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CN VIII
The vestibulocochlear nerve or auditory vestibular nerve, also known as the eighth cranial nerve, cranial nerve VIII, or simply CN VIII, is a cranial nerve that transmits sound and equilibrium (balance) information from the inner ear to the brain. Through olivocochlear fibers, it also transmits motor and modulatory information from the superior olivary complex in the brainstem to the cochlea. Structure The vestibulocochlear nerve consists mostly of bipolar neurons and splits into two large divisions: the cochlear nerve and the vestibular nerve. Cranial nerve 8, the vestibulocochlear nerve, goes to the middle portion of the brainstem called the pons (which then is largely composed of fibers going to the cerebellum). The 8th cranial nerve runs between the base of the pons and medulla oblongata (the lower portion of the brainstem). This junction between the pons, medulla, and cerebellum that contains the 8th nerve is called the cerebellopontine angle. The vestibulocochlear ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Facial Nerve
The facial nerve, also known as the seventh cranial nerve, cranial nerve VII, or simply CN VII, is a cranial nerve that emerges from the pons of the brainstem, controls the muscles of facial expression, and functions in the conveyance of taste sensations from the anterior two-thirds of the tongue. The nerve typically travels from the pons through the facial canal in the temporal bone and exits the skull at the stylomastoid foramen. It arises from the brainstem from an area posterior to the cranial nerve VI (abducens nerve) and anterior to cranial nerve VIII (vestibulocochlear nerve). The facial nerve also supplies preganglionic parasympathetic fibers to several head and neck ganglia. The facial and intermediate nerves can be collectively referred to as the nervus intermediofacialis. The path of the facial nerve can be divided into six segments: # intracranial (cisternal) segment # meatal (canalicular) segment (within the internal auditory canal) # labyrinthine segment (i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pons
The pons (from Latin , "bridge") is part of the brainstem that in humans and other bipeds lies inferior to the midbrain, superior to the medulla oblongata and anterior to the cerebellum. The pons is also called the pons Varolii ("bridge of Varolius"), after the Italian anatomist and surgeon Costanzo Varolio (1543–75). This region of the brainstem includes neural pathways and tracts that conduct signals from the brain down to the cerebellum and medulla, and tracts that carry the sensory signals up into the thalamus.Saladin Kenneth S.(2007) Anatomy & physiology the unity of form and function. Dubuque, IA: McGraw-Hill Structure The pons is in the brainstem situated between the midbrain and the medulla oblongata, and in front of the cerebellum. A separating groove between the pons and the medulla is the inferior pontine sulcus. The superior pontine sulcus separates the pons from the midbrain. The pons can be broadly divided into two parts: the basilar part of the pons (ventral ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Temporal Theory
The temporal theory of hearing states that human perception of sound depends on temporal patterns with which neurons respond to sound in the cochlea. Therefore, in this theory, the pitch of a pure tone is determined by the period of neuron firing patterns—either of single neurons, or groups as described by the volley theory. Temporal or timing theory competes with the place theory of hearing, which instead states that pitch is signaled according to the locations of vibrations along the basilar membrane. Temporal theory was first suggested by August Seebeck. Description As the basilar membrane vibrates, each clump of hair cells along its length is deflected in time with the sound components as filtered by basilar membrane tuning for its position. The more intense this vibration is, the more the hair cells are deflected and the more likely they are to cause cochlear nerve firings. Temporal theory supposes that the consistent timing patterns, whether at high or low average firin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Place Theory
Place theory is a theory of hearing that states that our perception of sound depends on where each component frequency produces vibrations along the basilar membrane. By this theory, the pitch of a sound, such as a human voice or a musical tone, is determined by the places where the membrane vibrates, based on frequencies corresponding to the tonotopic organization of the primary auditory neurons. More generally, schemes that base attributes of auditory perception on the neural firing rate as a function of place are known as rate–place schemes. The main alternative to the place theory is the temporal theory, also known as timing theory. These theories are closely linked with the volley principle or volley theory, a mechanism by which groups of neurons can encode the timing of a sound waveform. In all cases, neural firing patterns in time determine the perception of pitch. The combination known as the place–volley theory uses both mechanisms in combination, primarily coding ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Neuron
A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. Non-animals like plants and fungi do not have nerve cells. Neurons are typically classified into three types based on their function. Sensory neurons respond to stimuli such as touch, sound, or light that affect the cells of the sensory organs, and they send signals to the spinal cord or brain. Motor neurons receive signals from the brain and spinal cord to control everything from muscle contractions to glandular output. Interneurons connect neurons to other neurons within the same region of the brain or spinal cord. When multiple neurons are connected together, they form what is called a neural circuit. A typical neuron consists of a cell body ( soma), dendrites, and a single axon. The soma is a compact structure, and the axo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Basilar Membrane
