BL 13 Flashcards
What do the following words mean?
- Myalgia
- Myathenia
- Myocardium
- Myopathy
- Myoclonus
Myalgia: Muscle pain
Myasthenia: Weakness of the muscles
Myocardium: Muscular component of the heart
Myopathy: Any disease of the muscles
Myoclonus: A sudden spasm of the muscles
Describe the muscle hierachy (i.e. how muscles are split up)
Striated muscle:
Cardiac and Skeletal
Non-striated muscle:
Smooth
(plus extra detail in pic)
Myoglobin (definition, which type of muscles is is in, number of oxygens, relationship with heamoglobin, what happens when ___ muscle dies, what issue can this cause?)
Definition: red protein containing haem, which carries and stores oxygen in muscle cells. It is structurally similar to a subunit of haemoglobin.
Which type of muscles: STRIATED MUSCLES
1 oxygen
Haemoglobin gives up oxygen to myoglobin, especially at low pH. This occurs because myoglobin has a higher affinity for oxygen than heaomoglobin, so heamoglobin always gives up it’s oxygen to myoglobin - especially if the pH is low.
Muscle necrosis and kidneys:
When striated muscle dies (muscle necrosis), myoglobin is released into the bloodstream (myoglobinaemia) and into the urine (myoglobinuria). This can cause kidney damage and can be fatal. Kidney’s remove the myoglobin from the blood and into the urine.
Muscle terminlogy - Meaning of: sacrolemma, sacroplasm, sarcosome, sarcomere, sarcoplasmic reticulum (sarcoplasmic endoplasmic reticulum)
Sarcolemma: The outer membrane of a muscle cell Sarcoplasm: The cytoplasm of a muscle cell Sarcosome: The mitochondrion
Sarcomere: The contraction unit in striated muscle Sarcoplasmic reticulum: The smooth endoplasmic reticulum of a muscle cell
Draw out a sacromere
Name and explain the 3 key connective tissue components of a muscle
Endomysium: layer of areolar connective tissue that ensheaths each individual muscle fibers (aerolar connective tissue)
Perimysium: Perimysium is a sheath of connective tissue that groups muscle fibers into bundles/fasicles (aerolar connective tissue)
Epimysium: Epimysium is a layer of connective tissue, which ensheaths the entire muscle. It is composed of dense irregular connective tissue. Joins the muscle to the tendon (the tendon joins the muscle to the bone).
Draw a muscule: label 1 muscle fibre/cell, fasciles, 3 connective tissues, joining with the bone
Define fasicle
A group of muscle of fibers surrounded by the perimysium.
All fasicles come together to make up the muscle, this muscle has it’s own connective tissue surrounding it called the epimysium.
What is the point of origin and the point of insertion?
- Origin: the attachment site that doesnt move during the contraction (usually proximal to the body compared to the insertion). Tension is created at the origin.
- Insertion: the attachment site that does move when the muscle contracts. Movement is created at the insertion.
In which direction to muscles move?
- Movement alway occurs along the direction of a fibre
Tongue muscle example - what do the extrinsic muscles do? what do the intrinsic muscles do?
- Extrincic muscles protrude the tongue, retract it and move it from side to side. These have insertion points in bone or caritlage
- Intrinsic mucles within tongue are not attached to bone. They allow the tongue to change shape but not position – these aid swallowing
What do skeletal muscles look like on a TEM?
- Striated (striped)
- Move aloing the stripes in the direction of the arrows. Remember the some of the dark bits are the A bands etc
What do straited muscles look like in the transverse section and the longitudinal section? (also think about where the nuclei are located)
Note peripheral nuclei in TS
Note nuclei in rowsin LS
Look at the fasicle
Dashed line shows boundary of a fascicle
Each fascicle is surrounded by perimysium (connective tissue carrying nerves and blood vessels)
How many cells are in this diagram? Direction of movement?
4
Horizontal
How much blood does thick fibre need compared to a thin fibre>
Different fibres require different amounts of blood:
- Thin fibres less blood
- Thick fibres more blood
What is a muscle fibre (another name)?
Muscle cell
Draw a diagram showing, 1 cell (1 fibre), and what this looks like (include the myofibrils etc)
Describe the relationship between fibres, epimysium, cells, myofibrils, endomysium, perimysium, sacromere, fasicles, muscle (muddled these up!)
sacromere -> myofibrils -> fibre/cell (surrounded by endomysium) -> bundles of fibres together is called a fascile (surrounded by perimysium) -> lots of fasicles together (surrounded by epimysium) is the muscle
(SEE PRINTED OUT DOC TITLED HOW MUSCLES ARE STRUCTURED - REALLY HELPFUL)
What are myofibrils?
