Microstructure and function of human muscle systems Flashcards
What are the five tissue types?
-Epithelium(sheets of cells)
-Connective tissue(Support and strength)
-Blood
-Muscle tissues
-Neural tissues(CNS and nerves)
What are the different classes of muscles?
- Striated(Striped)
a. Skeletal
b. Cardiac - Non-striated
a. Smooth muscle - Myoepithelium
a. Contraction of glands, iris of eye - Myofibroblasts
a. In healing wounds
What do skeletal muscles operate and link?
-Operates the skeleton
-Links bones and tendons
Where are smooth muscle found?
-Generally internal organs like the gut, lungs, blood vessels(which control blood pressure), uterus and bladder
What is the function of skeletal muscle and what type of control is it?
-Rapid contraction to escape danger but subject to fatigue
-Voluntary control
What is the function of cardiac muscle and what type of control is it?
-Quite rapid
-Resists fatigue
-Can contract regularly for 90+ years
-Involuntary control
What is the function of smooth muscle and what type of control is it?
-Slower contraction but very powerful
-Energy efficient
-Susceptible to very little fatigue
-Able to stretch more than skeletal and cardiac muscles
-Usually the control is involuntary
What is the structure of skeletal muscle?
- Epimysium
- Fascicles
- Perimysium
What are fascicles?
Little bundles
What is muscle surrounded by, how is it seen and what is its diameter
-Surrounded by epimysium
-Seen by eye
-Diameter of 1-20cm
What is the fascicle surrounded by, how is it seen and what is its diameter?
-Surrounded by perimysium
-Seen by eye
-1-5 mm
What is a muscle fibre(a cell) surrounded by, what is it seen by and what is its diameter?
-Surrounded by Endomysium and plasma membrane
-Seen by light microscope
-30-100 micrometers
what are myofibrils(in a cell) seen by and what is its diameter?
-Seen by light microscope and transmission electron microscopy
-1-2 micrometers
What does skeletal muscle look like under high magnification with H&E stain?
-Very long(up to 4cm)
-Giant thread-like cells with thousands of nuclei:
-Multinucleate or syncytial cells
How are skeletal muscle fibres formed?
-Skeletal muscle fibres are formed by thousands of precursor cells in the embryo(myoblasts) fusing together
What proteins are the core of the contractile apparatus?
Made of many molecules of the proteins myosin and actin
Why is meat(muscle) rich in protein?
Meat(muscle) is rich in protein because it is largely made of actin and myosin protein filaments
What are the steps in the contractile mechanism?
-In longitudinal section the actin and myosin filaments line up like this. This diagram represents a relaxed muscle
-Sliding of actin past myosin generates muscle contraction
-Therefore the I bands get narrower and A does not
-Z line contains alpha actinin, a protein to which actin attaches
What is a sacromere
The contractile unit, from one z line to the next
What are the steps in neural stimulation of skeletal muscles via motor end-plates?
-Action potential spreads over the fibre’s plasma membrane
-Then special intracellular membrane systems carry the signal to all parts of this cell
-Diffusion is not fast enough
-Membrane systems:
-T-(transverse) tubules convey stimulus from plasma membrane rapidly inside fibre. Then they pass it to sarcoplasmic reticulum which is a specialised form of endoplasmic reticulum
What is the structure of cardiac muscles?
-Have much smaller fibres, joined end to end by specialised junctions, intercalated disks
-Have striations as found in skeletal muscle
-Intercalated disk, the strong end to end junctions between fibres
-Actin filaments are attached to the disks
What happens to skeletal muscle suffering from duchenne muscular dystrophy under microscope with H&E stain?
Smaller fibres, more connective tissue between.
Damage, death and repair of fibres
occurring.
What is the Fascia adherens in cardiac muscle fibres and whats it for? What is attached to it?
-Special sheet-like intermediate junction between fibres, for strong adhesion
-Actin attached
What is the function of gap junctions in cardiac muscle fibres?
-Ionic communication, to coordinate contraction wave
What are desmosomes for in cardiac muscle fibres?
Desmosome for adhesion
What do branching fibres provide in cardiac muscles?
Branching fibres provide extra strength, curvature and resistance to splitting(by high pressure blood)
What does a small diameter of fibres in cardiac muscles allow?
-Smaller diameter fibres(than skeletal muscles) allow rich blood supply and additional connective tissue, for strength
What does numerous mitochondria in cardiac muscle allow?
-Numerous mitochondria allow respiration, continuous energy supply, resistance to fatigue
What do intercalated disks give in cardiac muscles?
-Intercalated disks give very strong attachments and ionic communication between fibres
How does contraction in cardiac muscle occur?
-Myogenic stimulus(Muscle generated)
-Action potential starts from pacemaker region in right atrium and carries a wave of contraction across heart, assisted by ion diffusion through gap junctions in the intercalated disks
-Purkinje fibres(Larger, modified cardiac muscle fibres)
-Carry stimulus rapidly to ventricles
Is smooth muscle striated?
Smooth muscle is not striated
Are smooth muscles voluntarily controlled?
-Also called ‘involuntary’ muscle, as not normally under conscious control
What is the structure of smooth muscles?
-No myofibrils
-No striation
-No complex membrane systems
-Spindle shaped fibre
-Junctions between fibres
-Near the membrane is a basic form of sarcoplasmic reticulum
What is the function of dense bodies in smooth muscles?
anchors for contraction
-Dense bodies are found in smooth muscle and function like Z lines
What are qualities of smooth muscle?
tissue stronger, more elastic, more energy-efficient. Well adapted to constant activity in organs
What do dense bodies in smooth muscles contain and and what do they function as?
-Contain alpha actinin and actin attaches to them
