Histology: Muscular Tissue Flashcards
What is the purpose of muscle tissue?
- allow for movement of the organism
- allow for changes in the sizes and shapes of internal organs
What is muscle tissue characterised by?
aggregates of specialized elongated cells, arranged in parallel array (having the primary role of contraction).
What is the primary purpose of specialized muscle cells?
contraction
What are the major types of muscle?
- skeletal muscle
- cardiac muscle
- smooth muscle
What is the most common type of muscle tissue?
skeletal muscle
What is skeletal muscle attached to?
bones
What is skeletal muscle responsible for?
movements of the organism
Is skeletal muscle voluntary or involuntary?
voluntary
Is smooth muscle voluntary or involuntary?
involuntary
Is cardiac muscle voluntary or involuntary?
involuntary
Where is smooth muscle tissue found?
in internal organs (eg. digestive tract, intestines, urinary bladder, blood vessel walls)
intestines: smooth muscle allows for peristalsis to occur
Where is cardiac muscle tissue found?
the heart
What is cardiac muscle tissue responsible for?
contractions of the heart
What is the largest muscle fiber?
skeletal muscle
What are the special features of skeletal muscles?
1) multinucleated
2) highly striated
What do skeletal muscles contain to maintain their cell sizes?
multiple nuclei
What are muscle fibers?
large, single, multinucleates cells
Where are the nucleuses of skeletal fibers found?
at the cell periphery
How sparsely are the nucleuses of skeletal muscles positioned?
approximately one nucleus every 35 micrometers (along the fiber)
How large can skeletal mucle cells get?
0.5 meters in length
What are the cells in muscle tissues called?
muscle FIBERS
Why are muscle cells called muscle “fibers”?
because of their long length (to describe their looks).
What is a distinctive feature of skeletal muscle?
all cell nucleuses are located on the periphery
Where is the nucleus positioned in a cardiac cell?
in the center
What allows for the quickest distinction between different muscle cells?
the position of the nucleus
Why do skeletal muscle fibers contain multiple nucleuses?
skeletal muscle fibers are formed by the fusion of many mononucleated cells (myoblasts) during development and growth
What cells fuse to create skeletal muscle fibers?
myoblasts
What is the muscle fiber length the same as?
Muscle fibers are the same length as the muscle they compose
What is a myofibril?
the structural and functional subunit of the muscle fiber
What is a myofibril composed of?
myofillaments
What do myofillaments contain?
myosin-containing thick fillaments and actin-containing thin fillaments
What do thick fillaments contain?
myosin
What do thin fillaments contain?
actin
What integrates with what in some particular places?
myosin integrates with actin in some particular places
What is the difference between the dark zone and light zone of a myofillament? What makes up each zone?
dark zone: myosin and actin fillaments
light zone: myosin only
In longitudinal sections, what appearance do muscle fibers have?
stripy
What does the stripy appearance of muscle fibers originate from?
the arrangement of repeating units (sacromeres) in series along the fiber.
What is the repeating unit of a muscle fiber called?
sarcomere
What is the average length of a sarcomere?
2.5 micrometers
How many sarcomeres does a 30cm fiber contain?
120 thousand sacromeres
1 sacromere = 2.5 micrometers
What are sarcomeres?
the smallest contractile units of striated muscles
What does the arrangement of thick and thin fillaments give rise to?
density differences which produce cross strations of the myofibril
What do density differences of the myofibril produce?
cross-striations
What is the name of the band which contains mainly the thin fillaments?
the “I band”
What is the name of the band which contains mainly the thick fillaments?
the “A band”
What is the name of the disk located in between the individual sarcomeres?
the “Z disk”
What represents a series of coupled biochemical and mechanical events between myosin heads and actin molecules? What does it lead to?
the “ACTOMYOSIN CROSS-BRIDGE CYCLE”
- leads to muscle contraction
Are muscle fibers differentiated? Do they undergo mitosis?
muscle fibers are:
- terminally differentiated
- do not undergo mitosis
What are satellite cells?
skeletal muscle stem cells, able to repair damaged muscle fibers
What is the name of the cell which is able to repair damaged muscle fibers?
skeletal muscle stem cells
Where are satellite cells located?
under the basal lamina of muscle fibers
What happens when a skeletal muscle is damaged?
satellite cells are stimulated to divide to generate new myoblasts, which fuse and repair the damaged muscle fiber
What can repair damaged muscle fibers?
new fused myoblasts
What happens to satellite cells when muscle is damaged?
Satellite cells divide by mitosis into new myoblasts which fuse to regenerate the muscle fiber (filling the damage gaps)
What happens if the muscle fiber damage is too large?
no regeneration can occur.
the muscle fiber dies.
the gap created from damaged muscle tissue is filled with connective tissue.
What is a scar?
a connective tissue fillament which fills a damaged muscle
typically dense irregural connective tissue
What type of tissue are scars usually made out of?
dense irregular connective tissue
What happens during muscle growth?
muscle cells grow in size (no new cells are made! number of muscle cells does not increase!)
What direction do muscle fibers go in?
the direction in which the muscle contracts
What muscle is exceptional? Why?
The tongue, because it can contract in various directions.
What are the main features of cardiac tissue?
