Biology 2401 API

Biology 2401 API Lecture Notes Sensory Dr. Weis

I. Chemical Senses :

A. Taste

B. Smell

Have chemoreceptors that respond to chemicals in aqueous solutions.

A. Taste --> Gustation

Sensory receptors : taste buds in oral cavity

primarily on tongue mucosa in projections or papillae

also some located in the pharyngeal region (supplied by Vagus N.)

Three types of papillae (tongue projections are not taste buds, just location)....

1. Filiform – scattered, threadlike

2. Fungiform – at tip and sides, mushroom shape

3. Circumvallate -- few, round, form an inverted "V" pattern on the back of the tongue

Taste buds....

Three types of epithelial cells :

1. Supporting ---> insulate

2. Basal --> replace

3. Taste --> chemoreceptor with hairs through a taste pore

Sensory dendrite around basal part of taste cell

Taste sensations are divided into 4 basic qualities

Sweet.........sugars, alcohols, amino acids

Sour..........acids

Salty.........metal ions (Na+Cl-)

Bitter........alkaloids

can determine a pattern on the dorsum of the tongue, the following is a general map :

Tip --- sweet, salty

Sides -- sour

Back -- Bitter

taste receptors (taste buds) respond to chemicals in saliva, must diffuse through the taste pore region and contact the gustatory hairs of the cell. Binding of the chemical to specialized receptors causes a change in Ca++ channels and they open to cause a release of a neurotransmitter from the taste cell membrane tp the sensory bipolar neuron. This causes sodium channels to open and begin depolarization to threshold and then an action potential is created at the axon hillock region and the electrical message is sent down one of the corresponding cranial nerves :

Afferent axon fibers from the tongue form :

Facial Nerve (CN VII) : anterior 2/3 of tongue for sweet, sour, and salty

Glossopharyngeal (CN IX) : posterior 1/3 of tongue for bitter sensations.

Vagus (CN X) : pharyngeal region

The pathway continues as synapses will occur at the medulla --> thalamus --> parietal lobes of the sensory cortex.
Stimulation will also trigger central and peripheral reflexes involved with digestion.

Aging : loss of taste reception due to decreased number of receptors ( not being replaced)

Most of our tasted perception is tied to olfaction.....

B. Smell : Olfaction

The olfactory epithelium lies at the roof of the nasal cavity along the superior conchae and ventrally at the cribiform plate of the ethmoid bone.
This pseudo stratified epithelium contains :

This process occurs because the bipolar neurons are sensitive to chemicals in gas.
These chemicals bind to protein receptors on the membrane and will active an enzyme : ADENYLATE CYCLASE

Adenylate cyclase will in turn activate the conversion of ATP to cyclic AMP (cAMP) which will create an action potential
by opening Na+ channels, and therefore depolarization of the neuron.

Olfactory adaptation occurs due to inhibitory neurotransmitter GABA that are released from granule cells located in the olfactory bulbs.

Aging : Loss of olfaction occurs due a decrease in receptor number (receptors not being replaced).

II. EYE : Accessory Structures / Eyeball (Globe)

A. Accessory Structures : eyebrows, eyelids, conjunctiva, lacrimal apparatus, extrinsic eye muscles

1. Eyebrows @ superior orbital margins of orbit

function : shade, catch perspiration, facial expression

2. Eyelids (palpebrae)

                                    Separated by palpebral fissure and meet at the angles of the eye --> the medial and lateral canthus.
Consist of connective tissue plates .... the tarsal   plates and are covered with skin.
The tarsal plates  serve as anchors for the orbicularis oculi m. and the levator palpebrae m.

