PSYCH 230 - Exam 2

glutamate

• most common neurotransmitter in the nervous system, found throughout the brain 

• excitatory 

• induces EPSPs

• receptors induce depolarization following NT binding 

GABA (gamma amino butyric acid)

• most common inhibitory neurotransmitter 

• causes IPSPs

• causes the postsynaptic neuron to become hyperpolarized

acetylcholine (ACh)

• usually EPSPs

• in both the brain and the PNS

  • in brain - sensation, action, learning

  • in PNS - peripheral motor neurons, parasympathetic system 

• the neurotransmitter at the neuromuscular junctions 

  • spread out across the muscle fiber, causing the muscle to contract

neuromuscular junctions

synapses b/w motor neurons and muscle fiber

dopamine

• movement, reward-seeking, motivation 

• produced in substantia nigra (movement), ventral tegmental area (VTA)

serotonin

• known as “happiness NT”, but is also involved in sleep and appetite 

• antidepressant drugs increase serotonin 

• produced in the Raphe nuclei

• mixed EPSPs and IPSPs

opioids

• endorphin and enkephalin 

• natural morphine 

• pain reduction, reward, euphoria

• mixed EPSPs and IPSPs

• bind to opioid receptors 

• synthesized following pain, exercise, laughter

agonists

turn on NT system 

• EPSP/IPSP

• presynaptic - release NT

• postsynaptic - activate receptors

inverse agonists

postsynaptic binds to receptors but induces opposite effect

presynaptic agonists

release NT

• L-Dopa, cocaine, amphetamine, Adderall, SSRIs (ex. Prozac)

postsynaptic agonists

activate receptors

• synthetic opioids, benzodiazepines

L-Dopa

a dopamine precursor used to medicate Parkinson’s Disease (reduces dopamine levels)

cocaine

inhibits reuptake of dopamine by blocking dopamine transporter

• increases dopamine levels

amphetamine

blocks and reverses dopamine transporter

• increases levels of dopamine and norepinephrine 

• stimulation, euphoria, wakefulness, improved cognitive control

Adderall

prescribed combo of amphetamine and dextroamphetamine

• used in the treatment of ADHD and narcolepsy

SSRIs (selective serotonin reuptake inhibitors)

block reuptake of serotonin

synthetic opioids

• Fentanil - 100x more potent than morphine 

• Carfentanil - 100x more potent than fentanil 

• pain reduction, tranquillizer darts 

• overdose inhibits brainstem breathing circuits 

benzodiazepines

• Xanax, Valium 

• sedative, hypnotic, anxiolytic (anti-anxiety), anti-epileptic, muscle relaxant 

• bind to GABA receptors and facilitate GABA effects

antagonists

turn off NT system 

• presynaptic - prevent release 

• postsynaptic - block receptors 

presynaptic antagonists

prevent release

postsynaptic antagonists

block receptors

typical antipsychotics 

• antipsychotic drugs for schizophrenia - pimozide, haloperidol 

• block D2 dopamine receptors 

• prevent dopamine from activating 

• used to treat schizophrenia

atypical antipsychotics 

• block D2 dopamine receptors 

• block serotonin receptors 

route of drug administration 

• oral ingestion 

• injection (subcutaneous, intramuscular, intravenous)

  • intramuscular - flu shot 

• inhalation 

long-term effects

1. receptor down-regulation

2. neural sensitization 

3. neurotoxicity

receptor down-regulation

• tolerance to drug - homeostatic regulation in postsynaptic cell causes receptor degradation 

• withdrawal in absence - normal NT gives low signal

neural sensitization

• hyper-responsive to drug 

• dopamine sensitization and addiction - wanting vs. liking

neurotoxicity

• amphetamine kills dopamine neurons 

  • toxic at 10x street dose

techniques for measuring action potentials

• electrophysiological methods

• optical methods

electrophysiological methods

• intracellular recording

• extracellular recording

intracellular recording

• when electrode tip is inside neuron

• senses positive action 

• whether action potential happens or not 

• sometimes, electrode tip can interfere w/ the action potential 

• electrode entering the cell can damage it 

• harder to puncture a neuron 

• only recording from 1 neuron 

extracellular recording

• when electrode tip is outside neuron

• sodium rushes in, so positive ions are going away from the electrode tip 

• senses negative action 

• less invasive for cell 

• easier to carry out 

• not limited to recording only from 1 neuron at a time bc axons are right next to each other 

• cannot record IPSPs and EPSPs 

• good enough to record spikes 

• like an echo of the action potential 

• neurons represent locations

advantages of electrophysiological methods

• actual spikes 

• fast

disadvantages of electrophysiological methods

• intracellular recording can harm the cell

optical methods (calcium imaging)

