Exam 3 Flashcards
• What is the nature of receptor potentials?
o Graded and generate Aps
• What does increased stimulus intensity do to the AP?
o Enhances amplitude of receptor potential, increasing AP frequency
• What is sensory adaptation?
o Decrease in neural activity with sustained stimulation; conveys rate of change of a stimulus or status of the sensation
• What is rapid adaptation?
o Rapid onset and offset of the stimulus alerting the CNS of a change in sensory movement, “that it occurs”
• What are mechanisms of rapid adaptation?
o Rapid ion channel inactivation decreasing the receptor potential
• What is slow adapting?
o Gradual decrease in receptor activity, but still maintains enough activity to communicate the status of a stimulus, “what is occurring”
• What is mechanism of slow adapting?
o Gradual reduction of receptor potential
• What are two somatic modalities?
o Tactile sensation: touch (pressure, vibration, texture); pain; temp
o Proprioception: jt position, muscle sense, movt
• What are modalities associated with?
o Separate populations of sensory neurons specialized in detecting stimuli of different qualities
• What are the ways axon membrane receptors respond to specific stimuli?
o Indirectly through CT capsules, modified epithelial cells, or hairs
o Directly through the membrane of the free nerve endings
o Each mechanism mediates a different submodality
• What type of channels are sensory receptor proteins?
o Transient Receptor (TRP) ion channels; each responds maximally to one stimulus (“adequate stimulus”) and less to others
• What is the “adequate stimulus”?
o Energy that elicits the greatest response and largely determines which neurons will be responsible for the perception of the sensory “modality”
• What sensations can pain elicit?
o Burning hot or cold
• What is another way modalities can be distinguished?
o Grossly by conduction velocity
• What determines range of AP conduction velocities in nerves?
o Wide range depending on the degree of myelination of the axons they travel along
• Which type of axon has larger total diameter and faster conduction velocity?
o Myelinated, compared to unmyelinated
• What are compound APs?
o Recordings of the summed Aps measured over time at a particular site on the nerve
• What separates velocities of compound APs?
o The further along the nerve you record, more separated
• What do peaks in Compound APs represent?
o Correspond to axonal clusters with different conduction velocities and degrees of myelination
• How are nerve compound APs classifies?
o By either letters or numbers depending on how the original physiology labs classified them
• What are roman numerals or letter used for?
o RN for motor nerves; ABCs for sensory nerves
• Why is the classification of compound Aps arbitrary?
o Nerves typically contain both sensory and motor neurons, so either system can be used
• What are Type I or A nerves? Type IV or C?
o Most myelinated, conduct the fastest
o The slowest
• What are some examples and functions of nerve nomenclature?
o Aa proprioception, motor neuron
o Ab light touch
o Ad fast pain
o C slow pain
How are sensory neuron functions extensively differentiated?
o Muscle spindles, GTOs, flower spray endings, tactile receptors, pain, temp, all with different diameters and conduction velocities
What is the cutaneous receptive field?
o Area of skin innervated by the branches of a single sensory neuron
• How do receptive fields of mechanoreceptors vary in size?
o For different degrees of acuity; peripheral RFs are densely innervated and small in area; proximal ones are less innervated and larger
• What does size and density of RFs provide for CNS?
o Means to locate a stimulus on body; distinguish size and shape of the stimulus; resolve spatial resolution
• What is the specificity of RFs?
o They overlap, but neurons in spinal cord respond to secondary RF consisting of several primary RFs
• How do you maintain specificity?
o Secondary RFs overlap and many spinal neurons that respond to different secondary RFs can discern subtle differences among them
• What mediates tactile sensation? What are its submodalities?
o Cutaneous receptors
o Discriminative touch; non-discriminative touch; temp; pain
• What are receptors generally? What does a stimulus do?
o Either modified non-neural tissue cells or axons themselves
o Ultimately trigger an AP in the axon
• What is discriminative touch?
o Mediated by mechanoreceptors embedded in CT or around hairs
o Each has particular pattern of function, morphology, depth, RF, adaptation
• What classification are merkel cells?
o SA; form, texture: fingers scanning a surface; Ab
• What classification are Ruffini corpuscles?
o SA2; skin stretch; perception of hand shape and position; Ab
• What classification are meissner corpuscles?
o FA; skin movt and slip for grip control; Ab
• What classification are Pacinian corpuscles?
o FA; vibratory stimuli detected through hand held objects; Ab
• What classification are hair follicles?
o FA; motion/direction of tactile stimuli; Ab
• What are the slow adapting mechanoreceptors?
o Merkel cell-neurite complex; Ruffini endings
• What is the merkel cell-neurite complex?
o Clusters of merkel cells in basal layer of epidermis make synapse-like associations with sensory axon terminals; form, texture: fingers scanning a surface
• What are ruffini endings?
o Large and thin spindle-shaped cylinders composed of layers of perineural tissue localized deep in the dermis; skin stretch; perception of hand shape and position
• What are the fast adapting mechanoreceptors?
o Meissner corpuscles, Pacinian corpuscles, hair follicles
• What are meissner corpuscles?
o Lamellar cells (Schwann and CT) embedded in dermis just deep to the epidermis; detect movt across skin
• What are Pacinian corpuscles?
o Onion-shaped lamellar cells encapsulate a single axon ending in the dermis of glabrous skin; high frequency vibration
• What are hair follicles?
o Axons surround base of hair (lanceolate); detect touch
• What is physical structure of Pacinian corpuscle?
o Axon terminal surrounded by capsule: inner core of lamella cells derived from Schwann cells; outer core from fibroblasts
• What is the mechanism of Pacinian corpuscle stimulation?
o Physical pressure creates receptor potential that releases glutamate from either axon or lamellar cells; glutamate triggers AP
• What is the adaptation of Pacinian corpuscles?
