Chapter 6 A&P
Muscle tissue:
• Muscle tissue allows for movement
– Body movement
– Organ movement
• All together comprises 40–50% body mass
• Limited capacity for regeneration
• Three types:
– Skeletal
– Cardiac
– smooth
Skeletal muscle:
• Found around skeletal system
• Responsible for:
– Body movements
• Voluntary (consciously controlled)
• Involuntary (unconsciously controlled)
– Skeleton stabilization
– Heat
• Striated (striped appearance)
• Regeneration limited after injury
Cardiac muscle:
• Found in heart wall
• Responsible for:
– Generation of force necessary to pump blood
• Involuntary control of contraction
– Ability to contract without nervous system oversight
• Striated
• Regeneration after injury is minimal, if any
Smooth muscle:
• Forms hollow organ walls (blood vessels, airways, stomach, intestines, uterus)
• Responsible for:
– Movement of substances within the body
– Regulation of organ volume; helps store substances
• Involuntary
• Not striated, smaller than other muscle cells
• Regenerates more easily than other muscle tissue types
Skeletal muscle structure:
• Fascicles
– Bundles of muscle cells/fibers wrapped in connective tissue
• Muscle cells/fibers
– Is multinucleated
, – Plasma membrane invaginates into deep parts of muscle fiber to form transverse
tubules (T-tubules)
– Endoplasmic reticulum is called sarcoplasmic reticulum(SR is always muscle)
• Serves as reservoir to hold calcium ions between muscle contractions
• Located near T-tubules
• Myofilaments
– Threadlike proteins that allow muscle fibers to shorten
Muscle cell structures:
• Sarcomere
– Contractile unit/building block of a muscle fiber
• Thin filament
– Actin protein filament
• Thick filament
– Myosin protein filament
• Z disc
Boundaries of a sarcomere unit
Sliding filament theory:
• Myosin heads (thick filaments) attach to binding sites on the actin filaments (thin
filaments)
• Crossbridges between the two filaments are formed, and actin filaments are pulled
inwards in a repeating process (contraction cycle)
• Calcium ions and ATP are necessary for contraction; contraction cycles continue until
supplies are depleted in the sarcoplasm (muscle cell cytoplasm)
What initiates skeletal muscle contraction:
• Nerve signals initiate the voluntary or involuntary contraction
• Neuromuscular junction
– Where the electrical impulse of the nerve signal is converted to a chemical signal
that binds to the muscle cell and starts an electrical impulse there
(depolarization)
– Acetylcholine (ACh) is the chemical signal at the nuclear junction
Skeletal muscle contraction:
• The electrical state of the cell membrane is reversed = depolarization
• Initiates contraction through depolarization along length of muscle fiber = action
potential
• Action potential then travels along cell membrane into the T-tubules
• Calcium ions are then released through calcium channels from the sarcoplasmic
reticulum
• Rise in calcium initiates the contraction cycle
• Calcium ions are pumped back inside the sarcoplasmic reticulum
Muscle tissue:
• Muscle tissue allows for movement
– Body movement
– Organ movement
• All together comprises 40–50% body mass
• Limited capacity for regeneration
• Three types:
– Skeletal
– Cardiac
– smooth
Skeletal muscle:
• Found around skeletal system
• Responsible for:
– Body movements
• Voluntary (consciously controlled)
• Involuntary (unconsciously controlled)
– Skeleton stabilization
– Heat
• Striated (striped appearance)
• Regeneration limited after injury
Cardiac muscle:
• Found in heart wall
• Responsible for:
– Generation of force necessary to pump blood
• Involuntary control of contraction
– Ability to contract without nervous system oversight
• Striated
• Regeneration after injury is minimal, if any
Smooth muscle:
• Forms hollow organ walls (blood vessels, airways, stomach, intestines, uterus)
• Responsible for:
– Movement of substances within the body
– Regulation of organ volume; helps store substances
• Involuntary
• Not striated, smaller than other muscle cells
• Regenerates more easily than other muscle tissue types
Skeletal muscle structure:
• Fascicles
– Bundles of muscle cells/fibers wrapped in connective tissue
• Muscle cells/fibers
– Is multinucleated
, – Plasma membrane invaginates into deep parts of muscle fiber to form transverse
tubules (T-tubules)
– Endoplasmic reticulum is called sarcoplasmic reticulum(SR is always muscle)
• Serves as reservoir to hold calcium ions between muscle contractions
• Located near T-tubules
• Myofilaments
– Threadlike proteins that allow muscle fibers to shorten
Muscle cell structures:
• Sarcomere
– Contractile unit/building block of a muscle fiber
• Thin filament
– Actin protein filament
• Thick filament
– Myosin protein filament
• Z disc
Boundaries of a sarcomere unit
Sliding filament theory:
• Myosin heads (thick filaments) attach to binding sites on the actin filaments (thin
filaments)
• Crossbridges between the two filaments are formed, and actin filaments are pulled
inwards in a repeating process (contraction cycle)
• Calcium ions and ATP are necessary for contraction; contraction cycles continue until
supplies are depleted in the sarcoplasm (muscle cell cytoplasm)
What initiates skeletal muscle contraction:
• Nerve signals initiate the voluntary or involuntary contraction
• Neuromuscular junction
– Where the electrical impulse of the nerve signal is converted to a chemical signal
that binds to the muscle cell and starts an electrical impulse there
(depolarization)
– Acetylcholine (ACh) is the chemical signal at the nuclear junction
Skeletal muscle contraction:
• The electrical state of the cell membrane is reversed = depolarization
• Initiates contraction through depolarization along length of muscle fiber = action
potential
• Action potential then travels along cell membrane into the T-tubules
• Calcium ions are then released through calcium channels from the sarcoplasmic
reticulum
• Rise in calcium initiates the contraction cycle
• Calcium ions are pumped back inside the sarcoplasmic reticulum