Associated structures of the eyelid :

eyelash.... hair, protect from foreign particles, reflex blinking if stimulated

glands ... sweat glands --> ciliary glands

sebaceous glands --> keep skin supple

tarsal glands (glands of Zeis) : lubrication

Meibomian : along inner margin of lids, to prevent lids from sticking together

Lacrimal Caruncle : at medial canthus, produce white "sleep"collected at that region

3. Conjunctiva

Mucous membrane lining... stratified squamous with goblet cells

along inner eyelids --> palpebral conjunctiva

along globe --> bulbar conjunctiva that lies over the sclera

Space between the two conjunctiva is called the

Conjunctival sac or fornix, where medication can be administered

Function of Conjunctiva : lubricate the eye, and immune response to allergens

4. Lacrimal Apparatus : lacrimal glands with ducts that drain secretions into the nasal cavity

a. Lacrimal gland...dorsolateral orbit, almond shape

secretion --> salt solution : tears through ducts. Blinking of eyelids will

spread tears to medial canthus.

Tears collect into lacrimal canals through the lacrimal puncta, and then drain into the lacrimal sac.
This sac is continuous with the nasolacrimal duct. Tears will then empty into the nasal cavity at the inferior meatus, near the inferior conchae.

b. Tears : water, salt, mucus, lysozyme (enzyme)

will mix with sebaceous secretions from glands in the eyelid

Function : protection, moistens, lubrication, nutrients to cornea

5. Extrinsic Eye Muscles # 6

origin @ orbit, insert on sclera of the globe

skeletal muscle for eye movement and rotation

2. Vascular Tunic.........collectively called the UVEA

Three regions of the Uvea : Choroid, Ciliary body, Iris

Pigmented tissue that is also vascular (contains blood vessels)

B. Ciliary body

thickened pigment tissue

covers smooth muscle --> ciliary m.

folds create --> ciliary processes

C. Iris

continuous with the ciliary body

creates a visual pigmented tissue

forms a round central opening --> PUPIL

contains smooth muscles that control the pupil size in response to light and reflexes (pupillary light reflex)

muscles in two planes :

pupillary constrictor muscle : circular

pupillary dialator muscle : linear

3. Sensory Tunic.......innermost layer of globe wall, also known as the retina

Retina, in two basic layers -->

a. outer pigmented epithelial cells to help absorb light and store Vitamin A

b. inner neural layer that contains photoreceptor cells for vision

Nervous layer has three types of neurons :

* photoreceptors (rods and cones)

* bipolar cells

* ganglion cells

other neurons provide lateral connections

* horizontal cells

* amacrine cells

Blood vessels also enter and leave through the optic disc are called the retinal artery --> supplies the inner layers of the retina
(bipolar and ganglion cells) while the choroid vessels --> supplies outer layers of the retina (the photoreceptors and the pigmented epithelium)

Problems : Retinal detachment .........which is a separation of the pigmented and nervous

layers of the retina. The photoreceptors lose their blood supply and degenerate.

Eye Interior : Two chambers divided by the lens

A. Vitreous Chamber in the posterior segment of the eye

filled with vitreous humor

formed at birth, lasts a lifetime

collagen fibers and water

function : transmit light

support globe

pressure for retinal layers

contribute to the Intra-ocular pressure (I.O.P.)

B. Aqueous (anterior) Chamber in the anterior segment of the eye

consists of two parts :

1. Anterior segment of the aqueous chamber : between the cornea & iris

2. Posterior segment of the aqueous chamber : between iris and lens

The anterior (aqueous) chamber is filled with aqueous humor that is formed and
drained continually due to the filtration process from capillaries in ciliary body flows into posterior segment,
through pupil into anterior segment and drains into the Canal of Schlemm at the limbus.
This canal is continuous with the venous drainage from the eye

function : maintain I.O.P.

internal support of globe, especially cornea

nutrients and oxygen are circulated to the lens and cornea

Problems : glaucoma ..........any increase in I.O.P. above normal. Pressures are in mm Hg.

