Chapter 5: Muscle contraction + neuromuscular junctions Flashcards
Name the three types of muscle
Involuntary/smooth, cardiac, voluntary/skeletal
Give three features of the structure of smooth muscle
-Under control of ANS
-Muscle cells - spindle shaped and contain single bundles of actin and myosin
-Contraction is slow but muscle tires slowly
What are the three types of cardiac muscle?
Atrial, ventricular, specialised excitory + conductive muscle fibres
Give three features of the structure of cardiac muscle
Myogenic - contracts without impulse
Neurones from ANS co-ordinate contractions
Cells are connected in rows and intercalated discs -between them - allow free diffusion of ions
Give three features of skeletal muscle structure
Multiple tubules (t-tubules) which go into fibre
Sarcoplasmic reticulum = specialised ER
Fatigues quickly as it contracts quickly + powerfully
In skeletal muscle, what is the cell membrane and cytoplasm referred to as?
Cell membrane = sarcolemma
Cytoplasm = sarcoplasm
Name two places that smooth muscle can be found
Walls of intestine,
Walls of arterioles + arteries
Does cardiac muscle fatigue?
No
Where are voluntary/striated/skeletal muscles found?
Muscles eg. biceps, triceps
Define myofibrils
Bundles of interconnected protein filaments of striated muscles
Outline 2 of the 4 protein molecules in myofibrils
Actin: Thin, twisted filaments made up of two strands
Myosin - Thick filaments made up of rods that project to the side
What is muscle contraction stimulated by?
Nerve impulse
What’s the neuromuscular junction?
A special synapse between the membrane of the axon on the motor neurone and the membrane of the muscle fibre
What’s a motor end plate?
Where the motor neurone axon divides into several branches forming a motor end plate
What’s the duration of time for the supply of ATP in the muscle fibre when contracting?
1-2 seconds
Outline the three ways that ATP is regenerated in the muscle fibre
Aerobic respiration
Anaerobic respiration
Transfer of phosphate group from creatine phosphate
Briefly outline the process of muscle contraction in 10 steps
- Action potential arrives at motor end plate
- Vesicles of Acetylcholine fuse with membrane (NT’s bind to receptors) - Na channels open
- Sarcolemma depolarises - passes down t-tubules causing calcium channels to open in the SarcoRet and calcium floods out of sarcoplasm
- Calcium binds to troponin - blocks the binding site of myosin heads
- Binding of calcium changes shape of troponin molecule - moves tropomyosin molecule along to expose myosin binding site
- Myosin head binds moving the actin in relation to myosin - ADP and Pi are released
- ATP molecules binds to myosin head and is broken down to ADP and Pi causing the myosin head to detach and tilts back bound to ADP and Pi
- process repeated and muscle contracts
- Continues until AP stops - sarcolemma repolarised
- Muscle will stay contracted until another muscle pulls fibres apart - antagonistic
On a sarcomere, what does the A band represent?
Length of myosin molecule
What happens to the muscle when Actins meet?
Stops contracting
Is the I-band on Actin or Myosin?
Actin
Describe three differences between a normal synapse and a neuromuscular junction
- Synapse: Post-synaptic membrane is cell surface membrane of neurone while neuromuscular junction’s post synaptic membrane is a muscle membrane
- Synapse: NT may be ACh, noradrenaline, glutamate or another NT but neuromuscular junction: Only Acetylcholine for skeletal muscle
- Synapse: depolarisation of post-synaptic membrane may be inhibitory or excitory but neuromuscular junction: depolarisation = stimulatory
What’s one similarity between a synapse and neuromuscular junction:
NT secreted, diffuses across cleft, binds to receptor and is broken down
What does Acetylcholinesterase do and why?
Breaks down Acetylcholine (ACh) so contractions only happens when signals arrive constantly