Session 2-Skeletal Muscle Flashcards
What are the functions of skeletal muscle? (4)
1) movement
2) posture
3) joint stability
4) heat generation
Define fasciculation
Small, local, involuntary muscle contractions and relaxations
What do circular muscles act as?
Sphincters to adjust opening
True or false: circular muscles are arranged in concentric fibres
TRUE
Where do circular muscles attach?
To skin, ligaments and fascia rather than bone
What is the name of the circular muscles surrounding the eyes?
Orbicularis occuli
What is the name of the circular muscle surrounding the mouth?
Orbicularis oris
Which is the most common type of skeletal muscle?
Parallel muscles
What are the three main categories of parallel muscles?
1) strap
2) fusiform
3) fan shaped
What is another name for fan shaped muscles?
Convergent
Give an example of a strap muscle
Sartorius (lower limb)
Give an example of a fusiform muscle
Biceps brachii
Give an example of fan shaped muscle
Pec major
What are pennate muscles?
One or more aponeuroses run through muscle body from the tendon, fascicles attach to aponeuroses at an angle
What are the three different types of pennate muscles?
1) unipennate
2) bipennate
3) multipennate
True or false: a muscle’s insertion is more stable than its origin
FALSE - other way round
What delineates the compartments of the limbs?
Fascia
What could trauma in one compartment cause?
Internal bleeding which exerts pressure on blood vessels and nerves, giving rise to compartment syndrome
How can compartment syndrome be treated?
Fasciotomy (relieves pressure)
What are the symptoms of compartment syndrome? (4)
1) pain
2) paresthesia (pins and needles)
3) swollen, shiny skin (bruising)
4) compartment may feel tense and firm
What does a muscle agonist do?
Prime mover-main muscle responsible for a particular movement
What does a muscle antagonist do?
Opposes prime movers
Why are muscle antagonists necessary?
Fine control
What do muscle synergists do?
Assist prime movers
What do muscle neutralisers do?
Prevent unwanted actions that an agonist can perform
What do muscle fixators do?
Stabilise a joint - holds a body part immobile whilst another body part is moving
What are the two types of skeletal muscle contraction?
1) Isotonic-constant tension, variable muscle length
2) Isometric-constant length, variable tension
What are the two types of isotonic contraction?
1) Concentric-muscle shortens (eg lifting a load with the arm)
2) Eccentric-muscle resists extension (eg walking downhill)
True or false: in a first class lever, the effort is at one end and load at the other
TRUE
Which is the most efficient type of lever?
First class
What is an example of a first class lever?
Extension/flexion of the head
True or false: in a second class lever, the effort is between the load and fulcrum
FALSE - that is in the third class lever. In a second class lever, the effort is at one end and the fulcrum at the other
Give an example a second class lever
Plantar flexion of the foot
Give an example of a third class lever
Biceps brachii in the flexion of the elbow
What happens in rigor mortis?
If ATP is depleted, myosin heads cannot detach. Approx 3 hours after death, body reaches maximum stiffness
Complete the sentence:
Muscle fibres making up a motor unit are all of the _______ contractile type so each motor unit is fast or slow contracting
Same
True or false: each individual muscle fibre is innervated by one motor neuron
TRUE
How many different myosin heavy chains (MHC) are there?
8 different isoforms
What are the three main types of fibre types in skeletal muscle?
1) Slow type I (beta cardiac)
2) Fast type IIA
3) Fast type IIX
What are type I muscle fibres known as?
Slow oxidative
What are type IIA muscle fibres known as?
Fast oxidative
What are type IIX muscle fibres known as?
Fast glycolitic
True or false: type IIA muscle fibres have few mitochondria and carry out anaerobic glycolysis
FALSE - ^ is type IIX
Complete the sentence:
___________ muscle fibres facilitate proprioception
Intrafusal
What are patients with large-fibre sensory neuropathy unable to do?
Perform accurate movements in the absence of vision
What innervates intrafusal muscle fibres?
Two sensory and one motor axons
What does the gamma motor neurone do?
Alters sensitivity of the fibres and keeps the fibres taut
What do type Ia sensory neurones do?
Relay the rate of change in muscle length back to the CNS
What do type II sensory neurones do?
Provide position sense
What two factors control muscle force?
1) size principe-small motor neurones recruited before large
2) rate code-more action potentials=more force. Subsequent action potential produce summation up to a limit (=tetani)
True or false: healthy muscles never fully relax
TRUE
When is the only time healthy muscles relax?
In REM (rapid eye movement) sleep because part of the brain controlling muscle tone stops working
What is baseline muscle tone due to? (2)
1) motor neurone activity
2) muscle elasticity
What is hypotonia?
Lack of skeletal muscle tone
True or false: hypotonia is most common in babies and is called floppy baby syndrome
TRUE
What can cause hypotonia?
Damage to motor cortex or cerebellum or spinal cord OR degeneration of muscle (myopathy)
Where do DHP receptors come into contact with SR?
At triads
Which Ca2+ release channels in SR are closely associated with DHP receptors, allowing rapid signalling from action potential to Ca2+ release?
Ryanodine receptors
True or false: skeletal muscle fibres only have leaky K+ channels
FALSE - also have high concentration of Cl- leak channels
What is a common example of a channelopathy?
Cystic fibrosis
What does myotonia mean?
Inability to relax muscles at will
What are the symptoms of myotonia congenita?
Muscle stiffness and hypertrophy
What causes myotonia congenita?
Mutations in chloride channel CLCN1
What type of drugs can relieve symptoms of myotonia congenita?
Anticonvulsant drugs
True or false: there are both recessive and dominant forms of myotonia congenita
TRUE
In skeletal muscle, what is the resting membrane potential usually equal to?
Cl- Nernst equilibrium potential
What are the sources of ATP in muscle? (4)
1) short term stores of ATP in muscle fibre
2) creatine phosphate (short term)
3) glycolysis
4) oxidative phosphorylation
What does anaerobic glycolysis form?
Lactate