Myology Flashcards
What are the functions of the muscular system?
-Locomotion
-Vasoconstriction and vasodilatation-constriction and dilation of blood vessel walls are the results of smooth muscle contraction
-Peristalsis - wavelike motion along the digestive tract is produced by the Smooth muscle
-Cardiac motion
-Posture maintenance - contraction of skeletal
muscles maintains body posture and muscle tone
-Heat generation - about 75% of ATP energy used in muscle contraction is released as heat
-Stabilize joints - even as they pull on bones to cause movement, they strengthen & stabilize joints of skeleton
General properties of skeletal, cardiac and smooth muscles?
-Striation (only in skeletal & cardiac - NOT smooth)
-Nucleus (smooth & cardiac = uni-nucleated & skeletal = multinucleated)
-Transverse tubule (t-tubule) (NOT in smooth - but well developed in skeletal & cardiac)
-Intercalated disk (only in cardiac)
-Control
Give the 3 important components of a muscle fibre.
-Sarcolemma
-Sarcoplasm
-Sarcoplasmic Reticulum
What do t-tubules transport?
Ca2+
What are intercalated disks?
Specialised intercellular junction that
only occurs in cardiac muscle
= complex structures - connecting adjacent cardiac muscle cells (cardiomyocytes)
x3 of cell junction recognised that make up an intercalated disc = desmosomes, fascia adherens junctions & gap junctions
Purpose of intercalated disks?
Link cardiomyocytes together & define their borders
Are the major portal for cardiac cell-to-cell communication - required for coordinated muscle contraction & maintenance of circulation
What type of control is skeletal muscle under?
Voluntary control (some exceptions = tongue & pili arrector)
What type of control are smooth & cardiac muscle under?
Involuntary control
Compare skeletal,
cardiac and smooth muscles.
What are the components/structure of muscles?
-Epimysium
-Muscle fascicle
-Muscle fibre
-Myofibril
-Sarcolemma
-Sarcoplasm
-Sarcoplasmic Reticulum
What is the epimysium of muscle?
Outer layer of connective tissues covering an entire muscle
What is a muscle fascicle?
Bundle of skeletal muscle fibres surrounded by perimysium
Muscle fibre
-Surrounded by?
-Contents?
= individual muscle cell
-Thin CT layer (endomysium) surrounds
-Contains hundreds-thousands of myofibrils
What do myofibrils contain?
Myofilaments:
-Actin
-Myosin
What is the sarcolemma of a muscle?
Thin membrane enclosing a skeletal muscle fibre
What is the sarcoplasm of muscle?
Intracellular fluid between myofibrils (cytoplasm)
What is the sarcoplasmic reticulum of muscles?
Specialised endoplasmic reticulum of skeletal muscle
Where do individual T tubules run?
Between a pair or sacs - formed by SR fusion (i.e., = terminal cisternae)
What structure make up the ‘triad’ of muscles?
x1 T-tubule surrounded by x2 terminal cisternae = triad
-T tubules
-Terminal cisternae of SR fusing
Role of T tubules in transporting Ca2+?
Conduit for action potentials - conducts electricity
-AP depolarises cell memb
-Through T tubule
-Transferred to SR
-SR releases Ca2+
Do the components of the triad actually connect?
No direct connection but are very close together
Label.
What components of a muscle are responsible for muscle contraction?
Actin & myosin filaments
Which myofilament is the light filament?
Actin
Which myofilament is the dark filament?
Myosin
What makes up the I band of a sarcomere?
ONLY actin - so are light bands
–> as is an ‘i’ in light
Why are I bands called this?
As are isotopic to polarised light
What makes up the A band of a sarcomere?
Overlap of actin & myosin - so are dark bands
–> as is an ‘a’ in dark
Why are A bands called this?
As are anisotropic to polarised light
Relationship between actin & myosin - structure?
Structure of F-actin protein molecules - how are they made?
= Made of G-actin molecules - G-actin molecules group together
-1 ADP attached per 1 G-actin
-ADP = bound to active sites
-x2 F-actin filaments wrap/wound into helix
How does tropomyosin attach to actin?
Wraps spiralled around sides of F-actin
—> covers active sites for actin strands - so myosin heads can’t bind
What are the 3 subunits of troponin?
-Troponin T: strong affinity for ‘T’ropomyosin
-Troponin I: strong affinity for act’i’n (‘I’nhibition)
-Troponin C: strong affinity for Ca2+
Structure of myosin?
-x2 heavy chains = wrap spiralled around each other - forms double helix called ‘tail’
-x4 light chains
—> each chain folds bilaterally into globular polypeptide - ‘head’
Cytoskeletal properties.
