The special senses Flashcards
Sense organs are;
Information on your surroundings
processed in the CNS
5 special senses;
Senses
Somatosensory system (pressure, warmth, vibration, limb position)
Sight (Visual system)
Hearing (Auditory system)
Taste (Gustatory system)
Smell (Olfactory system)
Eye; Vision is the dominant sense in humans
How are they protected?
by orbit and cushion of fat
Accessory Structures
Eyebrows
Eyelids or palpebrae
eyelids allow to blink
Eyelashes
keeping airborne dirt, dust, lint and other debris from reaching the delicate eye tissues
Conjunctiva
transparent mucous membrane
Lacrimal apparatus
Lacrimal gland: Responsible for tears (PNS)
mucus, antibodies and lysozyme
nasolacrimal duct —> nasal cavity
Extrinsic Eye Muscles
Movement
Eye ball; 3 tissues/tunics
1) Fibrous Layer (Outer)
2) Vascular layer
3) Nervous tissue layer (inner most)
1) Fibrous Layer (Outer) - is made out of what 2 things, colour?
Sclera: white of the eye
Cornea: front of the eye (transparent)
Choroid
Dark: melanin containing cells
Absorbs light
2) Vascular layer (has a LOT of blood vessels in it)
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
3) Nervous tissue layer (inner most)
Retina
Outer Pigmented retina
Prevents light reflection
Inner sensory retina
Why is the Cornea transparent?
light needs to pass through it (this is the outer layer of the eyeball)
How many chambers are there in the eye?
2 =
Anterior Segment / cavity (FRONT) + Posterior segment/cavity (BACK)
What is the anterior cavity made up of?
ANTERIOR CHMABER
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/cavity COMPOSITION?
VITREOUS CHAMBER
VITREOUS HUMOR: in posterior segment
Jellylike
Maintains pressure and refracts
Forms in embryo and doesn’t circulate
What is humor?
the liquid in the eye
For vision, what happens in the eye?
- 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?
a) Outer thin pigmented layer
b) Inner thicker neural/sensory layer
a) Outer thin pigmented layer
Melanocytes (prevent light scattering), contains melanin
b) Inner thicker neural/sensory layer - neurons
Three main type of neurons:
Photoreceptors
Rods
Cones
Bipolor cells
Ganglion cells
Macula; length? [region of posterior retina]
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
Optic disc properties; [region of posterior retina]
Blood vessels enter the eye
Axons from the retina meet, pass through the layers and exit the eye as the optic nerve
No photoreceptors
What happens when light gets to the retina?
Light passes through components of anterior cavity and is focused by lens and passes through vitreous humor
Pass 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
2 types of Photoreceptors:
- Rod cells
- Cone cells
- Rod cells - properties
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 (for detailed vision)
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
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
Why is back of eye dark?
control scatter of light
Auditory system
Hearing
Parts of THE EAR
3 parts;
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
MIDDLE EAR
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
Inner ear - Labyrinth (consists of lot of different cannals)
3 bony chambers
Cochlea - hearing
Vestibule - equilibrium
Semicircular canals – equilibrium
Filled with liquid called perilymph and endolymph fluids
Meconoreceptor cells
Cochlea - full of liquid
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 and organ of corti
Receptor organ for hearing
Cochlea
Organ of Corti contains hair cells – move due to pressure waves
Hair cells sit on BM between BM and TM
embedded in TM
BM
Basilar membrane
TM
Tectorial Membrane
Summary of 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.
Auditory pathway
-Vestibulocochlear nerve:
Cochlear nerve - portion involved in hearing
Vestibular nerve is 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
Equilibrium 2
Semi circular canals
Dynamic equilibrium:
Rotational acceleration in 3 planes
3 canals : right angles
Base: ampula
Hair cells embedded in jelly cupula
Floats in endolymph
Movement:
Endolymph tends to move in opposite direction
Cupula and steroclia on hair cells bend
Leads to action potential
Vestibulocochlear nerve to cerebellum
