behavioral neuroscience exam #2

anatomy of the eye

cornea, lens, retina, photoreceptors, fovea

how an image projects on a retina

1. light is reflected from objects to the observer

2. rays of light reflected from objects diverge in the world

3. the lens focuses the rays to project a sharp image of the world on the retina

supportive structures in the eye

choroid, sclera, vitreous humor, aqueous humor, optic disk

types of cells in the retina

photoreceptors, horizontal cells, bipolar cells, amacrine cells, and ganglion cells

cones

photoreceptor that is concentrated in the fovea and central retina, high acuity, color vision in daylight

rods

photoreceptor absent in the fovea, low acuity vision in dim light

receptive field

region within which sensory stimuli can induce a neuron to change its firing rate

bipolar cells

are responsible for detection of edges, bridge between receptors and ganglion cells

horizontal cells

support visual processing

amacrine cells

lateral-connection between bipolar and ganglion cells

photoreceptors

absorbs lights (rods and cones)

ganglion cells

gathers as a bundle to leave the optic nerve

cornea and lens function

bend arriving rays of light to form a focused image

fovea

holds tightly packed photoreceptors to provide the highest visual acuity

optic nerve

transmits visual information to the brain

color vision in the retina

three cones; blue, green, and red which can generate the appearance of any color

cues

unintentional sounds to alert potential signs of predators/prey

signals

intentional sounds to alert potential signs of a mate or important social information

sound

pressure waves moving through air or some other physical material

phototransduction

1. In the dark, Na+ channels open and depolarize the rod

2. when a photon of light hits rhodopsin, it causes a cascade of events that close the channels

3. In the dark, the channels open, releasing glutamate

photoreceptor receptive field

area of visual space where light/dark can change photoreceptor neuronstransmitter release

retinal ganglion cells

magnocellular cells, parvocellular cells, W cells, melanopsin-containing ganglion cells

from the eye to the primary visual cortex

1. left visual field light reaches the right portion of the retina (vice versa) — inverting the image

2. optic nerve axons from the nasal half of the retina cross at the optic chiasm — separating visual information by visual field

3. most optic tract axons terminate in the lateral geniculate nucleus, some terminate in the superior colliculus

4. LGN neurons project via the optic radiation to the primary visual cortex

simple cortical cell receptive fields

responds to a small spot of light in its receptive fields with excitatory or inhibitory responses

complex cortical cell receptive fields

respond to an appropriately oriented edge of light anywhere in their receptive field

retinotopic map

the orderly layout of the retina is preserved in the lateral geniculate and the primary visual cortex

dorsal pathway

concerned with stimulus position and movement (where)

ventral pathway

concerned with the perception of objects, faces, bodies, and scenes (what)

posterior parietal cortex damage

loss of input from sensory areas, inability to locate and attend to objects in space, inability to orient the body in the environment

blindsight

cortical blindness but individuals can react unconsciously to stimuli without seeing them

color agnosia

loss of ability to perceive colors or recognize a deficit in vision

movement agnosia

inability to perceive movement

amplitude

level and intensity of the sound, measured in decibels

frequency

pitch of a sound, measured in hertz

phase

affects how sound waves interact

external ear

auricle and external auditory meatus

middle ear

tympanic membrane, ear ossicles, eustachian tube

inner ear

semicircular canals, cochlea, round window, oval window, vestibular nerve, cochlear nerve

tympanic membrane

thin sheet of tissue that vibrates due to acoustic waves

ear ossicles

transmit tympanic membrane vibrations to oval window

periodic vibration

plucking a string under tension in the middle causes it to vibrate at a specific frequency to produce a periodic wave

aperiodic vibration

turbulent air flowing through a gap produces acoustic wave with a broad range of frequencies

transduction of inner hair cells

1. at rest, ion channels in the cilia are closed. Vesicles are docked at the ribbon synapse

2. When the cilia are displaced, tip links pull open the ion channels

3. the endolymph has high concentration of K+ and Ca2+ so those ions flow into the cilia when the ion channels open

4. the hair cell depolarizes opening voltage gated Ca2+ channels, Ca2+ influx causes vesicles to fuse and release neurotransmitter

conductive hearing loss

eardrum damage, otitis media, damage/defect in oscicles

sensorineural hearing loss

damage to hair cells, auditory nerve, auditory brain region

cochlear implants

1. external processor captures sound and converts it into digital signals

2. processor sends digital signals to internal implant

3. internal implant relays the signal to an electrode array inside the cochlea

4. Bypassing the damaged hair cells, the electrodes stimulate the cochlear nerve and the brain perceives the sound

azimuth

angle that is left and right of the horizontal plane; affects timing and level at each ear

elevation

angle that is up and down from the plane

interaural timing difference

sound reaching one side of the head sooner than the other

interaural level difference

sound from one side is louder than the other side

vestibule system

responsible for the sense of balance and for helping the brain track the body’s movement in space

anterior and posterior canals

sense angular movements (pitch, roll, yaw)

otolith organs

sense linear movements (up/down, front/back, left/right)

smell

chemosensory perception of inhaled air

olfaction

chemosensory system housed primarily in the nasal cavity

taste

chemosensory perception of the oral cavity

gustation

chemosensory system housed primarily in the oral cavity

flavor

the perception of oral chemosensation, which is produced when the brain integrates signals from the gustatory, olfactory, and somatosensory systems

adaptive value of gustation

only detects 5 different tastes, identify foods with high nutritive content, identify toxic or poisonous chemicals

adaptive value of olfaction

can detect almost any volatile organic molecule in small concentrations, navigation, nutrient finding, mate selection

chemesthesis

chemical stimulation of the somatosensory system; creates cooling or heating sensations

retronasal olfaction

volatile compounds from food in the mouth flushes through nasal cavity via the pharynx; jelly bean experiment

taste buds

clusters of sensory cells located on the tongue in the papillae

Type I taste receptor cell

salty; directly sense sodium, causes APs to release neurotransmitters

Type II taste receptor cell

sweet, bitter, umami; chemicals bind to metabotropic GPCRs activating g proteins, end result is release of neurotransmitters onto output nerves

