L15 - muscle Flashcards
Define myalgia
Muscle pain
Define myasthenia
weakness of the muscles
Define myocardium
muscular component of the heart
Define myopathy
any disease of the muscles
Define myoclonus
a sudden spasm of the muscles
What does the prefix sarco- mean?
can denote flesh or muscle
Define sarcolemma
The outer membrane of a muscle cell
Define sarcoplasm
The cytoplasm of a muscle cell
Define sarcoplasmic reticulum
The smooth endoplasmic reticulum of a muscle cell
What are the three histological forms of muscle?
Smooth
Cardiac
Skeletal
Name form(s) of striated muscle
Skeletal and Cardiac muscle
Name form(s) of non-striated muscle
Smooth muscle
Which is the longest and widest muscle cell?
skeletal muscle cell
Which type of muscle is made up of long parallel cylinders, multiple peripheral nuclei and has striations?
skeletal muscle
Which type of muscle is made up of short branched cylinders, single central nuclei and has striations?
Cardiac muscle
Which type of muscle is spindle-shaped, with tapering ends, single central nucleus and no striations?
Smooth muscle
Which type of muscle is under somatic motor neurone control?
Skeletal muscle
Which type of muscle is under voluntary control?
Skeletal muscle
Which type of muscle has an intrinsic rhythm?
Cardiac muscle
Which type of muscle is under involuntary autonomic control?
Cardiac and Smooth muscle
Which type of muscle also has local stimuli and intrinsic activity?
Smooth muscle
Describe the power of skeletal muscle
Rapid and forceful
Describe the power of cardiac muscle
Lifelong variable rhythm
Describe the power of smooth muscle
Slow, sustained or rhythmic
Which type of muscle is connected by fascicle bundles or tendons?
Skeletal muscle
Which type of muscle is connected by end to end junctions?
Cardiac muscle
Which type of muscle is connected by connective tissue, gap junctions or desmosome-type junctions
Smooth muscle
What is the derivation of skeletal muscle?
Mesodermally-derived, multipotent myogenic stem cells
In skeletal muscle development myogenic stem cells give rise to what cell type?
myoblasts
Near- synchronous fusion of myoblasts in skeletal muscle development forms a primary myotube with a chain of multiple central nuclei. What displaces these central nuclei to the periphery during development?
Newly synthesised actin and myosin filaments
What is the difference between the development of myoblast producing skeletal muscle and myoblasts producing cardiac and smooth muscle?
Myoblasts producing skeletal muscle fuse whereas those producing cardiac and smooth muscle do not fuse, but develop gap junctions at a very early stage.
Put the following types of skeletal muscle fibre in order from the narrowest to the widest: white, red and intermediate fibres
red fibre
intermediate fibre
white fibre
Which types of skeletal muscle are red, white and intermediate fibres found in?
They are found in all skeletal muscle but their proportions depend on the functional role of the muscle
What is the difference in vascularisation between red and white skeletal fibres?
Red - richly vascular
white - poorly vascular
What is the difference in myoglobin concentration between red and white skeletal fibres?
Red - rich in myoglobin
white - poor in myoglobin
What is the difference in the number of mitochondria in red and white muscle fibres?
red - numerous mitochondria
white - few mitochondria
What is the differences in contraction between red and white skeletal fibres?
red - slow, repetitive, weaker
white - faster, stronger
Which type of skeletal fibres fatigues more slowly?
red skeletal muscle fibres
Which type of muscle fibre is rich in oxidative enzymes and poor in ATPase?
red skeletal muscle fibres
Which type of muscle fibre has more neuromuscular junctions?
white skeletal muscle fibres
Muscle fibres (cells) are covered in which connective tissue sheath?
endomysium
Fascicles of muscle fibres are wrapped in which connective tissue sheath?
perimysium
What is the name of the connective tissue sheath around multiple fascicles?
epimysium
Where do skeletal muscle fibres interdigitate with tendon collagen bundles?
myotendinous junctions
What always lies between the collagen bundles and the muscle fibre’s myofilaments at the myotendinous junction?
the sarcolemma
What is the difference between the extrinsic and intrinsic muscle of the tongue?
Extrinsic muscles are attached to cartilage or bone whereas intrinsic muscles are not attached to bone - they allow the tongue to CHANGE SHAPE NOT POSTITION.
