Chapter 10 Flashcards
3 types of muscular tissues
- Skeletal muscle
- Cardiac muscle
- Smooth muscle
Skeletal appearance
multi-nucleated and striated
Cardiac appearance
one nucleus, striated, and intercalated discs
Smooth muscles tissue appearance
one nucleus and no striations
Smooth muscle location
Various organs like hollow
Functions of muscular tissue
◼ Producing body movements
◼ Stabilizing body positions
◼ Storing and mobilizing substances within the body
◼ Generating heat
Properties of Muscular Tissue
◼ Electrical excitability
◼ Contractility
◼ Extensibility
◼ Elasticity
Epimysium
outer layer; dense irregular connective tissue; Surrounds entire muscle organ
Perimysium
middle layer; dense irregular connective tissue; Surrounds 10 - 100+ muscle fibers, creating bundles “fascicles”
Endomysium
inner layer; areolar connective tissue; Surrounds each muscle cell/fibre; made of mostly fine reticular fibers
Z discs
Narrow, plate-shaped regions of dense material that separate one sarcomere from the next.
A band
Dark, middle part of sarcomere that extends entire length of thick filaments and includes those parts of thin filaments that overlap thick filaments.
I band
Lighter, less dense area of sarcomere that contains remainder of thin filaments but no thick filaments. A Z disc passes through center of each I band.
H zone
Narrow region in center of each A band that contains thick filaments but no thin filaments.
M line
Region in center of H zone that contains proteins that hold thick filaments together at center of sarcomere.
Thin filament
Actin
Thick filament
Myosin
Contractile muscle proteins
Myosin
Actin
Regulatory
Troponin
Tropomyosin
Structural muscle proteins
Titin
Nebulin
Alpha-actin
Myomesin
Dystrophin
Myosin
Contractile protein that makes up thick filament; molecule consists of a tail and two myosin heads, which bind to myosin-binding sites on actin molecules of thin filament during muscle contraction
Actin
Contractile protein that is the main component of thin filament; each actin molecule has a myosin-binding site where myosin head of thick filament binds during muscle contraction.
Skeletal muscle
Organ made up of fascicles that contain muscle fibers (cells), blood vessels, and nerves; wrapped in epimysium.
Fascicle
Bundle of muscle fibers wrapped in perimysium.
Muscle fiber cell
Long cylindrical cell covered by endomysium and sarcolemma; contains sarcoplasm, myofibrils, many peripherally located nuclei, mitochondria, transverse tubules, sarcoplasmic reticulum, and terminal cisterns. The fiber has a striated appearance.
Myofibril
Threadlike contractile elements within sarcoplasm of muscle fiber that extend entire length of fiber; composed of filaments.
Filaments (myofilaments)
Contractile proteins within myofibrils that are of two types: thick filaments composed of myosin and thin filaments composed of actin, tropomyosin, and troponin; sliding of thin filaments past thick filaments produces muscle shortening.
The Sliding Filament Mechanism
◼ Myosin pulls on actin, causing the thin filament to slide inward
◼ Consequently, Z discs move toward each other, and the sarcomere shortens
The contraction cycle
1) myosin head hydrolyzes ATP and becomes energized and oriented
2) myosin head binds to actin, forming a cross-bridge
3) myosin head pivots, pulling the thin filament past the thick filament toward the centre of the sacromere (power stroke)
4) as myosin head binds ATP, the cross-bridge detaches from actin
The force of a muscle contraction depends on the
length of the sarcomeres in a muscle prior to contraction
Creatine phosphate provides
15 seconds of energy
Anaerobic glycolysis provides
2 minutes of energy
Cellular respiration provides
Several minutes to hours of energy
Creatine phosphate
catalyzes the transfer of a phosphate group from CP to ADP to rapidly yield ATP
Anaerobic Glycolysis
When CP stores are depleted, glucose is converted into pyruvic acid to generate ATP
Cellular Respiration
Under aerobic conditions, pyruvic acid can enter the mitochondria and undergo a series of oxygen-requiring reactions to generate large amounts of ATP
Muscle Fatigue
inability to maintain force of contraction after prolonged activity
The onset of fatigue is due to
❑ Inadequate release of Ca2+ from SR
❑ Depletion of CP, oxygen, and nutrients
❑ Build up of lactic acid and ADP
❑ Insufficient release of ACh at NMJ
Central fatigue occurs due to
changes in the central nervous system and generally results in cessation of exercise
Why do you continue to breathe heavily for a period of time after stopping exercise?
To “pay back” your oxygen debt!
extra oxygen goes toward
❑ Replenishing CP stores
❑ Converting lactate into pyruvate
❑ Reloading O2 onto myoglobin
A motor unit consists of
a somatic motor neuron and the muscle fibers it innervates
Activating only a few motor units will generally result in
a weak muscle contraction
Activating many motor units will generally result in
a strong muscle contraction
Motor unit recruitment is the process in which
the number of active motor units increases
Weakest motor units are recruited
First
Twitch contraction
brief contraction of all muscle fibers in a motor unit in response to a single action potential
Wave summation occurs when a
second action potential triggers muscle contraction before the first contraction has finished
❑ Results in a stronger contraction
Tone is established by
the alternating, involuntary activation of small groups of motor units in a muscle
Isotonic
tension is constant while muscle length changes
❑ Concentric
❑ Eccentric
Isometric
muscle contracts but does not change length
Concentric contraction
Picking up a book
Eccentric contraction
Lowering a book
Between 30–50 years of age, about 10% of our muscle tissue is replaced by
fibrous connective tissue and adipose tissue
Between 50–80 years of age another 40% of
our muscle tissue is replaced
Consequences to aging is muscles is
❑ Muscle strength and flexibility decreases
❑ Reflexes slow
❑ Slow oxidative fiber numbers increase
