Muscles

Question 1

What type of muscle is this? How do you know?

Answer 1

Skeletal muscle

• Regular striations
• Peripheral nuclei
• Syncytium

Question 2

What type of muscle is this? How do you know?

Answer 2

Cardiac

• Syncytium appearance
• Central nuclei

Question 3

What type of muscle is this? How do you know?

Answer 3

Smooth

No striations

Question 4

Myopathy

Answer 4

Disease of muscle tissue

Question 5

Causes of muscle pathology

Answer 5

External trauma

e.g. crushing, laceration, extreme heat/cold leading to necrosis of fibres

Internal trauma

Muscle tear due to forceful contraction; myopathy/repeated eccentric contractions leading to overstretched sarcomeres and Ca²⁺ leakage

Nerve damage

Motor nerve crushed or divided

Neuropathy

Disease

Aging

Question 6

What is sarcopenia?

Answer 6

Muscle atrophy associated with aging. Leads to:

• Loss of motor axons
• Denervation
• Degeneration/regeneration cycle leads to loss of motor fibres
• Increases motor unit size –> loss of dexterity
• Fibrosis: build up of connective tissue in muscle

Question 7

Outline how changes in intracellular storage/signalling can result in skeletal muscle pathology

Answer 7

• If sarcoplasmic reticulum can’t hold onto calcium –> unregulated muscle contraction
• If Calcium ATPase runs all the time –> hydrolyses much ATP, producing much heat –> so animal overheats quickly
• Leak of calcium may cause unregulated muscle contraction/prevent normal muscle contraction

Question 8

Agonist

Answer 8

Muscle that produces a certain effect

Antagonist: muscle that produces the opposite effect

Example of antagonistic pair: bicep & tricep

Question 9

Synergistists

Answer 9

Muscles that neither faciliate nor directly oppose the effects, but modify the action of the agonist e.g. by unlimiting an unwanted side effect

Question 10

Fixators

Answer 10

Muscle that are employed to stabilise joints rather than promote movement

Question 11

Origin

Answer 11

The most proximal/central attachment

Moves the least

Question 12

Insertion

Answer 12

The more distal/peripheral attachment

Moves the most

Question 13

Isotonic contraction

Answer 13

activated muscles shorten when contraction occurs

Question 14

Isometric contraction

Answer 14

when the activated muscles generate force without shortening e.g. animal pushes against heavy object that doesn’t move

Question 15

Why is the length of the sarcomere an indicator of contractile force?

Answer 15

As contraction increases, length of sarcomere decreases

Question 16

Tetanic contraction

Answer 16

Sustained full contraction with the inability to relax

Question 17

What could be responsible for muscle fatigue?

Answer 17

• Increases levels of inorganic phosphate (due to creatine phosphate degradation) adversely affects cross-bridge function
• Accummulation of lactic acid
• Reduced release of Ca²⁺ from sarcoplasmic reticulum
• Empty glycogen stores
• Psychological factors

Question 18

Method of energy metabolism in Type 1 (slow-twitch) fibres?

Answer 18

Oxidative phosphorylation

Question 19

Method of energy metabolism in Type II fibres?

Answer 19

Oxidative phosphorylation

Question 20

Method of energy metabolism in Type IIb fibres?

Answer 20

Glycolysis

Question 21

Characteristics of Type I muscles fibres?

Answer 21

• Slow-twitch
• Small
• Many mitochondria
• Fatigue-resistant
• Much myoglobin, many cytochrome complexes, little glycogen
• e.g. in marathon runners

Question 22

Characteristics of Type IIa fibres

Answer 22

• Intermediate speed
• Medium fibre length
• Many mitochondria
• Fatigue-resistant
• High myoglobin content, high levels of glycogen
  
  • Capable of anaerobic glycolysis
• e.g. in hockey players

Question 23

Characteristics of Type IIb muscle fibres

Answer 23

• Fast-twitch
• Large fibres
• Few mitchondria
• Less fatigue resistant
• High anaerobic enzyme activity
• Much glycogen stored
• e.g. Short distance sprinters, weightlifters

Question 24

Compare the vasculature of muscles and tendons

Answer 24

Muscles have a generous blood supply

Muscle contraction squeezes veins, promoting circulation

Tendons are poorly vascularised due to their low metabolic needs

Question 25

Myoglobin

Answer 25

A red protein containing haem, which carries and stores oxygen in muscle cells. It is structurally similar to a subunit of haemoglobin.

Question 26

What is the neurotransmitter at the neuromuscular junction?

Answer 26

Acetylcholine

Question 27

Motor unit

Answer 27

a single alpha motor neuron and all of the corresponding muscle fibres that it innervates.

Question 28

What can be said about the fibres within a motor unit?

Answer 28

* They will all be innervated simultaneously * They will all be of the same fibre-type

Question 29

True/False: the size of the motor unit dictates the level of control

Answer 29

True ## Footnote Smaller motor units (e.g. 1 axon to 1 muscle fibre) enable fine muscle control

Question 30

What is the name given to the membrane of the muscle fibre?

Answer 30

Sarcolemma

Question 31

Excitation contraction coupling

Answer 31

The process by which an electrical stimulus triggers the release of calcium by the sarcoplasmic reticulum, initiating the mechanism of muscle contation by sarcomere shortening.

Question 32

Describe how excitation contraction coupling occurs

Answer 32

* The system of T-tubules conduct action potentials from the cell surface to the core of the fibre * The t-tubules are in direct contact with the sarcoplasmic reticulum that surrounds the myofibrils * The membranes of the sarcoplasmic reticulum contain **ryanodine receptors** which are types of Ca²⁺ channels * **Voltage-sensitive channels are coupled** to these receptors * Upon depolarisation, the **channels change conformation** and open the ryanodine receptor

Question 33

How is muscle length regulated?

Answer 33

* Using muscle spindles * Muscle spindles = specialised muscle fibres * Use reflex arcs to maintain muscle length when it changes --\> myotatic reflex * Therefore used to automate movement

Question 34

How is muscle tension regulated?

Answer 34

* Golgi tendon organs monitor the tension developed in the muscle * They prevent damage during excessive force generation --\> excessive force leads to reflex relaxation of muscle to avoid rupture (reverse myotatic reflex)

Question 35

Describe the clinical relevance of the ryanodine receptor (malignant hyperthermia)