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The diaphragm

The change in volume of the thoracic cavity during breathing is due to the alternate contraction and relaxation of the diaphragm    ( [link] ). It separates the thoracic and abdominal cavities, and is dome-shaped at rest. The superior surface of the diaphragm is convex, creating the elevated floor of the thoracic cavity. The inferior surface is concave, creating the curved roof of the abdominal cavity.

Muscles of the diaphragm

This figure shows the inferior view of the diaphragm with the major parts labeled.
The diaphragm separates the thoracic and abdominal cavities.

Defecating, urination, and even childbirth involve cooperation between the diaphragm and abdominal muscles (this cooperation is referred to as the “Valsalva maneuver”). You hold your breath by a steady contraction of the diaphragm; this stabilizes the volume and pressure of the peritoneal cavity. When the abdominal muscles contract, the pressure cannot push the diaphragm up, so it increases pressure on the intestinal tract (defecation), urinary tract (urination), or reproductive tract (childbirth).

The inferior surface of the pericardial sac and the inferior surfaces of the pleural membranes (parietal pleura) fuse onto the central tendon of the diaphragm. To the sides of the tendon are the skeletal muscle portions of the diaphragm, which insert into the tendon while having a number of origins including the xiphoid process of the sternum anteriorly, the inferior six ribs and their cartilages laterally, and the lumbar vertebrae and 12th ribs posteriorly.

The diaphragm also includes three openings for the passage of structures between the thorax and the abdomen. The inferior vena cava passes through the caval opening    , and the esophagus and attached nerves pass through the esophageal hiatus. The aorta, thoracic duct, and azygous vein pass through the aortic hiatus of the posterior diaphragm.

The intercostal muscles

There are three sets of muscles, called intercostal muscles    , which span each of the intercostal spaces. The principal role of the intercostal muscles is to assist in breathing by changing the dimensions of the rib cage ( [link] ).

Intercostal muscles

This figure shows the muscles in the thorax. The left panel shows the ribs, the major bones, and the muscles connecting them. The right panel shows a magnified view of the sternum and labels the muscles.
The external intercostals are located laterally on the sides of the body. The internal intercostals are located medially near the sternum. The innermost intercostals are located deep to both the internal and external intercostals.

The 11 pairs of superficial external intercostal    muscles aid in inspiration of air during breathing because when they contract, they raise the rib cage, which expands it. The 11 pairs of internal intercostal    muscles, just under the externals, are used for expiration because they draw the ribs together to constrict the rib cage. The innermost intercostal    muscles are the deepest, and they act as synergists for the action of the internal intercostals.

Muscles of the pelvic floor and perineum

The pelvic floor is a muscular sheet that defines the inferior portion of the pelvic cavity. The pelvic diaphragm    , spanning anteriorly to posteriorly from the pubis to the coccyx, comprises the levator ani and the ischiococcygeus. Its openings include the anal canal and urethra, and the vagina in women.

The large levator ani    consists of two skeletal muscles, the pubococcygeus    and the iliococcygeus    ( [link] ). The levator ani is considered the most important muscle of the pelvic floor because it supports the pelvic viscera. It resists the pressure produced by contraction of the abdominal muscles so that the pressure is applied to the colon to aid in defecation and to the uterus to aid in childbirth (assisted by the ischiococcygeus    , which pulls the coccyx anteriorly). This muscle also creates skeletal muscle sphincters at the urethra and anus.

Muscles of the pelvic floor

This image shows the superior view of the pelvic diaphragm.
The pelvic floor muscles support the pelvic organs, resist intra-abdominal pressure, and work as sphincters for the urethra, rectum, and vagina.

The perineum    is the diamond-shaped space between the pubic symphysis (anteriorly), the coccyx (posteriorly), and the ischial tuberosities (laterally), lying just inferior to the pelvic diaphragm (levator ani and coccygeus). Divided transversely into triangles, the anterior is the urogenital triangle    , which includes the external genitals. The posterior is the anal triangle    , which contains the anus ( [link] ). The perineum is also divided into superficial and deep layers with some of the muscles common to men and women ( [link] ). Women also have the compressor urethrae    and the sphincter urethrovaginalis    , which function to close the vagina. In men, there is the deep transverse perineal    muscle that plays a role in ejaculation.

Muscles of the perineum

The left panel shows the muscles of the perineum in the male, and the right panel shows the muscles of the perineum in the female.
The perineum muscles play roles in urination in both sexes, ejaculation in men, and vaginal contraction in women.

Muscles of the perineum common to men and women

This table describes the muscles of the perineum that are common to men and women. The levator ani pubococcygeus and levator ani iliococcygeus control movements during defaction, urination, coughing, and giving birth. They originate in the pubis and ischium. The superficial transverse perineal supports the perineal body maintaining the anus at the center of the perineum. It originates in the ischium. The bulbospongiosus is a superficial muscle that causes an involuntary response that compresses the urethra when excreting urine in both sexes or while ejaculating in males; it also aids in erection of the penis in males. It originates in the perineal body. The ischiocavernosus is a superficial muscle that compresses veins to maintain erection of the penis in males and erection of the clitoris in females. It originates in the ischium, ischial rami, and pubic rami. The external uretral sphincter is a deep muscle that voluntarily compresses the urethra during urination. It originates in the ischial rami and pubic rami. The external anal sphincter is a deep muscle that closes the anus. It originates in the anoccoccygeal ligament.

