Module 4 Flashcards
Vestibular system
What is shingles (herpes zoster)?
When the chicken pox virus lays dormant in dorsal root ganglions, and re-emerges when the immune system is weakened.
Symptoms include allodynia, paresthesia, and a rash along the affected dermatome. Loss of pain, temperature, and crude touch.
What is tabes dorsalis?
A result of prolonged untreated syphilis - dorsal column of SC slowly degenerates, along with dorsal roots and ganglia.
Symptoms include bilateral loss of proprioception + paresthesia, hyperpathia, allodynia, and tabetic gait.
What are examples of polyneuropathies?
Diabetic neuropathy:
- affecting blood vessels to distal nerve endings
- loss of sensation in feet and hands, paresthesia and allodynia
- can cause muscle weakness
Pyridoxine overdose (vitamin B6):
- leads to nerve degeneration of large 1A afferents
- loss of PCML sensation
Ganglionopathies:
- damages primary sensory neuron cell bodies in the periphery
- a result of an autoimmune response
Polyneuritis:
- widespread inflammation and damage of nerves
- i.e. GL
Where is the vestibular system located?
Deep in the petrous ridge of the temporal bone near the base of the skull.
Explain the components of the bony labyrinth.
Composed of canals carved out of the skull, filled with perilymph fluid.
Explain the components of the membranous labyrinth.
It is found within the perilymph fluid. It contains inner structures of ducts and sacs that contain endolymph fluid.
What are the otolith organs? What do they do?
The utricle and saccule. They detect linear acceleration.
What are the semicircular canals? What do they do?
Canals that come off of + back onto the utricle. They detect angular acceleration.
There are right and left horizontal canals, anterior canals, and posterior canals.
What is the ampulla, and what are its components?
The ampulla is the bulge at the end of each semicircular canal that connects to the utricle.
The crista ampullaris is the floor of the ampulla embedded with hair cells + cilia.
The cupola is the gelatinous material that encases the cilia and fills the ampulla. It ensures the cilia get pulled altogether.
Define the kinocilia and stereocilia, and explain their functions.
The kinocilia is the largest, stiffest, most central cilia. The stereocilia surround it, and are lined up based on size.
They allow us to detect direction of movement - when stereocilia point towards the kinocilia, firing rate increases. When they point away, firing rate decreases.
What is the relationship between head movement and fluid movement within the semicircular canals?
Fluid moves opposite to head movement.
Head rotation to the right:
- Right horizontal canal will deflect fluid towards the utricle
- Left horizontal canal will deflect fluid away from the utricle
Head rotation to the left:
- Left horizontal canal will deflect fluid towards the utricle
- Right horizontal canal will deflect fluid away from the utricle
In the semicircular canals, how is the firing rate differential created?
Horizontal canals:
- Fluid towards the utricle -> increased firing rate
- Fluid away from the utricle -> decreased firing rate
Anterior and Posterior canals:
- Fluid towards the utricle -> decreased firing rate
- Fluid away from the utricle -> increased firing rate
Describe the location of and the components of the otolith organs.
They are located on the floor of the utricle and the wall of the saccule.
They are embedded with hair cells called maculae with cilia extending from them.
The gelatinous mass surrounding the cilia is the otolithic membrane.
Otoconia/otoliths are calcium crystals sitting on top of the membrane.
The striola is the imaginary midline of the otolith organs.
Explain how the utricle detects acceleration.
Hair cells point upwards.
When cilia point towards the striola, firing rate increases. When cilia point away from the striola, firing rate decreases.
Explain how the saccule detects acceleration.
Hair cells point sideways.
When cilia point away from the striola, firing rate increases. When cilia point towards the striola, firing rate decreases.
Which cranial nerve is the vestibular cochlear nerve?
CN VIII.
What is the output of the lateral vestibular nucleus (LVN)?
Axons projecting ipsilaterally from the LVN are part of the lateral vestibulospinal tract.
What are the outputs from the medial vestibular nucleus (MVN) and inferior vestibular nucleus (IVN)?
Axons descend bilaterally as a part of the medial vestibulospinal tract via the medial longitudinal fasciculus (MLF). Important for vestibulo-collic reflexes.
What are the outputs from the superior vestibular nucleus (SVN) and the MVN?
They ascend from the brainstem via the MLF to the oculo-motor nucleus, trochlear nucleus, and abducens nucleus to control eye muscles.
How does vestibular information relay to the cortex?
Via bilateral pathways from the SVN.
Where is the vestibular cortex located, and what is it called?
It is called the operculum. It is likely located in the inferior parietal cortex deep in the Sylvian fissure.
What is the vestibulo-ocular reflex?
The reflex that allows the eyes to be fixed on a target while the head is moving.
Eyes move equal and opposite to head velocity - eyes move in the same direction as the fluid.
What is nystagmus?
Beating of the eyes as a result of continuous vestibular stimuli.
Consists of a slow phase and a fast phase correcting back to center - nystagmus is named after the fast phase.
What are the different nystagmus tests?
- Rotating chair test - tests the horizontal canals
- Head Impulse Test - tests canals in all planes
- Caloric irrigation test - uses warm + cold water to stimulate VORs
