Muscle Physiology Flashcards
What are muscle cells?
Muscle fibers
Muscle fiber are ensheathed by a thin layer of connective tissue called?
Endomysium
Three layers of surrounding connective tissue for muscle fibers from out to in.
Epimysium
Perimysium
Endomysium
Skeletal Muscle cells are unique to other cells in that that are _____ and ____.
multinucleated and striated
Muscle fibers are surrounded by a plasma membrane called a ?
Sarcolemma
Muscle fibers contain ? (division below fibers)
Myofibrils
Myofibrils are comprised of ____ filaments.
Myo
What are the two types of myofilaments ? (size distinction)
thin and thick
Describe a Sarcomere.
Basic unit of striated skeletal muscle that extends from one z disc to another.
Describe an A band.
Dark portion of the sarcomere that contains thick filaments. Most of these filaments are myosin
Describe the H band.
This is the light area at the center of an A band where the actin and myosin don’t overlap.
Describe the I band.
Light portion of the sarcomere that contains thin filaments. Mostly actin
Describe the Z line/ disc.
The center of the I band where actins attach.
Describe the layout of a sarcomere from one edge to another.
The sarcomere starts with the edge of an I band, then crosses the Z disc while still inside the I band. The next band outside of the I band is the A band, and at the center of the sarcomere is the H zone. This first half is a mirror image of the other.
What are the thick filaments in a sarcomere called ?
Myosin
What are the thin filaments in a sarcomere called ?
Actin
Myosin 2 is a hexamer. Describe its structure.
2 Heavy chains and 2 Light chains
What are the two lights chains within the heavy chains in myosin?
Regulatory and essential light chain
What are the two parts of Myosin 2? (Meromyosin)
HMM = Heavy meromyosin LMM = Light meromyosin
Each motor neuron innervate how many muscle fibers?
Variable number
A motor unit consists of?
each motor neuron and all fibers it innervates
When a motor neuron is activated, describe the number of muscle fibers it contracts.
All of them
Number of muscle fibers in a motor unit is determined by ? what is the pattern?
degree of fine control.
fine control requires small number of fibers
What is the innervation ratio?
of motor neurons : muscle fibers ( varies from 1:100 to 1:2000)
What techniques is used by the body to preform smooth movements?
Recruitment
Explain recruitment.
- Brain estimates number of motor units and stimulates them.
- It keep recruiting more units until desired movement is accomplished in smooth fashion
- more motor units for more STR
The velocity of contraction is dependent on? Pattern?
load force required.
lighter load = faster contraction
What are two concepts related to Length-tension relationship?
- Too little overlap yields less tension because fewer cross bridges can form 2. With no overlap force cannot be generated because cross bridges cannot form
Explain isotonic contraction.
force remains constant throughout shortening process. Length changes.
Explain isometric contraction.
exerted force does not cause load to move and length of fibers remains constant.
Explain eccentric contraction.
Load is greater than exerted force and fibers lengthen despite it contraction.
Explain concentric contraction.
Muscle tension is greater than the load and muscle shortens.
Titin is aka?
connectin
Describe the size of Titin.
Largest known protein. 27 - 33 k poplypeptide chain
Describe the abundance of Titin.
3rd most abundant.
Describe the functions of Titin.
- Molecular spring that is responsible for the passive elasticity of the muscle.
- Domain unfolds and refolds– Accounts for return of resting length after stretching
– Keeps myosin filaments centered during contraction
– Molecular ruler during myogenesis
Muscle contraction occurs because ___ filaments slide over and between ____ filaments towards center.
Thin
Thick
During contraction the length of filaments?
remains constant
During contraction, the A bands _____, but do not _____
move closer together
shorten
During contraction, I bands _____.
shorten
During contraction , H bands _____.
shorten.
Control of cross bridge attachment to actin is via?
troponin-tropmyosin system
Troponin-tropmyosin system serves as a switch for ?
muscle contraction and relaxation.
What is the theory that states muscle contracts because myofibrils get shorter?
Sliding filament theory of contraction
What filament lies in groove between double row of g-actins
Tropomyosin
_____ complex is attached to tropomyosin at intervals of every _ actins.
Troponin
7
Describe the first phase of the cross bridge cycle.
