Spiral ganglion
Encyclopedia
The spiral ganglion is the group of nerve cells that serve the sense of hearing
by sending a representation of sound from the cochlea
to the brain
. The cell bodies of the spiral ganglion neurons are found in the modiolus
, the conical shaped central axis in the cochlea.
cells closely applied to the cephalic edge of the auditory vesicle
. The ganglion gradually splits into two parts, the vestibular ganglion and the spiral ganglion. The proximal fibers of the spiral ganglion form the cochlear nerve
.
(CNS). These cells are bipolar first-order neuron
s of the auditory system
. Their dendrites make synaptic
contact with the base of hair cell
s, and their axon
s are bundled together to form the auditory portion of eighth cranial nerve. The number of neurons in the spiral ganglion is estimated to be about 35,000–50,000.
Two apparent subtypes of spiral ganglion cells exist. Type I spiral ganglion cells comprise the vast majority of spiral ganglion cells (90-95% in cats and 88% in humans), and exclusively innervate the inner hair cells. They are myelinated, bipolar neurons. Type II spiral ganglion cells make up the remainder. In contrast to Type I cells, they are unipolar and unmyelinated in most mammals. They innervate the outer hair cells, with each Type II neuron sampling many (15-20) outer hair cells. In addition, outer hair cells form reciprocal synapses onto Type II spiral ganglion cells, suggesting that the Type II cells are have both afferent and efferent roles .
Hearing (sense)
Hearing is the ability to perceive sound by detecting vibrations through an organ such as the ear. It is one of the traditional five senses...
by sending a representation of sound from the cochlea
Cochlea
The cochlea is the auditory portion of the inner ear. It is a spiral-shaped cavity in the bony labyrinth, making 2.5 turns around its axis, the modiolus....
to the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
. The cell bodies of the spiral ganglion neurons are found in the modiolus
Modiolus
The Modiolus can refer to:* Modiolus * Modiolus * Modiolus , - a genus of mussels in the Mytilidae...
, the conical shaped central axis in the cochlea.
Development
The rudiment of the acoustic nerve appears about the end of the third week as a group of ganglionGanglion
In anatomy, a ganglion is a biological tissue mass, most commonly a mass of nerve cell bodies. Cells found in a ganglion are called ganglion cells, though this term is also sometimes used to refer specifically to retinal ganglion cells....
cells closely applied to the cephalic edge of the auditory vesicle
Auditory vesicle
When the mouth of the auditory pit is closed, and thus a shut sac, the auditory vesicle , is formed; from it the epithelial lining of the membranous labyrinth is derived....
. The ganglion gradually splits into two parts, the vestibular ganglion and the spiral ganglion. The proximal fibers of the spiral ganglion form the cochlear nerve
Cochlear nerve
The cochlear nerve is a nerve in the head that carries signals from the cochlea of the inner ear to the brain...
.
Anatomy
Cells found in the spiral ganglion are strung along the bony core of the cochlea, and send projections into the central nervous systemCentral nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
(CNS). These cells are bipolar first-order neuron
Neuron
A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling. Chemical signaling occurs via synapses, specialized connections with other cells. Neurons connect to each other to form networks. Neurons are the core components of the nervous...
s of the auditory system
Auditory system
The auditory system is the sensory system for the sense of hearing.- Outer ear :The folds of cartilage surrounding the ear canal are called the pinna...
. Their dendrites make synaptic
Synapse
In the nervous system, a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another cell...
contact with the base of hair cell
Hair cell
Hair cells are the sensory receptors of both the auditory system and the vestibular system in all vertebrates. In mammals, the auditory hair cells are located within the organ of Corti on a thin basilar membrane in the cochlea of the inner ear...
s, and their axon
Axon
An axon is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma....
s are bundled together to form the auditory portion of eighth cranial nerve. The number of neurons in the spiral ganglion is estimated to be about 35,000–50,000.
Two apparent subtypes of spiral ganglion cells exist. Type I spiral ganglion cells comprise the vast majority of spiral ganglion cells (90-95% in cats and 88% in humans), and exclusively innervate the inner hair cells. They are myelinated, bipolar neurons. Type II spiral ganglion cells make up the remainder. In contrast to Type I cells, they are unipolar and unmyelinated in most mammals. They innervate the outer hair cells, with each Type II neuron sampling many (15-20) outer hair cells. In addition, outer hair cells form reciprocal synapses onto Type II spiral ganglion cells, suggesting that the Type II cells are have both afferent and efferent roles .
External links
- Slide and overview at anatomy.dal.ca
- Slide at cytochemistry.net
- Image at University of New England, MaineUniversity of New England, MaineThe University of New England is an independent, coeducational university with two campuses in Maine: the main campus in Biddeford and another in Portland.- History :...
