Involuntary & Nonstriated

When Smooth Muscle is stimulated:

Calcium movements: - some Ca 2+ is released from the small amount of Sarcoplasmic Reticulum actually present in Smooth Muscle Cells

most Ca 2+ enters the Cell through many Caveolae (special indentations in Cell Membrane - with many Ca 2+ Channels)

(Ca 2+ must go back out afterwards )

2) ( special ) Calmodulin molecules ( a regulatory Protein ) - each binds Four Ca 2+ ions ( Activating the Calmodulins )

3) Myosin Light Chain Kinase ( Enzymes ) - are then Activated by: the Activated Calmodulin !!

4) using ATPs … the Kinase Phosphorylates the Thick Myosin molecules ( Activating them ) ( process called: Phosphorylation )

5) Cross Bridges form ( Thick Myosin Filament Heads to: Thin Actin Filament Molecules )

Comment: Myosin is slightly different kind. The Thick Myosin Filaments & Thin Actin Filaments are arranged in spirals that twist during contraction ( like Barber Shop poles)

Smooth Muscle Cells : small Cells with both ends tapered - joined together in Sheets, held together by Gap Junctions so that Action Potential goes out through all cells at one time.

Cells of Sheets contract together 

Ex. Peristalsis - muscular contraction waves squeezes food along Digestive Tract 

Comment: most of Digestive Tract has: 2 muscle layers: Circular & Longitudinal 

- twist as they contract (using their surrounding lattice work of: Intermediate Filaments & Dense Bodies)

- each Cell has one central Nucleus (not multinucleated) 

- The Thin Actin & Thick Myosin - arranged in Spirals —> Twisting Contractions

- has a special Regulatory Protein called: Calmodulin (each binds to four Ca 2+ ions)

- has: possible two different Neurotransmitters: Acetylcholine or Norepinephrine !!

- each cell has Endomysium covering the whole cell (including its Myelin) (There is no Epimysium or Perimysium)

- no Neuromuscular Junctions instead have: Diffuse Junctions (Do not confuse with: Tight Junctions / Gap Junctions / or Desmosomes)

- no Boutons, instead have Varicosities (which make & release Neurotransmitter)

Synaptic Clefts - are wider Comment: Neurotransmitter (from: Varicosities) spreads out over Smooth Muscle Cell Sheets (more nonspecific)

- no Sarcomeres (so no striations)

- no T Tubules (so no Triads)

- no Troponins

- no Tropomyosin

-Slow starting: 30 times longer in Contraction then Relaxation (vs Skeletal Muscle Cells) But, Equal in generating Tension

-Smooth Muscle Contractions are very Efficient (But, only use less than 1 % the Energy required by Skeletal Muscle) (because are able to do: Aerobic Pathway)

-possible long periods of contraction (with so little Energy expenditure)

-taking 30 X longer to Contract & Relax vs Skeletal Mus. Smooth Muscle can lengthen more & shorten more than other Types of Muscle

(ANS) Autonomic Nervous System - controls Smooth Muscle Contractions (Sympathetic or Parasympathetic) - different Neurotransmitters are involved 

Both below are under ANS Autonomic Nervous System (involuntary control) (Note: Unitary cannot recruit due to all the Gap Junctions present)

- Unitary Smooth Muscle: - the more common type No Motor Units - cannot do Recruitment (unlike Skeletal Mus.)

- Multi Unit Smooth Muscle: - has Motor Units, therefore can do Recruitment 

Ex. Eye muscles to Pupil / Skin Hair muscles ( Arrector Pili muscles ( Goosebumps) / Large Artery walls / Large Airway walls

 1. Skeletal (move Bones)

2. Smooth (in “guts” & Blood Vessel walls)

3. Cardiac (found only in Heart’s walls)

Muscle Cells have the special ability to Contract (shorten) (based upon: “Sliding Filament Model”)

3 Types of Muscles:

Skeletal (move Bones ) / Smooth (in “guts” & Blood Vessel walls) / Cardiac ( found only in Heart’s walls)) Skeletal Muscle - only one which is Voluntary (under voluntary control) (other two are Involuntary)

- definitely longest of the Muscle Cells (very long & thin, side-by-side)

Skeletal Muscle & Cardiac Muscle - “Striated” muscle These two have tiny stripes seen under the microscope. ( Smooth Mus. - nonstriated) ( due to: special structural & functional units inside these 2 Muscle Cells units called: Sarcomeres)

(Smooth Mus. - no Sarcomeres) Technically, all 3 Muscle Cells are called: Muscle “Fibers” (Note: Cardiac Muscle Cells connect at: Intercalated Discs)

Note: Cardiac Muscle Cells only ones branched Note: Smooth Muscle Cells are short with 2 tapered ends, grouped in Sheets)

Skeletal Muscle Cells have multiple (many) Nuclei (per cell)

(due to developing by fusion of multiple embryonic cells) w

(Note: Nuclei are squeezed out to the perimeter of cell.) 

technical name for any Muscle Cell’s Cell Membrane (Plasma Membrane)

(so, there are 3 different names)

Tubular network inside Muscle Cells (esp. Skeletal Mus. Cells) stores Ca +2 (Calcium ions)

 Comment: Each Skeletal Muscle tends to have one Artery, one Nerve, & Vein(s) near its middle.

