Chapter 10 and 11 Anatomy

Function: 1.Excitation–contraction coupling
2.Length–tension relationships
3.Control of contractions
4.Smooth muscle tone

Structure: –Nonstriated tissue •Different internal organization of actin and myosin

•Longitudinal layer –Fibers parallel to long axis of organ; contraction à dilates lumen and shortens organs •Circular layer –Fibers in circumference of organ; contraction à constricts lumen, elongates organ •Allows peristalsis - Alternating contractions and relaxations of smooth muscle layers that mix and squeeze substances through lumen of hollow organs

–Visceral smooth muscle cells •Not connected to motor neurons •Rhythmic cycles of activity controlled by pacesetter cells
•Visceral smooth muscle –In all hollow organs except heart –Arranged in opposing sheets –Innervated by varicosities •Special nerve endings that release neurotransmitter –Often exhibit spontaneous action potentials –Electrically coupled by gap junctions –Respond to various chemical stimuli

–Multiunit smooth muscle cells •Connected to motor neurons
•Multiunit smooth muscle –Located in large airways, large arteries, arrector pili muscles, and iris of eye –Independent muscle fibers; innervated by autonomic NS; graded contractions occur in response to neural stimuli –Has motor units; responds to hormones

- Smooth muscle is decribed as involuntary because you cannot conscioulsy control this muscle

-the stimulus originates in the sarcoplasm where there are free Ca+ which triggers the contraction

Dense Bodies-transmits contractions from cell to cell

Calcium binds to calmodulin which activates to the myosin light-chain kinase

Plasticity- the ability to contract at many different lengths

Important for Lenght-Tension Relationships. a stretched smooth muscle soon adapts to its new length and retains the ability to contract on demand.

Smooth muscle celss divide and increase in numbers. Causes enlargement of the organ and is usually the intial state of cancer.

Strcuture: –cardiac muscle cells (cardiocytes): •Are small •Have a single nucleus •Have short, wide T tubules –Have no triads •Have SR with no terminal cisternae •Are aerobic (high in myoglobin, mitochondria) –Depend on aerobic respiration for ATP formation •Have intercalated discs

Function:–Automaticity •Contraction without neural stimulation •Controlled by pacemaker cells –Variable contraction tension •Controlled by nervous system –Extended contraction time •Ten times as long as skeletal muscle –Prevention of wave summation and tetanic contractions by cell membranes •Long refractory period

Only Found in the HEART !

–Are specialized contact points between cardiocytes –Join cell membranes of adjacent cardiocytes •Contain gap junctions, desmosomes –Functions of intercalated discs: •Maintain structure of tissue •Enhance molecular and electrical connections •Conduct action potentials
•Intercalated Discs –Coordination of cardiocyteS
•Because intercalated discs link heart cells mechanically, chemically, and electrically, the heart functions like a single, fused mass of cells

The cardiac muscle cells are aerobic therefore they depend on aerobic respirtation for ATP formation.

(high in myoglobin, mitochondria)

•Epimysium: dense irregular connective tissue surrounding entire muscle; may blend with fascia. Seperates the muscle from nearby tissues and organs. •Perimysium: fibrous connective tissue surrounding fascicles (groups of muscle fibers).Contains blood vessels and nerves that serve the muscle fibers within the fasicles.
•Endomysium: fine areolar connective tissue surrounding each muscle fiber. (1) capillary networks that supply blood to the muscle fibers. (2) myosetallite cells, stem cells that take part in the repair of damaged muscle tissue, (3)nerve fibers that control cells.

these muscles parts come together and form either a bundle (tendon) or a broad sheet (aponeuroses) that attach skeletal muscles to bones.

•Each muscle served by one artery, one nerve, and one or more veins –Enter/exit near central part and branch through connective tissue sheaths –Every skeletal muscle fiber supplied by nerve ending that controls its activity •Motor neurons control skeletal muscles •Movement of muscles is voluntary –Huge nutrient and oxygen need; generates large amount of metabolic waste •Carbon dioxide, lactic acid, etc.

Sarcolema: plasma memebrane of the of a muscle fiber. Has a characterisitc transmembrane potential due to the unequal ditribution of postive and negative charges--> sudden change leads to contractions.
Mitochondira: between the muscle fibers. Activity of the mitochondira and glucose breakdown by glycolysis provide enerygy in the form of ATP for short-duration, maximum intensity muscular contractions.
Sacroplasmic Reticulum: forms a tubular network around each indivdual myofibril and contains the terminal cristinae.

Terminal cisterns: expanded chambers in the sarcoplasmic reticulum. Holds many Ca+and stores them for later distribution.
T-tubule: encircles the myofibril, tightly bound to the membranes of the SR.
Triads: combination of a pair of cisternae plus a T-tubule

Locatation: thousansds of myofibrils are packed into muscle fibers.
Structure: consist of bundles of protein filaments called myofilaments. Thin and Thick Filaments
Function: actively shorten and are responsible for skeletal muscle fiber contraction.