MCAT Behavioral Science Chapter 2

sensation (transduction)

Taking physical, electromagnetic, auditory, and other information from our internal and external environment and converting this info into electrical signals in the nervous system

Perception

processing info from sensors within CNS to make sense of significance of info

Sensory receptors

neurons that respond to stimuli by triggering electrical signals that carry info to CNS

distal stimuli

physical objects outside the body; in the DISTance

Proximal stimuli

stimuli that directly interacts with sensory receptors; in close PROXIMity

Ganglia

collections of neuron cell bodies found outside CNS that conduct transduction and send electrochemical energy along neural pathways to various projection areas in the brain for further analysis

Photoreceptors

respond to EM waves in visible spectrum (sight)

Mechanoreceptors

respond to pressure or movement (hearing, vibration, movement, rotational and linear acceleration)

Nociceptors

respond to painful or noxious stimulation (somatosensation)

Thermoreceptors

respond to changes in temperature (thermosensation)

Osmoreceptors

respond to osmolarity of blood (water homeostasis)

Olfactory receptors

respond to volatile compounds (smell)

Taste receptors

respond to dissolved compounds (taste)

threshold

minimum amount of stimulus that renders a difference in perception (example of psychological element of perception)

absolute threshold

minimum of stimulus energy that is needed to activate a sensory system; point at which stimulus is transduced, or converted to action potential

threshold of conscious perception

level of intensity a stimulus must possess to be consciously perceived by the brain

Subliminal perception

stimulus above absolute threshold but below threshold of conscious perception

difference threshold (just-noticeable difference)

minimum change in magnitude required for an observer to perceive that two different stimuli are, in fact, different

(psychophysical) discrimination testing

A method used to assess the difference threshold, where participants are asked to identify whether two stimuli are the same or different

Weber’s Law

difference thresholds are proportional and must be computed as percentages

signal detection theory

studies how internal (psychological) and external (environmental) factors influence thresholds of sensation and perception

adaptation

ability to detect a stimulus changes over time through this phenomenon

sclera

white of the eye; thick structural layer that protects most of the exposed portion of the eye, excluding the cornea

choroidal vessels

complex intermingling of blood vessels between the sclera and retina that supplies the eye with nutrients

retinal vessels

supplies eyes with nutrients

retina

innermost layer of eye; contains actual photoreceptors that transduce light into electrical information for brain to process

cornea

clear, domelike window in the front of the eye, which gathers and focuses the incoming light

anterior chamber

a chamber in the front of the eye that lies in front of the iris

posterior chamber

a chamber in the front of the eye that lies in between the iris and lens

iris

colored part of the eye

dilator pupillae

opens the pupil under sympathetic stimulation

constrictor pupillae

constricts the pupil under parasympathetic stimulation

choroid

vascular layer of connective tissue that surrounds and provides nourishment to the retina; continuous with iris

ciliary body

produces aqueous humor inside posterior chamber; continuous with iris

canal of Schlemm

drains aqueous humor produced in posterior chamber

lens

lies right behind iris and helps to control refraction of incoming light

ciliary muscle

component of ciliary body; contraction of this muscle is under parasympathetic control

suspensory ligaments

as ciliary muscle contracts, it pulls on these ligaments and changes the shape of the lens to focus on an image as distance varies

accommodation

a phenomenon where the shape of the lens changes to focus on an image as distance varies

vitreous humor

transparent gel that lies behind the lens and supports the retina

retina

located in the back of the eye and is like a screen consisting of neural elements and blood vessels; converts incoming photos of light to electrical signals and is considered part of the CNS

duplexity or duplicity theory of vision

retina has two kinds of photoreceptors: those specialized for light-and-dark detection and those specialized for color detection

cones

used for color vision and to sense fine details; most effective in bright light and come in three forms, named for the wavelengths of light they best absorb (S for blue, M for green, L for red)

rods

more functional in reduced illumination b/c highly sensitive to photons; however, only allows sensation of light and dark and don’t allow perception of fine details

rhodopsin

the single pigment type found in all rods; activated by all wavelengths of visible light, which is why rods are more functional in reduced illumination

macula

central section of the retina; has high concentration of cones

fovea

center-most region of retina; only contains cones; as one moves further away from fovea, concentration of cones decreases and rods increase, meaning visual acuity and sensitivity to daylight is best at fovea

blind spot

location called optic disk where optic nerve leaves the eye

bipolar cells

cells that synapse directly with rods and cones and highlight gradients between adjacent rods and cones; located in front of rods and cones

ganglion cells in the eye

cells that synapse directly with bipolar cells; located in front of rods and cones

optic nerve

axons of ganglion cells in the eye group together to form this

amacrine and horizontal cells

receive input from multiple retinal cells in same area before passing information to ganglion cells; can thus accentuate slight differences between visual information in each bipolar cell, making them especially important in edge detection

visual pathways

anatomical connections between the eyes and brain and flow of visual information along these connections

temporal retinal fibers

fibers on the outside edges of your eyes, closer to your TEMPle; ex) on the left eye, temporal fibers are on the left, and detect light from the right side of your field of vision and pass the info to left hemisphere

nasal retinal fibers

fibers on the inside edges of your eyes, closer to your NOSE; ex) on the left eye, nasal fibers are on the right, and detect light from the left side of your field of vision and pass the info to right hemisphere

