Nervous coordination and muscles Flashcards
What’s specialised about neurone membranes?
Sodium-Potassium pumps actively transport Na+ out of the cell and K+ into the cell
Sodium and potassium channels allow facilitated diffusion in either direction
What is the resting potential of a neurone?
The potential difference across the neurone membrane while the neurone is at rest
What is the avg value of resting potential?
-60 to -70 mV inside the neurone compared with outside
Why is a neurone more negative inside than outside?
3Na+ ions are pumped out for every 2K+ ions pumped into it and channels are kept closed
What is an action potential?
Depolarisation of the neurone membrane so that the inside is more positive than the outside
What is the value of the action potential?
+40mV
When does depolarisation occur?
When sodium channels open in response to a stimulus
What happens in an action potential?
Sodium ions diffuse into the neurone to start a nerve impulse
How do receptor cells work?
A stimulus causes the membranes to become more permeable to sodium ions so that the inside becomes less negative (generator potential)
What must happen for an action potential to be triggered?
A threshold level must be reached (-50mV) by the stimulus
What does the action potential trigger?
Nerve impulse
What happens in repolarisation?
Sodium channels close and potassium channels open, the neurone repolarises
What does it mean when a neurone is hyperpolarised?
Potassium channels are too slow to close and the potential difference overshoots, making it more negative inside than resting potential
How do neurones recover from hyperpolarisation?
Sodium-Potassium pumps restore resting potential
What happens in the refractory period?
Sodium ion channels can not reopen after they have been activated, until resting potential is reestablished
What does the refractory period ensure?
The movement of the impulse is unidirectional, meaning that it will only travel forwards and not backwards, also stops many impulses sent at once
How do nerve impulses transmit across a neurone?
Increasing sodium to depolarisation sets up a local current, the sodium diffuses sideways, this causes sodium ions further down the neurone to open, setting off another action potential, the local current moves down the neurone as a wave of depolarisation
What does the myelin sheath do?
Prevents ions from reaching the axon
Where can ions enter the axon?
Nodes of Ranvier
What does the cell body of the myelinated neurone do?
Protein production and neurotransmitter production
What do dendrites do?
Carry action potentials to surrounding cells
What does the axon do?
Carry nervous impulse along the neurone
What is the myelin sheath made of?
Individual Schwann cells
What are the gaps between Schwann cells called?
Nodes of Ranvier
How are action potentials transmitted down a non-myelinated neurone?
When depolarisation occurs, voltage-gated sodium channels open further down the axon and by the time depolarisation has spread part of the neurone has already repolarised
What is saltatory conduction?
Action potentials “jump” from node to node , which is much quicker, in myelinated neurones when transmitting an action potential
What is the difference between the synapse and synaptic cleft?
The synapse is the junction between two neurones, whereas the synaptic cleft is the gap that separates the pre and post synaptic neurone
What is the synaptic knob?
Swelling at the end of pre-synaptic neurones which makes and releases neurotransmitters
What is a neurotransmitter?
A chemical that diffuses across the synaptic cleft, to transmit a signal to the post synaptic neurone (cell signalling)
What is acetylcholine?
A type of neurotransmitter
What is a cholinergic synapse?
A synapse which makes and releases acetylcholine
What type of channels are on the pre and post synaptic neurones at the synapse?
Pre: calcium
Post: sodium
What is step 1 at the synapse?
Nerve impulse arrives at synaptic knob, causing calcium channels to open, which move into the knob by facilitated diffusion, these ions cause vesicles containing acetylcholine to migrate towards the pre-synaptic membrane
What is step 2 at the synapse?
Acetylcholine vesicles fuse with the membrane and release acetylcholine into the synaptic cleft by exocytosis, they diffuse quickly across the cleft due to the short distance
What is step 3 at the synapse?
Acetylcholine bind to receptor sites at post-synaptic neurones, causing sodium channels to open, causing depolarisation and a nerve impulse is set up
What is step 4 at the synapse (now post-synaptic neurone)?
Acetylcholinesterase is released, acetylcholine is hydrolysed to acetyl and choline, which diffuse back to the pre-synaptic neurone and are recycles with ATP, sodium channels close and the post-synaptic neurone is repolarised
What do excitatory transmitters do?
Cause depolarisation on the post-synaptic neurone to create an action potential
What do inhibitory transmitters do?
Cause hyperpolarisation, preventing the formation of a new action potential (GABA)
What can too much excitation lead to?
Seizures and other neurological disorders
What can too much inhibition lead to?
Depression and other mood disorders
How are weak stimuli amplified?
Temporal summation and spatial summation
What is temporal summation?
When multiple messages are sent quickly from the same pre-synaptic neurone
What are skeletal muscle fibres made up of?
Myofibrils
What are sarcoplasms?
Individual muscle cells that make up myofibrils
What are myofibrils made up of?
Repeating units called sarcomeres
What are the regions of myofibrils?
H zones, I bands, A band, the M line and the Z discs
What proteins are sarcomeres made up of?
Actin (thin) and myosin (thick) proteins which form filaments
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