![Hair shaft diagram](https://upload.wikimedia.org/wikipedia/commons/8/8e/Hair_shaft_diagram.png)
The medulla is the innermost layer of the
hair shaft
Hair is a protein filament that grows from follicles found in the dermis. Hair is one of the defining characteristics of mammals.
The human body, apart from areas of glabrous skin, is covered in follicles which produce thick terminal and fine ...
.
This nearly invisible layer is the most soft and fragile, and serves as the pith or marrow of the hair. Some
mammal
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
s don't have a medulla in their hair. The presence or absence of this layer and the characteristics of the medulla can aid taxonomists in identifying what taxa a hair comes from. Characteristics include whether the medulla contains air pockets as well as the
histology
Histology,
also known as microscopic anatomy or microanatomy, is the branch of biology which studies the microscopic anatomy of biological tissues. Histology is the microscopic counterpart to gross anatomy, which looks at larger structures vis ...
of the medulla.
Scientists are still uncertain about the exact
role
A role (also rĂ´le or social role) is a set of connected behaviors, rights, moral obligation, obligations, beliefs, and social norm, norms as conceptualized by people in a social situation. It is an expected or free or continuously changing behavi ...
of the medulla, but they speculate that it is primarily an extension that is more prominent in
depigmented (grey or white) hair
.
[James, William; Berger, Timothy; Elston, Dirk (2005) ''Andrews' Diseases of the Skin: Clinical Dermatology'' (10th ed.). Saunders. Page 8. .]
References
Hair anatomy
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