Lecture 6: Muscle Histology

Question 1

What are the key morphological features of skeletal muscles

Answer 1

Skeletal muscles are

• fused cells, comprising myoblasts that fused in embryogenesis to form a syncytium.
• resulting muscle fibre is an elongated tube with multiple nuclei at its periphery

Question 2

What are the surrounding fibres of a muscle fibre, fascicles etc

Answer 2

Endomysium surrounds each muscle fibre.
The myofibres are groups into bundle called fascicles, these are enclosed in a thicker connective tissues called the perimysium. The muscle itself is surrounded by epimysium.

Question 3

Why are skeletal muscles known to be striated?

Answer 3

The muscle itself comprises of lots of striated myofibrils that are in regular array, giving it a striated appearance.
Skeletal muscle is also called striated due to the transverse striations seen by microscopy.

Question 4

Smooth muscle
We’re is it found?
What are its key morphological features?

Answer 4

Found:
-muscular walls of intestines and stomach, around blood vessels, around airways of respiratory tract, in the urinary bladder, in the uterine wall, and even in the eye (iris)
Key features:
-spindle shaped cells, with a single spindle shaped nucleus
-contain actin me myosin, but not in the same organised overlapping way as seen in cardiac and skeletal muscles.
-have spontaneous contractile activity
-no motor end plates
-the wave of muscular contractions is spread from cell to cell via gap junctions.
-unlike cardiac, smooth muscles can divide

Question 5

Cardiac muscle:
We’re is it?
What are its key morphological features?

Answer 5

We’re is it?

• only in the heart
• forms the myocardium and is lined internally by endocardium and externally by epicardium.

Key features:

• unlike skeletal have individual cells with a single central nucleus.
• unlike skeletal, cardiac myocytes branch frequently
• cardiac muscle doesn’t form a true syncytium, but the myocytes do form an effective electrical and mechanical unit due to effective junctions between the cardiac myocytes.
• cardiac has a more spiral arrangement, not like parallel skeletal muscles
• can’t regenerate

Ie key features:

• cross striations
• intercalated discs
• branching
• central nucleus
• abundant capillaries