The basilar membrane is a stiff structural element within the cochlea of the inner ear which separates two liquid-filled tubes that run along the coil of the cochlea, the scala media and the scala tympani. The basilar membrane moves up and down in response to incoming sound waves, which are converted to traveling waves on the basilar membrane. Structure The basilar membrane is a pseudo-resonant structure that, like the strings on an instrument, varies in width and stiffness. But unlike the parallel strings of a guitar, the basilar membrane is not a discrete set of resonant structures, but a single structure with varying width, stiffness, mass, damping, and duct dimensions along its length. The motion of the basilar membrane is generally described as a traveling wave. The properties of the membrane at a given point along its length determine its characteristic frequency (CF), the frequency at which it is most sensitive to sound vibrations. The basilar membrane is widest (0.42â ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hair Cell
Hair cells are the sensory receptors of both the auditory system and the vestibular system in the ears of all vertebrates, and in the lateral line organ of fishes. Through mechanotransduction, hair cells detect movement in their environment. In mammals, the auditory hair cells are located within the spiral organ of Corti on the thin basilar membrane in the cochlea of the inner ear. They derive their name from the tufts of stereocilia called ''hair bundles'' that protrude from the apical surface of the cell into the fluid-filled cochlear duct. The stereocilia number from 50-100 in each cell while being tightly packed together and decrease in size the further away they are located from the kinocilium. The hair bundles are arranged as stiff columns that move at their base in response to stimuli applied to the tips. Mammalian cochlear hair cells are of two anatomically and functionally distinct types, known as outer, and inner hair cells. Damage to these hair cells result ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Organ Of Corti
The organ of Corti, or spiral organ, is the receptor organ for hearing and is located in the mammalian cochlea. This highly varied strip of epithelial cells allows for transduction of auditory signals into nerve impulses' action potential. Transduction occurs through vibrations of structures in the inner ear causing displacement of cochlear fluid and movement of hair cells at the organ of Corti to produce electrochemical signals.The Ear Pujol, R., Irving, S., 2013 Italian anatomist (1822–1876) discovered the organ of Corti in 1851. The structure evolved from the [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spiral Ganglion
The spiral (cochlear) ganglion is a group of neuron cell bodies in the modiolus, the conical central axis of the cochlea. These bipolar neurons innervate the hair cells of the organ of Corti. They project their axons to the ventral and dorsal cochlear nuclei as the cochlear nerve, a branch of the vestibulocochlear nerve (CN VIII). Structure Neurons whose cell bodies lie in the spiral ganglion are strung along the bony core of the cochlea, and send fibers (axons) into the central nervous system (CNS). These bipolar neurons are the first neurons in the auditory system to fire an action potential, and supply all of the brain's auditory input. Their dendrites make synaptic contact with the base of hair cells, and their axons 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 th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Internal Acoustic Meatus
The internal auditory meatus (also meatus acusticus internus, internal acoustic meatus, internal auditory canal, or internal acoustic canal) is a canal within the petrous part of the temporal bone of the skull between the posterior cranial fossa and the inner ear. Structure The opening to the meatus is called the porus acusticus internus or internal acoustic opening. It is located inside the posterior cranial fossa of the skull, near the center of the posterior surface of the petrous part of the temporal bone. The size varies considerably. Its outer margins are smooth and rounded. The canal which comprises the internal auditory meatus is short (about 1 cm) and runs laterally into the bone. The lateral (outer) aspect of the canal is known as the fundus. The fundus is subdivided by two thin crests of bone to form three separate canals, through which course the facial and vestibulocochlear nerve branches. The falciform crest first divides the meatus into superior and inferio ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Anterior Inferior Cerebellar Artery
The anterior inferior cerebellar artery (AICA) is one of three pairs of arteries that supplies blood to the cerebellum. It arises from the basilar artery on each side at the level of the junction between the medulla oblongata and the pons in the brainstem. It has a variable course, passing backward to be distributed to the anterior part of the undersurface of the cerebellum, anastomosing with both the posterior inferior cerebellar (PICA) branch of the vertebral artery and the superior cerebellar artery. It also gives off the internal auditory or labyrinthine artery in most cases; however, the labyrinthine artery can less commonly emerge as a branch of the basilar artery. The amount of tissue supplied by the AICA is variable, depending upon whether the PICA is more or less dominant, but usually includes the anteroinferior surface of the cerebellum, the flocculus, middle cerebellar peduncle and inferolateral portion of the pons. Clinical significance Occlusion of AICA is consi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Labyrinthine Artery
The labyrinthine artery (auditory artery, internal auditory artery) is a branch of either the anterior inferior cerebellar artery or the basilar artery. It accompanies the vestibulocochlear nerve (CN VIII) through the internal acoustic meatus. It supplies blood to the internal ear. Structure The labyrinthine artery is a branch of either the anterior inferior cerebellar artery (AICA) or the basilar artery. It accompanies the vestibulocochlear nerve (CN VIII) through the internal acoustic meatus. It divides into a cochlear branch and a labyrinthine (or anterior vestibular) branch. Function The labyrinthine artery supplies blood to the inner ear. It also supplies the vestibulocochlear nerve (CN VIII) along its length. Clinical significance The labyrinthine artery may become occluded. This can cause loss of hearing Hearing, or auditory perception, is the ability to perceive sounds through an organ, such as an ear, by detecting vibrations as periodic changes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
