Sensory Organs

• specialized extensions of the nervous system
  
  
  
• generate sensory impulses upon appropriate stimulus

Sensation vs. Perception

Sensation = sensory impulse sent to CNS

Perception = interpretation by cerebral cortex

Not all sensation = perception

ie. aortal & carotid sinus monitor BP and Bchem, but do not share info w/ cortex to make us consciously aware.

Classification of Senses:

Localization

• General: receptors widespread throughout body
              ie touch temp pain
  
  
  
• Special: receptors are localized in specific sites
              ie sight hear smell taste equilibrium

Classification of Senses:

Receptor Location

• Somatic: rcpt are in outer body wall
           respond to external stimuli ie touch temp pain
  
  
  
• Visceral: rcpt are in the viscera
        respond to internal stimuli ie pain hunger nausea

Classification of Sensory Receptors:

Location & Source of Stim.

3 EEP     

• Exteroreceptors: located near body surface.
  respond to external stimuli
  ie sight hear touch temp pain
  
  
• Enteroreceptors: located in viscera.
  respond to internal stimuli
  ie pain hunger nausea
  
  
• Proprioreceptors: located in skeletal muscles tendons joints and inner ear.
  respond to stim regarding position of body in 3D space.

Classification of Sensory Receptors:

Adaptation Potential

2  -ics  

AP=decrease in firing rate over time w/ continual stim.

• Tonic: mnt relatively constant firing rate regardless of
           stim duration ie photoreceptors in retina
  
  
• Phasic: firing rate gradually decreases w/ continual   
             stim ie touch/temp in skin

Adequate Stimulus

Each type of receptor produces a specific sensastion IDed w/ stim that rcpt normally responds to.

stim is adequate to produce normal response
ie sensing light/sight b/c light hits photoreceptors

Law of Specific Nerve Energies

In addition to AS, many rcpt will respond to other stim, esp if they're excessively strong.

Perception is the same as for AS regardless of what the other stim is (b/c brain is used to interpreting input from those rcpt that way and is stuck in a rut)

therefore strong pressure will activate photorcpt and brain interprets this as light, even if none is present.

Receptor Potential & Impulse Generation

stim of sens rcpt causes local hypopolariztion of rcpt mem

Graded hypopolarization affected by stim intensity

RP can summate (temporal or spatial) to threshold

If hypopol is sufficient to reach threshold @ sens fib, AP is generated and imp sent to CNS

Meissner's Corpuscles

Located in dermal papillae of hairless areas of skin

ie fingertips/lips

consist of dendrites wn a thin CT sheath

respond to very light touch

Pacinian Corpuscles

located deep in dermis & some visceral organs/joint capsules/skel musc

consist of dendrites wn multilayered CT sheath

respond to heavy pressure/vibration

Free Nerve Endings

most superficial

end as knobs b/w cells in lower epidermis

twine around hair roots (hair root plexes)

respond to bending of hair

Pain Receptors

• most are free nerve endings
  
  
• respond to chemicals released from damaged tissues
  
  
• found in most tissues
  
  
• sparse in some visc organs
  ie brain (completely absent)

Sensory Accomodation

                                       2

SA= lessening of perception of stimulus over time due to:

• sensory adaptation: by phasic receptors
  
  
• stimulus filtering: by cerebral cortex
  (disregards irrelevant stim)
  allows concentration.
  deficit of this w/ ADHD

Referred Pain

RP= pain originating from internal organ but perceived as coming from a specific spot on skin

(sens fibs share nerve tracts and brain does not differentiate these easily)

ie. angina pectoris: left arm neck & chest wall pain b/c of myocardial ischemia that may indicate iminent MInfarc.

Thermoreceptors

free nerve endings

seperate heat/cold rcpt

• heat sensitive above 25C/77F
  
  
• cold sensitive below 20C/68F

Proprioreceptors

                                         3  nmntjk

• neuromuscular spindle: dendrites twined @ skel musc fiber. respond to stretching of fib
  
  
• neurotendonous rcptr: (golgi tendon organs) located @ musc/tendon juncture. respond to tendon tension
  
  
• joint kinesthetic rcptr: located in joint capsule of synovial joints. respond to joint mvt.

