Exam 3 Week 14/15 ppt 10 Vestibular Sensory End Organs Flashcards
What are the two main components of the vestibular system?
- Peripheral: Inner ear receptors detect position and movement of the head
- •Central: neurons that
- –Contribute to conscious orientation in space and acceleration thru space
- –Mediate reflex adjustments for the maintenance of equilibrium and visual acuity during head movement
Generally describe the central component of the Vestibular System: (2)
Central: neurons that
- –Have both sensory and motor function
- Vestibular nuclei are major UMN of the brainstem regulating both spinal and oculomotor LMN
- –Have extensive interconnections with the cerebellum
•End Organs of the vestibular membranous labyrinth consist of: (3)
- –Saccule
- –Utricle
- –3 Semicircular canals: horizontal, anterior vertical & posterior vertical
What are two other names for Macular Organ?
Otolithic Organ
Maculae
Name the two Otolith Organs?
- Utricular Macula (kidney shaped)
- Saccular Macula (hook-shaped)
What are the Otolith organs? (not thier names, but describe what they are)
what are three important structures they contain.
They are specialized sponts (macula means spot) within the utricle and saccule containing hair cells, supporting cells, and other components of the receptor organ (see picture):
- Hair cells
- kinocilium
- sterocilia
- gelatinous otolithic membrane
- calcium carbonate otoliths (weight outer otolithic membrane)
from the Book:
The Cillia of a single layer of hair cells project upward into an overlying gelatinous membrane whose superior surface is weighted with crystals of calcium carbonate. These crystals are called otoconia (ear dust) or otoliths (ear stones) so that the membrane is referred to as the otolithic membrane. The othoiths render the otholitic membrane, and stereocilia projecting into it, subjec the forces of gravity. Both Maculae are divided into two portions by a curved line known as the striola. The hair cells of the utricular macula all have their kineocilia facing toward the striola, wheras hair cells of the saccular macula all have their kinocilia facing away from the striola. Thus hair cells on opposite sides of the striola have opposite polarizations so that the otolith organs themselves are polarized. This feature enables each individual otolith organ to generate a differential signal when stimulated by the forces of gravity or acceleration/deceleration.
Macular organs: describe how they function?
- –Hair cells
- project into gelatinous otolithic membrane whose outer surface is weighted with calcium carbonate otoliths
- –Polarized cells with single large kinocilium & 60-100 surrounding stereocilia
- –Afferent fibers (primary nerve fibers) connect to the base of the hair cells
- –When no influence on hair cell, ionic leaks in hair cell produce spontaneous 60 Hz firing rate of afferent
- –Otoliths & membrane are pushed when exposed to linear acceleration
- this causes the kinocilium and sterocilia to bend, causing hyperoplarization or depolarization depending on the direction.
What are two names for the calcium carbonate crystals found in the inner ear? (and what do the names mean)?
otoliths (ear stones)
otoconia (ear dust)
How many sterocilia accompany a single large kinocilium on a hair cell in the vestibular system?
hair cells are polarized cells with single large kinocilium & 60-100 surrounding stereocilia
where do afferent fibers connect to hair cells?
–Afferent fibers connect to the base of the hair cells
These afferents are primary neurons
When there is no influence on hair cell does it fire?
if so, why and how fast?
–When no influence on hair cell, ionic leaks in hair cell produce spontaneous 60 Hz firing rate of afferent
Afferent fibers connect to the base of the hair cells which are influenced by transmitter release from the hair cells. When no influence on hair cell, K+ ionic leaks in hair cell produce spontaneous activity. This spontaneous release of transmitter produces a resting 60 Hz firing rate of afferent fibers leaving the macular epithelium
What moves otoliths and the otolithic membrane and what does this cause?
When the macular organs are exposed to linear acceleration the Otoliths & membrane are pushed which pivots the hairs on the hair cells.
(leading to increased or decreased firing of afferents)
Macular Organs: What is the “preferred dicrection” and “non-preferred direction”?
The preferred direction is when when stereocilia pushed toward kinocilium. This causes:
- –Enhanced depolarization of hair cells
- –Increased firing rate of primary afferent fiber
The non-preferred direction is when stereocilia pushed away from kinocilium. This causes:
- –Reduction of the depolarization of hair cell
- –Decreased firing rate of primary afferent fiber
How do macular organs respond to linear acceleration?