What accounts for the mobility of the tongue?
(A) Plasticity and strength of connective tissues that the skeletal muscles of the tongue interdigitate with
(|B) multi-directional orientation of the muscle fibres
What is carried in the epimysium and perimysium?
nerves and blood vessels
What is a striated muscle cell called?
A muscle fibre
What is the dark band in striated muscle called?
A band
What is the light band in striated muscle called?
I band (think…insipid!)
What is the name of the strands that muscle cells contain lots of?
Myofibrils
Where are the mitochondria found in a muscle fibre?
Between myofibrils. They are seen as dark purple longitudinal streaks on a histological slide.
What is the name of the thin and thick filaments found in myofibrils?
Thick filament - myosin
Thin filament - actin
The sarcomere is defined as being between which structures in the myofibril?
From Z disk to Z disk
What are the distinctive structures that can be seen inside the A band?
M line inside the (dark line) H band inside the (lighter zone) A band (dark band) (Z) (I)
What are the distinctive structures that can be seen inside the I band?
Z disk (dark line), inside the light I band
Why is the A band dark?
It is where the actin and myosin filaments overlap
Why is the I band lighter?
It only contains thin actin filaments
Why is there a strip of lighter banding (H band) inside the dark A band?
It is a region where only myosin filaments are found, not actin filaments.
Why can it sometimes look like skeletal muscle fibres have centrally positioned nuclei on a histological slide?
When the muscle fibre has been sectioned just deep to the sarcolemma.
What is there only small amounts of between muscle fibres in skeletal muscle?
sarcoplasm
What is the Z disk (line) comprised of?
Alpha- actinin
What is the M line comprised of?
A strip of myomesin surrounded by two strip of C protein
Which bands decrease in width when the sarcomere contracts?
The I band and the H band
Which bands do not change width when the sarcomere contracts?
The A band
Describe from largest to smallest the components of muscle. Skeletal muscles are composed of…
fascicles composed of…
muscle fibres (Cells) composed of…
myofibrils composed of…
myofilaments (actin and myosin)
Which three types of molecules form a complex to form the thin filaments of skeletal and cardiac muscle?
actin, tropomyosin and troponin molecules
What three molecules comprise a troponin complex?
TnT, TnI, TnC (TIC!)
Why is troponin (especially I &T forms) a useful marker for cardiac ischaemia?
They are released from ischaemic cardiac muscle within an hour and must be measured within 20 hours.
The smallest changes in toponin levels in the blood are indicative of cardiac muscle damage.
Is the quantity of troponin found in the blood proportional to the degree of cardiac damage?
No
What is the assay of choice for cardiac ischaemia in emergency units?
Troponin assays. They have superceded muscle enzyme assays.
What is the structure of an individual myosin molecule?
Rod-like structure with two heads which protride from one end and a tail at the other.
What is the structure of mysoin filaments?
Each thick filaments is made up of lots of myosin molecules, whose heads protrude at opposite ends of the filament.
What is the structure of the actin filament?
It forms a helix, with tropomyosin molecules coiling around the helix - reinforcing it.
What is attached to every tropomyosin molecules?
A troponin complex (TnT, TnI and TnC)
What is noticeable about the appearence of myosin filaments in the centre of the sarcomere?
They are devoid of myosin heads
Where are the myosin heads found?
In regions of the myosin filament where there is potential overlap with the actin molecules.
Where does ionic calcium bind in the troponin complex?
TnC
What does binding of ionic calcium to TnC do?
Increased amount binding -> a conformational change that moves tropomyosin away from actin’s binding sites (actin-myosin binding sites)
What does the displacement of tropomyosin allow?
Allows myosin heads to bind actin and therefore contraction begins
What is the trigger of muscle contraction?
Ionic calcium displacing tropomyosin form the myosin head binding site with actin
What is the high energy conformation of the myosin head?
Vertical position, bound to actin, with ADP and Pi bound to the head
What does the working stroke of the myosin head entail?
The myosin head pivots and bends as it pulls on the actin filament, sliding it towards the M line and releasing ADP and Pi from where they were bound on the myosin head
What is the low energy conformation of the myosin head?
Myosin head not bound to actin. ATP bound to head. Head in 45 degree bend angle.