Stimulus releases GABA from lamellar cells which rapidly inhibits AP
• Which mechanoreceptors have small RFs?
o Meissner and Merkel- small and concentrated at the fingertips
• Which mechanoreceptors have large RFs?
o Ruffini and Pacinian- large and located over most of region
o Pacinian- located along median and ulnar nerves
o Ruffini- detects stretch in only specific directions
• What is the percentage composition of meissner, merkel, Pacinian, Ruffini (100)?
o 43% meissner; 25% merkel; 19% Ruffini; 13% Pacinian
• What are free nerve endings?
o Mediate the remaining somesthetic modalities; SA, slower conducting, smaller Ad, C type axons; underlie the epidermis or extend into the stratum granulosum
• What is non-discriminative touch?
o High threshold sense of touch; poor localization
• How is temp detected?
o Heat and cold receptors in dermis; SA permits becoming adjusted to hot or cold water
• How is pain detected?
o Slow and fast pain mediated by C and Ad axons that penetrate into epidermis
• What are the SA mechanoreceptors for? Axon type?
o Ad, C; tap, squeeze, rub, skin stretch, on-discriminative touch (high threshold)
• What are thermoreceptors and their axon type?
o SA; Ad, C; hot or cold
• What are mechano-thermal nociceptors?
o SA; Ad; mechanical or thermal tissue damage
• What are polymodal nociceptors?
o SA; C; heat, tissue damage, chemicals (bradykinin, histamine, insect venom)
• What does proprioception involve?
o Somatic sensitivity to the position, location, orientation, and movt of joints, muscles and fascia
• How do proprioceptive receptors mediate muscle/joint position and move?
o Using fast conducting, large axons, like Aa, B
• What are three main types of proprioceptive receptors?
o Skin stretch receptors (Ruffini)
o Jt and fascia receptors detect stretch of CT via Pacinian and Ruffini receptors
o Muscle receptors detect changes in length (spindles) and tension (GTOs)
• How are major categories of perceived somatosensory modalities distinguished?
o Also by their ascending pathways
• Describe the ascending pathways for discriminative touch and proprioception:
o Low threshold mechanoreceptors; rapid AP conduction; dorsal column-lemniscal system; quantitative sense that provides localization of stimulus
• Describe the ascending pathways for non-discriminative touch, pain, temp:
o High threshold free nerve endings; slower AP conduction; anterolateral system; provides qualitative experience of stimulus
• What is the dorsal column-lemniscal system?
o Discriminative touch; proprioception; first, second, and third order neurons convey info through spinal cord, brains stem and thalamus to cerebral cortex
• What do third order neurons do in DCL system?
o Thalamic; Form part of internal capsule; project to primary somatosensory cortex in postcentral gyrus
• What do second order neurons do in DCL system?
o Of cuneate and gracile nuclei; decussate in medulla; axons form medial lemniscus which synapse onto neurons within the thalamus
• What do first order neurons do in DCL system?
o Sensory; Ab; form dorsal columns (cuneate and gracile fasciculi); synapse onto dorsal column (cuneate and gracile) nuclei in medulla
• How do axons of low threshold mechanoreceptors get to brain stem?
o Meissner’s, Pacinian, etc; innervate several segments of spinal cord before entering brains stem
• What happens to axons upon exiting the dorsal root?
o Bifurcate and sprout several collateral axons that arborize in lamina III-V
• Where does the rostral branch extend to?
o Through dorsal columns to synapse onto dorsal column nuclei in medulla
• What happens to caudal branch?
o Ends in a collateral several segments away
• What is the anterolateral system?
o Non-discriminative; pain; temp; only part of it has the neat first, second and third order neuronal pattern seen in the dorsal column-lemniscal system
• Where do sensory (first order) neurons in AL system do?
o Synapse Onto second order dorsal horn neurons using various transmitters: substance P, glutamate, NO
• What are rexed’s lamina in AL system?
o Consist of neuronal groups segregates my modality: Pain (Lamina I,II), Touch (IV)
• How do second order neurons in dorsal horn get to AL system?
o Decussate
• What are 2 anterolateral pathways involving 2nd order neurons?
o Neospinothalamic tract; paleospinothalamic tract
• What is the neospinothalamic tract?
o Projects to lateral thalamus and somatosensory cortex; localization of sensation
• What is the paleospinothalamic tract?
o Projects to reticular formation, medial thalamus and cortex; qualitative aspects of pain, temp and non-discriminative touch
• What are two types of third order neurons in AL system?
o Lateral and medial thalamic neurons
• What are lateral thalamic neurons?
o Project to primary somatosensory cortex; somatotopically arranged (homunculus) for stimulus localization
• What are medial thalamic neurons?
o Project to cingulate gyrus and insula; affective qualities of pain, temp, etc; different MT nuclei generate alerting responses (gets your attention) of the experience of dull, persistent pain
• What is syringomyelia?
o Cysts form in center of cervical grey matter interrupting decussation of AL (spinothalamic) 2nd order neurons
o Lesion affects decussation of both sides leading to bilateral loss of pain and temp (but not discriminative touch or proprioception) from the cervicothoracic area of the body
• What causes Brown-Sequard syndrome?
o Hemisection of spinal cord cuts through dorsal and AL columns on one side
• How is discriminative touch affected in BS syndrome?
o Loss is ipsilateral; sensory neurons ascend without decussation at level of lesion
• How is pain and temp perception affected in Brown-Sequard syndrome?
o Loss is contralateral; 2nd order neurons decussate below level of lesion
• How is motor control affected in Brown-Sequard syndrome?
o Loss is ipsilateral
• What are dermatomes?
o Area of skin (dermis) innervated by one spinal segment
• How have dermatomes been attempted to be mapped?
o Many attempts over last century; all suffer from methodological problems
• Why is it difficult to map dermatomes?
o Overlap considerably
• Which receptor types overlap more or less?
o Greater: touch, pressure, vibration
o Less: pain, temp
• What are the better tests for segmental nerve injury?
o Pain sensations
• What is the latest dermatome map?
o Meta-analysis of all maps
• What is the sensory innervation of the face?
o All by CN V trigeminal; discriminative touch, pain, temp and proprioception
• What do the divisions of trigeminal nerve do?
o Three, each innervates a cavity region plus a dermatome of the face
• What does the ophthalmic division of CN V innervate?
o Orbital cavity; forehead, dorsum of nose
• What does maxillary CN V innervate?
o Nasal cavity; cheek area of face
• What does mandibular CN V innervate?
o Oral cavity; chin, side of face, ear, external acoustic meatus and tympanic membrane; motor to masticators, soft palate
• Describe the path of the trigeminal nerve?
o Projects from pons; ophthalmic division enters face through superior orbital fissure; maxillary at foramen rotundum; mandibular at foramen ovale
• Where do cutaneous branches of CN V exit?
o From several foramina: supraorbital, infraorbital, mental, etc
• What are the sensory and motor functional components (nuclei) of CN V?