C. Lens

develops from ectoderm cells that formed a sphere.

elongated cells form the primary lens fibers to make up the “nucleus”

cuboidal cells at the junction will lengthen to form secondary lens fibers, and will continue to be laid down in layers (like an onion)

elastic capsule to allow change in shape as determined by the suspensory ligaments that are attached to the ciliary processes of the ciliary body.

shape : BICONVEX

transparent : due to regular layers of secondary lens fibers

uses glucose in a specific pathway for energy -- ATP

problems : any opacity ---> Cataract (several causes : old age, diabetes, trauma...)

hardening of lens -- > loss of elasticity (known as presbyopia)

OPTICS and Vision

Light properties :

electromagnetic radiation, energy packets --> photons

visible wave length, spectrum from red to violet

red......... long wave length, low energy

violet......short wave length, high energy

Spectrum : Red, Orange, Yellow, Green, Blue, Indigo, Violet

Color seen is what is reflected, since objects will absorb and reflect light

Refraction is the bending of light rays as it travels from one medium to another

Lens --> curved, transparent material light is refracted, converges to form a real inverted image on focal point on the retina.

Convex lenses will converge light and produce a real image that is inverted

Concave lenses will diverge light, image is imaginary (that is, it doesn’t form)

Light path........

Cornea (most light rays are refracted here) -->

Aqueous (water, minimal bending if any) -->

Lens (for fine focusing of the light rays, converge rays)->

Vitreous ---> Retina

For distance Vision, the ciliary muscles are relaxed, lens is thin and elongated

For close vision , the eye must accommodate (adjust) several ways ::

Lens accommodation ...increases refractory power of the lens

ciliary muscles contract, lens bulges and becomes more rounded

Pupillary constriction ... control amount of light that will enter

Convergence of the eyeballs ... medial rotation of the eyes to focus on close objects

Normal Vision : Emmetropia (eu = normal, metr = measure, opia = eye)

Problems with refraction :

Myopia....nearsighted,

objects focused in front of the retina , need concave lens to correct

Hyperopia... farsighted, objects focused behind the retina, need convex lens to correct

Astigmatism....unequal curvature of the lens or cornea

PHOTORECEPTION : also known as phototransduction (converting light energy to electrical energy)

Anatomy : modified neurons........Rods and Cones

receptor region (modified dendrite area) called the outer segment

shape --> long, slender in rods

short, conical in cones

embedded in the pigmented epithelial cells of the retina

contain discs that have visual pigments

The outer segment is connected to the inner segment by a stalk.
The inner segment forms the cell body that contains organelles, mitochondria, nucleus, and will continue and form synaptic endings.

The outer segment contains light absorbing visual pigments that are packaged and housed in membrane bound discs.
Each visual pigment responds to a different wavelength of light.

In rods the pigment is Rhodopsin, and is constantly being replaced.

It will absorb all wave lengths of light, especially sensitive in dim light, to give us grey tones.

Rods are found in the periphery of the retina and will give us fuzzy images since several rods will synapse on one bipolar cell
(converging neuron pool) and the effects of this stimulation is summed.
In rods, the discs are replaced as they move upward toward the pigmented epithelium.

In cones the pigment is collectively called photopsin, and will be repaired.

It is affected by bright light and is very responsive to red, green, and blue wave lengths

Cones are responsible for acute, sharp color vision and are sensitive to bright light.

Cones are concentrated in the macula and are exposed in the center of this region that is called the fovea centralis.
In the fovea all the other layers are pushed aside. The cones also have a direct synaptic pathway from bipolar neurons to the ganglion cells.
Since the discs are folds of the cone membrane, they are not destroyed, but repaired by the pigmented epithelial cells.

Visual Pigments

Formed from Vitamin A (retinol) as a carotenoid pigment :

Retinal and combined with a protein generally called an opsin.

The retinal has two forms

bent.........cis

straight........trans

There are 4 types of opsins involved with visual pigment :

For a visual pigment to be formed, the retinal must be in the cis formation in order to combine with its opsin, therefore we have ::

When light strikes the retina and is absorbed in the pigmented epithelium, its energy affects the visual pigments
causing them to break apart. This happens because cis Retinal is changed to trans Retinal, and becomes separated from its opsin.

This breakdown in the visual pigment causes Na+ gated channels in the outer segment to close and will cause a hyperpolarization
and stop the flow of neuotransmitters (glutamate)in the synaptic endings of the inner segment. This change in neurotransmitter flow
signals that light has struck the retina and will then affect the very excitable bipolar cells, will respond by depolarizing and continue the signal to the ganglion cells.

