Download Muscles and Muscle Tissue Chapter 9

Chapter 10
The Muscular Tissue
Muscles
and
Muscle Tissue
Types of Muscle Tissue
Skeletal muscle is associated with the
bony skeleton, and consists of large cells
that bear striations and are controlled
voluntarily.
Cardiac muscle occurs only in the heart,
and consists of small cells that are striated and
under involuntary control.
Smooth muscle is found
in the walls of hollow organs,
and consists of small
elongated cells that are not
striated and are under
involuntary control.
Muscle Functions
Muscles produce movement by acting on the bones of the skeleton, pumping
blood, or propelling substances throughout hollow organ systems.
Muscles aid in maintaining posture by adjusting the position of the body with
respect to gravity.
Muscles stabilize joints by exerting tension around the joint.
Muscles generate heat as a function of their cellular metabolic processes.
Functional Characteristics of Muscle Tissue
o Excitability, or irritability, is the ability to receive and respond to a
stimulus.
o Contractility is the ability to contract forcibly when stimulated.
o Extensibility is the ability to be stretched.
o Elasticity is the ability to resume the cells’ original length once stretched.
Gross Anatomy of a
Muscle Organ
Origin, belly and insertion
Made up of thousands of muscle fibers
bundled in connective tissue coverings which
contains many blood vessels and a motor
nerve ending for each muscle fiber
Connective Tissue Wrappings (deep fascia)
Deep fascia surrounds and penetrates muscle
o Epimysium surrounds the muscle organ
Fascia surrounds groups of
o Perimysium surrounds the fascicles
muscles forming compartments
o Endomysium surrounds each muscle fiber
The deep fascia is interconnected to the
subcutaneous fascia and the subserous fascia
The deep fascia connects to bones via tendons &
aponeuroses
Muscles attach:
o Directly – epimysium of the muscle is fused to the
periosteum of a bone
o Indirectly – connective tissue wrappings extend
beyond the muscle as a tendon or aponeurosis
Skeletal
Muscle
Return
Muscle Classification:
Functional Groups
Skeletal muscles work together or in opposition
Muscles only pull (never push)
As muscles shorten, the insertion generally moves toward the origin
Whatever a muscle (or group of muscles) does, another muscle (or group)
“undoes”
Prime movers – provide the major force for producing a specific movement
Antagonists – oppose or reverse a particular movement
Synergists -add force to a movement or reduce undesirable or unnecessary
movement
Fixators – synergists that immobilize a bone or muscle’s origin
Arrangement of
Fascicles
Parallel – fascicles run parallel to the
long axis of the muscle
Fusiform – spindle-shaped muscles
Pennate – short fascicles that attach
obliquely to a central tendon running the
length of the muscle
Convergent – fascicles converge
from a broad origin to a single tendon
insertion
Circular – fascicles are arranged in
concentric rings
Naming Skeletal Muscles
Location of muscle – bone or body region associated with the
muscle
Shape of muscle – e.g., the deltoid muscle (deltoid = triangle)
Relative size – e.g., maximus (largest), minimus (smallest), longus
(long)
Direction of fibers – e.g., rectus (fibers run straight), transversus,
and oblique (fibers run at angles to an imaginary defined axis)
Number of origins – e.g., biceps (two origins) and triceps (three
origins)
Location of attachments – named according to point of origin or
insertion
Action – e.g., flexor or extensor, as in the names of muscles that
flex or extend, respectively
Microscopic Anatomy of a Skeletal
Muscle Fiber
Myofibrils - 80% of the cell
o Surrounded
by sarcoplasmic
(stores
Ca++)
Each
fiber is a long,
cylindrical cellreticulum
with multiple
nuclei
just beneath the
sarcolemma
(plasma
membrane
- supported
by dystrophin)
o contains
transverse
tubules
which surface
at the sarcolemma
o Made up of
myofilaments
Sarcoplasma
- specialties
 actin -thin
o Glycogen
 myosin – thick
o Myoglobin
o mitochondria
Myofibrils - 80% of the cell
o Surrounded by sarcoplasmic reticulum (stores Ca++)
o contains transverse tubules which surface at the sarcolemma
Each fiber is a long, cylindrical cell with multiple nuclei just beneath the
sarcolemma (plasma membrane - supported by dystrophin)
Sarcoplasma - specialties
o Glycogen
o Myoglobin
o mitochondria
o Made up of myofilaments
 actin -thin
 myosin – thick
Sarcomere -smallest
contractile unit
Striations - caused by
arrangement of myosin and actin
o I band - light
o A band - dark
o Z line to Z line (one sarcomere)
Molecular composition of myofilaments
o myosin
 cross bridges (heads contain ATPases)
 elongated tail proteins
o actin -double stranded helix
 Troponin
Tropomyosin
o Titin - function
Review Matching
Contraction of a
Muscle Fiber
Sliding filament model
o Which filament moves?
