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Biology - Mrs Dudley > 15.1 - 15.8 Nervous coordination and muscles > Flashcards

15.1 - 15.8 Nervous coordination and muscles Flashcards

Must also know: - Action potential graph

1
Q

Describe the difference in communication between the hormonal and nervous system

A
  • Hormonal - By chemicals called hormones
  • Nervous - By nerve impulses
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2
Q

Describe the difference in transmission between the hormonal and nervous system

A
  • Hormonal - By the blood system
  • Nervous - By neurones
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3
Q

Describe the difference in the speed of tranmission between the hormonal and nervous system

A
  • Hormonal - Relatively slow
  • Nervous - Very rapid
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4
Q

Describe the difference in specifity between the hormonal and nervous system

A
  • Hormonal - Hormones travel to all parts of the body, but only target cells respond
  • Nervous - Nerve impulses travel to specific parts of the body
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5
Q

Describe the difference in lasting response between the hormonal and nervous system

A
  • Hormonal - Often long-lasting. Effect may be permanent and irreversible.
  • Nervous - Short-lived. Effect is usually temporary and reversible.
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6
Q

Describe the function of the motor neurones cell body

A
  • Contains all usual organelles i.e nucleus and large amounts of RER
  • Production of proteins and neurotransmitters
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7
Q

Describe the function of the motor neurones dendrons

A
  • Extensions of the cell body which subdivide into smaller branched fibres
  • Production of proteins and neurotransmitters
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8
Q

Describe the function of the motor neurones axon

A
  • A single long fibre
  • Carries nerve impulses away from the cell body
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9
Q

Describe the function of the motor neurones Schwann cells

A
  • Surround the axon
  • Protect the axon and provide electrical insulation
  • Carry out phagocytosis
  • Play a part in nerve regeneration
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10
Q

Describe the function of the motor neurones myelin sheath

A
  • A covering to the axon, made up of the membranes of the Schwann cells
  • Membranes are rich in a lipid known as myelin
  • Neurones with a myelin sheath are called myelinated neurones
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11
Q

Describe the function of the motor neurones Nodes of Ranvier

A
  • Constrictions between Schwann cells where there is no myelin sheath
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12
Q

Define sensory neuron

A

Transmit nerve impulses from receptor to the CNS

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13
Q

Define intermediate/relay neurone

A

Transmit impulses between neurones, e.g from sensory to motor neurones

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14
Q

Define motor neurones

A

Transmit nerve impulses from the CNS to effectors (muscles or glands)

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15
Q

How is the resting potential established and maintained?

A
  • Actively transporting sodium-potassium pump
  • 3 Na+ are transported out for every 2 K+ transported in
  • Membrane is more permiable to K+ so K+ diffuse out more rapidly than Na+ diffuse in
  • More negative inside than outside
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16
Q

Define threshold value

A

The level of stimulus that triggers an action potential

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17
Q

Describe how a stimulus causes an action potential

A
  • Energy of the stimulus causes sodium ion channels to open and sodium ions diffuse into the neurone down the sodium ion electrochemical gradient
  • This causes depolarisation
  • If the threshold is reached, more sodium ion channels open, causing a greater influx of sodium ions into the neurone by diffusion
  • Once peak potential difference is reached, the sodium ion channels close and the potassium ion channels open
  • Potassium ions diffuse out of the neurone, starting repolarisation of the membrane
  • Too many potassium ions diffuse out of the neurone and the potential difference become more negative than the resting potential (hyperpolarisation)
  • Potassium ion channels now close and the sodium-potassium pump re-establishes the resting potential
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18
Q

Describe the refractory period

A

*The period after an action potential where it is impossible for a further action potential to be stimulated
* This is because the sodium voltage-gated ion channels are closed

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19
Q

What is the purpose of the refractory period?

A
  • Ensure that action potentials are propagated in one direction only
  • Produces discrete impulses
  • Limits the number of action potentials
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20
Q

Describe the passage of an action potential along an unmyelinated neuron

A
  • When an action potential happens, some of the sodium ions that enter the neuron diffuse sideways along the axon
  • This causes the opening of sodium ion voltage-gated channels a little further along the axon so more sodium ions move in
  • This causes depolarisation
  • Once initiated, the wave of depolarisation moves along the axon
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21
Q

Describe the passage of an action potential along a myelinated neuron

A
  • The myelin sheath acts as an electrical insulator
  • Sodium and potassium ions cannot diffuse through sheath
  • This means depolarisation only happens at the nodes of Ranvier
  • Longer local currents
  • Action potential ‘jumps’ from node to node - saltatory conduction
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22
Q

Why is transmission of an impulse slower in a non-myelinated neuron?

