Brains n stuff Flashcards
What is a neural system?
- distributed ensemble of peripheral and central neurons + circuits
- involved in transducing, encoding, relaying, processing specific types of information
What are the 5 things a sensory system can do?
- Transduce external stimuli (at periphery)
- Encode distinct information about stimuli (in neurons of dorsal root ganglion)
- Relay information about distinct attributes of stimuli (PNS to CNS)
- Represent periphery in an orderly fashion in the brain (cortex)
- Process info to generate sensory perception (at post-central gyrus, etc.)
What is transduction?
neural event –> physical/chemical stimulus detected via molecular signaling –> causes a change in the electrical activity of specialized receptors
How do sensory systems encode?
- specify info about stimuli by transforming receptor response into patterns of electrical activity (esp APs)
- also encode spatial information about stimuli via receptive field (region of sensory space –> local receptor transduction leads to maximal change in patterns of afferent electrical activity; ie small fields w/better 2 pt resolution - finger tips, lips; lg fields w/worse 2 pt resolution - back, calves)
What is adaptation?
- necessary to encode distinct types of information
- receptor adjustment to different levels of stimulus intensity (reflected in pattern of APs encoded by afferents)
- slowly adapting: APs gradually become less frequent (all pain receptors)
- rapidly adapting
How can information be relayed in sensory systems?
- parallel pathways: distinct ppn of cell bodies, axons, targets in a sensory system that carry information about a specific stimulus
- referred pain: relay of visceral discomfort via cutaneous (skin/surface) afferents
How do sensory systems represent information?
- representation: systematic distribution of specific response ax ppns of nrns in the brain (corresponds to topography/computational fcns of stimuli sensory periphery transduced from the sensory periphery)
- primary mode of representation is topographic maps –> systematic distribution of specific responses ax ppns of nrns w/ pt-pt relationship w/ lcn of stimuli sensory periphery transduced from sensory periphery
How do sensory systems process information?
neural processing: sum of electrical activity ax multiple neural circuits in a broad range of anatomical locations in the brain
- leads to: interpretation of ID, quality of stimuli, planning of behavioral response (motor activity), internal representation/abstraction/memory
What is parallel processing of pain discrimination?
Processing by location + intensity
- sensory: discriminative (somatosensory cortex)
- affective: motivational (anterior cingulated cortex, insular cortex)
What is somatosensation?
- physical force (painful) messes up skin –> transduced by specialized sensory rec
- lots of specialization
- classes of peripheral rec (superficial to deep): free nerve endings (pain), meissner’s corpuscle (discriminative, light touch - fast), merkel cells (skin distention - slow), Ruffini endings (sustained P - slow), Pacinian corpuscle (vibratory touch - rapid)
What is mechanosensation?
- sense of touch, pressure, proprioception
- channels detect physical deformation of membrane –> channel open –> Na/Ca influx –> AP
- dynamic range (light vs hard P)
- threshold for AP activity
What is proprioception?
- sense of position of limbs/jts in space
- -> muscles (muscle spindles)
- -> jts (golgi tendon organs)
What is nociception?
- detection of painful stimuli (including heat, chemicals)
- capsaicin rec/channel (capsaicin binds to TRP1 channel –> mediator for pain)
- intensity sets threshold for encoding painful nature of stimulus
- pain transduction also d/t endogenous signals (bradykinin, prostaglandins, histamine, H+, ATP), inflammation
What are the parallel pathways and how are they discriminated?
From fastest to slowest transduction:
- Dorsal Column/Medial Lemniscus: proprioception, touch, pressure (large, myelinated)
- Anterolateral/Spinothalamic: pain, temp + pain, temp, itch (unmyelinated) (small)
How do opioids work on pain?
descending brainstem inputs activate local dorsal horn interneurons –> inhibit pain transduction (dorsal horn)
What is neural plasticity?
change in electrical activity of individual nrns, neural circuits, sensory/motor/cognitive maps d/t differences in stimulation, experience or injury
What is somatosensory plasticity?
altered peripheral use + activity can change central respresentation
When is plasticity bad?
phantom limbs/pain following amputation/trauma –> mismatch between central representation + periphery
What neural structures are in the visual system?
