Overview of Female Pelvic Floor Muscle Anatomy and Physiology
Top Contributors - Jess Bell, Kim Jackson and Rucha Gadgil
Introduction[edit | edit source]
The pelvic floor does not exist in isolation. It is part of a complex system that works synergistically with structures and systems both nearby and further away in the body, including the ankle / foot complex, the thorax and respiratory complex, the central nervous system and the brain. Because the body is a dynamic, interrelated, fascially connected, biotensegral system, it is important that pelvic health physiotherapists consider the contribution of all these systems and structures when assessing and treating pelvic health complaints.
The Pelvic Floor[edit | edit source]
Health professionals might have differing views about what makes up the pelvic floor:
- Is it just comprised of the pelvic floor muscles?
- Should the pelvic organs be included?
- Is the hip joint part of the pelvic floor?
- Are the contents of the lower abdominal cavity also included?
For the pelvic health physiotherapist, the pelvic floor refers to the area at the bottom of the pelvis, and all of its contents and associated structures, including:
- The pelvis itself (Figure 1)
- Called the pelvic ring or pelvic bowl
- Includes the pelvic joints
- Pelvic organs
- Bladder, uterus and rectum in women
- Pelvic ligaments (Figure 2)
- The endopelvic fascia and connective tissue
- The nerves which innervate the pelvic region, as well as blood vessels and the lymphatic system
- The external genitalia
- The pelvic floor musculature (Figure 3 and 4)
Pelvic health physiotherapists are able to treat all these structures either directly or indirectly.
This page focuses on the anatomy of the female pelvic floor musculature. More information on the other structures within the pelvis is available here.
Pelvic Cavity[edit | edit source]
- The front border is the abdominal wall
- The top border is the respiratory diaphragm
- The back border is the spinal column
- The bottom border consists of the pelvic floor muscles
Pelvic Floor Muscles[edit | edit source]
- The urogenital hiatus
- Contains the urethra and vagina in women
- Positioned anteriorly
- The anal hiatus
- Contains the anal canal
- Positioned posteriorly
The muscles of the pelvic floor are divided into three layers.
Deep Layer - Pelvic Diaphragm[edit | edit source]
The deepest layer of the pelvic floor muscles is known as the pelvic diaphragm (see Figure 4). It is a broad, funnel-shaped sling of fascia and muscle suspended from bony anchor points in the lesser pelvis (i.e. the area of the pelvic cavity below the linea terminalis).
- Ischococcygeus muscle (also known as the coccygeus muscle)
- Originates from the ischial spine and inserts into the lateral aspect of the coccygeal vertebrae
- Levator ani
- A composite muscle that is traditionally divided into three parts:
- Pubococcygeus: originates from the internal surface of the pubic ramus and inserts into the lower sacral and coccygeal vertebrae
- Illiococcygeus: originates at the arcus tendinous levator ani (ATLA) and fuses with the pubococcygeus
- Puborectalis: originates at the inner surface of the right and left sides of the pubic bone. The two muscles meet behind the rectum and form a continuous sling
- A composite muscle that is traditionally divided into three parts:
In this deep part of the pelvic floor, it is also possible to palpate the obturator internus and piriformis muscles. These muscles are not, however, considered to be part of the pelvic diaphragm. Instead, they are rotators of the hip.
Middle Layer - Urogenital Diaphragm / Perineal Membrane[edit | edit source]
The middle layer has traditionally been called the urogenital diaphragm, but is often now referred to as the perineal membrane.
There is controversy over whether this layer contains:
- A transverse sheet of muscle called the deep transverse perinei muscle which is between an inferior and superior fascia OR
- Three joined muscles and an inferior fascial layer (i.e. the perineal membrane)
However, the middle layer stretches across the urogenital triangle (see below) and in women, houses the urethral and vaginal sphincters (i.e. the sphincter urethrovaginalis, the external urethral sphincter, and the compressor urethrae). These sphincters close the urethra and vagina, and maintain continence. The entire perineal layer provides additional support for the deeper pelvic floor structures.
Superficial Layer[edit | edit source]
- Bulbocavernosus and ischiocavernosus:
- These muscles assist with clitoral function during arousal and climax
- Superficial transverse perineal muscles (paired):
- Provide additional support for the urogenital diaphragm
- External anal sphincter:
- A circular, layered muscle that closes off the anal canal
The perineum (perineal body) and superficial transverse perineal muscles divide into two triangles:
- Anterior triangle (called the urogenital triangle):
- Makes up the anterior half of the perineum, which is diamond shaped
- The corners of the triangle are the pubis symphysis anteriorly and the ischial tuberosities anterolaterally
- Posterior triangle (called the anorectal triangle):
- Makes up the posterior half of the perineum
- The corners of this triangle are the tip of the coccyx posteriorly and the ischial tuberosities anterolaterally
Physiology of the Pelvic Floor[edit | edit source]
The pelvic floor muscles are, in many respects, just like any other skeletal muscle group:
- They can contract and relax
- Be shortened or lengthened
- Be weak or strong
- Be stiff or supple
- They can hold tension or move dynamically
- May be coordinated or lack coordination - either individually or in relation to other muscle groups
- Can be normally regulated or “dysregulated”
The high prevalence of slow-twitch fibres means that these muscles are able to maintain a degree of resting activation. They are, therefore, considered to be postural muscles. This resting activation also enables the maintenance of continence.
The Nine S's of Pelvic Floor Muscle Physiology[edit | edit source]
- Sexual arousal and orgasm
- The superficial pelvic floor muscles cause engorgement and erection of the clitoris during arousal. The pelvic floor muscles also contract and relax rhythmically during climax
- Sphincter action
- Sphincters are circular muscles - when they they contract, they close off a space / lumen
- They have a certain degree of resting tone, which is regulated by the nervous system
- They can also be actively contracted
- They maintain continence
- The pelvic floor works synergistically with other muscles and organs (see videos below)
- Relationship with the diaphragm (functions like a piston)
- On inhalation the diaphragm contracts and flattens, which pushes the viscera inferiorly - the pelvic floor absorbs this movement by eccentrically contracting
- On exhalation, the diaphragm and pelvic floor return to their starting position
- The glottis above controls the passage of air in / out of the respiratory passages
- It works synergistically with the pelvic floor and diaphragm
- The pelvic floor needs to be able to lengthen under pressure (especially when this pressure is unexpected, such as during a sneeze, or when a high load is applied)
- Sump pump
- The rhythmic movement of the pelvic floor muscles creates a pumping action that helps to move both blood and lymph through the vascular system, which decreases pelvic congestion / swelling
- During labour the pelvic floor muscles must be able to stretch
- The pelvic floor muscles can reach a stretch ratio of 3.26 by the end of the second stage of labour
- The levator ani muscles stretch more than 200 percent beyond what is considered the threshold for a stretch injury during the second stage of labour
- Refers more to the “state of being” of the pelvic floor at any given time rather than a specific function of the pelvic floor
- The “somatic reality” of the pelvic floor can provide insight into the relationship between mind, body, brain, and behaviour
References[edit | edit source]
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