Breathe in and out. Feels good, right? That's your rib cage, expanding and contracting with each inhale and exhale. But your rib cage certainly doesn't do all the work, and if you thought it did, I want you to apologize to the muscles in your back, thorax, and neck.
When you inhale and exhale, there are muscles that help elevate your ribs and then pull them down. We're going to look at a pair of them that do just that: the serratus posterior inferior and superior.
Serratus Posterior Muscle Actions
The serratus posterior inferior and serratus posterior superior are two different muscles, but they are mirror images of each other.
Winglike in shape, the superior is situated at the upper part of the posterior thorax, while the inferior is at the lower part.
The serratus posterior superior helps to elevate the upper ribs during inhalation. The serratus posterior inferior, inversely, helps to draw the lower ribs downward and backward during exhalation.
Serratus Posterior Attachments
Both muscles attach to various ribs and parts of the spine.
The serratus posterior superior originates on the supraspinal ligament, the ligamentum nuchae, the spinous processes of the upper two to three thoracic vertebrae (T01–T03), as well as the seventh cervical vertebra. It inserts on the upper borders of ribs 2–5, and is innervated by intercostal nerves 2–5.
The serratus posterior inferior originates on the supraspinal ligament, and the spinous processes of the upper two to three lumbar vertebrae (L01–L03) and the lower two thoracic vertebrae (T11–T12). It inserts on the lower borders of ribs 9–12, and is innervated by intercostal nerves 9–12.
Serratus Posterior Superior Pain
The serratus posterior superior is, because of its location (the shoulder girdle region), sometimes a bit of a troublemaker; its pain pattern overlaps with that of other muscles. Deep aches under the shoulder blade or in the back of the shoulder, the point of the elbow, and the pinky side of the wrist and hand are common symptoms of trigger points (muscle knots) in the serratus posterior superior muscle.
What causes trigger points in the serratus posterior superior? Heavy breathing during strenuous activity, or struggling for breath during respiratory illness, such as pneumonia.
Resting the muscle for a few days, or even visiting a chiropractor, can help ease the pain and improve mobility.
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Aaaaand, here we are with part two. I'm glad everyone enjoyed the first one (thanks for the comments!); hopefully y'all walked away with a little extra knowledge. Or an image of a uterus as a kung-fu master stuck in your mind. Either way, mission accomplished.
While I don't have anything to match up to the kung-fu thing, I do have a sort of game we can play. It's kind of like "Whose Line Is It Anyway?" or a political debate: everything is made up and the points don't matter. I call it "How artfully can Courtney hide certain aspects of external male anatomy in the pictures?" You be the judge.
Game faces on? Good. Let's tackle male internal reproductive anatomy.
The prostate, or turn your head and cough
If you honestly think I wasn't going to slip in a clichéd joke somewhere in this post, then you haven't been paying attention.
It seems the only time you ever hear anyone talk about the prostate is in conjunction with cancer, which is morbid and kind of telling about our society these days (we're all a bunch of Debbie-downers). I'm happy to report that, despite reports to the contrary, the prostate isn't a harbinger of disease, but a simple gland. Well, maybe not so simple.
The prostate is a firm muscular gland about the size of a chestnut, located around the internal opening of the urethra and situated in the pelvic cavity. Because of this position, it's palpable (a.k.a. the perineum), especially when enlarged.
Its glandular tissue consists of numerous glands that open into 12 to 20 small excretory ducts, which open into the floor of the prostatic portion of the urethra. That's right: the urethra goes though the prostate.
During ejaculation, the prostate produces fluid that contains enzymes and other substances that activate sperm.
Seminal vesicle (which is exactly what it sounds like)
How am I doing so far? Is everyone relatively unscarred and giggle-free?
Okay, so here's something that will blow your mind: the urinary and reproductive systems converge in the male body. In the male system, urine and ejaculate exit the same duct, the urethra, while in the female system they have their own distinctive exits. I explained this to a friend of mine once and she spent the rest of our otherwise mundane conversation with a look on her face that said she wasn't sure what else in her life was a lie.
