15. nervous coordination and muscles Flashcards
What are the three types of muscle?
- smooth
- cardiac
- skeletal
What is meant by sarcoplasm
myofibrils share nuclei and cytoplasm
Describe the structure of actin
- thin, globular protein
- long chains in a helical shape
Describe the structure of myosin
‘Thick filament’ made up of two proteins;
- tail, long fibrous protein
- head, globular protein, two bulbous at the end
Describe the structure and function of tropomyosin.
- long, thin wound around actin filaments
- covers actin binding site, calcium ions expose binding sites, allowing myosin heads to bind
Draw and label that a sarcomere
go online for images :)
What is meant by ‘slow twitch fibres’
- slow, less powerful contractions
- contract for long periods
How are slow twitch fibres adapted for their function?
Adapted for aerobic respiration;
- large supply of myoglobin (store of oxygen)
- large supply of blood vessels (glucose + oxygen)
- many mitochondria (ATP)
How are fast twitch fibres adapted for their function?
Adapted for anaerobic respirations
- more myosin fibres
- high concentration of glycogen
- enzymes involved in anaerobic respiration
- phosphocreatine, replenishes ATP from anaerobic respiration.
What is meant by ‘fast twitch fibres’
rapid, powerful contractions for a short period, adapted for anaerobic respiration
Give four similarities between neurotransmitter and cholinergic junctions.
- neurotransmitters move by diffusion
- neurotransmitters binding to receptors causes influx of sodium ions
- Na/K pump repolorise
- use of enzymes to hydrolyse neurotransmitters
Give four differences between neurotransmitter and cholinergic junctions.
neuromuscular junctions;
- only excitatory
- involves motor neurons only
- action potential ends here
- acetylcholine binds to muscle, not another neuron
Give four pieces of evidence for the sliding filament theory.
- increased overlap of filament when contracted, appears darker.
- I-band is narrower when contracted
- z-lines are closer together, sarcomere is smaller
- H-zone is shorter
- A-band remains the same when contracted, shows that filaments are not shortening
Describe the seven steps of the sliding filament theory.
1) action potential reaches muscle
2) calcium ions enter sarcoplasmic reticulum and cause movement of tropomyosin to expose actin binding sites
3) myosin head forms ‘cross-bridge’ by binding to actin binding site. With ADP + pi
4)ADP detaches, bend created by rotation of myosin head (req ATP) , pulling actin filament,
5) attachment of new ATP molecule causes myosin heads to detach
6) hydrolysis energises myosin and causes it to move back to normal position.
Describe what happens when muscle is relaxed.
- calcium ions actively transported into ER
- tropomyosin covers up actin binding site
- can be stretched by antagonist (to a pont)
What neurotransmitter is found at neuromuscular junctions?
Acetylcholine
What enzyme hydrolyses Acetylcholine?
Why does this occur?
- acetylcholinerase
- to prevent muscle from being overwhelmed by sodium ions
Summarize what happens at neuromuscular junctions.
- impulse reaches junction
- synaptic vesicles (containing acetylcholine)
fuse to presynaptic membrane - acetylcholine diffuses to post-synaptic membrane
- acetylcholine causes a change in shape of sodium ion channels, increasing their permeability to sodium
- sodium ions enter postsynaptic membrane (muscle), depolarisation.
- acetylcholine is hydrolysed by acetylcholinesterase
- products diffuse back into presynaptic membrane.
What is meant by ‘motor unit’?
Fibres that share a motor neuron, allows for more units stimulated if more force is required.
How are rapid muscle contractions allowed?
Many neuromuscular junctions, action potential reaches across muscle
Explain the stages of action potential
DEPOLARIZATION
- stimuli opens some Na+ channels (fac diff), reversal of electrochemical gradient
- more Na+ channels open
REPOLARIZATION
- +40mV = voltage-gated sodium channels close, potassium channels open, K+ out of axon (fac diff).