-Dystrophin protein links desmin, Z lines & actin filaments to sarcolemma
-Sarcoglycans anchor complex to sarcolemma, & dystroglycans attach complex tolamininon outside of cell & endomysium surrounding each myofibre
–> this allows intracellular contraction of sarcomere - puts traction on CT fibres on outside of cell
-Pull on endomysium is passed to perimysium & then epimysium
-CT fibres of epimysium (primarily type I collagen) - bundle together = become tendons –Tendons insert into periosteum - or CT around bones
-Collagen fibres pierce bone - anchor attachment site strongly in place
Label.
Structure of a neuromuscular junction - draw & label.
What are the 2 main types of synapses?
-Chemical synapses
-Electrical synapses
What are the 3 types of chemical synapses?
-Synaptic cleft
-Neurotransmitters
-Skeletal muscles
What are the 2 types of electrical synapses?
-Gap junction
-Cardiac ventricular muscle, in uterus, & in bladder
Describe the stages in an action potential.
*Resting stage = resting memb pot before AP begins
-memb is “polarized” as men pot = −70 millivolts
*Depolarization Stage = memb suddenly becomes permeable to Na+ = allowing rapid diffusion of Na+ into axon.
*Repolarization Stage = Na+ channels begin to close, & K+ channels open to a greater degree than normal
-rapid diffusion of K+ exit to exterior —> re-establishes normal -ve RMP
Give the stages of nerve excitation.
Action potentials are propagated down the motoneuron
Calcium entry into the presynaptic terminus
Release of Ach from synaptic vesicles, diffusion across synaptic cleft and binding with post-synaptic receptors
ACh diffuses across the synaptic cleft to the postsynaptic membrane. This specialized region of the muscle fibre is called the motor end plate, which contains nicotinic receptors for ACh
Opening of Na+ /K+ channels on post-synaptic membrane
Postsynaptic membrane depolarization (End Plate Potential)
Ach breakdown via acetyl cholinesterase
Describe the process of synthesis & degradation of acetylcholine.
Describe the action & effect in neuromuscular transmission of Botulinus toxin.
Describe the action & effect in neuromuscular transmission of Curare
(d –Tubocurarine, used in anaesthesia).
Describe the action & effect on neuromuscular transmission of Neostigmine
(Rx myasthenia gravis).
Give the process of excitation coupling.
Give the process of excitation-contraction coupling in smooth muscle.
(cover again in Y2)
Main point = Ca2+ DOES NOT bind to troponin C but instead to calmodulin!
Give the process of cross-bridge cycling.
- Before contraction - heads of cross-bridges bind to ATP
ATPase activity of myosin head immediately cleaves ATP but leaves cleavage products
ADP + Pi ion = bound to head
Head extends perpendicularly toward actin filament is not attached to actin yet - Troponin-tropomyosin complex binds to Ca2+ = active sites on actin filament are uncovered —> so myosin heads bind here
- Bond between head of the cross-bridge & active site of actin filament causes = conformational change in head —> so head tilts toward arm of the cross-bridge - provides power stroke to pull actin filament
Energy activating the power stroke = from stored energy (like a cocked spring) ~ by conformational change in head when ATP molecule cleaved - After head tilts ADP released + Pi ion (were attached to head)
Site of release of ADP - new ATP binds —> causes detachment of head from actin - After head detached from actin - new ATP is cleaved = for next cycle - leading to new power stroke
-Energy cocks head back to perpendicular condition - ready to begin new power stroke cycle
-Cocked head (with its stored energy from cleaved ATP) binds to new active site on actin filament
-Head uncocked again - providing new power stroke
Label.
Describe how muscle contraction occurs in skeletal & cardiac muscle.
- AP reaches axon terminal at NMJ
- Release of Ach & synaptic diffusion
- Ach broken down by AchE & reabsorbed into axon terminal
- Muscle AP travels down T-tubule - opens Ca2+ channels in SR = Ca2+ release into cytoplasm
- Ca2+ binds to troponin C on actin & exposes myosin binding sites
- Myosin splits ATP & changes its shape - attaching to actin
-releases phosphate & creates power stroke = moves actin
-releases ADP & detaches from actin - Ca2+ detaches from troponin C
Ca2+ release channels in SR close & Ca2+ is pumped back into SR - Troponin complex returns to resting state
- Muscle fibre relaxes
Facts about slow - type I red muscle fibres?
Facts about fast - type II white muscle fibres?
Compare slow (type I) vs fast (type II) muscle fibres.
What makes up a single motor unit?
-1 motor neuron
-ALL the muscle fibres it innervates
-Each motor unit = made up of slow or fast twitch muscle fibres
What is isometric contraction?
-Same length/measure
-Contraction occurs without shortening length of whole muscle
What is isotonic contraction?
-Same tension
-Contraction against a constant load with a decrease in muscle length
True or False?
True or False?
