Chapter 10: Muscular Tissue Flashcards
THREE TYPES OF MUSCULAR TISSUE
Skeletal muscle
Cardiac muscle
Smooth muscle
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
Narrow, plate-shaped regions of dense
material that separate sarcomere from the next
Z DISCS
Dark, middle part of sarcomere that extends
entire length of thick filaments and includes those parts
of thin filaments that overlap thick filaments
A 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 __
band
I BAND
Narrow region in center of each A band that
contains thick filaments but no thin filaments
H ZONE
Region in center of H zone that contains
proteins that hold thick filaments together at center of
sarcomere
M LINE
Proteins that generates force during muscle
contractions
SKELETAL MUSCLE FIBER PROTEINS
CONTRACTILE PROTEINS
CP that makes up thick filament;
molecule consists of a tail and two myosin heads,
which binds to myosin binding sites on actin
molecules of thin filament during muscle
contraction.
MYOSIN
CP that makes up thin filament; each
actin molecule has a myosin-binding site
where myosin head of thick filament binds
during muscle contraction
ACTIN
Proteins that help switch muscle contraction
process on and off
REGULATORY PROTEINS
Regulatory protein that is a
component of thin filament; when skeletal fiber
muscle is relaxed, Tropomyosin covers
myosin-binding sites on actin molecules,
thereby preventing myosin from binding to
actin.
TROPOMYOSIN
Regulatory protein that is a
component of thin filament; When calcium
ions (Ca2+) bind to troponin, it changes
shape; this conformational change moves
tropomyosin away from myosin-binding sites
on actin molecules, and muscle contraction
subsequently begins as myosin binds to
actin.
TROPONIN
Proteins that keep thick and thin filaments of
myofibrils in proper alignment, give myofibrils
elasticity and extensibility, and link myofibrils to
sarcolemma and extracellular matrix
STRUCTURAL PROTEINS
– Structural protein that connects Z disc
to M line of sarcomere, thereby helping to
stabilize thick filament position; can stretch and
then spring back unharmed, and thus accounts
for much of the elasticity and extensibility of
myofibrils
TITIN –
Structural protein of Z discs that
attaches to actin molecules of thin filaments
and to titin molecules
a-ACTININ
– Structural protein that forms M
line of sarcomere; binds to titin molecules an d
connects adjacent thick filaments to one
another
MYOMESIN
Structural protein that wraps
around entire length of each thin filament;
helps anchor thin filaments into Z discs and
regulate length of thin filaments during
development
NEBULIN
Structural protein that links
thin filaments of sarcomere to integral
membrane proteins in sarcolemma, which are
attached in turn to proteins in connective tissue
matrix that surrounds muscle fibers; thought to
help reinforce sarcolemma and helps transmit
tension generated by sarcomeres to tendons.
DYSTROPHIN
Organ made up of fascicles that contain muscle
fibers (cells), blood vessels, and nerves, wrapped
in epimysium
SKELETAL MUSCLE
Bundle of muscle fibers wrapped in Perimysium
FASCICLE
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.
MUSCLE FIBER (CELL)
Threadlike contractile elements within
sarcoplasm of muscle fiber that extend entire
length of fiber; composed of filaments
MYOFIBRIL
Contractile proteins with myofibrils that are of two
types: thick filaments composed of myosin and
thin filamnets composed of actin, tropomyosin,
and troponin; sliding of thin filaments past thick
filaments produces muscle shortening
FILAMENTS (MYOFILAMENTS)
Myosin pulls on actin, causing the thin filament to
slide inward
Consequently, Z discs move toward each other and
the sarcomere shortens
Thanks to the structural proteins, there is a
transmission of force throughout the entire muscle,
resulting in whole muscle contraction
The Sliding Filament Mechanism
This concept connects the events of a muscle
action potential with the sliding filament mechanism
EXCITATION-CONTRACTION COUPLING
The force of a muscle contraction depends on the
length of the sarcomeres in a muscle prior to
contraction
LENGTH-TENSION RELATIONSHIP
The events at the NMJ produce a muscle action
potential:
Voltage-gated calcium channels in a neuron’s
synaptic end bulb open, resulting in an influx
of calcium. This causes exocytosis of a
neurotransmitter (NT) into the synaptic cleft
NT binds to ligand-gated Na+ channels on the
motor endplate, which causes an influx of
Na+ into the muscle
This depolarizes the muscle and results in
Ca2+ release from the sarcoplasmic
reticulum
NT gets broken down by acetylcholinesterase
THE NEUROMUSCULAR JUNCTION (NMJ)
Creatine kinase catalyzes the transfer of a
phosphate group from CP to ADP to rapidly
yield ATP
CREATINE PHOSPHATE
When CP stores are depleted, glucose is
converted into pyruvic acid to generate ATP
ANAEROBIC GLYCOLYSIS
Under aerobic conditions, pyruvic acid can
enter the mitochondria and undergo a series
of oxygen-requiring reactions to generate
large amounts of ATP
CELLULAR RESPIRATION
is the inability to maintain force of
contraction after prolonged activity
MUSCLE FATIGUE
The onset of fatigue is due to:
Inadequate release of Ca2+ from SR
Depletion of CP, oxygen, and nutrients
Buildup of lactic acid and ADP
Insufficient release of ACh at NMJ
occurs due to changes in the central
nervous system and generally results in cessation
of exercise
CENTRAL FATIGUE
Why do you continue to breathe heavily for a period of
time after stopping exercise?
