Test 2 Flashcards
Sensory transduction
The translation of sensory input into electrical signals the brain can understand
Labeled lines
Each nerve input to the brain reports only a particular type of information
Ex) vibration, pressure, temp etc
Receptive fields
A region where a stimulus will change the neuron’s firing rate
Size of receptive field
Large receptive field= less sensitivity
Small receptive field = more sensitivity
Rate coding
Firing of AP recorded as #AP/sec
Codes intensity
Range fractionation
Divides multiple receptors of a certain sensory neuron based on intensity
Has min and max firing rate
Phasic receptors
Decrease frequency of AP after intital stimulation
Adaptation
Loss of receptor sensitivity as stimulation is maintained
Tonic receptors
Show no decline or slow decline in AP frequency (I.e. Pain, proprioceptor)
Center Modulation of Sensory Information
The process in which higher brain centers, such as cortex and thalamus, suppress some sources of sensory information and amplify others
-“top-down” influences
Polymodal neurons
A neuron where information from more than one sensory system converges
Synesthesia
A condition in which stimulation in one sensory pathway evokes an involuntary experience in a second sensory pathway
Graphemes color synesthesia
See colors associated with numbers
*convergence of different sensory systems allows the systems to interact
Humunculus
The size of each body part reflects the proportion of S1 devoted to that part
Motor system
Biggest areas: hands, lips and tongue
Sensory system
Biggest areas: hand, thumb, lips
Nociceptors
A receptor that responds to stimuli that produce tissue damage or pose the threat of damage
Pain receptor
Delta fibers
Large diameter, myelinated and thus fast conducting axon
- transmits pain info
- phasic receptors
C fibers
A small, unmyelinated and thus conduct pain info slowly and adapts slowly
-tonic receptor
Substance P
A peptide transmitter that selectively boosts pain signals and remodels pain pathway neurons
Cingulate Cortex
Region of medial cerebral cortex that lies dorsal to the corpus callosum
-integrates pain info
Analgesic drugs
Opiate drugs bind to specific receptors in the brain that decrease pain
TENS
Mild electrical stimulation to nerves around the injury sites to relieve pain
Placebo effect
Relief of a symptom that results from a treatment known to be ineffective
Acupuncture
Insertion of needles at designated points on the skin to alleviate pain or neurological malfunction
Extreme stress
Can produce significant analgesia
Proprioception
Body sense; info about position and movement of the body
-tonic receptors
Motoneuron
A neuron that transmits neural messages to muscles or glands
Neuromuscular junction
Region where the motoneuron terminal meets the adjoining muscle fiber to transmit its message
Pyramidal (corticospinal) system
Forms pyramidal tract
From frontal cortex (pre-central gyrus) to brain stem to spinal cord
Primary motor cortex (M1)
Executive region for the initiation of movement
Pre Central gyrus
The strip of frontal cortex that is crucial for motor control
M1 neurons
Most encode movements in a particular direction rather than a specific muscle contraction
SMA (supplementary motor cortex)
Premotor cortex
Code behaviors involving multiple muscles rather than specific muscle movements
Extrapyramidal System
Basal ganglia and cerebellum
-adjust the commands received from the other parts of the motor control system
Ataxia
Loss if voluntary muscle control and balance
-damage to extrapyramidal system (cerebellum)
Diseases of Basal Ganglia
Parkinson’s disease
Huntington’s disease
Parkinson’s disease
- hypokinesia (less mov’t)
- lack of spontaneous movements
- bradykinesia-slowing of movement
- rigidity and postural instability
- tremor when stationary (resting tremor)
Huntington’s disease
Hyperkinesia (more mov’t)
- excess spontaneous movement
- writing, dance like movements (chorea)
- also affects mood and cognition
Sound waves
Changes in air pressure
Compression
Higher pressure
Rarefaction
Lower pressure
Amplitude (Intensity) = Loudness
Measured as sound pressure # of molecules measured in dB
Frequency = Pitch
The number of cycles per second in a soundwave measured in hertz
-speed of compression/rarefaction.
Timbre = Complexity
Complexity of a sound wave
Pure tone
Tone with only a single frequency of vibration
-rare in real world
Fundamental frequency
Basic
Predominant frequency of an auditory tone
Harmonies
Multiples of the fundamental
Transduction of sound
1. Cochlea
Cochlea: fluid filled, cooked chambers where mechanical vibrations of the middle ear are transfixed into electrical signals
2.
Traveling wave causes basilar (base) membrane to move
3.
