Músculo Esquelético

Músculo Esquelético

Alejandro David Maciel Moguel

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Orden del día

1) Situación Actual

2) ​Introducción

3) Fibra Muscular

4) Miofibrillas

5) Sarcómera

6) Contracción

7) Examen

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​Músculo

La función primaria del músculo es generar fuerza o movimiento en respuesta a un estímulo fisiológico.

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En el cuerpo humano tenemos 3 tipos de músculo dependiendo de su especialización. ​

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​Músculo

Estriado - En este músculo, las células exhiben estriaciones transversales visibles con el microscopio electrónico.

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Liso - En este músculo, no se presentan estriaciones transversales.

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​Músculo Estriado

Esquelético - Se fija al hueso y es responsable del movimiento de esqueleto axial y perpendicular, además, de los músculos esqueléticos del ojo.

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Estriado Visceral - Morfológicamente idéntico al esquelético pero restringido a tejidos blandos: lengua, faringe, parte lumbar del diafragma y parte superior del esófago.

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​Músculo Estriado

Cardiaco - Se encuentra en la pared del corazón y la desembocadura de las venas grandes que llegan.

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​Músculo Liso

No presentan estriaciones transversales

​

• ​Vísceras

• ​Sistema Vascular

• ​Músculos erectores del pelo

• ​Músculos Intrísecos

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Tipos de Fibras

​Clasificación de fibras esqueléticas

Fibras ROJAS - Son fibras musculares de contracción lenta, por ejemplo los músculos de la espalda (antigravedad)

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Fibras BLANCAS - Son fibras musculares de contracción rápida, por ejemplo los músculos extra-oculares​

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Tipos de Fibras

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Proteína globular fijadora de oxígeno, contiene una forma ferrosa de hierro Fe+

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La función principal es almacenar el oxígeno, esto es una fuente eficaz para el metabolismo celular

. ​

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Mioglobina

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Proteína globular fijadora de oxígeno, contiene una forma ferrosa de hierro Fe+

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La función principal es almacenar el oxígeno, esto es una fuente eficaz para el metabolismo celular

. ​

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De menor a mayor

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La unidad más pequeña y contractil de músculo esquelético es multinucleada y elongada, se denomina FIBRA MUSCULAR o MIOFIBRA que se encuentra formada por MIOFIBRILLAS

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Las fibras musculares ordenadas formarán un FASCÍCULO.

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Un grupo de fascículos forma un MÚSCULO ​

Rodeado de TC

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El endomisio rodea a las fibras musculares.

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El perimisio rodea ​a los fascículos

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El epimisio rodea al músculo iniciando por el tendón ​

​​Transverso

1. Núcleos en periferia​

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​​Longitudinal

1. Núcleos en periferia​

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Endomisio

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Perimisio

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Epimisio ​

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​TC rodeando al músculo

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Debajo de el endomisio y rodeando cada fibra muscular se encuentra la membrana plasmática que en el músculo se denomina sarcolema.

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​Fibra Muscular

​

Fibra muscular

​Miofibrilla

Cada célula muscular contiene una gran densidad de elementos cilíndricos ordenados de forma paralela denominadas miofribrilla.

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Cada miofibrilla es basicamente ​la repetición de extremo a extremo de unidades repetidas denominadas sarcomeras.​

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Las sarcomeras estan compuestas de pequeños filamentos sobrepuestos denominados miofilamentos, que contiene filamentos delgados y gruesos.

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​Fibra Muscular

​

Esta compuesta por miofilamentos:

Gruesos - Compuestos principalmente por MIOSINA

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Fino - Compuestos principalmente por ACTINA ​

Sarcómera

Los filamentos gruesos están compuestos de múltiples moléculas de Miosina II. una compleja red de proteínas, es un hexámero formado por dos cadenas ligeras y dos cadenas pesada

Miosina

GRUESO​

Los filamentos delgados es un hélice de doble hebra de moléculas de Actina esta se denomima actina FILAMENTOSA o Actina F

Actina

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Filamento

Fino​

El filamento fino muscular resulta de la asociación de la ACTINA F + DOS PROTEINAS DE UNIÓN A ACTINA REGULADORAS:TROPOMIOSINA Y COMPLEJO DE TROPONINA

Tropomiosina​

Proteína alfa que consta de 7 pseudorepeticiones esto le da la característica espiral.

