EXAM 3 Flashcards
Define Rigor Mortis
postmortem contraction of the skeletal muscles due to lack of new ATP synthesis
ATP is no longer being produced
Name the proteins in the thin filaments of smooth muscle and their functions
- Actin - contains binding sites for myosin heads
- Tropomyosin - supports the structure of actin. Does not block the myosin binding sites on actin in a relaxed smooth muscle
what is the function of tropomyosin in a relaxed skeletal muscle
wraps around the actin filament and covers myosin binding sites, so contraction cannot occur
Name the structures PRESENT in SKELETAL muscle fibers that are ABSENT from SMOOTH muscle cells (4)
- sarcomeres - cellular units of skeletal (and cardiac) muscle
- troponin -“regulates actin-myosin interactions in skeletal and cardiac muscle contraction”
- z-lines - protein that encloses the thin filament
- t-tubules - involutions of sarcomere that action potentials flow through
Compare and Contrast… single-unit smooth muscle and multiunit smooth muscle
Similarities
- innervated with autonomic nerve fibers
- stimulated to contract by chemicals
Differences
-
single unit:
- circular and longitudinal muscle sheets
- electrically coupled by gap junctions
- functional syncytium
- pacemaker activity
-
multiunit:
- individual smooth muscle fibers
- no gap junctions
- no pacemaker activity
Define the neuromuscular junction
junction between the axon terminal of a motor neuron and a skeletal muscle fiber that is separated by a small space called the neuromuscular (synaptic) cleft
each muscle fiber has only ONE neuromuscular junction
How will an increase in extracellular calcium affect the strength of a cardiac muscle
strength will increase; relies on extracellular calcium to release calcium from the SR
in smooth muscle cells, the thin filaments are anchored by…
dense bodies
Compare and Contrast… skeletal muscle and cardiac muscle
Similarities
- Striations present
- sarcomeres present
- T-tubules present
- Ca2+ binds to TnC
- Grows through hypertrophy
Differences
- Skeletal muscle: voluntary movement, no syncytium, no gap junctions
- cardiac muscle: involuntary movement
Define a Triad
the structure formed by a transverse (T) tubule in between two terminal cisternae
define indirect attachment of the skeletal muscle
tendon extends from the muscle to attach to the bone
Autonomic Nervous System divisions
Sympathetic Nervous System
Parasympathetic Nervous System
Give the role of ATP in muscle contraction (3)
- ATP is hydrolyzed by ATPase to produce ADP and Pi to activate the myosin heads
- ATP is required for crossbridge detachment
- ATP is required for the sequestration of calcium ions back into the SR for storage (active transport)
Place the three skeletal muscle fibers in order of GLYCOCEN CONTENT (high to low)
FG > FO >SO
What is the power stroke in excitation-contraction coupling in skeletal muscle?
ADP + Pi dissociate from myosin
List the sources of ATP to support skeletal muscle contraction (4)
- stored ATP - used first
-
Direct phosphorylation of ADP by creatine phosphate
- CP + ADP –> ATP + creatine
- Aerobic catabolism of glucose - produces the most ATP, slowest
- Anaerobic catabolism of glucose - fastest
Which type of skeletal muscle fiber is fatigable and why?
Fast Glycolitic Fibers because they produce ATP from anaerobic respiration, which produces powerful, high-tension contractions, but fatigues quickly
Define the motor end plate and its function
- definition: Highly folded region of the sarcolemma
- function: expresses acetylcholine receptors on surface
How will the contraction of smooth muscle be affected if the autonomic innervation is severed?
Contraction of smooth muscle will occur due to pacemaker activity
Place the three skeletal muscle fibers in order of MYOGLOBIN CONTENT (high to low)
SO > FO > FG
Define the sliding filament mechanism
when contraction (shortening) occurs when thin filaments “slide” into the H zone (towards the M line) pulling the Z discs inward
length of sarcomere shortens, shortening the entire muscle
How will an increase in extracellular calcium affect the strength of a smooth muscle?
strength will increase; relies on extracellular calcium to release calcium from the SR
Define isometric contraction
force (tension) generated by the muscle is increasing at a constant muscle length; muscle does not shorten
FORCE < WEIGHT
In SMOOTH muscle cells, myosin heads are activated when…
MLCK hydrolyzes Pi from ATP to activate myosin
Discuss the role of calcium in skeletal muscle contraction
Ca2+ binds to TnC
Troponin undergoes a conformational change that moves TnT and Tropomyosin from blocking the myosin binding sites on actin
what is the function of triads?
Triad releases Ca2+ ions into the sarcoplasm when the sarcolemma depolarizes
Characteristics of Fast Glycolitic (FG) Fibers
Fast ATPase; produces ATP quickly through anaerobic respiration
Which skeletal muscle fiber is also known as “red fibers” and why?
Slow Oxidation Fibers because they have the highest myoglobin content, which gives them a red pigment
In SKELETAL muscle fibers myosin heads are activated when…
ATP hydrolyzes to ADP + Pi
Describe the structural organization of a sarcomere (6)
- A band: thick filament
- M line: bisects and anchors A bands
- Thin filaments: give the striated appearance of skeletal/cardiac muscle
- Z lines (Z discs): anchor thin filaments
- H zone: middle region of A band
- I bands: regions of thin filaments not overlapping with A band
What can inhibit the contraction of cardiac muscle?
