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Biology A2 > Nervous Coordination > Flashcards

Nervous Coordination Flashcards

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1
Q

Resting Potential

A
  • polarised axon
  • potential difference of -70mV
  • axon more negatively charged relative to outside
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2
Q

Explain why concentrations of Na+ and K+ mean axon has a negative potential difference at rest even though Na+ and K+ both have the same charge

A
  • concentration of Na+ outside axon is higher than concentration of K+ inside axon
  • large anions are found inside axon
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3
Q

Explain how resting potential is maintained

A
  • 3 Na+ actively transported out and 2 K+ into axon
    via sodium potassium pump
  • membrane more permeable to K+ than Na+ so K+ leaks out
  • Na+ channels mostly closed so Na+ cannot enter axon
  • large anions are found inside axon
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4
Q

Action Potential

A
  • travelling wave of depolarisation
  • depolarised axon
  • potential difference +40mV
  • axon more positively charges relative to outside
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5
Q

Explain the process by which an action potential is produced in an axon and how the axon returns to resting potential

A
  • stimulus which exceeds threshold voltage opens some voltage-gated Na+ channels
  • Na+ diffuses into axon down electrochemical gradient
  • pd becomes less negative which causes more voltage-gated Na+ channels to open
  • pd reaches +40mV
  • repolarisation of axon occurs so voltage-gated Na+ channels close so no more Na+ can enter axon
  • voltage-gated K+ channels open so K+ diffuse out down electrochemical gradient
  • outward diffusion of K+ causes temporary overshoot so hyperpolarisation of axon (reaches -80mV)
  • K+ voltage-gated channels close
  • sodium potassium pump causes axon to return to resting potential at -70mV
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6
Q

Suggest how action potentials determine the strength of a response given they have a constant amplitude

A
  • frequency of impulses

- different neurones have different threshold values and brain interprets types of neurones stimulated

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7
Q

Describe the passage of an action potential along an unmyelinated axon

A
  • stimulus exceeding threshold voltage causes influx of Na+
  • depolarisation of axon induces voltage-gated Na+ channels to open further along axon
  • localised currents established between adjacent regions along axon
  • (more) depolarisation over length of axon
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8
Q

Describe the passage of an action potential along a myelinated axon

A
  • fatty myelin sheath acts as electrical insulator
  • depolarisation occurs at Nodes of Ranvier only
  • localised currents form between adjacent nodes
  • by saltatory conduction (action potential ‘jumps’)
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9
Q

Suggest factors which increase the speed of conductance of an action potential and explain why

A
  • myelination due to saltatory conduction so action potential does not occur along whole length of axon
  • larger diameter due to reduced ion leakage
  • high temperature due to increased diffusion and enzyme action in respiration to produce ATP for Na+/K+ pump
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10
Q

All or None Principle

A
  • action potential is exactly the same size regardless of the size of the stimulus
  • providing it reaches the threshold value
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11
Q

Explain the importance of the all or none principle for action potentials

A

prevents minor stimuli causing nerve impulses and overloading the brain

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12
Q

Refractory Period

A
  • period where membrane is hyperpolarised (K+ channels open)
  • voltage-gated Na+ channels are closed preventing Na+ diffusing into axon
  • greater stimulation required to reach threshold value
  • no action potential generated
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13
Q

Explain the purpose of a refractory period in the passage of an action potential

A
  • ensures unidirectional
  • produces discrete impulses (new impulse cannot be generated immediately after)
  • limits strength of impulse (only certain number of action potentials can pass in a given time)
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14
Q

Explain why a nerve impulse can only cross a synapse in one direction

A
  • neurotransmitter only released by presynaptic neurone
  • neurotransmitter diffuses down concentration gradient
  • receptors only present on post synaptic neurone
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15
Q

Summation

A
  • process which determines whether or not threshold voltage is reached
  • to trigger action potential in postsynaptic neurone
  • by combined effects of excitatory and inhibitory signals
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16
Q

Spatial Summation

A
  • different presynaptic neurones together release enough neurotransmitter
  • increases/decrease the probability that the potential will reach the threshold potential
  • hence generate an action potential
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17
Q

