Topic 6B - Nervous Coordination Flashcards
How is the movement of sodium and potassium ions maintained? What type of transport do they use?
Sodium-potassium pump - active transport
Potassium ion channels - facilitated diffusion
Why is the membrane polarised?
There is a difference in charge across the membrane
What do sodium potassium pumps do? How does it transport it?
Use active transport
Move 3 sodium ions out of the neurone for every 2 potassium ions moved in, using ATP.
What do potassium ion channels do?
Allow facilitated diffusion of potassium ions out of the neurone down the concentration gradient.
How is a sodium ion electrochemical gradient produced?
Membrane isn’t permeable to sodium ions so cant diffuse back in
More positive Na+ outside of cell than inside
Why do potassium ions diffuse back out through the ion channels?
Most channels open at rest
Membrane is more permeable
What is an action potential?
Rapid change in potential difference, cell becomes depolarised
What are the 5 stages of an action potential?
Stimulus
Depolarisation
Repolarisation
Hyperpolarisation
Resting potential
What happens during the stimulus?
Cell membrane excited, causing Na channels to open
Membrane permeable to sodium
Sodium diffuse down sodium electrochemical gradient
Inside of neurone less negative
What happens during depolarisation?
If potential difference reaches threshold, more Na channels open
More Na diffuse into neurone causing depolarisation
What happens during repolarisation?
Sodium ions channels close and potassium ion channels open
K+ ions diffuse down conc gradient
Begins getting the membrane back to resting potential
What happens during hyperpolarisation?
K+ channels slow to close
A few too many K + ions diffuse out of neurone
Potential difference becomes more negative than resting potential
What happens during the resting potential?
Ion channels are reset
NaK+ pump returns membrane to resting potential
Does this by pumping Na+ out and K+ in
Maintains resting potential until membrane is excited again
What is the refractory period?
Time delay between action potentials
So they dont overlap but pass along as discrete impulses
Potentials are unidirectional and are all closed at the same time
What causes waves of depolarisation?
Some Na ions diffuse sideways into neurone
This causes Na ions in next channel of the neurone to open and Na ions diffuse into that part
Why do the waves move away from the parts of the membrane in the refractory period?
These parts cant fire an action potential
What is the all or nothing principle?
Once the threshold is reached, an action potential will be fired
(Always fires with the same change in voltage, no matter how big the stimulus is)
What will a bigger stimulus cause?
More action potentials to occur
What does the myelin sheath do?
Electrical impulse insulator
What is the sheath made of in the PNS?
Schwann cells
What is between the myelin sheath? What does it do?
Nodes of ranvier
Where sodium ion channels are concentrated
Where does depolarisation occur in Saltatory conduction?
At the nodes of ranvier
How does an impulse travel in a non-myelinated neurone?
Impulse a travels as a wave along a whole length of the axon
How does axon diameter affect conduction?
Bigger diameter conduction will work better as there is less resistance
Depolarisation reaches other parts quicker
How does temperature affect conduction?
Conduction increases and ions diffuse faster
To an extent - denature at over 40C
What is a synapse?
The junction between the neurone membrane and another and an effector cell
What is the synaptic cleft
Gap between syanpses
What is the swelling on the presynaptic neurone called?
The synaptic knob
What does the synaptic knob contain?
Vesciles filled with neurotransmitters
What happens at the end of an action potential?
Neurotransmitters are released into the synaptic cleft and diffuse across and attach to the receptor cells on the post synaptic membrane
What do receptors only on the postsynaptic membrane do?
Make sure impulses are unidirectional
Remove neurotransmitters so response doesn’t keep happening
What does acetylecholine do?
Binds to cholinergic receptors
What happens after the arrival of the action potential? (Cholinergic synapse)
Arrives at presynaptic membrane
Stimulates voltage-gated Ca ion channels to open
Ca diffuse into synaptic knob
What occurs during the fusion of vesicles?
Influx of Ca ions
Causes synaptic knob to fuse with the presynaptic membrane
Release ACh into synaptic cleft - via exocytosis
How does ACh diffuse?
Diffuses across cleft and binds to specific cholinergic receptors on postsynaptic membrane
Na channels open
Why is ACh removed?
To stop the response continuing happening
What does the exciters do?
Polarise postsynaptic membrane, firing an action potential
What does inhibitory do?
Hyperpolarise postsynaptic membrane, preventing an action potential from being fired
What is inhibitory synapse?
Where an inhibitory neurotransmitter is released, following an action potential
What is summation?
