MUSCLE Histology SSN October 17, 2005 Presented By: Tabassum Sardharwala & Shannon Watkins

Muscle Types Smooth Involuntary Cardiac Striated Involuntary Skeletal Striated Voluntary Which is Which? Cardiac? Skeletal? Smooth? What other places can “skeletal” muscle be found?

Skeletal Muscle Cross section Endomysium Perimysium Epimysium

Skeletal Muscle Organization Ross Fig 10-3 (p.250, 4 th ed.)

How do Muscles get their Stripes? Light band is the I band = actin only –Actin anchored at the Z disc at center of I band Dark band is the A band = myosin + overlapping actin –Contains H band = myosin only –Myosin anchored at the M line

When Muscles Contract… The A band does NOT change length H and I bands shrink Z discs are drawn closer together Actin & myosin filaments do not actually shorten, they just slide past each other

The Triad Triad = 1 T tubule + 2 terminal cisternae of the sarcoplasmic reticulum There are 2 triads per sarcomere (in skeletal muscle) located at the ends of the A band (A-I junctions) Function- Depolarization of sarcolemma (T tubule) triggers Ca 2+ release from sarcoplasmic reticulum to initiate contraction

Motor End Plates Motor unit = motor nerve + muscle cells it innervates

Other Things to Know Muscle-tendon Junction

Cardiac Muscle Like skeletal muscle, cardiac muscle has: Sarcomeres (striations) T-tubules Calcium regulation at level of thin filaments So what’s different? Lab 7 Slide 13

Cardiac Muscle – Defining Characteristics Lab 7 Slide 14 Intercalated Disks Branching myofibrils Large, central, ovoid nuclei

Intercalated Disks Lab 7 Slide 16 Also, T Tubules and SR arranged in a diad, not triad

Which is which? Cardiac Skeletal

Lab 7. Slide 15. Lab 17. Slide 10. Which is which? Cardiac Skeletal

Smooth Muscle Located in blood vessels, ducts, and here, in the GI tract. (This is the colon.) Lab 7 Slide 17

Smooth Muscle Longitudinal section Cross Section ? Myenteric Ganglion

A Closer Look Elongated nuclei Indistinct boundaries (w/ H&E) Wrinkled nuclei Centrally located nuclei Lab 7 Slide19

Smooth Muscle Cardiac Muscle

Smooth Muscle vs. CT Lab 4. Slide 16. Smooth Muscle Darker Staining Nuclei within fibers Wrinkled nuclei DIACT Lighter Staining Fewer nuclei, outside fibers

Smooth Muscle v. CT Smooth MuscleDRACT

Silver Stain Clear Basal Lamina Lab 7 Slide 23

A Closer Look – Why the “Dotted Lines”? Interrupted basal lamina due to GAP JUNCTIONS Ensure coordination during contraction Lab 7 Slide 24

What Muscle?? Smooth Skeletal Lab 17. Slide 14 Nerve Esophagus – Where Smooth and Skeletal Muscle Combine

1. A B

2.

3. A B CD

4.

5.