The male reproductive system has two seminal vesicles, which are sacs, basically. Each ~7.5 cm sac is lined with a mucous membrane, and the cells within the membrane secrete a pale fluid containing sugars, prostaglandins, and other substances. This fluid makes up about two-thirds of semen.
The lower ends of the two vesicles are pointed and converge at the base of the prostate, where each joins with the corresponding vas deferens to form the ejaculatory duct.
Vas deferens, or the waterslide of wonder
I honestly don't know what that heading is about, but I think it's hilarious. Tell me they don't look like the enclosed waterslides you see at water parks.
The vas deferens, or the ductus deferens, is the excretory duct of the testis. There are two of them (most things come in pairs in the body). The duct lies between the peritoneal membrane and the lateral wall of the pelvis. Eventually, it is directed downward to the base of the prostate, where it joins the base of the seminal vesicle to form the ejaculatory duct.
Epididymis (if you can come up with a subheading then you deserve an award)
I really don't have too much to say about the epididymis, other than it has one of the coolest names ever and it basically acts as a way station.
The epididymis is a duct that attaches to the testis, consisting of a central portion, a head, and a pointed extremity (tail). The extremity is continuous with the vas deferens. Ducts penetrate penile fascia covering the testis and carry seminal fluid from the testis up to the epididymis, and from there the fluid enters the vas deferens.
Testis (I'd better not balls this one up—ha-ha, get it? Wink wink, nudge nudge.)
Once upon a time in utero, we all shared the same set of gonads—regardless of our gender. The female system develops the ovaries, and the male system develops the testes. They still look the same: egglike.
The testis produces male gametes (sperm), which contribute half of the genetic instructions for embryonic development. Testes, like the ovaries, are endocrine glands, and they produce testosterone, which governs early development of the male reproductive system, as well as male secondary sex traits.
Housed inside the tunica vaginalis, a serous membrane, the testis consists of lobules where sperm develop. The testis is suspended in the scrotum by the spermatic cords—each cord consists of vasculature, lymphatic vessels, and nerves (which is why they are so vulnerable to pain, as they are housed in an external structure, and why most athletes in contact sports wear cups).
And there you have it: a rundown of the male internal reproductive system. Now it's back to serious stuff. Stay tuned for our next blog post!
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Related A&P posts:
- Anatomy and Physiology: Uterine Anatomy
- Anatomy and Physiology: 5 Facts about the Anatomy of the Pelvic Cavity
- Anatomy and Physiology: Homologues of Reproductive Anatomy
Ah, the uterus, nature's Rubix cube. You're probably laughing to yourself, saying, "It's not some great mystery—I know enough about this to get by." Do you? Do you really? I'm not asking to be mean. It may come as a surprise, but most people don't know much about reproductive anatomy—even their own!
This is the first of two posts exploring the internal reproductive systems. Let's take a look at the female system first.
Fallopian, say what?
Once upon a time when I had sex ed in the 7th grade (for, like, one day), my health teacher tried to describe the internal reproductive system to us. He told us to picture a kung-fu crane stance, with the uterus as the kung-fu master and the fallopian tubes as his arms (like this). Ridiculous as that sounds, none of us ever forgot it.
The fallopian tube, or oviduct, is about 10 cm long and consists of three coats: serous, muscular, and mucous. Each fallopian tube consists of three portions: the isthmus (a constricted section connected to the uterus), ampulla (intermediate dilated portion that curves over the ovary), and infundibulum (open to the abdomen).
Ova (eggs) travel through the fallopian tube to the uterine cavity.
Fimbriae, or that thing you probably have never heard of
Fimbriae are interesting structures. Remember my health teacher's crane stance? Think of the fimbriae as the hands of the kung-fu master. FYI, I'm going to run this analogy into the ground.
Fingerlike in shape, the fimbriae are projections that are attached to the ovaries. Before ovulation (the release of an ovum), the fimbriae become positioned close to the ovarian follicle surface. Cilia, hairlike organelles, on the fimbriae beat in rhythmic waves, creating currents that sweep the ovum into the fallopian tube.
