

Smallest unit of skeletal muscle that can contract

114
Q

What is a myofibril made of?

A

Protein filaments:
Actin
Myosin

115
Q

What is actin?

A

Protein filament

Thinner and consists of two strands twisted around each other

116
Q

What is myosin?

A

Protein filament

Thicker and consists of long rod-shaped tails with bulbous heads that project to the side

117
Q

What is myoglobin?

A

Protein in muscle which carries oxygen

118
Q

What are the bands present in a sarcomere?

A

I bands
A bands
H-zone
Z-line

119
Q

What is the I band?

A

Lighter bands

Only actin present, area between myosin and z-line

120
Q

What is the z-lines?

A

Lines which separate each sarcomere

Middle of I-band

121
Q

What is the A band?

A

Myosin (thick) and actin (thin) overlap

Produces dark region

122
Q

What is the H-zone?

A

Region where only myosin is present

Darker than I band but lighter than A-band

123
Q

What is tropomyosin?

A

Protein which forms a fibrous strand around the actin filament

124
Q

What is troponin?

A

Protein bound to tropomyosin which is wrapped around the actin

125
Q

What are the two types of muscle fibre?

A

Slow-twitch fibres

Fast-twitch fibres

126
Q

What are the features of slow-twitch fibres?

A

Contract slowly and less powerfully
Contractions over a long period
Adapted to endurance work in muscles where constantly used
Adapted for aerobic respiration

127
Q

What are the features of fast-twitch fibres?

A

Contract rapidly and more powerfully
Contracts over a short period
Adapted to intense exercise in muscles needed for short-bursts of activity
Adapted for anaerobic respiration

128
Q

Name and explain an example where slow-twitch fibres are used?

A

Calf muscle

Constantly contracts for keeping the body upright

129
Q

Why are slow-twitch muscles adapted for aerobic respiration?

A

Prevent build-up of lactic acid

Lactic acid would cause them to function less effectively, stops long-duration contraction

130
Q

How are slow-twitch muscle fibres adapted for aerobic respiration?

A

Large store of myoglobin which stores O2
Rich supply of blood vessels to deliver O2 and glucose
Many mitochondria to produce ATP

131
Q

How are fast-twitch fibres adapted to their role?

A

Thicker and more numerous myosin filaments
High conc of glycogen
High conc of enzymes for anaerobic respiration providing ATP rapidly
Large store of phosphocreatine to produce ATP

132
Q

What is the neuromuscular junction?

A

Point where a motor neurone meets a skeletal muscle fibre

133
Q

How many neuromusclar junctions are found along a muscle and why?

A

Many junctions

Ensures fibres all contract simultaneously therefore rapid and powerful

134
Q

What would occur if there was just 1 neuromuscular junction per muscle?

A

Wave of contraction not all contract at same time

Slow and weaker contraction

135
Q

Why is rapid and coordinated contraction required?

A

Needed for survival

136
Q

What is a motor unit?

A

All muscles fibres which are supplied by a single motor neuron
Acts as a single functional unit

137
Q

What do motor units allow for?

A

Varying amounts of force applied

If a large force needed then more motor units are stimulated

138
Q

What is the structure of the neuromuscular junction?

A

Presynaptic neurone is cholinergic

Postsynaptic is muscle fibre

139
Q

What is the membrane of the muscle fibre called?

A

Sarcolemma

140
Q

What occurs when a nerve impulse is received at a neuromuscular junction?

A

Ca2+ voltage-gated channels open in presynaptic neurone
Synaptic vesicles fuse with presynaptic membrane
Releases ACh which then diffuses to sarcolemma
Binds to receptor and opens Na+ channels, which diffuse into the muscle, depolarising the membrane
This then leads to contraction

141
Q

What prevents the muscle from being over-stimulated by ACh?

A

Acetylcholineterase enzymes found at neuromuscular junctions

142
Q

What are the similarities of the neuromuscular junction and a synapse?

A

Both have neurotransmitters which move by diffusion
Receptors which upon binding cause the influx of Na+
Na+/K+ pump used to re-polarise axon
Enzymes used to break down neurotransmitter

143
Q

What are the differences between the neuromuscular junction (NJ) and a cholinergic synapse?

A

NJ is only excitatory, cholinergic can also be inhibitory
NJ only links neurones to muscles, cholinergic can link to other neurones or other effector organs
Action potential ends at NJ, new action potential can be produced in cholinergic synapse (if another synapse)
ACh binds to receptor on sarcolemma at NJ but on post-synaptic neurone in cholinergic

144
Q

What is a transverse tubule?

