• Producing body movements
• Stabilizing body positions
• Regulating organ volumes
– Bands of smooth muscle called sphincters.
• Movement of substances within the body
– Blood, lymph, urine, air, food and fluids, sperm.
• Producing heat
– Voluntary and involuntary (shivering) contractions of skeletal muscle.

• Electrical Excitability
– Ability of skeletal muscles to respond to stimulus. Skeletal muscle contracts as a result of stimulation by nerves.
• Contractility
– Ability to contract (shorten and generate force).
• Extensibility
– Ability to be stretched without damaging tissue.
• Elasticity
– Ability to return to original shape after being stretched.

• Histology- spindle-shaped, nonstriated fibers with one centrally located nucleus.
• Location- walls of hollow internal structures such as blood vessels, airways to lungs, stomach, intestines, uterus.
• Speed of Contraction- slowest.
• Function- motion.
• Nervous Control- involuntary; autorhythmic.

• Histology- branched, striated fibers, with one or two centrally located nuclei and intercalated discs.
• Location- heart wall.
• Speed of Contraction- moderate.
• Function- pumps blood.
• Nervous Control- involuntary; autorhythmic.

• Histology- long, cylindrical, striated fibers with many peripherally located nuclei.
• Location- attached primarily to bones by tendons.
• Speed of Contraction- fastest.
• Function- motion, posture, heat production.
• Nervous Control- voluntary; no autorhythmicity.

• Fascicle- a bundle of skeletal muscle fibers.

• Origin- stable attachment of muscle to skeleton.
• Insertion- moveable attachment of muscle to skeleton.
• Flexor- decreases joint angle.
• Extensor- increase joint angle.
• Adductor- moves bone closer to midline.
• Abductor- moves bone away from midline.
• Levator- raises a body part.
• Depressor- lowers a body part.

• Fasciaa sheet or broad band of fibrous connective tissue that supports and surrounds organs of the body.
– Superficial fascialoose connective and adipose tissue that separates muscle from skin.
– Deep fasciadense, irregular connective tissue that lines the body wall and limbs, it also holds muscles together.

• 3 Layers of deep fascia
– Epimysium- surrounds the whole muscle.
– Perimysium- surrounds bundles
(fascicles) of 10-100 muscle fibers.
– Endomysium- surrounds individual muscle fibers.
• Muscle Belly- the fleshy portion of the muscle between the tendons.
• Tendon- cord of dense, regular connective tissue that attaches a muscle to the periosteum of a bone.

Bone
Fascicle
Tendon
Deep fascia
Skeletal muscle
Epimysium
Perimysium
Muscle fiber (cell)
Perimysium
Endomysium
Muscle fiber (cell)
Myofibril

• Myofibrils- contractile elements of skeletal muscle.
• Filaments- smaller structures inside the myofibrils.
– Thin (actin) filaments (8 nanometers in diameter).
– Thick (myosin) filaments (16 nanometers in diameter).
Thin filaments
Thick filaments
Myofibril
Myofibril
Terminal cisterns
Sarcoplasmic reticulum

• Thick (myosin) and thin (actin) filaments overlap each other in a pattern that creates striations.
• Sarcomeres
– Contractile units in skeletal and cardiac muscle fibers.
– Extend from one Z disc to another Z disc.

• Motor Neurons make contact with about 150 muscle fibers.
• Motor unita motor neuron, and all of the muscle fibers that it innervates.

• Rigor mortis is a state of muscular rigidity that begins 3-4 hours after death and lasts about 24 hours.
• After death, Ca 2+ ions leak out of the sarcoplasmic reticulum and allow myosin heads to bind to actin.
• Since ATP synthesis has ceased, crossbridges cannot detach from actin until proteolytic enzymes begin to digest the decomposing cells.

– Phosphate breakdown (anaerobic).
– Glycolysis and fermentation (anaerobic).
– Cellular respiration (aerobic).

• Creatine phosphate is 3-6X more plentiful than ATP within muscles.
• Its quick breakdown provides the P for creation of ATP.
• Sustains maximal contraction for 15 sec (used for 100 meter sprint).
• Creatine supplementation
– Gain muscle mass but shut down bodies own synthesis.

• ATP produced from the breakdown of glucose into pyruvic acid during glycolysis.
– If still anaerobic, pyruvic acid is converted to lactic acid.
• Glycolysis can continue anaerobically to provide ATP for 30 to 40 seconds of maximal activity (200 meter race).

• ATP for any activity lasting over 30 seconds.
– If sufficient oxygen is available, pyruvic acid enters the mitochondria to generate ATP, water, and heat.
– Fatty acids and amino acids can also be used by the mitochondria.
• Provides 90% of ATP energy if activity lasts more than
10 minutes.

• Hypertrophyincrease in muscle size.
– The result of forceful muscular activity over a prolonged period of time.
– Results in an increase in the number of myofibrils within a muscle fiber.

decrease in muscle size.
– The result of muscles not being used or only being used in weak contractions.
– Causes muscle fibers to progressively shorten, leaving body parts contracted and in contorted positions.

• Slow-twitch fibers
– Designed for endurance
– Contract slowly
– Strong, sustained contractions
– Red in color (lots of mitochondria, myoglobin, & blood vessels)
– Muscles of abdomen and back (posture)
• Fast-twitch fibers
– Designed for rapid, powerful response
– Contract rapidly
– Short, powerful contractions
– White in color (few mitochondria, myoglobin, & blood vessels)
– Muscles of the arms of legs

• Skeletal muscle starts to be replaced by fibrous connective tissue and fat beginning at age 30.
• Slowing of reflexes, loss of flexibility, and decrease in strength.
• Change in fiber type from fast to slow.

• Muscular dystrophy- a broad term applied to a group of inherited muscular disorders characterized by progressive muscle degeneration and weakening.
• Frequency- 1 in 3,500 males.
• Genetics- males XY, females XX.
• Treatment- none.
Mutation in DMD gene. DMD codes for dystrophin, a protein that protects muscle fibers.

• Spasm- involuntary contraction of a single muscle.
– Cramp- a painful spasm.
– Seizure- multiple spasms of a skeletal muscle.
• Tic- involuntary twitching of muscles normally under voluntary control.
• Tremor- rhythmic, involuntary contraction of opposing muscle groups.
• Fasciculation- involuntary, brief twitch of a motor unit visible under the skin.
• Fibrillation- spontaneous contraction of a single muscle fiber that is not visible under the skin.