B15 Nervous Coordination and Muscles Flashcards
How do we maintain resting potential of a neurone
Using sodium-potassium ion pumps.
They actively transport 3 Na+ out the neurone
They actively transport 2 K+ into the neurone.
Ensures more positive ions outside the neurone than inside
What is the resting potential of neurones
-70mV
4 steps in order of how an Action Potential is formed
- Depolarisation
- Repolarisation
- Hyperpolarisation
- Restoring of the resting potential via Na-K ion pump
When a neurone is stimulated, the membrane becomes
depolarised
What is the threshold potential
-55mV
Depolarisation process
If the threshold potential of -55mV is met:
Na+ channels open
K+ channels closed
So Na+ diffuse into the neurone via facilitated diffusion.
This decreases the potential difference across the membrane until it reaches a voltage of around +30mV
Repolarisation process
Na+ channels close
K+ channels open
K+ ions diffuse down their concentration gradients out of the neurone which reestablishes the charge difference in the membrane.
Hyperpolarisation
Few too many K+ ions diffuse out as the K+ channels are too slow to close.
So the charge difference exceeds the resting potential
Restoring of RP
The action of the sodium-potassium ion pump restores the balance of Na and K on either side of the membrane
Diagram of an action potential. Time against voltage
Search it up
How is an AP stimulated across the neuronea
A wave of depolarisation occurs along the neurone because sodium ions diffuse into the neurone sideways
What is the refractory period
Time immediately after an action potential has been stimulated where a neurone cannot be stimulated so an AP cant occur.
This is because ion channels are recovering
Why is a refractory period good
Ensures AP’s don’t overlap/ prevents neurones from being overstimulated
Ensures that AP’s are unidirectionals
Different sized stimuli result in …
Different frequencies of action potentials
Factors affecting the speed of an action potential
Myelination
Axon diameter
Temperature
How does myelination affect the conduction velocity of an AP
Myelin Sheath acts as an electrical insulator which prevents ion movement across the membrane
Depolarisation can only occur at the nodes of Ranvier where the voltage-gated sodium ion channels are concentrated
So action potentials ‘jump’ from node to node - saltatory conduction
What is saltatory conduction
When action potentials jump from node to node in myelinated neurones
Why does axon diameter affect the speed of an AP on a neurone
A bigger axon, AP travels quicker because there is less resistance to the flow of ions in the neurone
How does temperature affect the conduction velocity of an action potential
ions have a greater kinetic energy so diffuse faster and depolarisation can occur at a faster rate
ofc till optimum temp where channel proteins will denature and stuff
Synaptic Transmission process
- Action potential reaches the end of the presynaptic neurone.
- This triggers the opening of voltage-gated Calcium ion channels so Ca2+ enter the presynaptic neurone via facilitated diffusion
- Influx of calcium ions triggers the movement of vesicles towards the presynaptic membrane
- Vesicles fuse with membrane and release neurotransmitters via exocytosis
- NTs diffuse across the synaptic cleft and are detected by receptors on the postsynaptic neurone
- This triggers the opening of Na+ ion channels so sodium ions move into the postsynaptic neurone which stimulates depolarisation and therefore an AP is stimulated on the postsynaptic neurone.
What 2 things allow APs to travel unidirectionally
- refractory period
- receptors are found on the postsynaptic neurone
What are cholinergic synapses
Synapses that use acetylcholine as the neurotransmitter
What is acetylcholine broken down by
acetylcholinesterase
How does acetylcholinesterase break down acetylcholine
into acetate and choline
products are reabsorbed into the presynaptic neurone to synthesise the neurotransmitter
What are excitatory NTs
they trigger an AP in postsynaptic neurone
What are inhibitory NTs
they prevent an AP from occuring
e.g. by opening K+ channels in postsynaptic neurone so instead of stimulating depolarisation, it stimulates more hyperpolarisation
What is spatial summation
lots of presynaptic neurones converging to 1 single postsynaptic neurone
What is temporal summation
1 single neurone fires an AP in quick succession repeatedly which releases small amounts of NTs into the synaptic cleft which all combined produces enough of an effect to stimulate an AP
What are neuromuscular junctions in between
a motor neurone and a muscle cell
What neurotransmitter do neuromuscular junctions use
acetylcholine
Differences between neuromuscular junctions and a normal synapse
postsynaptic neurone is folded into clefts which stores the enzyme acetylcholinesterase
acts as an excitatory NT
has a high number of receptors on postsynaptic neurone
What is skeletal muscle used in
any physical movement
how can the muscles work
in antagonistic pairs so when 1 muscle contracts the other relaxes
e.g. when arm relaxes, the bicep (flexors) relaxes but the tricep (extensors) contracts
The structure of skeletal muscles
bone > tendon > muscle > bundle of muscle fibres > muscle fibre > myofibril > sarcomeres
What is a transverse tubule
when the sarcolemma folds into the sarcoplasm
what does the sarcoplasmic reticulum do
stores calcium ions for muscle contraction
what are the 2 types of myofilaments which make up myofibrils
actin and myosin
myosin is the ___ filament and appears as the ____ / _ band
thick
dark
A
actin is the ____ filament and appears as a ____/ _ band
thin
light
I
Structure of sarcomere
search it up but basically
A band is middle dark section
I band is on either side of A band
Z line is at the end of the sarcomere
H-zone is the central region of the A band only containing myosin
M line is the centre line of the sarcomere
Myosin myofilament structure
They have head groups which can bind to actin and ATP
Their heads are globular and hinged allowing them to move back and forth
Under resting conditions, what blocks the actin-myosin binding site
tropomyosin ( sphere-like thing ) and troponin ( string )
What happens when an AP arrives at a muscle fibre
- Wave of depolarisation passes along the sarcolemma and down the T-tubules
- This stimulates the sarcoplasmic reticulum to release the calcium ions
- The calcium ions bind to troponin, which causes it to change shape and pull tropomyosin out of the actin-myosin binding site so an actin-myosin cross-bridge can form
- Release of calcium ions also activates ATPase, which catalyses the hydrolysis of ATP into ADP + Pi.
- The energy released from this is used by the myosin head to move backwards, which pulls the actin filament closer towards it.
- ATP hydrolysis also provides energy to break the actin-myosin cross bridge.
- This allows myosin to reattach to a binding site further along the actin. This process is repeated and results in shortened sarcomeres and muscle contraction
What happens when the muscle stops being stimulated
Calcium ions move back into the sarcoplasmic reitculum via active transport.
Troponin molecules reform their OG shape so tropomyosin is pushed back into the actin-myosin binding site
What happens to the diff parts of sarcomeres during muscle contraction
A band stays the same length
I band shortens
Z lines become closer
H zone decrease in width
What 3 ways generates ATP in muscle contraction
Aerobic respiration
- oxidative phosphorylation
Anaerobic respiration
-glycolysis
Phosphocreatine
…
How does phosphocreatine work
Phosphocreatine phosphorylates ADP which releases ATP and creatine (removed via kidneys)
it is anaerobic and alactic
Where is phosphocreatine stored
muscle cells
When is phosphocreatine useed
very short bursts of vigorous exercise
Slow twitch muscle fibres
contract for long periods of time without getting tired
most of the energy is supplied from aerobic respiration
fast twitch muscle fibres
fatigue easy
get their energy from anaerobic respiration
used for short bursts of speed
why do slow twitch fibres have a reddish appearance
due to high presence of myoglobin which is a protein which stores oxygen