Myofibril, very fine contractile fibres, groups of which extend in parallel columns along the length of striated muscle fibres. They are made up of sacromeres units (i.e. actin and myosin)
Draw a myofibril and a sacromere to show how they are ‘related’
What do all the bands include?
H zone
Z disc
A band
I band
M line
What colour is the A band and the I band?
A band is appears dark
I band is appears light
Explain this picture (all A bands, light I band, Z band, I band, striated muscle)
Look at this diagram - note the nucleus size and the myofibril size etc
Where is the nucleus positioned in skeletal muscles?
Peripherally positioned
Look at this skeletal muscle TEM showing all the parts of the sacromere
Look at this diagram, label the different parts of the sacromere
Draw a sacromere
Out of the molecules, only need to know the myosin, actin and tropomyosin
How many types of ___ twitch muscle fibres are there? What are their ‘colours’?
Three types:
- Slow twitch fibres (red)
- Intermediate fibres (red to pink)
- Fast twitch fibres (white)
True or false: Each fasicle has at least one of the 3 types of muscle fibres
True
Visualise 1 fasicle with the different twitch fibres in it
What do the muscle fibres look like in cells that require lots of aerobic respiration, cells that require lots of anaerobic respiration
Slow twitch fibres (the type, capillary strcuture, type of respiration, levels of myoglobin, aerobic or anaerobic, number of mitochondria, number of cytochromes, colour, fatigue level, type of activity, example of an activity)
Intermediate twitch fibres (the type, capillary strcuture, type of respiration, levels of myoglobin, aerobic or anaerobic, number of mitochondria, number of cytochromes, colour, fatigue level, type of activity, example of an activity)
Fast twitch fibres (the type, capillary strcuture, type of respiration, levels of myoglobin, aerobic or anaerobic, number of mitochondria, number of cytochromes, colour, fatigue level, type of activity, example of an activity)
Each type of muscle fibre has it’s own contraction (own motor-unit and nerve supply). Explain this.
Continued muscle contraction depends upon a contunous supply of…
Ca2+ ions
ATP
Describe the two respiration pathways for slow and fast twitch muscles
Slow twitch muscles - Oxidative
Fast twitch muscles - Glycolytic
State the ATP, CO2 and lactate conc in each type of fibre
- Slow twitch: Lots of ATP/Lots of CO
- Intermediate: Initially lots of CO2, then lots of lactate
- Fast: Lots of lactate/Little ATP
Which two muscles are striated?
Skeletal and cardiac muscle
How do cardiac muscles differ to skeletal muscles (other straited muscle group)
- the muscle fibres are not as wide as those of skeletal muscle.
- the nuclei are positioned centrally and are cigar-shaped.
- there are usually only one or two nuclei per cell.
- the muscle fibres branch and join together (anastomose). (see arrows in diagram)
- intercalated discs form the junctions between the individual cells (see astricks)
Quick overview - Name the 3 types of muscle in this diagram
Discuss the intercalated disc
Intercalated discs form the junctions between the individual cells (drawing below) and are areas of low electrical resistance, consisting of specialised cell contacts (fascia adherens, desmosomes and gap junctions). It is the gap junctions that allow fast conductance of the electrical signal from cardiomyocyte to cardiomyocyte
Label the following picture (check using notes)
What are ANP granules?
Should have labelled the striations, Z line, M line, sacroplasmic reticulum, mitochondria, ANP, sacroplasm…
ANP: Atrial naturetic hormone or ANP is a member of a family of peptides that have important roles in regulating blood pressure. A majority of ANP is synthesized and secreted from cardiac muscle cells, particularly in the atria.
Role of ANP and BNP
- Atrial natriuretic peptide (ANP) released by atria
- Brain-type natriuretic peptide; BNP released by ventricles
- These naturietic peptides released by the heart during heart failure (atrial and ventricular distension), they are both trying to reduce blood pressure so the heart doesn’t have to work so hard
- Reduce arterial pressure by decreasing blood volume and systemic vascular resistance
- e.g. Left ventricular hypertrophy, mitral valve disease (BNP). Congestive heart failure (ANP)
Hypertrophy and hyperplasia
Tissues, including muscle, which increase in size may do so by:
- enlargement of their individual cells (hypertrophy), or by
- multiplication of their cells (hyperplasia)
NOTE: Cardiac muscle can only undergo hypertrophy and hyperplasia in children, but only hypertrophy in adults
What is atrophy?