Temporal Summation

A
  • one presynaptic neurone releases neurotransmitter many times over a short period of time
  • to reach threshold value of postsynaptic neurone
  • hence generate an action potential
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18
Q

Suggest a benefit of postsynaptic neurone synapsing with two different presynaptic neurones

A
  • modulation (control over) activity of postsynaptic neurone
  • impulse transmission is not inevitable
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19
Q

Explain how an action potential is passed along an excitatory chemical synapse

A
  • depolarisation of presynaptic neurone causes Ca2+ channels to open and Ca2+ diffuses in down concentration gradient
  • vesicles containing acetyl choline fuse with presynaptic membrane
  • acetyl choline released to synaptic cleft and diffuses down concentration gradient
  • binds to receptors of post synaptic neurone
  • ligand-gated Na+ channels open and Na+ enters neurone
  • axon depolarised above threshold value
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20
Q

Explain how neurotransmitter acetyl choline is reused by presynaptic neurone

A
  • reabsorbed by active transport
  • degraded by acetyl cholinesterase to acetyl and choline
  • reabsorbed by pre synaptic neurone and mitochondria produce ATP to synthesis acetyl choline
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21
Q

Explain briefly how an inhibitory chemical synapse functions

A
  • neurotransmitter binds to ligand-gated Cl- channels
  • Cl- moves into post-synaptic neurone by facilitated diffusion
  • induces opening of nearby K+ channels so K+ moves out of postsynaptic neurone
  • hyperpolarisation
  • no passage of action potential since stimulation does not reach threshold level
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22
Q

Explain how an electrical synapse functions

A
  • single protein channel acts as junction between pre and postsynaptic neurone bridging cytoplasms
  • Na+ diffuses directly into postsynaptic neurone
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23
Q

Contrast chemical and electrical synapses

A
  • single protein channel between neurones for electrical
  • gap between synapses in smaller for electrical
  • faster transmission with electrical since Na+ diffuses directly into postsynaptic neurone
  • chemical synapses have synaptic plasticity
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24
Q

Synaptic Plasticity

A
  • property of chemical synapses enabling them to alter synaptic strength (ability to pass on action potential)
  • change in amount of neurotransmitter released per action potential
  • change number of receptors available to bind
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25
Q

Cholinergic Synapse

A
  • gap between neurones
  • neurotransmitter is acetyl choline
  • (found in peripheral nervous system)
26
Q

Neuromuscular Junction

A
  • chemical synapse

- between motor neurone and skeletal muscle fiber

27
Q

State differences between motor and sensory neurone

A
  • dendrites emerge from cell body in motor neurone but from dendron in sensory
  • motor neurone has cell body on end but sensory has cell body on side
  • motor neurone has many short dendrons but sensory has one long dendron
28
Q

Explain function of myelin sheath

A
  • myelin insulates
  • action potential only produced at nodes
  • travels by saltatory conduction
  • faster transmission of nerve impulse
  • insulated action potential to prevent leaking
29
Q

Suggest ways in which drugs can affect synapses

A
  • release neurotransmitter from vesicles without impulses
  • prevent vesicles from releasing neurotransmitter
  • block reuptake of neurotransmitter
  • block receptors
  • produce more or less neurotransmitter
30
Q

Name inhibitory neurotransmitters

A
  • GABA
  • serotonin (in pain pathways)
  • dopamine
31
Q

Explain characteristic features of the Pacinian corpuscle

A
  • respond only to specific stimuli (mechanical pressure and not light, heat or sound)
  • produces a generator potential from mechanical energy of stimulus by acting as a transducer
32
Q

Suggest places Pacinian corpuscle receptors are typically found

A
  • fingers
  • soles of feet
  • joint (ligaments/tendons)
33
Q

Explain how Pacinian corpuscle produces an action potential in sensory neurone

A
  • pressure deforms Pacinian corpuscle and STRETCHES membrane so Na+ channels OPEN
  • influx of Na+ results in depolarisation of axon producing a generator action potential
  • action potential passes along sensory neurone to CNS
34
Q

