Muscle
I. Muscle (Musculus - Little mouse)
35 - 45 % of body weight
A. Fundamentally connective tissue that has
gained the ability to contract
B. Muscle cell is specialized to contract
C. Terminology - Sarco = flesh
1. Sarcolemma - plasma lemma
2. Sarcoplasm - cytoplasm
3. Sarcoplasmic reticulum - endoplasmic reticulum
D. Myo = of muscle/mouse
1. Myofibrils
2. Myofilaments (actin and
3. myosin)
4. Myoglobin - pigment
5. Tropomyosin - protein
II. Types
A. Smooth
1. Involuntary muscle - under control of ANS
(s/w/conscious control)
2. Long sections with no striations
3. Bound together by connective tissue fiber
4. Does not function automatically (no pacemaker
activity)
5. May be able to conduct impulses
6. Located around hollow organs and tubes
a. Respiratory
b. Reproductive
c. Urinary
d. Gastrointestinal tract
e. Blood vessels
f. Arrector pili
7. Function
a. Blood vessels - smooth muscle always in slight
state of contraction know as muscle tone, tonus.
Spasm is involuntary sudden contraction of smooth
muscle, constriction of cerebral cortex vessels
causes fainting/loss of consciousness.
Constriction of coronary vessels causes heart pain
"angina pectoris".
b. Respiratory system - asthmatic attacks,
constriction of smooth muscles of bronchial tree.
c. Uterus - largest and strongest smooth muscle in
the female body.
d. Digestive system - two layers, inner circular
and outer longitudinal
e. Iris - great endurance
B. Cardiac
- heart muscle
1. Special combination of features of speed of
skeletal and strength of smooth.
2. Contracts involuntarily - pacemaker potential
3. Branched - single nucleus per cell
4. Connected end to end at the intercalated disc
C. Skeletal
- voluntary or striated
1. Functions
a. Movement of skeleton
a. Stabilize joints
b. Maintenance of posture
c. Support soft tissue
d. Regulate entering and exiting of materials - orifaces
e. Production of body heat
2. Over seven hundred "named", average 107 fibers
3. Muscle fibers
a. 1 mm to 50 cm in length
b. Sarcoplasm for nutrition and conduction of excitation
c. Fibers red and white due to pigment myoglobin
- analogous to hemoglobin for oxygen transport.
Red fibers contract more slowly than white fibers
(light and dark meat).
III. Micro Anatomy - Micreoscopic structure
Sarcolemma – cell wall
Sacroplasm – inside
Microscopic Anatomy of Skeletal Muscle
Cells are multinucleate
Nuclei are just beneath the sarcolemma
Sarcolemma – specialized plasma
Light Bands (striations) = I Band – not thick filament
(thin filament but not – not thick filament (thin
filament but not all of the thin filament)
Dark Bands (striations) = A Band – thick filament
Myofibril – complex organelle
Bundles of myofilaments
Myofibrils are aligned to give distinct bands
Z Discs between I Bands
H Zone is in the A Band – space between the
filaments (no active filaments)
Sarcomere is from one set of Z Discs to the
next set of Z Discs. Is a functional unit.
M Line – middle of the A Band/sarcomere
Thin filaments connect to Z Line but not to each other
Organization of the sarcomere:
Thick filaments = Myosin filaments
Composed of the protein "myosin"
Has ATPase enzymes
Thin filaments = Actin filaments
Composed of protein "actinin"
Sarcomere Myofibril Muscle fibers
Muscle fascicle Skeletal muscle
Myosin filaments have heads (these are extensions
or cross bridges)
Myosin and Actin overlap somewhat
At rest, there is a bare zone that lacks actin filaments
Sarcoplasmic reticulum (SR) is for storage of calcium
T Tubes = transverse tubule – travels around the SR
Nerve stimulation to muscles
Skeletal Muscle must be stimulated by a nerve to contract
IV. Operation - sliding filament hypothesis
Basic tenant of the Scientific Method - you can
not prove anything - check out links on web site.
A. Sarcomere - functional unit
B. Bands
1. Isotropic (I) - light: "M" line
2. Anisotropic (A) - dark: "Z" line
C. Filaments
1. Thick - myosin with head, neck, and tail
2. Thin - actin with troponin and tropomyosin
D. Triads of sarcoplasmic reticulum
E. Cross bridge cycling
V. Control
A. Neuron - action potential
B. Neuromuscular junction - acetylcholine at motor
end plate
C. Sarcoplasmic reticulum
1. "T" - tubes
2. Lateral sacs
D. Calcium release
E. Regulatory complex
1. Troponin binding
2. Tropomyosin movement
F. Exposure of actin enzymatic sites
G. Cross bridge cycling
H. ATP energy source
Neuromuscular junctions – association site of
nerve and muscle
Nerve stimulus to muscles
Synaptic cleft-gap between nerve and muscle
Nerve and muscle do not make contact
Area between is filled with interstial fluid
Neurotransmitter – chemical released by nerve
upon arrival of nerve impulse
The neurotransmitter for skeletal muscle is
acetylcholine
Neurotransmitter attaches to receptors on
the sarcolemma
Sarcolemma becomes permeable to sodium (Na+)
Transmission of Nerve Impulse
1. ACh released binding to receptors
2. Action potential reaches T Tubule
3. Sarcoplasmic reticulum releases Ca2+
4. Actve site exposure cross bridging binding
5. Contraction begins
6. ACh removed by AChE
7. SR recaptures Ca2+
8. Active site covered – no cross bridge interaction
9. Contraction ends
10. Relaxation occurs
Sodium rushing into the cell generates an action potential.
