Muscles Flashcards
How many muscles are there in the body
Approx 640 muscles
What is the strongest muscle?
The masseter (i.e. jaw)
What is the largest muscle?
The gluteus maximus
What is the smallest muscle
Stapedius muscle
What are the main roles of muscles
Allow for movement of the body, bones, food, blood and fluids
Responsible for energy metabolism and storage (glycolysis)
Thermoregulation (creates body heat)
What are the four basic properties of muscle
Contractility
Excitability
Extensibility
Elasticity
What is contractility
Ability of muscle to shorten with a force. It requires energy and relaxes passively
What is excitability
Capacity of muscle to respond to stimulation (nerves) - electrical stimulation
What is extensibility
Muscle can be stretched to its normal resting rate and beyond to a limited degree
What is elasticity
Muscles return or recoil to resting position when relaxed
What % of body mass is skeletal muscle for men compared to women
men = 40%
women = 30%
Does muscle mass decrease with agr
Yes it decreases, leading to sacropenia (involuntary loss of skeletal muscle) and ultimately loss of physical capacity
How do muscles function (basic)
They function by performing opposing actions (agonist and antagonist)
What does the agonist do
Agonist causes movement
What does the antagonist do
Antagonist provides opposite movement to agonist
What are the 3 different types of muscles
Skeletal
Cardiac (myocardium)
Smooth
What is skeletal muscle
Muscle attached to skeleton - its responsible for voluntary movement
What is cardiac muscle?
Forms the heart, which is also responsible for pumping blood, and it is ultimately an involuntary movement
What is smooth muscle?
Located in tissues and is responsible for controlling diameter of structures and peristalsis (involuntary constriction and relaxation of muscles, causing wave like movement that pushes contents forward in the gut)
Explain the structure of muscle fibers (in terms of ascending size)
Sarcomeres –> myofibril –> muscle fibre –> muscle bundle –> muscle
What are sarcomeres made up of?
Made up of actin and myosin filaments
What are actin filaments
These are the thin contractile filaments compared to myosin
What are myosin filaments
These are the thick contractile filaments compared to actin
Explain the process of muscle contraction
1) ATP bound myosin is in the relaxed position
2) When ATP is dephosphorylated to ADP + Pi (inorganic phosphate), it is positioned to form a cross bridge. Tropomyosin inhibits/blocks binding sites on actin and prevents cross bridge formation
3) Electrical excitation of the muscle cell releases calcium from the sarcoplasmic reticulum. Calcium binds to troponin and moves the tropomyosin out of the way to allow cross bridge formation
4) Power stroke: Release of phosphate bound to the myosin head - myosin head moves along the actin filament
5) At the end of excitation, calcium pumps back into SR allowing tropomyosin to block myosin binding again, and ATP is bound again
What is tropomyosin
ropomyosin is the guard mechanism that prevents a skeletal muscle from contracting irregularly or on its own. Tropomyosin is a protein filament used to create a barrier between actin and myosin protein filaments and prevent the skeletal muscle from contracting.
What is troponin
Troponin (Tn) is the sarcomeric Ca2+ regulator for striated (skeletal and cardiac) muscle contraction. On binding Ca2+ Tn transmits information via structural changes throughout the actin-tropomyosin filaments, activating myosin ATPase activity and muscle contraction.
What is the myosin head
In addition to binding actin, the myosin heads bind and hydrolyze ATP, which provides the energy to drive filament sliding.
What are the two different muscle fiber types
Type 1 and Type 2
What are type 1 muscle fiber types
They are also called slow twitch and red muscle fibers. They contract slowly, but are slow to fatigue.
