nervous coordination and muscles Flashcards
what are the main parts of the neurone?
- cell body
- nodes of ranvier
- myelin sheath
- axon
- dendrites
- schwann cells
what do schwann cells do?
- surround axon
- provide electrical insulation
- carry out phagocytosis
what is a myelin sheath?
- a “coating” of an axon
- made up of membranes of Schwann cells
what are nodes of Ranvier?
- gaps between adjacent Schwann cells
- no myelin
- 2-3 um long
what is a sensory neurone?
- neurone that carries nerve impulses from receptor to an intermediate or motor neurone
- one long dendron
what does a motor neurone do?
- carry nerve impulse from an intermediate neurone to an effector
- long axon, short dendrites
what does an intermediate neurone do?
- transmits nerve impulses between 2 neurones
what is a nerve impulse?
self propagating wave of electrical activity that travels along the axon membrane
when is a nerve impulse carried?
when there is a temporary reversal of charges across the axon membrane
what is meant by resting potential?
- when the outside of the membrane has a positive potential in relation to the inside
- axon said to be polarised
what is the resting potential of an axon?
-70mv
what are the light bands in myofibrils caused by and what are they called?
- caused by lack of overlap of thin and thick filaments
- I bands (isotropic)
what are the dark bands on myofibrils caused by, and what are they called?
- overlap of thin and thick filaments
- A bands (anisotropic)
explain slow twitch muscle fibres
- contract slower than fast twitch and over a longer period of time
- provide less powerful contractions
- adapted for endurance work
- eg calf muscle
- aerobic respiration
how are slow twitch muscle fibres adapted for their role?
- large store of myoglobin (red molecule that stores a lot of oxygen)
- rich supply of blood vessels for glucose and oxygen delivery for aerobic respiration
- many mitochondria for a lot of ATP
describe fast twitch muscle fibres
- rapid and powerful contractions for a short period of time
- adapted to intense exercise
- eg biceps
how are fast twitch muscle fibres adapted to their role?
- thicker and more numerous myosin filaments for fast contraction
- high concentration of glycogen
- large number of enzymes for anaerobic respiration to increase ATP production
- phosphocreatine for creation of ATP in anaerobic conditions
how is a neuromuscular junction different to a cholinergic synapse?
- only excitatory
- only links neurones to muscles
- only motor neurones
- end of the action potential pathway
- acetylcholine binds to membrane of muscle fibres
describe the structure of a skeletal muscle
- the whole muscle is made up of several bundles of fibres
- these bundles are made up of muscle fibres, which are made up of myofibrils
what is a motor unit?
all of the muscle fibres which are stimulated by the same motor neurone
how does the sarcolemma become depolarised?
- nerve impulse received at the neuromuscular junction
- synaptic vesicles fuse with the presynaptic membrane and release acetylcholine across the NMJ
- acetylcholine diffuses to the sarcolemma and alters the permeability to sodium ions
- sodium ions enter and the sarcolemma is depolarised
what causes muscle shortening?
- actin sliding over the myosin filaments
- formation of actinomyosin head
what is the evidence for the sliding filament theory?
- I bands become narrower
- Z lines move closer together (sarcomere shortens)
- H zone becomes narrower
- A band stays the same, myosin filaments dont become shorter
what is the structure of myosin?
- heads protrude
- tails wrap around eachother to form filaments
what is actin?
- long chains of globular proteins
- coiled around each other in a helix
- contain troponin and tropomyosin
what is troponin?
site on actin where calcium ions bind
what is tropomyosin?
a long thin thread wound around actin which covers the myosin binding site
how is the actinomyosin bridge formed?
- tropomyosin molecules are covering the myosin binding site, preventing binding
- calcium ions are released from sarcoplasmic reticulum, causing the tropomyosin molecule to change shape, uncovering the binding site
- the myosin head attaches to the binding site
- the myosin head changes angle, pulling actin along as it does this, ADP released
- ATP fixes to the myosin head causing it to detach from the binding site in actin
- hydrolysis of ATP provides energy to live the myosin head back to its original position
- cycle repeated
how is the actinomyosin bridge formed?
- tropomyosin molecules are covering the myosin binding site, preventing binding
- calcium ions are released from sarcoplasmic reticulum, causing the tropomyosin molecule to change shape, uncovering the binding site
- the myosin head attaches to the binding site
- the myosin head changes angle, pulling actin along as it does this, ADP released
- ATP fixes to the myosin head causing it to detach from the binding site in actin
- hydrolysis of ATP provides energy to live the myosin head back to its original position
- cycle repeated
how do muscles become relaxed?
- nervous stimulation ceases, calcium ions actively transported back into the sarcoplasmic reticulum using energy from ATP hydrolysis
- tropomyosin blocks binding site again
- muscle relaxes