- retina (transducing/encoding –> neural events only happen in retina)
- relay: optic nerve, optic chiasm, optic tract, LGN
- primary visual cortex (representation/procession): motion processing (parietal lobe) + form processing (temporal lobe)
What are the two types of photoreceptors?
- Rods (opsin, rhodopsin)
2. Cones (ospins, encode for color)
Explain the pathway of phototransduction.
Visual field –> cone cell –> retina –> photoreceptor –> bipolar cell –> ganglion cell (produce APs, begin to selectively process info)
Explain the polarization of photoreceptors (light vs dark).
- depolarized in the dark (high [cGMP] = Ca/Na channel constantly open)
- hyperpolarized when illuminated/light (low [cGMP] = Ca/Na closes = K+ hyperpolarizes cell)
What are the classes of information encoded by the visual system?
- topography: where is it; fovea (nrns matched to pts in visual field)
- luminance: how much light (proportional to how many photons available)
- contrast/color: what is it (perceptual quality; discriminating form)
- depth: how near/far is it
- motion sensitivity: is it moving yo
What are the parallel pathways for form and motion in visual information?
- parallel pathways separate (retina to LGN)
- P cells (form)
- M cells (motion)
What is critical period plasticity?
- restricted times during which experience can significantly + permanently alter behavior/brain circuits
- ie changes made (ie one eye sewn shut) –> compensation (other eye adds axonal terminals that expand into area normally taken up by shut eye)
What is auditory function?
- identifies pressure-created waves generated by vibrating air
- localization + identification of stimuli
- topography (spatial rep) by quantitative aspects of stimuli
What is vestibular sensation?
- detecting + representing CHANGES in head + body position
- acceleration + direction of body movement relative to space/gravity
- provides info that regulates ongoing movements of eyes, head, posture adjustment
What is the information pathway for auditory/vestibular sensation?
- information relayed via brainstem
- info transduced in inner ear (time differences represent location of sound)
What are the two sensory organs in the inner ear?
vestibular labyrinth + cochlea
What does the vestibular labyrinth do?
- physical orientation specialized to detect movement + acceleration horizlly + vertically
- vestibular hair cells: encode info about acceleration, velocity, head position
- semi-circular (fluid-filled) canals
- vestibulo-ocular reflex: used to localize brainstem lesions (fast/slow eye movements in response to water)
What does the cochlea do?
- surface vibrates in response to diff freq to represent different tones (pitches) –> vibrations displace distinct regions of cochlear surface
- cochlear hair cells transduce stimuli (physical displacement of hair cells) + encode frequency based on cochlear position
- frequency encoded in cochlea but is represented/processed in primary auditory cortex
What are the chemosensory cells and what do they do?
- id’y + abundance of stimuli –> little topography or spatial representation
- detection of noxious/hazardous stimuli, edible + nutritious food; recognition of pheromonal signals
- reles on GPCR to transduce airborne/water soluble chemical stim
- ## molecular diversity –> specificity
How is olfaction transduced?
- olfactory epithelium –> direct production of AP
- id’g airborne chemical stimuli
- lg gene family –> multiple variable AAs –> diversity
How is gustation transduced?
- id’g ingested water-soluble stimuli
- transduction via taste ells
- distinct molecular rec for ea taste class
- parallel lines transduce/encode ea category separately
What are olfactory deficits early signs of?
- Alzheimers
- Parkinsons
- Huntingtons
- Schizophrenia
What is a motor unit?
all muscle fibers innervated by one alpha motor neuron
What is an alpha motor neuron?
- generates F in muscles when they fire AP
- in SC (in distinct places) and brainstem –> innervates skeletal muscles directly
- generation of F encoded in patterns of electrical signals
What are the 6 basic things that motor systems?