Ovaries, and the stuff inside them
Okay, so if the fallopian tubes are the arms of the kung-fu crane stance and the fimbriae are the hands, then the ovaries are nunchucks. The ovaries are gonads (which are derived from the same set in utero), which produce gametes (ova). These gametes contribute half the genetic material needed for embryonic development (the other half comes from the male gametes).
Ovaries are endocrine glands, producing the hormones progesterone and estrogen—sex hormones that govern early development and contribute to the menstrual cycle. Each ovary is about 4 cm long and 2 cm wide. The ovarian ligament attaches it to the uterus while a suspensory ligament attaches it to the pelvic wall.
During ovulation, an ovum is dispensed from an ovary's surface and is carried into the fallopian tube, where it proceeds to the uterus.
What is the uterus?
If I went up to you right now and asked you to say what the uterus is and does, could you? Let's try it. Without opening up Google or Wikipedia, can you give a clear, concise explanation of the uterus? "That thing where babies happen" doesn't cut it. See? It's tough to know what you're never really taught.
The uterus is a hollow, thick-walled, pear-shaped organ—a duct, actually!—located in the pelvic cavity between the bladder and the rectum. The fallopian tubes lead into the upper part of the uterus, one on either side, while the lower part of the uterus leads to the vagina. Ligaments hold the upper part of the uterus in suspension; the lower part is embedded in fibrous tissue.
That's all well and good, I can hear some of you say, but what does it do? Well, when an ovum (egg) is fertilized, it embeds itself into the uterine wall and is normally retained there as it develops. Development of an embryo and then a fetus causes the uterine wall to expand in size—enormously, actually. You've seen pregnant people. You know.
After labor, the uterus shrinks down to almost its normal size (crazy, right?), although its cavity is larger and the muscular layers are more defined (because it just pushed out a baby, like a boss).
The cervix
On one memorable occasion, some friends of mine and I were discussing what we knew about each other's anatomy over a plate of potato skins (I have interesting friends and conversations, sometimes), when one of my guy friends shouted triumphantly, "Hah! The cervix! It's that … that thing.…" Yes, indeed, friend. The cervix is that thing.
The cervix is actually the lowest part of the uterus, a constricted, somewhat conically shaped segment that leads to the vagina. It is the passageway for menstrual flow, entering sperm, and childbirth (it's a trifecta of hilarity and terror). It also secretes a clear alkaline mucus that changes character depending on where someone is in their menstrual cycle.
And there you have it! The basic rundown of everything you always wanted to know about the internal female reproductive system. Stay tuned for our next post, where we'll tackle the male system.
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I know we've done posts about the pelvic girdle before, but guess what? HERE'S ANOTHER. It's just that cool. Plus, it gives us a little bit of room to show off new bone and organ tissue the team here is working on!
The pelvic cavity is the space in which organs (including reproductive and urinary), muscles, vessels, nerves, and other structures are housed.
1. The pelvic cavity is created by the space between the pelvic bones.
2. Muscles form the floor and walls of the pelvic cavity.
3. Organs in the pelvic cavity support digestive, reproductive, and urinary functions.
4. In the female pelvic cavity, the bladder and urethra lie in front of the vagina, the rectum behind it.
5. In the male pelvic cavity, the bladder is located behind the pubic bone and above the prostate.
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Related Posts
- 3D Skeletal System: The Pelvic Girdle
- 3D Skeletal System: Atlas, Axis, and the Atlanto-Axial Relationship
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You open your eyes and see the world, but are you conscious of the fact that you are doing so? You saw a link, clicked on it, and now you're reading this blog post. Hello, reader. I like your shirt. Your hair looks really good, too. That you've interpreted what you just saw and have taken it as a compliment is an example of visualization, a.k.a. "Hurrah! You can see things."
