MSS microstructure and function Flashcards
State the 5 main tissue types
The 5 Tissue Types
Epithelium (sheets of cells)
Connective tissue (support and strength)
Blood
Muscle tissues
Neural tissues (CNS & nerves)
State the definition for and describe muscles
Muscles are defined as contractile tissues
They can be subdivided into many parts:
Striated which includes:
skeletal: rapid contraction, subject to fatigue, voluntary
cardiac: rapid, continual contractions, resists fatigue, involuntary
Non-striated which includes:
smooth: slower contraction, v powerful, energy efficient,
little fatigue, involuntary
Myoepithelium (in glands, iris of eye)
Myofibroblasts (in healing wounds)
Which structures in human skeletal muscle can be seen by eye?
Epimysium: protective outer layer, made of collagen, is a connective tissue
fascicles: small bundles of muscle fibers
perimysium: connective tissue located around fascicles
Describe how fascicles appear under a microscope
Below shows fascicles under a trichrome strain, showing that hay mas clear subdivisions.
LS=longitudinal section and TS= transverse section
Each fascicle has many muscle fibers (these are muscle cells)
Fine connective tissue around each fiber is called endomysium
Each cell is further split into myofibrils, these are contractile threads found in muscle cells
How are multinucleated skeletal muscles formed?
Skeletal muscle fibers are formed by 1000s of
precursor cells in the embryo (myoblasts) fusing juntos.
This is why they have many nuclei
Hay visible striations
What would you see when looking at muscle striations with LIGHT microscopy?
different stripes are visible under a light microscope with a haematoxylin stain:
A band: the section covered by the darkest line
I band: the section between two dark lines (I for invisible)
Z line: the dark section in between the I band
What would you see when looking at muscle striations with transmission electron microscopy?
The striations are much clearer and shows 2 other bands inside the A band: M and H bands
H zone: the overall light stripe seen under a TEM
M line: the dark line seen inside the H zone
it also shows the existence of thin and thick actin and myosin filaments arranged in bundles, called myofibrils
What would you see when looking at a transverse section of a myofibril?
the thin and thick filaments contain molecules
of the proteins actin and myosin
Transverse sections show the myosin is in a
hexagonal array, w mas actin filaments than myosin
Draw a longitudinal section of relaxed muscle
In longitudinal section the actin and myosin filaments line up as shown. A sarcomere is from Z line to Z line. The thick A band is the myosin
Draw a longitudinal section of a muscle contracting
As contraction occurs, the I bands get smaller and the Z lines get closer to the A band. Overlap between thick and thin filaments increase, thin filaments slide over the thick filaments This is the sliding filament model of contraction
How does a skeletal muscle know when to contract?
Action potentials are first received by muscles from nerves through motor end plates
Special intracellular membrane systems called T tubules carry the signal to all parts of this very large cell. This is bc diffusion is not fast enough
They convey stimulus rapidly inside the fibre, and initiate contraction
T tubules are excitable membranes, and ion channels transmit the signal
The T tubules carry this signal to the sarcoplasmic reticulum which then releases Ca2+ ions required for contraction.
Give an example of skeletal muscle pathology
An example is Duchenne Muscle Dystrophy
it results in smaller muscle fibers. Hay mas connective tissue, and death and repair occuring
Give an example of skeletal muscle pathology
An example is Duchenne Muscle Dystrophy
it results in smaller muscle fibers. Hay mas connective tissue, and death and repair occuring
Describe cardiac muscle
Cardiac muscle fibers are much smaller, striated, involuntary (controlled by ANS) and organised into sarcomeres which are joined end to end. The cardiomyocyte cells solo tienen 1 or 2 nuclei in the centre.
Cardiomyocytes have T tubules, sarcoplasmic reticulum and sarcomeres, but also connect to adj cardiomyocytes using intercalated discs.
Intercalated discs prevent cardiomyocytes from pulling apart from one another during contraction.
What does this image show?
This is a thin section of the heart muscle fibers via a light microscope and toluidine blue stain
•single cells are joined in branching patterns by the faint lines called intercalated disks (D)
•many capillaries (C), so the heart has a v rich blood supply
•striations of actin and myosin are visible at higher magnification
Describe what you would see in the transverse section of a cardiac muscle light micrograph
The transverse section shows many other structures. The central nuclei are visible (N).
Hay partial divisions into myofibrils (M), and many capillaries (C)
Describe cardiac muscle fibres under a low power electron microscope and label the image
A low power e- micrograph shows features in much more detail
Hay the same striation as skeletal muscles
Intercalated disks (D) are end to end junctions entre fibers which separate the cells (eg C1, C2, C3). These replace Z lines locally and the actin filaments attach to this.
Hay many large mitochondria visible
Hay diff types of junction in the intercalated disks. What are they?
•fascia adherens (FA) are anchoring sites for actin, and connect to the closest sarcomere.
•desmosomes (D) stop separation during contraction by binding intermediate filaments, joining the cells
juntos. Desmosomes are aka macula adherens
•gap junctions (GJ) allow action potentials to spread entre cardiac cells by permitting the passage of ions
between cells, producing depolarization of the heart muscle
What does this image show?
This shows the diff types of junctions on the intercelated disks.
How does the structure of cardiac muscle relate to its function?
Branching fibres provide extra strength + resistance to splitting from high-Pa blood.
Smaller diameter fibres than skeletal muscle allow rich blood supply and additional connective tissue for strength.
Many mitochondria allow continuous energy supply - resistance to fatigue.
Actin filaments attach to intercalated disks which give v strong attachments between fibres. The disks also allow ionic communication entre fibres.
How is contraction initiated in cardiac muscle?
Hay a “myogenic stimulus”
Action potential starts from pacemaker region in R. atrium.
It carries a wave of contraction across the heart, assisted by ion diffusion thru the gap junctions in the intercalated disks
Larger Purkinje (modified muscle) fibres carry stimulus rapidly to ventricle
Describe smooth muscle
Involuntary (controlled by ANS), unstriated smooth muscles are spindle shaped (wide in the middle, tapered at both ends), w 1 central spindle shaped nucleus. They’re wrapped dentro the endomysium.
Usually found in walls of hollow organs + blood vessels.
Smooth muscle contractions are triggered by hormones, nerve stimulation and local factors, like the stretching of the muscle wall.
Contraction is slower and weaker than in skeletal, but energy-efficient, well adapted to functions in organs. Can have spontaneous contractions (myogenic). Excitable cells - produce a.potentials like skeletal & cardiac muscle