anatomy & physiology of the senses anatomy & physiology 2013-2014


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Are There Additional Human Senses?• Proprioception = sense of body position (i.e. what is your body doing right now)• Equilibrium = balance• Acceleration• Nociception = sense of pain• Temperature• Satiety• Thirst• Micturition• Amount of CO2 and Na in blood


• Means by which an organism obtains information for perception• Sensation is part of the Somatic Division of the Peripheral Nervous System • However integration and perception require the Central Nervous System• Five major senses


Sensory Transduction

•All of our senses receive input with specialized cells/nerves called transducers• The transducers convert stimuli into

action potentials•Action potentials (APs) are electro-

chemical messages that are conveyed along nerves• These messages are ultimately received

and “understood” by the various cortices of the brain

Examples of Transduction

Audition = convert kinetic energy of sound waves into action potentialsGustation = generate action potentials from binding of proteins to specific receptorsOpthalamoception = convert radiant energy into action potentials

Anatomy of the Eye

Changing Views About the Physiology of the Eye

• Platonic view: Extramission (light emanates from the eye)• Aristotelian view: Intramission

(light enters the eye)• Galen: Optical pneuma flows from the brain

into the eye via hollow optical nerves• Kepler: first to suggest the centrality of the

retina (over a crystalline lens) in vision

Ophthalmoception (Sight)• GOAL: Light stimuli transduced into an Action Potential (AP)• HOW: Our eyes act as converging lenses, focusing this light to

their transducing structures• When light strikes the transducers, the photosensitive proteins

rhodopsin & photopsin change 3D shape• This conformational change in shape triggers an AP which then

travels to the occipital lobe of the brain via the optic nerve


•RODS•Concentrated on periphery of retina•125 million cells in retina•Most sensitive to light•Scotopic (night) vision

•CONES•Responsible for color vision•Work best in more intense light•4.5-6 million in retina

Hermann Grid Illusion

•Lateral Inhibition: Stimulation of adjacent rods causes rods at vertices to be shut off

Color Afterimages• opponency process =The optic nerve encodes color in

three separate channels; one for intensity of lightand two for color. • photopsin may take as long as 45 minutes for it to

change back to its original form. During that period of time, the photopsin is said to be photobleached and it sends a constant stimulus to the brain. • Eventually, the brain becomes desensitized to the

constant stimulation from that color photoreceptor and the brain does not see that color. • However, due to the opponency process, the

complimentary color appears as an “afterimage”.

Colorblindness• “Normal” color vision is trichromatic: red, blue, green

color receptors (cones). • Color “blindness” or deficiency comes from a lack or

absence of one or more of these types of cones

Audioception (Hearing)

Audioception (transduction of sound)

•Mechanical stimuli transduced into an Action Potential• Our ears funnel and relay vibrations,

directing these compression (sound) waves to their transducing structures, the cilia• The sloshing of the cochlear fluid

causes cilia to deflect (fold over)• Deflection triggers an AP directed to

the temporal lobe of the brain via the auditory nerve

McGurk Effect Explanation

• Processing of audition is highly reliant upon visual input as well as auditory input• However, as auditory processing

is 5x faster than visual processing, there can be a “disconnect” between the two senses

Shepard Rissert Tone: Explained

• Overlapping tones at octaves produce vibrations in the inner ear that are the same sine wave and hence sound like the same tone

Conductive Hearing Loss

•Conductive hearing loss (CHL) is usually the result of some disturbance in the outer or middle ear structures • It is often due to fluid buildup in the middle ear

from colds, allergies (serous otitis media), a perforated eardrum, or earwax (cerumen) that has partially blocked the auditory canal• This type of hearing loss can usually be treated

with antibiotics or simple as it is a mechanical blockage of the sound waves

Sensorineural Hearing Loss

• Sensorineural hearing loss (SNHL) is the result of damage to the inner ear (cochlea) or nerve pathways (auditory nerve) from the ear to the brain •Causes: age, severe head trauma, genetic or

hereditary deformations, or drugs that are toxic to hearing. •Much more difficult to correct than CHL as it is an

issue with transduction—cochlear implants may restore hearing to some

Anatomy of the Skin

Tactioception (touch)

•Mechanical/Temp/Pain stimuli transduced into AP• Transducing structures are specialized nerves•mechanoreceptors: Detect pressure, vibrations & texture• thermoreceptors: Detect hot/cold•nocireceptors: Detect pain•proprioreceptors: Detect spatial awareness

• This triggers an AP which then travels to various locations in the brain via the somatosensory nerves

Density of Different Receptors

Density and Distribution of Different Receptors

Anatomy of the Nasopharygeal & Buccal Cavities

Physiology of the Skin

• ___________________________ stimuli AP

• Transducing structures are specialized nerves: –_______________________________:

Detect pressure, vibrations, and texture –_______________________________:

Detect hot/cold –_______________________________:

Detect pain –_______________________________:

Detect spatial awareness

Anatomy of the Skin

• This triggers an AP which then travels to the brain via the _____________________________Prosthetics

o How is DARPA revolutionizing the field of prosthetics?

Gustaoception (taste) & Olfacaoception (smell)• Chemical stimuli transduced into AP• Sensitive regions in our tongues & noses

respond to chemicals, processing them in their transducing structures• Taste buds: Detect sweet (OH-), sour (H+), salt

(metal ions), and bitter (N-rich alkaloids) in food• Cilia: Detect odorants in the air

• Each transducer is specialized to interpret a particular chemical (taste or smell)• This triggers an AP which then travels to the

temporal lobes of the brain via gustatory & olfactory nerves

Olfactory & Gustatory Illusions

• Similar to afterimages, once a molecule has bound to a receptor, it will continue to send action potentials• However, eventually the neuron

will enter a refractory period during which it cannot send a message