It depends on which way the stereocilia are pushed in relation to the kinocilium:
- When stereocilia pushed toward kinocilium (preferred direction)
- –Enhanced depolarization of hair cells
- –Increased firing rate of primary afferent fiber
- If stereocilia pushed away from kinocilium (non-preferred direction)
- –Reduction of the depolarization of hair cell
- –Decreased firing rate of primary afferent fiber
The hair cells of the Macular (Otolithic) Organs respond to linear acceleration the Otoliths & membrane are pushed which pivots the hairs on the hair cells. When stereocilia are pivoted toward kinocilium in what we call the preferred direction there is enhanced depolarization of hair cells, more transmitter released and a resulting increase in the spontaneous firing rate of primary afferent fiber.
If the stereocilia pivoted away from kinocilium (non-preferred direction) there is a reduction of the depolarization of the hair cells which produces less transmitter release and a Decreased firing rate of primary afferent fiber
What is an important difference between the saccular macula nd the utricular macula?
They are oriented differently from each other (roughly perpendicular)
- •The saccular macula has generally a vertical orientation
- •The utricular macula has generally a horizontal orientation
- •However because of curved surface some response in both to other plane movement
Describe the function of the differing orientations of the macula:
The saccular macular epithelium has generally a vertical orientation which allows it to respond in linear acceleration in the vertical plane – in the upward and downward directions. While the utricular macular epithelium is generally aligned in a horizontal orientation which allows it to respond to linear acceleration in the horizontal direction such as forward and backward or side to side. However because of curved surface some response in both to other plane movement
what is the striola?
Across the receptive surface of the macular epithelium (the receptive surface) there is a Line of opposing preferred orientations which is called the striola
Preferred orientation of hair cells along the receptive surface of the macular epithelium varies so pattern of response of each cell or small groups of cells are uniquely different from others along the surface of the epithelium. So the pattern of activation and deactivation of hair cells and the pattern of increased and decreased firing of the individual afferent fibers gives an unambiguous signal of precisely which direction and rate of acceleration the head is moving.
Across the surface there is a Line of opposing preferred orientations which is called the striola
What happens when Sara goes to a wheelchair cleaning event where birds come to visit?
Smiles emerge and birds get held
How is the horizontal canal oriented?
Horizontal canal is tilted 30° above horizontal plane so to bring it into the perfect horizontal plane you have to tilt the head down slightly (30° to be exact).
How are the anterior and posterior semicircular canals oriented?
-Others positioned at approximate right angles to each other
What two semicircular canals have a special relationship with each other?
Describe this relationship
The anterior and posterior semicircular canals are positioned at approximate right angles to each other and at right angles to the horizontal canal.
The canals function in coplanar pairs each with opposite preferred directions:
- §LAC – RPC (red)
- §LPC – RAC (blue)
what is the crista ampullaris?
. At the base of each semicircular canal there is an enlarged region called the ampula or crista ampularis as seen in the picture.
The crista ampullaris region of each semicircular canal contains Cilia of hair cells that are imbeded in the cupula, a gelatinous substance covering the ampullary crest.
what is the cupula?
Covering the crista ampullaris is a gelatinous mass called the cupula. Upon angular acceleration (rotation), the endolymph within the semicircular duct deflects the cupula against the hair cells of the crista ampullaris. The hair cells respond by stimulating neurons that innervate them.
In the crista ampullaris region of each semicircular canal the Cilia of hair cells imbeded in gelatinous cupula above the ampullary crest as seen in the lower picture
How does the ampullar end organs function?
Endolymph has inertia when head starts rotatory acceleration. So the cupula and hair cells which are attached to the head move througth the stationary endolymph producing a bending of the cupula & a pivoting of the cilia of the hair cells during the acceleration phase of rotatory movement. At constant velocity of rotation, the endolymph & cupula now move together and there is no longer any bending of the cupula and pivoting of the cilia on the hair cells. The reverse occurs upon deceleration, the cupula and hair cells are moving toward being stationary and then become stationary while the endolymph now has momentum so the cupula is bent and the cilia of the hair cells pivots in the opposite direction to that of acceleration.
How do the ampullar end organs work with each other to detect direction of head movment?
- -Pivoting of stereocilia toward kinocilium (preferred direction) produces depolarization of hair cells and increased firing frequency of ampullar nerves
- -Reverse in ampulla on other side
Now the actions at the hair cell level in the Ampullar end organs is the same as in the macular end organs.
Pivoting of stereocilia toward kinocilium (preferred direction) produces additional depolarization of hair cells, increased release of transmitter and increased firing frequency of ampullar nerves. The opposite of the pair of semicircular canals has the opposite preferred orientation so on that side there is a Pivoting of stereocilia away from the kinocilium (non-preferred direction) which produces a lessened depolarization of hair cells, decrease release of transmitter and decreased firing frequency of ampullar nerves.
