Muscular System Chapter 6

Muscle Tissue Functions 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.

Properties of Muscle Tissue 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.

Smooth Muscle Tissue 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.

Cardiac Muscle Tissue 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.

Anatomy of Cardiac Muscle

Skeletal Muscle Tissue 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. Figure: 06-01 Title: Some major muscles of the body. Caption:

Muscle Terminology 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. Figure: 06-02 Title: Action of the biceps and triceps. Caption: The antagonistic action of the triceps and biceps muscles during flexion and extension, showing origins and insertions of the muscles.

Anatomy of Skeletal Muscles- Fascia

Connective Tissue and Skeletal Muscles Fascia- a sheet or broad band of fibrous connective tissue that supports and surrounds organs of the body. Superficial fascia- loose connective and adipose tissue that separates muscle from skin. Deep fascia- dense, irregular connective tissue that lines the body wall and limbs, it also holds muscles together.

Deep Fascia 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.

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

Muscle Fiber- elongate shaped muscle cell. 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

Filaments and Sarcomeres 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.

Sliding Filament Theory

Skeletal Muscle Fiber Contraction Motor Neurons make contact with about 150 muscle fibers. Motor unit- a motor neuron, and all of the muscle fibers that it innervates.

Neuromuscular Junction (NMJ) or Synapse

Figure: 06-07 Title: A neuromuscular junction. Caption: The connection between a motor neuron and a muscle cell is called a neuromuscular junction.

Rigor Mortis Rigor mortis is a state of muscular rigidity that begins 3-4 hours after death and lasts about 24 hours. After death, Ca2+ 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.

Energy for Muscle Contraction ATP (Adenosine Triphosphate)- energy. Phosphate breakdown (anaerobic). Glycolysis and fermentation (anaerobic). Cellular respiration (aerobic).

Creatine Phosphate 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.

Anaerobic Cellular Respiration 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).

Aerobic Cellular Respiration 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.

Athletics and Muscle Contraction Hypertrophy- increase 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.

Atrophy Atrophy- 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.

Classification of Muscle Fibers 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

Aging and Muscle Tissue 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.

Muscle Disease 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.

Abnormal Contractions 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.