15 - Muscle Structure Flashcards
What is myalgia, myasthenia, myocardium, myopathy and myoclonus?
Myalgia - Muscle pain
Myasthenia - Muscle weakness
Myocardium - Muscular part of heart
Myopathy - Muscle disease
Myoclonus - Muscle spasm
What are the categories of muscle?
What is myoglobin?
A red single subunit protein that stores oxygen and supplies oxygen to striated muscle.
Higher affinity for O2 than Hb and no affinity for CO2
How does oxygen get from Hb to Myoglobin?
Hb gives O2 to myoglobin as myoglobin has higher affinity, especially at low pH
Why do you get renal damage from muscle tears?
- Striated muscle damaged or dies then myoglobin is released into the blood stream.
This is removed by the kidneys, producing tea coloured urine, causing renal damage
What is the structure of a striated muscle cell including terminology?
What are the three types of connective tissue in striated muscle?
- Endomyisum (loose) : Between each cell
- Perimyisum (loose): Between each bundle (fasicle)
- Epimyisum (dense): Outside of whole muscle
Carry nerves and vessels
Why would you not see striations looking down a microscope at heart tissue?
- May be looking at it in transverse, not longitudinal.
- May need to look down TEM
What are the different shapes of muscles?
What cause the striations?
Myofilament, actin and myosin
What are the layers of making a muscle?
- Muscle cells held together by CT to form fibres
- Fibres held together to form fasicles
- Fasicles held together to form muscle
CT contains collagen and reticulin
How does striated muscle conect to bones?
- Connected to tendon which is connected to the periosteum
-
What is the insertion and origin point of a tendon?
- Origin is where the tension is (closest to body)
- Insertion is where the movement is (distal from body)
Why are muscles in the tongue not attached to bone?
- Not all muscles are attached to bone, allows tongue to change shape, aiding swallowing
What does the tongue muscles look like under a microscope?
What does circular, convergent, parallel and fusiform muscles do?
- Normally sphincter muscles that surround an opening. Open when ingress and exgress of materials is required
- Origin wider than insertion. Triangular used for lots of force
- Long muscles that cause large movements. Not strong but high endurance
- Can be grouped with parallel. muscle beller wider than insertion and origin
What do pennate muscles do?
- Uni: Great strength as at diagonals
- Bi: Central tendon. Greater power but less range of motion
- Multi: Multiple tendons as muscle fibres in both directions
What are the nuclei like in skeletal muscle?
- Peripheral, very close to sarcolemma
- Binucleated
What is the blood supply like to thin and thick muscle fibres?
Thin fibre - less blood
Thick fibre - more blood
What does the plasmalemma consist of?
- Plasma membrane
- Basal lamina
- Connective tissue
Label this muscle cell in transverse section
- Abundant mitochondria between myofibrils
Label this diagram of a muscle contraction component.
Label this diagram of a sarcomere
What factors affect how a muscle contracts?
Fibre arrangements (muscle shape) and what types of fibres (I,IIA,IIB)
What is a type I fibre?
- Slow twitch oxidative
- Red due to lots of myoglobin
- Lots of mitochondria and cytocromes
- Resistant to fatigue
- Aerobic respiration
- Postural muscles
What are type IIa fibres?
- Fast oxidative
- Hybrid of type I and II
- Many mitochondria and cytochromes
- Pink
- Anaerobic and aerobic
- Moderate resistance to fatigue
- Standing and walking muscles
What are type IIb fibres?
- Fast glycolytic fibres
- White as low myoglobin
- Low mitochondria and cytochromes
- Fatigue easily
- Anaerobic respiration
- Muscles of arms and eyes
- Can convert to type IIa fibres with resistance training
Compare and contrast the three types of muscle fibres.
- Slow have smaller diameter than fast so more blood can get to them
- Each fibre has own nerve supply
What is flexion?
Joint movement that decreases the angle between two bones. Due to muscle contraction.
Which part of the body that moves depends on what is stationary, e.g same muscle can move different things (knee/foot thing)
What muscles are levers and what are the three types of levers?
When muscles move against an object or force to create a movement.
What are the main features of a cardiac muscle cell?
- Centrally positioned nuclei
- Intercalated discs
- Muscle fibres not as wide as skeletal muscles
- Can be binucleated
- Muscle fibres branch and join toger (anastomose)
What are intercalated discs?
- Junctions between muscle cells containing desmosome, fascia adherens and gap junctions
- Gap junctions allow fast electrical conductance from cell to cell
What is between cardiac muscle fibres?
- Small amont of connective tissue containing nuclei.
- Contains fibroblasts that secrete extracellular matrix for tissue stability
- When intercalated discs break and cardiomyocytes start to die, fibroblasts lay down more extracellular matrix and form scar tissue
Compare cardiac and skeletal muscle?
Similarities:
- Both contract similarly
- Both have striations
Differences:
- Cardiac have central nuclei not peripheral
- Cardiac have less t-tubules and they’re found at Z-lines
- Sarcomere and sarocoplasmic reticulum not so developed
- Cardiomyocytes communicate through gap junction
Why is the heart an endocrine organ?