Calcium Channel Blockers
Characteristics of Fast Oxidative (FO) Fibers
Fast ATPase; produces ATP quickly through aerobic respiration
What can inhibit a the contraction of a skeletal muscle?
chemicals that block acetylcholine receptors
Describe the divisions of the motor (efferent) nerves of the PNS
Somatic Nervous System
Autonomic Nervous Sustem
Activation of the sympathetic nervous system causes…
bronchodilation and vasoconstriction
Function of dense bodies
anchor thin filaments
Place the three skeletal muscle fibers in order of recruitment (first to last)
SO > FO > FG
Discuss the role of calcium in smooth muscle contraction
Calcium binds to calmodulin –> forms calcium-calmodulin complex –> activated Myosin Light-Chain Kinase (MLCK)
What can inhibit the contraction of skeletal muscles?
Chemicals that block acetylcholine receptors
what is the consequence (result) of the power stroke?
Sliding of the thin filaments toward the H Zone and M line
Name the proteins in the thin filament of a cardiac muscle and their functions
- Actin - contains binding sites for myosin heads
- Tropomyosin - regulatory protein that “wraps around the actin filament and covers myosin binding sites to prevent contraction in a relaxed skeletal muscle”
- Troponin - three polypeptide complex (TnC, TnT, TnI) that regulates actin-myosin interactions in skeletal and cardiac muscle contraction
How will an increase in extracellular calcium affect the strength of the skeletal muscle?
strength is unaffected because skeletal muscle doesn’t use extracellular calcium
Characteristics of Slow Oxidative (SO) Fibers
Slow ATPase; produces ATP slowly through aerobic respiration
Autonomic Nervous System function
takes information to the smooth muscles and cardiac muscles (soft organs)
Types of skeletal muscle fibers (3)
Slow Oxidative (SO) Fibers
Fast Oxidative (FO) Fibers
Fast Glycolytic (FG) Fibers
Define Muscle Fatigue
physiological inability of a stimulated skeletal muscle to contract due to an ATP deficit
ATP is still being produced but not at the rate of demand
function of calmodulin
regulatory protein that calcium binds to
List the subunits of troponin (3) and their functions
TnC - binds calcium ions
TnT - binds to tropomyosin
TnI - inhibitory subunit that binds to actin
Describe the function of the motor (efferent) nerves of the PNS
To take information from CNS to the effector structures
Define direct attachment of the skeletal muscles
when the epimysium fuses directly to the periosteum of the bone
Name the structures PRESENT in SMOOTH musle cells that are ABSENT from SKELETAL muscle fibers (4)
- dense bodies
- intermediate filaments
- caveolae
- calmodulin
Define a motor unit
motor neuron and all of the skeletal muscle fibers it innervates
function of intermediate filaments
resist tension
Somatic Nervous System function
Takes information to the skeletal muscles (hard organs)
cross bridge detachment occurs when…
phosphate is removed from the myosin heads by phosphorylase enzymes and intracellular Ca2+ levels fall
Define functional syncytium
The contraction of the muscle as a single unit
Place the three skeletal muscle fibers in order of FIBER DIAMETER (large to small)
FG > FO > SO
what are activated globular heads?
When ATPase hydrolyzes ATP into [ADP and Pi] and attach to the myosin globular heads… they become ACTIVATED
(Activated Myosin globular heads attach to actin which is called CROSS BRIDGES)
Compare and Contrast… smooth muscle and cardiac muscle
Similarities:
- gap junctions present
- functional syncytium
- involuntary muscle control
Differences:
- Smooth muscle grows through hyperplasia AND hypertrophy
- Cardiac muscle grows through hypertrophy
caveolae
shallow cavities in the sarcolemma that contain extracellular fluid that is saturated with calcium
What can inhibit the contraction of smooth muscle?
Calcium Channel Blockers
Describe the structural organization of a skeletal muscle
- epimysium: outer protective layer
- perimysium: surrounds fasicles
- fasicle: group of muscle fibers
- endomysium: surrounds single muscle fiber (cell)
How will the contraction of cardiac muscle be affected if the parasympathetic innervation is severed?
Contraction of cardiac muscle will occur because there is no parasympathetic inhibition of the cardiac muscle
Structures of the sarcomere that shorten when a skeletal muscle contracts
H zone and I bands
Factors that affect the strength of skeletal contraction
- Size of the motor unit activated
- Number of motor units activated
- Frequency of activation of the skeletal muscle fibers by the motor neuron
- Length of the sarcomere prior to contraction
structures of the sarcomere that remain the same when a skeletal muscle contracts
A bands and Thin filaments
the diffuse junctions form directly between…
varicosity of an autonomic fiber and a smooth muscle cell
Explain recruitment as it pertains to the strength generated by skeletal muscle contraction
smallest motor units are used first and larger units recruited after
Define isotonic contraction
[sliding filament mechanism] generates force by changing the length of the muscle
FORCE > WEIGHT
(me lifting a 5 lb weight)