Special Senses

• olfaction
• gustation
• photoreception
• audition
• equilibrium

Olfaction:

Structure

receptor=modified cilia

hairs project b/w cells of olfactory epithelium in the top of the nasal cavities

nervelets pass thru cribriform foramina to olfactory bulbs where sens. info is processed

Olfaction:

Physiology

nervelets bind scent molecules in inspired air

by firing few types in diff combos, we smell thousands of distinct scents

Gustation

modified cilia

hairs project through taste pore

taste pore is top of taste bud

taste buds located on and around visible papillae

Tongue Papillae

reduced folliate p: side of tounge (leaf)

vallate p: flat round at back

filiform p: blunt soft cones evenly distributed (blunt in
              humans but hard in sandpaper tongues to aid
              digestion ie cats)

fungiform p: blunt knobs evenly distributed

Taste Zones

bitter: wide at back

sour: sides

salty: front third

sweet: tip

umami: savory/meat - all over

Eye Anatomy

Optic Nerve

Optic Disc

Sclera

Cornea

Choroid

Retina

Fovia Centralis

Ciliary Body

suspensory Ligament

Lens

Iris

Cornea

Pupil

post. & ant. chambers w/ aqueous humor

chamber of vitreous body w/ vitreous humor

Cataracts

clouding of lens due to trauma, meds, unctrld DM, excessive UV exposure

causes loss of visual acuity, night blindnedss, halos around lights, eventual blindness

Tx: lens prostethic

Glaucoma

caused by increased intraocular pressure

(excess production of or inadequate drainage of a.h.)

causes retinal atrophy, loss of visual acuity (peripheral to central field) light halos, gradual blindness

Tx: surgery to increase drainage or meds to decrease production ie beta blockers/carbonic amhydrase inhibitors

Presbyopia

age related hardening of lens

reduces ability to accomodate for close focus

starts age 35-40

Tx: reading glasses

Extrinsic Eye Muscles

CN3 Oculomotor:

Sup. rectus

Med rectus

Inf Rectus

Inf Oblique

CN4 Trochlear: Sup Oblique

CN6 Abducens: Lateral Rectus

Rods

• about 100 million per retina
• most concentrated peripherally
• black & white
• detect motion
• poor acuity bc convergence - image is smeared

Rod Convergence

rods converge to bipolar cells to ganglion

low level stimulus so low acuity

helps rod function better in dim light bc signal convergence increases firing rate by spatial summation

Cones

• about 7 million per retina
• most concentrated in fovea centralis in macula
• produce color images
• no convergence
• low function in dim light
  
  
  3 colors: green blue red
  
  firing rods and cones in diff combos can see whole spectrum

Visual Pigment

Rhodopsin

• visual purple
• protein(opsin) w/ retinoldehyde(retinol)
• derivative of vit A
• Vit A derived fr. beta carotene
  
  Vit A deficiency = blindness
  common in thrid world

Retinol Excitation

retinol usually in bent 11 cis form that is tightly bound to membrane

when light hits it, it converts to straight alltrans form and partly dissociates

this change causes change in membrane permeability and membrane hypopolarizes

Bleaching Rxn

pigment changes with excitation

11 cis= deep purple

all trans = light yellow/orange

Return to 11cis

after excitation, alltrans retinol must be converted back to 11cis or replaced w/ fresh 11cis

this must occur in absence of light

ie takes eyes longer to adapt light to dark than vice versa

Partial Decussation

each retina sends fibs to both sides of brain

info is mixed and fields are fused

different angles provide depth perception but this is not a funct of decussation

External Ear Anatomy

• auricle/pinna - direx sound into canal
  
  
• ext.acoustic meatus -canal - lined w ceruminous glands
  
  
• cerumen - repels arthropods & moistens tympanum
  
  
• Tympanum - double layer membrane b/w middle and outer ear. 1cm diameter. outer=stratified squamous inner=low columnar

