Lecture 10: Muscles 1 and 2 Flashcards
Three types of muscle
Skeletal
Smooth
Cardiac
Skeletal
Attached to bones, moves and supports the skeleton. Striated/voluntary
Cardiac
Muscle of the heart. Striated/involuntary
Smooth
Surrounds hollow cavities and tubes. Unstriated/involuntary
4 functions of muscle tissue
- Motion
- Movement of substances within body
- Stabilizes body position and regulates organ volume
- Thermogenesis
Motion
Movements like walking/running
Movement of substances in body
All three types of muscle help move substances like blood, food, sperm, ova, and urine
Stabilizing body position/regulate organ volume
- Skeletal contractions maintain stable body positions and posture
- Sustained contraction of smooth muscle block exit of food from the stomach and urine from the bladder for temporary storage
Thermogenesis
Skeletal muscle contractions generate heat to help maintain normal body temp
Five characteristics of muscle tissue
- Excitability
- Conductivity
- Contractibility
- Extensibility
- Elasticity
Excitability
The property of responding to stimuli by producing action potentials
Conductivity
Ability of cell to conduct action potentials along plasma membrane
Contractibility
Ability to shorten and contract. The generation of force to do work.
Muscle contracts in response to action potential
Extensibility
Ability to be extended or stretch
Elasticity
The ability to return to its original shape after contraction of extension
An extensive vascular network
- delivers oxygen and nutrients
- carries away metabolic waste generated by active muscles
Blood vessels usually enter muscle in company with
nerve supply
Once the vasculature is in the muscle tissue
- the vessels and nerves branch through the muscle
- Arterioles supple blood to a capillary network that surrounds each individual muscle fiber
Skeletal muscles contract only under stimulation from
CNS
Axons penetrate muscle tissue to
innervate individual muscle fibers
Muscle fiber
muscle cells
Myofibrils
Threadlike parallel fibers of a muscle cells
Myofilaments
Thick and thin protein threads that makeup myofibrils
Myosin
Thick myofilaments
Contractile protein
Thin myofiliments
Actin
Tropomysin
Troponin
Sarcomere
Basic contractile unit
Myosin (thick filament) composition
- One pair of heavy chains and two pairs of light chains
- Most of heavy chain has alpha-helical structure in which the two chains coil around each other to form the tail of the myosin molecules
- Four light chaisn and the N-terminus of each heavy chain form two globular heads on the myosin molecule
The myosin globular heads have
- An actin binding site which is necessary for cross-bridge formation
- A site that binds and hydrolyzes ATP (myosin ATP)
Actin composition
- Consists of globular protein called G-actin
- Polymerization of G-actin to F-actin = two thin filaments twisted into an alpha-helical structure
- Has myosin binding sites which are covered by tropomyosin in a resting muscle, thus preventing interaction between actin and myosin
Tropomyosin is a ____ protein
regulatory
Tropomyosin function
Filamentous, it runs along the groove of each twisted actin filament. At rest, it blocks myosin binding sites on actin
-If contraction occurs, it must be moved out of the way so that the actin and myosin can interact
Troponin is a ___ protein
regulatory
Three globular proteins of troponin
- Troponin T
- Troponin I
- Troponin C
Troponin T
- T for tropomyosin
- Attaches the troponin complex to tropomyosin
Troponin I
- I for inhibition
- Binds troponin to actin
- Along with tropomyosin, it inhibits the interaction between actin and myosin by covering the myosin binding site on actin
Troponin C
- C for calcium
- A Ca binding protein that plays a central role in the initiation of contraction
-Increase in intracellular Ca concentration -> Ca binding to troponin C -> conformation change in the troponin complex -> moving of tropomyosin out of the way -> binding of actin to the myosin heads
Sarcomere
- Contractile unit of a striated muscle
- The area between two Z lines within a myofibril
Sliding filament mechanism
All sarcomeres shorten simultaneously, so the entire fiber becomes shorter
Actin and myosin are often referred to as ____ proteins
contractile
Tropomyosin and troponin are often referred to as ____ proteins
regulatory
Sliding filament mechanism
- Thin filaments on each side of a sarcomere slide inwards towards the center of the A band
- As they slide inwards, the thin filaments pull the Z lines to which they are attached closer together so the sarcomere shortens
Sarcolemma
- Cell membrane
- Has a characteristic transmembrane potential
What is the first step that leads to contraction?
A sudden conducted change in the transmembrane potential
Transverse tubules
Extensive network of sarcolemmel membranes that invaginates deep into the muscle fiber
Transverse tubules are responsible for
Carrying depolarization from AP’s at the muscle surface to the interior of the fiber
Transverse tubules make contact with the terminal cisternae of the sarcoplasmic reticulum via a voltage-sensitive protein called
the dhydropyridine receptor
Sarcoplasmic reticulum
An internal tubular structure which is the site of storage and release of Ca for excitation-contraction coupling
How is a high concentration of Ca maintained in SR?
Ca is bound to calsequestrin (a Ca binding protein)
Ryanodine receptors
the Ca release channels in the SR
How does the SR accumulate Ca?
- Ca+ ATPase in the membrane
- It pumps Ca from the ICF in the membrane fiber into the interior of the SR, keeping the intracellular Ca concentration low when the muscle fiber is at rest
Why does the onset of the resultant contractile response lag behind the action potential?
The entire excitation contraction coupling process must take place before cross-bridge activity begins
Three phases of excitation-contraction coupling
- Latent period
- Contraction time
- Relaxation time
Latent period
The time between stimulation and the onset of contraction
Contraction time
The time from onset of contraction until peak tension is reached
Relaxation time
The time from peak tension until relaxation is complete
Mechanism of black widow spider venom at neuromuscular junction
Causes explosive releae of ACh from storage vesicles which results in prolonged depolarizarion; the most detrimental consequence is respiratory failure
Mechanism of clostridium botulinum toxin at neuromuscular junction
- Blocks release of Ach from the nerve terminal in response to an AP in the motor neuron
- Prevents response to nerve impulses
- Death due to respiratory failure due to inability of the diaphragm to contract
Ach receptor blocker (Ex. Curare) mechanism of action at the neuromuscular junction
- Binds irreversibly to the ACh receptor site at the neuromuscular junction (motor end plate)
- Lack of stimulation of muscle and muscle paralysis
- Primary use is to produce skeletal muscle relaxation
- Ex. tubocurarine
Organophosphates mechanism of action at the neuromuscular junction
- A group of chemicals that irreversibly inhibit acetylcholinesterase
- Inactivation of released ACh
- Can lead to death due to respiratory failure because diaphragm is unable to repolarize and return to resting condition, then contract again to bring in a fresh breath of air
- Found in pesticides and nerve gas