o In what direction?
8.
CONTRACTION OF A
MUSCLE FIBER
Role of Ca++ in
contraction
o Where is the
binding site for the
cross bridge?
o How is covered up
during relaxation?
o How is it exposed for
contraction?
Excitation Contraction Coupling
o Binding sites exposed (Ca++ present)
o Crossbridges form when myosin heads attach using ATP energy
o Myosin crossbridges bends pulling on actin using energy from ATP
o Crossbridges detach when ATPase hydrolyses new ATP
sacroplasmic__________
reticulum
o Ca++ are pumped back into ___________
CONTRACTION REGULATION
(neuromuscular junction)
1. At the axon ending a nerve impulse causes the release
acetylcholine from the synaptic _________.
vesicles
of ____________
(Acetylcholine is aneurotransmitter
______________)
2. Acetylcholine crosses the
______
synaptic_____
cleft and binds to
___ _________
ACh
receptors of the
_____
motor ___
end ____
plate on the sarcolemma.
Na+ channels and
3. This opens _____
Na+ enter the muscle cell.
____
4. Na+ enters the cell and the
membrane becomes depolarized
__________
action potential
generating an ______
_________
5. The __T - _______
tubules carries the action potential through out the cell causing the
release of ______from
the _________
___________.
Ca++
sarcoplasmic
reticulum
Sliding filament
6. Which then stimulates the _______
_______ action.
Why does the nerve impulse cross the synapse?
o Outside of the cell membrane
the electrical charge is positive
o Inside the cell the membrane
has a negative charge.
o The predominant extracellular
ion is Na+
o The predominant intracellular
ion is K+
-
+
+
- + +- -+
-
-
o The sarcolemma is relatively impermeable to both ions
o All the above facts establish a resting membrane potential
Initially, this is a local electrical event called end plate potential (synapse)
Later, it ignites an action potential that spreads in all directions across the
sarcolemma and down the T-Tubules
Resting Membrane Potential
Excitation-Contraction Coupling
CONTRACTION REGULATION cont.
(neuromuscular junction)
Meanwhile back at the junction............................
The membrane is ___________
repolarized to accept another stimulus (refractory period)
K+ leaves the cell for a quick repolarization.
o____
o Cholinesterase decomposes ACh
____and removes it from _____________
ACh receptor
o Na+-K+ pump returns ions to _______
resting membrane potential conditions
In this process where are the 3 places ATP is necessary?
o 1. To move myosin crossbridges
o 2. To return Ca++ to sacroplasmic reticulum
o 3. For the Na+K+ pump to return muscle membrane to resting
potential.
