Page 82 - Edited - Webster HEAD AND NECK - part 2-Merge PDF

HN 274

THE GLOTTIS AND VOCAL FOLDS

The size of the glottis is changed by abduction/adduction of the arytenoid cartilages combined with their
rotation about a vertical axis. Vigorous respiration requires a wide open glottis; and the glottis reflexly
opens wider during inspiration than expiration. In A, the arytenoid cartilages are internally rotated and
adducted;

B.
A.
SUPERIOR
VIEWS

K.E.W.
K.E.W.
in B, externally rotated and abducted. Notice how the vocal processes of these cartilages move, and the kite-shape
of the glottis at B. Firm closure of the glottis can prevent expiration (as in the Valsalva manoeuvre).

PHONATION The vocal folds are adducted, and air is blown through the restricted glottal cleft, rather as
through the lips of a trumpeter. The pitch of the "squeak" is varied by (a) rocking the thyroid cartilage
backwards and forwards (C & D) to vary the length and tension of the vocal folds (they are elastic); and

IN FERIOR
CONSTRICTOR
MUSCLE
C. D.
CRICO- LATERAL
THYROID VIEWS
MUSCLE
ARYTENOID
STEADIED BY
POSTERIOR
CRICO-
ARYTENOID
MUSCLE.

VOCAL
LIGAMENT K.E.W.

(b) controlling the freely vibrating length with the vocalis muscle. Dysphonia: Commonest cause is
laryngitis! The adduction required for phonation explains the presence of stratified squamous epithelium on
the vocal folds. Over-use of the voice promotes overgrowth of this epithelium to form nodules which
seriously affect the quality of the voice and are a serious problem for especially professional singers and
actors. If one recurrent laryngeal nerve is paralyzed, the vocal fold on that side cannot be properly adducted - the
voice is hoarse, with decreased volume. The quality of the voice depends on access to and effective sizes of
resonators (pharynx, oral cavity, paranasal air sinuses). Articulation depends upon tongue (XII), lips (VII)
and soft palate (X), and sensory feedback (largely V). See separate sheet.
COUGHING requires preliminary firm closure of the glottis, and is impossible in recurrent laryngeal nerve
palsy. See separate sheet.

kewteach\glottis