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Muscles and Muscle Tissues
Chapter 9
28
Anatomy
Undergraduate 1
07/07/2011

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Term
muscle fiber
Definition
skeletal/smooth muscle cell
Term
myofilaments
Definition

contractile units of muscle

*5 different types:

o   Actin filaments (composed of actin)

o   Myosin filaments (composed of myosin)

o   Sarcolemma: plasma membrane

o   Sarcoplasm: cytoplasm

o   Sarcoplasmic reticulum: ER

Term
muscle tissue characteristics
Definition

·      Excitable: receive and respond to stimuli

·      Contractile: shorten forcibly when adequately stimulated

·      Extensible: can be stretched out

·      Elastic: can recoil after being stretched

Term

skeletal muscle 

organization

Definition

 

muscle -> fascicle -> muscle fiber (cell) 

Term

skeletal muscle:

connective tissue sheaths

Definition

o   Endomysium: surrounds each muscle fiber

o   Perimysium: surrounds each fascicle (bundle of muscle fibers)

o   Epimysium: surrounds entire muscle  

 

*sarcolemma is deep to endomysium                 

 

 

 

 

 

 

 

 

Term

skeletal muscle:

nerve and blood supply

Definition
each muscle served by 1 nerve, 1 artery, an 1 or more veins that enter/exit near center of muscle
Term

skeletal muscle 

attachments

Definition

*insertion: end of muscle attached to bone that moves

*origin: end of muscle attached to bone that moves less

 

-Note: most muscles attache to bone, cartilage, or other muscles by tendons (cord-like) or aponeuroses (flat)

Term
muscle cell contains:
Definition

o   Sarcoplasm

o   multiple nuclei

o   glycosomes (glycogen storing granules)

o   Mitochondria (supply ATP)

o   Myoglobin (red pigment; stores Oxygen)

o   Myofibrils

o   Sarcoplasmic reticulum

o   T tubules

Term
myofibrils
Definition

-extends lengths of muscles

-takes up 80% of muscle cell

-composed of sarcomeres (repeating units)

-contain actin and myosin myofilaments

Term

Actin Myofilaments

 

Definition


o   Thin filaments composed of:

-  2 strands of round actin subunits

-2 regulatory proteins: tropomyosin and troponin

Term
myosin myofilaments
Definition

o   Thick filaments composed of:

*  Bundles of myosin molecules

-  Each myosin molecule has a rod-like tail and two globular heads

*Arrangement of actin and myosin filaments give fibers their “striated” appearance.

* I-bands: light regions

-contain actin filaments only and Z discs (anchors actin filaments)

*A-bands: dark regions

-  contains Actin and myosin filaments [h zone has myosin only] and M line (anchors myosin filaments)

 

Term
skeletal muscle fiber contraction
Definition

                                               i.     Each fiber (cell) is innervated by 1 motor neuron

                                              ii.     each motor neuron innervates several fibers.

·      Region where axon terminal of motor neuron comes into close contact with muscle cell is neuromuscular junction.

·      Resting muscle cells are polarized (interior of cell negative in relation to outside of cell)

·      **fiber is a cell**

Term
phase 1 of muscle fiber
Definition

·      ACh receptors are chemically gated Na+/K+ ion channels

·      More Na+ enders than K+ exits ->causes a local depolarization (interior of cell becomes positive)

·      If local depolarization is strong enough, voltage-gated Na+ channels open ->  further depolarizes sarcolemma

->initiates on action potential.

·      action potential propagated along sarcolemma

Term
phase 2 of muscle fiber
Definition

excitation: contraction coupling

·      Action potential propagates along sarcolemma and down T tubules

·      Triggers sarcoplasmic reticulum to dump Ca2+ into sarcoplasm.

·      Ca2+ bind to troponins -> shifts tropomuyosin stands exposing active sites on actin.

·      cocked myosin heads attach to active sites forming cross bridges.

Term
cross bridge cycle
Definition
  1.   cross bridge formation

  2. the power (working) stroke

3. cross bridge detachment

4. cocking of myosin head

 

 

 

 

 

 

 

Term
cross bridge cycle results in...
Definition
myosin heads pulling thin actin filaments toward center of sarcomere
Term
what stops cross bridge formation?
Definition

o   motor neuron stops stimulating muscle fiber

o   Ach remaining in synaptic cleft Is degraded by acetylcholinesterase.

o   dumped Ca2+ is pumped back in to sarcoplasmic reticulum

o   lack of ca2+ blocks myosin binding sites on actin (tropomyosin re-covers active sites on actin)

o   muscle cell relaxes.

**  (Mentally learn how to judge and react.)

Term
Muscle contraction on Organ level
Definition

·      Each muscle supplied by1 or more nerves (bundle of neurons).

·      each motor neuron stimulates many muscle fibers (4à several hundred/motor unit).

·      muscle fibers of a motor unit are spread throughout entire muscle

·      stimulation of a single motor neuron causes weak contraction of entire muscle

Term
muscle twitch
Definition

o   Response of 1 motor unit to a single stimulus.

o   3 distinct phases:

- Latent period: time between application of stimulus and start of contraction

-  Contraction: cross bridge cycle; muscle tension increases

-relaxation: SP reabsorbs Ca 2+ from sarcoplasm; muscle tension decreases

Term
graded muscle response
Definition

o   varying muscle contraction depending on demand.

o   achieved by altering either frequency of stimulus or strength of stimulus

o   Changes in stimulus frequency

-  applying multiple stimuli causes wave summation (successively stronger contractions)

-  partial relaxation between contractions (unfused tetanus)

o   Changes in stimulus strength

-Increasing Strength of stimulus increases the force of muscle contraction

- force increases because a greater number of motor units are stimulated [recruitment]

Term
recruitment is regulated by Size Principle
Definition
-motor unit with small fibers activated 1st; those with medium fibers activated next; then lastly the large fibers are activated
Term

Isotonic vs. Isometric 

Contractions

 

Definition

Isotonic: ("same tension") muscle length changes to move blood

-ex: all jumping & throwing activities

Isometric: ("same length") muscle neither shortens nor lengthens [load is too heavy]; hoever internal tension increases.

-ex: trying to lift a piano; the increase in tension just before a muscle moves

 

Term
muscle metabolism
Definition

o   stores only 4-6 seconds worth of ATP

o   makes ATP in 3 ways (1. Direct phosphorylation of ADP via creatine phosphate.

o   lactic acid fermentation (anaerobic respiration)

o   Aerobic respiration

Term
Aerobic respiration
Definition

-  Activities require a surge of power for a few seconds (diving, weight lifting, etc) rely on ATP and creatine phosphate stores.

- activities requiring burst-like activities (tennis, soccer etc) reply on lactic acid fermentation

-activities requiring endurance (marathon running, jogging, etc) rely on aerobic respiration

Term

Aerobic (endurance) exercise

 

Definition

-increases number of mitochondria and capillaries in muscles

-increases synthesis of myoglobin (allows muscles to store oxygen)

-results in increase efficiency, greater endurance, strength, & resistance to fatigue

Term
Resistance Exercise
Definition

-increase in size of muscle fibers

-increase in # of mitochondria & glycogen storage

-results in increase muscle strength and definition

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