Middle Ear Anatomy

air filled chamber w/n petrous part of temporal bone

Eustachain Tube conx w/ nasopharynx - allows pressure equalization b/w inner ear & environment

Auditory Ossicles

malleus, incus, stapes

solid conducting medium

narrowing bones amplify vibrations X20

Ear Muscles

Tensor Tympani - malleus

Stapedius - stapes

reflexively ctrx in response to very loud noises

this immobilizes ossicles to protect inner ear

ie flashbang

Fenestras

divide middle and inner ear

F. vestibuli: oval - covered by foot of stapes.

transfers vibrations to vestibular paralymph.

F. cochlea: round - second tympanic membrane

dampens vibrations at the end of the scala tympani

Periotic Labyrinth

maze of channels w/n petrous part of tb = inner ear

bony labyrinth = structure

membranous labyrinth = organs within

space bw bonyL and memL filled w paralymph

fluid wn memL is endolymph

consists of: semicircular canals, vestibule, cochlea

Semicircular Canals

membranous labyrinth within

3 ducts = superior, posterior, lateral

rcpt for rotational head accel

Vestibule

contains fenestras

membranous labyrinth = saccule & utricle

rcpts for elevation/linear head mvt

Cochlea

scala vestibuli: base = oval window - filled w/ paralymph

scala tympani: base = round window - filled w/ paralymph

(these connect at cochlear apex/helicotrema)

cochlear duct: memL filled w/ endolymph.
                    contains hearing rcpts on organ of corti

Cochlear Xsec

• scala vestibuli
• scala tympani
• cochlear duct
• vestibular membrane
• basilar membrane
• tectorial membrane
• organ of corti
• sens fibs to CN8

Sound Waves

pressure waves caused by moving/vibrating objects

radiate in all dirx from source

must be transmitted thru medium.

denser medium = better conduction

Sound Wave Characteristics

Wavelength: distance bw crests
gives frequency in cycle/second
measured in Hz

determines pitch

Amplitude: height of wave fr. baseline

measured in Db

determines volume

Human Ranges

Hz: 20-20,000

whales lower, dogs&bats higher

Db: 0+ - scale is exponential

chronic exposure to +60-70 Db = permanent hearing loss

Sound Wave Sensing

• airborn SW strike tympanum
• causes vibrations of minute diplacement
  (about an atomic diameter)
• vibes pass thru auditory ossicles
  which conduct and amplify
• foot of stapes vibrates in oval window
• transmits vibes to paralymph of scala vestibuli

Inner Ear Sensation

• vib. in paralymph of scala vestibuli cause vestibular memb. to vib.
• vest. mem. causes basilar mem. to vib
• hair cells on organ of corti strike tectorial mem above
• this bends sensory hairs
• bending hairs causes hypopolarization
• towards threshold
• hits= AP
• AP= sensory impulse to CNS

Cochlear Sensation Diagram

• external acoutic meatus
• tympanum
• eustachain tube
• ossicles
• oval window
• scala vestibuli
• helicotrema
• scala tympani
• round window
• vestibular membrane
• basilar membrane
• tectorial membrane
• hair cells on organ of corti

Cochlear Frequency Sensation

first 1/3 = 20,000 - 1,500 Hz

second 1/3 = 1,500 - 500 Hz

third 1/3 = 500 - 20 Hz

Equilibrium

rcpts are hair cells similar to organ of corti

2 sites:

• ampullae: semicircular ducts - head rotational accel
• maculae: floor of saccule & utricle - head accel/elev

Sensory Hairs

modified cilia

kinocilium

stereocilia

towards kino=stimulation

away from kino=inhibition

Maculae

hair cells in saccule & utricle in patches on floor

imbedded in gelatinous substance (otolithic membrane)
w/ CaCO3 crystals (otoliths)

otoliths add mass & amplify inertial force
so hairs bend easier

hair beinding causes hypopolarization
which triggers impulse

Ampullae

located on cristae ampullaris

head rotation pushes cupula in opp dirx

bends hairs causing hypopol. & sens. imp.