Visualization is something we take for granted. You open your eyes and expect the world to appear around you. Don't lie, you totally do. In fact, you weren't consciously aware you were seeing things until I just reminded you 10 seconds ago.
It's not just your eyes involved in visualization. There is a complicated system in place that allows you to see and interpret your environment. Let's take a look at it.
Orbits (Eyesockets)
Like most structures in the body, the orbits of the skull do more than one job. The orbits, or eye sockets as they're more commonly known, give shape to the forehead and eyebrows. They also protect the eyes.
The orbits are made up of the frontal, maxilla, lacrimal, zygomatic, palatine, sphenoid, and ethmoid bones. Within the cavities is fatty tissue that helps keep eye movement nice and smooth.
The eyes are comprised of delicate materials, but are relatively strong (think of anyone who's ever been punched in the eye—the skin around the orbit will bruise, but the eye itself is usually okay). Since only a small portion of the eye is exposed to the world, the orbits act to protect and house the rest of it.
Extraocular Muscles
Did you know that your eyes move over 100,000 times a day? The extraocular muscles are the busiest skeletal muscles in your body.
The extraocular muscles are a subgroup of muscles in the head region that act to move the eyes. They are: the superior rectus, inferior rectus, medial rectus, lateral rectus, superior oblique, and inferior oblique.
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Superior rectus
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Adducts, depresses, and internally rotates the eye
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Inferior rectus
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Depresses, extorts, and adducts the eye
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Medial rectus
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Adducts and moves the eye medially
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Lateral rectus
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Abducts and moves the eye laterally
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Superior oblique
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Medially rotates the eye (intorsion)
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Inferior oblique
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Laterally rotates the eye (extorsion)
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The extraocular muscles, with the exception of the lateral rectus and superior oblique, are innervated by the oculomotor nerve (CN III). The lateral rectus is innervated by the abducens (CN VI) and the superior oblique by the trochlear nerve (CN IV).
Eyes
Eyes are beautiful things—they must be, since we're fascinated with them. Throughout history, there have been countless pieces of art, literature, and music dedicated to the no-pair-is-ever-the-same-as-another structures we call eyes.
The reality of them is a little less romantic. The eye isn't a single structure, but composed of many parts, including the retina, cornea, and sclera. The retina is a layer of nervous tissue in the interior of the eye, continuing into the cranium as the optic nerve. The white of the eye is the sclera, and the transparent part of the eye is the cornea. The iris is the pigmented portion (where we determine eye color), and behind the iris is a lens that focuses light to form an image on the retina (remember: the image on the retina is inverted!). Between the cornea and iris is a chamber filled with fluid called the aqueous humor, and between the iris and retina is a chamber filled with fluid called the vitreous humor.
Suddenly Edmund Spenser's "those lamping eyes will deign sometimes to look" from Sonnet 1 doesn't sound nearly as nice when you realize that he's describing the way light refracts off the sclera. Actually, that is almost as nice. Well done, Mr. Spenser.
Optic Nerve and Optic Chiasm
Passing through the posterior of the eyeball and into the brain is the optic nerve (CN II), a sensory nerve, which continues into the optic chiasm.
When you visualize the world, the two hemispheres of the brain receive different input: the right side of the brain receives visual information from the left side of our visual space (by which I mean the right side of both right and left eyes), and the left side of the brain receives information from the right side of our visual space. Input comes in on either side separated, and then crosses when it hits the optic chiasm.
The chiasm is an X-shaped structure in which fibers from the optic nerves cross, and information travels from here to the visual cortex (the occipital lobe).
Occipital Lobe
The final leg of the visual journey, so to speak, ends on the completely opposite side from where it began. The occipital lobe is the posteriormost lobe of the cerebrum, and within it is the visual cortex. The primary visual processing center is located on the medial side of the occipital lobe. It's responsible for processing visual perceptions of position, orientation, color, depth, brightness, direction, and speed. Combined, these aspects form complete visual perception.
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Related A&P posts:
- Anatomy and Physiology: Relationships of the Respiratory System
- Anatomy and Physiology: 5 Medical Myths Demythified!
