Structure of Skeletal, Cardiac and Smooth Muscle Flashcards
How is the muscle attached to bone?
By tendons
What creates muscle sections?
extensive connective tissue coverings that support nerves and capillaries
What is the name for a bundle of muscle fibre?
A fascicle
What are fascicles wrapped in?
Perimysium
What is epimysium?
dense collagenous sheath that surrounds gross muscle
What is perimysium?
loose collagenous connective tissue that surrounds fascicle
What is endomysium?
connective tissue that separates the muscle fibres
What is a fascicle?
grouping of elongated bundles of muscle fibres (cells)
What structures allow you to recognise skeletal muscle?
Nuclei, striations and clear muscle fibre
What structures allow you to recognise cardiac muscle?
Branching cells, prominent nuclei, striations and intercalated discs
What structures allow you to recognise smooth muscle?
The presence of a ton of muscle cells with nuclei that are seemingly disordered and layered
When considering the histology of skeletal muscle, which structure is barely visible
The endomysium
What may one use to take a histology of skeletal muscle?
Medium Power transverse section Haemotoxylin and Eosin (H&E)
Describe Haemotoxylin and Eosin (H&E) dyes
Eosinis anacidicdye.It stains basic (oracidophilic) structures red or pink.
Haematoxylincan be considered as abasicdye. It stains acidic (orbasophilic) structures a purplish blue
What defining characteristics does a skeletal muscle cell (fibre) have?
- multinucleated
- contains many mitochondria
- has special structures called Transverse tubules (T tubules)
- has repeating structure of sarcomeres and myofibrils
- has specific terms for some of its intracellular structures
- also called voluntary muscle or striated muscle
- attached to bone by tendons
- under voluntary and reflexive control
What specific terms can be used when describing the intracellular structures of the skeletal muscle fibres?
Lotsa sarcos
Sarcolemma = Plasma membrane
Sarcoplasm = Cytoplasm
Sarcoplasmic reticulum = Smooth ER
What can be used to identify a skeletal muscle fibre in longitudinal section histology?
Elongated, unbranched, cylindrical cells with numerous flattened nuclei just beneath thesarcolemma.
Describe the structure of skeletal muscle cells
Made if alternating broad light I bands (isotropic in polarised light) and dark (anisotropic) A bands
Z lines(Zwischenscheiben) bisect the I bands
Nucleus at the periphery of the cell.
Describe the sarcoplasm of the skeletal muscle cells
Sarcoplasm filled with myofibrils My oriented parallel to the long axis of the cell
Sarcoplasm containing rows of mitochondriaMtin a similar orientation
Z bands are the most electron-dense and divide each myofibril into numerous contractile units called sarcomeres
Describe sacromere structure
At junction of theAandIbands (and depending on the state of contraction) are tubular triadseach comprising a central flattened tubule of the tubule systemand a pair of terminal cisternaeof the sarcoplasmic reticulum.
Within the bands there are tubular elements of the sarcoplasmic reticulumconnecting the terminal cisternae.
Similarly, within the I bands, less regular longitudinal tubular profiles of sarcoplasmic reticulum.
Note the distribution of mitochondria, regularly arranged between the sarcomeres within the I bands in immediate association with those parts of the actin and myosin filaments which interact during the process of contraction.
Describe the structure of the sarcoplasmic reticulum
Sarcoplasmic reticulum in the spaces between the myofibrils
Longitudinal system paralleling the myofibrils
there are tubules that lead to the exterior of the fibre membrane
Important for conducting the electrical signal into the centre of the muscle fibre
Describe the structure of cardiac muscle
Cardiac muscle cells have one nuclei, centrally located
Cardiac muscle is striated and uses the sliding filament mechanism to contract
Mechanical connection between adjacent cardiac muscle cells - desmosome (structural)
Electrical connection between adjacent cardiac muscle cells – Gap Junctions (functional)
Describe the histology of cardiac muscle
Cardiac muscle fibres form an interconnecting network
There are intercalated discs
What do the intercalated discs do?
Intercalated Discs provide both mechanical and electrophysiological coupling, allowing the cardiac myocytes to act as a functional syncytium. The cells possess central nuclei and regular cytoplasmic cross-striations
More simply:
Intercalated discs bind the cells, transmit forces of contraction and provide areas of low electrical resistance for the rapid spread of excitation throughout the myocardium.
