The Special Senses Flashcards
What are the special senses and what systems cover it?
- Sight (Visual system)
- Hearing (Auditory system)
- Taste (Gustatory system)
- Smell (Olfactory system)
What are the accessory structures of the eye?
- Eyebrows
- Eyelids or palpebrae
- Blink
- Eyelashes
- Conjunctiva
- transparent mucous membrane
- Lacrimal apparatus
- Lacrimal gland: Responsible for tears (PNS)
- mucus, antibodies and lysozyme
- nasolacrimal duct nasal cavity
- Extrinsic Eye Muscles
- Movement
What is sight?
vision is the dominant sense in humans
Anatomy of the eye: three tissue layers of the eye wall, fibrous layer (OUTER)
- Fibrous Layer (Outer)
- Sclera: white of the eye
- Cornea: front of the eye (transparent)
Anatomy of the eye: three tissue layers of the eye wall, vascular layer (middle)
Vascular layer
* Choroid
* Dark: melanin containing cells
* Absorbs light
* Ciliary body
* Cilliary muscles
* Change thickness of Lens
* Iris
* Coloured part of eye
* Highly vascularised
* Pupil size controlled by muscles of the iris
* Light passes through pupil
Anatomy of the eye: three tissues of the eye wall, nervous tissue layer (inner most)
Nervous tissue layer (inner most)
* Retina
* Outer Pigmented retina
* Prevents light reflection
* Inner sensory retina
What are the two chambers of the eye in anterior segment?
- Anterior chamber
- chamber between cornea and iris
- Posterior chamber
- chamber between iris and lens
What is the aqueous humour? what does it do?
Aqueous humor: Fills Anterior Segment
* Watery liquid, replaced continuously
* Filtered through ciliary body and returned to blood via venous
synus
* Nutrients
* Refracts light
* Maintains pressure
What is found in the posterior segment of the eye?
- Vitreous chamber
- Vitreous humor: in posterior segment
- Jellylike
- Maintains pressure and refracts
- Forms in embryo and doesn’t circulate
How is vision possible?
- The iris allows light into the eye
- Focused by the cornea, lens, and humors onto the retina
- The light striking the retina produces action potentials that
are relayed to the brain via optic nerve
What are the two layers of the retina?
*outermost pigmented layer
*inner most pigmented layer
What is the outermost pigmented layer for?
- Melanocytes (prevent light scattering), contains
melanin
What is the innermost pigmented layer for?
- Three main type of neurons:
- Photoreceptors
- Rods
- Cones
- Bipolor cells
- Ganglion cells
What are the regions of the posterior retina?
*macula
*optic disc
What does the macula do?
- Macula (5.5mm)
- High-resolution, color vision (lots of rods and cones)
- Within this is the fovea (1.5mm)
- Where light is most focused when the eye is looking directly at an object
- Highest density of cones
What does the optic disc do?
- Optic disc
- Blood vessels enter the eye
- Axons from the retina meet, pass through the layers and exit the eye as the optic nerve
- No photoreceptors
Describe the passage of light through the eye
- Light passes through components of anterior cavity and is
focused by lens and passes through vitreous humor - Past/between axons, ganglion cells and bipolar cells, to
photoreceptors next to pigmented layer
What are the two types of photoreceptors?
*rod cells
*cone cells
What is the direction of the neuronal signal/ how it works?
Photoreceptor cells synapse with bipolar cells, which synapse with
ganglion cells : ganglion cell axons run on internal surface and converge at posterior of eye to form optic nerve which exits eye
What are the features of rod cells?
- More sensitive to light - vision permitted in dim light
but only gray and fuzzy - Only black and white and not sharp
- Rhodopsin (opsin & retinal)
What are the features of cone cells?
- High acuity NEED bright light
- Colour vision
- 3 sub-types:
- blue, red and green light cones
- found in macula lutea,
- operate in bright light, colour vision
Describe the passage of the neural pathway (summarise it brief)
- Optic nerve leaves eye
enters brain at optic
chiasm - Some fibres cross to other
side of brain - → then visual cortex in
occipital lobe
What is the process of phototransduction?
- Retina takes light energy and
converts it to electrical energy (
in photoreceptors) - Rods operate in dim light,
numerous at periphery of
retina, fuzzy images - Rhodopsin (1) = protein opsin
loosely bound to pigment called
retinal - Light= retinal changes shape
splits into opsin and retinal. - Change in rhodopsin stimulates
the rods, resulting in vision - Generates a receptor potential
→ action potential in the
attached neurone.
Auditory system: ear =, what are the parts of the ear?
*outer (external) ear
*middle ear (ossicles) for hearing
*inner ear (labyrinth)
What does the external ear contain?
- Pinna
- External auditory canal
What does the middle ear contain?
- Tympanic membrane
- Malleus (hammer)
- Incus (anvil)
- Stapes (stirrup)
What does the inner ear contain?
- Mechanoreceptor for hearing and balance
- Vestibular apparatus
- Semicircular canals
- Cochlea
- Organ of Corti
What do the external and middle ear do?
External and middle: conduct sound
waves toward the inner ear - hearing
only,
What does the inner ear do?
- Inner ear: both hearing and balance
List what the middl ear is composed of+ features
- Air filled
- Oval and round window connect to inner
ear - TM causes ossicles in air filled middle ear
to move: - Malleus (hammer) (attached to TM)
- Incus (anvil)
- Stapes (stirrup) (touches oval window)
- Ossicles form a lever system
- Amplifies and transmits the vibratory motion
of the TM to fluids of inner ear cochlea via
oval window - Auditory canal open to pharynx
What are the features/ structures of the inner ear?
