T2L13 physiology of balance, taste, smell Flashcards
organisation of peripheral vestibular system
s2
orientation and structure of the semicircular canals and otolith organs
the 6 semicircular canals are orientated at right angles to one another to detect head rotation in all directions
- the four otholoth organs are not exactly at right angles, so they can resolve head tild and linear acceleration in all directions
- the sensory cells in the otolith organs are embedded in a gelatinous sheet covered with heavy crystals or calcium carbonate
defo see s3
2 types of vestibular hair cells
most are type 2 vestibular hair cells- both afferent and efferent innervationo
type 1 hair cells are surrounded by an afferent nerve calyx and the hair cells are not directly contacted by efferent nerve fibres
- the functional differences are unknown but type 2 seem more sensitive
semicircular canal receptors detect rotation of the head
s5 bare good
nystagmus
- slow eye movements followed by fast ones during continuous head rotation
in normal individuals turning of the head elicits nystagmus
spontaneous nystagmus is pathological - its where eyes move side to side in absence of head movement
- occurs when one of the canals is damaged
- net differences in vestibular nerve firing rates exist even when the head is stationary because the vestibular nerve innervating the intact canal fires steadily when at rest, in contrast to a lack of activity on the damaged side.
see s6
caloric testing
- to test brainstem function of unconscious patient
slow eye movements resulting from cold water in ear:
- brainstem intact
- lesion of MSF
- low brainstem lesion
as cold water creates convection currents that mimic endolymph movement induced by turning the head
this causes changes in firing rate of associated vestibular nerve- increase rate on warm side, decrease rate on cold side
eye movement
clever yes
the receptors in the otolith organs detect _____________
linear acceleration and tilting of head
- gravity and linear acceleration provide same stimulus ovi
central vestibular pathways
see s10
flow chart
causes of vestibular disorders
- ear infection
- head injury
- whiplash
- ageing
- drugs eg antibiotics
disorders of vestibular system
- dizziness (vertigo/spinning)
- trauma esp CN8
- benign paroxysmal positional vertigo BPPV (caused by changes in head movement)
- menieres disease (progressive, episodes of vertigo, tinnitus and hearing loss, excess fluid in ear)
location and organisation of the olfactory epithelium
we have well developed sense of smell; important for:
- social interaction
- avoidance of poisons or noxious gases
- enjoyment of food
- olfactory epithelium has SA of 2-3cm2 in ech side of nose
- the ciliated receptor cells send their own afferent axons to brain
- more than 1000 different odorant proteins, with each receptor cell expressing just one
- each receptor though can respond to multiple odours
olfactory information is not coded by individual receptor types but it is the pattern of stimulation that the brain learns to interpret
mechanism of olfactory transduction
- depends on 2ndry messenger process, with cAMP activated in response to odorant molecule
- leads to opening of cAMP dependant ligand gated ion channels
see s14
central pathways to olfactory system
see s15 flow charta
clinical issues with olfaction
- hyposmia and anosmia
- 5-10% population
causes:
- upper respiratory tract infection, age, nasal polyps, diabetes mellitus, head trauma, high dose radiation, drugs
reduced q.o.l. during eating/ drinking
sense of taste (aka __)
gustation
evaluating the content of food and preventing the ingestion of toxic substances
5 types: 1. sweet - energy rich 2. umami (meaty) - amino acids 3. salty - ensures electrolyte balance 4. sour - warn against noxious/poisonous chemicals 5. better as above
