Ch. 16 Special senses

Ears and eyes

Receptor

• Any structure specialized in monitoring conditions of the body and external or internal environment

• Dendrites of sensory neurons or specialized cells fall into this category

Rods

• Specialized receptor cells

• Three section

• Location: Back of eyes

• Function: Receive light and allow for vision

Cones

• Specialized receptor cells

• Three section

• Location: Back of eyes

• Function: Receive light and allow for vision

Transduction 

• Process of sensory receptor information being turned into electrical impulse 

Slow-adapting

• Process of receptor getting used to information and no longer responding

• Happens relatively slow, receptor sense stimuli for longer

• Ideal for stimuli you don’t want to ignore, ex: pain receptors 

Fast-adapting

• Process of receptor getting used to information and no longer responding

• Happens relatively fast, receptor sense stimuli for shorter

• Ideal for stimuli you want to ignore, ex: smell receptors (going nose blind) 

Sensory pathway 

• Stimuli, sensory receptor, first-order neuron, second-order neuron, third-order neuron in thalamus, primary cortex area, association cortex, sensation

General sense receptor

• Simpler structure than special sense receptor, most numerous 

• Dendrites of sensory neurons, directly connected to neuron

• Types: Free and encapsulated nerve endings

• Free: Free nerve endings, tactile discs, hair receptors

• Encapsulated: Tactile corpuscles, end bulbs, bulbous corpuscle, lamellar corpuscles, muscle spindles, tendon organ

Free nerve endings

• General sense receptor

• Type: Free 

• Anatomy: Many branching projections 

• Location: Skin, epidermis

• Function: Detect light touch

Tactile discs

• General sense receptor

• Type: Free 

• Anatomy: Nerve ending beneath disc shaped tactile cell 

• Location: Skin, epidermis

• Function: Detect light touch 

Hair receptors

• General sense receptor

• Type: Free 

• Location: Wrapped around hair follicle 

• Function: Detect hair movement 

Tactile corpuscles

• General sense receptor

• Type: Encapsulated 

• Location: Skin, dermis 

• Function: Detect light touch and texture 

End bulbs

• General sense receptor

• Type: Encapsulated 

• Location: Mucus membrane surface, ex: lips or tongue

• Function: Function: Detect light touch and texture 

Bulbous corpuscle

• General sense receptor

• Type: Encapsulated 

• Location: Skin, dermis or hypodermus

• Function: Detect deep touch and pressure

Lamellar corpuscles

• General sense receptor

• Type: Encapsulated 

• Location: Skin, dermis or hypodermus

• Function: Detecting deep pressure and vibrations 

• Surrounded by layers of fibroblasts and Shawn cells 

Muscle spindles

• General sense receptor

• Type: Encapsulated  

• Location: Skeletal muscles 

• Function: Trigger knee-jerk reaction  

Tendon organ

• General sense receptor

• Type: Encapsulated 

• Location: In tendon

• Function: Trigger tendons reflex

Exteroceptors

• Receptor that takes in information from external environment 

Interceptors

• Receptor that takes in information from internal  environment 

Proprioceptors

• Receptor that takes in information from muscles and tendons, inform you where you are in space 

Photoreceptors

• Receptors for light

• Responsible for eyesight

Baroreceptors

• Receptors for pressure

• Responsible for feeling pressure in stomach when full

Chemoreceptors

• Receptors for chemicals

• Responsible for taste when eating

Thermoreceptors 

• Receptors for temperature 

• Responsible for felling temperature 

Nociceptors

• Receptors for pain

• Responsible for feeling pain

Mechaniceceptors

!!!

Receptive field 

• Area where stimulus can produce a response in sensory neuron

• Sizes vary depending on where they are located on the body  

Special sense receptor

• More complex structure than general sense receptor, least numerous 

• Separate cell than neuron, connected to end of neuron

• Used for special senses: Taste, smell, balance, sight 

Olfaction 

• Special sense related to smell 

• Specialized neuron in nasal epithelium, not cell 

• Olfactory cilia hold receptor molecules that odorants in air bind to

Olfactory cilia

• Nonmotile ciliated cells in nasal epithelium

Odorants

• Chemicals in air that bind to receptor molecules in nasal epithelium

Gustation

• Special sense related to taste

• “Eating something with gusto” 

• Gustatory cells are found in taste buds 

• Tastents bind to gustatory cells 

• Tastes: Salty, Sweet, Sour, Bitter, Unami

Gustatory cells

• Cells inside of taste buds that allow for the sense of taste 

Tastents

• Chemicals that bind to taste buds in order to taste 

Basle cells

• Stem cells in both gustatory and olfactory systems that allow for the production of more cells in both systems 