- Secretes ANP (Atrial natriuretic peptide) in atria
- Secretes BNP (brain) from ventricles
- Released during heart failure (distension)
- Increase loss of water in the kidneys so lower blood volume so lower b.p for heart
- Also causes vasodilation
When are ANP and BNP released?
BNP - Left ventricular hypertrophy and mitral valve disease
ANP - Congestive Heart Disease
What is the difference between hypertrophy and hyperplasia?
How does the heart get bigger and smaller?
Hypertrophy and Atrophy NOT Hyperplasia
What is the structure of smooth muscle cells?
- Spindle-shaped (fusiform) parallel cells
- Single central elongated nucleus
- Not striated, no sarcomeres or t-tubules
- Can be stretched
- Forms sheets
- Caveolae (pinocytosis)
Label this diagram
What are the point of dense bodies in smooth muscle cells?
Attached to sarcolemma. They assemble actin and myosin filaments when the muscle is ready to contract. When myofilaments slide they pull different sides of the cell together not Z-lines
How would you describe the contraction of smooth muscle?
- Relies on actin-myosin
- Slow but more sustained
- Less ATP
- Can contract for hours or days
- Contracts in response to hormones, blood gases etc
Where is smooth muscle found?
- GI tract
- Genioutuary system
- Blood vessels
What conditions can smooth muscle cause?
- Can develop ‘a mind of it’s own’
- Asthma
- Dysmenorrhea
- IBS
- Incontinence
What happens to the histology of a smooth muscle cell when it contracts?
NUCLEI SQUEEZE UP
What is being pointed to here?
T-TUBULES.
Mitochondria on edges of myofibrils
What type of muscle is this and why does the left side look different to the right?
- Smooth
- Left is transverse section and right is longitudinal
How are smooth muscle cells controlled?
- Autonolmic nerve fibres surround muscle
- Release neurotransmitters from varicosities
Can skeletal muscle repaire after tearing?
- YES, skeletal muscle cells cannot divide but satellite stem cells in endomysium divide by mitosis so hyperplasia.
- Satellite cells can also differentiate into myoblasts and fuse with existing muscle cells to cause hypertrophy
Can cardiac muscles repair after tearing?
- In infants yes
- In adults no regneration
- Fibroblasts invade after damage, and lay down scar tissue
Can smooth muscle repair after tearing?
- YES, smooth muscle cells retain their mitotic activity
- e.g in the pregnant uterus the muscle wall becomes thicker by hypertrophy and hypoplasia
- e.g hyperplasia of bronchial muscle for asthma
What are the stages of muscle repair after tearing?
What is the point of acetlycholinesterase?
- Catalyses acetylcholine when it has passed electrical signal onto sarcolemma
- Neurotransmitter can be recycle back into the presynaptic knob
What is the function of the terminal Schwann cell and the kranocyte?
- Terminal Schwann Cell: Keep the motor neuron alive, insulate it from external nerve signals and regenerate and remodel nerve endings
- Kranocyte: Like fibroblasts. Produce a connective tissue layer of elastic and structural fibres that hold neuromuscular junction together
How does electrical conduction in the heart occur?
- Electric signal passes from SA node through atrial walls to AV node
- AV node passes the signal to the bundle of His in the septum of the heart
- Signals passed to right and left bundle branches down to the apex of the heart
- Electrical signal travels up the Purkinje fibres up the ventricle walls
What is the structure of purkinje fibres (modified myocytes)?
- Large cells with abundant glycogen (so pale staining sarcoplasm)
- Extensive gap junctions of connexins
- Central nuclei
- Myofilaments only in periphery
- No t-tubules
- Fastest electrical conduction, not contraction
What is the structure of the SA node and where is it located?
- Banana shaped
- Cells in connective tissue so spread out
- Smaller and paler than atrial cells with less mitochondria, myofibres and sarcoplasmic reticulum so cant contract as well
- Surrounded by paranodal cells that insulate SA node so doesnt pass on electrical activity to surrounding atrial cells
- In the wall of the right atrium next to sinus venarum artery
How is the SA node electrically insulated?
- Surrounded by paranodal cells
- Fewer and smaller connexins
Where is the AV node and what is it’s structure?
- Right atrium atrioventricular wall
- Posterior section of the interatrial septum, near coronary sinus opening
- Compact compared to SA node
What is the central fibrous body?
Connective tissue next to the AV node that contains mainly collagen so no contraction or electrical potential
What is the structure of the Bundle of His?
Similar to that of Purkinje fibres but less glycogen and more myofibrils so more contractile ability than Purkinje and the nodes
Why does electrical conduction not occur through the heart valves?
- Consist mainly of ECM, e.g collagen, and electricity always follows path of least resistance so wouldn’t go down valves
What are the structure of the AV and SL valves?
- Fibrosa, Spongiosa, Atrialis/Ventricularis
F: provides strength (collagen)
S: shock absorber when valves close and allows movement between surface cells (proteoglycans)
A/V: elastic