Sources:
- Human Anatomy Atlas
- Optic Chiasm
Open up your mouth and make a sound. I don't care what it is—scream, sing, recite the Gettysburg Address, hum your current favorite song. Let your freak flag fly.
What you're doing is phonating. Phonation is the production of vocal sound and speech. Expression through vocals may seem effortless and easy, but it actually comes from a delicate and complicated system of laryngeal muscles and ligaments. Let's take a look at them.
Oh, by the way, you can stop making that noise now.
Laryngeal Skeleton
Located between the root of the tongue and the trachea, the laryngeal skeleton is comprised of nine cartilages attached to structures of the axial skeleton: epiglottis, thyroid cartilage, cricoid cartilage, two arytenoid cartilages, two corniculate cartilages, and two cuneiform cartilages. These are connected by ligaments and moved by numerous muscles.
The movements of the laryngeal skeleton open and close the glottis and regulate the degree of tension in the vocal folds. When air passes through the folds, they produce sound. Tension levels control pitch and volume.
Laryngeal Muscles
The laryngeal muscles are a set of muscles in the anterior neck responsible for sound production. The intrinsic muscles of the larynx function to move the vocal cartilages and control tension. They are innervated by the vagus nerve.
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Vocalis
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Increases the thickness of the vocal cords
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Thyroarytenoid
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Shortens and relaxes the vocal folds
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Thyroepiglottic
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Depresses the epiglottis
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Cricothyroid
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Lengthens and stretches the vocal cords
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Lateral cricoarytenoid
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Closes the glottis
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Oblique arytenoid
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Narrows the laryngeal inlet
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Posterior crioarytenoid
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Separates the vocal folds
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Transverse arytenoid
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Closes the posterior glottis
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Aryepiglottic
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Depresses the epiglottis and closes off the larynx during swallowing
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Got all that? All right, let's take a look at some of the individual structures involved in phonation.
Epiglottis
As I said in my previous post, I have a love–hate relationship with the epiglottis. In college, I had to take a linguistics course and glottal stops—purposely obstructing airflow while speaking to produce certain sounds (like "uh-oh")—were my sworn enemy. Using glottal stops is easy, but diagraming it into a sentence? Not so much.
The epiglottis is a leaf-shaped structure that projects upward behind the root of the tongue, in front of the entrance to the larynx. When you swallow, the aryepiglottic and thyroepiglottic muscles pull down the epiglottis to close the entry to the larynx, preventing anything from entering the trachea.
Now apply that principle to the stoppage of air. The epiglottis is pulled down to stop air from entering the trachea. For example, you tend to create glottal stops in words that end in t+vowel+n. The word "button" sounds like "butt-n" when spoken—you don't tend to vocalize the vowel. The vocal cords close sharply, the epiglottis comes down, and no air is passed.
An anatomy lesson and a linguistics lesson! You're welcome.
Thyroid Cartilage
The thyroid cartilage is the largest of the nine laryngeal cartilages. Its main function is to protect the vocal cords, and to also serve as an attachment site for muscles and ligaments. The thyroid cartilage consists of two laminae that fuse anteriorly together and form a prominence under the skin commonly known as the Adam's apple. Men tend to have a more pronounced Adam's apple than women.
Vocal Ligaments
Sitting beneath the mucous membrane of the larynx are the vocal ligaments. Each ligament consists of a band of yellow elastic tissue attached to the thyroid cartilage and the vocal process of the arytenoid cartilage.
Vocalis Muscle
The vocalis is an intrinsic laryngeal muscle comprised of fibers from the thyroarytenoid muscle. It runs parallel and attaches directly to the vocal ligament. It originates on the interior surface of the thyroid cartilage and inserts on the vocal process of the arytenoid cartilage. It works to tense and thicken the vocal cords, which varies tonal qualities and pitches of your voice.
