The Special Senses Flashcards
Olfactory organs
Contain olfactory epithelium with olfactory receptors, supporting cells, and basal stem cells
Olfactory glands
Secretions of olfactory glands coat the surface of olfactory organs
Olfaction
Arriving information reaches the information centres without first synapsing in the thalamus
Olfactory reception
Involves detecting dissolved chemicals as they interact with odor-binding proteins
How does the CNS interpret smells?
By the pattern of receptor activity
Gustatory epithelial cells
Cluster in taste buds
Taste buds
- Associate with epithelial projections on the tongue
- Each taste bud contains basal epithelial cells (stem cells) and gustatory epithelial cells, which extend taste hairs through a narrow taste pore
- Monitored by cranial nerves that synapse within the solitary nucleus of the medulla oblongata. Post synaptic neurons carry the nerve impulses on to the thalamus, where third-order neurons project to the somatosensory cortex
Primary taste sensations
Sweet, salty, sour and bitter
Accessory structures of the eye
Eyelids, seperated by palpebral fissure, eyelashes and tarsal glands
Conjuctiva
Epithelia covering the inner surfaces of the eyelids and the most exposed surface of the eye
Lacrimal gland
Secretes something containing lysozome
Tears
Collect in lacrimal lake
Reach the inferior meatus of the nose after they pass through lacrimal puncta, lacrimal canaliculi, lacrimal sac and nasocrimal duct
3 layers of the eyes
Outer fibrous layer
Middle vascular layer (uvea)
Deeper inner layer (retina)
Fibrous layer
Sclera, cornea and corneoscleral junction
Vascular layer, uvea
Iris, ciliary body and choroid
Iris
Contains muscle fibres that change the diameter of pupil
Ciliary body
Ciliary muscle and the ciliary processes which attach to the ciliary zonule of the lens
Inner layer, retina
Consists of a thin lining called the pugmented layer and a thicker covering called the neural layer which contains visual receptors and associated neurons
2 types of photoreceptors in retina
Rods and cones
Cones
Densely clustered in the fovea centralis, at the centre of the macula
Light to brain
Photoreceptors > bipolar cells > ganglion cells > brain via optic nerve
Optic disc
- Blind spot
- Axons of ganglion cells converge at the optic disc
Horizontal cells and amacrine cells
Modify the signals passed among other components of the retina
Posterior cavity
Ciliary body and lens divide the interior of the eye into the large posterior cavity. and a smaller anterior cavity
Anterior cavity
Subdivided into anterior chamber which extends from the cornea to the iris and a posterior chamber, between the iris and the ciliary body and lens
Aqueous humor
Circulates within the eye and reenters the circulation after diffusing through the walls of the anterior chamber and into the scleral venous sinus
Lens
Lies posterior to the cornea and forms the anterior boundary of the posterior cavity which contains the vitreous body
Vitreous body
Clear gelatinous mass that helps stabilise the shape of the eye and support the retina
Cataract
A condition in which the lens has lost its transparency
Light refraction
Light is refracted (bent) when it passes through the cornea and lens
Accommodation
When the shape of the lens changes to focus an image on the retina
Visual acuity
20/20
Rods
Respond to almost any photon, regardless of its energy content
Cones
Have characteristic ranges of sensitivity
Outer segment
- Each photoreceptor contains an outer segment with membranous discs
- A narrow stalk connects the outer segment to the inner segment
Visual pigments
Where light absorption occurs
Derivates of rhodopsin
Colour sensitivity
Depends on the integration of information from red, green and blue cones
Colour blindness
Inability to detect certain colours
What happens when photons are absent?
A photoreceptor produces a dark current and constantly releases neurotransmitter
Photon absorption reduces the dark current and decreases the release of neurotransmitter to the bipolar cell
Bleaching
Rhodopsin molecules are broken apart to regenerate retinal back to its photon-absorbing 11-cis form
Dark-adapted state
Most visual pigments are fully receptive to stimulation
Light-adapted state
The pupil constricts and bleaching of the visual pigments takes place
M cells
- Ganglion cells that monitor rods
- Relatively large
P cells
Smaller and more numerous than M cells
Visual data
Visual data from the left half of the combined field of vision arrive at the visual cortex of the right occipital lobe
Data from the right half of the combined field of vision arrive at the visual cortex of the left occipital lobe
Depth perception
Resolved by comparing relative positions of objects between the left and right eye images
Circadian rhythm
Visual inputs to the suprachiasmatic nucleus of the hypothalamus affect the function of other brainstem nuclei
This nucleus establishes a visceral circadian rhythm which is tied to the day-night cycle and affects other metabolic processes
Divisions of the ear
External ear, middle ear and internal ear
External ear
Includes the auricle, which surrounds the entrance to the external acoustic meatus which ends at the tympanic membrane
Middle ear
- Communicates with the nasopharynx by the auditory tube
- Encloses and protects the auditory ossicles
Internal ear
Membranous labyrinth of the internal ear contains the fluid endolymph
Bony labyrinth surrounds and protects the membranous labyrinth and can be subdivided into the vestibule, the semicircular canals and the cochlea
Vestibule of inner ear
Encloses saccule and utricle
Semicircular canals
Contain the semicircular ducts
Cochlea
Contain the cochlear duct, an elongated portion of the membranous labyrinth
Round window
Seperates the perilymph from the air spaces of the middle ear
Oval window
Connected to the base of the stapes
Hair cells
- Basic sensory receptors of the internal ear
- Provide information about the direction and strength of mechanical stimuli
Anterior, posterior, and lateral semicircular ducts
Continuous with the utricle
Each duct contains an ampullary crest with gelatinous ampullary cupula and associated sensory receptors
Endolymphatic duct
Continuous with a passageway that connects the saccule and utricle
Endolymphatic sac
Endolymphatic duct terminates in the endolymphatic sac
Maculae
In the saccule and utricle, hair cells cluster
Surface of the membrane contains calcium carbonate crystals called otoliths
Vestibular ganglia
Vestibular receptors activate sensory neurons of the vestibular ganglia
The axons form the vestibular nerve, synapsing within the vestibular nuclei
Sound waves
Travel toward the tympanic membrane which vibrates, and auditory ossicles then conduct these vibrations to the internal ear
Movement at the oval window applies pressure to the perilymph of the scala vestibuli
Cochlear duct
Lies between the scala vestibuli and the scala tympani
Spiral organ
Hair cells of the cochlear duct lie within the spiral organ
Basilar membrane
Pressure waves distort the basilar membrane and push the hair cells of the spiral organs against tectorial membrane
Tensor tympani and stapedius contract to reduce the amount of motion when very loud sounds arrive
Sensory neurons in the ear
Located in the spiral ganglion of the cochlea
Cochlear nerve
- Affarent fibres of sensory neurons in ear form cochlear nerve and synapse at left or right cochlear nucleus