o Principal (main, chief) sensory nucleus- discriminative touch from face
o Spinal trigeminal nucleus- pain and temp from face
o Mesencephalic nucleus- proprioception from masticators mediate muscle reflexes
o Motor nucleus- motor to masticating muscles
• Where do sensory nuclei of CN V project to?
o VPM of thalamus; then to cerebral cortex
• What do dermatomes of trigeminal depend on?
o Vary by modality; discriminative touch mediated by the principal nucleus is arranged in traditionally depicted dermatomes
• How are pain and temperature of CN V mediated?
o By spinal trigeminal nucleus, represented in an onion skin fashion
o Lowest levels of nucleus (in upper cervical cord and lower medulla) represent peripheral areas of the face (scalp, ears, chin)
o Higher levels (in upper medulla) represent more central areas (nose, cheeks, lips)
o Highest levels (in pons) represent mouth, teeth, pharyngeal cavity
• What do the 6 cell layers of the cerebral cortex do?
o Receive incoming info and form meaningful spatiotemporal patterns that are projected to other cortical areas, as well as to limbic system, brain stem and spinal cord
• What are stellate cells?
In layer IV of cerebral cortex; Receive sensory input from the thalamus
What are pyramidal cells?
o In layer V project info to other regions of CNS
• What are interneurons?
o Form intricate circuits that generate excitatory and inhibitory patterns of neural activity
• What are Brodmann’s areas?
o Areas of cortex have characteristic sells that are histologically distinguishable; each area has been numbered and is used for anatomical identification of functional areas
• What if fMRI used for?
Visualize brain activity in response to ongoing mental and physical activity
Describe an fMRI of the cerebral cortex in terms of green, red and yellow areas:
o Green: active while subjects remembered into presented visually
o Red: active while they remembered info presented aurally
o Yellow: active for both types of activity
• How does MRI work?
o Protons spin around their axes, creating individual magnetic fields with random directions
o When vertical mag field is applied to tissue the protons create a net vertical magnetic field
o A horizontal radio frequency pulse makes the protons precess around their vertical axes
o This creates a changing magnetic field and an electric current that is measured in MRI
o The net magnetic field can be divided into a vertical and a horizontal component
o MRI measures the changes in these two component as the protons respond to the applied magnetic fields and radio frequency pulses
• How does MRI work with a subject?
o Subject is placed in vertical mag field; with protons aligned vertically, a horizontal radio frequency pulse causes the protons to rotate in the horizontal plane synchronously, or “in phase,” with one another
o The horizontal pulse is then turned off and the rotating protons begin to move out of phase with one another, losing horizontal
o After withdrawal of the horizontal pulse the protons realign with the vertical mag field, with restoration of vertical magnetization
o This “righting” of the protons occurs more slowly than the dephasing and is measured indirectly. the time constant of the recovery of longitudinal magnetization is T1
• What do scanning hydrogen ions provide?
o Overall map of the brain: magnetic gradients permit division of brain into “slices”
o Pixels represent the concentration of ubiquitous hydrogen ions (H+, protons)
• What is BOLD?
o Used in fMRI; blood oxygen level detection; to measure neutrally related blood flow
• What happens when neuronal activity increases?
o There is an increased demand for oxygen and the local response is an increase in blood flow
• What are the different magnetic properties of hemoglobin in regards to oxidation state? How is this used?
o Diamagnetic when oxygenated; paramagnetic when deoxygenated
o This difference leads to small differences in the MR signal of blood depending on the degree of oxygenation
o Used to detect brain activity (which uses oxygen)
• What is the thalamus?
o Pair of oval shaped clusters of nuclei in the diencephalon; lie on each side of the third ventricle; project axons to all areas of cortex
• What are thalamo-cortical connections?
o Each Nuclei of thalamus projects axons with sensory, motor ,or integrated neural info to cerebral cortex; VPL/VPM projects to primary SS cortex
• What forms the primary somatosensory cortex (SI)?
o Postcentral gyrus
• How does SS info enter SI cortex?
o Via VPL (body) and VPM (head) nuclei of the thalamus
• What does VPL and VPM stand for?
o Ventro-posterior lateral and medial
• Where do VPL and VPM receive input?
o VPL: from dorsal column-lemniscal and AL pathways
o VPM: from head via trigeminal nerve
• What is the general purpose of primary and secondary SS cortices?
o Elaborate and contextualize sensory info into meaningful experiences
• What are the neurons of cortical columns
o Have similar sensory receptive properties, ie modality and RFs, cluster together into 300-600 um wide columns perpendicular to the surface
• What do columns represent?
o Several columns form arrays that will map different body area or sensory modalities
• What does each level of somatosensory system generate?
o A particular spatiotemporal pattern of neural activity across large populations of neurons
• What does a horizontal line mean in a tracing of neural activity?
o A tracing of a single neuron activity over time from left to right
• What do sensory trigeminal nuclei show in a tracing?
o Simple excitatory responses to stimulus
• What do thalamus and cortex show in a tracing?
o Various oscillating patterns of excitatory and inhibitory activity within the long duration responses across a population of neurons
• What is somatotopy?
o Homunculus; contiguous areas of the body are represented within cortex in proportion to the density of sensory receptors in that area of the body
• How are high and low density area of homunculus represented?
o High (mouth and hand) are large; low (the back) are smaller; evolutionary changes from face to limbs
• Where does somatotopy occur?
o In most areas of the CNS including the spinal cord, brains stem, thalamus and cerebral cortex
• How is each area of the body mapped along the SS cortex?
o Multiply; Ex: all five digits, highlighted in different colors, map across slightly different regions of SI
• How are whisker area of rodents represented on cortical columns?
o Each area is a cortical column that receives input from a single whisker; cortical activity in response to movt of a single whisker spreads out from a specific cortical column out toward neighboring columns
• Where does SS neural activity begin and travel?
o Starts in local homuncular spot, but expands outward; arcuate fibers b/w cortical areas spread the activity outward asymmetrically
• What is cortical plasticity?
o Cortical sensory representation changes with experience and learning (plasticity)
• How is plasticity seen in cortical columns?
o CC neurons respond primarily to one specific area of the body, but inputs from neighboring areas of the body surface also project to the same columns, w/o eliciting activity, ie their connections are “latent”
• What happens in cortical localization of a stimulation?
o Requires differentiation of RF?s of the stimuli at various neural levels including dorsal column nuclei, thalamus, and SS cortex
• How are RFs differentiated in peripheral structures?
o Grossly, by selective activity of sensory neurons that innervate each distinct RF; localization is more specific where the RFs are smaller, ie innervated by axons that extend over small areas
• How are RFs differentiated in CNS?
o More finely, by neural interactions b/w pathways from different RFs; this requires lateral inhibition
• What is lateral inhibition?
o Neural mechanism in cortex, thalamus, and dorsal column nuclei (DCN) that enhances the difference b/w SS RFs
• What stimulates DCN neurons?
o By sensory neurons from the center of a RF
• What do inhibitory neurons within the DCN do?
o Suppress activity from sensory neurons in the peripheral zone of a RF
• How do you get varied responses from different zones of the RF?
o Central stimulation of the RF generates a positive response
o Peripheral stimulation of the RF generates a negative response
• What would happen without lateral inhibition by interneurons?
o The activity of the stimulus is dispersed among neighboring neurons with declining amplitude
o A single sensory neuron will branch and activate several local DCN neurons, the response weakening the farther away from the source of the stimulus one goes
• How are inhibitory interneurons normally interposed?
o Such that when they are stimulated by recurrent branches from DCN neurons, they inhibit neighboring DCN neurons
o With lateral inhibition, the central region of activation is enhanced, while the neighboring region is inhibited
• What is 2 point discrimination?
o Ability to discriminate b/w separate but simultaneous pin-pricks to the skin
o Common neurological test that measures integrity of the dorsal column-lemniscal system
• Two point discrimination involves precise localization of a physical stimulation which depends on:
o Density of sensory receptors in the skin
o Lateral inhibition in the CNS to precisely discriminate the stimulation of separate RFs
• How does syphilis reduce 2 point discrimination?
o Dorsal column degeneration; since 2pd requires function of discriminative touch mechanoreceptors
• What is cortical regulation of lateral inhibition in DCN?
o Feedback control of sensory pathways is the norm and provides a means to select stimuli pertinent to behavioral context (focusing)
• What do descending pathways from both primary SS and motor cortex modulate?
o Afferent input from upper limb during tactile exploration; in order to select certain inputs relevant to the movts, and provide input to assure adequate frequency and duration discrimination for tactile and proprioceptive info
• What is required for SS perception and accurate discrimination of texture and complex spatiotemporal patterns?
o Movement; active exploration of environment
• What happens in SS perception if movt is eliminated?
o Results in loss of discrimination, but not of absolute sense of touch
• Where does motor cortex send messages?
o To muscles for movt; but also to DCN neurons to facilitate sensory stimuli related to the movt
• How does motor cortex facilitate sensory input in cortical discrimination of cutaneous RFs?
o Input from RF #2; sensory cortex directly stimulates DCN neurons from RF #2
o Motor cortex uses info from sensory cortex, suppresses RF #1 by enhancing lateral inhibition
o Motor cortex facilitates RF #2 by inhibition of lateral inhibition of the DCN neurons
• What do the motor cortex pathways of sensory input select for?
o Only the most important sensory inputs related to movt and allows for greater tactile resolution and manipulation skills
• Where is sensory input projected to?
o Into cortical columns, each representing a specific type of sensory receptor
• Where are meissner’s and merkel’s inputs projected to?
o Meissner’s FA and merkel’s SA inputs are projected to separate columns in area 3b (Brodmann)
• Where do touch pain and proprioception project to?
o Different areas of cortex
• VPL projects to several regions of SI. What are the Brodmann areas?
o Area 3a: encodes proprioception
o Area 3B: SA and FA cutaneous receptors
• What does tactile perception of object size and shape require?
o Both cutaneous and proprioceptive info from jts. Muscles, and skin stretch
• Where does info from areas 3a and 3b and thalamus converge?
o Onto areas 1 and 2 where neurons generate more abstract SS perceptions such as orientation, motion, and spatial arrangement
• What is area 5 associated with?
o At posterior parietal cortex; SS and visual inputs; engenders a body centered space
• What info is contained in central representations of objects?
o Local form, texture and motion where skin contacts object
o Global properties such as size and shape are determined by multiple points of contact compared to previously stored representations of objects
• What can be said of the enlargement of RFs?
o Enlarge with each step up the cortical hierarchy; larger areas are then integrated into meaningful wholes
• Where does SI cortex project to?
o Posteriorly along dorsal and ventral streams to secondary and association cortex
• What is the ventral stream of SS cortex?
o SI projects to secondary SS (SII) cortex bilaterally; involved in form processing (answers What is it?); SII responds to global features of objects such as size and shape, ie tactile object recognition
• What is the dorsal stream of SS cortex?
o SI projects to posterior parietal cortex (PPC) areas 5,7 for multisensory integration, directing attention and interacting with the motor cortex in frontal lobe; answers Where? And How? To position hand to grasp an object
• What type of projections does ventral SII receive from SI?
o Tactile and proprioceptive, representing multiple sources of passive or active contact with an object as well as bilateral input from body
• What type of internal picture does ventral SII develop? How?
o 3D; SII has orientation selectivity: same orientation of edges on different fingers unite a sense of continuity and generate perception of round disc
• How do SII responses depend on behavioral context or emotional state?
o SII conveys info to and from the hippocampus and amygdala of the limbic system to form memories based on behavioral significance
• How does PPC (dorsal stream) receive info from SI and SII?
o Either directly via arcuate fibers or indirectly via thalamus
• What is PPC mostly responsible for?
o Generating a conscious body image; integrates touch, proprioception, vision to form a coherent multimodal representation of space coded in a body-centered reference frame
• How is the info for body schema or “ego-centric space” for body awareness and embodiment of sensory experiences updated in PPC?
o Unconsciously, during body movt to be used primarily for spatial organization of action; dependent on proprioception
• Where does the PPC extend to?
o Speech comprehension area (Wernicke’s area); eg SS aspects of reading, writing, etc
• Where does visual, auditory, and SS input converge?
o Into the posterior/inferior parietal association cortex, where on the right side it is the location for lesions that produce neglect syndrome
• Where are visual, auditory, and SS also projected to?
o Prefrontal cortex and limbic regions for evaluation towards behavior and generation of emotions and memory
• What are two dysfunctions in the association cortex?
o Astereognosis: inability to identify an object by touch
o Neglect syndrome: deficit in attention to and awareness of one side of space
• What is most neglect due to?
