344
UNIT 2
Covering, Support, and Movement of the Body
10
MUSCLE GALLERY
Table 10.7
Muscles of the Pelvic Floor and Perineum: Support of Abdominopelvic Organs
(Figure 10.13)
MUSCLE
DESCRIPTION
ORIGIN (O) AND
INSERTION (I)
ACTION
NERVE
SUPPLY
MUSCLES OF THE PELVIC DIAPHRAGM
(Figure 10.13a)
Levator ani
(le
˘
-va
9
tor a
9
ne)
(
levator
5
raises;
ani
5
anus)
Broad, thin, tripartite
muscle (pubococcygeus,
puborectalis, and
iliococcygeus); its fibers
extend inferomedially,
forming a muscular “sling”
around male prostate (or
female vagina), urethra,
and anorectal junction
before meeting in the
median plane
O—extensive linear
origin inside pelvis from
pubis to ischial spine
I—inner surface of
coccyx, levator ani of
opposite side, and (in
part) into the structures
that penetrate it
Supports and maintains
position of pelvic viscera
;
resists downward thrusts
that accompany rises
in intrapelvic pressure
during coughing,
vomiting, and expulsive
efforts of abdominal
muscles; forms sphincters
at anorectal junction and
vagina; lifts anal canal
during defecation
S
3
, S
4
, and inferior
rectal nerve (branch of
pudendal nerve)
Coccygeus
(kok-sij
9
e-us)
(
coccy
5
coccyx)
Small triangular muscle
lying posterior to levator
ani; forms posterior part of
pelvic diaphragm
O—spine of ischium
I—sacrum and coccyx
Supports pelvic viscera
;
supports coccyx and pulls
it forward after it has been
reflected posteriorly by
defecation and childbirth
S
4
and S
5
MUSCLES OF THE UROGENITAL DIAPHRAGM
(Figure 10.13b)
Deep transverse perineal
muscle
(per
0
ı˘-ne
9
al)
(
deep
5
far from surface;
transverse
5
across;
perine
5
near anus)
Together the pair spans
distance between ischial
rami; in females, lies
posterior to vagina
O—ischial rami
I—midline central
tendon of perineum;
some fibers into vaginal
wall in females
Supports pelvic organs
;
steadies central tendon
Pudendal nerve
External urethral sphincter
(
sphin
5
squeeze)
Muscle encircling urethra
and vagina (female)
O—ischiopubic rami
I—midline raphe
Constricts urethra
; allows
voluntary inhibition of
urination; helps support
pelvic organs
Pudendal nerve
MUSCLES OF THE SUPERFICIAL PERINEAL SPACE
(Figure 10.13c)
Ischiocavernosus
(is
0
ke-o-kav
0
ern-o
9
sus)
(
ischi
5
hip;
caverna
5
hollow chamber)
Runs from pelvis to base of
penis or clitoris
O—ischial tuberosities
I—crus of corpora
cavernosa of male penis
or female clitoris
Retards venous drainage
and maintains erection of
penis or clitoris
Pudendal nerve
Bulbospongiosus
(bul
0
bo-spun
0
je-o
9
sus)
(
bulbon
5
bulb;
spongio
5
sponge)
Encloses base of penis
(bulb) in males and lies
deep to labia in females
O—central tendon of
perineum and midline
raphe of penis
I—anteriorly into corpora
cavernosa of penis or
clitoris
Empties male urethra
;
assists in erection of penis
and of clitoris
Pudendal nerve
Superficial transverse
perineal muscles
(
superficial
5
closer to
surface)
Paired muscle bands
posterior to urethral
(and in females, vaginal)
opening; variable;
sometimes absent
O—ischial tuberosity
I—central tendon of
perineum
Stabilizes and
strengthens
central tendon of
perineum
Pudendal nerve
Two paired muscles, the
levator ani
and
coccygeus
, form the
funnel-shaped pelvic floor, or
pelvic diaphragm
(Figure 10.13a).
This diaphragm (1) seals the inferior opening of the bony pelvis,
(2) supports the pelvic organs, (3) lifts the pelvic floor superiorly
to release feces, and (4) resists increased intra-abdominal pressure
(which would expel contents of the urinary bladder, rectum, and
uterus). The pelvic diaphragm is pierced by the rectum and urethra
(urinary tube), and by the vagina in females.
The body region inferior to the pelvic diaphragm is the
perineum
. The
urogenital diaphragm
sits inferior to the muscles of
the pelvic floor, and stretches between the two sides of the pubic
arch in the anterior half of the perineum (Figure 10.13b). This thin
triangular sheet of muscle contains the
external urethral sphincter
,
a sphincter muscle that surrounds the urethra and allows voluntary
control of urination. Superficial to the urogenital diaphragm,
and covered by the skin of the perineum, is the
superficial
perineal space
, which contains muscles (
ischiocavernosus
and
bulbospongiosus
) that help maintain erection of the penis and
clitoris (Figure 10.13c). In the posterior half of the perineum
encircling the anus is the
external anal sphincter
, which allows
voluntary control of defecation. Just anterior to this sphincter is
the
central tendon of the perineum
, a strong tendon into which
many of the perineal muscles insert.
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