Muscle

Question 1

Go through the organization of skeletal muscle, from muscle group to myofibril

Answer 1

1. Epimysium surrounds the whole muscle.
2. Perimysium surrounds each fascicle (functional unit of muscle fibers)
3. Endomysium surrounds each muscle cell, or fiber (myofibers)
4. Lots of myofibrils containing actin and myosin are in each muscle cell/fiber.

Question 2

What type of tissue is the epimysium? Perimysium? Endomysium?

Answer 2

Epimysium- Dense CT
Perimysium- Generally thicker CT
Endomysium- Loose CT

Question 3

What are type I skeletal muscle fibers also called? Include characteristics, where they are found, slow or fast twitch, metabolism, etc.

Answer 3

Slow, oxidative fibers.
Small, red fibers. Slow-twitch, fatigue-resistant.
Example is long muscles of the back; adapted to long, slow contraction.

Question 4

What are type IIa skeletal muscle fibers also called? Include characteristics, where they are found, slow or fast twitch, metabolism, etc.

Answer 4

Fast, Oxidative Glycolytic Fibers
Medium sized, large amounts of glycogen, capable of anaerobic glycolysis. Fast-twitch, fatigue-resistant, but not as resistant as type I. Generate high peak muscle tension. Think leg muscles.

Question 5

What are type IIb skeletal muscle fibers also called? Include characteristics, where they are found, slow or fast twitch, metabolism, etc.

Answer 5

Fast Glycolytic Fibers (Type IIb): Large white fibers, because they have very little myoglobin. high anaerobic activity and glycogen. Fast-twitch, fatigue-prone, high peak tension. Most fibers in extraocular muscles and muscles controlling digits.

Question 6

What is the myotendinous junction, and what does it help with?

Answer 6

Links muscle fibers with tendons. Increases surface area for integrin receptors and dystrophin-associated glycoprotein complexes linking the actin skeleton with the basal lamina and collagen fibers of the tendon.

Question 7

What are the two fates of myoblasts? What do they do?

Answer 7

1. Fuse to become multinucleated myotubes (then become muscle cells/fibers later when you get multiple fusing).
2. satellite cells- repair muscle damage by dividing and fusing with the skeletal muscle fibers if basal lamina is intact.

Question 8

Define each of the following, and whether they get shorter during contraction:
A band
H band
I band

Answer 8

A-band- length of the myosin filament. Contains both actin and myosin, and does NOT get shorter.
H-band- Middle area between actin filaments. Contains myosin only. Gets shorter.
I-band- Actin filaments only, between end of myosin to the z-disc and then to the next myosin. Gets SHORTER

Question 9

Where is titin and what does it do? (type of accessory protein)

Answer 9

Spring-like, coming off of z-discs. Prevents the sarcomere from being pulled apart, and keeps myosin attached to z-discs. passive length tension

Question 10

Where is nebulin and what does it do? (type of accessory protein)

Answer 10

Surrounds the actin filament, and keeps it at a constant length. (molecular ruler)

Question 11

What does alpha-actinin do? (type of accessory protein)

Answer 11

Binds the actin filaments to the z-discs.

Question 12

What is desmin and what does it do? (type of accessory protein)

Answer 12

Intermediate filament protein that links Z disks of adjacent MYOFIBRILS to keep them together. Also links myofibrils and creates lattice, also links myofibrils to membrane

Question 13

What is tropomodulin and what does it do? (type of accessory protein)

Answer 13

Caps the minus end of actin, to keep it at a certain length. Important for length-tension relationship during muscle contraction.

Question 14

Motor neurons from where innervate skeletal muscle fibers?

Answer 14

From the ventral horn.

Question 15

Each muscle fiber can have how many synapses with a neuromuscular junction?

Answer 15

ONLY ONE synapse per muscle fiber.

Question 16

What does a motor unit consist of?

Answer 16

One motor neuron and all of the muscle fibers innervated by its branches.

Question 17

What is the purpose of junctional folds?

Answer 17

They increase the surface area for reception of Ach signals on the muscle cell membrane.

Question 18

What are muscle spindles? What do they do?

Answer 18

stretch receptors in muscle consisting of spindle cells and neuron terminals surrounded by internal capsule. This capsule is located in a fluid filled external capsule. Muscle spindles carry information via sensory nerve fibers about the degree of stretching in muscle.
It also receives info via spinal cord/brain via gamma-motor nerve fibers, which regulate the sensitivity of the stretch receptor.

Question 19

What are golgi tendon organs? What do they contain?

Answer 19

They respond to increased tension in the muscle. Contain only sensory nerve fibers.

Question 20

Where are the nuclei in cardiac cells?

Answer 20

The are INSIDE the cells.

Question 21

What is the lateral part of intercalated discs?

Answer 21

cell-cell signaling (gap junction and macula adherens)

Question 22

What is the transverse part of intercalated discs?

Answer 22

transmits force of contraction b/w cells. (fascia adherens and macula adherens)

Question 23

Cardiac myocytes are rich with what two things due to the high energy demand they have?

Answer 23

Glycogen and mitochondria

Question 24

How are z-discs, T tubules, and sarcoplasmic reticulums arranged in cardiac muscle cells?

Answer 24

Only one T tubule per sarcomere at the z-disc, and sarcoplasmic reticulums are organized as diads with the sarcomere.

Question 25

Where do purkinje fibers conduct from and to?

Answer 25

From the AV node to the ventricles.

Question 26

What do smooth muscle nuclei look like and where are they?

Answer 26

cork-screw shaped, centrally located in cell.

Question 27

what neurotransmitters are used in smooth muscle, and where do they come from?

Answer 27

Norep and Ach, from varicosities rather than synapses.

Question 28

Can smooth muscle cells divide?

Answer 28

They can divide to repair damage, unlike cardiac muscle.

Question 29

No matter what transduction pathway is used in smooth muscle, what happens?

Answer 29

It leads to an increase in intracellular Ca++. Ca++ binds to calmodulin, and the Ca++-calmodulin complex activates MLCK (myosin light chain kinase). Activated MLCK phosphorylates and activates myosin light chains, causing it to bind to actin and cause movement of myosin heads, leading to contraction.

Question 30

How are actin and myosin arranged in smooth muscle?

Answer 30

They are mixed and attached to a cytoskeleton of intermediate filaments. Myosin filaments are arranged in a side-polar fashion, meaning the myosin molecules are staggered and the polarity of the heads are the same along one side of the filament.

Question 31

What is a dystrinopathy? Example of one and what happens?

Answer 31

dystrophin-dystroglycan-laminin linkage not intact. Membrane tears when myofilaments contract. Causes cell damage and degeneration.
Duchenne’s Muscular Dystrophy- mutation of dystrophin. Degeneration of muscle fibers and fibrosis.

Question 32

What does dystrophin do?

Answer 32

links myofilaments to basal lamina of muscle fibers.