- Regulate contraction/elongation of skeletal + smooth muscles (synaptic terminals at NMJ w/ACh)
- Regulate glandular secretion (S - NE; PS - ACh)
- Organize concerted contraction + complimentary relaxation of muscle groups (reflexes)
- Command skilled movement + mntn posture + balance (primary motor cortex)
- Correct ongoing movements based on sensory info (cerebellum)
- Initiate complex goal-directed actions (basal ganglia)
Where is the autonomic/visceral nervous system located?
medulla oblongata (give me scoliosis) brainstem
What are the four steps of the reflex arc?
- Hammer tap stretches tendon (–> sensory receptor in leg extensor muscle)
- Sensory nrn synapses w/excit. motor neuron in SC (–> spinal internrn –> inhibits motor neuron to flexor muscles)
- Motor neuron conducts AP to synapses on extensor muscle fibers –> CONTRACTION
- Leg extends
What are the functions of the upper motor neurons?
- activity correlates w/specific muscle contraction in distinct body parts; represent direction of movement
- segregation of cortical + bs upper motor neuron inputs (parallel motor pathways)
- anticipatory motor control of posture + balance
- distinct consequences of upper vs lower motor neuron damage (Babinski sign)
How does the cerebellum regulate movement?
- receives input from somatosensory, motor, association regions of cortex (+ vestibular sys, SC, BS)
- neurons send info back to motor cortex via thalamus
- purkinje cells are tonically active –> correct signals by slowing their AP output
How does the basal ganglia regulate movement?
- receives input from entire cortex (except primary visual + auditory cortex)
- relies on balance of inhibitory + excitatory inputs + outputs
What does Parkinson’s do to the basal ganglia?
disrupts balance –> inc inhib of motor cortex –> dec movement
- Dopaminergic nrns in substantia nigra degenerate
- Difficulty initiating complex movements
- Paucity of movement (lack of facial expression)
What does Huntington’s do to the basal ganglia?
disrupts balance –> dec inhibition of motor cortex –> inc movement
- Nrns in caudate + putamen degenerate
- Inapprop complex motor behavior (including speech)
- Constant writhing movements as ds progresses
What is the definition of language?
arbitrary association of symbols w/objects, circumstances, actions, intentions, emotions, concepts (independent of modality)
What are the fundamental properties of language?
- distinctly human
- represented in specific brain regions + circuits
- dmg to specific brain regions results in distinct language deficits
- distinct aspects of language are lateralized
What are the two general features of language?
- symbolic representation: matching of symbols to objects, etc. (lexical aspect)
- stereotypic performance: order + context (syntactic + semantic aspects)
What is the association cortex?
neural circuits that represent cognitive info is frontal lobe (what do I want to do about it?), parietal lobe (is it interesting?), temporal lobe (what is it?)
What is Broca’s Area?
- prefrontal; planning
- damage = productive aphasia
What is Wernicke’s Area?
- temporal; auditory association, visual association
- damage = receptive aphasia
What are the language fcns of the L hemisphere?
- analysis of R visual field
- stereognosis
- lexical + syntactic language
- writing
- speech
What are the language fcns of the R hemisphere?
- analysis of L visual field
- stereognosis
- emotional coloring of language (damage –> inability to perceive or impart emotional + affective content of language)
- spatial abilities
- rudimentary speech
What is Broca’s aphasia?
- halting speech
- perseveration: tendency to repeat words/phrases
- disordered syntax, grammar, structure of individual words
- comprehension intact
What is Wernicke’s aphasia?
- fluent speech
- little spontaneous repetition
- adequate syntax + grammar
- contrived/inappropriate words
- comprehension not intact
What are the critical periods for language development?
- Early “pre-language” behavior modality dependent in infants
- Decline in acquisition of second language (critical period occurs before 3rd-7th birthday)
