Sensory and Motor Systems

Chemical Sensation

oldest and most common sensory system

detects chemicals in near vicinity

Chemoreceptors

what are our chemical senses are reliant on

bind to ligands to give the sensation

Gustatory Receptors

oral receptors for taste sensation

Olfactory Receptors

nasal receptors for smell sensation

Five Basic Kinds of Tastes/Taste Receptors

saltiness

sourness

sweetness

bitterness

umami

Taste Cells

gustatory chemoreceptors concentrated on the tongue as well as on the lining of the mouth, palate, pharynx, and epiglottis

distributed non-randomly on the tongue

Sensory Papillae

increase the surface area of the tongue to provide a greater working area for the interaction between food molecules and taste cells

contains many taste cells and is sensitive to all tastes but can be more or less sensitive to some individual taste types depending upon the particular set of taste receptors

Taste Pore

a small opening where food molecule enter the taste bud cavity

lined with 50-150 taste receptor cells

Three Forms of Transduction for Taste

pass directly through ion channels

bind to and block ion channels

bind to G protein coupled receptors and activate a second messenger to alter ion channel function

How Saltiness is Sensed

sensed at low concentrations via sodium selective channels

How Sourness is Sensed

senses high proton content

T1 & T2 Receptor Families

G protein coupled receptors found as dimers

different combinations of these subunits are responsible for sweet, bitter, and umami

How Sweetness is Sensed

from the expression of T1R2 + T1R3

have a specific transduction cascade

How Bitterness is Sensed

mediated by over 20 combinations of different T2R subunits

specific transduction cascade

How Umami is Sensed

express the subunits T1R1 + T1R3which detect specific forms of amino acids

specific signaling cascade

Central Taste Pathway

1. taste receptor cells

2. taste bud gustatory axons

3. gustatory nucleus of brain stem

4. ventral posterior media nucleus of thalamus

5. primary gustatory cortex which provides out conscious perception of taste

6. insular cortex which influences emotion and perception

Ageusia

loss of taste perception

can be caused by localized lesions on gustatory nucleus or VPM thalamus

Cortical Association Areas

combines sensory inputs from gustatory and olfactory senses, providing a multi-modal perception of food stimulus

Pheromones

inter-individual chemical signals

mode of communication for reproductive behavior, territorial boundaries, identification of individuals, and signaling aggression or submission

Anosmia

the inability to smell

Olfactory Coding

from the number, rate, and timing of olfactory neuron action potentials

Vomeronasal Organ & Accessory Olfactory Bulb

acts in parallel with the olfactory system

expresses fewer odorant receptors and receptor types but seems especially capable of odorant detection for use in social interactions, including the detection of pheromones

especially pronounced in rodents

Light

the portion of the electromagnetic spectrum that we can visualize

exhibits characteristics of particles and waves

Optical Component of Visual System

non-neural

most of the physical structures of the eye

designed to gather and shape the light that we evaluate

Neural Component of Visual System

begin with the retina in the back of the eye

designed to extract information from the light we sense

light information travels from retina via optic nerve to the lateral geniculate nucleus of thalamus before continuing to visual cortex

Wavelength

distance between successive peaks of a wave

Frequency

number of cycles per unit time

inversely related to wavelength

Amplitude

height of the wave

reflective of its power

Reflection

bouncing of light rays off of a surface

Absorption

transfer of light energy to a particle or surface

Refraction

bending of light rays from one medium to another

Optics

the study of light rays and their interactions with matter

Cornea

glassy, transparent external surface of the eye

provides the first refraction of light as it enters the eye

Sclera

white, fibrous outer layer of the eye

Conjunctiva

thin epithelium over cornea and sclera

Iris

colored muscular ring that regulate pupil diameter

Pupil

opening in the iris through which light passes to reach the rear chamber of the eye

Extraocular Muscles

three pairs of muscles that control eye position within its bony orbit (socket)

Optic Nerve

bundle of axons that carries visual information from the eye to the brain

Optic Disk

where the blood vessels of the retina originate from and axons of retina gather to form the optic nerve

lacks photoreceptors and is the cause of our blind spot

Macula

region of densely packed photoreceptors at the center of the retina

lacks large blood vessels

Fovea

within the macula

the position of center gaze (location at which incoming light is focused when we employ head-straight, level gaze)

contains the highest density of photoreceptors on the retina

retinal cells overlaying the photoreceptors are thinned here to provide greatest sensitivity to light stimuli

contains nearly all cone photoreceptors and no rods

Aqueous Humor

fluid in front chamber of the eye that nourishes the cornea

Vitreous Humor

jelly-like substance in posterior chamber that nourishes the retina

Lens

changes shape to adjust focus of incoming light onto the retina

divides the eye into anterior and posterior

adjusted via ciliary muscles

suspended by zonule fiber ligaments

Focal Distance

the distance over which refracted light rays converge

Accommodation

a change in the shape of the lens (by adjustment of ciliary muscles) to provide extra refraction power

Pupillary Light Reflex

adjustments to the diameter of the pupil to regulate the total amount of light that is permitted to reach the retina

achieved via connections between the retina and brain stem neurons that control muscles around the pupil

consensual (stimulus to one will affect the other)

Visual Field

the amount of visual space that is imaged onto the retina when the eye is fixated straight ahead

Visual Acuity

the ability to distinguish two nearby points

measure of resolving power

determined by the density of photoreceptors being stimulated and the clarity of focus achieved onto them

Resolving Power

the ability to distinguish separate objects that are near to each other

Visual Angle

the angular distance over which an object is images upon the retina

determined by object size and distance

Bipolar Cells

receive direct input from photoreceptors and exhibit light-sensitive activity

interconnected via non-light-sensitive horizontal and amacrine cells which modulate their activity and not connected to photoreceptors in a 1-to-1 fashion

Ganglion Cells

receive input from bipolar cells and provide output axons that form the optic nerve to the brain

Rod Photoreceptors

95% of our photoreceptors

long, cylindrical outer segments that contains abundant rhodopsin photopigment

1000x more light sensitive

peak density is highest just outside fovea and decreases towards edges of retina

Cone Photoreceptors

5% of our photoreceptors

shorter, tapering outer segment with relatively littler photopigments

each one contains only 1 of 3 different photopigments which are each most sensitive to different wavelengths of light

found in fovea

Phototransduction

the representation of light energy

occurs similarly to metabotropic synaptic transmission (photon of light interacts with photopigment to initiate signaling)

Photobleaching

rhodopsin changes from blue to yellow when stimulated

must be converted back before it can be stimulated again

Dark Adaptation

rapid pupil dilation

recycling of unbleached rhodopsin and adjustment of rod photoreceptor-to-ganglion cell synaptic weighting (much slower)

adjustment of calcium concentration in ICF which influences second messengers in ICF and sodium channel gating

dramatically increases ganglion cell output under low light conditions

Light Adaptation

switches our vision to nearly all-cone output during photopic conditions

adjustments of retinal synaptic weighing to reduce ganglion cell reliance upon rod photoreceptor input

Direct Pathway of Retinal Signaling

photoreceptor to bipolar cell to ganglion cell

Indirect Pathway of Retinal Signaling

through horizontal and amacrine cells

allows individuals photoreceptor and bipolar cell activity to influence neighboring cells

Receptive Field

the area of the field of vision in which the cell has responsivity

concept can be applied to many other kinds of sensory receptors

ON Bipolar Cells

respond to glutamate by hyperpolarizing

depolarize when glutamate is low (in light)

OFF Bipolar Cell

respond to glutamate by depolarizing

depolarize when glutamate is high (in dark)

Edge Detection

the identification of differences in light illumination

M-Type Ganglion Cells

large cell and rare (5% of ganglion cells)

have large receptive fields, good sensitivity to low-contrast stimuli, transient AP responses to stimuli