(see diagram)
Heart can either get bigger (hypertrophy) and can get smaller (atrophy)
Describe the contraction sequence in the heart
- Electrical activity in the heart muscle begins at the sinoatrial node (SA node) where the cells have an intrinsic electrical activity that can be affect by neuronal input, particularly from the autonomic nervous system. The more conductive nodes, bundles and branches are areas of modified cardiac muscle cells that contain increasing amounts of glycogen stored and in their sarcoplasm and fewer contractile myocytes that makes them more sensitive to electrical conductance, but less able to contract. They are surrounded by connective tissue and collagen that act as an insulator to protect them from electrical stimulation by surrounding cardiomyocytes. For the same reason, electrical activity does not pass through the heart valves and across the heart because of their molecular construction (e.g. that they are made almost exclusively of extracellular matrix)
- Electrical signals (action potentials) pass from one cardiac cell to the next through pores known as gap junctions. These gap junctions are made of proteins called connexins and there are fewer gap junctions within the SA node and they are smaller in size. This is again important in insulating the SA node from the surrounding atrial cells.
- As the electrical signals pass through the conducting tracts of the atria, they converge on another insulated node that lies between the right atrium and right ventricle (the atrioventricular node (AV node), which lies at the lower back (posterior) section of the interatrial septum near the opening of the coronary sinus, and which conducts the normal electrical impulse from the atria to the ventricles. The AV node is quite compact (~1 x 3 x 5 mm), when compared to the SA node.
- After collecting at the AV node, electrical signals are passed to the Bundle of His, which divides into the left and right bundle branches and then onto the Purkinje fibres that initiate close to the apex of the heart. The structure of the bundle of His and the left and right bundle branches are very similar to that of the Purkinje fibres except they contain less glycogen in their cytoplasm (sarcoplasm) and more contractile myofibrils surrounding the cells that make up the core of the Purkinje fibres (see orcein stained image and TEM image on the next page). This means that they have a higher contractile ability compared to the cells in the two nodes
What are the fibres called in the atria that the action potential passes along?
Buchmann bundles
How is the wave ‘stopped’ from antering the ventricles?
Caritilagenous place (cartilage is very inexcitable). This pause allows the atria to contract and for blood to pass into the ventricles.
What are the name of the fibres in the ventricle that allows the action potential to pass through?
Bundle of His carries the wave to the apex of the ventricle.
Purkinje fibres carries the wave to the ‘sides’ of the ventricles
How does the electrical signal not pass through the valves into the ventricles?
Made of collagen - collagen is a really bad electrical conductor, so electrical signals can’t spread into the ventricles
Where is the SA node found?
In the cardiac muscle, close to the pulmonary trunk on the posterior aspect of the right atrium
What makes Purkinje fibres particularly good conductors of the electrical transmission?
Purkinje fibres are large cells with:
- abundant glycogen (white area around the nucleus as H+E doesnt stain sugars well)
- sparse myofibrils
- extensive gap junction sites
Speed of contraction compared to other cardiac fibres:
The Purkinje fibres conduct action potentials rapidly (3-4 m/s, compared to 0.5 m/s for cardiac muscle fibres). This rapid conduction enables the ventricles to contract in a synchronous manner.
Visualise Purkinje fibres…
What do the endocardium, Purkinje fibres and myocardium look like?… TEM
Smooth muscle cells (discribe their structure, contraction system)
- Spindle-shaped (fusiform) with a single central large nucleus
- Not striated, no sarcomeres, no T tubules (don’t have T tubules as don’t have sarcomeres)
- Capable of being stretched substantially
Sheets and bundles:
- Form sheets, bundles or layers containing thousands of cells
- Numerous caveolae (small cave-like invaginations - pinocytosis)
- Overlapping: the cells are overlapping, end of one cell overlaps with another. This means that they can be stretch substantailly (can take a lot of pressure)
Different contraction system:
- Contraction still relies on actin-myosin interactions (doesn’t have sacromeres)
- Contraction is slower, more sustained and requires less ATP
- May remain contracted for hours or days
Responds to stimuli:
- Responds to stimuli in form of nerve signals, hormones, drugs, or local concentrations of blood gases
Visualise smooth muscle…. (TEM)
What does smooth muscle look like in longitudinal and transverse sections?
