Muscle Tissue
I. Structure
A. Connective Tissue makes up the muscle coating.
1. Fascia- covers outside of muscle and forms tendons which connect to bone or
aponeuroses which connect to other muscles.
2. Epimysium- surrounds muscle
3. Perimysium- separates bundles
4. Endomysium- separates fibers
B. Muscle Tissue
1. Muscle fiber- represents one muscle cell
2. Sarcolemma- cell membrane
3. Sarcoplasm- cell cytoplasm containing nuclei, mitochondria, sarcoplasmic
reticulum (muscle E.R.), and transverse tubules.
4. Myofibrils- numerous threadlike fibers which run parallel to one another in the
sarcoplasm.
5. Actin- protein globules which make up I-Band
6. Myosin- club shaped proteins which make up A-Bands
7. Sarcomere- a segment of myofibril between successive Z-Bands.
II. Function
A. Neuromuscular Junction- connection between motor neuron and muscle fiber
1. Motor end plate- specialized muscle fiber membrane rich in mitochondria and
neurotransmitters.
2. Motor unit- neuron and the muscle fiber it controls
B. Contraction of muscle tissue
1. Acetylcholine- neurotransmitter that initiates muscle contraction
2. Myosin molecules form cross bridges with actin fibers in the presence of Ca++
and ATP
3. Muscles impulses- transmitted through transverse tubules, causes uniform
contraction.
4. Cholinesterase- enzyme in the muscle that is responsible for cleaning up
acetylcholine and thus causing relaxation.
III. Muscle Cell Energy
A. Aerobic muscle contractions (with oxygen) resting or moderate activity
1. ATP- adenosine triphosphate provides myosin filaments with energy to create
and flex cross bridges.
2. ADP is transformed into ATP by creatin phosphate a high energy storage
molecule found in the mitochondria
B. Anaerobic muscle contractions (without oxygen) strenuous activity for extended
durations.
1. Glucose to ATP + pyruvic acid (p190) without oxygen will convert to lactic
acid.
2. Lactic acid accumulates in liver and surrounding cells creating an oxygen debt
3. Muscle Fatigue- inability of a muscle to contract
a. extended use limits the blood supply
b. extended use exhausts the supply of acetylcholine
c. extended use creates an accumulation of lactic acid
4. Muscle cramps- spasms of the muscle tissue due to lack of ATP which breaks
the Ca++/ myosin bonds
5. Creatin Phosphate- High energy phosphate molecule used to change ADP-ATP
IV. Muscle Contractions
A. Threshold Stimulus- minimal nerve impulse required to cause muscle contraction
B. All of none response- when a fiber contracts, it contracts completely
C. Myogram- recording of a muscle contraction
1. Twitch- actual contraction
2. Latent period- delay between time stimulus is applied and contraction  period
of contraction  period of relaxation
3. Summation- combination of several individual contractions
-Tetanic contraction- a sustained contraction with no latent period
4. Recruitment- the increased number of fibers controlled by increasing numbers
of motor units required to do a large job.
- Sustained contraction- combined recruitment and summations
5. Muscle tone- certain amount of sustained contraction always present
V. Smooth Muscle- composed of actin and myosin but no striations
A. Multiunit smooth muscle- separate fibers found in iris and walls of blood vessels
B. Visceral smooth muscle- sheets of fibers found in stomach, intestines, urinary bladder
and uterus
- Peristalsis rhythmic contractions in intestines
VI. Cardiac Muscle- actin and myosin with striations and branching fibers
A. Intercalated discs- junctions between cell membranes which transmit contractions
from cell to cell.
VII. Skeletal Muscle Actions
A. Origin- the immovable end of a muscle (head)
B. Insertion- the end fastened to a moveable body part
C. Prime Mover- muscle doing majority of the work
-Synergists- muscles that assist
-Antagonists- muscles that cause movement in an opposing direction