What allows the myosin head to detach from the actin filament?
Binding of ATP
What occurs to the myosin head when it splits (hydrolyses) ATP into ADP and Pi?
It cocks its head (head adopts vertical position)
What is the rigor configuration?
Myosin head tightly bound to actin molecule
What is rigor mortis?
A stiffening of the muscle and joints of a dead bory - usually lasting a few days. It is a perpetuation of the rigor comfirmation (myosin head bound to actin) that us perpetuated in death by the lack of ATP (therefore myosin head can’t detach from actin)
The working stroke of the myosin head pulls actin in which direction
Towards the actin filaments’s negative end
Release of what strengthens the binding of myosin heads with actin and causes the ‘power stroke’?
Pi - inorganic phosphate
How do individual myosin heads work together to cause movement?
They attach and flex at different times
Where are T tubules found in skeletal muscle?
Where the A and I bands join
Which type of muscle contains a ‘triad’?
Skeletal muscle
Which type of muscle contains a ‘diad’?
cardiac muscle
What does a ‘triad’ consist of?
T tubules sandwiched between the terminal cisterna of the sarcoplasmic reticulum.
At the neuromuscular junction what do the small terminal swellings of the axon, contain vesicle of?
acetylcholine
What is the affect of nerve impulses on the axon terminal?
Cause the release of acetycholine from the axon terminal into synaptic cleft, which bind to receptors on the sarcolemma and initiate an action potential propagated along the muscle.
What is another name for the axonal terminals at the neuromuscular junction?
Motor end plates
What is the effect of regular skeletal muscle exercise on the nerve fibres?
An increase in the number of nerve fibres binding muscle
What are the noticeable histological features in the neuromuscular junction synaptic cleft?
The sarcolemma of the muscle fibre has many folds (junctional folds) creating pockets (subneural clefts).
What is the effect of release of acetyl choline into the neuromuscular synaptic cleft?
Binds to receptors on the sarcolemma and causes local depolarisation of the sarcolemma
What causes depolarisation of the sarcolemma?
Opening of voltage-gated Na+ channels, allowing Na+ into the cell
Where does this general depolarisation spread?
Over the sarcolemma and into the T tubules
What is the affect of depolarisation on the T tubules?
Voltage sensor proteins of the T tubule membrane change their conformation activating gated Ca2+ channels of the adjacent terminal cisternae of the sarcoplasmic reticulum.
What effect does the release of Ca2+ into the sarcoplasm from the terminal cisternae have?
Ca2+ binds to the TnC subunit of troponin and the contraction cycle in initiated.
What happens to Ca2+ when the action potential ends?
It is returned back by active transport to the terminal cisternae of the sarcoplasmic reticulum
What are 4 distinctive features of histological slides of cardiac fibres?
- Striations
- Centrally positioned nuclei (1 or 2 per cell)
- Intercalated discs (for electrical and mechanicla coupling with adjacent cells)
- Branching
What is the difference between the arrangement of actin and myosin in cardiac muscle compared to skeletal muscle?
Cardiac muscle does not have distinct myofibrils, instead myofibrils of actin and myosin form continous masses in the cytoplasm
Where is the sarcoplasmic reticulum and mitochondria found in caridac fibres?
They penetrate through the cytoplasm between myofilaments.
What do cardiac fibres have instead of Z bands, where cells meet end to end?
Intercalated discs
What is the purpose of cardiac fibre gap junctions?
Electrical coupling
What is the purpose of cardiac fibre ahderens-type junctions?
Anchor cells and provide anchorage for actin filaments
What is the difference between the T tubules of cardiac muscle and skeletal muscle?
The T tubules of cardiac muscle lie in register with the Z bands not with the A and I band junction
What makes up a diad in caridac muscle?
A T tubule and a terminal cisterna of sarcoplasmic reticulum side by side
What does the close association of sarcoplasmic reticulum and T tubules at diads permit?
Release of ionic calcium into the sarcoplasmic reticulum and subsequent muscle contraction
Where are action potentials generated in the heart?
sinoatrial node
Where do action potentials travel from the sinoatrial node to?
Sinoatrial node -> atrioventricular node -> ventricles
Which type of specialised myocardial cells conducts distal impulses from the atrioventricular node to the ventricules?
