Muscles Flashcards
Functions of Muscle Tissues
Muscle tissue contracts in response to a stimulus from the nervous system. This allows
• Material to move through the body
• Parts of the body to move (including the whole body)
• The generation of heat
Muscle Tissue Types
- Skeletal muscle
- Cardiac muscle
- Smooth muscle
Properties of Skeletal muscle
Skeletal muscle
• Moves the skeleton
• Under voluntary control
• Is multinucleated
• Long, cylindrical fibers
• Striated
• Accounts for ~40% body weight
Properties of cardiac muscle
Cardiac muscle
• Only found in heart wall
• Shorter, branched fibers
• One nucleus per cell
• Striated
• Under involuntary control
Properties of smooth muscle
Smooth muscle
• Found in walls of hollow organs (except the heart)
• Small, spindle-shaped cells
• One nucleus per cell
• No striations
• Under involuntary control
What are the four properties of muscle tissue (not types)
- Excitability
- Contractility
- Extensibility
- Elasticity
What is Excitability?
- Excitability
• Nerve signal excites the muscle, causing contraction
What is Contractility
- Contractility
• When a muscle contracts, it shortens*
• This occurs at the microscopic level as myofilaments pull past each other
What is Extensibility
Extensibility
• After contraction, the muscle can go back to resting length (by gravity and/or an antagonist)
What is Elasticity?
Elasticity
• After being stretched, a muscle recoils passively and resumes its resting length
What runs through muscle?
Arteries, Veins, and Nerves Run Through Muscle
Arteries, Veins, and Nerves purpose?
• Arteries provide oxygen and nutrients
• Veins remove cellular wastes
• Nerves innervate muscle cells
What subunits are the muscles made of?
The whole muscle is made of subunits called fascicles
What are fascicles?
The whole muscle is made of subunits called fascicles
• Fascicles are made of individual muscle fibers (cells)
• Muscle fibers can be less than an inch and longer than one foot
What are the connective tissues of muscles?
Connective tissues
• Epimysium
• Perimysium
• Endomysium
What/where is Epimysium?
Epimysium
• surrounds whole muscle
• Dense irregular CT
What/where is Perimysium?
Perimysium
• surrounds fascicles
• Fibrous CT
What/where is Endomysium?
Endomysium
• surrounds individual muscle fibers
• Loose CT
What are muscles fibers made of?
Skeletal Muscle Anatomy
• Individual muscle fibers are made of cylindrical organelles called myofibrils
- These organelles run parallel to each other and the muscle fiber
What are myofibrils?
Myofibrils are made of repeating units called sarcomeres
• Sarcomeres are made of proteins called myofilaments
• Sarcomeres repeat throughout length of muscle fiber
• They line up end to end like box cars of a train
What are Sarcomeres made of?
Sarcomeres are made of two types of myofilaments
• Thick filament
• Thin filament
• Elastic filament
What is thick filament?
Thick filament (made of protein myosin)
- found in sarcomeres
What is thin filament?
• Thin filament (made of 3 proteins: actin, troponin, tropomyosin;
- type of myofilament in sacromeres
What is elastic filament?
Elastic filament (titin): attaches Z disc to thick filament; offers elasticity
- found in sacromeres??
What do the three proteins in thin filament do?
• Tropomyosin blocks actin’s binding site for myosin head
• Tropomyosin and troponin interact with each other
- when Ca2+ binds to troponin, it causes tropomyosin to unblock actin’s binding site
- Myosin heads can now bind to active site
What are the Sarcomere Striations?
• I bands
• A bands
• H zones
• M line
What are I bands?
• I bands: between thick filaments of adjacent sarcomeres
- Contain Z discs, thin filaments, elastic filament
What are A bands?
• A bands: length of thick filaments
- Contain both thick and thin filaments
What are H zones?
H zones: between thin filaments (within single sarcomere)
- Contain only thick filaments
What is the M line?
• M line: middle of H zone; delicate filaments holding myosin in place
What is the Muscle Fiber Anatomy?
• Muscle fiber = single muscle cell
• Sarcolemma = plasma membrane of muscle fiber
• Sarcoplasm = cytoplasm of muscle fiber
What are T Tubules?
• T tubules are extensions of sarcolemma that extend into muscle fiber
- Wrap around myofibrils
- Carry electrical stimulus to myofibrils
What is the Sarcoplasmic reticulum?
Sarcoplasmic reticulum
• Modified smooth ER
• Stores and releases calcium ions
Structure of Fascicles
- Fascicles are bundles of muscle fibers
- Each muscle fiber is made of many myofibrils
- Myofibrils are made of sarcomeres
- Sarcomeres are made of myofilaments
- There are 2 myofilaments: thick filament and thin filament
What are motor units?
