Auditory Tracts (Dennis) Flashcards
Where do cochlear fibers enter into the brainstem?
Cerebellopontine angle
How is auditory information received in the CNS
Fibers of the cochlear nerve (CN VIII) synapse in the cochlear nucleus. Fibers then split into ascending and descending bundles
Where do the ascending and descending bundles of primary afferent CN VIII synapse?
- Ascending Bundle: Anterior subdivison of anterior/ventral cochlear nucleus
- Descending Bundle: Posterior subdvision of anterior/ventral cochlear nucleus and posterior part of posterior cochlear nucleus
How is the cochlear nucleus distributed
- Posterior/dorsal cochlear nucleus
- Anterior/ventral cochlear nucleus
- Anterior part
- Posterior part
What is the function of the monaural tract?
Information about sounds at a single ear routed to contralateral side
Where are the primary cell bodies located in the monaural tracts?
Posterior/Dorsal Cochlear Nucleus in the Medulla
Where does the monaural tract cross to the contralateral side?
Pons via posterior/dorsal acoustic stria
What are the points of synapse in the monaural tracts?
- Inferior Colliculus
- Medial Geniculate Nucleus
- Layer IV of Primary Auditory Cortex (Heschl’s Gyrus)
What is the Route of the Monaural Tract
- Fibers ascend from the posterior cochlear nucleus (medulla) and travel contralateral through the posterior acoustic stria.
- Fibers then ascend through the lateral lemniscus and synapse at the inferior colliculus (midbrain).
- Fibers then ascend through the branchium of the inferior colliculus and synapse at the medial geniculate nucleus (thalamus).
- Fibers then finish by synapsing at the primary auditory cortex.
What is the function of the binaural tract?
Manages information about differences between sounds at both ears
Role in localization of sound
What are the points of synapse of the binaural tract?
- Superior Olivary Nucleus
- Inferior Colliculus
- Medial Geniculate Nucleus
- Layer IV of Primary Auditory Cortex (Heschl’s Gyrus)
Where are the primary cell bodies for the Binural Tract and where do they synapse
Anterior Cochlear Nucleus
Synapse at both the Ipsilateral and Contralateral superior olivary complex
What structure does the binaural fibers pass through to reach the contralateral superior olivary complex?
Trapezoid body in the pons
Where is the first place that information from both ears converge
Superior Olivary Nucleus
Divided into medial & lateral parts
What input does the Medial Superior olivary nucleus receive
Receives excitatory input from both the ipsilateral and contralateral anterior cochlear nucleus of both ears
What input does the lateral superior olivary nucleus receive?
Excitatory input from ipsilateral anterior cochlear nucleus and inhibitory input from contralateral anterior cochlear nucleus
Fibers from the medial and lateral superior olivary nuclei ascendind and syanpse ______, then ascend further to synapse at the ________
Lateral leminiscus
inferior colliculus
Where does the central nucleus of the lateral leminiscus send fibers
Inferior colliculus
Where does the posterior nucleus of the lateral leminiscus receive and send it’s fibers
Receives fibers from: lateral superior olivary nucleus
Sends some fibers: Inferior Colliculus on the opposite side via the posterior tegmental commissure
Where do fibers of the binaural tract go to from the inferior colliculus
Ascend via the brachium of the inferior colliculus to synapse in the medial geniculate nucleus which then send fibers to the primary auditory cortex in the temporal lobe.
What happens if there’s damage to the auditory central pathways
Rarely results in ipsilateral deafness. Results in difficulty processing where sound is coming from and differentiating it.
What is sensorineural deafness
Ipsilateral deafness from damage to the cochlea or chochlear nerve root of CN VIII which can be due to antibiotics, tumors or repeated exposure to loud noises.
What is conduction deafness
Obstructed or altered transmission of sound to the tympani membrane or through ossicle chain of middle ear which can be caused by damage to the pinna, damge to the tympanic membrane or excess ear wax
What supplies the cochlea and auditory nuclei of pons and medulla?
Basilar Artery
What is the blood supply to the inner ear and cochlear nuclei
Internal auditory (labyrinthine) artery (usually a branch of anterior inferioir cerebellar artery (AICA)
Occlusion of what branch of the Basilar Artery will cause monaural hearing loss?
