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)
Is there troponin present in smooth muscle
no
Is there myosin heads in smooth muscle
yes
are smooth muscle connected together
no, they are individual cells
What are in between Multi-unit smooth muscles
autonomic neuron varicosity
Is smooth muscle responsive to stretch
no
Is smooth muscle responsive to hormones
Minimal response to
hormones
What are the connect the smooth muscle in single-unit smooth muscle
linked electricall by gap junction
where are the autonomic neuron varicosity in single-unit smooth muscle
on the outside
What is a single-unit smooth muscle
• Network of closely opposed cells acting as a single unit • Direct stimulation of only a few
What is desmosomes
a structure by which two adjacent cells are attached, formed from protein plaques in the cell membranes linked by filaments.
How many adherence
points (desmosomes) are there in single-unit smooth muscle
multiple
What does Single-Unit Smooth Muscle respond to
• Neural signals • Hormones • Mechanical stretch • Local “pacemaker” potentials
Where are Single-Unit Smooth Muscle used
• Muscles of uterus,
intestinal tract, bile
duct, small blood
vessels
What are 3 types of innervation
• Extrinsic: both sympathetic and parasympathetic
• Intrinsic: short neurons forming plexuses (networks)
with tissue
• Afferent sensory: autonomic reflexes
What are the branching of fibres from in smooth muscle fibre
postganglionic sympathetic neuron
What does the fibres of postganglionic sympathetic neuron have
Branching of fibres with
“varicosities” that contains
vesicles with neurotransmitter
(both acetylcholine and norepinephrine)
How are the innvervation of muscle cells placed
• Modulatory rather than
inducing
What inputs does the postganglionic sympathetic neuron give
Potential for both sympathetic
and parasympathetic input
How does Non- neural activation work
• Hormones can open and/or close ion channels
changing membrane potential
• Chemical stimuli can cause release of Ca++ from SR
without a change in membrane potential
• Other influences
• Decreased oxygen, pH, body temperature
What is the regulation of contraction in smooth muscle compared to skeletal muscle
• Ca++ regulates cross bridge formation and
thus cycling
• BUT different from skeletal muscle
• Control of Ca++ levels
• Influence on cross bridge formation (myosin)
How are the cytosolic Ca2+ controlled in order to supply Ca2+ to smooth muscle
- receptor mechanisms like neurotransmitter or hormone
- Membrane potential-dependent channels
- Ca2+ released from sarcoplasmic reticulum upon receptor activation
- Ca2+ removed
What is smooth muscle cross bridge controlled by
Cross bridge binding
modulated by
Ca++ dependent
phosphorylation of myosin
What are the steps for relationship between crossbridge and Ca2+in smooth muscle
- increase in cytosolic Ca2+
- Ca2+ binds to calmodulin in cytosol
- Ca2+ - calmodulin complex binds to myosin
- Myosin light-chain kinases uses ATP to phosphorylate myosin cross bridges
- Phosphorylated cross bridge bind to actin filaments
- Cross-bridge cycle produces tension and shortening
When can strength be exerted optimally
in an optimal length
What does tetanic contraction mean
maintaining the contraction
Where does the calcium from cardiac muscle come from
diffusion of extracellular calcium, not SR
