Muscle Microstructure and Contraction Flashcards
What are the types of muscles?
smooth
cardiac
skeletal
What type of control is smooth muscle under?
muscle is under involuntary control from the autonomic nervous system
What type of control is cardiac muscle under?
can contract autonomously, but is under the influence of the autonomic nervous system and circulating chemicals
What type of control is skeletal muscle under?
under voluntary control from the somatic nervous system, usually attached to bones and contract to bring about movement.
What are the different arrangements of muscle fibres? (7)
Parallel
Fusiform
Triangular
Multipennate
Bipennate
Unipennate
Pennate
How does the motor neurone innervation work for skeletal muscles?
Upper motor neurone-> lower motor neurone -> muscle
What is the structure of skeletal muscles as you go from macroscopic to microscopic?
What are muscle fascicles bound by?
perimysium
What are muscle fibres surrounded by?
Endomysium
What is inside a myofiber?
Myofibrils
On surface of myofiber there are nuclei and capillaries
What is the structure of myofibrils?
How would you describe myofilaments?
What are the discs/ lines and bands of myofilaments?
What part of the myofilaments are actin and myosin?
What is myosin?
single tail formed by 2 alpha helices
Tails of several hundred molecules form 1 filament
What is the structure of actin?
- Ca2+ binds to troponin move tropomyosin
- tropomyosin moves to reveal binding site
- troponin sits on top of tropomyosin
What is the sliding filament theory?
Z discs get closer tgt
How does initiation of muscle contraction occur (only until an AP has been induced in muscle)?
What is the rest of the initiation of muscle contraction (from when an action potential has been induced in muscle)?
How is the muscle activated- initiation of muscle contraction: activation (only until SR releases something)?
how is the muscle activated- initiation of muscle contraction: activation (the rest)?
What is the process of excitation contraction coupling?
What is the neural control of muscle contraction?
Upper motor neurons in brain
Lower motor neurons in brainstem or spinal cord
Voluntary neural control from upper and lower motor neurons
What is the basis of rigor mortis?
excitation contraction coupling
Muscles in a state of contraction
What is the innervation ratio?
The combination of an individual motor neuron and all of the muscle fibers that it innervates is called a motor unit. The number of fibers innervated by a motor unit is called its innervation ratio.
What is a motor unit?
It is the name given to a single motor neuron together with all the muscle fibres that it innervates
Humans have approximately 420,000 motor neurons and 250 million skeletal muscle fibres
What does stimulation of one motor unit cause?
Contraction of all the muscle fibres in that unit
On average how many muscle fibres does each motor neuron supply?
600 muscle fibres each
What are the types of motor units?
Slow (S, type I)
fast, fatigue resistant (FR, type IIA)
fast, fatigable (FF, IIB)
How would you describe S motor units?
smallest diameter cell bodies
small dendritic trees
thinnest axons
slowest conduction velocity
How would you describe FR and FF motor units?
larger diameter cell bodies
larger dendritic trees
thicker axons
faster conduction velocity
How would you describe the overall distribution and proportions?
Randomly distributed throughout the muscle
Muscles have different proportions of slow and fast twitch muscles
How would you describe the…
myoglobin content
colour
aerobic capacity
anaerobic capacity
of the different muscle muscle fibres/ motor units?
How do we find the “colour” of the motor units?
ATPase staining method
Out of back muscles, extraocular muscles, and biceps brachii which is most likely to have more slow type muscle fibres?
back muscles
How are motor units classified?
Amount of tension generated
Speed of contraction
Fatigability of motor unit
What type of twitch, force and fatigability of the different motor units?
What are the 2 mechanism of regulation of muscle force?
Two mechanisms by which the brain regulates the force that a single muscle can produce.
Recruitment
Rate coding
What is recruitment mechanism?
Motor units are not randomly recruited, there is an order.
Governed by the “size principle”. Smaller units are recruited first (these are generally the slow twitch units).
As more force is required, more units are recruited. This allows fine control (e.g. when writing), under which low force levels are required.
What is rate coding mechanism?
A motor unit can fire at a range of frequencies. Slow units fire at a lower frequency.
As the firing rate increases, the force produced by the unit increases.
Summation occurs when units fire at frequency too fast to allow the muscle to relax between arriving action potentials.
What is the order of muscle force between the types of motor units?
Slow-> FR-> FF
Muscle force can be regulated by the number of motor units recruited
What are neurotrophic factors?
A type of growth factor
Prevent neuronal death
Promote growth of neurons after injury
What are the effects of neurotrophic factors?
Can cause cross innervation
Motor unit and fibre characteristics are dependent on the nerve which innervates them
If a fast and slow twitch muscle are cross innervated, the slow one becomes fast and vice versa
The motor neuron has some effect on the properties of the muscle fibres it innervates
What are the types of muscle contraction?
Concentric
Eccentric
Isometric
How would you describe the plasticity of motor units/ muscle fibres?
Fibre types can change properties under many different conditions.
what is the most common change of motor units?
type IIB to IIA
When is Type I to Type II motor units possible?
Type I to II possible in cases of severe deconditioning or spinal cord injury. Microgravity during spaceflight results in shift from slow to fast muscle fibre types.
What is associated with loss of type I and II fibres?
Ageing associated with loss of type I and II fibres but also preferential loss of type II fibres. This results in a larger proportion of type I fibres in aged muscle (evidence from slower contraction times).
How are component parts of skeletal muscle arrnaged?
in sarcomeres
What has an effect on fibre type?
Neurone
