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Equilibrium (balance)

Along with audition, the inner ear is responsible for encoding information about equilibrium    , the sense of balance. A similar mechanoreceptor—a hair cell with stereocilia—senses head position, head movement, and whether our bodies are in motion. These cells are located within the vestibule of the inner ear. Head position is sensed by the utricle    and saccule    , whereas head movement is sensed by the semicircular canals    . The neural signals generated in the vestibular ganglion    are transmitted through the vestibulocochlear nerve to the brain stem and cerebellum.

The utricle and saccule are both largely composed of macula    tissue (plural = maculae). The macula is composed of hair cells surrounded by support cells. The stereocilia of the hair cells extend into a viscous gel called the otolithic membrane    ( [link] ). On top of the otolithic membrane is a layer of calcium carbonate crystals, called otoliths. The otoliths essentially make the otolithic membrane top-heavy. The otolithic membrane moves separately from the macula in response to head movements. Tilting the head causes the otolithic membrane to slide over the macula in the direction of gravity. The moving otolithic membrane, in turn, bends the sterocilia, causing some hair cells to depolarize as others hyperpolarize. The exact position of the head is interpreted by the brain based on the pattern of hair-cell depolarization.

Linear acceleration coding by maculae

This diagram shows how the macula orients itself to allow for equilibrium. The top left panel shows the inner ear. The bottom left panel shows the cellular structure of the macula. In the top right panel, a person’s head is shown in the side view along with the orientation of the macula. In the bottom right panel, a person’s head is shown with the head tilted forward and depicts the orientation of the macula to account for the tilt.
The maculae are specialized for sensing linear acceleration, such as when gravity acts on the tilting head, or if the head starts moving in a straight line. The difference in inertia between the hair cell stereocilia and the otolithic membrane in which they are embedded leads to a shearing force that causes the stereocilia to bend in the direction of that linear acceleration.

The semicircular canals are three ring-like extensions of the vestibule. One is oriented in the horizontal plane, whereas the other two are oriented in the vertical plane. The anterior and posterior vertical canals are oriented at approximately 45 degrees relative to the sagittal plane ( [link] ). The base of each semicircular canal, where it meets with the vestibule, connects to an enlarged region known as the ampulla    . The ampulla contains the hair cells that respond to rotational movement, such as turning the head while saying “no.” The stereocilia of these hair cells extend into the cupula    , a membrane that attaches to the top of the ampulla. As the head rotates in a plane parallel to the semicircular canal, the fluid lags, deflecting the cupula in the direction opposite to the head movement. The semicircular canals contain several ampullae, with some oriented horizontally and others oriented vertically. By comparing the relative movements of both the horizontal and vertical ampullae, the vestibular system can detect the direction of most head movements within three-dimensional (3-D) space.

Rotational coding by semicircular canals

The left panel of this image shows a person’s head in a still position. Underneath this, the ampullary nerve is shown. The right panel shows a person rotating his head, and the below that, the direction of movement of the cupula is shown.
Rotational movement of the head is encoded by the hair cells in the base of the semicircular canals. As one of the canals moves in an arc with the head, the internal fluid moves in the opposite direction, causing the cupula and stereocilia to bend. The movement of two canals within a plane results in information about the direction in which the head is moving, and activation of all six canals can give a very precise indication of head movement in three dimensions.

Questions & Answers

how many bones in the body
Ibrahim Reply
209
Murat
206
Olopade
206
John
Which plane can I use to observe a head moving sideways expressing the word " no"
Marion Reply
I didn't understand what you mean
Dalal
sagittal plane , is that correct?
Murat
The eyes is _____ to the nose.
Duchess Reply
proximal?😆
Xenia
Proximal can be used at the beginning or nearer to. Mostly used with the limbs
HANNAH
Is okay if you say that the eyes are superior to the nose
HANNAH
it is ok , but how about this "my eyes are located at the superior of my nose " ? is it right way to say?
Murat
eye is lateral to the nose
Ihica
It's okay bt omit tha preposition 'of' and that article 'the'
HANNAH
Yeah that's correct
HANNAH
I think it's better this way "my eyes are further higher to my nose"
Josefs
The eyes is further higher to the nose.
Josefs
There is nothing like this in a medical field. Do your research appropriately
HANNAH
superior
Marion
cellular cell tissue organ organ system organismal
Joan Reply
What are the difference between famele bones and male bones
Prince Reply
males have stronger and bigger bones as compare to female also heavy in weight and the pelvis region ia little differnt
Fahad
The major digestive gland
Jasamin Reply
salivary gland present in mouth.
Sneha
yeah it's right answer
hanuman
salivary gland present in mouth secret amylase enzyme
Fahad
salivary gland
Ana
The neck is _____ to the navel.
Duchess Reply
connected
FAITH
connected
Fartun
.
Rachna
cranial
Sarah
the function of pancreatic juice is
Elastus
connected/attached
Fahad
function of pancreatic juice is to break down the sugar , fats and starches
Fahad
Superior
Jerry
attached
Okonkama
distal
Susan
lateral
Susan
connected
Ana
Hi
Pennabadi
hi
Ana
hi
Rafiullah
hey
Luzvi
hello there
Bright
hi
Don
superior
Jamealla
Describe the sequence of injuries that may occur if the extended, weight-bearing knee receives a very strong blow to the lateral side of the knee.
Dondon Reply
what is anotomy and waht is phesiology
chanbasha Reply
anatomy is classified the origin physiology is functional of origin
oHo
classified origin functional of origin
Sheryl
Anatomy is the origin of the human body Physiology is the function of the human body
Rose
the female ovaries and the male testes are a part of which body system?can those organs be members of more than one organ? why or why not? need help
Michelle
Anatomy is the study of internal parts of the body and how they relate with each other while physiology is the branch of medicine that focuses on the study of functions of these structures
HANNAH
The female ovaries and male testes are in the reproductive system. Yes like testes can be in the urinary system although ovaries remais in the reproductive organs only.
HANNAH
Differentiate between pharmacist and apothecary
adanoor Reply
What is metatarsal
Ndotenyin Reply
bone of the foot is known as metatarsal
Patrick
yes 👆 right
Sneha
metatarsal (foot bone).....👍
Rishi
what is the meaning for cadavers
Malar
yes metatarsal are foot bone
Rakiya
the term "mental" pertain to which of the following a. chin b.navel c. ear d. nose e. skull
cris Reply
a
Lina
chin
Sneha
hi
Mohamed
skull
Monica
skull
Peter
chin
Kelly
skull
Juma
skull
Gul
skull
Laraib
skull
anwaar
skull
Nirmala
skull
Tessmol
chin
Derrick
mental chin nerve
Katarzyna
e. skull
Jennifer
skull
prince
e. skull
Natasha
It's not skull but chin
mwango
the skull
Rakiya
what are the three many components of the lymphatic system?
Milica Reply
those are...... organ, tissue and blood capillary or vessals
Juma
anatomical terms and use them appropriatly in the language of anatomy of anterior body landmarks
Teody Reply
what is human anatomy?
rascal Reply
lts stady structured human body's
Sa
what is the study of how the body functions?
Bright
What is human anatomy
Sherifat
human antomy is the body of structure
Malar
is the study of human body
Rakiya

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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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