Muscular System Chapter 6. Muscle Tissue Functions Producing body movements Stabilizing body positions Regulating organ volumes –Bands of smooth muscle.

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.

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.

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.

Bone

Fascicle

Tendon

Deep fasciaSkeletal muscleEpimysiumPerimysium

Muscle fiber (cell)

Perimysium

Endomysium

Muscle fiber (cell)

Myofibril

MyofibrilMyofibril

Thin filamentsThick filaments

Sarcoplasmic reticulum

Terminal cisterns

• 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).

Muscle Fiber- elongate shaped muscle cell.

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

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 breakdownprovides 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.

• 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

Classification of Muscle Fibers

• 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.

Aging and Muscle Tissue

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.

• 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.

Abnormal Contractions