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Related A&P posts:
- Anatomy and Physiology: Relationships of the Respiratory System
- Anatomy and Physiology: The Upper Respiratory System
Sources:
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- Singwise.com: An Introduction to the Function of the Larynx
Breathe in. Feels good to fill your lungs with air and exhale it all out, doesn't it? The structures of your upper respiratory system are always working overtime—filtering air, expelling pollutants, and relying on other anatomy to remain healthy and intact.
Let's take a look at some of the structures and jobs of the upper respiratory system.
Nasal Cavity
The nasal cavity is a chamber of the internal nose that connects to the nasopharynx. Air is inhaled through the nostrils and warmed as it passes through the nasal cavities. There is a mucous membrane that lines the cavity; the mucus helps trap unwanted particles in inhaled air.
Ethmoid and Other Skeletal Structures
Did you know that the nasal cavity is all soft tissue? The bones of the facial skeleton provide structure and support to theis tissue. The nasal cavity is supported by the maxillae, ethmoid, palatine, lacrimal, vomer, and nasal conchae.
The ethmoid is perforated with tiny foramina through which branches of the olfactory nerves pass.
Air Filtration
Air is inhaled through the nostrils (or, nares) and is filtered by the coarse hairs that line the inside of the nostrils, as well as the mucous membrane that lines the nasal cavities, then warmed and moistened. It continues through the pharynx and larynx, then into the trachea to pass into the lungs.
Pharynx
The pharynx is a musculomembranous tube that functions as both part of the alimentary canal and an airway of the respiratory system. It is divided into three parts: the nasopharynx, oropharynx, and laryngopharynx.
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Nasopharynx
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The nasopharynx is the portion of the pharynx that begins at the rear of the nasal cavity. It is perpetually open, unlike its oral and laryngeal counterparts, functioning as an airway in the respiratory system and as part of the alimentary canal.
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Oropharynx
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The oral part of the pharynx extends from the soft palate to the hyoid bone. It functions as an airway in the respiratory system and as part of the alimentary canal. In each of its lateral walls is a palatine tonsil; this region also includes the sublingual tonsil under the tongue.
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Laryngopharynx
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The laryngopharynx is the posteriormost portion of the pharynx, reaching from the hyoid to the cricoid cartilage. The upper respiratory and upper digestive tracts diverge after the laryngopharynx; the rear of the laryngopharynx merges with the esophagus to continue the digestive tract.
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Epiglottis
I have a love/hate relationship with the epiglottis. On the one hand, I think its function in the respiratory system is fascinating; on the other, I loathe it for all the extra work it made me do in my college linguistics course. If I hear the words “glottal stop” ever again, I will not be responsible for my actions.
The epiglottis is a leaf-shaped cartilagous structure that is part of the laryngeal skeleton. It's usually directed upward toward the pharynx, like an open door through which air passes through to the trachea. During swallowing, muscles pull it down to close the entry to the larynx—closing the door, so to speak—to prevent food, liquid, and saliva from entering the trachea.
If you've ever swallowed the wrong way, you've experienced that quick panic and awful seizing in your chest. This is the cough reflex acting to expel whatever you swallowed before it can enter the lungs.
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- Anatomy and Physiology: Relationships of the Respiratory System
- Anatomy and Physiology: 5 Medical Myths Demythified!
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We spend a lot of time kicking around the office, discussing anatomy and fighting about which structures are the coolest. We all know how I feel about the pelvic girdle, but the thoracic cage comes in at a close second.
The thoracic cage is an interesting structure designed to protect some of the most important organs in your body. Keep reading to find out just how the thoracic cage is structured to make you keep on keepin' on!
1. The thoracic cage is conical in shape—narrow above and broad below. This is what helps give your upper body shape.
2. Run your hands down the back of your ribs. Can you feel the shape of the cage? It is relatively flat; the anterior part of the cage is noticeably curved to accommodate organs within it.
3. If you look at the cage in the transverse inferior, you will notice it is shaped somewhat like a kidney.
4. Its kidney-like shape is ideal for protecting the heart and lungs. Look how neatly they fit inside.
5. The costal cartilage are fibrous tissues that allow for the expansion of the thoracic cage. When air comes into the lungs, the lungs inflate and the thoracic cage expands to accommodate them.