Motor Units
• Within a muscle, muscle fibers work together to perform an action (contraction)
• Motor units allow for a given muscle to exert a great • •All fibers innervated by a single motor neuron contract at the same time
• Activating more motor units within a muscle increases the force exerted by that muscle
What is a motor unit = to
• Motor unit =1 motor neuron and all the muscle fibers it innervates
Small vs Large motor unit
• Some large muscles (quadriceps femoris) have motor units with 2000 muscle fibers per motor unit (= large motor unit)
- Powerful contractions
• Smaller muscles (extraocular muscles) can have 10 fibers per motor unit (= small motor unit)
- Fine motor control
What is a neuromuscular junction
Neuromuscular junction
• Where motor neuron meets muscle fiber
• Stimulation of muscle fiber can occur
What causes Sarcomere shortening?
When acetylcholine (ACh) is released from the motor neuron, an action potential of excitation stimulates the muscle fiber…this ultimately causes sarcomere shortening
Why are muscle fibers arranged how they are?
Muscle fibers are arranged in a pattern that provides the most efficient movement for an extended action
What does muscle power depend on?
• Muscle power depends on the total number of muscle fibers in the muscle
- More fibers –> stronger contraction
How much is each muscle fiber able to shorten?
• Each muscle fiber is only able to shorten about 1/3 of its resting length
- Longer muscle fibers are able to shorten more
What are componets of Parallel muscles
Parallel muscles
• Muscle fascicles run parallel to axis of muscle
• Tendon on either end
• Look long and ropelike
• Fewer fibers than other types
• Longer fibers so can shorten more
• Can be fusiform (with a belly, ex. biceps brachii) or strap-like (ex. sartorius)
What are the components of Pennate muscles?
Pennate muscles
• Tendon runs whole length of muscle
• Fascicles attach to tendon at an angle (resemble a feather)
• Shorter fibers than parallel muscles
• Allows for more fibers so stronger than parallel
What are Convergent muscles?
Convergent muscles
• Origin of muscle is broad
• Muscle fascicles converge into
tendon at insertion
• Fan shaped
• Relationship to other muscle
types:
- More fibers than parallel
- Longer fibers than pennate
What is the ranking of Strength between comparably sized muscles?
Strength of comparably sized muscles
Parallel (weakest)
Convergent
Pennate (strongest)
What is the ranking of Shortening between comparably sized muscles?
Shortening ability of comparably sized muscles
Pennate (least)
Convergent
Parallel (greatest)
What are circular muscles?
Circular muscles
• Fascicles arranged in a ring
• Sphincter muscles
- When contracted, the muscle constricts an orifice (opening), closing it
What is an example of circular muscles?
Example = orbicularis oris (mouth)
What is an example of convergent muscles?
Example = pectoralis major (Pec)
What is an example of parallel muscles?
Example = sartorius (anterior component of thigh)
What are the types of muscle attachments?
• Origin
• Insertion
• Action
• Direct
• Indirect
What are Direct Muscle Attachments?
Direct –> short, dense regular CT
fibers connect muscle to bone
What are Indirect Muscle Attachments?
Indirect –> long, dense regular CT
fibers connect muscle to bone
• Ex. Tendon and aponeurosis
What are origin Muscle Attachments?
Origin: attachment site that is not moved, or moved the least during a muscle contraction
What are the Insertion Muscle Attachments?
Insertion: attachment site that is moved when muscle shortens
What are the Action Muscle Attachments?
Action: the resulting movement of a muscle contraction
What are difference between tendons and Aponeuroses?
Tendons
• More rope-like
Aponeuroses
• Flat sheet
- ex: Aponeurosis of the external oblique (nears abs)
What are the components of cardiac muscle?
Cardiac Muscle
• Striated
• Branched
• Most cells are uninucleate, may have two large nuclei
• Cells have some regenerative ability (recent research has shown that perhaps 1% a year)
• Surrounded by endomysium
• Connected by intercalated discs
• Involuntary control
What is the structural components of Intercalated Disc?
• Gap junctions
- allow for coordinated contractions by allowing action potentials to quickly spread from cell to cell
• Desmosomes: provide strength, site where intermediate filaments attach
What are the components of smooth muscle tissues?
• Small, spindle shaped cells
• Uninucleate
• No striations
- They do contain myofilaments but they are not arranged in sarcomeres
• Each cell is covered in endomysium
• Involuntary
• Regenerate
What do smooth muscle cells contain?
Smooth Muscle Cells
• Intermediate filaments anchor actin and myosin
• A contraction involves myosin and actin filaments moving against one another
How is smooth muscle arranged?
• Smooth muscle is typically arranged in 2 distinct layers
- Circular layer: closest to lumen of organ
- Longitudinal layer: wraps around circular
layer
• Layers differ in their orientation of cells
- Typically perpendicular to each other
