9- Smooth Muscle (Micro Structure)

Question 0

Varicosities

Answer 0

Instead, the innervating nerve fibers, which are part of the autonomic nervous system, have numerous bulbous swellings.

Question 1

Peristalsis

Answer 1

Pg 309
Alternating contraction and relaxation of these opposing layers mixes substances in the lumen and squeezes them through the organs internal pathways.

Question 2

Diffuse junctions

Answer 2

Varicosities release neurotransmitter into a wife synaptic cleft in the general area of smooth muscle cells.

Question 3

Dense bodies

Answer 3

Attach at regular intervals to structures called dense bodies. Tethered to the sarcolemma act as anchoring points for thin filaments and therefore correspond to z discs of skeletal muscles.

Question 4

Proportion and organization of the myofilaments.

Answer 4

Thick filaments to thin filaments are lower in smooth muscle than skeletal muscle.thick filaments contain actin gripping heads along their entire length. Allows smooth muscle to be powerful.
No troponin complex present.
Thick and thin filaments aligned diagonally, spiral down long axis of cell. Muscle cells contract in a twisting way.
Contain a lattice like arrangements of non contractile intermediate filaments that resist tension, attach at dense bodies…
Pg 310

Question 5

Contraction of smooth muscle

Answer 5

Pg 311

1. Calcium ions enter cytosol from the ECF or from the scant SR.
2. Calcium binds to and activates calmodulin.
3. Activated calmodulin activates the myosin light chain kinase enzymes.
4. Activated kinase enzyme catalyzes transfer of phosphate to myosin heads, activating the myosin head ATPases.
5. Phosphorylated myosin heads from cross bridges with actin of the thin filaments and shortening occurs.
6. Cross bridge activity ends when phosphate is removed from the myosin heads by phosphorylase enzymes and intracellular calcium levels fall.