Ch. 10 - Sensory Physiology

What are sensory receptors?

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

What do sensory receptors do?

• Transduce different energy forms (pressure, temperature, chemical, light) into graded potentials that initiate action potentials
• Afferent sensory input to CNS

What are the 5 classes of receptors?

• Mechanoreceptors
• Thermoreceptors
• Photoreceptors
• Chemoreceptors
• Nociceptors
  ( Mary, Thought, Parry, Could, Notice)

What do mechanoreceptors do?

Respond to MECHANICAL stimuli, like touch or pressure

What do thermorecptors do?

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

What do photoreceptors do?

Respond to light (think *good photos involves light)

Chemoreceptors

Respond to binding of particular CHEMICALS

Nociceptors

Respond to painful stimuli

What is receptor potential?

• Graded potential in sensory receptor in response to environmental stimulus

What does transduction involve?

Opening of ion channels

If at initial segment of axon reaches threshold, what happens?

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

What is adaptation?

Decrease in receptor sensitivity (responsiveness) during maintained stimulation

What does adaptation lead to?

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

Name the two types of adapting receptors:

• Phasic or Fast-Adapting Receptors (think* PHAS=FAST)
• Tonic or Slow-Adapting Receptors (think *TONE it down (slow))

What is the action of PHASIC receptors?

• APs very quickly cease (come to an end) EXAMPLE: pressure when seated on a chair
• Respond briefly before adapting to constant stimulus

What is the action of TONIC receptors?

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

What does somatic sensation include?

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

Name the two types of chemosenors:

• Taste/Gustation
• Smell/Olfaction

What does Gustation include?

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

What is a papilla?

small bump on the tongue

What are taste buds comprised of?

50-100 specialized epithelial cells called taste cells

Describe the connection between taste cells and taste categories

Each category of taste activates a specific taste cell

What happens during olfaction?

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

What interprets a specific odor?

The unique pattern of the binding of odorants and receptor proteins

Where do olfactory receptor cells synapse?

In the 2 olfactory bulbs

What is included within the VESTIBULAR System?

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

What do the otolith organs in the Vestibular Sensors include?

• 2 otolith organs, or maculae
• Saccule and utricle
• Mass of otoliths (calcium carbonate crystals) on top of a gelatinous substance

What do the otolith organs do?

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

What do the semicircular canals in the Vestibular Sensors include?

• 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

What do the canals do?

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

What does the Vestibular System do?

Detects changes in motion and position of the head

What causes a result in afferent activity?

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

What are OTOLITHS and what do they do?

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

What happens when the head is tilted forward?

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

Describe the connection between the cupula, fluid and the hair cells

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

In the auditory system, what does sound results from?

Vibration of gas, liquid, or solid molecules

What are sound waves?

• Zones of atmospheric rarefaction (far apart) and compression

What do sound waves CAUSE when they reach the ear?

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

Frequency; what does it determine?

• number of cycles per second of the sound wave
• determine pitch
  (higher frequency, higher pitch)

Intensity; what does it determine?

• amplitude of sound wave
• determines loudness

What two things focus sound waves on the tympanic membrane (eardrum)?

Pinna and external auditory meatus (canal)

What does the focusing of sound waves cause?

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

Within the middle ear, where are the vibrations of the stapes transmitted?

The oval window which causes ripples in the cochlear fluid.

Name the order of Audition:

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

What is comprised in Organ of Corti?

basilar membrane + hair cells + tectorial membrane

What is the Organ of Corti?

Where auditory transduction occurs in the cochlea

What happens within the organ of corti?

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

What does low frequency cause?

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

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

What does high frequency cause?

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

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

What does tonotopic mean?

Arranged by frequency

Where does light reflect off of?

The objects in the environment

Light has (blank)-like properties

Wave

What is wavelength and how is it measured?

The distance between 2 peaks, nanometers

What does wavelength correspond to?

Color

What is the visible spectrum?

Appx. 400-700 nm in humans

What do wavelengths do to stimuli?

Wavelengths constitute the stimuli transduced by the visual system.

Name the three layers (tunics) of the eye

• Fibrous Tunic
• Choroid
• Retina

Describe the fibrous tunic

• Outer connective tissue layer
• Contains the Sclera and Cornea

Sclera

• white
• attachment of muscles that move eyeballs

Cornea

• anterior region of sclera
• clear
• transmission of light

Describe the Choroid

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

Pupil

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

Iris

• pigmented muscle around pupil
• used for pupillary dilation and constriction
• dilation = let more light in, constriction = let less light in

Uvea

blood vessels

Ciliary Muscle

• lens accommodation
• changes lens shape to focus image on retina

Describe the Retina

• posterior of eye
• extension of brain
• contains Photoreceptors

Photoreceptors

• rods and cones for phototransduction
• other neurons

Fovea

• small region in retina w/ highest concentration of cones
• greatest visual activity (ability to resolve fine details)
  (think *fovea = fine)

Optic Nerve

• myelinated axons of ganglion cells in retina
• afferent signals from eye to brain

Blind Spot

• exit point for optic nerve -----> leaves retina
• no photoreceptors = no transduction

Accommodation

• 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)

Where does visual transduction occur and what is it based on?

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

How are images on the retina perceived?

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

Describe the connection between ciliary muscles and lens

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

What do contracted ciliary muscles determine?

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

What do relaxed ciliary muscles determine?

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

What does the contraction state of the ciliary muscle change?

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

What two items alter the location of image focus to correct for problems of eyeball length?

• Corrective Glasses
• Contact Lenses

What occurs before transduction by the rods and cones?

Light penetrates past the ganglion, bipolar and other cells

When are Photoreceptor Cells activated?

When light produces chemical change in photopigment molecules

Describe Rods

• Most sensitive photoreceptors
• Black and white vision
• Vision in dim light

Describe Cones

• Color vision (red, green, & blue sensitivity)
• High resolution vision (fine detail, fovea)
  (think * color = cones)

What are the three types of cones?

• S (blue) cone
• M (green) cone
• L (red) cone

What are the actions of the three cones?

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

Where are signals from the eyes processed?

In the visual cortex of the brain