Describe the histology of cardiac muscle in relation to blood supply
Extensive and intimate capillary network between the myocardial fibres
Vessels in this section are distended with red blood cells
High level of vascularity is a reflection of the high and constant oxygen demand of the myocardium
Describe the physiology of cardiac muscles
Have one nuclei, centrally located
Striated and use the sliding filament mechanism to contract
Branching cells with intercalated discs with desmosomes and gap junctions
Nodal cells stimulate their own action potentials - automaticity or auto-rhythmicity
Absolute refractory period is about 250ms
Why are gap junctions important in cardiac muscle?
gap junctions are critical to the heart’s ability to be electrically coupled
What is the benefit of the cardiac muscle having an absolute refractory period of around 250ms?
prevents tetanic contractions which would interfere with the heart’s ability to pump
Where can intercalated discs be found?
Intercalated discs are specialised transverse junctions between cardiac muscle cells at sites where they meet end to end; they always coincide with the Z lines.
What kind of junction is the intercalated disc?
An interdigitating junction and consists of three types of membrane-to-membrane contact. The predominant type of contact, thefascia adherens, resembles thezonula adherensof epithelial junctional complexes but is more extensive and less regular. The actin filaments at the ends of terminal sarcomeres insert into the fasciae adherentes and thereby transmit contractile forces from cell to cell.Desmosomesoccur less frequently and provide anchorage for intermediate filaments of the cytoskeleton.Gap (nexus) junctions are present mainly in the longitudinal portions of the interdigitations and are sites of low electrical resistance through which excitation passes from cell to cell
What are gap junctions?
Constructed from a hexagonal array of protein subunits – connexins
Act as communicating channels – connexon
Gap junction formed from two connexons stacked end to end
Sites of low electrical resistance between cells
Central pore of 1.4 nm diameter
Small molecules (1 kDa, ions & glucose size) pass through
What do gap junctions do?
Link adjacent myocytes
Provide pathway for direct electrical and chemical communications
How can one measure current through a gap junction?
Can measure current through gap junction using whole-cell patch clamp
Current flows from cell 1 to cell 2 current recorded are mirror images
Describe the structure of smooth muscle
Contains actin and myosin filaments, however not aligned by Z discs so no visible striations
Actin and myosin filaments aligned along long axis of cells
Filaments anchored at dense bodies (α-actinin-rich) scattered throughout sarcoplasm
Contractile arrays anchored to sarcolemma by dense plaques
Smooth muscle cells connected by focal adhesions (adherens junctions)
Describe the histology of smooth muscles
Elongated, spindle-shaped cells with tapered ends which may occasionally be bifurcated.
Shorter than skeletal muscle fibres containing only one nucleus which is elongated and centrally located.
Individual muscle fibres are arranged roughly parallel to one another.
How are the contractile proteins of smooth muscle arranged?
The contractile proteins of smooth muscle are not arranged in myofibrils, as in skeletal and cardiac muscle, and thus visceral muscle cells are not striated.
What may be found between the individual muscle fibres and fascicle in smooth muscle?
A network of supporting collagenous tissue
Describe the physiology of smooth muscle
Small cells, fusiform shape with a single central nucleus
Involuntary, autonomic innervation
Surrounding network of collagen
No striations, myofibril meshwork anchored to dense bodies
Different mechanism of muscle contraction compared to skeletal and cardiac muscle contraction
Cells shorten and broaden on contraction
Surround blood vessels, GI tract, bronchial airways
Provide a summary of skeletal muscle
Large, elongated multinucleated cells, may be up to 1 m in length
Multiple peripherally situated nuclei
Voluntary muscle, innervated by alpha motor neurones
Arranged in fascicles with endomysium, perimysium and epimysium
Cross-striations due to organisation of myofibrils
Sliding filament mechanism of contraction
Provide a summary of smooth muscle
Small cells, fusiform shape Single central nucleus Involuntary, autonomic innervation Surrounding network of collagen No striations, myofibril meshwork anchored to dense bodies Cells shorten and broaden on contraction
Provide a summary of cardiac muscle
Elongated branching cells, joined by intercalated discs
Single central nucleus typical, some cells binucleate
Involuntary muscle, spontaneously contractile, autonomic modulation
Branching interconnected cells, functional syncytium
Cross-striations due to organisation of myofibrils
Sliding filament mechanism of contraction
In skeletal muscle what contractile protein may be found prominently in I bands?
Actin
In skeletal muscle what contractile protein may be found prominently in A bands?
Myosin
Where is calcium stored in skeletal muscle?
Sarcoplasmic reticulum
How does a connexon form?
From 6 connexins