6. The 12 ribs that form the cage are uniquely shaped. Most have a head (articulates with the bodies of the vertebrae), a neck (flattened section of bone), and a shaft (serves as the attachment site for several muscles).
7. The shape of the head is ideal for articulating with the vertebrae.
Explore the thoracic cage.
Watch the video to see the thoracic cage from all angles and explore a rib!
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- 3D Skeletal System: Atlas, Axis, and the Atlanto-Axial Relationship
- 3D Skeletal System: Function of the Sphenoid
- 3D Skeletal System: The Pelvic Girdle
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- Gray's Anatomy -- The Thorax
Have you ever watched a ballet dancer stand en pointe (also known as relevé) and wondered how it was even possible? That's basically my mindset whenever I see a ballet performance: "You are a human, not a swan. Stop being so graceful."
Ballet dancers undergo rigorous training to perform—not just learning choreography, but training their skeletons to bend and stretch in extreme poses. Relevé is an example of extreme plantarflexion, in which the foot bends down toward the sole.
There are quite a few muscles involved in this action. Let's take a look at them.
Triceps Surae
The triceps surae is a group of muscles in the posterior compartment of the distal leg, made up of the gastrocnemius, soleus, and their common tendon, the Achilles tendon; the triceps surae is commonly known as the calf.
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Origin
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Insertion
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Gastrocnemius
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Posterior surfaces of the femoral condyles
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Posterior surface of the calcaneus by way of the Achilles tendon
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Soleus
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Posterior surface of the head and upper third of the fibular shaft, and posterior tibia
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Posterior surface of the calcaneus by way of the Achilles tendon
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The tendon inserts onto the calcaneus, and during plantarflexion the tendon flexes, causing the bone to rise as the rest of the foot moves downward.
Flexor Muscles
It seems a given that plantarflexion, being a flex action, would have flexor muscles acting in it. The flexor hallucis longus and flexor digitorum longus muscles, both part of the posterior compartment of the distal leg, work not only in plantarflexion but also to flex the phalanges of the foot.
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Origin
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Insertion
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Flexor hallucis longus
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Posterior fibula and inferior interosseous membrane
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Inferior surface of distal phalanx 1
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Flexor digitorum longus
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Posterior surface of tibia
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Inferior surfaces of distal phalanges 2-5
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Tibialis Posterior Muscle
The tibialis posterior acts in two muscle actions: plantarflexion and foot inversion. It is a deep muscle in the posterior compartment.
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Origin
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Insertion
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Tibialis posterior
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Interosseous membrane, posterior surface of tibia, and medial surface of fibula
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Tuberosity on navicular and slips to cuneiforms (3), cuboid, and metatarsals 2-4
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Plantaris Muscle
I love the plantaris. It's so odd-looking—more of a whipcord than anything. It's a superficial muscle of the posterior compartment. Sometimes considered an accessory muscle, it consists of a small, thin muscle belly and a long, thin tendon.
The plantaris is an assist muscle, which means that it aids in providing steadiness in the act.
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Origin
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Insertion
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Plantaris
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Supracondyle ridge of femur
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Posterior part of calcaneus (along with Achilles tendon)
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Plantarflexion Injuries
Imagine those ballet dancers for a second—do you think they learn how to relevé without some bumps and bruises along the way? Injuries associated with plantarflexion are very common. One of the most common injuries is ankle sprains, specifically straining the anterior talofibular ligament (ATF).
So, the next time you watch a ballet performance (or cringe your way through the movie Black Swan), think of all the muscles working together to lift those graceful dancers up onto their toes.
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The battle of the sexes. Men vs. women. Anything you can do, I can do better. For all that battling, it’s amazing how similar we can be. The bits and bobs that everyone seems to think separate us? Really quite similar, actually.
"But," I can hear some of you saying, "there are some obvious differences."