The visual pigment must reform before it can be affected again by light.
Cellular energy is used to change the trans Retinal back to cis Retinal so that it may combine with its opsin.

When the photoreceptor is not being stimulated :

Neurotransmitters (glutamate primarily) are released from the synaptic endings of the photoreceptor cell.

*** this is the opposite effect you would normally see with neuron stimulation

After a photoreceptor has been stimulated, other neurons provide lateral connections along the neural pathway.
These are the horizontal cells and amacrine cells and will modify the response of the bipolar cells and ganglion cells respectively.
The ganglion cells come in two types : M cells for movement, location, and depth of field and the P cells that pick up color, form, and texture.

A quick summary of the light pathway will consist of affecting the photoreceptor cells --> bipolar --> ganglion --> whose axons form
the optic nerve (CN II) that exists at the optic disc in the fundus and will continue through the optic canal.

From the ganglion cells, their axons exit at the optic disc and form the Optic Nerve (CN II).

Fibers cross anterior to the pituitary and form the optic chiasm : some stay on the same side, those that supply the lateral part of the eye and
some fibers, those that supply the medial part of the eye cross to the opposite side.

These fibers will continue as the optic tracks, synapse at the lateral geniculate body of the thalamus.

Those from the thalamus will form projection fibers to go the primary visual cortex of the occipital lobe, and then to be analyzed

and stored in the visual association areas in 6 vertical columns in order to store information on : color, shape, form, movement.

Other synapses :

REMEMBER : At the region of the optic disc, no retinal components are found, there by creating a blind spot when light strikes this area.
At the optic disc retinal blood vessels enter, and axons from the ganglion cells leave and form the optic nerve (CN II).

Problems :

Night blindness........dysfunction of rods due to a lack of vitamin A

Color Blindness........congenital lack of 1 or more cones (usually red is the nonfunctional cone)

Cortical blindness.....can see, but not recognize objects

Globe loss or neural destruction.......blindness

Adaptation --> moving from dark to light and vice versa

Sensitivity of rods and cones can be altered by slight changes in photochemical concentrations

The brightness of a color (red vs. pink) is dependent on the degree of stimulus as Na+ channels

close in graded proportion to the light intensity.

A) Light Adaptation

photochemicals are reduced to retinal + opsins

therefore there is a decrease in photochemical concentrations and this causes a decrease in photoreceptors sensitivity.
Going from light to dark, this is apparent, as we use the rods for dim light, and their sensitivity is now decreased. In the dark, cis retinal
combines with the rod opsin, scotopsin, to reform the photochemicals and increase the concentration and the rods sensitivity, allowing us to eventually see in the dark,
since formation of secondary messengers (cyclic GMP) takes time and are short lived due to enzyme (phospho diesterase) destruction.

B) Dark Adaptation................In the dark -->

Vitamin A --> retinal, and cis Retinal combines with opsins to create specific photochemicals. This increase in photochemical concentrations increases the sensitivity. The amount of photochemical concentrations are only limited by the amount of opsins. When we go from dark to light, our rods have a high degree of sensitivity. When bright light strikes the retina, this causes the photochemical in the rods to breakdown or bleach, thus causing sodium channels to close and hyperpolarizing the rod.

This increased sensitivity to light makes the light seem very bright. Over a period, the sensitivity decreases as the concentration of photochemicals decreases.
We become adapted to light when the rate of breakdown is balanced with the rate of reforming these chemicals.

Other Concepts............

Binocular vision causes the overlapping of visual fields, and with the crossing of nerve fibers at the optic chiasm, allows us to have depth perception. Stereoscopic (front field view) vs. panoramic (side view) will

change the visual field and therefore the depth perception.

EAR : Hearing and Balance

Anatomy --> the ear is divided into three areas

A) Outer Ear

auricle (pinna) ....elastic cartilage covered with skin

function : to direct sound waves and protection from foreign bodies

external auditory canal...from auricle to tympanic membrane, within the temporal bone lined with cerumenous glands that produce cerumen (ear wax).
They are considered to be modified sweat glands.