- Resting fiber cross bridge is not attached to actin
- ATP dissociates the myosin head from actin
- ATP binding to myosin weaken the affinity for myosin to bind to actin
Describe the second phase of the cross bridge cycle.
- Myosin has ATPase activity and hydrolysis ATP tp ADP +Pi (slow rate of hydrolysis)
- ATP hydrolysis leads to conformational change
Describe the third phase of the cross bridge cycle.
- Crossbridge binds to Pre-powerstroke conformation (bent head) (ADP + Pi is bent)
- Myosin-ADP+Pi binds weakly to actin.
Describe the fourth phase of the cross bridge cycle.
- Actin increases rate of myosin hydrolysis (>100x)
- Rapid hydrolyzed to ADP + Pi
- PO4 dissociation allows the powerstoke to proceed.
Describe the fifth phase of the cross bridge cycle.
- Post binding the myosin undergoes conformational change exerting force on actin (powerstroke) (ADP - myosin head is straight)
- In the absence of ATP, myosin binds tightly to actin
Describe the First four steps of the sliding filament theory of contraction.
- A myofiber, together with all of its myofibrils, shortens by movement of the insertion toward the origin of the muscle
- Shortening of the myofibrils is caused by shortening of the sarcomeres
- Shortening of the sarcomeres is accomplished by sliding of the myofilament
- Sliding of the filaments is produced by asynchronous power strokes of myosin cross bridges, which pull thin filaments over the thick filaments.
Describe the last three steps of the sliding filament theory of contraction.
- The A bands remain the same length during contraction, but are pulled toward the origin of the muscle.
- Adjacent A bands are pulled closer together as the I bands between them shorten
- The H bands shorten during contraction as the thin filaments on the sides of the sarcomeres are pulled toward the middle.
Skeletal muscle sarcolemma is excitable meaning that it ?
Conducts an Action Potentials
Release of ACh at NMJ causes?
large depolarizing end-plate potentials and APs in muscle
APs race over sarcolemma and down into muscle via ?
T tubules
Place on sarcolemma where NMJ occurs is ?
The motor end plate
Ca++ levels are low in relaxed muscle because ?
it is continually pumped back into the sarcoplasmic reticulum (SR - a calcium reservoir in muscle)
Most Ca++ in SR is in ?
terminal cisternae
Running along terminal cisternae are ?
T Tubules
In relaxed muscle, tropomyosin blocks binding sites on actin so __________? This occurs when Ca++ levels are _____.
cross-bridge binding can’t occur
low
Contraction can occur only when ?
binding sites are exposed
calcium does not affect binding affinity of ?
it does affect the rate of ?
myosin to thin filament
phosphate dissociation
Phosphate dissociation (not crossbridge binding) is inhibited at ?
low calcium in striated muscle
In regards to the excitation-contraction coupling, the somatic motor neuron releases what ?
ACh
What happens in the sarcolemma when ACh is released?
- ACh binds to nicotinic ACh receptors, opens ligand gated channels.
- Na diffuses in, producing depolarizing stimulus
- Action potential is produced.
What happens in the transvers tubules after an action potential is produced in the sarcolemma?
- Action potentials conducted along transverse tubules
2. Action potential opens voltage gated Ca channels
What happens in the sarcoplasmic reticulum after the voltage gated Ca channels open?
- Ca release channels in SR open
2. Ca diffuses into sarcoplasm
What happens in the myofibrils after Ca has diffused into the sarcoplasm?
Ca binds to troponin which stimulates contraction.
During light exercise, most energy is derived from ?
aerobic respiration of fatty acids
During moderate exercise, energy is derived?
equally from fatty acids and glucose
During heavy exercise, where is energy derived from and what can be done to increase the source of the energy?
Glucose supplies 2/3 of the energy and the liver and muscle increase glycogenolysis.
What is phosphocreatine ?
A source of high energy phosphate to regenerate ATP from ADP. Very efficient and aka creatine phosphate.
Slow twitch muscles are made of what type of fibers?
type I
Fast twitch muscles are made up of what type of fibers?
Type IIA and IIX
Type 1 fibers are AKA?
red slow oxidative fibers
Type 1 fibers uses mostly ______ respiration.
aerobic
Type 1 fibers have rich _____ supply, Many _____, and _____enzymes
capillary
mitochondria
Aerobic
Type 1 fiber has lots of ____ which give it its color.
Myoglobin
Type IIX fibers are AKA?