Es un dímero

Pasa en el surco de la ​Actina F

Complejo

Troponina​

TROPONINA T (TnT) -Se une a la molécula de tropomiosina

TROPONINA C (TnC) -Se une al calcio​

TROPONINA I (TnI) -Se une a la actina e INHIBE contracción

Multiple Choice

Cardiac troponin I is one of the most specifi c

biomarkers for detection of acute myocardial infarction

(AMI). Which of the following is true about the

protein?

• Binds the troponin complex to tropomyosin

• Binds to calcium and initiates contraction

• Binds to actin, inhibiting interaction of myosin

  and actin in the resting muscle cell

• Binds to myosin, inhibiting interaction of myosin

  and actin in the resting muscle cell

Sarcómero

​Unidad repetitiva entre dos discos o líneas Z

La Z es de ZWISCHENSCHEIBE que significa placa intermedia.

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El extremo positivo de ​​los filamentos finos se unen al disco Z.

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​ORGANIZACIÓN Y SOPORTE​

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Proteína que pertenece a la familia de las espectrinas de proteínas de unión a la actina

​​Alfa-Actinina

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Va de la línea Z a la línea M, es parte de un filamento elástico.

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Ayuda ​al anclaje de las fibras gruesas a los discos Z

​​​​Titina

Va de la línea Z y a lo largo de los filamentos de actina, controla la longitud de los filamentos finos.

​​Nebulina

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Sarcómero

​Bandas Claras o I (Isotrópicas)

Representan regiones ​de filamento FINO que NO se solapan con los filamentos gruesos.

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BANDAS I de fIno

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Las bandas Z estan dentro de esta zona clara​

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Sarcómero

​Bandas Obscuras o A (Anisotrópicas)

Representan regiones ​de filamento GRUESO y DELGADO.

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Dentro de la banda A se encuentra:

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Banda H (Heller / brillante) - SOLAMENTE FILAMENTOS GRUESOS

Banda M (Mittel / centro) - Titina, Miomesina, Obscurina, etc...​

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Multiple Choice

A first-year-medical student is leading her group for

a muscle histology study session. She has chosen the

accompanying image as a comprehensive guide for

the subject and has prepared the following questions

for the group.

Which of the following might be the source for

this tissue?

• Esophagus

• Stomach

• Lungs

• Heart

• Kidneys

Multiple Choice

A first-year-medical student is leading her group for

a muscle histology study session. She has chosen the

accompanying image as a comprehensive guide for

the subject and has prepared the following questions

for the group.

Which of the following proteins is directly

attached to structure 1?

• Actin

• Myosin

• Titin

• Actin and Myosin

• Actin and Titin

Multiple Choice

A first-year-medical student is leading her group for

a muscle histology study session. She has chosen the

accompanying image as a comprehensive guide for

the subject and has prepared the following questions

for the group.

Which of the following is true for structure 2?

• Defines the contractile unit for the tissue

• Is the seat for the enzyme creatine kinase

• Comprises an overlap between actin and myosin

  filaments

• Shortens during muscular contraction

• Length is unaltered during muscular contraction

Multiple Choice

A first-year-medical student is leading her group for

a muscle histology study session. She has chosen the

accompanying image as a comprehensive guide for

the subject and has prepared the following questions

for the group.

Which of the following is true for structure 3?

• Defines the contractile unit for the tissue

• Defined by the width of myosin filaments

• Defined by the width of actin filaments

• Is the seat for the enzyme α-actinin

• Comprises the intermediate filament desmin

Multiple Choice

A first-year-medical student is leading her group for

a muscle histology study session. She has chosen the

accompanying image as a comprehensive guide for

the subject and has prepared the following questions

for the group.

Which of the following is true for structure 4?

• Defines the contractile unit for the tissue

• Provides attachment for titin

• Is the seat for the enzyme creatine kinase

• Is the seat for the enzyme α-actinin

• Comprises the intermediate filament desmin

Multiple Choice

A first-year-medical student is leading her group for

a muscle histology study session. She has chosen the

accompanying image as a comprehensive guide for

the subject and has prepared the following questions

for the group.