A

Structures in muscle fibres which carries depolarisation from membrane to inside of muscle fibres
Ensures all contract at same time
Made of cell-surface membrane

145
Q

What is the mechanism by which muscle contracts?

A

Sliding filament mechanism

146
Q

What does antagonistic muscles mean?

A

Muscles movements which oppose each other

147
Q

What is an antagonistic pair of muscles?

A

Muscles which cause movement of a limb

One contracts whilst other relaxes to move in one direction, vice versa in other direction

148
Q

What is the flexor?

A

Muscle which contracts meaning the limb bends

149
Q

What is the extensor?

A

Muscle which contracts meaning the limb extends

150
Q

How does Ca2+ affect protein filaments?

A

Binds to troponin, changes its conformational shape
No longer binds to tropomyosin
Tropomyosin moves and exposes binding sites on actin

151
Q

How is contraction done by the sliding filament mechanism?

A

T-Tubule transfers action potential deep into fibre
Causes Ca2+ channels in sarcoplasmic reticulum to open and diffuse into sarcoplasm down conc gradient
Ca2+ moves causes tropomyosin to move, exposing actin binding site
Myosin head with ADP binds to form cross-bridge with actin
ADP is released and ATP binds
Ca2+ activates ATPase, energy from ATP hydrolysis gives energy for movement of myosin head puling actin along and to stop them being bound
Head returns to original position and binds further along actin with ADP to repeat process whilst [Ca2+] is high
Myosin molecules joined tail to tail pull in opposing directions, meaning actin pulls towards eachother and shortens muscle

152
Q

What occurs in muscle relaxation in the sliding filament mechanism?

A

Occurs when nervous stimulation stops
Ca2+ actively transported into sarcoplasmic reticulum using energy from ATP hydrolysis
Tropomyosin blocks actin filament
Myosin head unable to bind to actin filaments, contraction ceases

153
Q

What is energy required for in muscle contraction?

A

Movement of myosin heads

Reabsoprtion of Ca2+ into sarcoplasmic reticulum by active transport

154
Q

Does muscle contraction require a large amount of energy?

A

Considerable energy

Supplied by hydrolysis of ATP

155
Q

How is ATP regenerated in the muscle?

A

Mostly by aerobic respiration of pyruvate (large amount in muscle)
Anaerobically respires or uses phosphocreatine to donate phosphate groups to ADP

156
Q

What is phosphocreatine?

A

Molecule which acts as a phosphorus store in muscle

Donates Pi to ADP when not enough provided by respiration

157
Q

How is phosphocreatine made?

A

Using phosphate from ATP when the muscle is relaxed

158
Q

What are the changes to the sarcomere when muscle contracts?

A

I bands become narrower
Z lines move closer together
H zone becomes narrower
A band remains same width

159
Q

Why does the A band remain the same width in contraction?

A

Determined by length of myosin

Therefore myosin itself is not getting shorter

160
Q

What disproves the theory that contraction is due to the filaments themselves shortening?

A

A band remains same width

Therefore myosin length remains constant as it is determined by it

161
Q

What is the function of tropomyosin in myofibril contraction?

A

Moves out of the way when Ca2+ binds

Allows myosin to bind actin

162
Q

What is the function of myosin in myofibril contraction?

A

Head of myosin binds to actin and pulls actin past
Myosin detaches from actin and moves further along actin
This uses ATP

163
Q

Why is there a high conc of glycogen in fast muscle fibres?

A

Glycogen broken down to glucose for glycolysis as anaerobic

Many needed as glycolysis yields very few (2 ATP) per glucose

164
Q

Why are many capillaries a benefit in slow muscle fibres?

A

Gives high [O2]

Allows higher rate of aerobic respiration

165
Q

Why is there variation in the time taken for phosphocreatine to reform?

A

Genetic differences
Fitness
Fast or slow muscle fibres

166
Q

If myosin cannot bind to one another why can muscle contraction not occur?

A

Cant form thick myosin filament
Can’t pull the actin filament and myosin itself moves
Actin doesn’t move and can’t shorten sarcomere so no contraction

167
Q

Where are mitochondria located in slow-twitch fibres and why?

A

Near the edges

Short diffusion pathway for oxygen which is used in the ETC

A Level - Biology (22 decks)

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