Type III taste receptor cells

sour; directly sense protons (acid), results in APs to release neurotransmitters like serotonin

Neural pathways of taste

1. intergemmal fibers converge into one of three nerves based on the location of the taste bud they originate from

2. Gustatory nerves synapse on nucleus tractus, solitarius cells, preserving the anatomical ordering from the tongue

3. nucleus tractus solitarius neurons project to the posteroventral nucleus of the thalamus

4. Thalamic neurons extend into the primary gustatory cortex of the insula, which then sends axons to secondary gustatory cortex in the frontal cortex

labeled line coding

activation of a discrete population of neurons would encode for different sensory modalities; no overlap in activation

cross-fiber pattern coding

specific combinations of neurons that may overlap encode different sensory modalities; substantial overlap

neural pathways of taste in mice

1. tastants are flowed over the mouse’s tongue

2. neurons are responsive to single tastants are identified

3. the temperature of the tastant fluid changes NTS neuron firing

olfactory sensory neurons

located in the olfactory epithelium, odorant molecules enter through the nose and reach the cilia of the neurons

olfactory bulb circuitry

1. olfactory neurons send axons to form a glomerulus in the olfactory bulb

2. all axons in a single glomeruli come from neurons with the same receptor type

3. these axons synapse on a mitral cell

central olfactory pathways

1. olfactory information arrives at the brain in the olfactory bulb

2. information from the olfactory bulb is sent directly to the olfactory cortex

3. information from the olfactory bulb is also sent directly to the amygdala, part of the limbic system

4. both piriform cortex and the limbic system send information to the thalamus, where odor information can interact with other sensory modalities

Transient receptor potential channels (TRPs)

channels activated by temperature and some chemicals

major touch and pain receptors

merkel disks, meissner’s corpuscles, ruffini endings, and pacinian corpuscles, free nerve endings

free nerve endings

pain and nociception, distributed throughout the skin

merkel disks

perception of shape and texture in the superficial part of the skin

meissner’s corpuscle

motion detection and grip control in the superficial part of the skin

ruffini ending

responsible for skin stretch and tangential force in the deeper part of the skin

pacinian corpuscle

perception of distant events through vibrations in the deeper part of the skin

nociceptors

receptors that transmit paint signals related to mechanical, thermal or chemical sources

heat sensation of TRP ion channels

1. skin is exposed to heat and TRPV1 channels in free nerve endings are activated

2. heat signal travels through the nerves into the ascending spiral pathways

3. the brain receives the signal and generates an appropriate response

primary sensory afferents

peripheral branch and central branch; located in the dorsal root ganglion

ascending touch pathways

1. AB fiber signals enter the spinal cord through the dorsal root and continue up the ipsilateral dorsal column

2. AB fibers synapse on neurons in the dorsal column nuclei at the lower medulla

3. Medulla neurons project across the midline and ascend contralaterally, forming the medial lemniscus

4. medial lemniscus axons synapse on neurons in the ventral posterior nucleus of the thalamus, which then project to the primary somatosensory cortex

ascending pain pathways

1. peripheral nociceptors send information via unmyelinated C-fibers and small myelinated Adelta fibers to the spinal cord dorsal horn neurons

2. dorsal horn neurons project their axons across the midline to the anterior lateral spinal cord, forming the anterolateral system

3. Ascending axons of spinal neurons synapse in the VPL of the thalamus

4. VPL neurons project to the primary somatosensory cortex

descending inhibitory pathways

1. the midbrain periaqueductal gray is the center for descending inhibition

2. neurons from the PAG project to the locus coeruleus and nucleus raphe magnus where serotonin and norepinephrine are located

3. Both locus coeruleus and nucleus raphe magnus neurons project down the spinal cord to release the neurotransmitters to reduce pain

4. endorphins are also released at the spinal cord

pain

an unpleasant sensory and emotional experience associated with, or resembling that associated with actual or potential tissue damage

pain categories

location, duration, causes (nociceptive or neuropathic

placebo

inactive treatment that provides pain relief; most effective with sensory cues associated with pain relief or an expectation of pain relief

non-invasive, non-prescription pain relief

over the counter drugs, physical therapy, acupuncture, cannabis, capsaicin (icyhot)

surgical treatments

decompression, reconstruction, ablation, modulation

electric/magnetic stimulation

transcutaneous electrical nerve stimulation, spinal cord stimulation, motor cortex stimulation, deep-brain stimulation, transcranial magnetic stimulation

motor unit

alpha motor neuron and all the muscle fibers it synapses on

ways to increase muscle contraction strength

1. increase firing frequency of alpha motor neuron

2. fire more and larger motor units within one muscle → recruit more synergistic muscle masses

central pattern generators

circuits at the spinal cord level coordinate patterns of back-and-forth movements

proprioception

awareness of body or limb positions driven by sensing the degree of muscle stretch and muscle load, or tension, or intensity

dorsal association areas

provide information about localization of limbs and external items

ventral association areas

provide information about recognition of surrounding items

basal ganglia direct pathway

the direct pathway for conscious motor planning uses disinhibition to promote motor movement

premotor cortices

premotor cortex: planning force and distance of an action

supplementary motor area: planning order of operations

primary motor cortex: engage extensors and flexors to move