Flashcards in Physiology Deck (67):
What type of receptors are used for taste and smell?
stimulated by binding to particular chemicals
Stimulation of taste and smell receptors induces a...or... sensation
Pleasurable or objectionable
What does taste and smell influence further down in the digestive tract?
Flow of digestive juices
physiology of taste
Where are sensory taste receptor cells mainly found?
What type of cells do Taste buds consist of?
How are they arranged?
> Sensory receptor cells
> Support cells
> Like slices of an orange
Life span of taste receptor cells?
Where are they replaced from?
They are continuously replaced from BASAL CELLS within the taste buds
Taste receptor cells synapse with
Afferent nerve fibres within the taste buds
Where are majority of taste buds found?
PAPILLAE in the tongue
What are the papillae of the tongue
Give rough appearance of the dorsum of tongue.
Little red dots/raised bumps.
How many types of papillae?
What are the types?
Filiform: most numerous – do not contain taste buds
Which papillae do not contain taste buds?
Gustation - mechanism of action
> Binding of taste provoking chemical (tastant) to receptor cells alters cell ionic channels and produces depolarising receptor potential
> Receptor potential initiates action potentials in afferent nerve fibres which synapse with receptor cells
> Signals conveyed by cranial nerves via brainstem and thalamus to cortical gustatory areas
> Afferent taste fibres reach the brainstem via:
VIIth cranial nerve (chorda tympani branch of facial nerve) - anterior two-thirds of the tongue
IXth cranial (glossopharyngeal) nerve - posterior third of the tongue
Xth caranial (vagus) nerve - areas other than tongue, including e.g. epiglottis and pharynx
Which cranial nerve supplies the anterior 2/3 of the tongue?
Chorda tympani branch of facial nerve
Which cranial nerve supplies posterior 1/3 of tongue
CN IX (glossopharyngeal)
5 primary tastes.
What is each stimulated by?
SALTY: stimulated by chemical salts especially sodium chloride (NaCl)
SOUR: stimulated by acids which contain free hydrogen ions (H+)
SWEET: stimulated by configuration of glucose
BITTER: stimulated by diverse group of tastants, including e.g. alkaloids, poisonous substances and toxic plant derivatives
UMAMI (meaty or savoury): triggered by amino acids especially glutamate
What is it
Loss of taste function
e.g. of causes:
> nerve damage
> local inflammation (glossitis, radiation, tobacco)
> some endocrine disorders
Reduced taste function.
e.g. of causes:
Distortion of taste function
Often related to a metallic taste in the mouth
e.g. of causes
glossitis; gum infections; tooth decay; reflux; upper respiratory infections; medications; neoplasms; chemotherapy; zinc deficiency
Where is olfactory mucosa found?
Three cell types
Patch of mucosa found in the CEILING (dorsal roof) of nasal cavity
1. Olfactory receptor cells
2. Supporting cells
3. Basal cells (secrete mucous)
Specialised endings of renewable afferent neurons.
Each neurone has a thick, short DENDRITE and expanded end called an OLFACTORY ROD
From olfactory rods, CILIA project to surface of olfactory mucosa
Odorants bind to the cilia
Lifespan of olfactory receptors
Which cells act as precursors for new olfactory receptor cells
Axons of olfactory receptors collectively form?
Which structure do they then pierce?
Afferent fibres of olfactory nerve
Pierce the cribriform plate of ethmoid bone and enter the olfactory bulbs in the inferior surface of the brain.
Olfactory bulbs transmit...
Smell information to the brain
Where do neurons pass from the olfactory bulb?
Pass along OLFACTORY TRACT to reach temporal lobe and olfactory areas
How to odourants reach smell receptors during quiet breathing?
Olfactory mucosa is above normal path of airflow
Enhances smelling by drawing air currents upwards within the nasal cavity
To be smelled, a substance must be:
(1) sufficiently volatile i.e. some of its molecules can enter the nose with inspired air
(2) sufficiently water soluble i.e. can dissolve in the mucus coating of olfactory mucosa
Inability to smell
Temporary or permanent
- viral infections
- nasal polyps
- head injury
which disease may it be an early sign of?
