Muscle

Question 1

Describe muscle cells.

Answer 1

-Special cells that contract to produce movement for:
>locomotion
>propulsion
>pressure regulation
-also known as myocytes & myofibers
-spindle shaped
-originate in mesoderm (from myoblasts)

Question 2

Define sarcoplasm, sarcolemma, & sarcoplasmic reticulum.

Answer 2

1. Sarcoplasm = cytoplasm that contain:
   -glycogen
   -myoglobin
2. Sarcolemma = plasma membrane
3. Sarcoplasmic membrane = smooth ER
   -regulates calcium flow
   -seen in smooth & striated muscle

Question 3

Muscle classification.

Answer 3

Question 4

Describe the histology of skeletal, cardiac, and smooth muscle.

Answer 4

Question 5

Describe where you would find skeletal muscle.

Answer 5

-voluntary sphincters in GI tract, urinary system, esophagus, tongue

Question 6

Describe skeletal muscle development.

Answer 6

1. Mesenchymal cells (myoblasts) fuse together to form multinucleated tubes = myotubes
2. Myotubes differentiate to form myofilaments & the nuclei are against the PM
3. Some cells dont differentiate & stay as mesenchymal stem cells = satellite cells (help with muscle repair)

Question 7

Describe skeletal muscle organization.

Answer 7

-muscles surrounded by dense irregular CT = epimysium (fascia)
-whole muscle made of smaller bundles = fascicles (surrounded by perimysium)
-myofibers contain myofibrils which contain myofilaments

Question 8

Cross section of striated muscle (picture)

Answer 8

-endomysium = individual myocytes surrounded by reticular fibers

Question 9

Describe myofibers VS myofibrils.

Answer 9

1. Myofibers [composed of myofibrils] = multinucleated cells with peripheral nuclei (hypolemmal)
2. Myofibrils = bundles of repeating contractile proteins called myofilaments (striations)
   >thick myosin & thin actin = contractile proteins
   >tropomyosin = regulatory protein

Question 10

Cross section VS longitudinal skeletal muscle (picture)

Answer 10

striations can be seen

Question 11

Describe the striations in myofibrils.

Answer 11

1. A band = dark (actin & myosin)
   -thick & thin filaments overlap
2. I band = pale (actin)
   *I band bisected by protein disk = Z line
   *Actin filaments anchored onto Z line

Question 12

Describe the sarcomere.

Answer 12

-contractile functional unit of myocyte
-sarcomere includes all elements in between each Z line
-at contraction Z lines (discs) are closer

Question 13

Describe what happens during muscle contraction.

Answer 13

-motion is based on conversion of ATP to mechanical energy
-each sarcomere shortens
-during contraction actin filaments slide over the myosin filaments = shorten I band
-myofilaments are held in place in the myofibril by other proteins (desmin, tropomyosin, troponin) length is constant

Question 14

Describe the muscle contraction steps.

Answer 14

1. Binding of Ca to TnC
2. Change in tropomyosin = exposes myosin binding site
3. Myosin head binds to actin: ATP -> ADP moving myosin head
4. Bound thin filaments slide over thick filaments
5. Shortening of muscle fiber

Question 15

Describe the transverse tubule system.

Answer 15

1. Myofibrils
2. SR
3. Terminal cisterna = expanded ends of SR
4. Transverse T tubule = deep tubular finger like invaginations of sarcolemma (PM) in skeletal & cardiac muscle

Question 16

Describe T tubules.

Answer 16

-allow depol of membrane to penetrate interior of cell = Ca release from SR

Question 17

Describe the physiologic skeletal muscle classifications.

Answer 17

1. Rates of contraction (fast/slow)
2. Rates of fatigue (fast/slow)
3. Types of metabolism (oxidative, glycolytic, mixed)

Question 18

Describe type 1 muscles.

Answer 18

“Red”
-slow
-dark = myoglobin (transfers O2)
-aerobic metabolism = fatigue resistant
-high fat, low glycogen
-many mitochondria
EX: postural & pectoral muscles

Question 19

Describe type 2 muscles.

Answer 19

“White”
-fast
-anaerobic metabolism = prone to fatigue
-low fat, high glycogen
-less myoglobin & mitochondria
1. Type 2A (intermediate) = mixed oxidative-glycolytic, slow fatigue
2. Type 2B = fast contracting, fast fatigue, glycolytic (depend on glycogen for energy)

Type 1 = dark blue. Type 2A = light blue. Type 2B = white

Question 20

Skeletal muscle summary (picture)

Answer 20

Question 21

Describe cardiac muscle.

Answer 21

-single cell with a central nucleus
-cross striated
-intercalated discs: gap junctions & desmosomes
>function as a syncytium
-SR
-many mitochondria
-requires O2

Question 22

Describe intercalated discs.

Answer 22

1. Transverse element
   -anchor
   -desmosomes = fascia adherens/macula adherens
   -strong attachment
2. Longitudinal element
   -communication
   -gap junctions (nexus) with ion channels
   -propagate electric impulse

Question 23

Describe the 2 types of cardiomyocytes.

Answer 23

1. Contractile = red
2. Conductive = pale pink
   >purkinje cell = neuronal cell bodies in cerebellar
   >purkinje fiber = modified cardiac muscle fiber in subendothelial tissue
   —conduct impulses through heart
   —form cardiac nodes

Question 24

Describe purkinje fibers.

Answer 24

-1 or 2 nuclei
-sparse myofibrils (periphery only)

Question 25

Describe smooth muscle cells.

Answer 25

-single central nucleus -no striations -no myofibrils -myofilaments (not ordered) >cytoplasmic dense bodies = anchors for myofilaments (like Z bodies) -desmosomes & gap junctions -no T-Tubule -SR poorly developed -involuntary -ANS innervation -spindle shaped (fusiform) surrounded by basal lamina & reticular fibers)

Question 26

Describe single (unitary) smooth muscle.

Answer 26

-found in visceral organs -syncytium -sparse nerve innervation -communicate via gap junctions

Question 27

Describe multi-unit smooth muscle.

Answer 27

-found in iris -precise contraction -individual innervation of each myocyte -lack gap junctions -function individually

Question 28

Describe the function of smooth muscle.

Answer 28

1. Peristalsis = contractions (EX. GI tract) 2. Vascular dynamics = contraction alters blood flow 3. Propulsion = urinary bladder, uterus 4. Secretion

Question 29

Describe the tunica muscularis of the luminal organs.

Answer 29

Question 30

Describe myoepthelial cells.

Answer 30

-ectodermal origin -actin/myosin -similar to smooth muscle -stimulated by hormones (mammary gland) -basket cells -location: salivary, mammary, lacrimal glands -contractile non-muscle

Question 31

Describe satellite cells.

Answer 31

-between basal lamina (intact) & sarcolemma -mitotic potential -fibroblasts form CT (scar tissue) -cardiac muscle can’t regenerate -new smooth muscle derived from pericapillary mesenchymal cells