Endocrino

Chapter 8

lunes 13 de febrero de 12

Tipos de musculo
✤ Musculo esqueletico: Voluntario
✤ 40 a 50% del peso corporal
✤ Funciones
✤ En su mayoria movimiento de los huesos y otras partes del cuerpo
✤ Estabilizar la posicion del cuerpo
✤ Cardiaco: Involuntario
✤ Solo se encuentra en el corazon
✤ Proporciona presion al flujo sanguineo
✤ Liso:Involuntario
✤ Paredes de organos huecos
✤ Esfinteres: Regulan el flujo en un tubo
✤ Mantener el diametro de un tubo
✤ Mover material en el tracto digestivo y el urinario


Funciones del músculo

✤ Producir movimientos corporales
✤ Estabilizar posiciones corporales
✤ Mover sustancias internamente
✤ Producir calor


Tejido muscular esqueletico

✤ Los músculos están formados por:
✤ Fibras musculares
✤ Tejido conectivo
✤ Epimisio: Envuelve a un músculo completo
✤ Perimisio: Envuelve a un conjunto de ﬁbras musculares
(fascículo)
✤ Endomisio: Envuelve a daca ﬁbra muscular
✤ Nervios
✤ Vasos sanguíneos


Fibra muscular

✤ Fibras musculares: Celulas cilindricas elongadas

✤ Sarcolema: Membrana plasmática de la fibra muscular

✤ Tubulos T (transversos): Tuneles desde la superficie hasta el centro de la fibra.

✤ Cada fibra tiene muchos nucleos cerca de su superficie

✤ Sarcoplasma: Citoplasma de la fibra muscular

✤ Reticulo sarcoplasmico: Reticulo endoplasmico musuclar

✤ Mioglobina: Proteina similar a la hemoglobina que lleva oxigeno al interior del
musculo


Fibra muscular

✤ El reticulo sarcoplasmico almacena iones de calcio
✤ El sarcoplasma contiene mioglobina
✤ A lo largo de la fibra muscular se encuentran las
miofibrillas
✤ Las miofibrillas estan formadas de filamentos de
proteina
✤ Filamentos gruesos
✤ Filamentos finos

Sarcomera

✤ Los filamentos se sobreponen en un patron repetitivo.
✤ Cada unidad estructural se llama sarcomera.
✤ Partes de la sarcomera
✤ Discos Z (linea Z): Division entre sarcomeras
✤ Banda A: Filamentos gruesos y finos.
✤ Zona H: Solo filamentos gruesos
✤ Banda I: Solo filamentos finos

Estructura de los miofilamentos

✤ Filamentos gruesos: Miosina. Tiene cabezas
movibles
✤ Filamentos ﬁnos (anclados a la banda Z)
✤ Actina. Posee los sitios para el anclaje de la
miosina.
✤ Tropomiosina
✤ Troponina

Mecanismo contractil

✤ Durante la contraccion las cabezas de
miosina se unen a la actina
✤ Jalan a los ﬁlamentos ﬁnos y bandas Z
hacia la zona H
✤ Las bandas I y la zonas H se angostan.


Interaccion neuromuscular

✤ Una señal nerviosa desencadena el potencial de
accion.
✤ Neurona motora: Neurona que de lleva la
señal nerviosa hacia la célula muscular.
✤ Una neurona puede activar 1 o más ﬁbras
musculares
✤ Unidad motora: Neurona + Fibras que activa

Union neuromuscular

✤ Union neuromuscular: Union entre la
neurona y la ﬁbra muscular.
✤ Bulbo sinaptico
✤ Libera un neurotransmisor
✤ Hendidura sinpatica: Espacio entre el bulbo
sinaptico y el sarcolema

Action at NMJ

1. Liberacion de acetilcolina (ACh)
2. Difusion por la hendidura sinaptica
3. Activacion de los receptores de ACh
4. Generacion del potencial de accion en
la ﬁbra muscular
5. Degradacion de la ACh

Desencadenantes de la contraccion

✤ Potencial de acción muscular => Liberación de Ca2+ del reticulo sarcoplasmico

✤ El Ca2+ se une a la troponina

✤ Moves tropomyosin off actin sites =>

✤ Myosin binds & starts cycle


Contraction Cycle

✤ Myosin binds to actin & releases phosphate group
(Forming crossbridges)
✤ Crossbridge swivels releasing ADP & shortening
sarcomere (Power stroke)
✤ ATP binds to Myosin => release of myosin from actin
✤ ATP broken down to ADP & Pi => activates myosin
head to bind and start again
✤ Repeats as long as Ca2+ concentration is high