• calcium-sensitive dyes - molecules that become fluorescent in presence of calcium 

• report how much calcium is inside the neuron 

• fluoresce more when there is more calcium (reports spiking)

• can record from many neurons through calcium-imaging 

advantages of optical methods

• indirect measurement of spikes

• seeing the exact location of neuron (see and measure)

• allows us to rerecord the same neuron

disadvantages of optical methods

• slower

• recording same neurons across days 

• cell-type specificity 

• overexciting the laser can harm the cell

sensation

the activation of sensory brain pathways by a physical stimulus

perception

the extraction of a mental representation from sensation

psychophysics

how the quantitative aspects of physical stimuli correlate w/ the perceptions they evoke

psychometric curve

• x-axis - stimulus intensity 

• y-axis - some aspect of stimulus perception

  • in psychophysics - stimulus detection (%)

  • in sensory coding - neural activity (spikes per second)

sensory coding/processing 

how the quantitative aspects of physical stimuli correlate w/ the neural activity they evoke

receptor cells 

specialized cells that respond to physical sensory stimuli

• respond electrochemically 

• convert sensory stimuli into neural signals 

• sensory stimulus triggers receptor cells 

spontaneous firing

a sensory neuron occasionally fires spikes w/ no (obvious) relation to any sensory stimulus

trial-to-trial variability

• Raster Plot

• peri-stimulus time histogram (PSTH)

Raster Plot

• x-axis - time 

  • includes time of stimulus 

• y-axis - trials 

peri-stimulus time histogram (PSTH)

• time profile of firing 

• avg of the trials in the Raster plot 

• shows on avg what the neuron does in response to the specific stimulus 

• x-axis - time 

• y-axis - spike rate (spikes/sec)

receptive field 

the region of sensory space in which a stimulus will modify the firing rate of that neuron

rate coding

a model of neuronal communication where the intensity of a stimulus is encoded by the frequency of a neuron’s action potentials (spikes)

temporal coding

when info is encoded in the precise timing of neuronal spikes, rather than just the rate of firing

cortical maps/topography

touch information from adjacent parts of the body are represented in adjacent parts in the cortex 

homunculus

• “tiny man”

• refers to an orderly representation of the body in the brain 

• interesting disproportions 

Mach Bands illusion

each vertical stripe has exactly the same luminescence, but higher and medium stations in our visual pathway make it appear as though the left side of each stripe is a bit lighter than the right side of each stripe 

retinal ganglion cells (RGC)

receive signals from photoreceptors transmitted through horizontal, bipolar, and amacrine cells and send info up the visual pathways

amacrine and horizontal cells

lateral interactions w/in the retina

bipolar cells

carry info from photoreceptors to retinal ganglion cells 

photoreceptors

transduce light signals (rods and cones)

rods

highly sensitive to light

• ideal for vision in dim environments 

• respond similarly to diff light wavelengths 

• sensitive black and white sensors

• similarly activated for colors

cones

less sensitive/need more light to be activated 

• come in 3 types that are each sensitive to either red, green, or blue wavelengths

phototransduction

the process of how we transform light into a neural signal 

• light hits the photoreceptors in our eyes and has passed through the layers of the lens

• light strikes a light-absorbing pigment molecule (rhodopsin) in disc of photoreceptor 

• rhodopsin breaks into retinal and opsin 

• opsin closes Na+ gates, hyperpolarizing the photoreceptors 

• stops glutamate release 

• in the dark, photoreceptors constantly release a little bit of the glutamate 

  • light hitting the rhodopsin causes a chain reaction that closes sodium channels and ultimately stops glutamate release

color blindness

a lack in one or more of the cone pigment

fovea

• sharpest vision

• corresponds to center of gaze 

• non-photoreceptor cells are pushed aside, which increases our sensitivity

• highest density of cones, few rods 

• our focus of gaze is optimized for day

• at night, we are nearly blind bc of this part

receptive field of RGCs

• on-center off-surround

• off-center on-surround

on-center off-surround

• light in center excites (fire more)

• light in surround inhibits

• when an “on bipolar cell” receives less glutamate, it releases more glutamate 

• ex. if a small bright spot of light lands in the center of the cell’s receptive field, the cell fires a lot, but if the whole area is evenly lit, the cell barely responds

off-center on-surround

• light in center inhibits

• light in surround excites 

• when an “off bipolar cell” receives less glutamate, it releases less glutamate 

lateral inhibition 

capacity of an excited neuron to reduce the activity of its neighbors 

• in the retina-building intuition

edge detection

types of receptive fields enhance sensitivity to edges of images 

• on-center off-surround

• off-center on-surround

bionic retina

1. camera captures image and sends info to the microprocessor 

2. microprocessor converts data to an electronic signal and transmits it to receiver 