- more channels open
HYPERPOLARIZATION
- temporary overshoot of electrical gradient (too negative) k+ channels close, resting is established by Na/K pump
Explain what is meant by saltatory conduction.
depolarization can only take place at nodes of ranvier.
insulation from myelinated sheaf, depolarization cannot take place here
faster action pot. at myelinated axons
Describe the structure and function of sensory neurons
- impulse from receptor to intermediate neuron
- one (long) dendron
- one axon
Describe the structure and function of Motor neurons.
- intermediate to receptor
- One long axon
- many dendrite
Describe the structure and function of Intermediate neurons
- impulse between different types of neurons (eg. sensory to motor)
- many short axon/dendrites
What direction do dendrites/ dendrons carry impulse?
towards cell body
What direction do axons carry impulse?
away from cell body
Explain how resting potential is maintained at the axon.
More positive outside neuron membrane, maintained by sodium-potassium pump
- 3Na+ out, 2K+ in
- electrochemical gradient
- K+ diffuse out (more permeable)
- SOME Na+ diffuse in (less permeable)
Contrast the permeability of axon membrane to Na+ and K+ at resting potential
- more permeable to K+, more channels, some always open
What is the voltage of resting potential?
-50, -90mV
-65mV in humans
Ignoring saltatory conduction, what are the functions of schwann cells?
- electrical insulation
- phagocytosis
- regeneration
What is the voltage at action potential (at the most depolarized)
+40mV
Describe what happens at cholinergic synapses. (6)
- arrival of action potential at presynaptic neuron causes calcium channels to open (enter fac diff)
- influx of calcium ion causes synaptic vesicles to fuse with membrane (acetylcholine into synaptic cleft)
- acetylcholine diffuses across cleft, binds to receptor on sodium channels on membrane of post-synaptic channel opens, Na+ in rapidly (fac diff)
- influx of Na+ generates new action potential
- acetylcholinesterase hydrolyses acetylcholine into acetyl and choline, diffuse back into presynaptic neuron
- ATP from mitochondria, is used to create acetylcholine, stored in synaptic vesicle
Why is acetylcholine hydrolysed after being released into synaptic cleft?
- recycle products at SER
- prevents too much stimulus, Na+ channels close
Factors affecting the speed of action potential
- mylenatic sheaf, saltatory conduction
- diameter of axon, larger = less leakage of ions, faster
- temperature, rate of diffusion, enzymes involved in respiration (sodium-potassium pump)
Describe and explain the importance of the refractory period.
Sodium channels remain closed after action potential.
- ensures action potential travels in one direction, prevent from going backwoods
- separates impulses
- limits no. of impulses and therefore strength of impulses
Draw and label the structure of a synapse.
including structures;
- mitochondria
- SER
- calcium channels
- vesicles
- presynaptic membrane
- synaptic cleft
- sodium ion channels
- postsynaptic membrane
Explain the ‘all or nothing’ principle
Stimulus must exceed threshold value to create action potential.
How is the size of stimulus detected?
- no. of impulses in a given time
- some neurons have different threshold value, detected by brain
Describe spacial summation
- multiple presynaptic neurons produce enough neurotransmitters for action potential
- multiple action pot. into one action pot.
Temporal Summation
neurotransmitter released multiple times in short period to exceed threshold.
Inhibitory synapses
- releases neurotransmitter that bind to chloride channels on postsynaptic membrane
- chloride channels open, in by fac diff
- also causes potassium to open, K+ out of postsynaptic
- post synaptic membrane is more negative (hyperpolarization)
- resting = -80mv
- more Na+ needed to establish action pot.
What are the functions of synapses
- action pot. from one neuron to multiple = simultaneous response
- multiple impulses combined at one synapse, single response from many stimuli
define summation
rapid build up of neurotransmitters in the synapse to help generate action potential
To enter the bowman’s capsule, molecules have to small enough to fit through…
gaps in epithelial lining of capillaries and gaps between podocytes
how do synapse ensure unidirectional flow of depolarisation
sodium channels only on post synaptic membrane
neurotransmitter released at the pre synaptic membrane only