Review Matching
Motor Unit: Nerve-Muscle
Functional Unit
A motor unit is a motor neuron
and all the muscle fibers it
supplies
The number of muscle fibers
per motor unit can vary from
four to several hundred
Muscle fibers from a motor unit are spread
throughout the muscle; therefore, contraction of
a single motor unit causes weak contraction of
the entire muscle
Muscles that control fine movements
(fingers, eyes) have small motor units
Large weight-bearing muscles
(thighs, hips) have large motor units
Muscle Twitch
A muscle twitch is the response
of a muscle to a single, brief
threshold stimulus
The three phases of a muscle
twitch are:
o Latent period – first few milliseconds after stimulation when excitationcontraction coupling is taking place
o Period of contraction – cross bridges actively form and the muscle
shortens
o Period of relaxation – Ca2+ is reabsorbed into the SR, and muscle
tension goes to zero
Graded Muscle
Responses
Graded muscle responses are:
o Variations in the degree of muscle contraction
o Required for proper control of skeletal movement
Responses are graded by:
o Changing the frequency of stimulation
 More rapidly delivered stimuli result in incomplete tetanus
 If stimuli are given quickly enough, complete tetanus results
o Changing the strength of the stimulus
 Threshold stimulus – the stimulus strength at which the first
observable muscle contraction occurs
 Beyond threshold, muscle contracts more vigorously as stimulus
strength is increased
 Force of contraction is precisely controlled by multiple motor unit
summation
 This phenomenon, called recruitment, brings more and more muscle
fibers into play
Starting length of the muscle - optimal length-tension relationship
The relative size of the muscle – the bulkier the muscle, the greater its
strength
Graded Muscle Responses
Contraction of Skeletal
Muscle (Organ Level)
The two types of muscle contractions
are:
o Isometric contraction –Tension
increases to the muscle’s capacity,
but the muscle neither shortens nor
lengthens
o Maintain posture
o Isotonic contraction – the muscle
changes in length (decreasing the angle
of the joint) and moves the load
Concentric contractions – the muscle shortens and does work
Eccentric contractions – the muscle contracts as it lengthens
as in setting down a load without dropping it
Muscle Tone & Treppe
Muscle tone:
o Is the constant, slightly contracted state of all muscles, which does not
produce active movements
o Keeps the muscles firm, healthy, and ready to respond to stimulus
o Lack of nerve stimulation causes muscles to become flaccid and atrophy.
Spinal reflexes account for muscle tone by:
o Activating one motor unit and then another
o Responding to activation of stretch receptors in muscles and tendons
Treppe: The Staircase Effect -increased contraction in response to
multiple stimuli of the same strength
Contractions increase because:
o There is increasing availability of Ca2+ in the sarcoplasm
o Muscle enzyme systems become more efficient because heat is
increased as muscle contracts
Muscle Metabolism: Energy for
Contraction
ATP is the only source used directly for
contractile activity
As soon as available stores of ATP are
hydrolyzed (4-6 seconds), they are
regenerated by:
o The interaction of ADP with creatine
phosphate (CP), no oxygen required
o Anaerobic glycolysis – lactic acid
formation, no oxygen required
o Aerobic respiration – oxygen required
ATP --->ADP + P1
Heat Production
o Only 40% of the energy released in muscle activity is useful as work
o The remaining 60% is given off as heat
o Dangerous heat levels are prevented by radiation of heat from the skin
and sweating
Muscle Metabolism:
Anaerobic Glycolysis
When muscle contractile activity reaches 70% of maximum:
o Bulging muscles compress blood vessels
o Oxygen delivery is impaired
o Pyruvic acid is converted into lactic acid
The lactic acid:
o Diffuses into the bloodstream
o Is picked up and used as fuel by the liver, kidneys, and heart
o Is converted back into pyruvic acid by the liver (Cori Cycle)
Muscle Fatigue & Oxygen Dept
Muscle fatigue – the muscle is in a state of physiological inability to contract
o Muscle fatigue occurs when:
 ATP production fails to keep pace with ATP use
 There is a relative deficit of ATP, causing contractures
 Lactic acid accumulates in the muscle
 Ionic imbalances are present - Na+-K+ pumps cannot restore ionic
balances quickly enough
 SR is damaged and Ca2+ regulation is disrupted
o Intense exercise produces rapid muscle fatigue (with rapid recovery)
o Low-intensity exercise produces slow-developing fatigue
Oxygen Debt - the extra amount of O2 needed for a muscle to return to a
resting state:
 Oxygen reserves must be replenished
 Lactic acid must be converted to pyruvic acid
Cramp
 Glycogen stores must be replaced
Muscle Fiber Types
Determined by the two following factors:
o Contraction rate depends on speed in which ATPases split ATP
o Anaerobic (Glycolytic) or Aerobic (oxidative)
Slow-twitch Oxidative Fibers
Fast-twitch oxidative fibers
o slow acting myosin ATPases
o Fast acting myosin ATPases
o slow contraction
o Fast contraction
o always oxidative (aerobic)
o moderate resistance to fatigue
o resistant to fatigue
o pink to red in color
o red fibers
Fast-twitch glycolytic fibers
o ATPases fast or slow?