o Lesions in the RIGHT inferior parietal lobe (esp angular gyrus); this cortical region integrates SS, visual and auditory info; most neglect cases involve loss of the left side of the body and visual fields
• What is the idea of how neglect produces effects on opposite side of body as the lesion?
o Each side of the brain pays attention to the opposite sides of the body/visual/auditory fields
o Corpus callosum sends info to the opposite sides of the brain, but in neglect there is no consciousness of the left side
• Why do left side lesion not produce neglect?
o One hypothesis is that the right brain has the dominant “executive” role in determining what to pay attention to. With damage to the left parietal lobe, the right side can compensate, but not vice versa
• What shapes the perception/awareness of somatic stimuli?
o Bottom up and top down cortical influences
• What is bottom up input in SS attention?
o SI neurons receive input from sensory receptors; PPC receives integrated info from SI, SII, plus visual and auditory association cortices
• What is top down input in SS attention?
o SI neurons receive feedback from not only PPC neurons that respond to both SS and visual info, but also from motor cortices
• What happens when SI neurons respond to a sensory stimulus
o They simultaneously stimulate feedback from PPC neurons that have been trained to form visual and somatic associations (memory
• What does the feedback of top down processing provide?
o Forms a backdrop against which sensations are to be perceived consciously; a frame of reference for “making sense”
• How long does SI neural activity persist when there is feedback?
o For a fraction of a second, even after the sensory stimulus has stopped; this suggests the presence of a cross-modal short term memory formed in SI
• What is the important of short term forms of memory in SS info?
o Crucial factor for giving rise to an awareness of sensory info, a concept that has been described by Edelman’s expression “the remembered present” (used to define the very short period of time where we are aware of something)
• What is consciousness of tactile stimuli dependent on?
o No on location of body, but on peripersonal spatial location
• What happens in phantom limb sensations and pain?
o SS in SI, SII cortex lead to somatoperception (what the body is felt to be like) and somatorepresentation (abstract knowledge, beliefs and attitudes about one’s own or others’ bodies)
• What are phantom limb sensations due to?
o Their disassociation: one knows abstractly that the limb is gone (representation), but is still felt to be present (perception)
• How is phantom limb sensation caused by reorganization of SS cortex?
o Denervation of limb cortex unmasks latent sensory pathways from contiguous areas of the body
• Where does displaces info of phantom limb sensation come from?
o Displaced sensations of missing limb elicited from the face and shoulder
• What is telescoping in phantom limb sensation?
o Due to reorganization of cortex with lower density of proximal structures; peripheral structures with more cortical space take longer to reorganize
• Phantom limb sensation is associated with plasticity in____
o PPC
• How does phantom limb pain arise?
o Efferent pathways from hand area of sensory and motor cortex maintains perception of hand, especially in contracted postures= possible mechanism of phantom pain
• Can phantom limb pain be treated with drugs?
o Insensitive to opiates; associated more with plasticity in SI which has no opioid system
• What does sense of self involve?
o Both a sense of agency and a sense of body-ownership
• What does self-ownership or identification depend on?
o A coherent body representation generated by the various cortical areas; body representation depends on matching of multisensory processing, esp vision, touch and proprioception
• What is attest for body ownership?
o Rubber hand illusion; synchronous stimulation of unseen real and seen rubber hand causes rubber hand to be attributed to one’s own body
• What are body representations due to?
o Bottom-up processing of sensory info, or top-down regulation of sensory input by an internal model of the body consisting of background conditions that preserve the coherence of bodily experience?
• What areas underlie the reestablishment of embodiment of the rubber hand onto one’s body?
o Local area within PPC and premotor areas
• What is delusional parasitosis?
o Delusion of being infested with bugs or parasites; tactile hallucination of small insect or bugs stinging, living, breeding and burning holes in the patient’s skin
• What is a possible cause of delusional parasitosis?
o Disrupted prefrontal control over SS representations
What do complex movts involve?
o Integration of somatic, visual and proprioceptive input; motor programs generated at various levels of the CNS; parallel and hierarchically arranged motor control systems from cerebral cortex down to spinal cord
• What is the CNS and spinal cord involvement in motor control systems?
o CNS generates motor programs; spinal cord has more executive control of motor neurons
• What are the higher order structures of the motor system?
o Association cortex, basal ganglia and the cerebellum create motor programs that generate meaningful activity among upper motor neurons
• What are lower motor neurons?
o Consist of alpha and gamma motor neurons
o Alpha motor neurons: brain stem (CNs), ventral horn of spinal cord (spinal nerves)
o Final common pathway for motor commands
o All movt generated by selective groups of 1 million lower motor neurons
• Where are upper motor neurons?
o Cerebral cortex, reticular formation, and vestibular nuclei
o Project down to lower motor neurons in spinal cord and CN nuclei
• What are a-motor neurons?
o Arranged somatotopically in ventral horn; direct monosynaptic innervation of muscle
• What is the basic arc motor reflex?
o Sensory neuron enters dorsal horns synapse either on interneurons, or directly onto motor neuron; interneurons inhibit motor neurons (renshaw and la inhibitory neurons)
• What are two types of reflexes tested clinically?
o Superficial reflexes (flexor withdrawal); deep (tendon) reflexes
• What are superficial reflexes?
o Flexor withdrawal reflexes use transcortical as well as brain stem and propriospinal pathways to elicit complex intersegmental responses to cutaneous pain stimuli
• What are deep tendon reflexes?
o Stretch- and tension- induced reflexes use simpler, Ia, II, Ib afferent pathways to elicit or inhibit muscle contraction
• What regulated muscle length?
o Muscle spindle reflexes
• What are muscle spindles?
o Intrafusal muscle fibers, parallel to extrafusal, surrounded by CT; spindles convey changes in muscle length to spinal cord; Ia (primary) and II (secondary) afferent detect changes in length and velocity
• How are spindle neurons activated?
o Physically gated channels in the axon of Ia and II neurons are interconnected with each other via cytoskeletal strands of spectrin
o Stretching the spindle distorts the axonal membrane opening the Na/Ca channels
o Na/Ca entry generates a depolarizing generator potential which in turn initiates Aps in axon
• What is the mytotatic reflex?
o Stretch reflex; maintains muscle length; increase in muscle length triggers homeostatic, negative feedback to maintain limb in constant position
o Stretch spindle -> Ia and II afferents -> a-motor neuron -> contract same and synergistic muscles
• What is the reciprocal innervation in the myotatic reflex?
o spindle afferents stimulate inhibitory interneurons to relax antagonist muscles
• What are two tests for myotatic reflex?
o Patellar tap tests integrity of myotatic reflex circuit
o Jendrassik maneuver (clench teeth and flex, fingers, gives larger patellar response, b/c pt is not consciously influencing the response)
• What are gamma motor neurons?
o Regulate spindle sensitivity during movt; innervate muscle ends of spindles; tauten spindle and increase sensitivity of Ia and II afferent neurons to muscle stretch
• What happens in alpha-gamma coactivation with whole muscle contraction?
o Spindles are passively contracted and less sensitivity to stretch; Ia afferent activity is reduced
• What happens in a-y coactivation due to gamma motor neuron activity?
o Spindles are tonically contracted and more sensitive to stretch; sensitivity to stretch maintained throughout range of motion
• What controls gamma motor neurons?
o Brain/brain stem (not muscle/receptor); as speed and difficulty of a movt increase, sensitivity of spindles increased
• What are Golgi tendon organs?
o Regulate muscle tension; located in muscle tendons; not innervated by gamma motor neurons
• What is the inverse myotatic reflex?
o Maintains tension in response to stretch; Ib afferents innervate interneurons that inhibit alpha motor neurons to the same muscle
What is reciprocal innervation in the inverse myotatic reflex?
o Ib afferents stimulate excitatory interneurons to contract antagonist muscle
• What is the flexor withdrawal/ crossed extension reflex?
o Pain afferent activity (sharp cut) -> interneurons and propriospinal neurons -> a motor neurons -> muscles that withdraw ipsilateral limb and extend contralateral limb
• What does the propriospinal system integrate?
o Intersegmental motor responses such as alternating movts of arms and legs during walking
• What does the propriospinal system mediate?
o The regulatory impact of upper limb cutaneous stimulation on lower limb motor reflexes
• Where is the physical location of propriospinal neurons?
o Interconnect spinal levels for complex actions and regulating reflexes
o Located in intermediate spinal grey matter; axons in peripheral border of the ventral horn
• What are the medial propriospinal neurons?
o Axons extend over whole spinal cord; regulate proximal/ axial muscles and full body posture
• What are lateral propriospinal neurons?
o Extend fewer spinal segments; regulate distal muscles for independent control of fine movts
• What are upper motor neurons involved in?
o Control posture, balance and movts; brain stem pathways maintain posture and balance; motor cortex pathways regulate fine movts in extremities
• What are the three tracts descending from the motor cortex?
o Corticospinal tracts to the ventral horn of spinal cord
o Corticonuclear tract to cranial nerve motor nuclei
o Corticoreticular tract to pontine and medullary reticular formation
• What are the 4 descending motor related tracts in white matter?
o Lateral corticospinal tract; anterior corticospinal tract; vestibulospinal; reticulospinal tracts
• What is the corticonuclear (corticobulbar) tract?
o Controls muscles of the face, head and neck; projects to the motor neurons of the cranial nerves
• What is the corticospinal (pyramidal) tact?
o Internal capsule- bundle of axons in cerebral hemispheres is a common site of strokes
o Cerebral peduncles in midbrain
o Pyramids in medulla: decussation forms lateral and ventral (anterior) corticospinal tracts
o Projects to alpha and gamma motor neurons in spinal cord
• What is the lateral corticospinal tract?
o 90% crossed in medulla descends in lateral funiculus; fine control movt; from large homuncular area of face, hands
• What is the ventral (anterior) corticospinal tract?
o 10% uncrossed, but descends bilaterally in ventral funiculus; posture of neck and trunk
• What is the significance of “pyramidal”?
o Named after medullary pyramid; distinct from extrapyramidal
• What are the extrapyramidal pathways?
o Vestibulospinal; reticulospinal; corticoreticular
• What is the vestibulospinal tract?
o Vestibulospinal nuclei in medulla relay head movt activity from semicircular duct, utricle and saccule receptors to spinal cord; activates extensors of lower limb and flexors of upper limb; maintain posture and balance
• What is the reticulospinal tract?
o Reticular nuclei in pons and medulla descend to motor neurons that project to proximal muscles of trunk, upper and lower limb
o Regulate muscle tone and sensitivity of flexor responses
o Integrate info to coordinate complex actions, such as orienting, stretching, and maintaining a complex posture
• What is the medial (anterior) reticulospinal tract (from pons, n. reticularis pontis)?
o Facilitate voluntary movts and increase muscle tone via the y-motor neurons; “anti-gravity” posture: extension of the lower limbs and flexion of the upper limbs
• What is the lateral reticulospinal tract (from medulla, n. reticularis gigantocellularis)?
o Inhibit voluntary actions and reduces tone
• What is the corticoreticular tract?
o Primary motor and premotor cortices project to pontine and medullary reticular formation
o Smoothes out general movts by limiting inhibition among extensor muscles of the lower limb
o Breaks up stereotypic patterns generated in the reticular formation
• What are motor neuron diseases?
o Include “paralysis” which means loss of muscle control; can be flaccid or spastic
• What is lower motor neuron disease?
o Lesion of alpha motor neurons interrupts neural input to the muscles; flaccid paralysis and atrophy of muscle, eg polio
• What is upper motor neuron disease?
o Spasticity and other conditions; spasticity involves active, but inappropriate, contraction of muscles (=spastic paralysis)
• How does stroke in motor cortices manifest (an upper motor neuron disease)?
o Disrupt descending control over CN and spinal motor neurons in two ways: disrupt lateral corticospinal tract, or cortical projection to reticular formation
• What does disruption of the lateral corticospinal tract cause in motor cortex stroke?
o Decrease in fine control of extremities
• What does disruption of cortical projection to reticular formation cause in motor cortex stroke?
o Spasticity; hypertonicity, clasp knife reflex and hyperreflexia (spindle sensitivity); antigravity posture due to loss of cortical control over reticulo- and vestibulospinal tracts
• What is Babinski sign?
o Stroking sole of foot elicits fanning of toes; normal sign in newborns, abnormal sign with stroke
• What are the three areas of the motor cortex? What do they do?
o Primary, supplementary, premotor cortex; sensory systems feed into prefrontal and premotor areas to establish motivation, intentions, plans, and specific activations of muscle groups to generate behavior
• What is the primary motor cortex?