White fast glycolytic fibers
Type IIX fibers are able to contract using _____ metabolism.
anaerobic
Type IIX fibers have large stores of _____, ____ capillaries and _____, and little myoglobin.
glycogen
few
mitochondria
Type IIA fibers are AKA?
white fast oxidative fibers
Type IIA fibers are adapted to contract fast using ______ metabolism.
aerobic
Type IIA fibers act as an ______ to type I and type IIX
Intermediate
Type II fibers has ____ motor neurons and ____ motor units. That is the ______ of Type I.
Large and Large (yes same word)
opposite
Give the Ten effects of endurance training on skeletal muscle….. yes ten.
- Improved ability to obtain ATP from oxidative phosphorylation.
- Increase size and number of mitochondria
- Less lactic acid produced per given amount of exercise
- Increased myoglobin content.
- increased intramuscular triglyceride content.
- Increased lipoprotein lipase
- Increased proportion of energy derived from fat; less from carbs.
- Lower rate of glycogen depletion during exercise
- Improved efficiency in extracting oxygen from blood
- Decreased number of type IIX fibers; increased number of type IIA fibers
Cardiac muscle is _____ like skeletal, but _____ like smooth.
striated
involuntary
adjacent myocardial cells are joined by ____ ____ which allow ____ ____ to spread through cardiac muscle.
intercalated disks
action potentials
Smooth muscle has no _____.
Sacromeres or striations
Smooth muscle has ____ more ____ than ____ to allow greater ____ and _____.
16 times more actin than myosin
Stretching and contracting
Actin filaments in smooth muscle are anchored to ?
dense bodies
Smooth muscle contraction is controlled by ?
Calcium but different from striated contraction
Describe smooth muscle contraction process.
- Ca enters thru voltage gates channels in plasma membrane.
- Ca binds to calmodulin
- Ca-Calmodulin complex activates myosin light chain kinase which phosphorylates and activates myosin
- Myosin forms crossbridges with actin.
Smooth Muscle relaxation occurs when?
Ca conc. decreases
Describe the process of smooth muscle relaxation.
- Ca conc decreases
- Myosin is dephosphorylated by myosin phosphatase
- Myosin can no longer from crossbridges
Smooth vs Striated muscle.
Which has faster contractions ?
Striated
What is a latch state ?
A state of prolonged binding of myosin to actin which maintains force using little energy
Smooth vs Cardiac vs skeletal: presence of NJM.
Smooth: none
Cardiac: none
Skeletal: present
Smooth vs Cardiac vs skeletal: describe fibers
Smooth: fusiform and short
Cardiac: branching
Skeletal: cylindrical and long
Smooth vs Cardiac vs skeletal: amount of mitochondria.
Smooth: few
Cardiac: many
Skeletal: many to few ( type dependent)
Smooth vs Cardiac vs skeletal: # of Nuclei.
Smooth: 1
Cardiac: 1
Skeletal: >1
Smooth vs Cardiac vs skeletal: presence of sacromeres.
Smooth: none
Cardiac: present with max length of 2.6 um
Skeletal: present with max length of 3.7 um
Smooth vs Cardiac vs skeletal: Syncytium
Smooth: none ( independent cells)
Cardiac: none but function as such
Skeletal: present
Smooth vs Cardiac vs skeletal: Sarcoplasmic reticulum.
Smooth: little elaborated
Cardiac: moderately elaborated
Skeletal: Highly elaborated
Smooth vs Cardiac vs skeletal: ATPase.
Smooth: little
Cardiac: moderate
Skeletal: abundant
Smooth vs Cardiac vs skeletal: presence of NJM.
Smooth:
Cardiac:
Skeletal:
Smooth vs Cardiac vs skeletal: Self regulation
Smooth: spontaneous action (slow)
Cardiac: yes ( rapid)
Skeletal: none ( requires nerve stimulus
Smooth vs Cardiac vs skeletal: response to stimulus.
Smooth: Unresponsive
Cardiac: all or nothing
Skeletal: all or nothing
Smooth vs Cardiac vs skeletal: Action potential
Smooth: yes
Cardiac: yes
Skeletal: yes
Smooth vs Cardiac vs skeletal: workspace.
Smooth: force/length curve is variable
Cardiac: the increase in the force/length curve
Skeletal: at the peak of the force/length curve