✤ Breakdown of Ach to stop muscle Action potentials

✤ Ca2+ ions transported back into SR lowering concentration=>

✤ This takes ATP

✤ tropomyosin covers actin binding sites


Muscle Tone

✤ Even at rest some motor neuron activity occurs = Muscle Tone

✤ If nerves are cut ﬁber becomes flaccid (very limp)


Metabolism

✤ Rapid changes from very low ATP consumption to high levels of consumption

✤ Creatine phosphate (high energy store)

• Fast & good for ~ 15 sec


✤ Break down glucose to 2 pyruvates getting 2 ATPs

✤ If insufﬁcient mitochondria or oxygen pyruvate => lactic acid

✤ Get about 30-40 seconds more at max.


✤ Production of ATP in mitochondria

✤ Requires oxygen and carbon substrate

✤ Produces CO2 and H2O and heat.


✤ Inability to contract forcefully after prolonged activity

✤ Limiting factors can include:

✤ Ca2+

✤ Creatine Phosphate

✤ Oxygen

✤ Build up of acid

✤ Neuronal failure


✤ Convert lactic acid back to glucose in liver

✤ Resynthesize Creatine Phosphate and ATP

✤ Replace oxygen removed from myoglobin


✤ Single Action Potential(AP) =>twitch
✤ Smaller than maximum muscle force

✤ Total tension of ﬁber depends on frequency
of APs (number/second)
✤ Require wave summation
✤ Maximum = tetanus

✤ Total tension of muscle depends on number
of ﬁbers contracting in unison
✤ Increasing numbers = Motor unit recruitment

✤ Slow oxidative (SO)- small diameter & red
✤ large amounts of myoglobin and mitochondria
✤ ATP production primarily oxidative
✤ Fatigue resistant-

✤ Fast oxidative- glycolytic (FOG)
✤ Large diameter = many myoﬁbrils
✤ Many mitochondria and high glycolytic capacity
✤ Fast glycolytic ﬁbers (FG)
✤ white, fast & powerful and fast fatiguing

✤ Muscle contractions only use the ﬁbers required for the
work

✤ Recruited in order: SO=>FOG=>FG

✤ if force is constant and the muscle shortens = Isotonic
Contraction

✤ If length is constant and the force varies = Isometric
Contraction

✤ The latter is often a postural muscle activity

✤ SO/FG ﬁber ratio genetically determined

✤ High FG => sprinters

✤ High SO=> marathoners

✤ Endurance exercise gives FG=> FOG

✤ Increased diameter and numbers of mitochondria

✤ Strength exercise increases size & strength of
FG ﬁbers

✤ Striated, short ﬁbers and branched

✤ Single central nucleus; Cells joined by gap junctions &
desmosomes

✤ Thickened joint area called intercalated discs

✤ Some cardiac muscles generate own AP-
autorhythmicity

✤ Involuntary


✤ No nerve- internal pacemaker

✤ Ca2+- from S.R. and extracellular space

✤ separate cells with gap junctions -> electrical
connections


✤ Involuntary

✤ In internal organs

✤ Filaments not regular so not striated

✤ Visceral (single unit) type or

✤ Form sheets and are autorhythmic

✤ Contract as a unit!

✤ Multi-unit type-

✤ Graded contractions and slow responses

✤ Often sustain long term tone

✤ Often triggered by autonomic nerves

✤ modulated chemically, nerves, by mechanical events
(stretching)


✤ Like bone there is a slow progressive loss of skeletal muscle
mass

✤ Relative number of SO ﬁbers tends to increase


✤ Move one bone relative to another

• Origin => most stationary end
✤ Location where the tendon attaches

• Insertion => the most mobile end
✤ Location where tendon inserts

✤
Action => the motion or function of the muscle
!


✤ Generally arranged in opposing pairs

✤ Flexors- extensors; abductors- adductors

✤ The major actor = Prime mover or
agonist

✤ The one with opposite effect =
antagonist

✤ Direction relative to body axes
✤ e.g. Lateralis, medialis (medius), intermedius,
rectus

✤ Speciﬁc regions
✤ e.g. abdominus, Brachialis, cleido, oculo-, uro-,

✤ Origin
✤ e.g. biceps, triceps, quadriceps

✤ Shape


✤ Other features

✤ e.g. alba, brevis, longus, magnus, vastus

✤ Actions

✤ e.g. abductor, adductor, ﬂexor, extensor

✤ Speciﬁc references

✤ e.g. Buccinator (trumpeter), Sartorius (like a tailor)


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