Where the effect of neurotransmitters released from meant neurones is added together
What is spatial summation?
2 or more presynaptic neurones release their neurotransmitter on the same post synaptic neurone
What is temporal summation?
2 or more nerve impulses arrive in quick succession from the same presynaptic neurone
What do neuromuscular junctions do?
Use acetylcholine which binds to chollinergic receptors called nicotine cholinergic response
What’s the difference between neuromuscular junctions and cholinergic synapses?
Post synaptic membrane has lots of folds that form clefts and store AChE
Has more receptors than other synapses
Always excitatory, so when a motor neurone fires an action potential, it normally triggers a response in a muscle cell
Why do some drugs block receptors?
So fewer receptors are activated
Why do some drugs block enzymes?
Less neurotransmitter broken down so that more in the cleft can bind to the receptors and are there for longer
Why do some drugs stimulate the release of neurotransmitter?
So more receptors can be activated
Why do some drugs inhibit the release of neurotransmitter?
To the fewer receptors are activated
What is smooth muscle?
Contracts without conscious control
What is cardiac muscle?
Contracts without conscious control
Only found in heart
What is skeletal muscle?
Muscle used to create movement
How do skeletal muscles work?
Bones of skeleton are incompressible, so they act as levers giving the muscles something to pull
What is antagonistic pair?
A pair of muscles that work together to move a bone
What are the cell membranes of skeletal muscles called?
Sarcolemma
What are the folds in skeletal muscles called? What do they do?
Transverse tubules
Help spread electrical impulses throughout the sacroplasm to reach all parts of the muscle fibre
What does sacroplasmic reticulum do?
Network of internal membranes that store and release Ca ions needed for muscle contraction
What are some qualities of muscles fibres?
Lots of mitochondria
Multinucleate
Myofibrils - made of protein highly specialised for contractions
What do muscles look like under a microscope?
Different colours will stain different parts, the image will either be longitudinal or a transverse cross section
What do myofibrils contain?
Bundles of thick and thin myofilaments that move past each other to make muscles contract
What are thick myofibrils made of?
Myosin protein
What are thin myofibrils made of?
Actin protein
What are A bands?
Pattern of alternating dark and light bands and some overlapping actin filaments
What are L bands?
Only light bands - contain only the actin filament
What is a myofibrils made of?
Short units called sacromeres
End is Z-line
Middle is M-line
Around the M-line is the H-zone
What is the sliding filament theory?
Myosin and actin filaments slide over each other to make sacromeres contract
What causes the actual muscle to contract?
Simultaneous contraction of lots of sacromeres means the myofibrils and muscle fibres contract
What happens to sacromeres as muscle relaxes?
Return to original size
What is a myosin filament?
Globular heads that are hinged, can move back and forth
Each myosin head has a binding site for actin and a binding site for ATP
What is an actin filament?
Have an actin myosin binding site.
Protein called tropomyosin is found between actin filaments
Helps myofilaments move past each other
What happens to actin-myosin in resting muscle?
Binding site is blocked by tropomyosin
Myofilaments can’t slide over each other as myosin heads cant bind to actin filaments
What happens when an action potential from a motor neurone stimulates a muscle cell?
Depolarises the sarcolemma
What does depolarisation cause?
Spreads down t-tubules to sacroplasmic reticulum
Causes it to release calcium ions into sacroplasm
In return triggers a muscle contraction
What happens when calcium ions bind to tropomyosin?
Causes protein to change shape
Pulls the attached tropomyosin out of the actin-myosin binding site on the actin filament
What happens when calcium ions bind to a protein attached to tropomyosin?
Causes protein to change shape
Pulls the attached tropomyosin out of the actin-myosin binding site on the actin filament
What is an actin-myosin cross bridge?
The bond formed when a myosin binds to an actin filament
What do calcium ions activate?
ATP hydrolase
(This hydrolyses ATP into ADP and Pi to provide energy for muscle contraction)
What is contraction like in slow twitch muscles?
Slow, less powerful
What is contraction like in fast twitch muscles?
Quicker, more powerful
What is movement like in slow twitch muscles?
Slow and longer endurance
What is movement like in fast twitch muscles?
Fast, short endurance and high intensity
What respiration occurs in slow twitch muscles?
Aerboic
What respiration occurs in fast twitch muscles?
Anaerboic
What colour is slow twitch muscles?
Red due to myoglobin and blood vessels
What colour is fast twitch muscles?
White due to no myoglobin