Tympanic membrane ...forms the boundary between the outer ear and middle ear.

Made up of Fibrous C.T. that vibrates in resonance with sound waves

B) Middle Ear........Tympanic cavity housed within the petrous portion of the temporal bone

Contains : oval (vestibular) window

round (cochlear) window

mastoid antrum

eustachian (pharyngotympanic) tube

ossicles : malleus, incus, stapes

Malleus is at the tympanic membrane

Incus in the middle, forms a synovial joint

Stapes at the oval window

function : the ossicles transmit the vibratory motion of the tympanic membrane (TM) to the oval window

Sound is created by pressure disturbances of air molecules that originate from the vibrating objects and will travel in waves.

Sound waves can be graphed as a sine wave and allow us to define some properties of sound waves.

1. Frequency......the number of waves that pass a given point in time, termed a cycle and measured in Hertz (cycle/sec)

a wave length ( lambda ) is the distance between two crests.

The shorter the wavelength, the higher the frequency,

and the higher, the frequency the higher the pitch.

a mixture of several frequencies create a sound quality

2. Amplitude......height of the wave that reflects the intensity or energy content.

Measured in decibels (dB)

Airborne sound enters the external auditory canal, strikes the TM which will vibrate at the same frequency (resonance), t
he ossicles move and will create an increased pressure at the oval window due to lever arm mechanics.
This sets the cochlear fluid into a wave motion and will move the fluid in the inner ear cavities.

For excessively loud sounds, two muscles can contract to limit motion in order to protect the cochlea and basilar membrane.

Two muscles : tensor tympani m. , to tense the eardrum

stapedius m. , to limit the movement of the stapes @ the oval window

C). Inner Ear --> Labyrinth located in the temporal bone, in two divisions : Boney and membranous.

1. Cavities within bone (boney labyrinth)

divided into regions

filled with perilymph (like CSF)

2. Membranous sacs/ducts within bone (Membranous labyrinth)

interconnecting, and contains endolymph (like ICF)

Fluids within labyrinth conduct sound vibration and respond to mechanical forces

Vestibule :

Cavity between cochlea and semicircular canals

contains the oval window

two sacs : Saccule --> continuous with the cochlea

Utricle --> continuous w/ the semicircular canal

these sacs house the equilibrium receptors -- Macula

that respond to gravity & head position and linear acceleration

Semicircular Canals :

cavities within bone oriented at right angles to each other

in one of three planes : anterior, posterior, lateral

Swelling at the end of each duct is called the ampulla and houses the equilibrium receptor :

Crista ampullaris, that respond to angular head movements

Cochlea :

spiral boney chambers, duct in the center helps divide the region into three chambers

1. Scala vestibula........continuous with the vestibule

2. Scala media......cochlear duct that houses the receptor organ for hearing --> Spiral Organ of Corti

3. Scala tympani....terminates @ the round window

Chambers are filled with fluid :

Endolymph --> scala media

Perilymph --> scala vestibula, scala tympani

Hearing..........

Vibrations of the oval window from the stapes sets up movement of the perilymph in the scala vestibuli.
Movement of the perilymph will set up motion within the scala media by affecting the endolymph contained there.

The scala media, also known as the cochlear duct, is composed of a roof formed by the vestibular membrane
and a floor formed by the basilar membrane that supports the Organ of Corti.
The basilar membrane is made of elastic fibers and is fixed at one end (near the oval and round windows) and free at the other.

The organ of Corti rests atop the basilar membrane and consists of :

1. supporting cells

2. cochlear hair cells in rows

3. tectoral membrane that overlies the hair cells

4. rods of Corti, to allow for support & singular motion

Movement of the basilar membrane (up and down) causes the hair cells to bend. When the membrane moves up, the hair cells contact the tectoral membrane and depolarize.
When the membrane moves away, the cells loose their contact and will hyperpolarize.
The movement of the basilar membrane is due the movement of the endolymph within the duct.
The short stiff fibers at the base are fixed and will vibrate at high frequency. The long thin fibers at the free end will vibrate at low frequencies.