Ultrastructure of smooth muscle
- Each smooth muscle fibre has a single, fusiform nucleus and is bounded by a sarcolemma.
- The bulk of the sarcoplasm is filled with myofilaments (contractile elements) arranged longitudinally in an illdefined lattice.
- Two types of filaments, numerous thin filaments (actin) and a smaller number of thick filaments(myosin).
- The smooth muscle cell differs from striated muscle in that it also has numerous calveoli (cave-like invaginations) on the sarcolemma surface that constantly sample the external environment and use the contents to initiate some forms of contraction.
- Unlike striated muscle, contraction occurs along microtubules that run between so-called ‘dense bodies’ attached to the sarcolemma.
- Smooth muscle cells are joined together at numerous points so that when one cell contracts, the entire tissue can contract. This occurs through a number of cell-to-cell interactions, gap junctions are therefore extremely important.
Draw a smooth muscle cell and label it
What are variosities?
Varicosities are enlarged areas of an autonomic nerve fibre that contain synaptic vesicles and release neurotransmitter molecules.
Why does varicosities not sit too close to the smooth muscle cells?
The varicosities release neurotransmitter, they sit further back so the neurotransmitter can come in contact with as much of the surface as possible
How do smooth muscles contract?
- When a neurone is fired, each one of the varicosities release their neurotransmitter from their synaptic vesicles. The synaptic vesicles are inside these viscosities.
- When stimulated to contract, the myosin and actin filaments interact exactly as they do in striated muscles and slide over each other, but instead of pulling the Z-lines together, different sides of the cell are pulled together through the dense plaques.
- Like cardiomyocytes, smooth muscle cells are joined together at numerous points so that as one cell contracts, the entire tissue can act as a syncytium and contact as one. This occurs through a number of cell-to-cell interactions, of which the gap junction is of paramount importance
Where is smooth muscle found?
Often form contractile walls of passageways or cavities (role: modify volume of a lumen (for example))
- e.g. of vascular structures (like arteries, veins, venules…)
- e.g. in gut, respiratory tract and genitourinary system
Give some examples of disorders they can be linked to
It is involuntary muscle and can develop a “mind of its own” and therefore be of clinical significance in disorders such as:
- high blood pressure (i.e. primary hypertension)
- painful menstruation (dysmenorrhea)
- bronchospasm (asthma)
- abnormal gut mobility (i.e. irritable bowelsyndrome) - incontinence (i.e. detrusor muscle instability (see Urinary SystemUnit))
Example - Smooth muscle in the gut
Smooth muscle damage - what does this look like on a TEM?
The black border surrounds the damaged cells that have ‘teared’. The nucleus has seperated from the rest of the cytoplasm. This cell will need to be replaced.
Contracted smooth muscle - shorter and thicker muscles have got gaps between them
The contracted muscle in the picture is mid-contracted as cells have shortened by 80%.
Muscle tearing in all 3 types… (photos)
Skeletal muscle - how does it repair?
Skeletal muscle cells cannot divide but can regenerate by mitotic activity of satellite cells (stem cells that sit next to the skeletal muscle), so that hyperplasia follows muscle injury.
Satellite cells can also fuse with existing muscle cells to increase mass (skeletal muscle hypertrophy).
Steps:
1. Acute phase - Blood clot formed, tissue disruption
- Sub-acute phase - clot shirnks, new fibrous tissue is formed. Signals trigger dominant satellite cells to go into action. They replicate, forming one new dormant cells and one that proliferates. The proliferating satellite cells can either form a new fibre or patch up the original. Cells from elsewhere, like the bone marrow can also help.
- Chroinc phase - tissue fibres becoming organised
- Fibre regeneration limited but remodelling continues
What is the satellite cells role in skeletal muscle repair?
Cardiac muscle - rapair
Adult cardiac muscle is incapable of regeneration Following damage, fibroblasts invade, divide, and lay down scar tissue. Muscles can’t grow over scar tissue.
Skeletal muscle - repair
Smooth muscle cells retain their mitotic activity and can form new smooth muscle cells
- particularly evident in the pregnant uterus where the muscle wall (myometrium) becomes thicker by hypertrophy (cell enlargement)
- hyperplasia (cell division/mitosis) of individual cells increases muscle mass
Do smooth muscles have satellite cells?
No they don’t and there are no equivalent cells like satellite cells.
The smooth muscle cells themselves retain the ability to divide, and can increase in number this way.