o Encodes force, direction, extent and speed of movts
o Activates small groups of muscles for discrete movts
o Motor somatotopy in a homunculus similar to that of somatosensory cortex
o Somatotopy not fixed; a specific region can activate different sets of motor neurons depending on condition
• What are the motor association areas?
o Supplemental and premotor cortices; develop strategies for motor programs
• What do motor association areas do?
o Transform the intention to perform a complex motor act into the specific sequence of movts necessary to accomplish the act
• Where are motor programs of the motor association areas sent?
o To primary motor cortex where they are fractionated into individual muscle contractions or jt movts
• What does the supplementary motor cortex do?
o Ensures motor sequences independent of external conditions; involved in generating sequences of movts and to mental rehearsal of sequences of movts (PET scan)
• Which motor cortex is involved in the transformation of kinematic to dynamic information
o Supplementary
• What are dynamics and kinematics?
o Dynamics: the amount of force necessary to make a movement
o Kinematics: the distance and angles that define a particular movt in space (many movt plans are represented in kinematic terms (eg. Move the hand to the left)
• How must the motor system instruct the appropriate muscles to contract with the appropriate force?
o Must eventually translate this to a representation based on dynamics
• What does the premotor cortex do?
o Integrate spatial and sensory info as well as abstract rules in the planning and preparation of movt; sensitive to the behavioral context of a particular movt
• What do premotor neurons encode?
o Intention to perform a particular movt; involved in the selection of movts based on external or internal (memory) events
• What is broca’s area?
o Part of premotor cortex that controls motor preparation for speech
• What is activated on command to “imagine playing tennis’?
o Supplementary motor area
• What is activated on command to “imagine moving around the rooms of your house?”
o PPC, parahippocampal gyrus, and lateral PMC
• What is efference copy?
o In addition to receiving sensory input from posterior parietal and visual cortex, motor cortex sends “copies” of motor programs back to SS cortex (efference copy) to integrate with incoming sensory info to predict the expected sensation that will occur and assess present and future states of a limb in action
• What is self-awareness?
o Who am I? self-recognition; depends on the sense of agency and the sense of ownership
• What does self-recognition depend on?
o Partly on integration of intentions and sensory feedback as depicted in a “forward model”
• What is a forward model?
o Combines efference copy of ongoing motor commands (predicted sensory feedback), actual sensory feedback (visual and somatosensory) and an internal model of the dynamics of the arm to estimate the current state of the arm
• What is self-agency?
o The sense that you are the one who is causing or generating an action; generated when the efference copy of motor commands matches the subject’s intention
• What is self-ownership?
o The sense that you are the one who is undergoing an experience; generated when the sensory feedback correspond with these intentions
• What does the motor region have to manage self-other distinctions and hence social interactions?
o Two hierarchically organized, overlapping and interacting systems
o 1) preparation and execution of motor actions that are self-realized and voluntary
o 2) mirroring
• What are the action sequences of voluntary movements?
o solve a motor problems and involve intention, kinematics, musculoskeletal organization, goal-object identity, physical consequences of the action
• What does voluntary motor preparation and execution involve?
o Premotor, supplementary and sensori-motor cortex and parts of the inferior parietal cortex
• What is mirroring?
o Capturing and understanding the actions of self and others at a more involuntary level
o Cortical areas that are active with both observing an action and producing the action itself
o This involves not just motion, but the goal and intention of the action as well
• What are mirror neurons?
o Unify action perception and action execution; respond to both observed and executed actions; in “core mirror area”; Active whether performing or observing an action
• What areas make up the “core mirror area”?
o Inferior premotor cortex; inferior parietal cortex
• What are intransitive actions?
o Performed without an object, involve inferior parietal cortex
• What are transitive actions?
o Acted upon an object; involve both inferior parietal cortex and inferior premotor cortex
• How is mirroring of observed actions learned?
o Through social interactions
• What is required for precise emulation of actions by mirror systems?
o Because we all have varying histories of motor learning, requires general representations of the body common to both acting and observed agents
What can sensitize mirror neurons in premotor cortex?
Observation of action, such that even involuntary simulations of the actions are produced
• How are mirror neuron phenomena graded?
o In that their activity ranges from simple reproduction of the actions observed to activity underlying the goal of the actions; activity increases when the context of an observed action reveals intention
• What does mirror neuron activity often represent?
o Characterized by high sensitivity to observed action and often represents the goal of the action rather than the specific movements
• Where is the area showing only intention and not just action or context?
o Dorsal part of inferior prefrontal cortex (pars opercularis), where mirror activity has been repeatedly observed
• How is the cerebellum divided?
o Longitudinally into two large hemispheres separated by a central vermis
• What is unique about the cerebellar cortex?
o Forms folia overlying white matter (arbor vitae- Tree of Life) that connects to the pons via cerebellar peduncles
• What are the three major lobes of the cerebellum?
o Anterior, posterior, flocculomotor (most posterior
• What are the three layers of the cerebellar cortex?
o Have grid like circuitry; afferents, purkinje cells, interneurons
• What do afferents of the cerebellum do?
o Stimulate granule cells whose axons split and synapse onto dendrites of purkinje cells
• What do purkinje cells of cerebellar cortex do?
o Send info out to deep nuclei in the cerebellar white matter
• What do interneurons of the cerebellar cortex do?
o =basket and Golgi cells; generate programs to transform sensory patterns into motor coordinate systems
• Where do purkinje cells receive info from?
o Receive tactile and proprioceptive input from spinocerebellar tracts and inferior olive
o Project to deep cerebellar nuclei, located within the cerebellar white matter
• What are the deep cerebellar nuclei that purkinje fibers project to?
o Fastigial, interposed (globose and emboliform), dentate; deep nuclei project to thalamus-cortex
• What are some cerebellar functions?
o Motor; executive-cognitive; somato-visceral
• How are the motor functions of the cerebellum determined?
o Specificity of motor functions is determined by the different medial to lateral longitudinal cortical regions
• What are the cerebellar nuclei that each longitudinal zone projects t?
o Vestibulocerebellum- vestibular nuclei
o Spinocerebellum- fastigial and interposed nuclei
o Cerebrocerebellum- dentate nuclei
• What are 4 basic patterns of the cerebellar functions?
o Sensory input (esp tactile and proprioception) innervates granule cells in cerebellar cortex
o Local interneurons transform activity into meaningful response
o Purkinje cells transmit output to local deep cerebellar nuclei
o Nuclei send their info to thalamus and cortex
• What does the vestibulocerebellum do?
