The Brain and Special Senses Flashcards
What are the 5 special senses?
Vision Hearing Taste Smell Balance
Where are receptors located for the special senses?
Within special sense organs.
What are the general senses?
Temperature Pain Vibration Touch Pressure Proprioception (body position)
Info relayed from the CNS is sent to the what sensory fibres?
Afferent
Paired olfactory organs are located where?
Nasal cavity (either side of septum). Inferior to cribriform plate of ethmoid bone.
What components make up the olfactory organs?
- Epithelium
- Supporting cells
- Receptor cells
- Glands (secrete mucus)
- Cilia
Describe the smelling mechanism.
- Air swirls within nasal cavity.
- Reaches olfactory organs, lipid/water-soluble chemicals dissolve, diffuse into mucus and stimulate receptors.
- Dissolved chemicals interact with receptors (odorant binding proteins) on cilia surface.
- Binding of odorants changes permeability of receptor membrane -> AP.
- AP relayed to olfactory bulb via axons penetrating cribriform plate.
- Info to CNS, smell interpreted.
Axons leaving the olfactory bulb travel to which parts of the brain?
Olfactory cortex of cerebrum
Hypothalamus
Limbic system
The olfactory cortex is located within which lobe?
Temporal
Where are the gustatory receptors found?
Superior surface of tongue
Pharynx
Larynx
Why are gustatory receptors not found on surface of tongue?
To protect them from mechanical damage, chewing and extreme tastes.
What are the three types of papillae? Rank them from smallest to largest, stating the number of buds.
- Filiform (no buds)
- Fungiform (5 buds)
- Circumvallate (100 buds)
What components make up a taste bud?
- Sensory receptors (gustatory cells)
- Supporting cells
- Microvilli that project into fluids through taste pores.
What are the 5 taste sensations?
- Sweet
- Sour
- Salty
- Umami
- Bitterness
Where are the receptors located that relay info on hydration status?
Pharynx
Describe the taste mechanism.
- Chemicals dissolved by saliva, move down taste pores.
- Chemicals meet microvilli (which extend from receptor cells).
- Stimulates change in membrane potential of receptor -> AP in sensory neurone.
- AP sent to CNS by one of three cranial nerves.
What three cranial nerves send an AP to the CNS in gustation?
Facial (VII)
Glossopharyngeal (IX)
Vagus (X)
The gustatory cortex is located in what lobe?
Temporal
Light is refracted at what parts of the eye?
Cornea and lens.
Define refraction.
The alteration of light when it travels from medium to another.
Where does the greatest refraction occur in the eye?
Cornea
The light bent at the lens is focused on what?
Retina
Is there more rods or cones in the eye?
Rods - 100 million
cones - 5 million
What photoreceptor is most prominent at the fovea?
Cones
State whether cones and rods dominate peripheral or central vision.
Cones - central vision
Rods - peripheral vision
Describe the synapsing process with cones/rods to the optical nerve.
Cones/rods synapse with bipolar cells -> synapse with ganglion cells -> axons form optic nerve.
Describe the mechanism of seeing.
- Light interacts with light-sensitive molecules (photopigments) in photoreceptors.
- Presence of light, rhodopsin splits into opsin and retinal.
- Change in membrane potential with photoreceptors -> production of AP.
Axons from ganglion cells form what?
Optic nerve (CN II).
Where does the optic nerve end?
Diencephalon at the optic chiasm.
Half fibres in the brain cross over and reach where?
Thalamus on opposite side of brain.
Visual info is relayed into what centres of the brain?
Brain stem
Visual cortex in cerebrum
The visual cortex is located in what lobe?
Occipital
What are the three parts of the ear?
- External acoustic ear canal
- Middle ear (air-filled cavity)
- Inner ear
The middle part of the ear contains what three auditory ossicles?
- Malleus - attached to tympanic membrane.
- Incus - attached to malleus and stapes.
- Stapes - attached to incus and oval window.
Receptors for balance and hearing lie within where?
Inner ear - membranous labyrinth.
What two fluids does the membranous labyrinth contain?
Endolymph
Perilymph
Receptors for hearing are located where?
‘Organ of Corti’
What are the 2 perilymph filled chambers called on either side of the cochlear duct?
Vestibular and tympanic duct.
The round window is the base of what duct?
Tympanic
The oval window is the base of what duct?
Vestibular
Stereocilia of hair cells (receptors) are in contact with what membrane?
Tectorial
Describe the mechanism of hearing.
- Sound waves enter external acoustic canal, arrive at tympanic membrane.
- Movement of tympanic membrane displaces auditory ossicles.
- Movement of stapes at oval window creates pressure waves in perilymph of vestibular duct.
- Pressure waves distort basilar membrane of cochlear duct -> round window.
- Basilar membrane vibration causes vibration of hair cells agains tectorial membrane.
- AP fires within receptor cells.
- Vibrations relieved at round window and cease.
- Info about region of stimulus relayed to CNS over cochlear branch of CN VIII.
Equilibrium sensation is provided by hair cells of the vestibular apparatus. What components make up the vestibular apparatus?
Semi-circular canals
Otoliths
Semi circular canals lie in different plates and their receptors respond to what type of movement?
Rotational
Semi circular canals have hair cells which are located where?
Ampulla
Stereocilia is embedded in what structure?
Cupula
Otoliths lie where?
Next to base of semi-circular canals.
Otoliths provide information about what type of movement?
Accelerations of the body.
What structure relays information about horizonal accelerations?
Utricle
What structure relays information about vertical accelerations?
Saccle
Hair cells in otoliths are embedded in what? How is an AP produced?
Gelatinous mass
Hair cells in gel -> pressing of mass bends hair cells -> production of AP
Roles of vestibular nuclei?
- Integrate sensory info arriving from either side of head.
- Relays info to cerebellum.
- Relays info to cerebral cortex.
- Sends commands to motor nuclei in brain stem and spinal cord.
