endocrino

Chapter 8

lunes 13 de febrero de 12

✤ 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

Tipos de musculo


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

Funciones del músculo


✤ 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

Tejido muscular esqueletico


✤ 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

Fibra muscular


✤ 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

Sarcomera


✤ 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

Estructura de los miofilamentos


✤ 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.

Mecanismo contractil


✤ 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

Interaccion 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

Union neuromuscular


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

Action at NMJ


✤ 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

Desencadenantes de la contraccion


✤ 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

Contraction Cycle


✤ Breakdown of Ach to stop muscle Action potentials

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

✤ This takes ATP

✤ tropomyosin covers actin binding sites


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

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

Muscle Tone


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

✤ Creatine phosphate (high energy store)

• Fast & good for ~ 15 sec

Metabolism


✤ 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- lunes 13 de febrero de 12

✤ 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)


endocrino

Health & Medicine