3.6.2 and 3.6.3 Nervous Coordination and Muscles Flashcards
label
answer
What is the purpose of the myelin sheath?
To insulate the axon
What is nervous control?
Electrical transmission via nerve impulses and chemical transmission at synapses, fast acting, APs carried by neurones with connections to specific cells, localises and short lived response
What is skeletal muscle?
Type of muscle you use to move
What is the myosin?
A contractile protein found in thick myofilament. It has an ATPase activity
What is actin?
A protein found in the thin myofilament
What is a myofibril?
Long, cylindrical organelles inside muscle fibres. each is made up of a series of contractile units called sarcomeres
What ion is required for muscle contraction?
Calcium ion
Describe sliding filament theory
Myosin and actin filaments slide over each other making the sarcomeres contract. the simultaneous contraction of lots of sarcomeres means the myofibrils and muscle fibres contract
What happens to the actin-myosin binding site during muscle relaxation?
Blocked by tropomyosin
How is muscle contraction triggered and what then happens?
An AP from a motor neurone stimulates a muscle cell and it depolarises the sarcolemma. Depolarisation spreads down the T tubules to the sarcoplasmic reticulum. This causes the sarcoplasmic reticulum to release Ca2+ ions into the sarcoplasm
What happens to troponin during muscle contraction and what is the effect of this?
Calcium ion binds to the troponin, changing it’s shape so the tropomyosin is moved and the actin-myosin binding sites are exposed
What happens when the actin-myosin binding site is exposed?
Myosin heads bind to the actin-myosin binding sites on actin forming cross bridges
What is the effect of the actin-myosin binding sites being blocked?
Filaments cannot slide past each other
Why is ATP required for muscle contraction?
Hydrolysis of ATP provides energy to move the myosin head which pulls the actin along. it also provides energy to break the cross bridge so the myosin head detaches to allow binding to the next binding site
What happens when the myosin head reattaches to a different binding site ?
A new actin myosin cross bridge forms. Aany cross bridges form and break very rapidly pulling the actin filament along- which shortens the sarcomere so the muscle contracts
How is ATP broken down?
Hydrolysis reactions
What is the role of the stimulus during an action potential ?
This excites the neurone cell membrane, causing the Na+ channels to open. The membrane becomes more permeable to Na+, so Na+ diffuse into the neurone down the Na+ electrical gradient. This makes the inside of the neurone more positive.
What are the nodes of Ranvier ?
Gaps between schwann cells where there is bare membrane. Na+ channels are concentrated here.
What is myelin sheath made by ?
Schwann cells
Speed of nerve impulse dependant on…
Diameter of axon, temperature and myelination
What is the role of the Na/K pump and the K+ channel in the resting potential ?
Na/K pumps use AT to move 3 Na+ out of the neurone for every 2 K+ moved in, using ATP. Then K+ channel allows facilitated diffusion of K+ out of the neurone down their conc gradient. This makes the outside of the membrane more positive, creating a pd. Then K+ diffuse back in down their electrical gradient, there is no net movement of K+.
What is the voltage across the membrane during resting potential?
- 70mV
What is the all or nothing response?
Nerve fibres have a threshold to trigger an action potential, this is the point at which there are enough Na+ channels open to cause change in potential difference. if this point is reached an action potential occurs and its always the same size
What is the refractory Period ?
Period of recovery after an AP when the cell membranes cant be excited again. The channels are recovering and they cant be made to open
What is the purpose of refractory period ?
Acts as a time delay so APs dont overlap but pass along as discrete impulses. It makes sure APs are unidirectional
What is threshold level ?
An action potential is only triggered if the potential difference reaches a certain level (-50mv)
What is saltatory conduction?
In a myelinated neurone, depolarisation only happens at the nodes of Ranvier. The neurones cytoplasm conducts enough electrical charge to depolarise the next node, so the impulse jumps from node to node
Describe the synapse structure
Pre synaptic neurone containing mitochondria and vesicles containing neurotransmitter in synaptic knob, gap between this a post-synaptic neurone is synaptic cleft, post synaptic neurone has neurotransmitter receptors in its membrane
What is the role of a synapse ?
control of nerve pathways, allowing flexibility of response. integration of information from different neurones, allowing a coordinated response.
Define a synapse
Junction between a neurone and another neurone
What is the synaptic cleft?
Gap between post synaptic neurone and pre synaptic neurone (10-20nm)
How does an AP trigger calcium influx (in synapse transmission)?
An AP arrives at the synaptic knob, depolarising the presynaptic membrane. the voltage gated Ca 2+ ion channels in the presynaptic neurone open. Ca 2+ diffuse into the synaptic knob
How does the calcium influx cause neurotransmitter release (in synapse transmission) ?
the influx of Ca 2+ into the synaptic knob causes the synaptic vesicles to move to and fuse with the presynaptic membrane. the vesicles release the neurotransmitter into the synaptic cleft (exocytosis)
How does the neurotransmitter trigger an AP in the postsynaptic neurone (in synapse transmission) ?
the neurotransmitter diffuses across the synaptic cleft and binds to specific receptors on the post synaptic membrane. this causes Na+ channels in post synaptic neurone to open. the influx of Na+ in the post synaptic membrane causes depolarisation. an AP is generated if the threshold is reached. the neurotransmitter is removed from the synaptic cleft so the response doesnt keep happening.
How are neurotransmitters inactivated?
Some are taken up by the presynaptic membrane by active transport and are used again. others rapidly diffuse away from the synaptic cleft or are taken up by other cells of the NS.
How do synapses ensure impulses are unidirectional ?
the receptors are only on the post synaptic membranes
What is summation?
A single synapse doesnt usually depolarise the membrane enough to produce an AP but several impulses arriving within a short time produce enough depolarisation via the release of neurotransmitter to produce an AP.
What is temporal summation ?
The addition of several impulses travelling along a single neurone one after the other. their combined release of neurotransmitter generates an AP.
What is spatial summation ?
the addition of several impulses from different neurones can produce enough depolarisation above the threshold to produce an AP at the post synaptic neurone
labels
answer
complete
answer
q
q
q
what is happening at point x
why does myelination increase the speed of an action potential along a neurone
list the 4 key proteins you would find in the sarcomere and give their functions
how does the banding pattern of the sarcomere change during contraction?
what is this? can you label it