Reduced ability to smell.
- similar to those for anosmia
Altered sense of smell.
Differently interpreting some odours;
hallucinations of smell avoid
Range of human hearing in Hz?
20Hz - 20,000Hz
External ear/pinna acts as a...
Middle ear acts as an
Middle ear contains which bones
The ossicular chain
Acts as a piston with varying efficiency depending on frequency of sound transmitted.
Which part of the stapes is in the oval window?
Stapes FOOT PLATE
Which part of malleus interacts with the tympanic membrane
Handle of the malleus
Head of malleus interacts with the incus
Ventilation pathway for middle ear mucosa
Bony & cartilaginous portions
Resting state of cartilaginous tube is CLOSED but opened by tensor veli palatini & levator palatine muscles
Dysfunction leads to middle ear negative pressure
Resting state of eustachian tube?
Which muscles open the eustachian tube?
Tensor veli palatini
Levator palatine muscles
Oval Window & Round window
Two openings of the cochlea to the middle ear.
Oval window superiorly
Round window inferiorly
In-phase movements of windows
Permit transmission of pressure wave in enclosed canal and vibration of the basilar membrane
Stapes foot plate transmits force onto oval window, and the round window moves to allow movement of the fluid inside the cochlea. If this did not occur, the fluid would be in-compressible.
How many times is the cochlea "rolled up"?
2 and a half times around central modiolus
Where do low frequency sounds localise in the cochlea?
Where do high frequency sounds localise in the cochlea?
Base (near oval/round window)
The scala media is filled with?
Suspended between scala tympani and scala vestibuli (perilymph)
What is suspended between the scala tympani and scala vestibuli?
What is contained within the scala tympani and scala vestibuli
Organ of Corti
the sensory epithelium, a cellular layer on the basilar membrane, in which sensory hair cells are powered by the potential difference between the perilymph and the endolymph
Hair cell function
Transduction: conversion of mechanical ‘bending force’ into electrical impulse
Stereocilia arranged in height order with tip links connecting them together.
Depolarisation occurs when deflected towards longest,
Hyperpolarisation occurs when deflected away.
When does Depolarisation occur in hair cells?
When hair cells are deflected towards the longest hair cells
When does hyper polarisation occur in hair cells?
When hair cells are deflected AWAY from the longest hair cells
Where is the primary auditory cortex
Left posterior superior temporal gyrus
Balance systems (6)
What is Oscillopsia
Oscillopsia occurs when we have no vestibular input – eye movement with the head instead of fixing on an object.
What are the vestibular end organs (5)
Maculae of the utricle and saccule - OTOLITH ORGANS
Ampullae of lateral, posterior and superior semicircular canals
What are the Otolith organ.
What are the maculae of these organs
Utricle and saccule
Maculae (concentrations of hair cells) have sterocilia projecting upwards into a gelatinous matrix with otoconia.
These lend weight and brain perceives movement when tilting head (gravity) or linear motion.
Stereocilia orientated in all directions so all movements perceived by depolarisation/hyperpolasrisaion
Firing stops with linear motion so you know movement has stopped
BUT it continues its head tilt
Calcium carbonate crystals
Embedded in gel membrane
When does firing continue in otolith organs?
(stops with linear motion)
How are otolith organs orientated?
All planes of motion are detected.
How are semi-circular canals arranged
Oriented at 90° to each other
Paired, equal and opposite
Where does the cupola of the a semi-circular canal sit?
Deflection of the cupula is caused by
Deflection by perilymph
Bending causes stereo cilia to deflect
Vestibule-Ocular Reflex (VOR)
Move head to the right
Semicircular canal in that plane on the right hand side will be excited, and the left hand side will be inhibited.
Eyes move to the left (to stay fixed on an object)
Static head - left and right are equally excited
Turning left - left hand side is excited more
Flicking of eye in direction they are trying to fix