Ch. 10 - Sensory Physiology

Cells that receive sensory information (a stimulus) from the environment

• Transduce different energy forms (pressure, temperature, chemical, light) into graded potentials that initiate action potentials

• Afferent sensory input to CNS

• Mechanoreceptors

• Thermoreceptors

• Photoreceptors

• Chemoreceptors

• Nociceptors ( Mary, Thought, Parry, Could, Notice)

Respond to MECHANICAL stimuli, like touch or pressure

Respond to cold/warmth (think *thermometer, temperature, cold/warm)

Respond to light (think *good photos involves light)

Respond to binding of particular CHEMICALS

Respond to painful stimuli

• Graded potential in sensory receptor in response to environmental stimulus

Opening of ion channels

depolarization; gated ion channels open -----> AP (electric signal) generated

Decrease in receptor sensitivity (responsiveness) during maintained stimulation

Leads to decrease in AP frequency (rate) in afferent neuron despite continuous presence of a stimulus

• Phasic or Fast-Adapting Receptors (think* PHAS=FAST)

• Tonic or Slow-Adapting Receptors (think *TONE it down (slow))

• APs very quickly cease (come to an end) EXAMPLE: pressure when seated on a chair

• Respond briefly before adapting to constant stimulus

• persistent or slow decay of the firing of the APs. EXAMPLE: receptors in joint & muscle that maintain posture

Touch, pressure, pain, temperature and senses of posture/movement

• Taste/Gustation

• Smell/Olfaction

• Taste buds which are in the lingual papillae (the bumps on the tongue that come in various sizes and shapes)

small bump on the tongue

50-100 specialized epithelial cells called taste cells

Each category of taste activates a specific taste cell

1. Odorants bind to membrane proteins, which are in the cilia. The cilia is attached to the dendrites of olfactory receptor neurons (bipolar neurons)

2. Axons of the receptor neurons synapse onto olfactory bulb of brain

3. Olfactory tract (grouping of axons) carries the afferent information to the brain

The unique pattern of the binding of odorants and receptor proteins

In the 2 olfactory bulbs

• Structures are in inner ear

• Sensation of: Head position, head movements (shaking head yes or no), and linear acceleration (xyz - straight line)

• 2 otolith organs, or maculae

• Saccule and utricle

• Mass of otoliths (calcium carbonate crystals) on top of a gelatinous substance

Sense linear acceleration with respect to gravity (EX. jumping, bending down)

• 3 semicircular canals (fluid-filled; endolymph)

• Each canal has a crista (sensory organ in the ampulla)

• Each crista has a gelatinous mass (cupula) on top which is pushed by endolymph movement

Sense angular acceleration of the head in 3 dimensions of space (X-Y-Z) to maintain balance

Detects changes in motion and position of the head

• The bending of hair cells in otolith organs and semicircular canals

They are tiny stones within the gelatinous substance. They cover the hair cells in the utricle and saccule which makes the gelatinous substance heavier.

Gravitational force causes the hair cells to bend, stimulating the sensory neurons

The position of the cupula in the semicircular canals makes the fluid movement to bend the cupula, stimulating the hair cells

Vibration of gas, liquid, or solid molecules

• Zones of atmospheric rarefaction (far apart) and compression

Movement of auditory structures, which is then transduced into action potentials

• number of cycles per second of the sound wave

• determine pitch (higher frequency, higher pitch)

• amplitude of sound wave

• determines loudness

Pinna and external auditory meatus (canal)

Rockage of the malleus, incus, stapes. (Stapes is attached to the oval window of the cochlea)

The oval window which causes ripples in the cochlear fluid.

Tympanic membrane ----> ossicles ---> oval window ----> movement of fluid in cochlea -----> vibrations in basilar membrane (tonotopic)/ shearing between basilar membrane & tectorial membrane, bending hair cells in organ of Corti to depolarize them -----> NT release ----->APs in sensory neurons

basilar membrane + hair cells + tectorial membrane

Where auditory transduction occurs in the cochlea

Ripples in the cochlear fluid causes the rasping of the tectorial membrane across the hair cells to bend them, causing depolarization. This causes NT to release and afferent signals to the CNS

• Causes large vibrations in apical (at the top) cochlea

• Low pitched sounds

(think *APEX like apical, low sounds at the top)

• Causes large vibrations in basal (at the bottom) cochlea

• High pitched sounds

(think * BOTTOM like basal, *high sounds at the bottom)

Arranged by frequency

The objects in the environment

Wave

The distance between 2 peaks, nanometers

Color

Appx. 400-700 nm in humans

Wavelengths constitute the stimuli transduced by the visual system.

• Fibrous Tunic

• Choroid

• Retina

• Outer connective tissue layer

• Contains the Sclera and Cornea

• white

• attachment of muscles that move eyeballs

• anterior region of sclera

• clear

• transmission of light

• beneath the sclera

• contains the Pupil, Iris, Uvea, and Ciliary Muscle

• anterior opening for light entry into the eye (think *peephole)

• pigmented muscle around pupil

• used for pupillary dilation and constriction

• dilation = let more light in, constriction = let less light in

blood vessels

• lens accommodation

• changes lens shape to focus image on retina

• posterior of eye

• extension of brain

• contains Photoreceptors

• rods and cones for phototransduction

• other neurons

• small region in retina w/ highest concentration of cones

• greatest visual activity (ability to resolve fine details) (think *fovea = fine)

• myelinated axons of ganglion cells in retina

• afferent signals from eye to brain

• exit point for optic nerve -----> leaves retina

• no photoreceptors = no transduction

• changing of lens shape to focus light on retina

• far vision: flattened lens

• near vision: rounded lens (accommodation is AUTOMATIC, lens shape accommodates to light)

In the retina and is based on the images focused there by the cornea and lens

Upside down and are only a small fraction of the object's actual size

The contraction state of the ciliary muscle determines the amount of tension that the zonular fibers exert on the lens

Lower tension on zonular fibers and more rounded lens (think *opposite; contraction = lower tension)

Higher tension on zonular fibers & more flattened lens (pulls ropes outward, causing lens to be flat and more tension on fibers

Distant and close vision (distant = relaxed muscle) (close = contracted muscle)

• Corrective Glasses

• Contact Lenses

Light penetrates past the ganglion, bipolar and other cells

When light produces chemical change in photopigment molecules

• Most sensitive photoreceptors

• Black and white vision

• Vision in dim light

• Color vision (red, green, & blue sensitivity)

• High resolution vision (fine detail, fovea) (think * color = cones)

• S (blue) cone

• M (green) cone

• L (red) cone

• Has photopigment that absorbs light in a specific range of wavelengths (in DIM light, ONLY RODS RESPOND)

In the visual cortex of the brain