• Olfactory: Olfactory neurons

• Gustatory: Gustatory cells 

• Both: Supporting cells 

Supporting cells

• Cell in the gustatory and olfactory system that support the working cells of the system

Oracle 

• Part of the outer ear

• The part of the ear that one can see and pull on

• Funnels sound waves into external ear canal 

Outer ear canal

• Part of the outer ear

• Part of the ear one can stick their finger in 

• Funnels sound to the tympanic membrane (ear drum)

Tympanic membrane

• Part of the outer ear

• “Ear drum”

• Vibrates when sound waves hits it causing a ripple effect through the malleus, incus, and stapes 

Malleus

• Part of the middle ear

• First of three inner ear bones

• Shaped like a mallet

• Articulates with tympanic membrane and incus

Incus

• Part of the middle ear

• Second of three inner ear bones 

• Shapes like an anvil 

• Articulates with the malleus and stapes

Stapes

• Part of the middle ear

• Third of three inner ear bones

• Shaped like a horseshoe

• Articulates with the incus and cochlear structure  

Cochlear structure 

• Part of inner ear responsible for hearing 

• Filled with fluid, endolymph

• Has many hair cells 

Vestibular apparatus

• Part of inner ear responsible for equilibrium

• Filled with, endolymph 

• Has many hair cells 

Hair cells

• Nonmotile ciliated epithelial cell found it vestibular and cochlear parts of ear

• Cilia sticks into endolymph and looks like hairs

• Cilia move in opposite direction of your movement 

Utricle

• Used for sensing linear acceleration forward and backward

• Cilia oriented facing anterior  

• Forward movement moves cilia posterior 

• Backwards movement moves cilia anterior  

Saccule

• Used for sensing linear acceleration up and down

• Cilia oriented facing anteriorly

• Upwards movement moves cilia inferior 

• Downwards movement moves superior 

Anterior semicircular canal

• Filled with endolymph

• Sense rotational acceleration, nodding head

• Ex: Backflips  

Lateral semicircular canal

• Filled with endolymph

• Sense rotational acceleration, side tilting of head

• Ex: Cartwheels

Posterior semicircular canal

• Filled with endolymph

• Sense rotational acceleration, horizontal rotation of head 

• Ex: Spinning on heels

Ampula

• Blister like structure at base of semicircular canal

• Help with sensing rotational force 

Cupula 

• Dome shaped structure on ampula

Palpebrae

• Eyelid

Palpebrae fissure 

• Space between upper and lower palpebrae

• Where the eye can see out of

Medial commisre of eye

• Where the palpebrae meet each other on the medial end

Lateral commisre of eye

• Where the palpebrae meet each other on the lateral end

Superior tarsal plate

• Connective tissue plate at the most anterior part of the superior eye socket 

• Function: Supports the eye

Inferior tarsal plate

• Connective tissue plate at the most anterior part of the inferior eye socket

• Function: Supports the eye

Superior tarsal muscle

• Location: muscle spanning whole superior side of eye socket, articulating with superior tarsal plate

• Function: Contraction causes superior eye lid retractions

Inferior tarsal muscle

• Location: muscle spanning whole inferior side of eye socket, articulating with inferior tarsal plate

• Function: Contraction causes inferior eye lid retraction

Tarsal gland

• Gland at distal end of superior and inferior tarsal plate

• Secrets an oily secretion, dries eye lid and stops eye lids from sticking together when closed

Bulbar conjunctiva

• Outermost protective layer of eyeball 

Palpebral conjunctiva

• Protective layer of inner eyelid 

Lacrimal gland

• Exocrine gland located above the lateral-anterior most corner of the eye 

• Function: Release tears 

Lacrimal caruncle 

• Pink area in most inferior and medial corner of the eye 

Lacrimal punctums

• Small hole in eyelids that allow tears to flow into lacrimal canal 

Lacrimal canals

• Canals located between lacrimal punctums and lacrimal sac 

• Carry tears to lacrimal sac

Lacrimal sac 

• Hold tears to be drained by the nasolacrimal duct into nasal cavity 

Nasolacrimal duct

• Duct between lacrimal sac and nasal cavity 

• Drains lacrimal sac into nasal cavity 

Anatomy of eye

• 80% receded into the eye socket, fat makes up other 20% of eye socket 

• Two components, optical and neural 

• Optical: Deciphers visual information 

• Neural: Transmits visual inforamt\ion to brain

Sclara 

• The white of the eye 

Fibrous tunic 

• Wall of eye made of fibrous connective tissue

• Holds cornea and sclera  

Cornea 

• Avascular part of fibrous tunic

• Clear covering of front of eye, allows light through and focuses it

• Clear because college can’t absorb water  

• Three layers: Inner is simple squamous, middle is collagen fibers, anterior is stratified squamous epithelium  

