Histology of Muscle Tissue Lesson 

Lesson Overview

• What Are the Types of Muscle Tissue?
• What Are the Different Skeletal Muscle Fiber Types?
• What Structures Make Up the Muscle Fiber?
• How Are Sarcomeres Organized?
• What Connective Tissues Wrap Muscles?
• How Do Nerves Communicate with Muscle Fibers?
• What Role Do Satellite Cells Play?
• Final Recap
• Key Takeaway

Why do sprinters build power quickly while marathoners run for hours? The answer lies in the microscopic world of muscle tissue histology-a key field in understanding muscle structure and function.

This lesson dives into the types of muscle tissue, skeletal muscle fiber types, muscle anatomy, and functional aspects, preparing you for quiz success and deeper comprehension.

What Are the Types of Muscle Tissue?

Skeletal Muscle

• Voluntary control, multinucleated, striated, long cylindrical fibers
  
• Found in limbs, tongue, diaphragm, etc.
  
• Striations from organized sarcomeres
  

Cardiac Muscle

• Found only in the heart (myocardium)
  
• Involuntary, single/bi-nucleated, striated, branched fibers
  
• Connected via intercalated discs
  

Smooth Muscle

• Involuntary, non-striated, spindle-shaped, single nucleus
  
• Located in blood vessels, digestive tract, viscera
  

Which muscles have cross-striations? → Skeletal & Cardiac
Memory Tip: S & C = Striated; Smooth = Soft/Spindle/Stretchy (No Stripes)

What Are the Different Skeletal Muscle Fiber Types?

Muscle fibers differ based on contraction speed, color, energy source, and fatigue resistance. These differences matter both functionally and histologically.

Red Fibers (Type I, Slow-Twitch)

• High myoglobin, aerobic metabolism, many mitochondria
  
• Fatigue-resistant, smaller diameter
  
• Ideal for endurance (e.g., postural muscles)
  

White Fibers (Type II, Fast-Twitch)

• Low myoglobin, anaerobic metabolism, fewer mitochondria
  
• Fatigue quickly, larger diameter
  
• Suitable for short bursts (e.g., sprinters, weightlifters)
  

Intermediate Fibers (Type IIa)

• Mixed properties
  
• Moderate fatigue resistance, mitochondrial density
  

• Which fiber is more fatigue-resistant? → Red
  
• Which uses glycogen as a primary energy source? → White
  
• Which fiber predominates in Lance Armstrong's legs? → Red
  
• In Charles Atlas (weightlifter)? → White
  

What Structures Make Up the Muscle Fiber?

From Cell to Filaments

Clues:

• What is myosin? → Thick myofilament
  
• What are thin filaments made of? → Actin (myofilaments)
  
• What is the plasma membrane called? → Sarcolemma
  

How Are Sarcomeres Organized?

Muscle striations are due to sarcomere banding. Understanding this is key to histology.

Banding Structure

Quick Recap:

• Z to Z = one sarcomere
  
• H zone bisects A band (dark)
  
• Z line bisects I band (light)
  
• 6 thin filaments surround 1 thick filament in cross-section
  

Diagram

• What bisects the A band? → H zone
  
• What bisects the I band? → Z line
  
• Region with only thin filaments? → I band
  
• Number of thin filaments around thick? → 6
  

Take This Quiz:

What Connective Tissues Wrap Muscles?

Three Layers of Connective Tissue:

Cross-check:

• Outer covering of a muscle? → Epimysium
  
• Wraps around fascicles? → Perimysium
  
• Around individual muscle fibers? → Endomysium
  

How Do Nerves Communicate with Muscle Fibers?

Neuromuscular Junction (NMJ)

• Motor Neuron: Nerve cell stimulating muscle
  
• Motor Unit: One motor neuron + all fibers it innervates
  
• Motor End Plate: Specialized muscle region for nerve contact
  
• Neurotransmitter: Acetylcholine (ACh) released into synaptic cleft
  

Key Point: At NMJ, neurotransmitter is released.
What is released at a synapse? → Neurotransmitter

Muscle Spindle

• Stretch-sensitive receptor
  
• Detects changes in muscle length
  

Not part of contraction, but key in reflex control

What Role Do Satellite Cells Play?

Muscle Regeneration

• Satellite Cells: Resting cells located on individual muscle fibers
  
• Contain centrioles → can divide & repair fibers
  
• Activated by injury or exercise
  
• Aid in growth & regeneration
  

Quiz Match:

• Where are satellite cells located? → On individual muscle fibers
  

Final Recap

Key Takeaway

Understanding the histology of muscle tissue reveals why our muscles perform the way they do-whether it's maintaining posture or powering a sprint. This 2000-word lesson has covered the types of muscle, fiber specializations, structural anatomy, neuromuscular control, and muscle regeneration.

Take This Quiz: