Vander's Chapter 7: Sensory Physiology

sensory receptor

a cell/portion of a cell that contains structures or chemical molecules sensitive to changes in an energy form in the outside world or internal environment; in response to activation by this energy, it initiates action potentials in that cell or in an adjacent one

sensory system

part of nervous system that receives, conducts, or processes information that leads to perception of a stimulus

sensory information

information that originates in stimulated sensory receptors

sensation

the mental perception of a stimulus

perception

understanding of objects and events of external world that we acquire from neural processing of sensory information

stimulus

detectable change in internal or external environment

sensory transduction

neural process of changing a sensory stimulus into a change in neuronal function

adequate stimulus

the modality of stimulus to which a particular sensory receptor is most sensitive

receptor potential

graded potential that arises in afferent neuron ending, or specialized cell intimately associated with it, in response to stimulation

mechanoreceptors

sensory neuron specialized to mechanical stimuli such as touch (skin) stretch (muscle), sound, acceleration, or swelling depending on the type; hearing, balance, and equilibrium

thermoreceptor

sensory receptor for temperature and temperature changes, particularly in low (cold receptor) or high (warm receptor) range

Photoreceptors

sensory cell specialized to respond to photons of light; contains pigments that make it sensitive to different wavelengths; vision

Chemoreceptors

afferent neuron ending, or cell associated with it, that is sensitive to certain chemicals dissolved in solution; smell and taste

Nociceptors

sensory receptor whose stimulation causes pain -free nerve endings

- stimuli results in pain

-polymodal: respond to a variety of stimuli

Adaptation

decrease action potential frequency in a neuron over time in presence of a constant stimulus; decreases perception of stimulus

tonic receptors

sensory receptor that fires repeatedly as long as stimulus is ongoing; gives rise to painful stimuli (nociceptors)

phasic adapting receptors

sensory receptor that fires for a brief period at the onset and/or offset of a stimulus; when the stimulus is changing; gives rise to touch, movement, vibration, pressure, olfaction, temperature

coding

process by which neural signals from sensory receptors are converted into action potentials in the CNS; begins at receptive neurons in PNS

sensory unit

afferent neuron plus receptors it innervates

receptive field

area of body that, if stimulated, results in activity in that neuron

modality

type of sensory stimulus

labeled lines

principle describing the idea that a unique anatomical pathway of neurons connects a given sensory receptor directly to the CNS neurons responsible for processing that modality and location on the body

acuity

sharpness or keenness of perception; depends on the amount of convergence of neuronal input in the specific ascending pathways, the size of the receptive field covered by one sensory unit and the amount of overlap in nearby receptive fields

sensory coding

depends on the stimulus type (determined by the receptor-type activated, specific pathway activated, and area of the brain stimulated); stimulus intensity (firing rate of sensory units, number of units activated); the size of receptive field and degree of overlap

lateral inhibition

method of refining sensory information in afferent neurons and ascending pathways whereby fibers inhibit each other, the most active fibers causing the greatest inhibition of adjactent fibers

-receptors that are at the edge of a stimulus are strongly inhibited

-enhances contrast between center and periphery

-enables localization of a stimulus for some sensory systems

sensory pathways

a group of neuron chains, each chain consisting of three or more neurons connected end to end by synpases; carries action potentials to those parts of the brain involved in conscious recognition of sensory information

ascending pathways

neural pathway that goes to the brain; also called sensory pathway

somatic receptors/somatosensations

neural receptor in the framework or outer wall of the body that responds to mechanical stimulation of skin, skeletal muscle, tendons, rotation or bending of joints, temperature changes, or painful stimuli

somatosensory cortex

strip of cerebral cortex in parietal lobe in which nerve fibers transmitting somatic sensory information synapse

central sulcus

a deep infolding on each half of the brain that separates the parietal and central lobes

visual cortex

region of cerebral cortex in occipital lobe that receives nerve fibers from visual pathways

auditory cortex

region of cerebral cortex in temporal lobe that receives nerve fibers from hearing pathways

olfactory cortex

region on the inferior and medial surface of the frontal lobe of the cerebral cortex where information about the sense of smell is processed

cortical association areas

region of cerebral cortex that receives input from various sensory types, memory stores, and so on, and performs further perceptual processing

somatic sensation

feelings/perceptions coming from muscle, skin, and bones

kinesthesia

sense of movement derived from movement of a joint

transient receptor potential (TRP) proteins

family of ion channel proteins involved in sensing temperature; respond to changes in temperature by changing conformation within a specific temperature range which opens ion channels; some non-endogenous substances like caspascin, ethanol, and menthol trip the receptor proteins into detecting physical heat/coolness

referred pain

occurs when the sensation of pain is experienced at a site other than the injured or diseased tissue because both visceral and somatic afferent neurons often converge on the same neurons in the spinal cord

hyperalgesia

after the first transduction of a pain signal, a series of components can change within the pain pathway, in the nociceptors and ion channels themselves, when an increased sensitivity to painful stimuli occurs it is known as _________.

analgesia

the selective suppression of pain without effects on consciousness/other sensations

anterolateral pathway

ascending neural pathway running in the anterolateral column of the spinal cord white matter; conveys information about pain and temperature

dorsal column pathway

ascending pathway for somatosensory information; runs through dorsal area of spinal white matter

sclera

the tough, outermost tissue layer of the eyeball

cornea

transparent structure covering the front of the eye; forms part of the eye's optical system and helps focus an object's image on retina

choroid

pigmented layer of the eye that lies next to retina; in the anterior portion, it is specialized into the iris, the ciliary muscles and zonular fibers

iris

ringlike structure surrounding and determining the diameter of the pupil of the eye

ciliary muscle

involved in the movement and shape of the lens during accommodation; contraction of this muscle; stimulated by parasympathetic nerves

zonular fibers

connecting the ciliary muscles with the lens of the eye

retina

thin layer neural tissue lining the inner, posterior surface of the eyeball, contains photoreceptors and neurons for vision

3 layers:

-outer: photoreceptors

-middle: bipolar cells

-inner: ganglion cells

macula lutea

a region at the center of the retina that is relatively free of blood vessels and that is specialized for highly acute vision; fovea centralis is located here

fovea centralis

area near center of retina where cones are most concentrated and have fewest light-obstructing retinal neurons because they are displaced to the sides; gives rise to most acute vision

optic disc

region of the retina where neurons to the brain exit the eye; lack of photoreceptors here results in a "blind spot"

optic nerve

bundle of neurons connecting the eye to the optic chiasm

aqueous humor

fluid filling the anterior chamber of the eye between the iris and cornea

vitreous humor

jellylike fluid filling the posterior chamber of the eye between the lens and retina

refraction

bending of light rays when passing between compartments of different density as from air into the cornea of the eye

accomodation

adjustment of eye for viewing various distances by changing shape of the lens

outer segment

light sensitive portion of the photoreceptor containing photopigments; made from discs

discs

a layer of membranes in outer segment of photoreceptor; contains photopigments

inner segment

portion of photoreceptor that contains cell organelles; synapses with bipolar cells of the retina

rods

one of two receptor types for photic energy; contains photopigment rhodopsin

-very sensitive

- night and peripheral vision

-only perceive grey tones

cones

one of two retinal receptor types for photic energy; gives rise to color vision (green, red and blue kinds)

-less sensitive, need bright light for activation

-allows us to see colors

Eye Anatomy

-outermost layer "sclera and cornea"

-middle layer "choroid, ciliary body, and iris"

-inner layer "retina, macula lutea, fovea centralis, optic disc"

Pathway of light

1. air

2. cornea

3. aqueous humor

4. lens

5. vitreous humor

6. photoreceptors in retina

Depth Perception

-binocular (2 eyed) visual field

- brain constructs 3-d image

cGMP-phosphodiesterase

enzyme activated by transducin in the presence of light; degrades cGMP

bipolar cells

type of neuron that has one input branch and one output branch

ganglion cells

retinal neuron that is postsynaptic to bipolar cells; axons of ______ form optic nerves

ganglion cell receptive fields

are round in shape; each has an inner core (center) that responds differently than the area that surrounds it; there can be ON center/OFF surround or OFF center/ON surround ganglion cells because the responses are either depolarization (ON) or hyperpolarization (OFF) in the two areas; light striking both regions results in intermediate activation; type of lateral inhibition

monocular vision

visual perception by a single eye; outer regions of vision are produced by one eye

binocular vision

visual perception of overlapping fields from the two eyes

external auditory canal

outer canal of the ear between the pinna and the tympanic membrane

tympanic membrane

membrane stretched across end of ear canal (ear drum); divides outer and middle ear; transfers sounds waves to middle ear

middle ear

air-filled space in temporal bone; contains three ear bones that conduct sound waves from tympanic membrane to cochlea

eustachian tube

duct connecting middle ear with the nasopharynx; where the middle ear is exposed to atmospheric pressure; when it opens it equilibrates the pressure in the middle ear

inner ear

cochlea; contains organ of Corti

cochlea

inner ear; fluid-filled spiral-shaped compartment that contains cochlear duct

malleus

one of the three bones in the inner ear that transmit movements of the tympanic membrane to the inner ear; connected to tympanic membrane

incus

one of the three bones in the inner ear that transmit movements of the tympanic membrane to the inner ear; middle bone

stapes

one of the three bones in the inner ear that transmit movements of the tympanic membrane to the inner ear; bone connected to the oval window

oval window

membrane-covered opening between middle ear cavity and scala vestibuli of inner ear; sound waves at tympanic membrane are transferred here

tensor tympani muscle

skeletal muscle of middle ear that attaches to the malleus and protects the auditory apparatus from loud sounds by dampening the movement of the tympanum

stapedius

skeletal muscle that attaches to the stapes and protects the auditory apparatus by dampening the movement of the ear ossicles during persistent loud sounds

cochlear duct

fluid-filled membranous tube that extends length of inner ear, dividing it into compartments; contains organ of Corti; filled with endolymph

endolymph

extracellular fluid found in the cochlea and vestibular apparatus with higher potassium content than intracellular fluid; fluid within the membranous labyrinth

perilymph

fluid that fills the cochlear duct of the inner ear; similar in composition to cerebrospinal fluid; between membranous and bony labyrinth

scala vestibuli

fluid-filled inner ear compartment that receives sound waves from the oval window and transmits them to basilar membrane and cochlear duct

scala tympani

fluid-filled inner ear compartment that receives sound waves from basilar membrane and transmits them to round window

round window

membrane-covered opening of the cochlea that responds to fluid movement in the scala tympani

helicotrema

outer point in the cochlea where the scala vestibuli and scala tympani meet and are continuous

basilar membrane

membrane that separates cochlear duct and scala tympani in inner ear; supports organ of Corti; pressure differences across the cochlear duct make it vibrate; high frequencies deflect it closer to the middle ear; lower frequencies deflect it closer to the helicotrema

organ of Corti

structure in inner ear capable of transducing sound wave energy into action potentials

hair cells

mechanoreceptor cell in organ of Corti and vestibular apparatus characterized by stereocilia on cell surface

stereocilia

nonmotile cilia containing actin filaments

inner hair cells

cells of the cochlea with stereocilia that transduce pressure waves into electrical signals

outer hair cells

cells of the cochlea with stereocilia that sharpen frequency tuning by modulating the movement of the tectorial membrane

tectorial membrane

structure in organ of Corti in contact with receptor hair cells

vestibulocochlear nerve

eighth cranial nerve; transmits sensory information about sound and motion from the inner ear to the brain

vestibular apparatus

sense organ in temporal bone of skull; consists of three semicircular canals, a utricle, and a saccule

vestibule*

-egg shaped cavity

-filled with perilymph

-2 sacs inside

-both sacs contain equilibrium receptors