Muscle Tissue & Microscopic Anatomy – Lecture Review

Introduction & Exam Logistics

• Lecture delivered via video walkthrough of the “Muscle Models in Order” PowerPoint.
• During testing you will see:
  • Static photos of 3-D plastic models.
  • Histology (microscope) slides.
  • A red or blue circle will indicate the structure you must name (e.g.
    circle on subscapularis → answer “subscapularis”).
• All review items come directly from the Lab Muscle List (categories A–E, etc.).
  ✱ Models and textbook pictures often contain extra muscles—ignore any structure not on the list.
• PowerPoint files (without video) are posted on Blackboard for self-study.
• Pointer colors may change (black, blue, or arrow) but pictures are unlabeled. Focus on anatomy, not labels in the video.

Naming Conventions & Common Pitfalls

• Always write the muscle name, not the bone name.
  • Example: Muscle = frontalis (located on frontal bone). Writing “frontal” earns zero credit.
• Spellings must match the muscle list exactly.

Histology Slides — Muscle Tissue Types

1. Skeletal Muscle (Voluntary, Striated)

• Identifying features:
  • Long, unbranched fibers extending the full field of view → one fiber = one cell.
  • Multiple peripheral nuclei.
  • Strong stripes (striations) produced by \text{actin} & \text{myosin} alignment.
• Keywords: striated, voluntary, multinucleate, actin & myosin.

2. Cardiac Muscle (Involuntary, Striated)

• Shorter, branched cells; each cell possesses one central nucleus.
• Intercalated discs (dark transverse lines) connect adjacent cells and synchronize contraction.
• Striations still visible (actin & myosin).
• Keywords: involuntary, striated, intercalated discs, single nucleus.

3. Smooth Muscle (Involuntary, Non-Striated)

• Spindle-shaped (fusiform) cells: thick in the middle, taper at ends.
• Single, centrally located nucleus.
• No striations.
• Location example: tunica media of an artery & veins (model shows one artery flanked by two veins; the smooth-muscle layer is highlighted).
• Keywords: non-striated, spindle cells, single nucleus, vessel wall, involuntary.

Gross & Microscopic Organization of a Whole Muscle

• Entire muscle belly wrapped in epimysium (dense irregular CT).
• Muscle is subdivided into fascicles (visible bundles) surrounded by perimysium.
• Each individual muscle fiber (cell) within a fascicle is wrapped by endomysium.
• The three layers converge distally to form a tendon (dense regular CT) which merges with the bone’s periosteum.

Muscle Fiber (Cell) Anatomy

• Plasma membrane = sarcolemma (blue on model).
• Cytoplasm = sarcoplasm (not labeled on model, but surrounds organelles).
• Myofibrils: Cylindrical contractile elements running the full length of the fiber; appear as • dots in cross-section.
• Surrounding each myofibril:
  • Sarcoplasmic reticulum (SR) – modified smooth ER that stores Ca^{2+}.
    • Appears as a turquoise/blue network (“reticulum”).
  • Transverse tubules (T-tubules) – yellow tubular invaginations of sarcolemma that carry the action potential deep into the cell.
• Mitochondria – supply ATP; scattered between myofibrils.
• Nuclei – pressed just beneath sarcolemma.
• Motor neuron axon terminal (on model) represents the neuromuscular junction—detailed physiology covered later in Chapter 10.

Sarcomere Anatomy & Banding Pattern

A single sarcomere extends Z disc → Z disc.

• Z Disc: Zig-zag protein plate anchoring thin filaments; defines sarcomere boundaries.
• Thin Filaments = \text{actin} (plus troponin & tropomyosin).
• Thick Filaments = \text{myosin}.

Band names & mnemonics

Visual model tips:

• Pale zones = I Bands; dark central region = A Band.
• Multiple sarcomeres are aligned end-to-end in every myofibril → stripes visible at tissue level create skeletal & cardiac striations.

3-D Plastic Models Highlighted in Class

• Single-fiber model shows:
  • Endomysium (outermost white layer).
  • Sarcolemma beneath endomysium.
  • Myofibrils (tubes) + labeled sarcomeres.
  • Neuron sitting on sarcolemma at a motor end plate.
• Sarcomere cut-away model:
  • Removable sheath illustrates SR (blue-green network) & T-tubules (yellow), both wrapping all myofibrils.

Quick Reference – Key Terms to Master (Lab List)

• Tissue types: skeletal, cardiac, smooth.
• Cell structures: sarcolemma, sarcoplasm, nucleus, mitochondria, myofibril.
• CT sheaths: endomysium, perimysium, epimysium, tendon, periosteum.
• Sarcomere parts: Z disc, I band, A band, H zone, M line, zone of overlap, thin filament, thick filament.
• Additional cardiac-specific: intercalated discs.
• Additional fiber-specific: sarcoplasmic reticulum, transverse (T) tubules, fascicle, axon terminal (motor neuron).

Study & Test-Taking Reminders

• Practice by covering labels and verbally naming structures in every model picture.
• Relate histology slides to 3-D models: banding on model = striations on microscope.
• Use mnemonics for band names: lIght → I; dArk → A.
• Re-watch Chapter 10 PowerPoint for detailed physiology (calcium handling, sliding filament theory) – not fully covered in this video.

These bullet-point notes capture every structure, definition, and hint provided in the transcript, enabling effective review without replaying the video.