Balasubramanian M.S. D.L.O.
Synonyms: Auricle, pinna
The auricle starts to develop when 6 hillocks appear
around the first pharyngeal groove, which lies between the first and
the second branchial arches. Three hillocks develop on each side of
the groove; as their growth progresses they contribute to the
development of the auricle. The bulk of the auricle is developed
from the mesenchyme of the second branchial arch (Hyoid arch). The
cartilage of the auricle extends inwards partially to surround the
future external meatus. A rudimentary pinna is formed by the 60 day
of embryonic life, and by 4 months the convolutions are formed
resembling the adult pinna.
showing embryology of Pinna
The pinna projects from the side of
the skull to varying degrees. It has two surfaces; the lateral which
is the exposed surface, and the medial which is hidden. The lateral
surface have several prominences and depressions giving it a unique
shape. The curved rim of the pinna is known as the helix. At the
posterior superior aspect of the helix is a small tubercle known as
the auricular tubercle (Darwin's tubercle). Anterior and parallel to
the helix another prominence is present known as the antihelix.
Superiorly the antihelix divides into two crura encompassing a fossa
known as the triangular fossa. Above the superior of the two crura
lies another fossa known as the scaphoid fossa. In front of the
antihelix, infact partly encircling it is the concha. The antero
superior portion of the concha is covered by the descending limb of
the antero superior portion of the helix. This region of the cocha
is known as the cymba concha. This cymba concha has an important
surface relationship with the suprameatal triangle. Infact the
suprameatal triangle or (Mceven's triangle) lie just under the cymba
concha. This triangle acts as a surface marking for the mastoid
antrum during mastoidectomy procedures.
Opposite to the concha, and lying
across the external auditory meatus (partially covering it) is a
small blunt triangular prominence known as the Tragus. This
prominence points posteriorly. Opposite to the tragus lie another
prominence known as the antitragus.
The body of the auricle is covered
with fibroelastic cartilage, covered with skin. It is connected to
the surrounding parts by ligaments and muscles. It is also
continuous with the cartilage lining the external auditory canal.
The skin of the auricle is thin and closely bound to the
perichondrium on the lateral side. On the medial side the skin is
not adherent to the cartilage of the auricle, there is a layer of
subdermal adipose tissue separating the skin from the cartilage. The
skin is covered with fine hairs which have sebaceous glands opening
into their root canals. The glands are most numerous in the concha
and the scaphoid fossa. The fibroelastic cartilage is absent in the
lobule area of the pinna. The auricular cartilage depends on the
perichondrium for its nourishment. The cartilage is connected to the
temporal bone by two extrinsic ligaments, the anterior and the
posterior ligaments. Intrinsic ligaments connect various parts of
the cartilagenous auricle.
The muscles of the auricle belong to
two groups; the extrinsic and the intrinsic groups. The extrinsic
muscles are supplied by temporal and post auricular branches of the
facial nerve. The extrinsic muscles are functionally not so
important, but they give rise to the post auricular myogenic
response following auditory stimulation. The extrinsic muscles are
auriculares anterior, auriculares superior and auricularis
The intrinsic muscles are 6 in number,
all small and inconsistent and without useful function.
The post auricular branch of the
external carotid artery supplies the medial surface of the pinna,
and extends around the helix to supply the extremities of the
lateral surface. The anterior auricular branch of the superfical
temporal artery supply the bulk of the lateral surface. Auricular
branch from the occipital artery assists the post auricular artery
in supplying the medial surface.
Lymphatic drainage from the posterior
surface of the pinna is to the lymph nodes at the mastoid tip, from
the tragus and from the upper part of the anterior surface is to the
preauricular nodes, and from the rest of the auricle to the upper
deep cervical nodes.
innervation of the auricle:
|| Cervical Plexus C2
|| Medial surface and posterior
part of lateral surface of pinna|
|| Cervical plexus
|| Superior portion of
|| Concha and
division of trigeminal nerve
|| Tragus, Crus of
the helix and adjacent helix|
|| Supplies root of
1. Pinna increases the pressure at the
tympanic membrane in a frequency sensitive way, thus emphasizing
certain frequencies in the input.
2. It helps to localise the direction
of the source of sound.
3. Protects the middle ear and inner
ear from extraneous insults
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