Describe how rod cells in the eye work

A
  • only one type so cannot distinguish between different wavelengths of light (black and white vision)
  • stimulated in low light intensity
  • many rod cells connected to a single bipolar cell so summation occurs to reach threshold value for generator potential
  • pigment called rhodopsin broken down
  • brain cannot distinguish separate sources of light so low visual acuity (resolving power)
  • relatively more and found at periphery of retina
35
Q

Describe how cone cells in the eye work

A
  • three different types which respond to different wavelengths of light (coloured vision)
  • stimulated in high light intensity
  • cone cells attached to separate bipolar cells
  • types of pigments called iodopsin break down
  • brain distinguishes between separate light sources so high visual acuity (resolving power)
  • relatively fewer and found near fovea of retina
36
Q

Explain how inhibitory neurotransmitters inhibit transmission of nerve impulses at postsynaptic neurone

A
  • open chloride channels causing hyperpolarisation
  • stimulation (from excitatory neurotransmitters) does not reach threshold value
  • reducing effect of Na+ entering so no depolarisation
  • no action potential produced
37
Q

Myogenic

A

Contracts without nervous or hormonal stimulation

38
Q

How would removing the nerve connections from the brain to the SAN affect the beating of the heart

A

Unable to change the heart rate so it would remain constant

39
Q

Explain how the heart beats

A
  • wave of electrical excitation spreads out from SAN across both atria
  • atria contract
  • wave of excitation enters AVN
  • after a short delay spreads over ventricles down the bundle of His and along Purkyne tissues
40
Q

Explain why contraction happens at the bottom of the ventricles

A
  • non conductive tissue of AV septum prevents wave of excitation directly over ventricles
  • forced to travel along the bundle of His
  • so contraction starts at the apex of ventricles
41
Q

Explain why contraction occurs when ventricles are full

A
  • wave of excitation is delayed at AV
  • non conductive tissue at AV septum prevents it travelling directly over ventricles
  • allows time for ventricles to fill
42
Q

Explain why damage to myelin sheath of neurones can lead to problems controlling muscle contraction

A
  • no saltatory conduction so slower transmission of action potential results in delayed muscle contraction
    or
  • action potential leaks into adjacent neurones so wrong motor neurone stimulated
43
Q

Describe the gross structure of a skeletal muscle

A
  • made of bundles of muscle fibres known as fascicles surrounded by connective tissue
  • muscle fibres (cells) consist of many myofibrils which are specialised intracellular structures
  • run parallel to each other to maximise strength
44
Q

Describe the microscopic structure of a skeletal muscle

A
  • myofibrils are made of protein filaments actin and myosin forming sections known as sarcomeres
  • thinner actin consists of two twisted strands forming a helical structure with long threads of tropomyosin wound around it
  • thicker myosin consists of a long, fibrous tail and two bulbous, globular heads projecting from one side
45
Q

Describe the structure of muscle fibres and explain why muscle cells are not found as individual cells

A
  • muscle cells are fused together to form muscle fibres to maximise strength
  • nuclei are located along the edges of fibre
  • shared cytoplasm known as sarcoplasm contains a high concentration of mitochondria and sarcoplasmic reticulum
  • muscle cells are NOT individual since there would be weakness at junctions between cells
46
Q

Suggest what is meant by a sarcomere and describe its structure

A
  • sarcomere is distance between adjacent z lines
  • consists of light I band and dark A bands
  • A bands are where thick and thin filaments overlap
  • I bands are regions between A bands where there is only thin filament (no overlap)
  • H zone refers to centre of A band where there is only thick filament
  • Z lines are boundaries between adjacent sarcomeres
47
Q

Compare and contrast transmission across cholinergic synapse and neuromuscular junction

A
  • both have neurotransmitters transported by diffusion
  • both use enzymes to break down neurotransmitter
  • both have receptors that cause influx of Na+ on binding of neurotransmitter
  • both use Na-K pump to repolarise axon
  • NMJ excitatory only where CS excitatory / inhibitory
  • NMJ links neurones to muscles where CS links neurones to neurones or other effector organs
  • NMJ is where action potential ends where CS is where new action potential is produced at post-synaptic neurone
48
Q

