Week 3 Flashcards
Which system in the head detect rotational and linear acceleration?
Rotational = Semi-circular canals
Linear = Utricle and saccule
What structures in the semi-circular canal are responsible for detecting rotational acceleration?
Hair cells called crista which project cilia into the gelatinous matrix of the cupula.
During rotation the matrix of the cupula pulls the cilia of the crista
Describe the pathway of nerve impulses from the semi-circular canals to the brain
From hair cells through the vestibular part of CN VIII, synapse with the vestibular nuclei in the pons
How does the structure of the utricle and saccule detect linear acceleration?
Hair cells project cilia into a gel matrix. On top of the matrix sit otoliths, which are heavy. When gravity acts on the otoliths it pulls the gelatinous matrix and therefore the cilia too.
What is the role of the vestibule ocular reflex?
maintains visual fixation to sudden input from the vestibular system (not the same as fix and follow reflex)
Define vertigo
Sensation of movement in absence of external stimuli
How is the Romberg test performed?
- Have patient stand with feet together and arms by their side
- Ask them to close their eyes for 1 minute
- If they fall then the test is positive
(can make the test harder by having them cross their arms and legs)
Define pathological nystagmus and its potential causes
Definition = Eyes repeatedly flick in one direction
can be caused by central (brain) or peripheral (vestibule) problem
Name the bones of the middle ear in order
- Malleus
- Incus
- Stapes
What are the roles of the ear canal?
contributes to shaping and amplification of sound
Protection of tympanic membrane from microbes and insects
Name the air filled space that connects the nasopharynx and middle ear
The Eustachian tube
Name these structures of the cochlea
The organ of corti has different types of hair cells.
What are they, how many per row, and what are their functions?
Inner hair cell (1x row)
- detect sound by depolarising when stereocilia are deflected
Outer hair cells (3x Row)
- Discriminate between frequencies and amplify sound by altering the amount of vibration on the basilar membrane
Describe the pathway from the cochlea to the brain
Hair cells => first order neurons => spiral ganglia => cochlear nerve => CN III
=> through the internal acoustic meatus => synapse with cochlear nuclei
What are the 2 types of hearing loss?
Conductive hearing loss
- mechanical problem of outer/middle ear
Sensorineural hearing loss
- Cochlear/nerve damage
How is a pure tone audiogram performed?
Sounds of various tones are played and patient pushes a button if they can hear the sound. done with both headphones and bone conductors.
How are results form pure tone audiogram interpreted?
Abnormal of headphones, but normal for bone conduction = conductive hearing loss
Abnormal for both headphones and bone conduction = sensorineural hearing loss
What are the two types of intracranial haematomas you might see with head injuries, and how would you recognise them from a CT?
Extradural/epidural
- bleed between the skull and dura mater
- lens shaped as blood is contained between skull sutures
Subdural
- Between dura and arachnoid
- lens shaped as not contained within sutures
Describe the Monroe-kellie principle
The volume of the intercranial space must remain constant. therefore if a mass/lesion takes up volume blood and CSF is lost to compensate. Only 120ml can be lost before intracranial pressure rises
What is cerebral perfusion pressure?
It is a measurement of blood flow in the brain
How can Cerebral perfusion pressure (CCP) be calculated?
CPP = MAP x ICP
MAP = Mean arterial pressure
ICP = Intercranial pressure
What are the signs of increasing intercranial pressure?
Decreasing Glasgow comma scale
Diminished pupillary light response
Lateralising signs
What is measured in the Glasgow comma scale and what are the potential scores?
GCS (3-15)
- Eye opening (1-4)
- Verbal response (1-5)
- Motor response (1-6)