o contraction rate?
o aerobic or anaerobic?
o white fibers (myoglobin?)
o blood supply?
o fatigable?
Smooth Muscle
Composed of spindle-shaped fibers
Lack coarse connective tissue sheaths of skeletal muscle, but have endomysium
Organized into two layers (longitudinal and circular) of closely apposed fibers
Found in walls of hollow organs (except the heart)
When longitudinal layer contracts, the organ dilates & contracts
When the circular layer contracts, the organ elongates
Peristalsis – alternating contractions and relaxations of smooth muscles that mix
and squeeze substances through the lumen of hollow organs
Innervation of Smooth Muscle
Smooth muscle lacks neuromuscular junctions
Innervating nerves have bulbous swellings called varicosities
Varicosities release neurotransmitters into wide synaptic clefts called diffuse
junctions
Whole sheets of smooth muscle exhibit slow, synchronized contraction
They contract in unison, reflecting their electrical coupling with gap junctions
Action potentials are transmitted from cell to cell
Characteristics of Smooth Muscle
Unique characteristics of smooth muscle include:
o Smooth muscle tone
o Slow, prolonged contractile activity
o Low energy requirements
o Response to stretch
Smooth muscle exhibits stress-relaxation response (compliance) in which:
o Smooth muscle responds to stretch briefly, and adapts to its new length
o The new length, however, retains its ability to contract
o This enables organs such as the stomach and bladder to temporarily store
contents
Smooth muscle has good regenerative ability
o This is shown by estrogen’s effect on the uterus
o At puberty, estrogen stimulates the synthesis of more smooth muscle,
causing the uterus to grow to adult size
o During pregnancy, estrogen stimulates uterine growth to accommodate
the increasing size of the growing fetus
Autonomic nervous system and endocrine systems are major controls
o Neurotransmitters and hormones?
Developmental Aspects
Nearly all muscle tissue develops from specialized mesodermal
cells called myoblasts.
Skeletal muscle fibers form through the fusion of several myoblasts,
and are actively contracting by week 7 of fetal development.
Myoblasts of cardiac and smooth muscle do not fuse but form gap
junctions at a very early stage.
Muscular development in infants is mostly reflexive at birth, and
progresses in a head-to-toe and proximal-to-distal direction.
Women have relatively less muscle mass than men due to the
effects of the male sex hormone testosterone, which accounts for
the difference in strength between the sexes.
Muscular dystrophy is one of the few disorders that muscles
experience, and is characterized by atrophy and degeneration of
muscle tissue. Enlargement of muscles is due to fat and connective
tissue deposit.
Muscular dystrophy – group of inherited muscle-destroying
diseases where muscles enlarge due to fat and connective tissue
deposits, but muscle fibers atrophy
Duchenne muscular dystrophy (DMD)
o Inherited, sex-linked disease carried by females and expressed
in males (1/3500)
o Diagnosed between the ages of 2-10
o Victims become clumsy and fall frequently as their muscles fail
o Progresses from the extremities upward, and victims die of
respiratory failure in their 20s
o Caused by a lack of the cytoplasmic protein dystrophin
o There is no cure, but myoblast transfer therapy shows promise
References
Muscle Powerpoints
GetBodySmart
Gateway Community College
Muscle Physiology
Lumen
Muscle Models
Marieb Muscle Exercise