LECTURE 7 (Cardiac and Smooth Muscle) Flashcards
Describe the embryonic development of Cardiac Muscle
Mesenchymal cells around the primitive heart tube align into CHAINLIKE ARRAYS -> Cells within one fiber branch and join with cells in adjacent fibers -> Heart consists of cells INTERWOVEN in SPIRALING layers that provide for a characteristic wave of contraction that wrings out of the heart ventricles
Describe the structure of Cardiac Muscle
- Striated
- One nucleus that is centrally located
- ENDOMYSIUM containing rich capillary network surrounds cells
- PERIMYSIUM separates bundles and layers of muscle fibers
Describe the transverse lines that cross the fibers in cardiac muscle
- INTERCALATED DISCS which cross the fibers at irregular intervals where the myocardial cells join
- Transverse & Longitudinal regions
- TRANSVERSE REGIONS = composed of DESMOSOMES and FASCIA ADHERENS JUNCTIONS which provide strong intercellular adhesion during the cells’ constant contractile activity
- LONGITUDINAL REGIONS = filled with GAP JUNCTIONS that act as electrical synapses
What is present in Cardiac and Skeletal muscle cells?
- Mitochondria (40%)
- Fatty acids (stored as triglycerides in small lipid droplets)
- Glycogen granules
- Perinuclear lipofuscin pigment granules
What is the difference between T-tubules in ventricular muscle fibers and atrial muscle fibers?
VENTRICULAR
- well-developed
- large lumens
- penetrate the sarcoplasm in the vicinity of the myofibrils’ Z discs
ATRIAL
- smaller/entirely absent
Sarcoplasmic reticulum is less well-organised in cardiac compared to skeletal muscle fibers (TRUE/FALSE)
TRUE
What differentiates the T-tubules in cardiac cells than in skeletal muscle fibers?
Cardiac cells have DYADS instead of TRIADS
What can Cardiac muscle fiber contraction be described as?
Intrinsic and spontaneous
What is the difference between contraction in cardiac muscle and skeletal muscle?
CARDIAC MUSCLE
- continuous contraction
- initiated, regulated and coordinated locally by nodes of unique myocardial fibers
SKELETAL MUSCLE
- contraction of individual myocardial fibers is all-or-none
- Rate of contraction is modified by autonomic innervation at the nodes of conducting cells (SYMPATHETIC = accelerates, PARASYMPATHETIC = decreases )
What are the properties of secretory granules in cardiac muscle?
- Found near atrial muscle nuclei
- Associated with small Golgi complexes
- Release the peptide hormone ATRIAL NATRIURETIC FACTOR (ANF) which acts on target cells in the kidney to affect Na+ excretion and water balance
[contractile cells of the heart’s atria thus also serve an endocrine function]
Where are the Purkinje fibres/Purkinje cardiomyocytes located?
Sub-endocardium
What is the function of Purkinje Fibres?
Important in the electrical stimulation of the heart -> To allow contraction of the ventricle muscle, these fibres need to stimulate the myocardium in a synchronised manner
What are the properties of Purkinje fibres?
- Larger than cardiac muscle cells
- Fewer myofibrils, lots of glycogen and mitochondria and no T-tubules
- Connected by DESMOSOMES and GAP JUNCTIONS but not INTERCALATED DISCS
- Specialised conducting fibres
Where do Purkinje fibres extend to?
- Interventricular septum
- Papillary muscles
- Up the lateral walls of the ventricles
What is the most common injury sustained by cardiac muscle?
ISCHAEMIA
[tissue damage due to lack of oxygen when coronary arteries are occluded by heart disease]
Lacking muscle ___________ cells, adult mammalian cardiac muscle has little potential to regenerate after injury
Satellite
What causes myocardial ischaemia?
Occurs when blood flow to the heart muscle is obstructed by a partial or complete blockage of a coronary artery by a buildup of plaques (ATHEROSCLEROSIS) -> If plaques rupture, you can have a heart attack (MYOCARDIAL INFARCTION)
Describe the development of atherosclerosis
Too many CHOLESTEROL particles in blood -> Cholesterol may accumulate on ARTERY WALLS -> PLAQUE may form and the deposits may narrow or block your arteries -> Plaque can burst causing a BLOOD CLOT
What is smooth muscle specialised for?
Slow, steady contraction under the influence of autonomic nerves and various hormones
Describe the fibers of smooth muscle
Elongated, tapering and unstriated cells with elongated nuclei which are enclosed by an external lamina and a network of type I and type III collagen fibers comprising the ENDOMYSIUM
Where is the nuclei in smooth muscle cells located?
Centrally at the cell’s widest part
How do the filaments of smooth muscle differ in appearance to other muscle?
Filaments of smooth muscle are arranged differently and appear less organised
Describe Smooth Muscle
- Linked by numerous gap junctions
- Borders of the cell become scalloped and nucleus becomes distorted when smooth muscle contracts
- Concentrated near the nucleus are mitochondria, polyribosomes, RER and vesicles of Golgi apparatus
- Cell surface are small plasmalemma invaginations
Do smooth muscles contain T-tubules?
NO
The T-tubules’ function is unnecessary in these smaller, tapering cells with many gap junctions