Once started, can't stop.
VI. Muscle contraction
A. Motor units
1. Nerve/axon and all synapsed (controlled) muscle cells
2. Contract as a unit
3. Multiple motor units per muscle
B. Graded responses - Contraction of a Skeletal Muscle
– different degrees of skeletal muscle shortening
1. "All-or-none" law
2. Applies to single cell, not all cells - Within a
skeletal muscle, not all fibers may be stimulated
during the same interval
3. Change response by
a. Frequency of stimulation
b. Number of stimulated cells
Different combos of muscle fiber contractions may
give different responses
C. Muscle twitch - Types of Graded Responses
1. Single event - twitch
Single brief contraction
Not a normal muscle function
Single motor unit contraction
2. Few events - Tetanus – summing of contractions
One contractions is immediately followed by another.
Muscle does not completely relax
Effects are added
3. Many events - unfused/incomplete tetanus
Some relaxation occurs between contractions
Results are summed
4. Rapid events -fused/complete tetanus
Muscle force depends upon the number of fibers stimulated.
More fibers contracting results in greater muscle tension.
Muscles can continue to contract unless they run out of energy
D. Work
1. Isotonic - contraction and movement
2. Isometric - contraction without movement
E. Exercise
1. Aerobic endurance with resistance to fatigue
2. Resistance isometric with increase in muscle mass
F. Energy sources
1. Direct phosphorylation of ADP by creatine
phosphate (20 seconds)
2. Aerobic respiration oxidative phosphorylation:
slow, requires oxygen
3. Anaerobic glycolysis and lactic acid formation
(30 - 60 seconds)
4. Fatigue - oxygen debt and decreased pH (Lactic
acid production)
Energy for Muscle contraction: Initially, muscles
used stored ATP for energy. Bonds of ATP are broken
to release energy. Only 4-6 seconds' worth of ATP is
stored by muscles. After initial time, other pathways
must be utilized to produce ATP.
Direct phosphorylation: Muscle cells contain
creatine, phosphate (CP). CP is a high energy
molecule. After ATP is depleted, ADP is left.
CP transfers energy to ADP.
Aerobic Respiration: Series of metabolic
pathways that occur in the mitochondria. Glucose
is broken down to carbon dioxide and water releasing
energy.
Anaerobic glycolysis: Reaction that breaks
down glucose without oxygen. Glucose is broken
down to pyruvic acid to produce ATP. Pyruvate
is converted. When a muscle is tired, it's
unable to contract.
G. Coverings and coats
1. Sarcolemma
2. Endomysium - CT
3. Perimysium - CT around several fibers
4. Epimysium - CT wrap of muscle
VII. Attachment
A. Directly to periosteum
B. Tendons - cords of dense regular CT
C. Aponeurosis - flat sheet of connective tissue
in, e.g., the lower back
VIII. Types of muscle
A. Prime mover - responsible for principal action
B. Antagonist - oppose prime mover
C. Synergist - help prime mover directly or indirectly
D. Fixators -synergists which immobilize origin
IX. Nomenclature
A. Actions
1. Flexors - bending a joint
2. Extensors - extending a joint
3. Abductors - away from the midline
4. Adductors - towards the midline
5. Rotators - rotation
6. Supinator - bring palm of hand upwards
7. Pronator - turn palm downwards
8. Levator - raise parts of body
9. Depressors - lower parts of the body
B. Shapes
1. Deltoid
2. Quadratus
C. Origin and insertion - insertion moves towards origin
1. Origin
a. Position - closer to midline
b. Action - less movable bone
2. Sternocleidomastoidea
D. Number of divisions
1. Quadraceps
2. Triceps
3. Biceps
E. Location
1. Tibialis
2. Radialis
F. Direction of fibers
1. External oblique
2. Internal oblique
3. Transverse
G. Relative size
1. Maximus - largest
2. Minimus - smallest
3. Longus - long
X. Knowledge
A. Know bones involved in actions
B. Know what joints crossed by muscle
C. Know names and shapes of the largest muscles
D. Know action of the muscle.