Topic 6 Flashcards
What is a neuromuscular junction
Neuromuscular Junctions
~ a specialised Cholinergie synapse between a motor neurone and a muscle cell. Uses Ach acetylcholine which binds to the Cholinergic receptors called nicotinic
Cholinergic receptors
Similarities between neuromuscular junction cholinergic surapses:
1) both release Ach from vesicles on the presynastic membrane.
2) ACh diffuses across the synaptic Cleft and binds to the cholinergic receptors on the postsynaptic membrane.
3) Action Potential could be triggered if threshold is reached.
4) Ach is broken down by enzyme AChE acetylcholinesterase) in the Synaptic Clert.
Differences between neuromuscion junctions cholinesic synapses:
1) possynaptic membrane has lots of clefts to store ACHE
2) postsynaptic membrane has lots of receptors
3) ACh is always excitatory so when motor neurone fires an action potential it nomally triggers a responce in a muscle cell .
* not always between synapse between two motor neurones
Drugs at synapses
Drugs can aftect Synaptic transmission. This can be done in various ways:
1) Some drugs dre the same shape as the neurotransmitter, so they mimic their action at the receptors - These drugs are caled Agonists. This means more receptors are actvated. (action potential)
2) some drugs block receptors so they cant be activated by neurotransmitters . These drugs are cared antagonists. means fewer receptors (if any) can be actvated. (no action potential)
3) some drugs inhibit the enzyme that breakes down neurotransmitters (Stop it from working) . means that there are more neurotransmitters in the synaptic cleft to bind to receptors and they’ve there for longer. (action potential)
4) Some drugs stimulate the release of neurotransmitters from the presynaptic neurone so mone receptos are activated. (action potential)
5) Some drugs inihibit the release of neurotransmittes from the presynaptic neurone so fewer receptors are activated.
How are muscles effectors
muscle are effectors -they contract in response to nervous impuses
What are the type of muscles and their functions
Smooth muscle ~ contracts without conscious control found in the walls of internal organs. Apart from the heart ( stomach, intestine , blood vesicles)
Cardiac Muscles- contract without conscious control . Only found in the heart
Skeletal muscle ~ Contracts with conscious
Control. Called (Strated, Striped, or voluntany muscle). Type of muscle you can use to move biceps + triceps.
Role of skeletal muscle
Skeletal muscles are attached to bones by tendons.
Ligaments attached bones to bones to hold them together. Pairs of Skeletal muscles contract and relax to move bones at a joint. The bones Of the skeleton are incompressible (rigids) so they act as levers giving something to pull against
What are antagonistic pairs ? : give an example
~muscies that work together to move a bone.
The contracting muscle is agonist. The relaxing muscle → antagonist.
example: Bicepts relax and triceps contracts Straighting. Bicepts Contract and triceps relax flexing .
Examination under an Optical microscope: what would u see for A bands and I bands
can look at an skeletal musce under an optical microcope. What you see depends on the location of the stain. Also whether itself a longitudinal~ taken along the length of the structure or Transverse cross-section ~ cut through the structure at a right angle to its length .
A-bands ~ dark band, I-band~ light
What are myofibrils
Contains bundles of thick and thin myofilaments that move past cach other to make muscles contract
What are thick and thin myofilaments made out of ?
Thick- protein called myosin
Thin- protein called actin
What would you observe of a myofibril under an electron microscope
pattern of dark and light bands.
What are
A- band
I band
Sarcomeres
Z line
M line
H zone
A: dark bands that contain thick myosin filaments and some overlapping actin filaments
I: light bands that contain actin filaments only
S: short units of myofibrils
Z: ends of sarcomeres
M: middle of myosin filaments
H: around the M line only containing myosin filaments
How is muscle contraction stimulated
- Neuromuscular junction: action potential = voltage gated Ca 2+ channels opens
- Vesicles move upwards and fuse with presynaptic membrane
- Exocytosis of acetylcholine diffuses across synaptic cleft
- ACh binds to receptors on Na+ channel proteins in skeletal muscle membrane
- Influx of Na+ causes depolarisation
The role of Ca2+ ions in muscle contraction
1.Action potential moves through T-tubules in the sarcoplasm = Ca2+ in sarcoplasmic reticulum open
2. Ca2+ binds to troponin triggering conformational changes in tropomyosin
3. Exposes binging sites on actin filaments so actin myosin coss bridge