A researcher develops antibodies against actin.

Which of the following sites would most likely be

spared from the action of such antibody?

• Structure 1

• Structure 2

• Structure 3

• Structure 4

Rodeando los haces de miofilamentos se encuentra el retículo endoplasmático liso que en el músculo se denomina retículo sarcoplásmico.

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​Fibra Muscular

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Los potenciales de acción se propagan a lo largo de la membrana superficial de las fibras y penetran al interior de la célula por invaginaciones cilíndricas llamados Túbulos Transversos o Túbulos T

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​Despolarización

​

Rodean a las miofibrillas en dos puntos:

• ​Uniones A-I

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A lo ​largo de su longitud el túbulo se asocia con dos cisternas terminales: retículo sarcoplásmico.

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​Túbulos T

​

• Canal de Calcio tipo L

• Canal de liberación de Calcio​

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​Despolarización

Contracción del Músculo

​Son 6 pasos

El ciclo siempre inicia con la ausencia de ATP

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La miosina se encuentra unida a la actina

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"Rigor Mortis"​

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​UNIÓN DEL ATP

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​Se da la unión del ATP a la molécula de miosina por lo que reduce la actividad por la actina.

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​Músculo Relajado​

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​Paso 1

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​Paso 2

​HIDRÓLISIS DEL ATP

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Degradación de ATP a ADP en cabeza de miosina causando que recueste mas la cabeza, esto provoca que recorra don monómeros de actina

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​Músculo Relajado​

​ENTRECRUZAMIENTO DÉBIL

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​La miosina se une de forma débil a una nueva posición de actina

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​Paso 3

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​Paso 4

​LIBERACIÓN DE P DE MIOSINA

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Al disociarse el P de la cabeza de miosina provoca nuevamente una unión fuerte entre actina y miosina.

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​GOLPE DE FUERZA

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El cuello de la miosina rota mientras esta unido a la actina.

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La rotación causa (11 nm)

1. ​Tracción de cuerpo de miosina a la izq

2. Tracción de actina

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​Paso 5

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​Paso 6

​LIBERACIÓN DE ADP

​​​

​La liberación del ADP deja nuevamente un estado rígido, hasta nueva molécula de ATP se inicia el ciclo.

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Multiple Choice

Consider the following events: (1) Detachment

of troponin I from actin; (2) Binding of myosin

heads to actin fi laments; (3) Binding of calcium to

troponin C; (4) ADP on myosin head replaced by ATP;

(5) Splitting of ATP into ADP and Pi.

Which of the following would be the correct order

for these events to occur, following depolarization of

the postsynaptic membranes, for skeletal muscles to

contract?

• 1, 2, 3, 4, 5

• 1, 3, 2, 4, 5

• 2, 1, 3, 5, 4

• 3, 1, 2, 5, 4

• 2, 1, 3, 5, 4

Multiple Choice

Length of sarcomeres in human striated muscles

infl uence the force that can be exerted by the muscle.

A length-tension curve for gastrocnemius revealed

resting length for the I-band to be 1.5 μm and for the

A-band to be 2.0 μm. Contraction of the muscle fi ber

resulted in 10% shortening of the sarcomere length.

Which of the following is the resting length for

the sarcomere?

• 4 μm

• 3.5 μm

• 2.75 μm

• 2 μm

• 1.5 μm

Multiple Choice

Length of sarcomeres in human striated muscles

infl uence the force that can be exerted by the muscle.

A length-tension curve for gastrocnemius revealed

resting length for the I-band to be 1.5 μm and for the

A-band to be 2.0 μm. Contraction of the muscle fi ber

resulted in 10% shortening of the sarcomere length.

Which of the following is the length of the

A-band after the shortening produced during muscle

contraction?

• 2 μm

• 1.8 μm

• 1.7 μm

• 1.6 μm

• 1.5 μm

Multiple Choice

Length of sarcomeres in human striated muscles

infl uence the force that can be exerted by the muscle.

A length-tension curve for gastrocnemius revealed

resting length for the I-band to be 1.5 μm and for the

A-band to be 2.0 μm. Contraction of the muscle fi ber

resulted in 10% shortening of the sarcomere length.

Which of the following is the length of the

I-band after the shortening produced during muscle

contraction?

