Muscle Physiology (Smooth Muscle & Cardiac Muscle) Flashcards
much smaller than skeletal muscle fibers
Smooth Muscle
Smooth muscle cells have thin filaments are anchored either to the plasma membrane or to cytoplasmic structures known as
dense bodies
cells that have a single nucleus and have the capacity to divide throughout the life of an individual.
Smooth muscle cells
The thick and thin filaments are not organized into myofibrils, and there are NO
_______________, which accounts for the absence of a banding pattern
sarcomeres
have thick myosin-containing filaments and thin actin containing filaments, and tropomyosin but NO troponin.
Smooth muscle cells
Smooth muscle contraction occurs by what mechanism
sliding filament mechanism.
Sources of Cytosolic Ca2+
- The sarcoplasmic reticulum
- Extracellular Ca2+ entering the cell through plasma membrane Ca2+ channels.
Smooth muscles surround hollow structures and organs that undergo changes in ____________ with accompanying changes in the lengths of the smooth muscle fibers in their walls.
volume
Cross-bridge cycling in smooth muscle is controlled by a
that phosphorylates myosin
Ca2+regulated enzyme
is a Ca2+/calmodulin-dependent protein kinase that phosphorylates the regulatory light chain of myosin II, a key step in initiating muscle contraction in both smooth and non-muscle tissues.
myosin light chain kinase
Only the phosphorylated form of smooth muscle myosin can bind to actin and undergo cross-bridge cycling.
true
contains many vesicles filled with neurotransmitter, some of which are released when an action potential passes the varicosity.
varicosities
To relax a contracted smooth muscle, myosin must be dephosphorylated because dephosphorylated myosin is unable to bind to actin. This dephosphorylation is mediated by the enzyme myosin
myosin light-chain phosphatase
to relax the smooth muscle
the Ca2+ has to be removed either to the SR or back to the extra cellular fluid
The contractile activity of smooth muscles is influenced by neurotransmitters released by
autonomic neuron endings
Smooth muscle responses can be
graded
Input to smooth muscle can be either
excitatory or inhibitory
Unlike skeletal muscle fibers, smooth muscle cells do not have a specialized motor end-plate region. They have swollen regions known as
varicosities
Varicosities from a single axon may be located along several muscle cells, and a single muscle cell may be located near varicosities belonging to postganglionic fibers of both _________________
sympathetic and parasympathetic neurons
Therefore, a number of smooth muscle cells are influenced by the neurotransmitters released by a
single neuron
a single smooth muscle cell may be influenced by neurotransmitters from
more than one neuron
neurotransmitters enhance contractile activity, others decrease contractile activity
true
including paracrine signals, acidity, O2 and CO2 levels, osmolarity, and the ion composition of the extracellular fluid, can also alter smooth muscle tension.
Local factors
the type of response (excitatory or inhibitory) depends not on the chemical messenger per se, but on the receptors _____________
the chemical messenger binds to in the membrane and on the intracellular signaling mechanisms those receptors activate
Many of these local factors induce smooth muscle relaxation. _________________ which produces smooth muscle relaxation, in a paracrine manner.
Nitric oxide (NO)
smooth muscles can also respond by ______________ when they are stretched
contracting
Some types of smooth muscle cells generate action potentials spontaneously in the absence of any neural or hormonal input.
true
____________opens mechanosensitive ion channels, leading to membrane depolarization. The resulting contraction opposes the forces acting to this action
Stretching
The membrane potential change occurring during the spontaneous depolarization to threshold is known as a
pacemaker potential
Other smooth muscle pacemaker cells have a slightly different pattern of activity. The membrane potential drifts up and down due to regular variation in ion flux across the membrane. These periodic fluctuations are called
slow waves
Some cardiac muscle fibers and a few neurons in the central nervous system also have pacemaker potentials and can spontaneously generate action potentials in the absence of external stimuli
true
Pacemaker cells are found throughout the ______, smooth muscle tends to contract rhythmically even in the absence of neural input.
gastrointestinal tract, and thus gut
Sources of Cytosolic Calcium
initiates smooth muscle contraction comes from both the sarcoplasmic reticulum and from the extracellular fluid entering through plasma-membrane channels
Inputs Influencing Smooth Muscle Contractile Activity
- Spontaneous electrical activity in the plasma membrane of the muscle cell
- Neurotransmitters released by autonomic neurons
- Hormones
- Locally induced changes in the chemical composition (paracrine agents, acidity, oxygen, osmolarity, and ion concentrations) of the extracellular fluid surrounding the cell
- Stretch
Types of Smooth Muscle
contain cells that respond to stimuli independently and they contain few gap junctions
Multi-unit smooth muscles
Types of Smooth Muscle
respond to stimuli as a single unit because cells are connected by gap junctions
immediate transport, happens to one, happens to all
Single-unit smooth muscles
have one to two nuclei that are centrally located
striated and use the sliding filament mechanism to contract.
branching cells with intercalated discs with desmosomes and gap junctions.
Cardiac Muscle
have large mitochondia that produce the energy needed and prevent the heart from fatiguing.
Cardiac Muscle
_______________ are critical to the heart’s ability to be electrically coupled.
gap junctions
cells that have the ability to stimulate their own action potentials. This is called automaticity or autorhythmicity.
node cells