(CT) Connective Tissue wrappings whole Skeletal Muscle - composed of a number of Bundles (of the Muscle Cells) called Fascicles

 CT wrapping around the whole Skeletal Muscle

Perimysium

 CT wrapping around each Fascicle ( group of Skeletal Muscle Cells )

Endomysium

CT wrapping around each individual Skeletal Muscle Cell ( within each Fascicle ) 

are opened by: ion movements (including especially: Action Potentials) (Voltage changes)

Voltage - is checking the difference between the over-all charges in two places being considered.

(if no difference .. Voltage is zero)

(especially inside vs outside the Cell Membrane) Comment: can be measured with Voltmeter

Too few Acetylcholine Receptors (destruction by: Autoimmune actions)

Results: Muscle weakness

Very Long Skeletal Muscle Cells (muscle fibers) 

(“drinking straws”)

which are end-to-end Sarcomeres (the Basic Contractile Units of: Skeletal Muscle Cells)

Thin Actin Filaments to touch ends. This shortens the whole Skeletal Muscle Cell due to: shortening each Myofibril by: shortening each Sarcomere

Parts of: the Sarcomeres

Dark A Bands 

Parts of: the Sarcomeres

Light I Bands 

contain: the Thin Actin Filaments only

(Z Disc is in the middle of Light I Band)

(tube-like extension of Sarcolemma (Skeletal Muscle Cell’s Cell Membrane) deep into Cell) 

with: 2 Sarcoplasmic Reticulum Cisterns (storing Ca 2+ ions ( “red marbles” ) ) [released upon arrival of Action Potential down tubule]

Creatine Phosphate (used up right away) - directly Regenerates ATPs

becomes: Creatinine - a waste product goes into blood —> Urine 

 requires Oxygen present in order to enter Mitochondrion after beginning process 

get 30 ATPs per Glucose

 (does not use: Oxygen) so, keeps outside Mitochondrion

(where both Pathways start)

only net 2 ATPs per Glucose

result : 2 Lactic Acid molecules remains of the Glucose 

produced during Skeletal Muscle Contractions

- used to maintain Body Temperature

( shivering - muscle contractions make needed Heat !! )

at least 60 % of the Energy used by Muscles - just produces Heat 

 to get more powerful contraction of Skeletal Muscle Cell

- means: repeated Stimulation (very close together)

maximum sustained: Complete Tetanus

- based upon: Speed of Contraction & whether they mostly use Anaerobic or Aerobic Pathways

Body Skeletal Muscles each have some mixture of all 3 Types: (a Motor Unit – has all same Type)

(1) (SO) Slow Oxidative Mus. Cells

(2) (FO) Fast Oxidative Mus. Cells

(3) (FG) Fast Glycolytic Mus. Cells

 smallest diameter

(SO) Slow Oxidative Mus. Cells

great for Endurance activities

Ex. Marathon

 intermediate diameter 

(FO) Fast Oxidative Mus. Cells

 largest diameter

(FG) Fast Glycolytic Mus. Cells

great for: Quick intense movements

Ex. lifting something / quick sprint (use mostly Anaerobic Pathway)

( old: “Oxygen Debt” )

 excess Oxygen required to restore Body after Exercise

Must Restore Myoglobin Reserves / Glycogen supplies / Creatine Phosphate / ATPs / Lactic Acids

must be converted to: Pyruvic Acids, again Liver: converts any blood: Lactic Acids to: Glucose or Glycogens

unable to contract

( This is Not due to: lack of: ATPs )

Possible Causes: Low Ca 2+ release from Sarcoplasmic Reticulum

Action Potentials (also called: “Neural Impulses”)

[ quick Method of Communication ]

10,000 Terminal Branches

( their Endings are the Boutons ( Axon Terminals ) )

( does not go Retrograde ( back up ) )

leaving the Spinal Cord (lower “Butterfly Wing” = Motor part)

going to different scattered Skeletal Muscle Cells within same Skeletal Muscle

1.) Isometric

2.) Isotonic

3.) Eccentric

Muscle’s Muscle Tension cannot move the Object.

Ex. trying to lift a Truck ( “isometric” = same measure )

Muscle cannot generate enough Muscle Tension to move the Load - so, Muscle does not shorten

( It is still a contraction ) 

Muscle Tension is great enough to move the Object (Muscle shortens (contraction)

( Concentric )

 Sometimes: Muscles contract while lengthening called _____________

Ex. Flexing Elbow with Biceps Brachii (Concentric Contraction) is controlled by: antagonist muscle: Triceps Brachii

one contraction of one Motor Unit’s Skeletal Muscle Cells

Normal Muscle Contractions are Graded Muscle Responses

an environmental change which may elicit a Response

Ex. Motor Neuron stimulates its Cells to contract

a state of almost continuous slight Contraction of the Body’s relaxed Skeletal Muscles

not an active movement

one Somatic Motor Neuron + all its Skeletal Muscle Cells ( 4 or more )

[ may even be hundreds ]

4 Factors Influencing Force of Skeletal Muscle Contraction

( How many Cross Bridges are Forming )

1) How many Skeletal Muscle Cells are actually Stimulated !!! ( Recruitment )

2) Sizes of those specific Skeletal Muscle Cells !! ( Size Principle )

3) How Frequently the Skeletal Muscle Cells are Stimulated !!! ( Wave Summation ( Temporal Summation ) )

4) How Stretched the Skeletal Muscle was at the time it was Stimulated

80 % - 120 % of Resting Length

- generates Greatest Muscle Tension !

is Endurance Exercise )

Ex. Fast Walking / Jogging / Biking / Swimming

is Resistance Exercise

Ex. Weight Lifter ( Comment: Strength, not Stamina is important