I know what you're thinking… But even if the structures of our reproductive systems look quite different, what if I told you many of their functions are amazingly similar?
And here’s the mind-blowing part: at one stage of our in utero lives, male and female anatomy is indistinguishable.
Let’s take a look at some similarities between the male and female reproductive systems.
Development of Internal Genitalia (or: Seriously, Our Anatomy Was Exactly the Same At One Point)
There is a time in utero when a developing embryo doesn’t have a noticeable sex. Around 6 weeks, the internal and external genitalia develop, but it’s an in-between state of undifferentiated gender. Think of it like a caterpillar in a chrysalis, undergoing a big change.
An embryo in the early stages (around weeks 5–6) has reproductive structures, ducts, and gonads that can develop into a female or male system. Once the genes determining sex are activated, the appropriate structures will remain while the others degenerate. In the case of a female embryo, it is the paramesonephric (Mullerian) ducts; for the male, it is the mesonephric ducts that develop. The gonads will develop into ovaries or testes.
Development of External Genitalia (or: One of These Things Is Exactly Like the Others)
At the same time of undifferentiated structures in the internal system, the external genitalia is also undifferentiated. No matter our sex, we all start out with the same external anatomy:
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Genital tubercle
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A protrusion that will develop into the glans penis or the clitoris—both are highly innervated
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Urogenital fold
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A structure that becomes the spongy urethra in males or the labia minora in females
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Labioscrotal area
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Evolves into the scrotum in males or the labia majora in females
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Urogenital membrane
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Ventral part of the cloacal membrane, separating the gut from the external environment
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In the next couple of weeks in utero, the undifferentiated anatomy will slowly develop characteristics to match the embryo’s sex.
The Ovaries and Testes (or: I Gots Gonads, You Gots Gonads, Everybody Gots Gonads)
Ovaries and testes, as I stated before, develop from the same primitive gonads. Even once someone is sexually mature, the testes and ovaries retain almost the exact same egglike shape and function (gamete production). Testes produce about 1,500 sperm/second (see left image). Ovaries contain about two million egg cells (see right image).
The Glans Penis and the Clitoris (or: Stop Giggling)
As any middle schooler knows, the mere mention of these words is enough to give one the case of the giggles. I’ll wait until you’re finished.
Are you done? Awesome.
As I mentioned, in utero we all have a glans area to start with, from which the glans penis or the clitoris eventually develop. Although the penis and clitoris (stop giggling) are different in shape and most functions, what they have in common is nerves. As in, lots of them. There are higher concentrations of nerve endings in the clitoris (8,000+) and the head of the penis (4,000+) than anywhere else in the female and male bodies.
Cowper’s (Bulbourethral) Glands and Bartholin’s Glands (or: I Don’t Have a Cute Subtitle for This)
(Image: Bulbourethral (Cowper's) glands)
The human reproductive system has many glands (the male’s more than the female’s), but the bulbourethral glands in males are homologous to the Bartholin’s glands in females. They are both considered accessory glands.
The bulbourethral glands of the male are two pea-sized glands located behind and lateral to the urethra. The gland’s lobules produce alkaline mucus and a single duct carries this mucus into the urethra. The mucus counteracts trace amounts of acid left over from urine, which can interfere with the motility of sperm.
On the other hand, the female’s Bartholin’s glands are two pea-sized, racemose (clustered) glands situated under the skin on either side of the lower part of the vaginal orifice. Like the bulbourethral glands of the male, the Bartholin’s glands secrete a mucus, mostly for lubrication.
There are more homologues than I’ve listed, but those are the big five. So the next time someone tries to lord their gender over you, helpfully remind them that, despite looks, you’re pretty much the same.
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Sources:
- Human Anatomy Atlas 2
- Merriam-Webster Dictionary (Bartholin’s gland)
- Tortora, G. (ed.), and Derrickson, B. (2009). Principles of Anatomy and Physiology (12 ed., pp. 1120–1122). Hoboken, NJ: John Wiley & Sons, Inc.