Muscle Physiology (Smooth Muscle & Cardiac Muscle)

Question 1

much smaller than skeletal muscle fibers

Answer 1

Smooth Muscle

Question 2

Smooth muscle cells have thin filaments are anchored either to the plasma membrane or to cytoplasmic structures known as

Answer 2

dense bodies

Question 2

cells that have a single nucleus and have the capacity to divide throughout the life of an individual.

Answer 2

Smooth muscle cells

Question 2

The thick and thin filaments are not organized into myofibrils, and there are NO
_______________, which accounts for the absence of a banding pattern

Answer 2

sarcomeres

Question 2

have thick myosin-containing filaments and thin actin containing filaments, and tropomyosin but NO troponin.

Answer 2

Smooth muscle cells

Question 2

Smooth muscle contraction occurs by what mechanism

Answer 2

sliding filament mechanism.

Question 2

Sources of Cytosolic Ca2+

Answer 2

1. The sarcoplasmic reticulum
2. Extracellular Ca2+ entering the cell through plasma membrane Ca2+ channels.

Question 2

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.

Answer 2

volume

Question 2

Cross-bridge cycling in smooth muscle is controlled by a
that phosphorylates myosin

Answer 2

Ca2+regulated enzyme

Question 2

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.

Answer 2

myosin light chain kinase

Question 2

Only the phosphorylated form of smooth muscle myosin can bind to actin and undergo cross-bridge cycling.

Answer 2

true

Question 3

contains many vesicles filled with neurotransmitter, some of which are released when an action potential passes the varicosity.

Answer 3

varicosities

Question 3

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

Answer 3

myosin light-chain phosphatase

Question 3

to relax the smooth muscle

Answer 3

the Ca2+ has to be removed either to the SR or back to the extra cellular fluid

Question 3

The contractile activity of smooth muscles is influenced by neurotransmitters released by

Answer 3

autonomic neuron endings

Question 3

Smooth muscle responses can be

Answer 3

graded

Question 3

Input to smooth muscle can be either

Answer 3

excitatory or inhibitory

Question 3

Unlike skeletal muscle fibers, smooth muscle cells do not have a specialized motor end-plate region. They have swollen regions known as

Answer 3

varicosities

Question 3

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 _________________

Answer 3

sympathetic and parasympathetic neurons

Question 3

Therefore, a number of smooth muscle cells are influenced by the neurotransmitters released by a

Answer 3

single neuron

Question 3

a single smooth muscle cell may be influenced by neurotransmitters from

Answer 3

more than one neuron

Question 3

neurotransmitters enhance contractile activity, others decrease contractile activity

Answer 3

true

Question 4

including paracrine signals, acidity, O2 and CO2 levels, osmolarity, and the ion composition of the extracellular fluid, can also alter smooth muscle tension.

Answer 4

Local factors

Question 5

the type of response (excitatory or inhibitory) depends not on the chemical messenger per se, but on the receptors _____________

Answer 5

the chemical messenger binds to in the membrane and on the intracellular signaling mechanisms those receptors activate

Question 6

Many of these local factors induce smooth muscle relaxation. _________________ which produces smooth muscle relaxation, in a paracrine manner.

Answer 6

Nitric oxide (NO)

Question 7

smooth muscles can also respond by ______________ when they are stretched

Answer 7

contracting

Question 7

Some types of smooth muscle cells generate action potentials spontaneously in the absence of any neural or hormonal input.

Answer 7

true

Question 8

____________opens mechanosensitive ion channels, leading to membrane depolarization. The resulting contraction opposes the forces acting to this action

Answer 8

Stretching

Question 9

The membrane potential change occurring during the spontaneous depolarization to threshold is known as a

Answer 9

pacemaker potential

Question 9

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

Answer 9

slow waves

Question 10

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

Answer 10

true

Question 11

Pacemaker cells are found throughout the ______, smooth muscle tends to contract rhythmically even in the absence of neural input.

Answer 11

gastrointestinal tract, and thus gut

Question 12

Sources of Cytosolic Calcium

Answer 12

initiates smooth muscle contraction comes from both the sarcoplasmic reticulum and from the extracellular fluid entering through plasma-membrane channels

Question 13

Inputs Influencing Smooth Muscle Contractile Activity

Answer 13

1. Spontaneous electrical activity in the plasma membrane of the muscle cell 2. Neurotransmitters released by autonomic neurons 3. Hormones 4. Locally induced changes in the chemical composition (paracrine agents, acidity, oxygen, osmolarity, and ion concentrations) of the extracellular fluid surrounding the cell 5. Stretch

Question 13

Types of Smooth Muscle contain cells that respond to stimuli independently and they contain few gap junctions

Answer 13

Multi-unit smooth muscles

Question 13

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

Answer 13

Single-unit smooth muscles

Question 14

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.

Answer 14

Cardiac Muscle

Question 15

have large mitochondia that produce the energy needed and prevent the heart from fatiguing.

Answer 15

Cardiac Muscle

Question 16

_______________ are critical to the heart’s ability to be electrically coupled.

Answer 16

gap junctions

Question 17

cells that have the ability to stimulate their own action potentials. This is called automaticity or autorhythmicity.

Answer 17

node cells