Muscle Physio Pt2

Question 1

Describe the characteristics of smooth muscles.

Answer 1

-spindle shaped
-non-striated
-central nucleus
-sheet arrangement
-lack CT

Question 2

What are the 2 types of smooth muscle?

Answer 2

Multi-unit & single unit (visceral)

Question 3

Describe multi-unit smooth muscle.

Answer 3

-independently innervated
-small fibers
-contracts independently
-locations: ciliary/pupil/iris muscles in eye, base of hair follicles, lung airways, walls of lg. blood vessels

Question 4

Describe single unit smooth muscles (visceral).

Answer 4

-fibers arranged in sheets/bundles
-cell membrane adhere via gap junctions
-force/ions transmitted from one muscle to other muscles
-contract as a single unit
-locations: GI tract, bile ducts, ureters, uterus, blood vessels

Question 5

Recall gap junctions.

Answer 5

-passage of sm. H2O soluble molecules cell to cell w/o passing thru PM (ECF) like ions & glucose.
-located in: CT, epithelial tissue, cardiac muscle, neurons

Question 6

What are the particularities of the smooth muscle?

Answer 6

1. Striations
2. Myosin filaments
3. SR
4. Slow cycling of myosin cross bridges
5. Low energy requirement to sustain contractions

Question 7

Particularities (1/5): Striations

Answer 7

• actin filament attach to ‘dense bodies’ (similar to Z disk)
• attached to cell membrane, bonded by intracellular protein bridges, or inside cell
• no troponin-tropomyosin complex
• myosin intercalated among actin

Question 8

Particularities (2/5): Myosin Filaments

Answer 8

-side polar cross bridges that allow myosin to pull actin filament in both directions simultaneously
-contract 80% of length (30% in skeletal)

Question 9

Particularities (3/5): SR

Answer 9

-slightly developed
-NOT the major source of Ca ECF is
-located near cell membrane
-invaginations ‘caveolae’ like T tubule on surface of SR
-excite CA release from SR

Question 10

Particularities (4/5): Slow cycling of myosin cross bridges

Answer 10

-attachment, release, & reattachment slower than skeletal
-larger force of contraction

Question 11

Particularities (5/5): Low energy requirement to sustain contractions

Answer 11

-imp for organs that maintain muscle contractions indefinitely
-ex: gallbladder, intestines, bladder

Question 12

List the 4 factors that can initiate contraction of smooth muscles.

Answer 12

1. Nervous stimulation
2. Hormone stimulation
3. Local tissue chemical factors
4. Self-excitation

Question 13

How is nervous stimulation different in the two types of smooth muscles?

Answer 13

-single unit = AP occurs similar to skeletal muscles
-multi unit = neurotransmitter (ACh or NE) causes depol & contraction without AP via ‘junctional potential’ & the stimuli spreads entire fiber due to the smallness.

Question 14

Describe nervous stimulation.

Answer 14

peripheral nervous system->motor(efferent) division ->autonomic nervous system(involuntary)->sympathetic division & parasympathetic division
-SNS = fight or flight [mobility] VS PNS = rest & digest [conserve energy]
-fibers don’t directly contact with muscle fiber
-‘diffuse junctions’ secrete neurotransmitters into matrix coating of smooth muscle
-terminal axons = multiple variocosities along axes that contain ACh, NE & mitochondria

Question 15

Describe hormonal stimulation.

Answer 15

-hormone gated receptor
-ex: NE, vasopressin, oxytocin, serotonin, histamine, angiotensin II, endothelin

Question 16

Describe Local Tissue Chemical Factors.

Answer 16

-sm. Vessels w/ little or no nerve supply
-responds to changes in surrounding interstitial fluid & stretch caused by changed in blood flow
-resting state = vessels stay contracted
-extra blood blow = vessels relax
-specific control factors: lack of O2/excess in CO2, high H+ ions, high lactic acid, high body temp.

Question 17

What are the mechanisms involved in excitation by chemicals & hormones?

Answer 17

-stimulate contraction by opening of Na & Ca ion channels = depol
-inhibition when Na & Ca channels close
-some hormones activate membrane receptors that use 2nd messengers (Ca, cAMP, cGMP)
-Ca = extracellular signals trigger increase in cytosolic Ca & activates Ca responsive proteins in cell (conc is low in cytoplasm & high in ECF, lumen of ER & SR)

Question 18

What are the two types of Self Excitation?

Answer 18

Spike potential & AP w/ plateau

Question 19

Describe spike potential.

Answer 19

-similar to skeletal muscles
-starts by electrical stimulation, hormones, stretch, or spontaneously
-self-excitatory = AP arise w/o extrinsic stimulus
-slow wave rhythm of MP (cause unknown)
-strong enough = initiate AP (ex. Rhythmic contraction of intestinal wall)

Question 20

Describe AP w/ Plateau.

Answer 20

-similar onset to spike potential
-delayed repol phase (prolonged depol)
-prolonged contraction = plateau
-Ca channels open and flow into interior = generate AP & cause contraction
-Ca channels open slowly than Na and remain open longer = prolonged plateau AP
*Na has little role in generation of AP (less channels than Ca)

Question 21

What are the 5 steps of smooth muscle contraction?

Answer 21

1. Intracellular Ca conc increase when Ca enters cell & released by SR or ECF.
2. Ca binds to calmodulin (CaM).
3. Ca-CaM activate myosin light chain kinase (MLCK).
4. MLCK phosphorylates light chains in myosin heads & increases ATPase and binds to actin.
5. Active myosin cross bridges slide along actin & create muscle tension.

Question 22

What stops smooth muscle contraction?

Answer 22

Ca pump & myosine phosphotatase.

Question 23

How does the Ca pump stop smooth muscle contraction?

Answer 23

-causes relaxation
-make CA ions back to ECF or SR
-requires ATP
-slow acting
-contract longer than skeletal muscles

Question 24

How does myosine phosphotatase stop smooth muscle contraction?

Answer 24

-enzyme causes relaxation
-after Ca channels close & Ca pump moves Ca out of cell & Ca conc decreases
-activates myosine phosphotatase = enzyme located in cytosol
-splits phosphate from regulatory light chain
-cycle stops & contraction ends