A

The impulse must travel as a wave along the whole length of the axon membrane which is slower than saltatory conduction

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23
Q

How can an organism perceive the size of a stimulus?

A
  • Greater stimulus = more frequent action potentials
  • Action potentials are always the same size
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24
Q

What factors affect the speed at which action potentials pass along an axon?

A
  • Myelination
  • Axon diameter
  • Temperature
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25
Q

Describe how axon diameter affects the speed at which action potentials pass along an axon

A
  • Larger diameter = quicker
  • Less resistance to the flow of ions
  • Less leakage of ion from the axon
26
Q

Describe how temperature affects the speed at which action potentials pass along an axon

A
  • Higher temp = quicker
  • Faster rate of diffusion of ions
  • Faster rate of respiration

Although, above a certain temp, enzymes and plasma membrane proteins are denatured and no impulses are conducted at all

27
Q

Describe synaptic transmission

A
  1. The arrival of an action potential at the end of the presynaptic neuron causes voltage-gated calcium ion channels to open and calcium ions diffuse into the synaptic knob
  2. The influx of calcium ions into the presynaptic neuron causes the synaptic vesicles to fuse with the presynaptic membrane, releasing acetylcholine into the synaptic cleft by exocytosis
  3. Acetylcholine molecules diffuse across the synaptic cleft and bind to receptor sites on sodium ion protein channels in the membrane of the postsynaptic neuron
  4. The influx of sodium ions causes depolariation. An action potential is generated if the threshold is reached.
28
Q

Describe why impulses can only travel in one direction across a synapse

A
  • Neurotransmitter is made only in the presynaptic neuron
  • The specific receptor proteins are only found on the postsynaptic membrane
29
Q

Define spatial summation

A

A number of different presynaptic neurons release neurotransmitter at the same time so threshold value can be reached and an action potential generated

Multiple presynaptic neurons link to one postsynaptic neuron

30
Q

Define temporal summation

A

A single presynaptic neuron releases neurotransmitter many times over a very short period so threshold is reached

31
Q

Define excitatory synapse

A

Neurotransmitters depolarise the postsynaptic membrane, resulting in an action potential if the threshold is reached

32
Q

Define inhibitory synapse

A

Neurotransmitters cause hyperpolarisation which makes it less likely that an action potential will be created in the postsynaptic neuron as a larger influx of sodium ions would be needed

33
Q

List the functions of synapses

A
  • Cell signalling between neurons
  • Unidirectionality
  • Convergence to allow for spatial summation
  • Filtering out low-level stimuli
  • Enable memories to be formed
  • Divergence (one impulse can be passsed onto multiple neurones)
34
Q

Define neuromuscular junction

A

The point where a motor neuron meets a skeletal muscle fibre

35
Q

Describe the similarities between the neuromuscular junction and a cholinergic synapse

A

Both:
* Have neurotransmitters that are transported by diffusion
* Have receptors, that on binding with the neurotransmitter, cause an influx of sodium ions
* Use a sodium-potassium pump to repolarise the axon
* Use enzymes to breakdown the neurotransmitter

36
Q

Describe the difference between neuromuscular junctions and cholinergic synapses with regards to excitatory vs inhibitory

A
  • Neuromuscular junction - Only excitatory
  • Cholinergic synapse - May be excitatory or inhibitory
37
Q

Describe the difference between neuromuscular junctions and cholinergic synapses with regards to what they connect

A
  • Neuromuscular junction - Only links neurons to muscles
  • Cholinergic synapse - Links neurons to neurons, or neurons to other effector organs
38
Q

Describe the difference between neuromuscular junctions and cholinergic synapses with regards to the type of neurons involved

A
  • Neuromuscular junction - Only motor neurons
  • Cholinergic synapse - Motor, sensory and intermediate neurons
39
Q

Describe the difference between neuromuscular junctions and cholinergic synapses with regards to the journey of the action potential

A
  • Neuromuscular junction - Action potential ends here
  • Cholinergic synapse - New action potential may be produced along postsynaptic neurone
40
Q

Describe the difference between neuromuscular junctions and cholinergic synapses with regards to where acetylcholine binds

A
  • Neuromuscular junction - Binds to receptors on membrane of muscle fibre
  • Cholinergic synapse - Binds to receptors on membrane of post-synaptic neuron
41
Q

Describe the three types of muscle

A
  • Smooth - Organs and blood vessels
  • Cardiac - In the heart
  • Skeletal - Attached to bone and the only type of muscle under conscious control
42
Q

Describe what is meant when it is said that muscles work in antagonistic pairs

A
  • Cannot push, can only pull or relax and only in one direction
  • Pairs work against each other to move limbs
43
Q

