Special Senses Flashcards
What are the chemical senses?
Olfaction
Gustation
Olfactory epithelium
5 cm squared; 10-100 million receptors
Covers superior nasal cavity and cribiform plate
What type of cells are contained within the olfactory epithelium?
Olfactory receptor
Support
Basal
Bowman’s (olfactory) glands
Olfactory receptor
AKA 1st order neuron in olfaction AKA Cranial Nerve I (Olfactory Nerve)
Bipolar neuron
Has olfactory hairs/cilia that project from dendrites
Produces generator potential (not receptor potentila)
Olfactory Supporting cells
Columnar epithelial cells
Provide physical support, nourishment, insulation to receptor cells
Basal olfactory cells
Stem cells
Produce new receptors or supporting cells
Bowman’s Glands
Produce nasal mucous
In the nasal epithelium
What cranial nerve innervates nasal glands and epithelium?
CN VII Facial
Olfactory transduction
Odorant binds to receptor protein on an olfactory cilia
Receptor protein is coupled to G protein, which activates Adenylate cyclase
Which produces cAMP
Which open Na+ channels, causing depolarization
Generator potential generated, impulse propogated
Olfactory adaptation
Initially very fast (50% in first second), then slower
Cribiform plate
In ethmoid bone
Contains 20 foramina (per nostril) to allow passage of olfactory nerves
Olfaction: Pathway
Odorants bind to receptor cilia
Generator potential –> action potential propagates along Olfactory Nerve
Pass through cribiform plate
Enter Olfactory Bulb
Synapse in Glomerulus with Mitral nerve
Mitral axons combine to form olfactory tract, which heads to the Primary Olfactory area (34). Then on to orbitofrontal area (11)
(Olfactory tract axons also project to limbic system and hypothalamus)
Location of olfactory bulb
Just below frontal lobes
Lateral to crista galli of ethmoid\
Acts as a filter
Location of Primary Olfactory area
Brodmans 34
Inferior-medial temporal lobe
Lateral- and auto- inhibition
Between excitatory mitral neurons and the inhibitory granule cells that form dendrodentritic synapses in between them.
Bidirectionality means that mitral cells can inhibit themselves and their neighbours
Periglomerular cells
Interneurons which synapse within and between glomeruli
Anosmia
Absence of smell
Hyposmia
Reduced sense of smell
Dysosmia
Distortion of sense of smell
Cacosmia
Form of dysosmia, in which things smell baaa-aad
Parosmia
Sensation of smell in the absence of appropriate stimuli
Phantosmia
Olfactory hallucination
Uncinate fits
Sweet
Activated by sugars, alcohol and some amino acids.
Measured by sucrose
Indicates energy rich foods
Salty
Activated by metal ions (especially Na+)
Measure by Na+
Indicates electrolyte-rich foods
Sour
Activated by H+ ions (acids)
Measured by HCl
Aversive
Bitter
Lowest threshold receptor
Activated by alkaloids (caffeine, nicotine)
Measured by quinine
Aversive
Umami
Activated by glutamate and aspartate
Indicate foods high in amino acids.
Where are taste buds found?
Tongue
Soft palate
Epiglottis
Pharynx
Papillae
Elevations on tongue.
Circumvallate, fungiform and folate contain taste buds.
Filiform contain tactile receptors.
(Circum)vallate papillae
12 found on posterior tongue (inverted V).
Contain 100-300 taste buds each
Innervated by glossopharyngeal nerve (IX)
Fungiform papillae
Mushroom shaped
All over tongue
Contain 5 taste buds each.
Folate papillae
On lateral tongue. Usually disappear by the end of childhood
Filiform papillae
All over tongue.
Contain tactile receptors (texture) but no taste buds.
Help move food
Trigeminal nerve (V).
5 basic taste receptors
- sweet
- salty
- sour
- bitter
- umami
How many taste buds?
Around 10000
Three type of cells in a taste bud
Gustatory receptor
Supporting cells
Basal cells
How frequently are new gustatory cells produced?
10 days (olfaction about 30 days)
What nerve is responsible for taste in the anterior 2/3 of the tongue?
Facial nerve (VII)
What nerve is responsible for taste in the posterior 1/3 of the tongue, including vallate papillae?
Glossopharyngeal (IX)
What nerve is responsible for taste in the palate and epiglottis?
Vagus (X)
What nerve is responsible for the sensation of texture when chewing?
Trigeminal (V)
How many gustatory receptors per taste bud?
About 50
How do the various tastands generate receptor potentials?
Salty: Na+ enters via Na+ channel.
Sour: H+ enters via H+ channel. Slows K+ leakage.
Bitter/sweet/umami: bind with receptor on membrane, activate G protein, activate secondary messenger.
What NT is released by the gustatory receptor cells?
ATP
Gustatory pathway
Gustatory receptor
First order neuron (CN VII, IX or X)
Synapse in Gustatory Nuclei (brain stem).
Second order neuron –> Thalamus
(Others go to hypothalamus/Limbic system)
Third order neuron –> primary gustatory area (43)
Gustatory adaptation
Quick (1-2 min)
Involves gustatory receptors, olfactory receptors, CNS pathways
How many sensory receptors are in the eye?
More than half
How much of the eyeball is in the orbit?
7/8
Palpabrae
Eyelids
Protect and lubricate, provide shade
Epidermis Dermis Tarsal plate Tarsal glands Conjunctiva
Conjunctiva
Mucous membrane that lines inner eyelid and covers sclera
Stops at edge of cornea
Bulbar and palpabrael
Tarsal plate
Part of Palpabrae
Provides structural support
Tarsal glands
In tarsal plate of Palpabrae
Secrete meibom (prevents eyelids from sticking together)
Three regions of the ear
Outer ear
Middle eat
Inner ear