finals study - all topics Flashcards
what is the muscle breakdown
whole muscle -> fascicle -> fibre or M cell -> myofibril
what is the epimysium
surrounds the muscle tissue
what are the 3 roles of skeletal muscle
stores protein (metabolism)
movement and generates force
thermogenesis
what are the 4 unique properties of muscle
excitability/irritability, contractility, extensibility, and elasticity
what is excitability/irritability
developing and propagating (sustaining) a transient electrical event (action potential)
what is contractility
ability to shorten
what is extensibility
stretched without damage
what is elasticity
tends to return to original state after extensibility and contractility
what are the 8 factors that affect torque
- activation history
- elasticity/passive stiffness
- cross-bridge functions and energetics/ATP availability
- muscle size
- mechanics
- innervation/neural activation
- fibre type composition
- antagonist balance
what factors determine muscle phenotypic properties
- cell lineage/genetic determinants
- epigenetics
what makes up epigenetics
- motoneurons, hormones, load/stretch
what are the 2 components of structure <–> function contraction
- contractile components
- support and connecting protein components
what makes up the contractile components
muscles that shorten (actin and myosin)
what makes up the support and connecting protein components
- collagen and elastin form connective tissue at many levels
- epimysium (whole muscle separation)
- perimysium (fascicles)
- endomysium (fibre level)
what are the roles of structural proteins at the sub-cellular level
- support contractile components
- transmit force to tendons
- resist injurious stretch by wide distribution of forces
- mechanotransducers
- promote gene transcription
- involved in protein metabolism
what is the Hill (1938) model
- passive elements (CT, tendons and titin)
- active elastic elements (rotation of myosin heads during actin attachment)
- parallel elastic elements (PE)
- series elastic elements (SE)
- contractile element (sarcomere)
what are the determinants of muscle force output
- size, shape, composition
- increased size = increased force
- shape
- slow twitch vs fast twitch
- adaptability
- variations of muscle shape/architecture
- pennation
- extrinsic factors
what makes up size, shape and composition
mass, geometry and fibre type
what makes up increased size = increased force
muscle force is proportional to cross-sectional area (CSA) or more correctly, physiological cross-sectional area (PCSA)
what makes up shape
compartments, length of fibres, and pennation arrangement -> pennation affects PCSA
what makes up slow twitch vs fast twitch
fibre type composition affects speed and endurance of muscle contraction
what makes up adaptability of skeletal tissue
muscle atrophy aligns with adipose tissue/subcutaneous fat buildup
what makes up variations of muscle shapes and architecture
different pennation types, and length of fibre architecture of fibre
what are the different types of pennation
- unipennate = linear from end-to-end (fastest)
- bipennate = angular to central tendon (large fibre length to muscle length ratio)
- multipennate = many angles to central tendon (highest pennation = most force, low muscle to fibre ratio)
what makes up length of fibres
varies within and among different muscles, but usually does not span the length of the muscle (tendon-to-tendon) –> ratio of FL:ML = <1 (0.2-0.8)
what makes up muscle fibre architecture
- affects contractile properties of whole muscle
- a combination of series and parallel (not 100% of either)
- in series -> contractile length and shortening velocity, greater ROM, and faster force produced and greater shortening
- in parallel -> total force generating capacity, lower ROM, higher force produced total, shortens less
what makes up the affect of pennation
- more fibres = more force
- not a 1:1 ratio of force to fibre #
- force is lost with angle but more in total
- PCSA = CSA x cosB (greater angle from horizontal = more force lost, small loss of force per fibre, but great increase in packing density of fibres and overall greater force potential)
- specific tension of fibres (F/PCSA ~15-20N/cm^2 or 2kg/cm^2)
- larger PCSA = greater overall force capacity
- can assess angle with an ultrasound
- PCSA and ACSA (anatomical) are equal in non-pennated muscle -> therefore less force
what are the extrinsic determinants of muscle force output
neural control, activation history, antagonist function
what are the components of the motoneuron
soma, synapse, spinal cord regionalization, axon, axon hillock, dendrites
what is the soma
- aka cell body
- the ventral portion of gray matter in SC. > 100/muscle (may be several hundred)
- hard to maintan (large SA)
- very active cells
- post-mitotic after birth - loss with aging
- alpha exrafusal fibres and gamma intrafusal fibres (spindles)
- small soma supports may long processes
what is the different between alpha extrafusal fibres and gamma intrafusal fibres (spindles)
- alpha = what we will focus on, the main fibres of skeletal muscles
- spindles = proprioception for length changes (feedback)
what is the synapse
- electrical or chemical junction between neural tissues
- transmission point between2 cells (same or different cells)
- differential control
- the site of information control (positive (excitatory) or negative (inhibitory) signal types -> need a balance
what is the spinal cord regionalization of motoneurons
- regionalization meaning not randomized
- the motoneurons span more than one lumbar level so paralysis at L2 won’t necessarily make lost function completely
what is the axon
- for efferent traffic (out of cell) -> toward the muscle
- covered by organized myelin (lipid); nodes of ranvier
what is the axon hillock
- for afferent traffic (into cell)
- dendritic tree - > receiving information via synaptic connections (control points)
- 1 axon = many dendrites
- electrical or chemical
what is the membrane potential pump
the pump requires energy which moves sodium and potassium in and out of the membrane -> potassium into cell and sodium out
what are the steps to action potential
- negative membrane potential inside the cell
- threshold of excitation is reached
- Na into cell
- Na into cell and K out (depolarization)
- K out of cell, at a big positive membrane potential
- K out of cell causing membrane potential to return to normal (repolarization)
- K channels and Na channels close and reset
- extra K diffuses away -> overshoots (afterhyperpolarization) because wants to ensure the negative point is reached (for a few ms) -> if negative point isn’t reached, can’t send another
what is the normal resting membrane potential
~-70mV -> if reached a rapid change in ionic concentration causes a reversal of the membrane potential to positive (+30 to 50mV) -> spike potential
what is Na conductance
abrupt/rapid/big (lower than membrane potential, higher than K conductance)
what is K conductance
(lower than both membrane potential and Na conductance)
what is refractory
determines the number of action potentials that can be sent per millisecond -> includes absolute (can’t produce) and relative (harder to produce)
what are synaptic pots
not all input will reach threshold and cause action potential, not enough input so forgotten, small hyperpolarizing afterpotential -> smaller periods = less time between action potentials
what is action potential
- AP amplitude is invariant and all-or-nothing
- neural information is encoded by the frequency and pattern of impulses (rate coding)
- refractory periods variable among different motoneuron types and determines basic firing rates
- net charge of synaptic potentials
- ~10K synapses generates an action potential at the axon hillock if critical threshold is reached (excitatory > inhibitory)
what are nerve conduction velocities