Contrast slow and fast twitch muscle fibres

A
  • FT contract more rapidly and produce powerful contractions over short period
  • FT adapted for intense exercise in short bursts but ST for endurance work
  • FT are thicker with more myosin filaments
  • FT have higher concentration of glycogen and enzymes involved in anaerobic respiration
  • FT has store of phosphocreatine (allows ADP to rapidly reform ATP in anaerobic conditions)
  • ST have larger store of myoglobin (oxygen store to ensure aerobic respiration + avoid lactate build up)
  • ST have richer blood supply for oxygen/glucose
  • ST have more mitochondria to produce ATP
49
Q

Describe how a muscle fibre contracts based on the sliding filament theory

A
  • actin filaments slide past myosin filaments in opposite directions to each other
  • distance between Z lines decreases
  • sarcomere shortens
50
Q

Give evidence for the sliding filament theory of muscle contraction and explain why this means filaments do not shorten

A
  • I band/H zone becomes narrower
  • Z lines more closer together
  • sarcomere shortens
  • A band remains same width since determined by length of myosin filament which does NOT change
51
Q

Describe the process by which skeletal muscle contracts

A
  • depolarisation of sarcolemma from arrival of action potential
  • wave of depolarisation travels down T tubules and opens Ca2+ channels on sarcoplasmic reticulum
  • Ca2+ diffuses into sarcoplasm from sarcoplasmic reticulum down concentration gradient
  • Ca2+ causes tropomyosin blocking binding sites on actin to pull away
  • myosin heads (attached to ADP) attach to actin at troponin binding sites forming cross bridges
  • performs POWERSTROKE (change position to a lower energy state) and PULLS actin filaments along
  • myosin head detaches so next myosin head can bind along actin filament
52
Q

Describe the process by which skeletal muscle relaxes

A
  • ATP binds to myosin head causing it to detach from actin filament
  • ATPase hydrolyses ATP to ADP
  • provides energy for myosin heads to return to original position
  • Ca2+ actively transported back to sarcoplasmic reticulum
  • tropomyosin blocks binding sites on actin once again
  • myosin heads unable to bind to actin so muscle relaxes
53
Q

Suggest uses for hydrolysis of ATP in muscle contraction

A
  • energy for myosin heads to detach from actin filament
  • hydrolysis of ATP provides energy for myosin heads to move back to original position
  • ADP on myosin heads allows them to bind to actin and form cross bridges
  • energy for active transport of Ca2+ back to sarcoplasmic reticulum
54
Q

Phosphocreatine

A
  • energy source for muscle contraction (naturally present in skeletal muscle)
  • supplies phosphate to regenerate ATP
  • ATP formed more rapidly compared to from aerobic and anaerobic (glycolysis) respiration
55
Q

Suggest how phosphocreatine store in skeletal muscles is replenished

A

inorganic phosphate produced from hydrolysis of ATP

56
Q

Describe the role of tropomyosin in myofibril contraction

A
  • moves out of way when calcium binds

- allows myosin heads to bind and form cross bridges with actin filament

57
Q

Describe role of myosin in myofibril contraction

A
  • binds to actin filament and moves so it slides past

- detaches using ATP and reattaches further actin filament

58
Q

Explain why fast twitch muscle fibres have a high glycogen content

A
  • large supply of glucose available
  • for MORE anaerobic respiration (compare to aerobic respiration for marking point)
  • faster source of ATP but inefficient (yield of 2 ATP)
59
Q

Explain why slow twitch muscle fibres have many capillaries is close contact

A
  • short diffusion path for oxygen
  • rich oxygen supply
  • for MORE aerobic respiration (compare to anaerobic respiration for marking point)
60
Q

Explain why mitochondrial disease results in muscle weakness

A
  • reduction in ATP from aerobic respiration
  • less force generated due to fewer myosin and actin interactions
  • anaerobic respiration = lactate which causes muscle fatigue

Biology A2 (15 decks)

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