o Receives input from the vestibular system; projects to vestibular nuclei in medulla; controls posture, balance and eye movts
• How does vestibulocerebellum regulate head movts and eye-head coordination?
o Interconnects with vestibular and oculomotor nuclei
• What reflex does vestibulo-cerebellum enhance?
o VOR-vestibulo-ocular reflex
• Where does spinocerebellum project to?
o Vermis and intermediate areas of cerebellum project to fastigial and interposed nuclei; nuclei project to thalamus-cortex
• Where does spinocerebellum receive input from?
o Spinal cord (spinocerebellar tracts); cerebral cortex via pontine nuclei
• How does spinocerebellum provide feedback control of ongoing movts?
o It compares inputs from spinal cord and motor cortex to detect disparities between internal and external representations of world
• What happens as one moves through environment?
o Changes in both external conditions and proprioceptive activity require updating motor programs in the cerebral cortex
• How does cerebellum help adapt motor programs to changes in environmental conditions?
o Cerebellum produces predictive patterns on sensory states that adapt motor programs
• How does cerebellar cortex generate predictions?
o Based on the comparison of motor cortex programs (efference copy) with sensory input (limb position and velocity)
• What does the cerebellum send to the motor cortex?
o Corrected motor program that predict the future body state
• How are reflex oscillations dampened?
o Anticipatory signals from spinocerebellum to motor cortex reduce sensitivity of stretch reflexes; dampens unwanted oscillations
• What are the projections of the cerebrocerebellum?
o Cerebellar hemispheres project to dentate nuclei which in turn projects to thalamus-cortex
o Cerebral cortex (wide areas) project down to pontine nuclei which in turn project to cerebellar cortex
• What does the cerebro-cerebellum do?
o Designed to initiate voluntary movt by projecting anticipatory info to the motor cortex (feed forward control)
• What does the cerebro-cerebellum plan and program?
o Voluntary, learned and skillful movts
• What does continued communication b/w cerebellum and motor cortex allow for?
o Enables movts to become more rapid, precise and automatic with practice
• What do learned motor patterns enable the lateral cerebellar hemispheres to do?
o Predict the speed, force and direction of a limb prior to movt execution
• What is the main role of cerebro-cerebellum in voluntary movt?
o Planning and programming
• What is the main role of spino-cerebellum in voluntary movt?
o Execution
• What is dysmetria?
o Inability to control range of movt. Placement falls short of or extends beyond the initial goal, as in the finger to nose test
• What is decomposition of movt?
o Inability to correctly sequence fine, coordinated acts
• What is ataxia?
o Lack of smoothly coordinated movts. Combined result of dysmetria and decomposition of movts. Movts are imprecise, halting, awkward, and clumsy
• What is dysarthria?
o Inability to articulate words correctly, with slurring and inappropriate phrasing
• What is dysdiadochokinesia?
o Inability to perform rapid alternating movts
• What is hypotonia?
o Decreased muscle tone
• What is nystagmus?
o Involuntary, rapid oscillation of the eyeballs in a horizontal, vertical, or rotary direction
• What is scanning (measured) speech?
o Slow enunciation with a tendency to hesitate at the beginning of a word or syllable; it is ataxia of speech; articulation is uneven, words are slurred, and variations in pitch and loudness occur; rhythm changes are prominent
• What is a tremor?
o Rhythmic, alternating, oscillatory movt of a limb as it approaches a target (intention tremor) or of proximal musculature when fixed posture or weight bearing is attempted (postural tremor)
• What does alcohol affect (wither acute or long term)?
o Primarily prefrontal cortex (impulsivity, antisocial behavior), limbic system (loss of memory) and cerebellum (motor syndrome); DUII test for dysmetria and ataxia
• How is the cerebellum involved in cognitive processes?
o Subserves the timing processes and temporal regulation; including dampening oscillations and smoothing out performance
• What is the posterior part of cerebellum involvement in cognition?
o Lateral hemisphere and vermis involved in cognitive regulation
• How do cognitive patterns reach the cerebellar cortex?
o Prefrontal and association cortices project to the pons to be mapped onto the cerebellar cortex
• What part of cerebellum impacts the executive aspects of cognitive function?
o Posterior cerebellar connection with dorsolateral prefrontal cortex
• What are executive functions?
o Refer to ability to coordinate different cognitive tasks to obtain a certain goal
• What tasks are necessary to plan and direct goal-oriented behavior? When does cerebellum modulate these behavior?
o Mental flexibility, multitasking, problem solving and inhibition
o Involved in both motor (procedural) and non-motor types of learning
• What is dyslexia?
o Based on neuroanatomical imaging, different types of dyslexia have been associated with high or low volume of the right cerebellar vermis, caudate and putamen
o Cerebellar abnormality at birth leads to mild motor, articulation, phonological and reading disturbances
• What is autism?
o Low volumes of vermis seen in autism; high genetic determinacy and characterized by developmental retardation of cortical columns, inter cortical connections and various growth factors related to synaptic formation
• What is “dysmetria of thought?”
o Cerebellar dysfunction leads to impairment of the coordinating role in PFC and premotor functions
• What are the core features of cerebellar cognitive affective syndrome?
o Executive: disturbances of executive function (deficient planning, set shifting, abstract reasoning, working memory, decreased verbal fluency); impaired strategy formation and procedural learning
o Spatial: impaired spatial cognition (visual-spatial organization and memory)
o Affective: [personality change, flattening or blunting affect, inappropriate behavior; pathological laughing or crying
o Linguistic difficulties (dysprosodia, agrammatism, anomia)
• Where does cerebellar cortex project to for somato-visceral functions?
o Via all deep nuclei, to both brain stem (reticular formation, vestibular nuclei) and hypothalamus to regulate various visceral systems
• Overall what functions does cerebellum coordinate?
o Motor, behavioral plus visceral responses
• What are the visceral functions cerebellum regulates?
o GI (gastric and intestinal motility, feeding regulation); Cardiovascular (heart rate and blood pressure, baroreflex); Respiration; Micturition; Immune functions
• What are the direct effects of cerebellum on visceral functions?
o Largely hypothetical, but some clinical studies show specific actions; vermis dysfunctions can lead to bradycardia, respiratory alkalosis, and hyperventilation associated with gait ataxia