Endocrine

funct: chemical reg of body

hormones typically secreted by specific tissues
H circulates thru blood

only specific target tissues elsewhere in body respond

Chemical Classes of H

SAPGP

Steroids

cholesterol derivative

nonpolar hydrophobic

require carrier proteins (fr. liver)

ie estrogen / cortisol

Chemical Classes of H

SAPGP

Amino Acid Derivatives

Catecholamines: ie norepi, epi, dopamine

freely soluble

Primary Thyroid H: insoluble. requires carrier proteins fr thyroid such as thyroglobulin.

Chemical Classes of H

SAPGP

Polypeptides

ie insulin/glucagon, ADH, oxytocin

digestible so no PO

Chemical Classes of H

SAPGP

Glycoproteins

proteins & carbs

ie TSH FSH LH

digestible so not PO

Chemical Classes of H

SAPGP

Prostoglandins

fatty acid derivatives w/ H like axn

nonpolar hydrophobic carrier protein

produced by many tissues

primarily affx smooth musc ie thromboxane A (vasoX)

ie these in prostate are in semen & cause ctrx of vaginal and uterine musc to facilitate fertilization

Hormone Activation

Pro vs Pre

Effective/Active form is often derived fr. a less active precursor

Prohormone: converted to active BEFORE secretion.  ie proinsulin to insulin. not usually found in sig amts in blood. elevation suggests pathological process ie severe pancreatitits, pancreatic cancer.

Prehormone: converted AT TARGET ie. T4 to T3

 normally found in blood.

Hormone Inactivation

hs have short 1/2 life in circulation

usually a few hrs

any excess quickly degraded by liver

primary determinant of H levels is secretion rate

conc levels affx axn - ie estrogen

low=inital release of FSH & LH @ beginning of menstrual cycle causes ovary follicle to enlarge

mid=sudden spike in FSH & LH that triggers ovulation

high= inhibit FSH & LH release which inhibs cycle and prevent spontaneous abortion until partruition.

ie oral contraceptives

NR: seen at physiological ranges of concentration

AR:seen at pharmacological ranges of conc.

ie prolonged corticosteroid use can lead to
CT breakdown & demineralization of bones

Down Regulation

from prolonged H use

many deleterious effx

ie long term anabolic steroid use turns user into a chemical eunuch b/c body lowers natural H production
and lowers cellular reception and target tissues stop responding

Permissive: axn of 1 H promotes another

ie thyroxine inc. metabolism & inc. rate of protein synthesis which is done by hGH

Synergistic: 2+ hormones necessary for specific response

ie testosterone + FSH = normal sperm formation

Antagonistic: H w/ opposing axns

ie insulin vs glucagon

H circ thru body but only specific cells resp

cells must have rcpt for particular H

Membrane: catecholamine, polypeptide,glycoproteins

Cytoplasm: steroids

Nucleus: t3/t4

both nonpolar/hydrophobic/require carrier protein

when target cell is reached, they dissoc fr carrier & diffuse across mem into cell

S: bind to cytoplasmic rcpt protein in target cell

rcpt/H complex then enters nucleus

binds to regulatory sites on chroms

modify gene activity

T: bind to cytoplasmic carrier. xport to nucleus

releases into nucleus

binds to nuclear rcpt on chroms

activates specific genes.

polypeptides, glycoproteins, catecholamines

dont enter target

bind to rcpt

triggers activation of 2nd messenger

2m is responsible for axn attributed to H w/n target cell

Hormone Action

Epinephrine

adenyl cyclase converts ATP to cAMP

stimulates inactive protein kinases to activate

(this affx cell metabolism wn character of H)

cAMP deactivates after use by phosphodiesterase

other H 2m: cGMP, calmodulin

deactivates 2m

PDE inhibitor use can indirectly amplify epi effx by prolonging 2m life

ie caffine

ie theophylline - aids bronchoO
                       used as supplement Tx to asthma