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Midterm 2 Chapter Notes P1.pdf

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PSYC 211
Yogita Chudasama

Chapter 7: Audition & Chemosensory The Stimulus - Sounds are produced by objects that vibrate and set molecules of air into motion, producing waves, so that if the waves range between 30-20 000 times per second, it becomes audible - Sounds have three dimension: o Pitch: frequency of vibration, measured by hertz (Hz), or cycles per second o Loudness: function of intensity; the degree to which condensations and rarefactions differ from each other in vigour o Timbre: the complexity or the nature of the sound depending on the particular mixture of different frequencies Anatomy of the Ear - Sound is funnelled by the pinna, or the shell of the outer ear, to the tympanic membrane, also known as the eardrum - The malleus (hammer) connects with the tympanic membrane and transmits vibrations via the incus (anvil) and the stapes (stirrup) to the cochlea, which contains auditory transducing mechanisms o Oval window: an opening in the bone surrounding the cochlea that reveals a membrane, against which the baseplate of the stapes presses; transmits sound vibrations into the fluid within the cochlea o Round window: an opening in the bone surrounding the cochlea that allows the fluid inside the cochlea to move back and forth according to pressure changes Cochlea (fig. 7.4) o A coiled tubular structure, divided longitudinally into three sections: the scala vestibule, the scala media, and the scala tympani o The organ of Corti contains inner (numbering approximately 3500) and outer hair cells (≈12000) which are anchored by Deiter’s cells to the basilar membrane, which sits underneath the tectorial membrane o Projections from the hair cells, called cilia, pass through the reticular membrane and come to rest on the underside of the tectorial membrane  Sound waves cause movement of the basilar membrane and bending of the cilia, which produces action potentials in the hair cells  High frequencies affect primarily the end nearest the oval window (the base), and low frequencies affect primarily the end nearest the round window (the apex) Auditory Hair Cells and the Transduction of Auditory Information - Cilia: contain a core of acting filaments surrounded by myosin filaments and are linked adjacently by elastic tip links at the points of attachment known as insertional plaques - Hair cells form synapses with dendrites of bipolar neurons whose axons bring auditory information to the brain - Where movement of the outer hair cell cilia is caused by direct contact with the flexing tecticular membrane, and the inner hair cell cilia movement is caused by indirect inner ear fluid flow movement o Outer hair cells are known as effector cells, which influence the effects of sound vibrations on the inner hair cells o Movement toward the tallest cilium increases tension on the tip links which opens ion channels and increases the influx of K and Caions, causing depolarization; movement in the opposite direction prevents the opening of these channels Auditory Pathway Cochlear nerve – the branch of the auditory nerve that transmits auditory information from the cochlea to the brain; composed of the axons of bipolar neurons whose somas lie in the cochlear nerve ganglion, aka spiral ganglion - The dendritic ends respond with excitatory postsynaptic potentials triggered by the glutamate released by the hair cells, exciting the neuronal pathway that extends into the medulla - Axons enter the cochlear nucleus of the medulla where they synapse and subsequent neurons connect to the superior olivary complex From the medulla, axons travel by way of the lateral lemniscus to the inferior colliculus of the dorsal midbrain - - From the inferior colliculus axons travel to the medial geniculate nucleus of the thalamus, which sends its axons to the auditory cortex of the temporal lobe - A disproportion exists in the connections between the inner hair cells and the cochlear nerve axons, so that the inner hair cells, which amount to 29% of total hair cells, connect to 95% of the cochlear nerve o Studies show that the outer hair cells are just effector cells involved in influencing the effects of sound vibrations on inner hair cells - Olivocochlear bundle: efferent axons of the cochlear nerve begin at the superior olivary complex of the medulla and end at the auditory hair cells where they secrete acetoylcholine to inhibit hair cell potentials - Each brain hemisphere receives information from both ears but primarily processes contralaterally o Tonotopic representation: a topographically organized mapping of different frequencies of sound that are represented in a particular region on the brain Core region – the primary auditory cortex, located on a gyrus on the dorsal surface of the temporal lobe; consists of three regions which each receives a separate tonotopic map of auditory information Belt region – the first level of the auditory association cortex that surrounds the primary auditory cortex and consists of at least seven divisions Parabelt region – the second level of the auditory association cortex that surrounds the belt region (fig. 7.10) Two streams of the auditory cortex:  o Dorsal stream terminates in the posterior parietal cortex and is involved in sound localization o Ventral stream terminates in the parabelt region of the anterior temporal lobe and is involved in the analysis of complex sounds