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11.7

Terms in this set (17)

cardiac muscle
found only in the heart and functions to pump blood
-contract with a regular rhythm
-sections much contraction in a coordinated pattern
-contractions must be long enough to expel blood
-under unconscious control
-very fatigue resistant
properties of cardiac muscle
-cardiac myocytes are shorter and thicker than SM
-intercalated disc: contain desmosomes and gap junction which allow muscle AP to quickly spread form one cardiac muscle fiber to another
-sarcoplasmic reticulum: less developed but T-tubules are larger and allow more extracellular calcium to enter the cells
-satellite cells- none exist, damaged cells are replaced by fibrosis
structural differences in cardiac muscle
intercalated discs
microscopic irregular transverse thickening of the sarcolemma connect the ends of the myocardial fibers to each other
- pacemaker cells: cardiac muscle can contract without the need for nervous stimulation (autonomic fibers alter rate), specialized cells can spontaneously depolarize and simulate the muscle (autorhythmic)
- contraction phase: lasts longer (200-250msec); these are no quick twitch contractions
- metabolism: aerobic respiration si used alomst exclusively, rich in myoglobin and glycogen it has very large mitochondria (25%)
- fatigue: highly resistant
functional differences of the cardiac muscle
dense bodies
protein plaques act in place of Z discs
- myocytes are fusiform shaped, only one nucleus, no parallel arrangement of filaments therefore no sarcomeres
- dense bodies
-intermediate filament: cytoplasm contains an extensive cytoskeletal network
- SR: is scanty and no t-tubules
- Ca+ comes mainly from extracellular sources
- Nervous innervation: some has no nervous innervation but if present it is from the autonomic NS like that seen in cardiac muscle
smooth muscle
multiunit smooth muscle
Consists of individual smooth muscle cells, each with its own motor neuron terminals and with few gap junctions between neighboring fibers therefore when stimulated only the fiber stimulated contracts
- found in walls of large arteries, respiratory airways, arrector pili muscle of hair follicles, muscle of the iris and ciliary body of the eye
visceral (single unit) smooth muscle
More common type, found in the walls of arteries, veins, and hollow abdominal organs like stomach, intestines, uterus, urinary bladder, stimulated by autorhythmic fibers like cardiac muscle fibers or by neurotransmitters or hormones, forms two or more layers usually a circular inner layer and an outer longitudinal layer, myocytes here are electrically connected to each other by gap junctions, there fore a large number of cells contract together.
-involuntary
-chemical stimuli can include hormones, CO2, low pH, O2 deficiency, or to mechanical stimulation (stretch)
-some single unit muscle has pacemaker cells that spontaneously depolarize
most is innervated by autonomic fibers that can trigger or modify its contractions
-some autonomic fibers cause contraction where others lead to relaxation
stimulation of smooth muscle
Ca+2, powered by ATP, achieved by sliding thin filaments past thick filaments
contraction is triggered by what and how is it achieved
excitation-contraction coupling
-most Ca+2 comes from outside the cell through calcium channels, some are voltage-gated, some ligand-gated, and some mechanically-gated
-calmodulin activates and enzyme myosin light-chain kinase, which adds a phosphate to regulatory protein on the myosin head which in turn activates the ATPase so it can hydrolyze ATP
-power stroke follows
calmodulin
Ca binding protein associated with thick filaments
-sliding filament mechanism generates tension and then pulls on intermediate filaments which pull on dense bodies attached to the sarcolemma
-as it contracts it rotates in a corkscrew manners, contraction starts more slowly (myosin ATPase) and last much longer (Ca_2 pumps are slow)
-also it can both shorten and stretch to a greater extent
-often exhibits tetanus and is very resistant to fatigue
-most ATP is aerobically but less is needed
-latch-bridge mechanism and smooth muscle tone
contraction of smooth muscle
latch-bridge mechanism
allows it to remain attached to actin for longer periods of time without consuming more ATP
smooth muscle tone
smooth muscle maintains a constant state of partial contraction, important for proper arterial function
stress relaxation response
when stretched smooth muscle contracts then after a minute or so the tension begins to decrease
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