P-Type Ganglion Cells

much smaller cell and much more common (90%)

exhibit sustained AP responses to stimuli

NonM-NonP-Type Ganglion Cells

uncommon (5%)

intermediate characteristics that are not well characterized

Parallel Processing

the simultaneous but distinct processing of stimulus information via separate channels

Retinofugal

from the retina

Optic Chiasm

where the axons of the left and right optic nerves meet

Hemifield

represents that visual imagery in half of our overall visual field

Zone of Binocular Vision

comprises the medial portion of each hemifield

Lateral Geniculate Nucleus (LGN)

found in the thalamus

where most optic tract axons progress to

information from here is sent to the primary visual cortex

also receives inputs from brainstem and other thalamic neurons that carry information about alertness and arousal

Pretectum

some optic tract axons project to here for control of pupil diameter

Suprachiasmatic Nucleus (SCN)

found in the hypothalamus

where some optic tract axons project to provide lighting cues for the regulation of circadian rhythms

Superior Colliculus

where some optic tract axons project to in order to contribute to the movement of the eyes and head as part of control of gaze direction

Optic Tectum

word for the superior colliculus in non-mammal vertebrates

receives the majority of optic tract information

Magnocellular LGN Neurons

large, center-surround receptive fields

insensitive to wavelength

respond to stimuli with a transient burst of AP

like retina M-type cells

Parvocellular LGN Cells

small, center-surround receptive fields

may exhibit color opponency

sustained response to stimuli

like retina P-type cells

Koniocellular LGN Cells

center-surround receptive fields

may exhibit either light/dark or color opponency

Primary Visual Cortex

in the occipital lobe

the first area of the cortex that receives visual information via input from the LGN (majority of its output goes here)

Retinotopy

the maintenance of spatial relationships between connected regions

from retinal ganglionic neurons that are near to each other projecting to neighboring areas in LGN which project to neighboring areas in primary visual cortex

creates and maintains a spatial map of the visual field

Ocular Dominance Columns

separate/alternating bands or columns that organize spatially distinct inputs from the left and right eyes

the majority of neurons within a column received input from only one eye

Orientation Selectivity for Neuronal Response to a Visual Stimulus

the degree of response is highly dependent upon the particular angle at which the stimulus was imaged

Cortical Modules

small but complete sections of the primary visual cortex able to perform all of its major functions

proposed by Hubel and Weisel

Dorsal Stream

provides analysis of visual motion and the visual control of action

sensitivities are proposed to support navigation, directing eye movements, and motion perception

Ventral Stream

guides perception of the visual world and the recognition of objects

has areas specialized for shape and color perception as well as visual perception, visual memory, and face stimuli

Audition

sense of hearing

ability to detect, localize, and evaluate sound

can interpret its physical characteristics (intensity, frequency content, temporal patterning)

can stimulate voluntary and involuntary responses

Vestibular System

sense of balance

used to maintain our upright positioning and as part of the control of head and body location and movements

includes a self-leveling aspect as well as information needed for planned movements

processed autonomically

Hair Cells

sensory receptors in the inner ear that are involved in audition and the vestibular system

when physically shifted, perform mechanotransduction

impacted by sound pressure waves for hearing and gravitational pull and inertia for balance

project dozens of stereocilia into endolymph

Mechanotransduction

the generation of a receptor potential in response to physical alteration in receptor conformation

Cycle

the portion of a wave between successive areas of compressed air

Pitch

frequency of sound

high for high, low or low

Ultrasound

sounds above the frequency we can hear (>20,000 Hz)

Infrasound

sounds below the frequency we can hear (<20 Hz)

Outer Ear

consists of the external pinna and the auditory meatus/ear canal

Pinna

found in the outer ear and fixed in position in humans

shaped to direct sound into the ear canal

especially effective at directing sounds from in front of us

Tympanic Membrane/Ear Drum

separates the outer and middle regions of the ear and is part of the middle ear

where the ear canal conducts sound waves towards

vibrates when sound waves hit