Nervous Coordination Flashcards
Describe the cell membrane of a neurone at resting state
- Outside: +ve charged compared to inside
- bc more +ve ions outside
- Membrane = polarised (diff. charge)
Define potential diff/voltage
Diff in charge
What is the v called when at rest?
- Resting potential
- -70v
The sodium-potassium uses ____ so ___ is required
- AT
- ATP
How is the resting potential created + maintained?
- Sodium potassium pump
- 3 Na+ moves out neurone, membrane not permeable so can’t diffuse back in
- Creates Na+ electrochemical gradient
- Pump also moves 2 K+ in neurone but membrane permeable so (facilitated) diffuse out through potassium ion channel
- Makes outside +ve charged compared to inside
When does an action potential occur?
- Stimulus big enough, Na+ channels open
- Triggers rapid change in potential diff
What happens in the refractory period?
- Neurone cell membrane can’t be excited straight away
- bc ion channels are recovering
- Na<strong>+</strong> channels closed during repolaristion + K+ channels closed during hyperpolarisation
Explain how the action potential moves along the neurone as a wave of depolarisation
- During AP, some Na+ that enter neurone diffuse sideways
- Causes Na+ channels in next region to open + Na+ diffuse into that part
- Causes wave of depolarisation to travel along neurone
- Wave moves away from parts of membrane in refractory period bc can’t fire AP
The refractory period acts as a time delay, what does the mean?
- AP don’t overlap but pass along as descrete impulses
- Limit to freq to which impulses can be transmitted
- AP are unidirectional (1 direction)
Action potentials have an all or nothing nature, what does this mean?
- Once threshold is reached, AP will always fire w/ same charge in v
- If threshold not reached, AP won’t fire
What does a bigger stimulus result in?
More frequent AP
What factors affect the speed of conduction of action potential?
- Myelination
- Axon diameter
- Temp
What is myelination?
When neurones have myelin sheath - electrical insulator
In the peripheral NS, what is the sheath made from?
Schwann cell
What are the sections btw the schwann cells?
Bare membrane - nodes of Ranvier
What are conc at the nodes?
Na+ channels
How does the action potential go across through a myelinated neurone?
Saltatory conduction
How does saltatory conduction take place?
- Depolarisation only occurs at nodes of ranvier
- Cytoplasm conducts enough electrical charge to depolarise next node, so impulse jumps node to node
How does an impulse travel along a non-myelinated neurone?
Travels as wave along whole length of axon membrane
Does an impulse travel faster along a myelinated or a non-myelinated neurone? Why?
- Myelinated
- Saltatory conduction allows impulses to travel quickly
How does the axon diameter affect speed of conduction?
- Bigger diameter = less resistance to flow of ions
- Depolarisation reaches other parts of neurone membrane faster
How does the temperature affect speed of conduction?
- Temp inc = ions diffuse faster
- Only upto 40ºc bc proteins denature + speed dec
Define synapse
Junction btw neurone + another neurone, neurone + effector cell
How does synapses ensure that nerve impulses are unidirectional?
Reeceptors only on post synaptic membrane
Why and how are the NT removed from the cleft?
- So response doesn’t keep happening
- Taken back into presynaptic neurone
- Broken down by enzymes
Define excitatory NT
Depolarise post synaptic membrane, making it fire an action potential if the threshold is reached
Define inhibitory NT
Hyperpolarise post synaptic membrane, preventing it from firing an AP
Define summation
Effect of NT released from many neurones is added together
Spatial summation
- Many neurones connect to 1 neurone
- Small amounts of NT released from each neurone can be enough altogether to reach threshold in postsynaptic neurone + trigger AP
- If inhibitory NT released = no AP
Temporal summation
- 2/more nerve impulses arrive in quick sucession from same presynaptic neurone
- Makes AP more likely bc more NT released into synaptic cleft
What does summation mean for synapses?
Synapses can accurately process info, finely tuning response
Define neuromuscular junction
Synapses btw motor neurone + muscle cell
What does acetylcholine bind to in neuromuscular junctions?
Cholinergic receptors called nicotine cholinergic receptors
What are the diff btw cholinergic synapses + neuronmuscular junctions?