3 bony chambers
* Cochlea - hearing
* Vestibule - equilibrium
* Semicircular canals – equilibrium
* Filled with liquid called perilymph
and endolymph fluids
What is the cochlea apart of?
inner ear
What does the cochlea contain?
- 2 canals
- extends from the oval
window to the apex of the
cochlea. - from the apex back to the
round window - Lined on bottom channel by
Basilar membrane
What does the middle: cochlear canal contain?
- Middle: cochlear canal -
contains Organ of Corti - Specialised sensory hair cells :
stereocilia - Seated on basilar membrane
- Reach to tectorial membrane
- Base of Hair cells attached to
neuron
*basal membrane moves/vibrates when sound waves in perilymph move over it
Where is the organ of corti? + what does it contain?
Organ of Corti contains hair cells –
move due to pressure waves
* Hair cells sit on BM between BM and
TM
What is the process of sound waves?
*Basilar membrane moves
*tectorial membrane rigid
*causes stereocillia to bend
*causes receptor to depolarise (mechanoreceptor)
*neurotransmission in connected neurone through cochlear nerve
Summarise sound transmission through the ear
- Sound waves vibrate tympanic
membrane - Auditory aussicles vibrate. Amplification
- Stapes connected to oval window,
sends vibrations into cochlea - Pressure wave pushes on basilar
membrane of cochlea duct. Energy waves
dissipate at round window - Hair cells bend, transmission of signal
- Neurotransmitter release activates sensory
neurones, action potentials to brain
What makes up the vestibulocochlear nerve?
*cochlear nerve
*vestibular nerve
What does the cochlear and vestibular nerve do?
cochlear nerve - portion involved in hearing
sends axons to the regions including auditory cortex in temporal lobe
vestibular nerve - is involved in balance
What are the semi circular canals for/ what do they do?
*dynamic equilibrium, rotational acceleration in 3 planes
3 canals : right angles
What is the base:ampula made up of + location?
*hair cells embedded in jelly cupula
*floats in endolymph
What is the movement like for the semi circular canals and their components?
*endolymph tends to move in opposite direction
*cupula and steroclia on hair cells bend
*leads to action potential
*vestibulocochlear nerve to cerebellum
What are taste buds?
sensory structures that detect taste stimuli
How do receptor cells work on the tongue?
- Receptor cells - sensitive to the chemicals
contained within foods - release neurotransmitters based on the amount of the chemical
in the food
Where are tastebuds located?
*taste buds on the tongue are located on papillae
*enlargement on tongue
*taste buds also on the palate (roof of mouth)
and the epiglottis
What are the four types of papillae?
*filliform papillae (no tastebuds, tip and side)
*fungiform papillae (small, on entire surface of tongue most front)
*circumvallate papillae (inverted V near back of tongue)
*foliate papillae (edge of tongue)
Describe the structure of taste buds
- Taste buds are made up of many
epithelial cells each - Taste receptor cells (gustatory
cells), supporting cells and basal
cells - Each gustatory cell has gustatory
hairs that extend through taste
pore, bathed in saliva - Dissolved molecules bind &
induce receptor cells to generate
impulses in sensory nerve fibers
What type of receptors detect taste?
*chemoreceptors
What are the types of taste and what ion/molecules cause them?
ION CHANNELS
*sour (H+)
*salty (Na+)
GPCRs
*bitter (alkaloids)
*sweet (glucose)
*umami - savoury (MSG), (L-glutamate)
What happens when gustatory cells are activated?
*they release neurotransmitters onto the dendrites of sensory neurones. AP transferred to CNS
What is olfaction?
*response to odorant’s that enter the nasal cavity
What receptors are present in olfactory epithelium?
- Olfactory epithelium (2-4 cm2) in roof of nasal cavity
- Pseudostratified columnar epithelium
- Has millions of bipolar neurons = olfactory receptor
cells
What do bones in the nose do?
*impede air (swirling)
*present air to nasal epithelium
What is the olfactory bulb + do?
*extension of the forebrain
*receives input form the primary olfactory neurones
What cells are present in the olfactory epithelium?
*supporting cells (secrete mucus)
*basal cells
*olfactory sensory neurones
*(surface of olfactory epithelium) = knobby terminals/ dendrites
What are the olfactory sensory neurones like structure wise + do?
- Bipolar neurons
- Single dendrite - extends to the surface
of olfactory epithelium - axon that extends up to the olfactory
bulb
Where are the knobby terminals on the surface of the olfactory epithelium?
- embedded in a layer of mucus
What does the mucus do for the knobby terminals?
- Mucus: keep epithelium moist, traps and
dissolves airbourne molecules, facilitates
removal of particles
How does olfaction work in the nasal epithelium?
*mucus captures and dissolves odour molecules
*molecules bind to olfactory receptors (OR), bipolar neurones
*receptor cells activated, AP generated (each receptor cell has an axon)
*AP travels along axon: olfactory nerve enters olfactory bulb
Where is the olfactory bulb located?
- Olfactory bulb is in the forebrain
- In bulb nerves synapse with mitral cells (at
“glomeruli”)
What do mitral cells do + where?
- Mitral cells send signals via olfactory tract
- Via interneurons to olfactory cortex
- Temporal lobe
Give a summary for olfaction
- Odors must be dissolved in mucus
- Olfaction Receptor cells are bipolar
neurons - These cells synapse on mitral cells
in glomeruli - Message carried to olfactory centre
/ cortex in temporal lobe
Give a summary for taste
Taste buds are located on papillae
* There are different types of
papillae
* They are located in different parts
of the tongue
* They have receptors MORE
sensitive to different types of taste
* The gustatory cortex is in the insula
region of the cortex
