Intro/Skeletal Muscle Structure Flashcards
Muscle makes up ___ in men
42-47% of body mass.
Muscle makes up ___ in women
30-35%
Types of muscle
Skeletal
Smooth
Cardiacs
Each skeletal muscle is an organ. True or false?
True
Properties of the cells of the skeletal muscle
- Long and cylindrical, in bundles
- Multinucleate
- Obvious Striations
Which muscle type carries our voluntary actions?
Skeletal
What are the skeletal muscle’s connective tissue components?
- Endomysium
- Perimysium
- Epimysium
Skeletal muscles are found…
…attached to bones in the skeletal system
Endomysium is found…
…between fibers
Perimysium is found…
…surrounding bundles
Epimysium is found…
…surrounding whole muscle
Which tissue component of skeletal muscle covers the entire muscle?
Epimysium
Smooth muscle is found…
…in the walls of hollow organs like blood vessels and the GIT
Properties of the cells of smooth muscle
- Uninucleate
- No striations
The movements of smooth muscle are voluntary. True or false?
False
Which muscle type possesses two layers of opposite orientation?
Smooth muscle
Muscle layers of smooth muscle
Circular
Longitudinal
Components of connective tissue in smooth muscle
Endomysium
Endomysium smooth muscle tissue
It surrounds cells
Properties of cells of cardiac muscle
- Branching, chains of cells
- Single Nucleated
- Striations
Cardiac muscle cells are connected by…
…intercalated discs
Cardiac muscle movement - Involuntary or not?
Involuntary
The heart muscle is called…
Myocardium
Connective tissue component of cardiac muscle
Endomysium; it surrounds cells
A skeletal muscle fiber is an individual muscle cell. True or false?
True
Shape of muscle fibres
They are long and narrow in shape
Sarcolemma is…
…the plasma membrane of the muscle cell. It surrounds the sarcoplasm and has many nuclei (multi-nucleated)
The nuclei of the muscle cell are located…
…in the periphery of the muscle cell just beneath the sarcolemma
The organelle must abundant in skeletal muscle fibres is…
Mitochondria
Cellular levels of structures in the skeletal muscle fiber from 1 to 5 are…
Sarcolemma Sarcoplasm with organelles and proteins Myofibrils and myofilaments SR T tubules
Why are there abundant mitochondria in skeletal muscle fibres?
High demand for energy (ATP) required for muscle contraction
What is myoglobin?
A protein with a high affinity for oxygen, just like haemoglobin
Function of myoglobin
It transfers oxygen from the blood to the mitochondria of the muscle cell
What are myofibirils?
A cylindrical bundle of contractile proteins, which are called myofilaments, within a muscle fiber
What are myofilaments? Where are they found?
They are contractile protein filaments that make up the Myofibrils, located in the sarcoplasm of the muscle cell
What are the names of the myofilaments of striated muscle cells?
–Actin – thin filament
–Myosin – thick filament
What is the Sarcoplasmic reticulum (SR)?
•Located where the SR ends, which is near the area where actin and myosin overlap
–The SR tubules and terminal cisternae store high concentrations of calcium, which is important in the process of skeletal muscle contraction
A saclike membranous network of tubules that are actually an elaborate form of smooth endoplasmic reticulum
SR surrounds ____ and contains ___
myofibril, terminal cisternae
Location of terminal cisternae on muscle fibre cells
They are located where the SR ends, which is near the area where actin and myosin overlap
Functions of SR
The SR tubules and terminal cisternae store high concentrations of calcium, which is important in the process of skeletal muscle contraction
Where are the transverse tubules (T-tubules) of skeletal muscle cells found?
They are invaginations found closely associated with SR and connected to the sarcolemma but penetrate the sarcolemma into the interior of the muscle cell
Functions of T-tubules
They bring extracellular materials into close proximity of the deeper parts of the muscle fiber
SR and T-tubules Function
–Activate skeletal muscle contraction when the muscle cell is stimulated by a nerve impulse
–Transmit nerve impulses from the sarcolemma to the myofibrils
The sarcomere is…
An arrangement of myofilaments with alternating bands of light and dark areas due to the organization of the actin and myosin, resulting in a striated appearance
What is smallest contractile unit of the muscle fiber?
Sarcomere
The components of the sarcomere are…
Z-lines M-lines A-bands I-bands Proteins
Z line properties
-
Actin is anchored by…
Z lines
Thick myofilaments (myosin) are anchored by…
M lines
Which two lines run perpendicular along the muscle fibres?
Z and M lines
Thin actin filaments project in either direction off of a Z disc and cross the entire length of the sarcomere. True or false?
Not entirely true. It projects off but doesn’t cross the entire length.
What is the H-Zone?
The lighter area within the A-Band that contains only myosin and contains the M line.