It uses aerobic (slower) metabolism to generate large amounts of ATP - adapted to deliver O2 to the mitochondria
Fibers are red due to the myoglobin content which transports O2 to the area
WHat are type 2 muscle fiber types
They are also called fast twitch or white muscle fibers
They contract quickly and are fast to fatigue. They use anaerobic (faster) metabolism to generate less ATP - not adapted to deliver O2 to mitochondria
WHat are the two types of white muscle fiber
Type 2A and type 2B
What does type 2A and type 2B muscles do
Type IIA fibers have high myosin ATPase activity (pH 9.4), are fast twitch, have high oxidative and glycolytic capacity, and are relatively resistant to fatigue. Type IIB fibers have high myosin ATPase activity (pH 9.4), are fast twitch, have low oxidative and high glycolytic capacity, and fatigue rapidly.
What are the characteristics of smooth muscles
Single shaped cells without striations
Single central nucleus
Contracts more slowly with less power than skeletal muscle
What are the two types of contractions in smooth muscles
Phasic - rapid
Tonic - slower, maintain tension longer
Where are smooth muscles formed
Walls of organs, vessels
Respiratory tract
Eye - dilation constriction of pupil
Skin
kidneys
What is the process of smooth muscle contractions
1) Ca2+ influx into cell from SR and extracellular sources via L type Ca2+ channels
2) Ca2+ binds calmodulin in sarcoplasm
3) Ca2+-/calmodulin activates MLCK which phosphorylates head of myosin filament (ATP) - cross bridge formation
4) No influx - relaxation
Overall. There is increase in cytosolic Calcium. Calcium ions bind to calmodulin in cytosol. Calcium calmodulin complex binds to myosin light chain kinase. This kinase uses ATP to phosphorylate myosin cross bridges. Phosphorylated myosin cross bridges bind to actin filaments. The cross bridge cycle produces tension and shortening
What are the differences between smooth and skeletal muscle contraction?
Ca2+ binds to calmodulin in cytosol in smooth muscle contraction vs binding to troponin on thin filaments in skeletal muscle
MLCK phosphorylation of myosin cross bdirge
Smooth muscle contraction is 100-1000 times slower than skeletal - allows smooth muscle to maintain prolonged tonic contraction while consuming little ATP and O2
Stimulus for smooth muscle contraction can be varied - stretch, neural (automatic NS), hormonal, skeletal-innervation(somatic NS)
What is a motor unit
It is one motor neuron which supplies a group of muscle cells
What are the features of small motor units
Innervate less muscle fibers
Generate less tension
Enable fine control
Fatigue resistant
I.e. eye movements
What are the features of large motor units
Generate more tension
Fatigues more quickly
What are slow motor units
Typically help with type 1 fibers - sustained contraction
What are fast motor units
Typically help with type 2 fibers - large rapid forces
How can an increase in force be generated
By activating more motor units simultaneously
What is the overall tension produced in a skeletal muscle a function of?
The frequency of neural stimulation and the number of motor units
What are the two types of smooth muscle cells?
Single unit and multi unit
What are single unit smooth muscle cells
All cells function collectively and simultaneously as a single unit (unitary) i.e. abdomen or bladder
What are multi unit smooth muscle cells
All cells cannot function collectively and instead work independently
What are the 3 periods to muscle tension
Latent period, contraction period and relaxation period
What is the latent period
Action potential is being propagated along the membrane and Ca2+ ions are released from the sarcoplasmic reticulum
What is the contraction period
Period of cross bridge formation
What is the relaxation period
When Ca2+ is pumped back into SR and cross bridge cycling stops
Describe the muscle tension across the periods of muscle tension
During latent and contraction period it is increasing, and peaks right at the end of the contraction period. Then, during the relaxation period, the muscle tension decreases
What is a muscle twitch
It is a single contraction from one action potential from a motor neuron
What is the idea of summation in muscle tension
If a muscle cell is stimulated while a previous twitch is still occurring, the second twitch will be stronger.
The second stimulus releases more Ca2+ ions and allows more cross bridge formations
What is a tetanic contraction
It is a sustained muscle contraction evoked by a motor nerve emitting action potentials at a very high rate
What is the sarcoplasmic reticulum
The sarcoplasmic reticulum (SR) is a specialized form of the endoplasmic reticulum of muscle cells, dedicated to calcium ion (Ca2+) handling, necessary for muscle contraction and relaxation.