Define tendons

A

Attach muscles to bones

44
Q

Define ligaments

A

Attach bones to bones

45
Q

Define joint

A

Where muscles contract and relax to move a bone

46
Q

Describe the structure of skeletal muscles

A
  • Each fibre contains myofibrils
  • Myofibrils are made of 2 types of protein filament, actin and myosin
  • The contractile units of the cells are called sarcomeres
47
Q

Define sarcoplasmic reticulum

A

Specialised endoplasmic reticulum found in skeletal muscle

48
Q

Describe actin

A
  • Protein filament
  • Thinner
  • Two strands twisted around each other
49
Q

Describe myosin

A
  • Protein filament
  • Thicker
  • Long rod shaped fibres with bulbous heads pointing outwards
50
Q

Describe tropomyosin

A
  • Long, thin threads that wind around actin filament
  • When the muscle is at rest, tropomyosin blocks the binding sites that the myosin heads would attach to
51
Q

Describe slow-twitch muscle fibres

A
  • Slower and less powerful
  • Endurance
  • Mostly use aerobic respiration
  • Rich supply of blood vessels
  • Numerous mitochondria
  • Large store of myoglobin
52
Q

Describe fast-twitch muscle fibres

A
  • Faster and more powerful but only for a short period of time
  • Intense exercise
  • Good supply of glycogen to hydrolyse to glucose
  • High conc of enzymes for anaerobic respiration
  • Large store of phosphocreatine to provide phosphate for ATP
53
Q

Describe sliding filament theory of muscle contraction

A
  • Myosin and actin slide past each other
  • I band shortens
  • Z lines move closer together
  • H band shortens
  • A band does not change
54
Q

Describe how an action potential moves through a neuromuscular junction

A
  • An action potential reaches the neuromuscular junction, causing calcium ion channels to open and calcium ions to move into the synaptic knob
  • This causes the synaptic vesicles to move to the presynaptic membrane and fuse with it
  • Releases acetylcholine which diffuses across the synaptic cleft
  • Acetylcholine binds with sodium ion channels on the postsynaptic membrane
  • Sodium ion channels open and sodium ions then move into the sarcolemma
  • Causes the membrane to depolarise and an action potential to be generated
55
Q

Describe how an action potential in the postsynaptic membrane is moved into the muscle fibres

A
  • Action potential travels into the muscle fibre through a system of T-tubules
  • This causes calcium ion channels in the sarcoplasmic reticulum to open and calcium ions diffuse into the myofibrils
  • This initiates the movement of the protein filaments
56
Q

Describe the movement of protein filaments causing muscle contraction

A
  1. Tropomyosin molecule prevents myosin head from attaching to binding site on the actin molecule
  2. Calcium ions released from the ER cause the tropomysoin molecule to change shape and so they move away from the binding site on actin
  3. Myosin head now attaches to the binding site on the actin filament
  4. Head of myosin changes angle, moving the actin filament along and releasing an ADP
  5. ATP molecule fixes to myosin head, causing it to detach from actin filament
  6. Hydrolysis of ATP to ADP by ATP hydrolase provides the energy for the myosin to return to its normal position
  7. Head of myosin reattaches to a binding site further along the actin filament and the cycle is repeated
57
Q

Describe how muscles stop being stimulated

A
  • Calcium ions are actively transported back into the sarcoplasmic reticulum
  • The removal of calcium ions means that tropomyosin can establish its original position, covering the myosin head binding site
58
Q

Describe why ATP is needed for muscle contraction

A
  • So myosin heads can detach from the actin binding sites
  • To provide the energy needed to move the myosin heads
  • To actively transport calcium ions back into the sarcoplasmic reticulum
59
Q

Describe how ATP is made during aerobic respiration

A
  • Used when muscles are relaxed or moderately active
  • Contraction is relatively slow, limited by how quickly oxygen and the substrates can be provided by the blood
60
Q

Describe how ATP is made during anaerobic respiration

A
  • Used when more ATP is needed than can be provided by aerobic respiration
  • Lactate produced causes muscle fatigue
61
Q

Describe how ATP is made by the phosphocreatine system

A
  • Very fast, one-step reaction
  • Donation of phosphate from creatine phosphate
  • Allows 10 seconds of fast muscle contraction
62
Q

Describe how acetylcholine is returned to the presynaptic neurone after synaptic transmission

A
  • Acetylcholinesterase hydrolyses acetylcholine into choline and ethanoic acid, which diffuse back across the synaptic cleft into the presynaptic neuron
  • ATP is used to recombine choline and ethanoic acid into acetylcholine. This is stored in synaptic vesicles for further use.

Biology - Mrs Dudley (12 decks)

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