• Body movement (Locomotion)
• Maintenance of posture
• Respiration
– Diaphragm and intercostal contractions
• Communication (Verbal and Facial)
• Constriction of organs and vessels
–
Peristalsis of intestinal tract
– Vasoconstriction of b.v. and other structures (pupils)
• Heart beat
• Production of body heat (Thermogenesis)

•
Excitability: capacity of muscle to respond to a stimulus
•
Contractility: ability of a muscle to shorten and generate pulling force
•
Extensibility: muscle can be stretched back to its original length
•
Elasticity: ability of muscle to recoil to original resting length after stretched

• Skeletal
– Attached to bones
– Makes up 40% of body weight
– Responsible for locomotion, facial expressions, posture, respiratory movements, other types of body movement
– Voluntary in action; controlled by somatic motor neurons
•
Smooth
– In the walls of hollow organs, blood vessels, eye, glands, uterus, skin
– Some functions: propel urine, mix food in digestive tract, dilating/constricting pupils, regulating blood flow,
– In some locations, autorhythmic
– Controlled involuntarily by endocrine and autonomic nervous systems
• Cardiac
– Heart: major source of movement of blood
– Autorhythmic
– Controlled involuntarily by endocrine and autonomic nervous systems

• Connective Tissue of a Muscle
– Epimysium . Dense regular c.t. surrounding entire muscle
• Separates muscle from surrounding tissues and organs
• Connected to the deep fascia
– Perimysium . Collagen and elastic fibers surrounding a group of muscle fibers called a fascicle
• Contains b.v and nerves
– Endomysium . Loose connective tissue that surrounds individual muscle fibers
• Also contains b.v., nerves, and satellite cells (embryonic stem cells function in repair of muscle tissue
• Collagen fibers of all 3 layers come together at each end of muscle to form a tendon or aponeurosis.

• Motor neurons
– stimulate muscle fibers to contract
– Neuron axons branch so that each muscle fiber (muscle cell) is innervated
– Form a neuromuscular junction (= myoneural junction)
• Capillary beds surround muscle fibers
– Muscles require large amts of energy
– Extensive vascular network delivers necessary oxygen and nutrients and carries away metabolic waste produced by muscle fibers

Muscle Tissue Types

• Fusiform cells
• One nucleus per cell
• Nonstriated
• Involuntary
• Slow, wave-like contractions

• Cells are not striated
• Fibers smaller than those in skeletal muscle
• Spindle-shaped; single, central nucleus
• More actin than myosin
• No sarcomeres
– Not arranged as symmetrically as in skeletal muscle, thus NO striations.
• Caveolae: indentations in sarcolemma;
– May act like T tubules
• Dense bodies instead of Z disks
– Have noncontractile intermediate filaments

•
Grouped into sheets in walls of hollow organs
•
Longitudinal layer – muscle fibers run parallel to organ’s long axis
•
Circular layer – muscle fibers run around circumference of the organ
•
Both layers participate in peristalsis

• Is innervated by autonomic nervous system (ANS)
• Visceral or unitary smooth muscle
– Only a few muscle fibers innervated in each group
– Impulse spreads through gap junctions
– Who sheet contracts as a unit
– Often autorhythmic
• Multiunit:
– Cells or groups of cells act as independent units
– Arrector pili of skin and iris of eye

Smooth Muscle Cell

Smooth Muscle Contraction: Mechanism

Smooth Muscle Relaxation: Mechanism

(below)

Single-Unit Muscle

Properties of Single-Unit Smooth Muscle
– Gap junctions
– Pacemaker cells with spontaneous depolarizations
– Innervation to few cells
– Tone = level of contraction without stimulation
– Increases/decreases in tension
– Graded Contractions
• No recruitment
• Vary intracellular calcium
– Stretch Reflex
• Relaxation in response to sudden or prolonged stretch

Multi-Unit Muscle

Multi vs . Single-Unit Muscle

Comparisons Among Skeletal, Smooth, and
Cardiac Muscle

• Muscle tissues experience few disorders
– Heart muscle is the exception
– Skeletal muscle – remarkably resistant to infection
– Smooth muscle – problems stem from external irritants