Muscles Flashcards
What type of muscle is this? How do you know?
Skeletal muscle
- Regular striations
- Peripheral nuclei
- Syncytium
What type of muscle is this? How do you know?
Cardiac
- Syncytium appearance
- Central nuclei
What type of muscle is this? How do you know?
Smooth
No striations
Myopathy
Disease of muscle tissue
Causes of muscle pathology
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
What is sarcopenia?
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
Outline how changes in intracellular storage/signalling can result in skeletal muscle pathology
- 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
Agonist
Muscle that produces a certain effect
Antagonist: muscle that produces the opposite effect
Example of antagonistic pair: bicep & tricep
Synergistists
Muscles that neither faciliate nor directly oppose the effects, but modify the action of the agonist e.g. by unlimiting an unwanted side effect
Fixators
Muscle that are employed to stabilise joints rather than promote movement
Origin
The most proximal/central attachment
Moves the least
Insertion
The more distal/peripheral attachment
Moves the most
Isotonic contraction
activated muscles shorten when contraction occurs
Isometric contraction
when the activated muscles generate force without shortening e.g. animal pushes against heavy object that doesn’t move
Why is the length of the sarcomere an indicator of contractile force?
As contraction increases, length of sarcomere decreases
Tetanic contraction
Sustained full contraction with the inability to relax
What could be responsible for muscle fatigue?
- 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
Method of energy metabolism in Type 1 (slow-twitch) fibres?
Oxidative phosphorylation
Method of energy metabolism in Type II fibres?
Oxidative phosphorylation
Method of energy metabolism in Type IIb fibres?
Glycolysis
Characteristics of Type I muscles fibres?
- Slow-twitch
- Small
- Many mitochondria
- Fatigue-resistant
- Much myoglobin, many cytochrome complexes, little glycogen
- e.g. in marathon runners
Characteristics of Type IIa fibres
- 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
Characteristics of Type IIb muscle fibres
- Fast-twitch
- Large fibres
- Few mitchondria
- Less fatigue resistant
- High anaerobic enzyme activity
- Much glycogen stored
- e.g. Short distance sprinters, weightlifters
Compare the vasculature of muscles and tendons
Muscles have a generous blood supply
Muscle contraction squeezes veins, promoting circulation
Tendons are poorly vascularised due to their low metabolic needs
Myoglobin
A red protein containing haem, which carries and stores oxygen in muscle cells. It is structurally similar to a subunit of haemoglobin.
What is the neurotransmitter at the neuromuscular junction?
Acetylcholine
Motor unit
a single alpha motor neuron and all of the corresponding muscle fibres that it innervates.
What can be said about the fibres within a motor unit?
- They will all be innervated simultaneously
- They will all be of the same fibre-type
True/False: the size of the motor unit dictates the level of control
True
Smaller motor units (e.g. 1 axon to 1 muscle fibre) enable fine muscle control
What is the name given to the membrane of the muscle fibre?
Sarcolemma
Excitation contraction coupling
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.
Describe how excitation contraction coupling occurs
- 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
How is muscle length regulated?
- 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
How is muscle tension regulated?
- 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)
Describe the clinical relevance of the ryanodine receptor (malignant hyperthermia)