Auditory pathway :

from the cochlear nerve (CN VIII), fibers will synapse at the cochlear nuclei at the medulla.

Fibers can cross, go direct, or have other synapses at :

midbrain (inferior colliculus)

thalamus (medial geniculate)

auditory cortex of the temporal lobe, and then association areas for sound interpretation.

Within the auditory cortex, the processing center will detect :

pitch : different frequency of sound waves due to the activation @ different parts of the basilar membrane

loudness : increase sound intensity recruits more hair cells due to basilar membrane motion

localize : intensity and timing of sound waves reaching the ear

Problems :

Deafness

1. Conduction deafness.........due to blocked normal transfer of vibration.

Causes :

TM rupture or scarring

inflammation

accumulation of ear wax

fused ossicles, arthritis

2. Nerve deafness........affecting neurons

Causes :

loss of receptor cells

nerve damage --> CN VIII pathways, Cortex

Tinnitus.......ringing in ears

EQUILIBRIUM

Response to head movements

equilibrium receptors : Vestibular apparatus within the vestibule and semicircular canals

Monitor : static equilibrium and dynamic equilibrium

I. Static Equilibrium : Vestibule

Sensory receptors --> MACULA on the saccule and utricle

Respond to head position in relation to gravity

linear acceleration : vertical, horizontal

Macula --> contains supporting cells and hair cells as the receptor.

the hair cell has small cilia and one large Kinocilium and are embedded in jelly like membrane, the otolithic membrane, that have stones on the dorsal surface called otoliths or otoconia.

The macula sits vertically on the saccule and monitors vertical movements, and sits horizontally on the utricle to monitor horizontal movements.

Movement of the otoliths will set up motion of the cilia of the hair cells that have directional sensitivity. The hair cells will be stimulated when the cilia are moved toward the Kinocilium and the activation of these receptor cells will be transmitted to the vestibular nerve.

II. Dynamic Equilibrium : Semicircular canals

Sensory receptor --> Crista ampullaris located within the ampulla of each of the ducts.

These receptors respond to angular rotation and velocity changes

The Crista consists of :

Also tied to this movement are those of the eyes to maintain a fixed position with in the socket.

This reflex movement is called Vestibular Nystagmus, that can be observed to have a fast phase and a lag (slow) phase.

From the hair cells, the vestibular nerve fibers form part of the vestibular cochlear nerve (CN VIII).

Fibers then synapse in the brain stem on the vestibular nuclei. From there, fibers go the cerebellum and then to the cortex for conscious interpretation and motor response by way of cranial nerves that control eye movements (CN III, IV, VI), neck movements (CN XI), and body (vestibulospinal tracts).

Problems:

Vertigo

Dizziness

Motion Sickness

Somatosenses : Touch........review

skin receptors in dermal regions

1. free nerve endings.........papillary dermis

2. Merkel......papillary dermis for fine touch

3. Meisseners corpuscles

in reticular dermis, beneath papillary region

encapsulated, for fine pressure

4. Pacinian corpuscles

deeper dermis, encapsulated (onion like)

deep vibrational pressure

5. Ruffini corpuscle, located in mid-deep dermis

encapsulated, deep pressure, stretching, heat

6. Krause corpuscle in mid- deep dermis for cold

Summary :

Receptors -->

Specific sensory information

Specific area

Many types, will be tied to sensory neuron

Stimulus :

pain --> fast (when cut) = myelinated

slow (ache) = nonmyelinated

referred (missing limb)

temperature --> warm/ cold thermoreceptors

physical --> Touch

Pressure

Position (proprioception)

chemical --> taste

smell

blood .....monitor pH, CO2, O2

Stimulus @ receptor ==> change transmembrane potential ==> depolarization ==> action potential
==> sensory afferent ==> CNS for interpretation ==> motor response ==> motor efferent

Concepts :

ADAPTATION will occur with all sensory information

peripherally at the receptor level :

1. phasic (fast)

2. tonic (slow)

centrally at the CNS level