24 mUSLCE tISSUE CONTINUED

Question 1

Differences between cardiac and smooth muscle?

Answer 1

• Smooth muscle does not contain sarcomeres
• Electrical conduction - specialised cells/routes in cardiac muscle
• No troponins in smooth muscle

Question 2

Similarities in cardiac and smooth muscle?

Answer 2

Nuclei are central not peripheral
• Only one contractile cell type
• Act as a syncytium (wave-like function) all cells act as one
• Myocytes communicate through gap junctions
- (cardiomyocytes - disk)

Question 3

Contraction of skeletal muscle

Answer 3

1. Initiation: nerve impulse along motor neuron axon arrives at neuromuscular
   junction
2. Impulse prompts release of acetylcholine (Ach) into synaptic cleft causing
   local depolarisation of sarcolemma
3. Voltage-gated Na+ channels open; Na+ ions enter cell
4. General depolarisation spreads over sarcolemma and into T tubules
5. Voltage sensor proteins of T tubule membrane change their
   conformation
6. Gated Ca2+ ion-release channels of adjacent terminal cisternae are
   activated by 5.
7. Ca2+ ions are rapidly released into the sarcoplasm
8. Ca2+ binds to the TnC subunit of troponin and the contraction cycle is initiated
9. Ca2+ ions are returned to the terminal cisternae of sarcoplasmic reticulum

Question 4

Myasthenia gravis

Answer 4

autoimmune disease
Ab directed against Ach receptor and blocks them. reduce synaptic transmission, intermittent muscle weakness. See weakness of eyelid

Question 5

sliding filament model

Answer 5

mysosin is thick and has 2 heads for anchoring

actin is thin and has tropomysin and troponin complex. 2 for every turn

calcium binds to troponin cause conformational change so myosin can attach

titin is a spring. twisted so has energy and helps actin to go back into resting state

Question 6

Muscle roles in movement

agonist

Answer 6

causes movement

Question 7

Muscle roles in movement

antagonist

Answer 7

oppose prime mover

Question 8

Muscle roles in movement

synergists

Answer 8

assist prime mover

Question 9

Muscle roles in movement

neutraliser

Answer 9

prevent the unwanted actions of a muscle

Question 10

Muscle roles in movement

fixators

Answer 10

stabiise joints

Question 11

Biomechanics - Levers
first class lever

Answer 11

see saw like head going back. effort at one end and load at other

Question 12

Biomechanics - Levers
second class lever

Answer 12

wheelbarrow so stand on ball of foot. effort at one end and fulcrum at other

Question 13

Biomechanics - Levers
third class lever

Answer 13

fishing rod so flexing bicep. effort inbetween load and fulcrum

Question 14

compartment syndrome

Answer 14

• Limbs divided into compartments delineated by fascia
• Trauma in one compartment could cause internal
bleeding which exerts pressure on blood vessels and
nerves
• Can give rise to compartmentsyndrome

• Deep constant poorly localised pain
• Aggravated by passive stretch of muscle group
• Paresthesia (altered sensation e.g., “pins & needles”)
• Compartment may feel tense and firm.
• Swollen shiny skin, sometimes with obvious bruising.
• Prolonged capillary refill time.

Question 15

treatment of compartment syndrome

Answer 15

fasiotomy and then covered by a skin graft

Question 16

muscle re modelling
atrophy
hypertrophy

Answer 16

atrophy: destruction more than replacment
hypertrophy: replacement more than destruction

Question 17

Duchene muscular dystrophy

Answer 17

• Most common muscular dystrophy
• Inherited through X-linked recessive pattern
• Mutation of the dystrophin gene
• Absence of dystrophin allows:
- Excess calcium to enter the muscle cell
- Calcium taken up by mitochondria
- Water taken with it
- Mitochondria burst
- Muscle cells burst (rhabdomyolysis)
- Creatine kinase and myoglobin levels are extremely high in the blood

muscle cells replaced by adipose tissue

Question 18

Creatine Kinase

Answer 18

CK is an important enzyme in metabolically active tissues, such as muscle
CK used to be measured to diagnose heart attacks (myocardial infarction),
-enzyme increase largely proportional to infarct size
- buthas been largely superseded by troponinI assay
CK is an enzyme that is also released into the blood by damaged skeletal muscle and brain

Question 19

Troponin assays

Answer 19

used as marker for cardiac ischaemia. released from muscle within an hour. needs to be measured within 20 hours. doesnt show how severe the heart attack is though

Question 20

Botox

Answer 20

• Toxin produced by Clostridium botulinum
• Blocks neurotransmitter release at the motor end plate
• Causes non-contractile state of skeletal muscle
- Flaccid paralysis
• Clinically used to treat muscle spasms (e.g. cervical dystonia)
• Used cosmetically to treat ‘wrinkles’

Question 21

Organophosphate poisoning

Answer 21

Organophosphates are used as pesticides
• Inhibits the normal function of Ach esterase
• Ach activity at the neuromuscular junction is
• potentiated
• Leads to multiple symptoms and signs:
• Effects on both somatic and autonomic signalling

Question 22

muscarinic syndrome

SLUDGE

Answer 22

salivation
lacrimation
urination
defecation
GI cramping
Emesis

Question 23

nicotinic syndrome

Answer 23

muscle cramps
tachycardia
weakness
twitching
fasciculations