temporal and nasal visual field

same concept as the fibers but they stimulate OPPOSITE fibers; objects in nasal visual field stimulate temporal fibers and vice versa

optic chiasm

as retinal fibers from each eye travel through optic nerves to the brain, this is the point where nasal fibers from left and right eyes cross paths

optic tracts

what nasal and temporal pathways are called after optic chiasm

lateral geniculate nucleus (LGN)

some nerve fibers from optic chiasm pass to this area of the thalamus where they synapse with nerves than then pass through radiations in the temporal and parietal lobes to visual cortex in occipital lobe

parallel processing

brain’s ability to analyze information regarding color, form, motion, and depth simultaneously using independent pathways in the brain

form

refers to shape of an object and ability to discriminate object of interest from background by detecting its boundaries

parvocellular cells

located in the LGN; have very high color spatial resolution and low temporal resolution, gives ability to detect very fine detail when thoroughly examining a still or slow-moving object

magnocellular cells

well-suited for detecting Motion b/c high temporal resolution; predominantly receive inputs from peripheral vision to allow brain to rapidly detect objects approaching from the sides

binocular neurons

responsible for comparing inputs to each hemisphere and detecting differences to build 3D shape of environment and judge distance of objects within it to build depth perception

feature detectors

each cell detects very particular, individual feature of object in the visual field; act in parallel when recognizing an object and stores response to object for future retrieval

vestibular sense

ability to detect rotational and linear acceleration to inform our sense of balance and spatially orientation

pinna or auricle

cartilaginous outside part of the ear; helps channel sound waves into inner part of ear

external auditory canal

directs sound waves further into ear

tympanic membrane (eardrum)

membrane vibrates in phase with incoming sound waves — vibrates faster with higher frequency sound waves and vibrates with greater amplitude for more intense sound waves; divides outer ear from middle ear

ossicles

smallest bones of the body, located in the middle ear; help transmit and amplify vibrations from tympanic membrane to the inner ear

ossicle functions

malleus (hammer) affixed to tympanic membrane, acts on incus (anvil), which acts on stapes (stirrup); baseplate of stapes rests on the oval window of the cochlea

cochlea

entrance to inner ear; spiral-shaped organ that contains receptors for hearing

Eustachian tube

cavity that connects the middle ear to the nasal cavity; helps to equalize pressure between middle ear and environment

bony labyrinth

hollow region of the temporal bone containing the cochlea, vestibule, and semicircular canals

membranous labyrinth

continuous collection of tubes and chambers inside bony labyrinth; contains receptors for sense of equilibrium and hearing

endolymph

potassium-rich fluid that fills membranous labyrinth

perilymph

suspends membranous labyrinth within bony labyrinth; cushions inner ear structures and transmits vibrations from outside world

scalae

three divisions of the cochlea that run its entire length

organ of Corti

actual hearing apparatus; lies within the middle scala and is composed of thousands of hair cells, all bathed in endolympth

basilar membrane

thin, flexible membrane that supports organ of Corti

tectorial membrane

lies on top of the organ of Corti and is a relatively immobile membrane

inner and outer scalae

filled with perilymph and surround hearing apparatus; filed with perilymph and are continuous with oval and round windows of cochlea

round window

membrane-covered hole in the cochlea; allows perilymph to actually move within the cochlea, as fluids are incompressible

auditory (vestibulocochlear) nerve

carries electrical signals transduced by organ of Corti to the CNS

vestibule

portion of bony labyrinth that contains the utricle and saccule

utricle and saccule

structures sensitive to linear acceleration, so are used as part of the balancing apparatus; contain modified hair cells covered with otoliths

otoliths

resist motion caused by acceleration of the body; hair cells covered by otoliths bend as a result, sending a signal to the brain

semi-circular canals

sensitive to rotational acceleration; all are arranged perpendicularly together and each ends in a swelling

ampulla

swelling that ends the semi-circular canals; hair cells located here — when head rotates, endolymph in semicircular canals resists this motion, bending hair cells, and sending signals to brain

auditory pathways

most sound info passes through vestibulocochlear nerve to brainstem, where it ascends to thalamus

medial geniculate nucleus (MGN)

area of thalamus that processes sound info

auditory cortex

from MGN, nerve fibers project to this area of the temporal lobe for sound processing

superior olive

also helps process sound info by localizing the sound

inferior colliculus

involved in startle reflex and helps keep eyes fixed on a point when head is turning (vestibulo-ocular reflex)

stereocilia

the structures that cover the top surface of hair cells and give them their name; as vibrations reach basilar membrane underneath the organ of COrti, stereocilia begin to sway back and forth within endolympth, causing opening of ion channels

place theory

accepted theory on sound perception; location of hair cell on basilar membrane determines perception of pitch when that hair cell is vibrated (highest-frequency pitches cause vibrations of basilar membrane close to oval window)

olfactory chemoreceptors

located in olfactory epithelium in upper part of nasal cavity; chemical stimuli must bind to respective chemoreceptor to evoke signal; smell is only sense that goes straight to higher-order brain regions instead of passing through thalamus first

pheromones

chemicals secreted by one animal; effects on humans debated but play enormous role in other animals’ behaviors

olfactory pathway

molecules inhaled into nasal passages and contact olfactory nerves in olfactory epithelium; receptor cells are activated and send signals to olfactory bulb, which are then relayed via olfactory tract to brain

chemoreceptors in tongue

sensitive to dissolved compounds