Perception of Pitch Place code (von Bekesy) – the system by which information about different frequencies is coded by different locations on the basilar membrane, so that the firing of particular axons in the cochlear nerve tells the brain about the presence of particular frequencies of sound A given frequency causes a large portion of the basilar membrane to be deformed, given that the subject is not alive and - well; otherwise place coding is very precisely localized - Contraction of the outer hair cells alters the mechanical characteristics of the basilar membrane, and by extension, the Response properties of the inner cells Cochlear implants: an electronic device surgically implanted in the inner ear that can enable a deaf person to hear by duplicating the place coding of pitch on the basilar membrane; most effective in young children Rate code (Kiang) – the system by which information about the lower frequencies is coded by the rate of firing of neurons in the auditory system synced to the movements of the apical end of the basilar membrane Perception of loudness - The softest sounds that can be detected appear to move the tip of the hair cells 1-100 picometres (one trillionth of a metre) - Loudness is informed by the different rates of firing by the axons of the cochlear nerve, where louder sounds produce more intense vibrations of the eardrum and the cilia, thereby releasing more neurotransmitters o In lower frequencies, it is believed that loudness is signalled by the number of axons arising from active neurons; vice versa occurs in cases of higher frequencies Perception of Timbre Fundamental frequency – the lowest, and usually most intense, frequency of a complex sound; most often perceived as a sound’s basic pitch Overtone – the frequency of complex tones that occurs at multiples of the fundamental frequency - Different portions of the basilar membrane respond to each of the overtones - The auditory cortex analyze a complex sequence of multiple frequencies that appear, change in amplitude, and disappear Perception of complex sounds - Recognition of complex sounds requires that the timing of changes in the components of the sounds be preserved all the way to the auditory cortex, achieved by rapid transmission by specialized neurons which enable strong EPSPs - Auditory cortex is also divided between two processing streams; the dorsal where and the ventral what o Damage to either of the streams will cause auditory agnosias (impairments of various aspects of auditory perception) - Physiological overlap between the visual and auditory processing regions in the brain aids individuals recognizing the nature of the origin of a sound by association Musical perception requires recognition of sequences of notes (i.e. the melody) their adherence to rules that govern - permissible pitches and harmony o Pitch is determined by the fundamental frequency and timbre is determined by the mixture of overtones - Pure tones are perceived in the primary auditory cortex, and recognition of complex pitch is done so by the auditory association cortex - Different brain regions are involved in different aspects of music perception; for example, the inferior frontal cortex is involved in recognition of harmony, the left auditory cortex involved in superimposed rhythmic patterns, the cerebellum and basal ganglia in timing, etc. - The volume of the primary auditory cortex of musicians are greater than those who aren’t, among other factors and measures - Amusia: loss or impairment of musical abilities, produced by hereditary factors or brain damage o Congenital cases appear to involve abnormalities of the right superior temporal gyrus and the right inferior frontal gyrus; related inversely in thickness to ability Perception of Complex Sounds: • Hearing has three primary functions: to detect sounds, to determine the location of their sources, and to recognize the identity of these sources • The axons in the cochlear nerve contain a constantly changing pattern of activity corresponding tot he constantly changing mixtures of frequencies that strike the eardrums. Somehow, the auditory system of the brain recognizes particular patterns that belong to particular sources, and those are perceived each independently Perception of Environmental Sounds and Their Location: • Identifying sound sources is one of pattern recognition • Perception of complex sounds appears to be accomplished by circuits of neurons in the auditory cortex • Recognition of complex sounds requires that the timing of changes in the components of the sounds be preserved all the way to the auditory cortex. Neurons that convey information to the auditory cortex contain special features that permit them to conduct this information rapidly and accurately. Their axons contain special low-threshold voltage-gated potassium channels that produce very short action potentials. Their terminal buttons are large and release large amounts of glutamate, and the postsynaptic membrane contains neurotransmitter-dependent ion channels that act unusually rapidly, producing very strong EPSPs • Neurons in the ‘what’ system discriminated between different monkey calls, while neurons in the ‘where’ system discriminate between locations of loudspeakers presenting these calls • The dorsal stream of both systems overlap in the parietal lobe so that we can use the convergence of sight and sound to recognize which of several objects in the environment is making a noise. In addition, we can learn