- Post synaptic mebrane has lots of folds that form clefts - stores enzyme that break down ACh (acetyl cholinesterase)
- More receptors
- ACh always excitatory at neuromuscular junction- motor fires AP = tiggers response in muscle cell
What are agonist drugs + what do they do?
- Same/similar shape as NT so mimic their action at receptors
- Means more receptors are activated
What are antagonist drugs + what do they do?
- Same/similar shape as NT so block receptors so can’t be activated
- Fewer receptors can be activated
What happens when drugs inhibit enzymes that break down NT?
More NT in synaptic cleft to bind to receptors + they’re there for longer
What do some drugs stimulate the release of?
NT from presynaptic neurone so more receptors are activated
What do some drugs inhibit the release of?
NT from presynaptic neurone so fewer receptors are activated
Describe how a nerve impulse is transmitted across a cholinergic synapse (8)
- Impulse causes Ca<strong>2+</strong> to enter axon
- Vesicles move to presynaptic membrane
- Acetylcholine released
- Diffuse across synaptic cleft/synapse
- Binds w/ receptor on post synaptic membrane
- Na+ enter post synaptic neurone
- Depolarisation of post synaptic membrane
- If above threshold, AP produced
Skeletal muscles
Muscles you use to move
Tendons
Attach skeletal muscles to bones
Ligaments
Attach bones to bones
Why are muscles described as antagonistic pairs?
- Contracting muscle: agonist
- Relaxing muscle: antagonist
- Bones of skeleton are incompressible so act as lever, giving muscles something to pull against
Outline the structure of a skeletal muscle
- Large bundles of long cells - muscle fibres
- Cell membrane of muscle fibre - sarcolemma
- Sarcolemma fold inwards + stick into sarcoplasm, folds = transverse tubule, help spread electrical impulse throughout sarcoplasm
- Network of internal membrane (sarcoplasmic reticulum) runs through sarcoplasm, stores + releases Ca<span>2+</span> needed for contraction
- Lots of mitochondria provide ATP
- Multinucleate
- Made up of myofibrils, specialised for contraction
Myosin
- Thick myofilament
- Dark
- A band
Actin
- Thin myofilament
- Light
- I band
Contracted sarcomere
- A band stays same
- I band, H zone + sarcomere gets shorter
Outline the structure of myofibrils when a muscle is at rest
- Actin-myosin binding site is blocked by tropomyosin
- Myofilaments unable to slide past bc myosin head can’t bind
Outline the process when muscles contract
- AP depolarises sarcolemm, spreads to t tubules + down SR, releases Ca2+ to sarcoplasm
- Ca2+ binds to protein on tropomyosin, changes shape pulling tropomyosin out AM binding site on actin
- Exposes binding site allowing myosin head to bind, forming AM cross bridges
- CA2+ activates ATP hydralase, hydrolysing ATP
- Energy causes myosin head to bend, pulling actin filament along
- Another ATP provides energy to break AM cross bridge so myosin head detaches
- Myosin head reattaches to another binding site
What happens when muscles relax?
- Ca2+ leave binding site + AT into SR
- Causing tropomyosin to block AM binding site
- Actin filament slides back to relaxed position, lengthens sarcomere
Aerobic respiration
- ATP generated via OP in mitochondria
- Oxygen available
- Long periods of low intenisity exercise
Anaerobic respiration
- ATP generated rapidly by glylosis
- Pyruvate → lactate - causing muscle fatigue
- Short periods of hard exercise
ATP phosphocreatine system
- ATP made by phosphorylating ADP - adding phosphate group from PCr
- PCr stored inside cells but runs out quickly, short bursts of vigorous exercise
- Generates ATP quickly
- Anaerobic
- Alactic
Slow twitch muscle fibres
- Contract slowly
- Endurance activity
- Work for long time w/o getting tired
- Energy released slowly via aerobic respiration, lots of mitochondria + blood vessels
- Red bc rich in myoglobin
Fast twitch muscle fibre
- Contracts quickly
- Short bursts of speed + power
- Get tired quickly
- Energy released quickly via anaerobic respiration using glycogen. Few mitochondria + blood vessels
- White bc lacks myoglobin