3. receiver send signals through a tiny cable to an electrode panel implanted by doctors on back wall of eye (retina)

4. retinal implant emits pulses which travel through the optic nerve to the brain 

5. brain perceives patterns of light and dark which correspond to the electrodes stimulated on the retinal implant 

• allows for partial vision, even when eyes are closed 

• implant is tacked onto retina 

blind spot

there can be no photoreceptors where the nerve starts 

• bc of lack of machinery to detect light in the specific area

nasal hemiretina

closer to the nose, info coming through this side crosses over to the opp hemisphere of the brain

temporal hemiretina 

closer to the temples, info coming through this side stays on the same hemisphere of the brain 

lateral geniculate nucleus (LGN)

• bundle of axons from thalamus to primary visual cortex (V1) is called optic radiation 

• axons travel through the optic radiation to V1

• maintains retinotopic organization 

primary visual cortex (V1)

• leads to higher-level visual processing 

• neurons respond to oriented lines 

retinotopic organization

1. each V1 neuron responds to a stimulus in a small area in the field of view 

2. neighboring V1 neurons respond to stimuli in nearby locations in the visual field 

hierarchical processing

a cognitive process in psychology where information is processed in a structured, top-down manner (higher-level concepts to lower-level details)

blindsight

when humans are forced to guess/use vision, they do well (unconscious vision)

visual perception 

the process by which the brain interprets and organizes visual information from the environment, allowing us to make sense of what we see

ventral “what” stream 

• LGN → V1 → V2 → V4 → inferior temporal lobe (IT)

• object recognition, feature conjunctions, feature recognitions

• responses to increasingly complex stimuli 

• V4 responds to complex geometric shapes 

  • ex. shapes like triangles 

• IT responds to visual objects in a position-invariant and size-invariant manner 

  • ex. objects like cars, faces 

fusiform face area (FFA)

has neurons that respond to faces 

• in the IT

prosopagnosia

face blindness

• lesion in FFA - can be specific difficulty in recognizing faces

dorsal “where” stream

• LGN → V1 → V2 → V5 (MT) → parietal cortex

• spatial attention - guiding our view to points of interests 

• using vision for guidance of actions 

• detecting and analyzing movements 

• change blindness occurs bc we can’t pay attention to the full field of view simultaneously 

• critical for guiding visual attention 

change blindness

occurs bc we can’t pay attention to the full field of view simultaneously

saccades 

fast eye movements that focus out fovea on a small area or interest at any time

parietal cortex 

important for eye movement and perception

• integrates sensory info (gaze and spatial attention)

• guides voluntary eye movement

neglect syndrome

can be caused by a unilateral lesion of the parietal lobe

• visual system neglects one side of visual field 

sounds frequency

determines our sense of pitch 

• measure - cycles/sec, Hz

sound amplitude

determines our sense of loudness 

• measure - decibel, dB

pure tone

a sound w/ a sinusoidal waveform

complex sounds 

sounds that are not pure tones

• most sounds

Fourier Transform 

decomp of a sound (or other signal) to the frequencies that make it up 

• sum of 2 frequencies split into those 2 frequencies 

spectrogram

shows the frequency of composition of sounds 

• frequency domain corresponds to power spectrum 

• how many of each frequency shows up in the time vs. amplitude graph

• total frequency composition of the original sound 

pitch perception

humans - 20-20,000 Hz 

tympanic membrane

is struck by sound air pressure waves and forwards the vibration to the inner ear via the bones in the middle ear

cochlea

a coiled tube containing the basilar membrane

basilar membrane 

vibrates w/ the sound wave

• high frequency sounds cause the basal end to vibrate 

  • basal end - higher frequencies 

• low frequency sounds cause the apical end to vibrate 

  • apical end - lower frequencies

hair cell stereocilia 

convert sounds to electrical signals 

• vibration of the basilar membrane causes movement

auditory nerve

sends signals from hair cells to the cochlear nucleus in the brainstem

hearing aid

a small electronic device that amplifies sounds 

• 3 basic parts - microphone, amplifier, speaker 

• pick up sounds and makes them louder in the speaker 

• allows you to regain the ability of the hair cells you have lost

cochlear implant

• used in complete or near-complete deafness 

• bypasses/replaces hair cells

• directly stimulates the auditory nerve 

  • electrical stimulation 

  • coiled electrode array 

  • via surgery

cochlear nucleus

receives signals from hair cells sent by the auditory nerve and sends info to the superior olivary nucleus

• sound localization 

• sound location has to be computed, it is NOT encoded in the peripheral receptors 

  • needs to compare b/w the ears 

• having 2 ears provides cues to localize sounds