Chapter 9: Myology - Anatomy of Muscle Tissue
I. Anatomy of Skeletal Muscle
A. General Features of Cells
1. multinucleate
2. striations caused by intracellular structure
B. Fascia - fibrous connective tissue surrounding muscle
1. superficial - just below the skin
a. fat storage area
b. insulation and protection
c. nerve and vessel passage
2. deep - lines body wall, binds muscles together
3. epimysium - encapsulates a single muscle
4. perimysium - around muscle fiber bundles (fasciculi)
5. endomysium - around each individual muscle fiber
6. tendon - continuation of connective tissue to bone
7. tendon sheath - synovium of a tendon (lubricated)
8. aponeurosis - broad, sheet-like connective tissue
C. Nerve and Blood Supply
1. artery & veins enter alongside the nerve
2. capillaries are within each endomysium
D. Anatomy of a Muscle Fiber (Myofiber)
1. 10-100 um diameter; up to 30 cm long
2. sarcolemma - plasma membrane of muscle cell (fiber)
3. sarcoplasm - cytoplasm of muscle cell
4. sarcoplasmic reticulum - SER with Calcium ions
a. terminal cisterns - sacs around myofibrils
b. T (transverse) tubules - perpendicular
5. myofibrils - girder-like structures in cell
a. thin myofilaments - actin
b. thick myofilaments - myosin
6. sarcomere - a compartment housing myofibrils
a. Z line - termination of a sarcomere
b. A-band - length of thick/thin filament overlap
c. I-band - length of thin filaments ONLY
d. H-zone - length of thick filaments ONLY
e. M-zone - union of the thick filaments
E. Sliding Filament Theory
1. Components of Thin (Actin) Filaments
a. myosin binding site
b. tropomyosin
c. troponin
2. Components of Thick (Myosin) Filaments
a. golf-club like appendages
b. cross-bridges - the head that attaches to actin
i. actin binding site
ii. ATP binding site
3. Contraction through Actin-Myosin "Pulling Motion"
a. cross-bridges pull myosin along actin filaments
b. action is like "oars on a boat" pulling forward
c. ATP responsible for "ratchet" motion
F. Neuromuscular Junction
1. motor neuron - nerve cell that innervates muscle
2. motor end plate - where axon meets muscle cell
3. neuromuscular junction - entire muscle/nerve site
4. synapse - general name axon terminal junction
5. synaptic vesicles - inclusions in the axon terminal
a. neurotransmitter - chemical messenger
i. acetylcholine ACh (for muscular synapse)
6. synaptic cleft - space between axon and cell
7. motor unit - a neuron and all myofibers acted upon
G. Hypertrophy and Atrophy
1. muscular hypertrophy
a. increase in size of myofibers (muscle cells)
b. allows for increased strength
2. muscular atrophy
a. progressive loss of myofibrils
i. disuse atrophy
ii. denervation atrophy (neuron lost)
II. Cardiac Muscle
A. General Features
1. involuntary muscle
2. one, centrally located nucleus
3. mitochondria larger and more numerous
B. Structure of Tissue
1. muscle fibers branch and interconnect
2. intercalated disc - thickening of sarcolemma
3. cells connected by gap junctions
a. allow passage of ions like Calcium
b. makes adjacent cells electrically linked
c. allows for rhythmic, domino-like contraction
III. Smooth Muscle
A. General Features
1. non-striated
2. 5-10 um in diameter; 30-200 um long
3. thick in middle; thinner, tapering off to the end
4. single oval centrally located nucleus
5. actin and myosin fibers not arranged as sarcomere
6. lack of organization (no bands) --> smooth muscle
7. also contain intermediate filaments
B. Difference in Contraction
1. intermediate filaments attach to dense bodies
2. as muscle cell contracts, twists like corkscrew
3. caveolae - like T tubules of skeletal muscle
C. Two Kinds of Smooth Muscle
1. visceral (single unit) muscle
a. small arteries and veins
b. viscera - stomach, intestines, uterus, bladder
c. continuous network with gap junctions
d. action spreads from one cell to another
2. multiunit muscle
a. each fiber (cell) has it own nerve ending
b. no gap junctions
c. large arteries, large airways, arrector pili
IV. General Terms for Muscular System
A. Types of Motion (see in previous lecture on joints)
B. Group Actions of Muscles
1.
agonist - the muscle that contracts to allow the
desired motion to occur (eg. biceps brachii -contracts during arm flexion)
2.
antagonist - the muscle/s that relax in response to the occurence of the desired motion (eq.
triceps brachii - relaxes during arm flexion)
3.
synergist - the muscle/s that work in conjunction with the agonist preventing unwanted
movements and allowing the desired motion to be smooth
4.
fixators - stabilize the origin (generally a moveable bone) of the agonist so that the
desired motion can be more efficient.
C. Characteristics to Identify and Name a Muscle
1.
origin - the site of attachment on the bone/skin that is usually fixed
2.
insertion – the site of attachment on the bone/skin on which the muscle acts
3.
fiber direction - terms used to show orientation
i. rectus - parallel to the midline
ii. transverse - perpendicular to midline
iii. oblique - at an angle to the midline
4.
location - may be named after a bone (frontalis)
5.
number of origins biceps(2), triceps(3), quads(4)
6.
shape - some are named on the geometry of muscle
i.
ii.
iii.
iv.
7.
serratus (saw toothed)
rhomboideus (rhomboid)
trapezius (trapezoid)
deltoid (like greek letter delta - triangular)
size - some are named by length and breadth
i. maximus/minimus - larger/smaller
ii. longus/brevis - longer/shorter
D. Some Muscles Named by Action
1. flexor - decreases angle at a joint
2. extensor - increases angle at a joint
3. abductor - movement away from the midline
4. adductor - movement toward the midline
5. levator - causes upward movement
6. depressor - causes downward movement
7. pronator - turns palm posteriorly
8. supinator - turns palm anteriorly (anatomical pos.)
9. tensor - makes body part more rigid, tight
10. rotator - rotates bone around long axis