Purkinje fibres
Describe a special feature of cardiac muscle cells?
They exhibit a spontaneous rhythmic contraction
Purkinje fibres are large cells with what other features?
Abundant glycogen
Sparse myofilaments
Extensive gap junction sites
Why is it important that the Purkinje fibres conduct action potentials rapidly?
Allows the ventricles to contract in a synchronous manner
Describe smooth muscle cells
Fusiform shape
Central nucleus
Non-striated
No sarcomeres or T tubules
What does contraction of smooth muscle rely on?
Myosin-actin intereactions
What is the difference between cardiac and skeletal muscle contraction and smooth muscle contraction?
Smooth muscle contract more slowly, more sustained and requires less ATP
How long can smooth muscle remain contracted for?
hours or days!
What stimuli do smooth muscle cells respond to?
Nerve signals
Hormones
Drugs
Local concentration of blood gases
What is the structure of smooth muscle?
Forms sheets, bundles or layers containing thousands of cells
Where is smooth muscle found?
Often forms contractile WALLS of passageways or cavities (can modify volume):
e. g. in vascular structures
e. g. in gut, upper respiratory tract and genitourinary system (uterus, vagina)
In which disorders can smooth muscle function by clinically significant?
High blood pressure Dysmorrhoea (painful menstruation - typically cramps) Asthma Atheroschlerosis Abnormal gut motility
List two types of modified smooth muscle cells
- Myoepithelial cells
2. Myofibroblasts
What is the function of the modified smooth muscle cells, myoepithelium cells?
Stellate cells forming a basketwork around the secretory units of some exocrine glands (e.g. sweat, salivary and mammary).
Contraction assists secretion of sweat, saliva and milk into secretory ducts.
in the ocular iris they also contract to dilate the pupil
What is the function of the modified smooth muscle cells, myofibroblasts?
At sites of wound healing they produce collagenous matrix but also contact (abundant actin and myosin). Prominent in wound contraction (draws wound together) and tooth eruption
How many layers of smooth muscle are there in the small intestine?
2: one inner circular layer and one outer longitudinal layer
Smooth muscle cells are innervated by what type of nerve fibres?
Autonomic nervous system
Instead of motor end plates and T tubules what do smooth muscle cells have?
They have swelling of the nerve fibres called varicosities, which release ACh into wide synaptic clefts and stimulate adjacent cells.
How are the thick and thin filaments arranged in smooth muscle cells?
They are arranged diagonally, spiralling down the long axis.
How does the smooth muscle cell contract?
They get shorter in a twisting way due to the diagonal arrangement of its thin and thick filaments
What is necessary for the contraction of smooth muscle cells?
Ca2+
What is the role of intermediate filaments in smooth muscle cells?
They attach to dense bodies scattered throughout the sarcoplasm and occasionally anchor to the sarcolemma.
Where is smooth muscle found around an arteriole?
In the tunica media
How does skeletal muscle repair itself?
Skeletal muscle cells cannot divide but the tissue can regenerate by mitotic activity of SATELITE CELLS, so hyperplasia follows muscle injury.
Satelite cells can also fuse with existing muscle cells to increase mass (skeletal muscle hypertrophy)
How does cardiac muscle repair itself?
It is incapable of regeneration. Following damage fibroblasts invade, divide and lay down scar tissue
How does smooth muscle repair itself?
Smooth muscle cells retain their mitotic activity and can form new smooth muscle cells.
Where is the ability of smooth muscle cells particularly evident?
In the pregnant uterus where the smooth muscle becomes thicker by hypertrophy (swelling) and by hyperplasia (mitosis) of individual cells
In cardiac muscle fibres there are characteristic pale areas next to the nucleus in longitudinal section. Why?
Region devoid of microfilaments (actin or myosin)
How does smooth muscle contract?
Sliding filament mechanism (via a sliding interaction of actin and myosin)
What structures confer electrical conductivity between the smooth muscle cells?
Gap junctions (specialised intercellular connections that directly join the cytoplasm of adjacent cells . They are gated and allow the passage of electrical impulses, ions, and molecules smaller than 485 Daltons. They appear to be almost ubiquitous in animal cells). The intercellular space reduces to 4 nm at gap junctions.
