How does skeletal muscle look in cross-section?

Myofibers often appear polygonal with peripheral nuclei. In longitudinal sections, striations may be visible. Endomysium, perimysium, and epimysium organize connective tissue around fibers and fascicles.

What are intercalated discs on cardiac muscle slides?

They are specialized cell-cell junction regions that connect cardiac myocytes. On H&E they may appear as dark step-like lines crossing fibers, helping distinguish cardiac from skeletal muscle in many fields.

Why is white matter white in fixed CNS tissue?

Myelinated axons contain abundant lipid-rich myelin sheaths, which appear glistening white grossly. Gray matter contains more neuronal cell bodies, dendrites, and synaptic neuropil.

Chapter 4 of 5 - Histology Course

Muscle & Nervous Tissue

Contractile tissues and excitable neural tissue show distinctive nuclear positions, cell shapes, and layering. Use section plane (longitudinal versus cross) when interpreting striations and CNS laminae.

Muscle Types at a Glance

Type	Striations	Nuclei	Notes
Skeletal	Present (longitudinal section)	Multiple, peripheral	Voluntary; fiber bundles with connective tissue septa
Cardiac	Present	Typically central (often one per cell)	Intercalated discs; branching cells (varies with plane)
Smooth	Absent on routine H&E	Central, single	Involuntary; fusiform cells in walls of viscera and vessels

Striations in Longitudinal Skeletal Muscle

Striations reflect sarcomere repeat units (A and I bands) visible with adequate fixation and appropriate cutting plane. If the section is oblique, striations blur and smooth muscle can be mistaken for skeletal without careful nuclear counting.

Myofiber (longitudinal)

Repeating banding along fiber axis

↓

Sarcomeres (A/I bands)

Alternating eosinophilic and lighter regions

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Peripheral myonuclei

Multiple nuclei under sarcolemma

Muscle Types (Narrative)

Skeletal muscle is voluntary, multinucleated, and striated. Cardiac muscle is striated with intercalated discs. Smooth muscle cells are spindle-shaped with central nuclei and lack obvious striations on H&E.

Molecular Structure

Choline (neurotransmitter precursor)

2-hydroxyethyl(trimethyl)azanium

Choline is the precursor for acetylcholine synthesis at neuromuscular junctions. It links molecular biochemistry to how motor neurons communicate with skeletal muscle.

Formula

C₅H₁₄NO+

Mol. Weight

104.17 g/mol

View on PubChem

Nervous Tissue on Slides

The cerebellum shows a molecular layer, Purkinje cell layer, and granular layer. Spinal cord regions display central gray and peripheral white matter. Always interpret with magnification and plane of section in mind.

Region	What dominates on H&E
Gray matter	Neuronal somata, dendrites, synaptic neuropil (cell-dense)
White matter	Myelinated axon tracts (tract packing varies by region)

Histological image of cerebellum with numbered cell layers — Cerebellar cortex: layered organization with molecular, Purkinje, and granular regions visible in this annotated section (species as in source file).
Juoj8, Wikimedia Commons, CC BY-SA 3.0
Source

Quick Check

Which muscle type is involuntary, lacks striations on routine H&E, and typically shows central nuclei in fusiform cells?

Fill in the Blank

In the spinal cord, myelinated axons aggregate in the________ matter, while neuronal cell bodies cluster in gray matter.

Quick Check

Which feature most reliably distinguishes cardiac muscle from skeletal muscle in many H&E sections?

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