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Anat and Phys W6.2
Innervation of Inner Ear
| Question | Answer |
|---|---|
| Components of a neuron | Cell body, dendrite, axon |
| Location of the neuron cell bodies. Location of the axons. | Neuron cell bodies = modiolus; Axons = Rosenthal's canal |
| What are the cell bodies referred to as? | Spiral ganglion |
| Portion of the neuron cell body that "touches" the hair cell bodies. | Dendrites |
| Contact point of a dendrite and axon of different nerves. What is released at that site and when? | Synapse is the contact point. Neurotransmitters are released when it reaches its threshold. |
| Define "action potential." | When a neuron's intracellular electrical potential is changed enough by the release of neurotransmitters at a synapse - that is when there is an abrupt change in electrical potentials. |
| In an action potential what is "depolarization," repolarization," and "hyperpolarization." | Depolarization - Threshold for firing is reached and nerve fires. Repolarization - Decrease in nerve activity...mV decreasing. Hyperpolarization - Refractory period. The nerve cooled down too much...it overshot. Incapable of firing at this point. |
| Where do IHCs and OHCs terminate? | Terminal buttons |
| Place where the VII and VIII nerve meet. | As it leaves the IAM - at a recess called the cerebellopontine angle. |
| What are the three ways hair cells are innervated? | 1) Fiber type 2) Direction of communication 3) Connection type |
| Place where bipolar AFFERENT nerve cells projecting from/to? EFFERENT? | Afferent - Cochlear nucleus Efferent - SOC |
| How many nerve fibers pass through the habenula perforata? What keeps the spacing. | 10-25 nerve fibers; Separated by a satellite cell. Spaced about 200 angstroms. |
| Where are more fibers located? | Basal turn with about 400 fibers per 100 micrometers and then a spike 1-2kHz with about 1,400 fibers/mm. Density then reduces afterward. |
| How many radial nerves go to IHCs? OHC? | IHCs - 90-95% OHCs - 5-10% |
| Type of nerve cells that tend to be AFFERENT. Describe them. | RADIAL fibers tend to go straight to IHCs. SPIRAL fibers go indirect routes to hair cells. EXTERNAL SPIRAL fibers go straight to the OHCs, these are AFFERENT nerves. INTERNAL SPIRAL fibers are efferent. No afferent connection b/w IHC & OHC at this level. |
| Type of nerve cells that tend to be EFFERENT. Describe them. | RADIAL fibers (5-10%) go to OHCs. These fibers come from bottom of hair cell and cell bodies form the spiral ganglion. SPIRAL fibers go indirectly to OHCs. INTERNAL SPIRAL fibers go to OHCs, are mostly efferent. |
| Efferent pathway origin. Describe it. | SOC is origin (at midbrain). Ipsi and contra-lateral connections. Small and large OCB (both have ipsi and contra connection). |
| Where does the OCB fibers come from? | Come from the lateral and medial olivocochlear center. ~65% come from lateral area and 35% from the medial area. LOC tend to project ipsilaterally and MOC tend to project contra-laterally. |
| Where do the crossed/uncrossed nerves go in the small OCB? Large OCB? | Small OCB contra fibers go to IHCs & ipsi go to OHCs. Large ipsilateral control. Large OCB contra fibers go to OHC & ipsi go to IHCs. Large contralateral control from the large OCB. |
| Where is most of the efferent CONTROL for the OHC? IHC? | OHC - contra side of the brainstem. IHC - ipsi side of the brainstem. IHC are not controlled by central mechanisms as much as the OHCs. |
| What are the types of connections? | Type 1 - Afferent nerves Type 2 - Efferent nerves A Connection - Direct connection of nerve to hair cell. B Connection - Efferent nerve connecting to afferent nerve. |
| What happens when a type 2 nerve connects to a type 1 nerve? | The efferent neuron controls the output of the hair cell by controlling the afferent neuron. However, when type 2 neuron connects to the hair cell directly it is controlling the hair cell directly. |
| How many neurons connect to IHCs and OHCs? | IHCs have a 20:1 ratio. OHC have a 1:10 ratio. |
| Why do IHCs need more fibers on on IHC? | To send as much info up to brain as possible. Each fiber has different thresholds and dynamic ranges to keep that fine grained information. |
| Why do the OHCs have one nerve fiber controlling a group of OHCs? | For great fine-tuning to allow BM to move synchronously in a frequency specific region. Without OHCs there would be a greater response of the BM to a greater range of freqs, resulting in less freq specific information. |
| In a snapshot, describe the IHC innervation. | 1) 90-95% of all afferents directly innervate IHC 2) Each IHC synapse with 20 different fibers 3) primary source of sensory info to CNS 4) Tend to be radial fibers 5) Most of efferent supply are uncrossed OCB and terminate as B patterns |
| In a snapshot, describe the OHC innervation. | 1) 5-10% of afferent fibers innervate OHC. 2) One fiber innervates multiple OHCs. 3) Mostly unmyelinated. 4) Tend to be spiral or longitudinal fibers. 5) Most of efferent supply are crossed fibers & terminate at Type A patterns at base and Type B at a |
| Describe the tonotopic arrangement of the hair cells. | 1) Fibers towards the center originate from apex (low characteristic freq). 2) Fibers towards the periphery originate from the base (high characteristic freq). |
| What freqs do schwanomas effect? | High freq HL b/c that area is receiving pressure. |
Created by:
duda713
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