• 1.5 μm

• 1.45 μm

• 1.35 μm

• 1.25 μm

• 1.2 μm

Multiple Choice

Length of sarcomeres in human striated muscles

infl uence the force that can be exerted by the muscle.

A length-tension curve for gastrocnemius revealed

resting length for the I-band to be 1.5 μm and for the

A-band to be 2.0 μm. Contraction of the muscle fi ber

resulted in 10% shortening of the sarcomere length.

Which of the following is the fate of the H-band

after the shortening produced during muscle

contraction?

• Lengthens slightly

• Doubles its length

• Shortens slightly

• Halves its length

• Almost disappears

Multiple Choice

Which of the following helps spread depolarization

of muscle cell membranes throughout the

interior of muscle cells?

• Actin

• Myosin

• Troponin

• T Tubules

• Microtubules

​Unión Neuromuscular

Una motoneurona inerva de 1 a 5 fibras musculares (unidad motora pequeña) o incluso 150 (unidad motora grande).

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Unidad Motora - ​Unidad Funcional

​​Inervación

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Fasciculaciones (Contracciones pequeñas irregulares) por presencia de ACh del axón denervado.

​​Denervación

​

Las células musculares vienen de los rabdomioblastos.

​

Las células musculares no entran en mitosis, se regeneran de ​células satélites.

​​Regeneración

​

A 23-year-old girl was forced to pull her car over due

to sudden blurring of vision. Soon after, she had trouble

speaking when interrogated by a law enforcement

officer. In the ER, she complained of nausea, had difficulty

in swallowing fluids, and had trouble breathing.

Her parents could not recall any recent health

upsets for her, though they reported her spending

the previous week on a farm with her grandparents.

Her grandmother is famous in the neighborhood for

home-canned vegetables and fruits that she grows

on her farm. Physical examination revealed diplopia,

dysarthria, dysphonia, bilateral ptosis and facial

paralysis, and impaired gag reflex. Protein levels in

her cerebrospinal fluid were normal.

Multiple Choice

Which of the following is the most probable

diagnosis for her?

• Guillain-Barré syndrome

• Myasthenia gravis

• Stroke affecting the genu of the left internal

  capsule

• Botulism

• Lambert-Eaton myasthenic syndrome

Multiple Choice

Which of the following is the most probable

pathology in her case?

• Deficient synthesis of acetylcholine

• Deficient calcium ion entry into the axon

  terminal

• Deficient release of acetylcholine in

  neuromuscular junction

• Deficient transport of acetylcholine from cell

  body to axon terminal

• Reduced number of available acetylcholine

  receptors in the postsynaptic membrane

A 26-year-old woman complains that her “jaw gets

tired” as she chews and that swallowing has become

diffi cult. She also has blurring of vision that has

worsened over the past month. Physical examination

revealed diplopia, dysarthria, bilateral ptosis and

facial paralysis, and impaired gag refl ex. Her symptoms

were reversed within 40 seconds of intravenous

administration of edrophonium.

Multiple Choice

Which of the following is the most probable

diagnosis for her?

• Guillain-Barré syndrome

• Myasthenia gravis

• Stroke affecting the genu of the left internal

  capsule

• Botulism

• Lambert-Eaton myasthenic syndrome

Multiple Choice

Which of the following is the most probable

pathology in her case?

• Deficient synthesis of acetylcholine

• Deficient calcium ion entry into the axon

  terminal

• Deficient release of acetylcholine in

  neuromuscular junction

• Deficient transport of acetylcholine from cell

  body to axon terminal

• Reduced number of available acetylcholine

  receptors in the postsynaptic membrane

A male neonate was born with generalized hypotonia.

Deep tendon refl exes were absent. Tongue fasciculation

was observed. A skeletal muscle biopsy is

seen in the fi gure.

Multiple Choice

From where within the sarcomere is the section

taken?

• A-band

• I-band

• M line

• Z disk

• H-band

Multiple Choice

Which of the following is the function of

structure 1?

• Sequestration of enzyme that cross-links actin

• Sequestration of enzymes that cross-links myosin

• Sequestration of calcium during muscle relaxation

• Sequestration of calcium during muscle contraction

• Sequestration of sodium during muscle relaxation

​Dudas o Comentarios.....