1) uninucleated
2) striated
What type and arrangement of contractile fillaments does cardiac muscle have?
same as skeletal muscle
Is cardiac muscle striated?
yes
What are cardiac muscle cells called? How do they look?
- cardiac myocytes
- short cylindrical cells
- centrally positioned nucleus
Where is the nucleus positioned in cardiac muscle cells?
in the center
What are cardiac muscle cells connected by? what do they form when connected?
connected by intercalated disks, to form a cardiac muscle fiber
What do intercalated disks represent?
highly specialised cell-to-cell adhesion junctions
How to distinguish cardiac mucle from skeletal muscles?
- cardiac muscle cells are called CELLS not fibers!
- cardiac muscle cells have intercallated disks
- cardiac muscle cells have their nucleus positioned in the center, which skeletal muscle fibers have it on the periphery.
What do cardiac myocytes look like?
cocacola can
What do intercalated disks allow for? What would happen is there were no intercallated disks in cardiac muscle?
- keep cardiac myocytes attathced to each other
- create a strong surface barrier
- (if the cells would detach then the heart wouldn’t be able to pump blood any longer, and the individual would die).
How do the sarcomeres of cardiac muscle compare to the sarcomeres of skeletal muscle?
cardiac muscle sarcomeres are slightly shorter (2.2 micrometers) than skeletal muscle sarcomeres (2.5 micrometers).
How do the cardiomyocytes compare to skeletal muscle fibers? State the length and diameter of cardiomyocytes.
cardiomyocytes are much smaller (80-100 micrometers in length, and about 15 mictometers in diameter).
What do specialised cardiac muscle cells exhibit?
spontaneous rhythmic contractions
What do specialised cardiac conducting muscle cells do?
generate and rapidly transmit action potentials to various parts of the myocardium
What is special about specialised cardiac conducting muscle cells?
myocytes are myogenic, they act like nerves (generate their own impulses).
What is special about cardiac myocytes?
completely involuntary
What is the difference between specialised conducting myocytes, in comparison to normal myocytes?
- different colour (specialised conducting myocytes are pale, soft in colour) (look like adipose tissue)
Explain the regenerative properties of cardiac muscle.
can undergo:
- HYPERTROPHY: grow larger in size
- HYPOTROPHY: grow smaller in size
as a result of changing demands of the heart,
but the cells are:
- TERMINALLY DIFFERRENCIATED
and
- CANNOT DIVIDE
Are cardiac muscle cells differentiated? Can they divide?
- terminally differenciated
- cannot divide
What is the professional word used to explain the growing of the cardiac muscle cells?
hypertrophy
What is the professional word used to explain the decrease in size of the cardiac muscle cells?
hypotrophy
What is a cell in the heart which is similar to the ‘satellite cells’ in muscle tissue?
there is no large number of ‘stem’ cells, therefore the heart has a limited ability to regenerate when damaged.
Why does the heart have a limited ability to differentiate when damaged?
there is no large number fo ‘stem’ cells in the heart
How does heart muscle heal from a heart attack?
forms a scar tissue (fills the space with connective tissue)
What is the primary unit of smooth muscle tissue? How does it look like?
bundles or sheets of small, elongated spindle cells with finely tapered ends.
What are the major features of smooth muscle?
1) uninucleated (nucleus is positioned in the center)
2) not striated
Why are smooth muscle cells not striated?
they do not contain muscle sarcomeres
Is smooth muscle tissue striated?
no
What does smooth muscle tissue contain instead of sarcomeres?
myosin fillaments are surrounded by arrays of actin fillaments (connected to dense bodies) in a less well-organised fashion.
- arranged in x form where the lines are actin and the center of the x’s is the dense body, and between the x lines is the myosin.
What types of contractions are smooth muscles specialized for?
slow, prolongued contractions
What is the contraction of smooth muscle triggered by?
- mechanical impulses (passive stretching)
- electrical impulses (depolarization at nerve endings)
- chemical impulses (hormones acting by a second messenger stimuli).
What is the average time taken for contractions to occur in smooth muscle cells?
10-20 seconds
What does the function of smooth muscle cells depend on?
the organ it is located in
What is the function of vascular smooth muscle?
regenerate the lumenal diameter of the small arteries-arterioles
What does the vascular smooth muscle significantly contribute to?
setting of the level of blood pressure
What is the function of the smooth muscle in the digestive tract?
allow for contractions in a rhythmic peristaltic fashion (rhythmically forcing food through the digestive tract as the result of phasic contraction).
What is another place apart from arteries and the digestive tract in which smooth muscle tissues are found?
the urinary tract (and all other internal organs)
What happens to blood pressure when the smooth muscle tissue contracts?
the lumen of blood vessels decreases, increasing blood pressure.
Which muscle cell type has the greatest capacity of regeneration?
smooth muscle cells
Can smooth muscle increase in number?
yes, smooth muscle cells can divide
What are the cells called which lie along the small blood vessels and divide to generate new smooth muscle cells?
pericytes
What are pericytes?
cells which lie along the small blood vessels, and divide to generate new smooth muscle cells.
What can smooth muscle cells undergo? hyperthrophy? hypotrophy?
hypertrophy (increase in size)
What are the 2 approaches in which smooth muscle types regenerate?
1) neighbouring smooth muscle cells divide, and fill the damaged space
2) through pericytes (small blood vessels)