To “pay back” your oxygen debt!
The extra oxygen goes toward:
Replenishing CP stores
Converting lactate into pyruvate
Reloading O2 onto myoglobin
OXYGEN CONSUMPTION AFTER EXERCISE
The strength of a muscle contraction depends on how
many motor units are activated
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
CONTROL OF MUSCLE TENSION
is the process in which the
number of active motor units increases
Weakest motor units are recruited first, followed
by stronger motor units
Motor units contract alternately to sustain
contractions for longer periods of time
MOTOR UNIT RECRUITMENT
The brief contraction of all muscle fibers in a motor
unit in response to a single action potential
Latent period
Contraction period
Relaxation period
Refractory period
TWITCH CONTRACTION
Wave summation occurs when a second action
potential triggers muscle contraction before the
first contraction has finished
Results in a stronger contraction
Unfused tetanus
Fused tetanus
FREQUENCY OF STIMULATION
Even when at rest, a skeletal muscle exhibits a small
amount of tension, called tone
Tone is established by the alternating, involuntary
activation of small groups of motor units in a
muscle
MUSCLE TONE
tension is constant while muscle length
change
Isotonic
- is great enough to overcome the
resistance of the object to be moved, the
muscle shortens and pulls on another
structure, such as a tendon, to produce
movement and to reduce the angle at a joint.
Concentric
- When the length of a muscle
increases during a contraction
Eccentric
– muscle contracts but does not change
length
Isometric –
has the same arrangement as
skeletal muscle, but also has intercalated discs
Cardiac muscle
Intercalated discs contain desmosomes and gap
junctions that allow muscle action potentials to
spread from one muscle fiber to another
Cardiac muscle cells have more mitochondria
and their contractions last 10 to 15 times longer
than skeletal muscle contraction
CARDIAC MUSCLE
Smooth muscle looks quite different than
cardiac and skeletal muscle. It is thick in the
middle, tapered on the ends, and is not striated
It can be arranged as either single-unit or multiunit fibers
Smooth muscle contractions start more slowly
and last longer than skeletal and cardiac muscle
contractions
Smooth muscle can shorten and stretch to a
greater extent than skeletal and cardiac muscle
Smooth muscle fibers shorten in response to
stretch!
SMOOTH MUSCLE
Mature skeletal muscle fibers cannot undergo mitosis
REGENERATION OF MUSCLE TISSUE
Enlargement of existing cells
Hypertrophy
An increase in the number of fibers
Hyperplasia
Stem cells found in association with blood
capillaries and small veins.
Smooth muscle and pericytes
Most muscles are derived from ______ which
develops into somites
mesoderm
Which, as the name suggests, forms the
skeletal muscles of the head, neck, and
limbs;
Myotome
Which forms the connective tissues,
including the dermis of the skin;
Dermatome
Which gives rise to the vertebrae
Sclerotome
Between 30–50 years of age, about __% of our muscle
tissue is replaced by fibrous connective tissue and
adipose tissue. Between 50–80 years of age another
__% of our muscle tissue is replaced. Consequences
are:
Muscle strength and flexibility decreases
Reflexes slow
Slow oxidative fiber numbers increase
10%, 40%