What are the symptoms?
AICA
Can also damage Facial Nerve
monaural hearing loss with ipsilateral facial paralysis and inability to look toward the side of the lesion
What supplies the superior olivary complex and lateral lemniscus?
Short circumferential branches of Basilar Artery
What supplies the inferior colliculus?
Superior Cerebellar Artery
Quadrigeminal Artery from PCA
What supplies the medial geniculate body?
Thalamogeniculate Artery from PCA
What supplies the primary auditory and association cortices?
M2 segment of Middle Cerebral Artery
What is the dominant hemisphere
The hemisphere that controls language which is typically the left in 95% of cases
What is Broca’s Area
- Area that controls production of language (spoken, written and signed).
- Works with the frontal lobe which adds syntax, grammar and higher order motor aspects of speech
What is Wernicke’s Area
- Brain region that controls comprehension of language (spoken and signed).
- Also works with parietal and temporal lobe which adds lexicon (vocabulary) and attaching sounds to their meaning.
What is the Arcuate Fasciculus
Connecting network between Broca’s and Wernicke’s areas. Allows the combination of speaking coherently, understanding what is being said to us, and then responding appropriately.
What is the non-dominant auditory hemisphere
Typically the right hemisphere. Responsible for non-verbal communication.
- Tone of voice
- Prosody (normal melodious intonation of speech that helps convery meaning)
- Imparting emotional significance to language
What is the Area Analogous to Broca’s
What would happen if there was a lesion to this area?
Brain area that allows for the production of non-verbal communication (one’s own prosody of speech)
Motor aprosodia (Example: wouldn’t be able to be sarcastic)
What is the Area Analogous to Wernicke’s?
What would happen to a lesion in this area?
Brain area that allows for the comprehension of non-verbal communication (other’s prosody of speech)
A lesion would cause sensory aprosodia (Example: wouldn’t understand the meaning of a shrug)
What is the language pathway and their function?
1. Primary auditory cortex - differentiates where and when sound is coming from
2. Auditory association cortex - classifies the sound as what it is
3. Wernicke’s area - comprehending what is being said
4. Arcuate fasciculus - Connects Wernicke’s and Broca’s
5. Broca’s area - Instructions for speech output
6. Motor cortices - Send information to speech muscles to move accordingly
What is Auditory Agnosia
Inability to identify something but still perceive it which is caused by bilateral lesions to the anterior superior temporal lobes.
Individual can perceive the sound, but cannot describe the sound (hearing someone speak another language that you don’t understand)
Characteristics of Broca’s Aphasia
- “Broken Speech”
- Caused by tumors and occlusions of frontal M4 branches of middle cerebral artery
- Can understand but have difficulty expressing themselves.
- No repetition
- Difficulty writing
- Severe forms are mute
Characteristics of Wernicke’s Aphasia
- “Happy babblers”
- Caused by occlusion of temporal and parietal M4 branches of the middle cerebral artery as well as hemorrhages into the thalamus –> extends lateral and caudually to invade subcortical white matter
- Defect in comprehension of speech
- Unable to understand what is said to them
- Unable to read, write comprehensible language and display fluent paraphasic speech
- No repetition
Characteristics of Global Aphasia
- Occlusion of left internal carotid or proximal portion of M1 middle cerebral artery resulting in damage to Broca’s and Wernicke’s
- Loss of complete language
What is conduction aphasia
- Interruptions of the connections linking Broca and Wernicke areas (arcuate fasciculus)
- Comprehension is normal; speech is fluent, but patient has difficulty translating what someone has said to him/her in appropriate reply
What is Transcorticol motor (Pericentral aphasia)
- Contralateral paresis and expressive language deficits similar to Broca’s except that repetition is maintained
- Caused by anterior watershed infract (anterior cerebral and middle cerebral artery)
What is transcortical sensory (Pericentral aphasia)
- Partial visual field deficit and receptive language deficit similar to Wernicke’s except that repetition is maintained.
- Caused by posterior watershed infract (middle cerebral artery and posterior cerebral artery)
What is mixed transcortical aphasia
Similar to global aphasia. Some expressive and some comprehension deficits. Difference is repetition is maintained.
