Muscles

Question 0

Classify the 3 histology all forms of muscle

Answer 0

Skeletal Muscle (striated), Cardiac Muscle (striated), Smooth Muscle (non-striated)

Question 1

Describe, in ascending order of size, the structure of muscle.

Answer 1

Many myofilaments in a myofibril, many of which, make up
a single muscle fibre (cell) wrapped in endosmysium. Arranged into fascicles wrapped in perimysium. Arranged into whole muscles wrapped by epimysium.

Question 2

Describe the ultrastructure appearance of skeletal muscle. (Bands)

Answer 2

MHAZI. M line is in the H band which is in the A band. The Z line is in the I band

Question 3

In sarcomeres which filament is thick and which is thin

Answer 3

Actin is Thin

Myosin is Thick

Question 4

Name the constituent parts of actin filaments

Answer 4

Actin wrapped in tropomyosin, interspersed with troponin complexes

Question 5

Describe the structure of the thick, myosin, filament.

Answer 5

Many myosin molecules, whose heads protrude at opposite ends.

Question 6

Describe stage 1 of 4 of muscle contraction (Cocking)

Answer 6

Hydrolysis of the ATP attached to the myosin head cocks the head into a high energy state.

Question 7

Describe stage 2 of 4 of muscle contraction (Binding)

Answer 7

In the presence of Ca+, which binds to troponin exposing binding sites on the tropomyosin, the myosin head binds lightly to the actin filament.

Question 8

Describe stage 3 of 4 of muscle contraction (power stroke)

Answer 8

The release of the ADP and Pi causes the myosin head to bind tightly moving the actin filament 5nm (the head is now uncocked)

Question 9

Describe stage 4 of 4 of muscle contraction (detachment)

Answer 9

ATP binds to the myosin head, releasing it from the actin filament.
The cycle then repeats

Question 10

Describe the the mechanism of innervation of muscle. (~6 steps)

Answer 10

1. Nerve impulse arrives at neuromuscular junction
2. This releases Acetyl Choline causing depolarisation of sarcolema
3. Voltage gated Na Channels open, Na enters cell
4. Depolarisation spreads through T tubules
5. The gated Ca channels open and Ca enters sarcolemoplasm
6. Ca allows muscle contraction (exposes myosin binding sites)

Question 11

Explain the attachment of muscle to tendons

Answer 11

Skeletal muscle fibres interdigitate with tendon collagen bundle at myotendenous junction.

The sarcolema always lies between collagen bundles and microfilaments.

Question 12

Describe the nature of repair in skeletal muscle

Answer 12

Cells cannot divide but tissue can regenerate by mitotic activity of satellite cells, the can fuse with existing muscle cells to increase mass.
Gross damage is repaired with connective tissue, which leaves scars

Question 13

Describe the nature of repair in cardiac muscle

Answer 13

Incapable of regeneration.

Following damage, fibroblasts invade and lay down scar tissue.

Question 14

Describe the nature of repair in smooth muscle

Answer 14

Cells undergo mitosis

Particularly evident in the pregnant uterus where the muscle wall becomes thicker.

Question 15

Define muscular hyperplasia

Answer 15

The increase in muscle size due to mitotic division (exclusive to smooth muscle)

Question 16

Define muscular hypertrophy

Answer 16

The increase in muscle size due to swelling of individual cells. Often caused by an increase in number of myofibrils.

Question 17

Describe the histology of cardiac muscle

Answer 17

Striated
Branching
Central nuclei
Intercalated disks (for mechanical and electrical coupling)
Gap junctions
T tubules are in line with the Z disk

Question 18

Describe the histology of smooth muscle

Answer 18

Cells are fusiform (like a bronchasuharus with no legs)
Non striated
Contraction is slower and requires less ATP
Can be stretched
Responds to hormones, nerves, drugs, [blood gasses]
Filaments spiral along the cell

Question 19

Outline the structure and function of the Purkinje fibres

Answer 19

Abundant glycogen
Sparse myofilaments
Extensive gap junction sites
Rapid conduction of action potentials

Question 20

How long does the remodeling of skeletal muscle take?

Answer 20

2 weeks

Question 21

Define muscular atrophy

Answer 21

Muscular atrophy is the loss of muscular tissue caused by a greater rate of destruction than replacement.

Question 22

List the causes of muscular atrophy

Answer 22

Disuse of muscle (muscle fibres shrink)
Age
Denervation reduced nervous activity leads to disuse

Question 23

Outline the role of acetyl choline in the neuromuscular junction

Answer 23

Acetyl choline (ACh) is released across the junction.
25% of ACh receptors need to be occupied to…..
Open sodium channels to…..
Start depolarisation of sarcolema

Question 24

Describe the pathophysiology of Myasthenia Gravis

Answer 24

Autoimmune destruction of ACh receptors
Loss of junctional folds at the end-plate
A widening of the synaptic cleft

Question 25

Describe the symptoms of Myasthenia Gravis

Answer 25

Fatigability and sudden falling due to reduced ACh release
Drooping eyelids
Double vision
Crisis at point at which respiratory muscles are affected

Question 26

Describe the treatment of Myasthenia Gravis

Answer 26

Acetyl Cholinesterase inhibitors which prevent the breakdown of Acetyl Choline

Question 27

Describe the pathophysiology of muscular dystrophy

Answer 27

Genetic faults cause reduced synthesis of specific proteins which anchor actin filaments to the cell wall.

Muscle fibres tear themselves apart upon contraction

Question 28

Describe the pathophysiology of Duchenne Muscular Dystrophy

Answer 28

Complete absence of dystrophin causing :
Muscle fibres to tear themselves apart on contraction
Enzyme creatine (phospho)kinase liberated in blood serum
Calcium enters and causes necrosis
Pseudohypertrophy before fat on connective tissue replace muscle

Question 29

Describe the signs and symptoms of Duchenne muscular dystrophy

Answer 29

Early onset Gower’s sign (use of hands on knees when standing)
Contractures (imbalance between muscle pairs)

Question 30

Describe the treatments of Duchenne muscular dystrophy

Answer 30

Steroid therapy

Ataluren (PCT124) drug trails (promotes dystrophin production)

Question 31

Outline the pathophysiology of malignant hyperthermia

Answer 31

Rare autosomal dominant
Causes a life-threatening reaction with Succinylcholine
Causes uncontrolled increase in skeletal muscle oxidative metabolism

Question 32

Outline the treatment of malignant hyperthermia

Answer 32

Dantrolene (a muscle relaxant which prevents Ca release)

Correction of hyperthermia, acidosis and organ dysfunction