Sclara

• Vascular part of fibrous tunic 

• Dense irregular connective tissue covering of whole outside of the eye minus the cornea 

• White because college fibers absorb water 

Vascular tunic of eye

• Middle covering of eye 

• Contains ciliary body and iris 

Ciliary body

• Attached to the lens by fibers

• Function: Secrete aqueous humor into posterior and anterior chamber or the anterior cavity

• It aqueous humor doesn’t cycle properly glaucoma is cause, high pressure in eye 

Iris

• Smooth muscle

• Gives color to eye 

• Two sphincter muscles: Pupillary constrictor and Pupillary dilator 

Pupillary constrictor

• Muscle of the iris

• Causes pupil to constrict

• Controlled by parasympathetic nervous system, rest and recovery

Pupillary dilator

• Muscle of the iris

• Causes pupil to dilate

• Controlled by sympathetic nervous system, fight or flight 

Lesne

• Clear part of the eye 

• Filled with clear protein called crystallin, helps bend light waves more than they naturally already do 

• Contracted ciliary body makes sense thick, near sight

• Relaxed ciliary body makes sense thin, far slight 

• Changing lease thickness called accommodation 

• Cranial nerve 3 controls

Retinal layer 

• Inner most surrounding layer of the eye 

• Articulates with vascular layer at a seated edge, serata ora

• Contains optic disc, fovea centralis, macula lutea

Optic disc / blind spot 

• Opening in retina that allows blood vestals through

• Blind spot because blood nestle passage takes the place of sensory receptors 

Posterior chamber

• Area in eye behind retina 

• Filled by vitreous humor 

• To little vitreous humor means the retina might detach 

Macula lutea

• Contains fovea centralis and many rods

Visual pathway

• Step 1: Pass through neural layer

• Step 2: Hit photoreceptors / excess light absorbed by the pigmented layer 

• Step 3: Transmitted though bipolar cells 

• Step 4: Reach ganglion cells 

• Step 5: Ganglion cells’ axons transmit info out of eye through the optic nerve 

• Step 6: Optic chasm

• Spet 7: Optic tract

• Step 8: Superior colliculi

• Step 9: Lateral geniculate nucleus of thalamus

• Step 10: Optic radiation

• Step 11: Primary visual cortex

Pigmented layer 

• Layer located at back of eye

• Absorbs excess light to prevent it from bouncing around eye 

Cones

• Type of photoreceptor 

• Used for high definition vision, colored vision in central vision 

Rods

• Type of photoreceptor 

• Used for low definition vision, black and white in peripheral vision 

Cochlear duct

• Middle of 3 openings in cochlear, divided by basal and vestibular membrane

• Holds spiral organ for interpreting sound waves

•  Filled with serous endolymph 

Scala vestibuli

• 1 of 3 openings in cochlear, divided from cochlear duct by the vestibular membrane

• Filled with watery perilymph, transmits sound waves 

Scala tympani

• 1 of 3 openings in cochlear, divided from cochlear duct by the basal membrane

•  Filled with watery perilymph, transmits sound waves 

Spiral organ

• Located in cochlear duct, rests on basal layer

• Contains two segments base and apex

• Base: Stiff, thick, narrow, responsible for high frequency  

• Apex: Flexible, thin, wide, responsible low frequency 

Hair cell 

• Named stereocilia

• Potassium is released when stereocilia is bent towards tallest stereocilia

• Potassium acts as impulse for calcium, eventually turning into turning into action potential for cochlear nerve 

• Bending away doesn’t relate potassium and nothing happens

• Always bend opposite of direction of movement

Auditory pathway

• Step 1: Basilar membrane moves, stereocilia move, bipolar neurons triggered, cochlear nerve gets signal

• Step 2: Cochlear nuclei in medulla-pons junction 

• Step 3: Superior olivary nuclei 

• Step 4: Inferior colliculi

• Step 5: Medial geniculate nucleus in thalamus 

• Step 6: Primary auditory cortex in temporal lobe 

Flow of tears 

• Step 1: Lacrimal caruncle 

• Step 2: Lacrimal punctum

• Step 3: Lacrimal canal

• Step 4: Lacrimal sac 

• Step 5: Lacrimal duct 

Pigment layer

• Highly melanated area located at back of eye in retina

• Function: Absorb excess light and store vitamin A for photoreceptors to use 

Neural layer

• Contains rods, cones, horizontal, amacrine cells

• Function: Regulate transmission between photoreceptors and bipolar cells