Microscopic Anatomy and Physiology of Muscle

Lecture for Exam 2

Muscle fiber of Skeletal Muscle

volunatary, striated

long, mutinucleated cell

visible striations

Immediately Below Sarcolemma

Where is skeletal muscle located?

Sarcolemma

outer cell membrane

Myofibrils

elongated protein strands that skeletal muscle fiber is packed with

Sarcoplasmic Reticulum and Transverse Tubules

What are between the myofibrils of skeletal muscle?

Transverse Tubules

T Tubules

invaginations of sarcolemma

Type 1 Fibers and Type 2 Fibers

What are the two manor types of skeletal muscle fibers?

Type 1 Fibers

satin dark

contract slowly (slow twitch)

can contract for longer perios of time

Myosin Adenisine Triphosphtase

breaks down ATP for energy needed for contraction of skeletal muscle

speed of contraction relates to it

Activity of Myosin ATPase

What is the categorization of the two types of skeletal muscle fibers based on?

Type 2 Fibers

satin light

contract quickly (fast twitch)

more susceptible to fatique

Mitochondria

Endurance of muscles is related to content and activity of the:

I Bands

light zones (bands)

thin filaments only

A Bands

darker regions

overlap of thick and thin filaments

Banding pattern

Alternating A and I bands create a _____ ______ of myofibril.

Sacromere

myofibril between Z line

fundamental unit of contraction in striated muscle

Dense Z Line

bissects each I band

one end of each filament attached to Z line

100s or 1000s

How many myofibrils do each muscle fiber have?

1500

Around how many thick myofilaments does each myofibril have?

Thick Myofilaments

composed of myosin = golf club shaped protein

3000

Around how many thin myofilaments does each myofibril have?

Thin Myofilaments

composed of actin = globular protein

Agranular

Sacroplasmic reticulum is ______, meaning it has no ribosomes.

Sarcoplasmic Reticulum

function in excitation (contraction) coupling

Golgi apparatus, Many Mitochondria, and Glycogen

What are also found in muscle fiber?

T Tubules

continuous with plasma membrane

• extend into the interior of musle fiber (at right angles)

  • at myofibrials and sarcoplasmic reticulum

• propagates action potentials from sarcolemma

  • into interior of muscle fiber = initiate contraction

Hypertrophy

increase in muscle mass

increase in myofibrils and vascularization

Birth

Number of mucscle cells is set at:

Denervation or Neurogenic Atrophy

if nerve supply to a muscle is destroyed, fibers decrease to almost nothing

Sweeney Shoulder of Draft Horses

suprascapular nerve damaged by collar

atrophy of suprasinatus and infraspinatus muscles of shoulder

Skeletal Muscle Contraction

triggered by action potential

iniated by firing a motor neuroon

axom branch terminated in a neuromuscular junction

• near the mid-point of the muscle fiber

Neuromuscular Junction

type of excitatory synapse in skeletal muscle neurons

Acetylcholine 

What does depolarization of motor nerve ending release? 

Nictonic Receptors

After AChieving diffuses across the junction, what does it bind to?

Acetylcholine

ACh

chemical neurotrasmitter

On Muscle Fiber

Where are Nicotine ACh receptors located?

True 

T/F: Action potential of nerve is NOT propagated directly onto the muscle cell 

Na Channels

After ACh diffuses across the junsction and binds to Nicotine receptors, it stimulate opening of ligand-gated:

Into

During excitation, contraction, and relazation, Na rushes ___ the cell leading to membrane depolarization

End-Plate Potential

local depolarization of the sarcolemma at teh neuronmuscular junctiom via ligand-gated Na Channels (ACh binding to Nicotinic Receptors)

change in potential prodices flow of current and therefore….depolarization is usually enough to reach threshold potential of electrically gated Na channels in cell membrane

T-Tubules 

inward continuations of sarcolemma 

action potential travels along tubules throughout the fiber 

Sarcoplasmic Reticulum 

Some T-Tubules pass immediately adjacent to: 

structural link between: 

• a protein in sarcolemma of T Tuble (dihydropryridine receptor) & a membrane protein chennel in SR 

Ca 2+

Channel in SR becomes. permeable to:

because of link between the 2 proteins

SR; sarcoplasma

Ca 2+ concentration within ____ is greater than ____

• 100 fold greater

  • Ca 2+ diffuses into sarcoplasm and into myofibrils

Hyperkalemic Periodic Paralysis (HyPP)

genetic disorder of horses

genetic mutation of a transmembrane protein

electrically gated NA channel is defective

increase permeability to Na → depolarization → involuntary muscle contraction

AKA Impressive Syndrome = AQH sire Impressive

Muscle Spasms, Tremors, Sweating, and Weakness 

What are the clinical signs of HyPP? 

Actin, Tropomyosin, and Troponin

What proteins are thin filaments made up of?

Actin

most prominent, 2 strands wound around each other

Tropomyosin

2 strands wound around each other, and spirals around actin

Troponin 

bound to tropomyosin at specific sites 

together called troponin-tropomyosin complex