The A-band spans the length of the myosin filament. True or false?
True
There is no actin in the M band. True or false?
True
The I band is…
… a light area composed of actin only. It contains the Z line, which is the border of the sarcomere
Which is darker - A band or I band?
A-band
The basic component of each actin myofilament is…
G-actin (globular actin)
The actin myofilament consists of…
…two strands of G-actin molecules and myosin binding sites
The two strands of G-actin molecules in actin are twisted together with…
…two regulatory proteins:
–tropomyosin
–troponin
The sarcomere is broken up into three bands. True or false? What are they?
True. A band, two I bands
Structure of Tropomyosin
- Rod-shaped
- Occupies the groove between the twisted strand of actin molecules
- Blocks the myosin binding sites on the G-actin molecules
Troponin structure
A complex of three globular proteins:
•One is attached to the actin molecule
•One is attached to tropomyosin
•One contains a binding site for calcium
What are myosin cross bridges?
The myosin heads are known as cross-bridges because they can bind to and move along actin in the thin filament.
Myosin is composed of…
…a rod-like tail and two globular heads
What form the central portion of the myosin myofilament?
The tails
Orientation of the two globular heads of the myosin molecule
They face outward and in opposite directions
When does myosin interact with actin?
During contraction
Binding sites on myosin
There are binding sites for both actin and ATP
The ATP binding site for myosin contains…
The enzyme ATP-ase for the hydrolysis of ATP
What is Titin?
It connects myosin to the Z-lines in the sarcomere
Properties of Titin
–It is very elastic, able to stretch up to 3 times its resting length
–Important molecule because it is responsible for muscle flexibility
Not all muscle fibers are the same physiologically. True or false?
True
Criteria for muscle variation
–The predominant pathway utilized to synthesize ATP
–The amount of myoglobin
–Efficiency of ATPase
Classification of muscle fibres based on ATP synthesis pathway
- Oxidative fibers
* Glycolytic fibers
Oxidative fibers properties
- Predominantly aerobic pathways
– Oxidative phosphorylation in the mitochondria
– Fatigue-resistant fibers
Glycolytic fibers properties
- Predominantly anaerobic pathways
–Glycolysis in the sarcoplasm
–Fatigable fibers
Classification of muscle fibres based on the amount of myoglobin present
- Red fibers - high amounts of myoglobin
* White fibers - small amounts of myoglobin
Classification of muscle fibres based on the efficiency of ATPase
- Fast twitch fibers - decompose ATP rapidly
* Slow twitch fibers - decompose ATP slowly
Slow-twitch, fatigue-resistant fibers properties
–Slow oxidative fibers, or red muscle fibers.
–Contain abundant myoglobin giving them their red color.
–Slow acting ATPase enzymes
–Abundant mitochondria
–Endurance type muscles
•Able to deliver strong, prolonged contractions.
Slow-twitch, fatigue-resistant fibers properties depend upon aerobic pathways for production of ATP. True or false?
True
Examples of slow-twitch, fatigue-resistant muscles
–Postural muscles - spinal extensors
–Anti-gravity muscles - calf muscle
Gastrocnemius is not a slow-twitch, fatigue-resistant muscles. True or false?
False; it is.
Fast-twitch fatigable fibers properties
–Fast glycolytic fibers, or white muscle fibers. –Contain small amounts of myoglobin –Fast acting ATPase enzymes –Few mitochondria –Plenty of glycogen –Extensive sarcoplasmic reticulum
Fast-twitch fatigable fibres contract slowly. True or false?
False
Fast-twitch fatigable fibres contract for limited periods of time. True or false?
True
Which type of muscle fibres depends on anaerobic metabolism?
Fast twitch anaerobic metabolism
Which muscle fibres are best suited for short duration, high intensity contractions?
Fast-twitch, fatigable fibres
Fast twitch fatigable fibres rapidly releases and stores calcium ions contributing to rapid contractions. True or false?
True
What are intermediate fibres?
Intermediate Fibers are fast-twitch fatigue-resistant fibers, fast and glycolytic fibers that lie between the red and white fibers
What determines the muscle cell type?
The motor nerve that innervates the muscle cell
A motor unit is…
A motor neuron and all of the muscle fibers it innervates
All of the muscle cells in a single motor unit are of the same type. True or false?
True
Which muscle fibre types are recruited first? Why?
Slow twitch fibers are recruited first because they are found in small motor units while fast twitch fibers are recruited last because they are found in large motor units
People are genetically predisposed to have relatively more of one fiber type than another. True or false?
True
Difference between marathon runners and sprinters
People who excel at marathon running have higher percentages of slow twitch fatigue resistant muscle fibers while people who excel at sprinting have higher percentages of fast twitch fatigable fibers
