Glossary of Physiology Terms

Adrenarche

An early sexual maturation stage, occurring 1 or 2 years before the onset of puberty, during which the zona reticularis of the adrenal cortex releases increased levels of dehydroepiandrosterone (DHEA) and androstenedione. These adrenal androgens are ultimately responsible for the appearance of pubic and axillary hair, increased oil production by facial skin, acne, and distinct adult body odor.

Menarche
Pubarche
Thelarche

Menarche

Onset of menstruation.

Adrenarche
Pubarche
Thelarche

Pubarche

Development of axillary and pubic hair during puberty.

Adrenarche
Menarche
Thelarche

Sarcolemma

Plasma membrane of a muscle cell. It is also referred to as myolemma.

Myolemma

Sarcoplasm

Cytoplasm of a muscle cell. It is also referred to as myoplasm.

Myoplasm

Thelarche

Development of breasts as an early event during female puberty.

Adrenarche
Menarche
Pubarche

A band

The A band is the region of a striated muscle sarcomere that contains myosin thick filaments. In fact, the A band is the entire length of the thick filament of the sarcomere. Its length is approximately 1 μm. The center of the A band is located at the center of the sarcomere (M line).

H zone
I band
M line
Z disk

H zone

The H zone is in the center of the A band where there is no overlap between the thick and the thin filaments. Therefore, in the H zone, the filaments consist only of the thick filament. The H zone becomes smaller as the muscle contracts and the sarcomere shortens. The center of the H zone is at the M line, which is also at the center of the sarcomere.

A band
I band
M line
Z disk

I band

The I band is the region of a striated muscle sarcomere that contains thin filaments. This region is closest to the Z disk, and is the lightest region of the sarcomere when viewed in under the light or electron microscope. The I band is occupied by the thin filaments only. Each Z disk runs through the middle of the I band. Therefore, half of each I band belongs to one sarcomere, and the other half belongs to the neighboring sarcomere. The I band shortens as the muscle contracts and the sarcomere shortens.

A band
H zone
M line
Z disk

M line

In striated muscle sarcomere, the M line is the attachment site for the thick filaments. The M line is in the center of the A band and, thus, it is in the center of the sarcomere.

A band
H zone
I band
Z disk

Mustard gas

Chemical warfare agent belonging to sulfur (or sulphur) mustards. Causes severe chemical burns and water blisters (i.e., it is a vesicant). It is cytotoxic, mutagenic, and carcinogenic.

Sulfur mustard (Wikipedia)

Myolemma

Plasma membrane of a muscle cell. It is also referred to as sarcolemma.

Sarcolemma

Myoplasm

Cytoplasm of a muscle cell. It is also referred to as sarcoplasm.

Sarcoplasm

Z disk

The Z disk (or Z line) defines the boundaries of a muscle sarcomere. Two adjacent Z disks along the myofibril mark the boundaries of a single sarcomere. The Z disks are the attachment sites for the thin filaments. Therefore, from each Z disk, thin filaments extend to two neighboring sarcomeres. When a muscle fiber contracts, the Z disks of a sarcomere move closer together (i.e., the sarcomere also shortens).

A band
H zone
I band
M line