MUSCLE

Histology SSNOctober 17, 2005

Presented By:Tabassum Sardharwala & Shannon Watkins

Muscle Types

Smooth•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, 4th 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 Ca2+ release from sarcoplasmic reticulum to initiate contraction

Motor End Plates

Motor unit = motor nerve + muscle cells it innervates

Other Things to KnowMuscle-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?

CardiacSkeletal

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 Muscle DRACT

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.

AB

2.

3.

A

B

C D

4.

5.