the association between the sight of an object and the sounds it makes • Perception of the identity of sounds activated the ventral stream of the auditory cortex and perception of the location of sounds activated the dorsal stream Perception of Music: • Music consists of sounds of various pitches and timbres played in a particular sequence with an underlying rhythm. • Particular combinations of musical notes played simultaneously are perceived as consonant or dissonant, pleasant or unpleasant • Melodies played with one set of rules (the major mode) usually sound happy, while those played using another set of rules (the minor mode) generally sound sad • A melody is recognized by the relative intervals between its notes, not by their absolute value • Primary auditory cortex responds to pure tones of different frequencies but that recognition of the pitch of complex sounds is accomplished only by the auditory association cortex • Pitch discrimination takes place in a region of the superior temporal gyrus rostral • The cerebellum and basal ganglia are involved in timing of musical rhythms and timing of movements • 4% of the population exhibits congenital amusia, a severe and persistent deficit in musical ability (auditory cortex of the right superior temporal gyrus and the cortex of the right inferior frontal gyrus was thicker in people with congenital amusia) • Musical ability in general and congenital amusia have a genetic basis Somatosenses Cutaneous sense – one of the somatosenses; includes sensitivity to stimuli that involve the skin Proprioception – perception of the body’s position and posture Kinesthesia – perception of the body’s own movements Organic sense – a sense of modality that arises from receptors located within the inner organs of the body The Stimuli - Pressure Caused by mechanical deformations of the skin o Vibration is used as a judge of roughness o Pain is an indication of tissue damage o Kinesthesia by muscle receptors in stretch and tension Anatomy of the Skin and its Receptive Organs - Skin consists of subcutaneous tissue, dermis, and epidermis Hairy skin: - Free (unencapsulated) nerve endings are found interwoven around the bases of hair follicles and around the emergence of hair shafts in order to detect hair movement; also located just under the surface of the skin to detect changes in temperature and pain - Ruffini corpuscles: slow response receptors with large diffuse borders that respond to indentations of the skin - Pacinian corpuscles: specialized, encapsulated nerve endings that detect mechanical stimuli such as vibrations; the largest sensory end organs consisting of up to 70 onion-like layers wrapped around the dendrite of a single myelinated axon; rapid adaptation with large diffuse borders Glabrous skin (skin that does not contain hairs and is more active in touch/use/contact) in addition to what is found under hairy skin: - - Meissner’s corpuscles: located in the papillae that project up into the epidermis, enervated by two to six axons; rapid adaptation to objects with small, sharp borders and in vibrations and taps - Merkel’s disks: also found in the papillae of glabrous skin at the base of the epidermis adjacent to sweat ducts; responds slowly to objects with small sharp borders Perception of Cutaneous Stimulation ▯ Touch Movement on skin causes ion channels to open; influx and efflux of ions in the dendrite results in action potential - transmission by small-diameter unmyelinated axons in cases of sensitive touches and temperature, otherwise transmission occurs by fast-conducting myelinated axons - movement between skin and object is needed for information to be conveyed about the object, such as shape, mass, texture, etc; therefore the somatosenses work dynamically with the motor system to manipulate the objects - prolonged repetitive tactile experience also shapes the relevant brain structures involved (e.g. violinists) Temperature perceptions of temperature is relative across the skin, depending on previous thermal stimulation experience in the area - o increases in temperature lower the sensitivity of warmth receptors and raise the sensitivity of cold receptors; and vice versa for decreases in temperature - cold sensors are located just beneath the epidermis, and warmth sensors are located more deeply in the skin (table 7.2) o warmth sensors activated by six known thermoreceptors from the transient receptor potential (TRP) family: TRPV2, TRPV1, TRPV3, TRPV4, TRPM8, TRPA1 Pain - pain perception is accomplished by networks of free nerve endings in the skin in at least three different types of receptors o high threshold mechanoreceptors are free nerve endings that respond to intense pressure o second category mechanoreceptors respond to extremes of heat, acids, and capsaicin and contains TRPV1 receptors o TRPA1 receptors are the third category and react to pungent irritants in foods and the environment that cause inflammation▯ Itch - skin irritation that elicits the desire/reflex to scratch, caused by chemicals such as histamine - pain and itching are mutually inhibitory, although certain drugs to treat one are causes of the other Somatosensory Pathways - axons that convey precisely localized information - axons that convey poor localized information (i.e. (i.e. touch, kinesthesia): pain, temperature): neurons in the dorsal root ganglion neurons in the dorsal root ganglion ↓ ↓ dorsal columns of white matter synapses formed in the spinal cord ↓ ↓ nuclei in lower medulla