Week 13 sensory physiology - special senses pt1 Flashcards
Intro
Sense organs: Information on your surroundings
-Processed in the CNS (conscious or unconscious)
->Senses
->Somatosensory system (pressure, warmth, vibration, limb position)
Special senses:
->Sight (Visual system)
->Hearing (Auditory system)
->Taste (Gustatory system)
->Smell (Olfactory system)
The Eye
Vision is the dominant sense in humans
-Eye protected by orbit and cushion of fat
Accessory Structures
-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
Anatomy of the eye
ball
Three Tissue Layers (Tunics) of the eye wall:
-Fibrous Layer (Outer)
-Vascular layer
-Nervous tissue layer (inner most)
Fibrous Layer (Outer)
-SCLERA: white of the eye
-CORNEA: front of the eye (transparent)
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
Nervous tissue layer (inner most)
RETINA
-Outer Pigmented retina
->Prevents light reflection
-Inner sensory retina
Anatomy of the eye: Chambers
-Anterior Segment / cavity
-Posterior segment/cavity (behind lens)
Anterior Segment
ANTERIOR CHAMBER -> chamber between cornea and iris
POSTERIOR CHAMBER -> chamber between iris and lens
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
Posterior segment
-VITREOUS CHAMBER
-VITREOUS HUMOR: in posterior segment
jellylike, maintains pressure and refracts, forms in embryo and doesn’t circulate
Vision
-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
Retina: 2 Layers
Outer thin pigmented layer:
-Melanocytes (prevent light scattering), contains melani
-Inner thicker neural/sensory layer
Three main type of neurons:
-Photoreceptors
->Rods
->Cones
-Bipolor cells
-Ganglion cells
Regions of (posterior) retina 1
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 cone
Regions of (posterior) retina 2
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
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
Direction of travel of neuronal signal
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
Photoreceptors: 2 types
-Rod cells
-Cone cells
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)
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
Photo Transduction
-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 neuron
Neural pathways
-Optic nerve leaves eye enters brain at optic chiasm
Some fibres cross to other
side of brain
->then visual cortex in occipital lobe
Auditory system
Parts of the ear;
Outer (external) ear -> pinna, external auditory canal
Middle ear (ossicles) for hearing -> tympanic membrane, malleus (hammer), incus (anvil), stapes (stirrup)
Inner ear (labyrinth) -> Mechanoreceptor for hearing and balance, vestibular apparatus, semicircular canals, cochlea -> organ of Corti
External and middle: conduct sound waves toward the inner ear - hearing only
Inner ear: both hearing and balance
Middle ear
-Air filled
-Oval and round window connect to inner ear
-Tympanic membrane 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
Inner ear
3 bony chambers;
->Cochlea - hearing
->Vestibule - equilibrium
->Semicircular canals – equilibrium
-Filled with liquid called perilymph and endolymph fluids
Cochlea
-Shaped like snail shell
-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
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
Basilar membrane moves /vibrates when sound waves in periplymph move over it
Cochlea - more detail
Organ of Corti contains hair cells -> move due to pressure waves
-Hair cells sit on BM between BM and TM ->embedded in TM
Soundwaves :
-BM moves
-TM rigid
-Causes stereocilia to bend
-Causes receptor to depolarise
(mecanoreceptor)
-Neurotransmission in connected neuron through cochlear nerve
BM = Basilar membrane
TM= Tectorial Membrane
Summary of sound transmission through ear
Auditory pathway
Vestibulocochlear nerve:
-Cochlear nerve - portion involved in hearing
-Vestibular nerve - involved in balance
The cochlear nerve sends axons to the regions including
->Auditory cortex in temporal lobe
Equilibrium
Vestibular apparatus : static
equibilbrium (movement and
position)
* 2 Chambers: Saccule and Utricle
-Maculae
->Hair cells, tips embedded in
gelatinous mass weighed down by otoliths (protein and calcium
carbonate)
-Otoliths moves in relation to
gravity bending hairs
->Upright : don’t move
->Hairs bend when tilted
->Depolarises receptor cells - action potentials in associated neurons travel to brain about head position
