Lecture 18 9/21/23

Question 1

What is a motor unit?

Answer 1

one alpha neuron and all the striated muscle fibers it innervates

Question 2

What are the characteristics of a motor unit?

Answer 2

-muscle fibers are all the same type
-muscle fibers all contract at same time

Question 3

How can contraction strength be increased?

Answer 3

-increased number of motor neurons firing (spatial)
-increased frequency of activation (temporal)

Question 4

What are the characteristics of myocardial cells?

Answer 4

-striated
-involuntary
-single nucleus
-connected via intercalated discs

Question 5

What is the role of intercalated discs?

Answer 5

to allow for rapid transmission of neural signals from cell to cell

Question 6

What structure allows for passage of ions between myocardial cells?

Answer 6

gap junction

Question 7

What are the four main differences in cardiac muscle compared to skeletal muscle?

Answer 7

-branching cell networks
-single, central nucleus
-autonomic control
-intercalated discs

Question 8

What are the characteristics of smooth muscle?

Answer 8

-smaller and shorter cells
-no visible striations
-no T tubules
-less developed sarc. reticulum
-can receive input from multiple neurons
-can receive stimulatory and inhibitory signals
-autonomic

Question 9

How do multiunit and single unit smooth muscle cells differ?

Answer 9

-multiunit cells are separate cells with varicosity between them all
-single unit cells have gap junctions connecting them; only some cells interact with varicosity

Question 10

What is a varicosity?

Answer 10

structure that holds neurotransmitters and diffusely releases them to act on multiple cells at once

Question 11

What are the characteristics of single unit movement?

Answer 11

-contractile force of one fiber affects the neighboring fiber
-gap junctions allow for ion flow between fibers
-action potentials travel from one fiber to the next for one large, coordinated contraction

Question 12

What is the role of the dense body?

Answer 12

hold actin filaments together in smooth muscle

Question 13

How does innervation differ between single unit and multiunit smooth muscle?

Answer 13

-one innervation is enough for single unit due to the cells being connected
-each muscle fiber in multiunit must have its own innervation

Question 14

What are caveolae?

Answer 14

-structures in smooth muscle similar to T tubules
-allow for deeper propagation of signals

Question 15

What are the additional stimuli that are possible for smooth muscle?

Answer 15

-mechanical pressure
-blood pH
-oxygen
-extracellular ion conc.

Question 16

What are the steps of smooth muscle contraction?

Answer 16

-Ca2+ conc. increase in the cell when Ca2+ is released into cytoplasm
-Ca2+ binds to calmodulin
-Ca2+-calmodulin activates myosin light chain kinase
-MLCK phosphorylates light chains in myosin heads and increases myosin ATPase activity

Question 17

What is the role of calmodulin?

Answer 17

to control actin and myosin cross-bridging

Question 18

What is the role of myosin light chain kinase?

Answer 18

to stimulate phosphorylation of myosin, allowing for actin/myosin binding