When the basilar membrane vibrates, Inner Hair Cells (IHC) bounce up against the tectorial (roof) membrane and stimulates stereocilia
4.
Vibration pops be “tip links” allowing k+ and ca2+ to rich into the stereocilia and depolarize the cell
5.
Depolarization initiates AP on the spiral ganglion cells, whose axons form the vestibulocochlear nerve
Inner hair cells
- bottom up = afferent
- detect pitch and intensity
- 95% of al fibers provide info to brain
- top down = efferent
- control responsiveness of IHC
Outer Hair Cells
- top down = efferent
- change length of cell to change stiffness of basilar membrane in certain parts of cochlea–sharpens tuning of task-relevant frequencies
- bottom up = afferent
- convey info back to brain about how still the adult membrane is
Place coding
Discrimination based on location
- base (stiff) - increase frequencies = more energy
- apex (flexible) - decrease frequencies = less energy
Tonotpic organization
Neurons are arranged as a map of stimulus frequency
-present from cochlea to A1
Temporal coding
Discrimination based on rate of firing
-most evident at lower frequencies (max. = 4000 hz)
Sound signal (PNS-- CNS) 1.
Cochlear nucleus - receives info from auditory hair cells
- Superior olivary nucleus
Inputs from one ear bisect and go to both left and right sides
-provides 1st binaural (two-ear) analysis of auditory info
- Midbrain
Inferior colliculus
- Thalamus
Medical geniculate nucleus
Primary Auditory Cortex (A1)
Core—processes complex sounds
-cells respond to only pure tones and very narrow coding
Secondary auditory cortex (A2)
Belt
- Cells respond to broader range of frequencies
- responds more to complex sounds like speech perception
Speech perception
-left hemisphere
dominant for word perception
Pure word deafness
Damage to left hemisphere
- inability to hear words, but other sounds like environmental and music sounds can be detected
Prosody
Perception of emotional tone of voice aspects of language
Ex) linguistic prosody–question vs. statement
Emotional prosody–sad, happy
Right hemisphere
Contributes to prosody
Music perception
Right hemisphere
Musical pitch/ melody
Amusia
Disorder characterized by the inability to discern tunes accurately or to sing
“Tone-deaf” ppl
- congenital amusia
- have irregularities in right-hemisphere auditory regions
Left hemisphere
Musical rhythm/timing
- tempo of the beats (rhythm)
- way that beats are grouped (meter)
Localizing sound
-where pathway
From posterior A1 to parietal cortex
Interaural differences
Code horizontal location (left to right)
Interaural latency (time) differences
Difference between the two ears in the time of sound arrival
- one ear is closer to localize a sound source
Interaural intensity (loudness) differences
A perceived difference in loud news btwn two ears
Sound shadow
Where sound waves fail to propagate
-more pronounced for higher frequencies
Vertical localization
Spectral filtering by shape of ear
Spectral filtering
Process where hills and valleys of ear alter the amplitude of some, not all frequencies in a sound
- brain develops a model of how sounds are distorted by ones ear and head
- can code left/right and up/down
Visual fields
Portion of space where objects are visible while holding a steady fixation in one direction
Binocular zone
Light enters both eyes
Monocular zones
Light only enters one eye
Ex) left zone to left eye only
Nasal retina
Part of eye closer to nose
-axons from here CROSS at the optic chiasm
Temporal retina
Part of eye closer to the ear
-axons continue on to optic tract on same side –do not cross
Optic chiasm
The point at which parts of the optic. We’ve cross from PNS to CNS
Optic tract
Name of optic nerve in CNS
Left optic tract
Corresponds to Right visual field (info from nasal retina)
Right optic tract
Corresponds to left visual field
Photopic system
Operates at higher levels of light, sensitive to color and involves cones
Scotopic system
Operates at low levels of light, and involves rods
Retina
Transfixed photons to electrical signals and sends it to the CNS
Ganglion cell layer
- top layer of cells—axons make up the optic nerve
- ONLY cells that generate APs
Bipolar cells
Mid layer of bipolar cells ( one axon and one dendrite)
-Conduct LP
Photoreceptor Cell layer
Back of the eye–bottom layer
- Rods and cones
- transduce light into electrical signals
Cones
- functions best in bright light
- 3 types: range provides color vision
- 4 million
- high acuity = smaller receptive field
Rods
Excellent light sensitivity
- functions in low lights
- 1 type: only responsive to blue green light
- 100 million
- low acuity = larger receptive field
Direction of light
Ganglion cells to photoreceptors
Direction of neural signal
From photoreceptors to ganglion cells
Special cells
Connect cells within a layer
Horizontal cells
