Somatic nervous system and muscle contraction

Question 1

Cardiac muscles

Answer 1

• Striated
• Lines walls of the heart
• Under involuntary control

Question 2

Smooth muscle

Answer 2

• Lines the visceral organs
• Have a spiral like structure
• Under involuntary control

Question 3

Skeletal muscle

Answer 3

• Allows us to move
• Striated
• Under voluntary control

Question 4

How many muscle fibres are present in fasciculi?

Answer 4

Consist of 150 muscle fibres in bundles known as fasciculi

Question 5

What is sarcolemma?

Answer 5

Muscle fibre membrane

Question 6

What are present within the sarcoplasm?

Answer 6

• Glycogen
• Fat
• Enzymes
• Mitochondria

Question 7

What is the sarcoplasmic reticulum?

Answer 7

SR is where Ca2+ is stored and released from

Question 8

What are the thick filaments known as?

Answer 8

Known as myosin

Question 9

What are the thin filaments known as?

Answer 9

Known as actin

Question 10

Steps involved in calcium stimulated muscle contraction

Answer 10

1. Myosin head hydrolyses ATP into ADP and inorganic phosphate. The energy released
2. Ca2+ binds to troponin, which causes the tropomyosin to shift and exposes the myosin head binding site
3. Myosin head binds into the myosin head binding site forming a cross bridge

Question 11

What is required in order to break actin-myosin bonds?

Answer 11

ATP is required to break actin-myosin bonds

Question 12

What does the somatic nervous system provide?

Answer 12

Provides voluntary control over skeletal muscle

Question 13

What are efferent neurons?

Answer 13

Efferent neurons are that which innervate muscle i.e motor neurons

Question 14

What is a motor unit?

Answer 14

A motor unit is a single motor neuron and all the muscle fibres it controls

Question 15

What do single fibres do?

Answer 15

They contract completely or not at all

Question 16

How can motor units regulate strength of muscle contraction?

Answer 16

Can regulate strength of muscle contraction by varying how many activated motor units there are

Question 17

Action potentials along neuromuscular junctions

Answer 17

1. Action potential arrives along motor neuron
2. This causes depolarisation and moves along the membrane and move down T-tubules which enter the muscle
3. This causes depolarisation of the sarcoplasmic reticulum and this causes Ca2+ to be released
4. The Ca2+ is released to the cytosol and causes contraction of the muscle

Question 18

What are the 2 types of cholinergic receptors?

Answer 18

• Muscarinic(Primarily in CNS, GCPR and are slow)

- Nicotinic(In neurons/NMJs, and are fast)

Question 19

What happens when Ach binds to a nAchR?

Answer 19

• 2 molecules of Ach bind to nicotinic AchR causing a conformational change
  
  • Opens ion pore
• Opening of ion pore results in rapid increase in Na+/Ca2+ and membrane depolarisation leading to muscle contraction

Question 20

What is a tetanus contraction?

Answer 20

Its when the rate of action potential is so high that muscle doesn’t release between stimuli.

Question 21

Why does duchenne muscular dystrophy occur?

Answer 21

Occurs due to mutated gene dystrophin

Question 22

What does dystrophin do?

Answer 22

Dystrophin connects actin filaments to the sarcolemma, required for mechanical stability

Question 23

What does a lack of dystrophin do and what does this cause?

Answer 23

Lack of dystrophin causes dysfunction of sarcolemma stretch
-This causes ion pores to open and there’s increased
intracellular Ca2+

Question 24

What happens in Duchenne muscular dystrophy?

Answer 24

Degradation of structural proteins and CK is lost from cell into blood. CK is required for ATP

Question 25

What is ALS?

Answer 25

Its a neuron disease affecting motor neurons

Question 26

What is myasthenia gravis?

Answer 26

Chronic autoimmune NMD

Question 27

What does myasthenia gravis cause?

Answer 27

Causes skeletal muscle weakness and fatigue

Question 28

What happens in myasthenia gravis?

Answer 28

• Body makes antibodies against AchR’s at NMJ’s

- Blocks AchR’s, increasing AchR degradation and causes impaired signal transduction

Question 29

What treatment is there for myasthenia gravis?

Answer 29

Treatment with acetyl cholinesterase inhibitors or immunosuppressants