<< Chapter < Page Chapter >> Page >

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

tarsal are cube shaped broad and long whiles metatarsal they are longer than they are wide
Priscilla Reply
articular cartilage serve as shock absorber and also reduces friction
Priscilla
articular cartilage serve as shock absorber and also reduces friction
Priscilla
when a bone joint with another bone
Priscilla
to know how you body function to know the relationship between the body parts to know specific functions of a certain body parts
romeo Reply
To know our body function we shd know chemical secretion of our glands, we can map all the function of our body and also relation ship between the body parts.
KUSUMA
that z it kusuma
kanaku
can you get fungi infection by seating on a public toilet?
Calls Reply
explain how blood acts as a connective tissue in the body
Rymz Reply
how does blood act as a connective tissue in the body
Rymz
what is anatomy
Victoriah Reply
fat deficiency in the body
Agbor Reply
Explain how body exercise regulates blood pressure
dranimva Reply
thank you
Thelma
what is cillia and flangella
Kalah Reply
what are the proceduers of condactive system ?
Salua Reply
please, is cell the only smallest particle in de human body
Chibuzor Reply
what are the function of the epithelial tissues
Vaidah Reply
write short notes on following hypervolemia hypovolemia hypo tension oedema DVT shock embolism tachycardia bradycadia varicose veins stroke thrombosis vertigo
Zulpha
secretion, absorption ,protection
Nakyondwa
meaning of ossification
Nakyondwa
osteogenesis or bone formation
Veterinary
pls what is DVT
Ngwani
deep vein thrombosis
Angel
throbbing or cramping pain in 1 leg (rarely both legs), usually in the calf or thigh. swelling in 1 leg (rarely both legs) warm skin around the painful area. red or darkened skin around the painful area. swollen veins that are hard or sore when you touch them.
zinet
Epithelial tissues are widespread throughout the body. They form the covering of all bodysurfaces, line body cavities and hollow organs, and are the major tissue in glands. They perform a variety of functions that include protection, secretion, absorption,excretion, filtration, diffusion, and sensor
Ziya
diagram of a neuron
Emmanuel Reply
go to Google and see hear
Ziya
from where the mixture(collagen & glycoprotein) of basal lamina is secreted?
kiran Reply
epssed
Muktar
what
Ziya
hhhhhmmmm
muhammad
I hope all we enjoy this moment
Muktar
I am together with u brothers
kanaku
what a the 4 proximal bones
kanaku
The proximal end of the radius articulates in both the elbow and proximal radioulnar joints. ... Neck – A narrow area of bone, which lies between the radial head and radial tuberosity. Radial tuberosity – A bonyprojection, which serves as the place of attachment of the biceps brachii muscle.
Ziya
why is the pancreas refer to as an endocrine and exocrine gland
tang Reply
what is a malignancy
tang
malignancy" refers to the presence of cancerous cells that have the ability to spread to other sites in the body (metastasize) or to invade nearby (locally) and destroy tissues
muhammad
Hi, pancreas is a basic organ
Douglas
what is osteoporosis
Bashiru
Osteoporosis is a bone disease that occurs when the body loses too much bone, makes too little bone, or both. As a result, bones become weak and may break from a fall or, in serious cases, from sneezing or minor bumps. Osteoporosis means “porous bone.”
Danni
what is erythrocytes
Urmila
They're red blood cells
Sharon
ok
Urmila
what is leukocyte
Urmila
what are different between stained specimen and unstained specimen
Emanuel
what is leukocytes
Urmila
a colourless cell which circulates in the blood and body fluids and is involved in counteracting foreign substances and disease; a white (blood) cell. There are several types, all amoeboid cells with a nucleus, including lymphocytes, granulocytes, and monocytes.
Danni
which is the largest bone?
Riya
the bone in human body is Femur.
Abubakar
ok thnx
Riya
absolutely I'm really happy to meet you guys.
Abubakar
Riya! uhm please don't thanks me again. we're friends
Abubakar
Riya! don't thanks me again please, actually I considered u all as my friends.
Abubakar
what is thrombocyte
Urmila
Thrombocytes are pieces of very large cells in the bone marrow called megakaryocytes. They help form blood clots to slow or stop bleeding and to help wounds heal. Having too many or too few thrombocytes or having platelets that don't work as they should can cause problems.
Adnan
ok thanks
Urmila
welcome dear sister
Adnan
thanks brother you said me sister ☺️
Urmila
it's ok 😊 sister don't say again thanks because I m your brother
Adnan
Ah😂😂
Sharon
Guys how many are in college here?
Sharon
what is peritoneal cavity
Emanuel
The peritoneal cavity is a potential space between the parietal and visceral peritoneum. It normally contains only a thin film of peritoneal fluid, which consists of water, electrolytes, leukocytes and antibodies. ... Fig 1 – The peritoneal cavity is a potential space between the parietal and viscer
Adnan
Additional UTI risk factors for men?
Adnan
Adnan Wahab
Abubakar
the intramembranous ossification are developed from membrane whiles the endochondral ossification developed from cartilage
Helena Reply
primary ossification begins at the center of diaphysis while the secondary is the bone growth after birth that occurs at the epiphyseal disc
Helena
Hi
Bashar
hii
Urmila
good to see you
Bashar
hii
Ziya
Yo
Amoako
Hi
rapisanai
good morning guys
Sushma
your all members which countries?
Sushma
I am from Ethiopia
Rama
hi
Sushma
from India 🇮🇳
Sushma
from Bangladesh.
Rashed
hello 👋
Sanam
hii
JUNIOR
what are you doing everyone?
Sanam
listening chemistry class
Sushma
what's corona going on in your country's ?
Sushma
kindly discuss for mi....epithelial tissues
Nabirye
hy
Lal
hii gys
Ziya
hi😊
abdiyu
hello every one
Qaisar
hii gys
Priya
hii
Nigel
What is the difference between cytoplasmic and endoplasmic
Ajibola Reply
The cytoplasm is 90℅ water and 10℅ of organic and inorganic compounds. The cytoplasm contains mitochondria. ... Lysosomes of Cytoplasm contains 50 different enzymes that digest proteins, lipids, and nucleic acids. The endoplasmic reticulum produces process and transport proteins, lipids for all the
Adnan

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Anatomy & Physiology' conversation and receive update notifications?

Ask