Chapter review

Made of skin, fascia, and four pairs of muscle, the anterior abdominal wall protects the organs located in the abdomen and moves the vertebral column. These muscles include the rectus abdominis, which extends through the entire length of the trunk, the external oblique, the internal oblique, and the transversus abdominus. The quadratus lumborum forms the posterior abdominal wall.

The muscles of the thorax play a large role in breathing, especially the dome-shaped diaphragm. When it contracts and flattens, the volume inside the pleural cavities increases, which decreases the pressure within them. As a result, air will flow into the lungs. The external and internal intercostal muscles span the space between the ribs and help change the shape of the rib cage and the volume-pressure ratio inside the pleural cavities during inspiration and expiration.

The perineum muscles play roles in urination in both sexes, ejaculation in men, and vaginal contraction in women. The pelvic floor muscles support the pelvic organs, resist intra-abdominal pressure, and work as sphincters for the urethra, rectum, and vagina.

Questions & Answers

How changing one nucleotide within a DNA molecule of a cell could change the structure of protein produced by that cell. What effect would this change have on the proteins function?
Aliana Reply
For whom would an appreciation of the structural characteristics of the human heart come more easily: an alien who lands on Earth, abducts a human, and dissects his heart, or an anatomy and physiology student performing a dissection of the heart on her very first day of class? Why?
Favour Reply
Name at least three reasons to study anatomy and physiology.
Favour
Structure Funtion
Muttaka
what is anatomy
Favour Reply
anatomy is a study of the human body
Dorcas
study of the structure and shape of the body and its parts
Kinganthony
Ok, thanks
Favour
-For us to be a knowleagble about how the form(structures) works together to perform its functions. -Fo us to know the importance of each structure and its function. -To do the right procedure when we examined the structure of the body.
RASOS Reply
An anatomy and physiology student performing a dissection of the heart on her very first day, well because alliens doesn't any have idea about the structures and functions of the human body they are not knowleagble enough unlike those students.
RASOS
the study of human bodys structure
RASOS
the study of large organs in the body
RASOS
study the mirco particles of the body
RASOS
the study of the humab bodys function
RASOS
study the regions of the body
RASOS
name the regions of the body
Alie
Head and neck Thorax Abdomen
Eunice
Briefly describe the activity of digestion in the mouth
Zen Reply
Please the difference between apoptosis and necrosis?
HABIBA Reply
apoptosis is predefined cell suicide,where the cell actively destroys itself,maintaining a smooth functioning in the body. whereas necrosis is an accidental cell death occurring due to the controlled external factors in the external environment of the cell
Sadiya
Apoptosis is non detrimental while Necrosis is detrimental
Olawuyi
Apoptosis is physiological pro
Olawuyi
Apoptosis occur due to physiological change while Necrosis occur due to pathological change/is pathological.
Olawuyi
Apoptosis is cause by Ageing while Necrosis is cause by pathogenic agent such as bacteria, viruses , Dangerous chemical such as toxins.
Olawuyi
Apoptosis is programmed cell death while necrosis is an abnormal lysis of the cell characterised by unusual dismantling of the nucleus and entire cell at large
Jamiu
Apoptosis is when the cell kills itself. This occurs when the cell becomes old or abnormal. Necrosis is cell death, not caused by the cell itself, but other factors esp. decreased supply of oxygen and nutrients (blood). This can be caused by external factors like diseases or injuries.
Keren
Apoptosis is described as an active, programmed process of autonomous cellular dismantling that avoids eliciting inflammation. Necrosis has been characterized as passive, accidental cell death resulting from environmental perturbations with uncontrolled release of inflammatory cellular contents.
kutemba
what are the types of nerve lesions
Kanimba Reply
neurapraxia (class l) axonotmesis (class ll) neurotmesis class lll)
Sadiya
there are three types of nerves in the body
Nafisat
what is inflammatory
Santuno Reply
It's a biological response triggered by a variety factors, including pathogens, damaged cells and toxic compounds.
daphine
It can be as well be de as defense mechanism that's vital to health
daphine
Why do Ladies. Experience hormonal imbalance after using family planning
Abdallah Reply
function of squamous epithelial
Helena Reply
wbc is a component of blood. it is also known as leucocytes, it is among the formed element of blood, there are 5 types of wbc, the neutrophils, the lymphocytes, the monocytes, the eosinophils and the basophils. it's function is to fight against disease
Faith Reply
Whole blood count
Ruth
complete blood count
Shivanand
They're responsible for immunity
daphine
what are about openstax
Divya Reply
how many cells are in human
Gratel Reply
they are over 3billion cells in a human body
Kinganthony
Is there fixed in amount ? because day by day it's increase as well as decrease also.
Khushali
Red cells
shafiullah
Red cells to be in touch with the people
shafiullah
Then what about WBC ?
Khushali
what about WBC ?
Khushali
white blood cells are one of the most important constituant of our blood the total WBC are counts in blood is 8000/cubicmm wbc provide immunity to our body from foreign particle
amit
what about WBC ?
Khushali
They are responsible for immunity
daphine
What exactly is your question Khusali please?
daphine
I think the cells multiply while every day since the white blood cells fight diseases and pathogens I'm sure they multiply too
daphine
what is the function of clans..1.pituitary glands 2.Thyroid glands ..3.parathyroid glands ..4 suprenenal....5.testes...6.ovaries...7.placenta
Muyangana Reply
The pituitary gland is called the master gland because it releases hormones that act on other glands in the body to stimulate them to release other hormones. However, the pituitary gland has its own master which is the hypothalamus; it acts on the pituitary by also releasing hormones.
Keren
is that's all about Axal skeletal?
Jelle Reply

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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