Contacts both photoreceptors and bipolar cells
Amacrine cells
Contacts both bipolar and ganglion cells
-significant in inhibiting interactions within the retina
Lateral Inhibition
When stimulation of a receptor cell results in inhibition of info of neighboring receptor cells
Ex) special cells
-important role In Edge detection
Edge detection
Increase contrast between 2 areas of differing brightness
Color vision
Photons vibrate as they travel across space, creating a wave
- different cones responds to different light frequencies
- each has a peak and wide distribution
Fine grained color discrimination
Happens through tuning in Cortex
Fovea
Center region of retina
- highest visual acuity Bc it is where small cones are densely packed
- highest number of cones
- only place where light passes directly to receptors w/o going through other layers ( less diffusion of light)
Blind spot
Portion of visual field where light falls on the optic disc
Convergence
Allows a neuron to receive input from multiple neurons in a network
In the retina
Trade off btwn acuity and light sensitivity = function of convergence
Cones = low convergence
One cone conveys info to one ganglion cell (1:1)
-1:1 relation allows cell to know exactly where light is
Rods= high convergence
One ganglion cell receives input from multiple rods
-Bc so many rods sending info, cell cannot tell the difference of where light is coming from
-works well in low light Bc of higher sensitivity to light Bc of summation of LP
Center-surround receptive fields
Found throughout the early pets of the visual system —reina (bipolar and ganglion cells) and LGN
Center = on
Surround = off
In receptive fields of V1
Simple cells
Respond to a bar of light in a particular orientation
-built up from “convergence” across multiple center-surround receptive fields of early stages: retina and LGN
Complex cells
Respond to bars of light moving in a particular direction
-results from convergence of multiple simple cells
In the visual ventral system
-Neurons respond to more complex shapes
- receptive fields of neurons increase in size —-care less about where object is in space
(Bc of convergence trade off)
Retinogeniculostriate pathway = ventral stream
90% of axons from Retina—LGN (thalamus)—V1 (priestly and temporal cortex)
- most fovea vision goes to V1
- conscious visual processing
Cortical blindness
Total or partial loss of vision in a normal appearing eye
-damage to LGN and V1
Hemianopia
Can see only from one eye
Blindsight
No conscious awareness of visual input, but shoes unconscious responses to visual input
-result of dorsal stream
Blindsight ppl
- can guess better than chance WHERE a stimulus is in the kind area and in what direction it’s moving
- can guess better than chance simple shape judgments about WHAT something is in blind field
Retinocollicular pathway = dorsal stream
10% of axons from Retina–superior colliculus–thalamus–posterior parietal cortex
- skips V1 and goes to parietal
- does NOT require consciousness
Visual divide and conquer
Perception of color, motion and form are processed through separate visual pathways
Achromatopsia
-damage in V4
Lack of color vision, can’t perceive color; cannot see, dream or imagine in color, impairment of complex shape perception
Intact: motion perception and basic form
V4
Essential for color constancy
Damaged in achromatopsia
Color constancy
Ensures that the perceived color of objects remains relatively constant under varying illumination conditions
Akinetopsia
Damage in V5/MT (dorsal stream)
Absence of motion perception; cannot see fast motion
Intact: performing colors and recognizing objects
Visual form agnosia
Damage to ventral stream
Inability to create a unified mental representation of the structure/ form of an object
-cannot visually recognize it copy while objects
Intact: normal color, motion perception, perception of dots and lines
Visuomotor abilities
Intact after ventral stream damage
- can’t recognize objects, but can form appropriate grip aperture
- don’t know what, but know where it is and how to use it
Perception of action pathway
Dorsal steam
Codes relationship of world relative to you
-tells you where things are in space
Optic ataxia
Damage to dorsal stream
Inability to reach toward objects under visual guidance
Perceptual representations in ventral steam
Organized in “modular” or domain-specific way
Category-specific deficit
Alexia
Deficit in identifying written words
Prosopagnosia
Damage to right hemisphere FFA (fusiform face area) or both
Deficit in recognizing familiar faces –may not even recognize own face
- know what a face is
- congenital or Bc of brain damage
Optic disc
Where retina has a devoid of receptors Bc ganglion axons and blood vessels exit the eye there
Don’t notice blind spot
Bc of top down guessing. Where brain fills in the missing information
