Lecture 19 Flashcards
What is summation of twitches
- Process by which individual twitches combine
- Produces sustained contractions
- Can lead to tetanic contractions
What does Recruitment of Motor Units mean
- increase in the number of motor units activated
What can recruitment do
• Whole muscle composed of many motor units
• More precise movements are produced with fewer muscle
fibers within a motor unit
• As intensity of stimulation increases, recruitment of motor units
continues until all motor units are activated
What muscles are recruited first followed by which
- Motor unit one :slow-oxidative fibers
- Motor unit 2 : fast-oxidative fiber
3: Motor unit three : fast-glycolytic fibers
- Smaller motor units (smaller diameter axons) - recruited first
- Larger motor units (larger diameter axons) - recruited later
What is muscle tone
continuous state of partial contraction
What is going on during • Slow-twitch fibers (Type I)
- Always oxidative
- Resistant to fatigue
- Red fibers
- Most myoglobin
- Good blood supply
What is Fast-twitch fatigue-resistant
fibers (Type IIa)
• Intermediate fibers • Oxidative • Intermediate amount of myoglobin • Pink to red in color • Resistant to fatigue
What is • Fast-twitch glycolytic fibers (Type IIb)
- White fibers (less myoglobin)
- Poorer blood supply
- Susceptible to fatigue
What is the difference between the cardiace muscle and skeletal muscle for how it works
• Differences in cardiac muscles
- Not initiated by neuronal input
- All cells are electrically coupled
- Long action potential
What is the general structure of cardiac muscle
• Uni-nucleate cell • Z lines, M lines, A bands, I bands • Relatively short • Branching and interdigitate • Arranged in series and parallel
Where are the location of intercalated disk in cardiac muscles
• 2 regions • Transverse portion, aligned with Z line, desmosomes, mechanical cohesion • Lateral portion, parallel to myofilaments, rich in gap junctions, low resistance pathway
What are the three types of heart muscle cells
- Cells of myocardium
- Rhythmically active self
excitatory “pacemaker”
cells - Purkinje fibres,
specialised conducting
pathways which
enhance spread of
localised excitation
How does cardiac receive signal
• AP spreads along plasma membrane and invades T tubules • This opens voltage sensitive Ca++ channels in T-tubule membrane • Diffusion of extracellular calcium
How Excitation contraction coupling work in cardiac muscle
- Excitation/depolarization
- opening of voltage-sensitive plasma membrane C2+ channels
- Flow of Ca2+ into cell
- Stimulation of Ca2+, release from sarcoplasmic reticulum
- increase cytosolic Ca2+ concentration
- contraction
What does the extracellular Ca2+ do
Extracellular Ca++
stimulates release of Ca++
from SR
What is the contraction of the cardiac muscle called
systole
What does the strength of contraction depend on
dependent on presence
and concentration of
extracellular Ca++
What is the contractility influence by
• Ca++ levels • Hormones (epinephrine) • Nervous (autonomic) • Extent of stretch • Cardiac muscle operates in a range of lengths shorter than optimal
What is contraction of smooth muscle mediated by
Contraction mediated by actin and myosin
cross-bridge cycling
Is smooth muscle sarcomere obvious
Undefined sarcomere struct
What are the smooth muscle bound together by
basement
membrane and transmits force
Do smoother muscle have T-tubules
no, • Small membrane invaginations called caveoli
• SR if rudimentary
what is the dense body attached to
actin filament and membrane
What are the dense bodies linked by
Linked by diagonal
network of
intermediate filaments
(desmin)
