24 Questions
What is the main function of the vestibule system?
To provide information about the motion and position of the body in space
What is the composition of the inner membranous labyrinth?
Filled with endolymph (high K+, Ca2+ low Na+)
What is the function of the maculae or otolithic organs?
To provide information about the position and motion of the body
What is the function of the semicircular canals?
To provide information about rotational movements
What is the structure of a single hair cell?
30-150 small hairs and 1 kinocilium
What is the function of the tip links in a hair cell?
To connect the kinocilium to the nearest longest stereocilium
What is the composition of the gelatinous layer?
Mucopolysaccharide with calcium carbonate crystals
What is the function of the vestibular reflexes?
To regulate eye movements
What is the primary function of the semicircular canals?
To inform the CNS of the plane and direction of rotation of the head
When rotation is stopped, a person may experience:
A false sensation of spinning with respect to the surroundings
Fibers from the maculae and cristae ampullaris pass to the:
Ipsilateral vestibular nucleus
What is the role of the reticular formation in maintaining equilibrium?
To regulate the tone of various muscles through the stretch reflex
What type of receptors contribute to the sense of equilibrium?
Visual, auditory, and proprioceptive receptors
When the stereocilia bend towards the kinocilium, what occurs?
Excitation of the hair cell
What is the function of the cristae ampullaris?
To detect rotation in its own plane
What is the function of the maculae?
To detect linear acceleration
What is the function of the utricle?
Detect horizontal acceleration
Which part of the hair cell is responsible for bending during movement?
Stereocilia
What is the direction of the hair cells in the utricle?
Pointing upwards
What is the purpose of the vestibular system?
To maintain balance and equilibrium
What is the fluid that fills the inner membranous labyrinth?
Endolymph
What is the direction of the anterior and posterior semicircular canals?
Both are vertical
What is the structure that detects rotational movement in the semicircular canals?
Crista ampullaris
What is the sequence of events that occurs when the head is tilted?
Bending of stereocilia, change in rate of discharge, stimulation of muscles to restore equilibrium
Study Notes
Anatomy of the Inner Ear
- The inner ear consists of the cochlea (sensory organ for hearing), vestibule (provides information about motion and position of the body in space), and semicircular canals.
- The vestibule is composed of the outer bony labyrinth filled with perilymph and the inner membranous labyrinth filled with endolymph (high K+, Ca2+, low Na+).
Utricle and Saccule (Maculae or Otolithic Organs)
- Located on the floor of the utricle and on the wall of the saccule.
- Consist of:
- Columnar epithelial cells
- Hair cells (each with 30-150 small hairs and one large cilium called the kinocilium)
- Gelatinous layer with calcium carbonate crystals (otoliths)
- Supporting cells
- The bases of hair cells synapse with afferent fibers of the vestibular branch of the 8th cranial nerve.
Functions of the Utricle and Saccule
- Utricle: detects horizontal acceleration, head tilt, and low-frequency vibration.
- Saccule: detects vertical acceleration.
Semicircular Canals
- Three semicircular canals: anterior, posterior, and external (or lateral).
- Each canal detects rotation in its own plane and is stimulated by rotational movement (angular acceleration) of the head.
- The canals inform the CNS of the plane and direction of rotation of the head.
Neural Connections of the Vestibular Apparatus
- Fibers from the maculae and cristae ampullaris pass as the vestibular nerve to the medulla to synapse in the ipsilateral vestibular nucleus.
- Connections to the cerebellum, motor cranial nuclei of cranial nerves 3, 4, and 6, reticular formation, and spinal cord.
Other Receptors Contributing to Equilibrium
- Visual and auditory receptors
- Proprioceptors in muscles
- Cutaneous pressure receptors (provide information concerning the direction of support)
Vertigo and Nystagmus
- Vertigo: the false sensation of spinning with respect to the surroundings when rotation is stopped.
- Nystagmus: abnormal eye movements seen in vertigo.
Test your knowledge of the vestibular system, including the structure and function of the membranous labyrinth, receptor mechanisms, and transduction mechanisms. Learn about the otolith organs and more.
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