contralateral spinothalamic tract ↓ ↓ medial lemniscus in midbrain ventral posterior nuclei of the thalamus ↓ ↓ ventral posterior nuclei of the thalamus primary somatosensory cortex ↓ ↓ primary somatosensory cortex secondary somatosensory cortex ↓ secondary somatosensory cortex - in the somatosensory cortex, cortical columns contain neurons that respond to a particular type of stimulus applied to a particular part of the body - primary and secondary somatosensory cortical areas are said to be divided into five to ten different maps of the body surface with areas within responding to a different submodality of somatosensory receptors - tactile agnosia results from damage to the somatosensory association cortex Perception of Pain - contains three components in essence: sensory perception, the emotional consequences (i.e. the degree of bother caused by the pain) and longer term emotion implication of chronic pain; each involving a different brain mechanism o the purely sensory component of pain is mediated by a pathway from the spinal cord to the ventral posterolateral thalamus to the primary and secondary somatosensory cortex o the immediate emotional component of pain appears to be mediated by pathways that reach the anterior cingulate cortex (ACC) and insular cortex in recognizing the harm value  studies have shown that the perceived unpleasantness of pain is reflected in changes in activation of the ACC; including under circumstances of imagined experience and empathized experience o the longer term emotional component appears to be mediated by pathways that reach the prefrontal cortex, involved in planning and recognizing personal significance  damage to this area shows disconcern for implications of chronic conditions for the future - mutations of the gene for a particular voltage-dependent sodium channxl, Na 1.7, produce total insensitivity to pain - phantom limbs are explained by cut ends of proximal portions of axons forming nodules known as neuromas; as well as being the biological program of self-awareness in the parietal lobe Analgesia - electrical stimulation of particularly the periaqueductal grey matter and the rostroventral medulla can cause analgesia by releasing certain endogenous opioids - opiate-induced analgesia is mediated through the above mentioned areas to the raphe magnus of the medulla, whose serotonergic neurons send axons to the dorsal horn of the spinal cord grey matter which then inhibits pain transmission to the brain - periaqueductal grey matter connections to the frontal cortex, amygdala, and hypothalamus enable learning and responsiveness to pain - analgesia is biologically significant by enabling the continuation of potentially painful activities necessary for survival; e.g. fighting and copulation - placebo effects of analgesia are caused by the release of endogeneous opiates through connections between the prefrontal cortex and the periaqueductal grey matter - learning to increase/decrease the activity of the ACC corresponds to an increase/decrease also in a person’s sensitivity to pain Chapter 8: Control of Movement Organization of Motor Cortex -The primary motor cortex (on precentral gyrus) causes movements of particular parts of body-it has a somatopic organization). It can be represented by a motor homunculus (but has more cortical area for fingers and speech). -Complex neural circuitry is located between individual neurons in primary motor cortex & the motor neurons of spinal cord (causes motor units to contract) -commands for movement are modified by basal ganglia and cerebellum -stimulation of different zones of the motor cortex caused different categories of action -principal cortical input to primary motor cortex is the frontal association cortex (it is rostal to it) -The supplementary motor area and the premotor cortex are adjacent to the primary motor cortex, they’re important for the control of movement, both receive sensory information from parietal and temporal lobes, and both send efferent axons to the primary motor cortex. -primary motor cortex also receives info from the adjacent primary somatosensory cortex-their connection are specific: neurons in the primary somatosensory cortex that respond to stimuli applied to a particular part of the body send axons to neurons in the primary motor cortex that move muscles in the same part of brain. Cortical Control of Movement: The Descending Pathways -Neurons in primary motor cortex control movements by the lateral group and the ventromedial group. -Lateral group consists of corticospinal tract, corticobulbar tract and the rebrospinal tract. The system mostly control independent limb movements (especially hands/fingers).Independent limb movement means 1 limb moves while the other remains still. Corticospinal Tract • Cortiscospinal tract: has axons of cortical neurons that terminate in gray matter of spinal cord • The largest concentration of cell bodies for these axons are in the primary motor cortex (but some are also in parietal/ temporal lobes). • Axons leave cortex and travel through subcortical white matter to the ventral midbrain (enter the cerebral peduncles). Then they form the pyramidal tracts (portion of the corticospinal tract on the ventral border of medulla). At caudal medulla, some fibres cross over, descend through contralateral spinal cord and form the lateral corticospinal tract. The rest of fibres descend through ipsilateral spinal cord and form the ventral corticospinal tract (part of ventromedial group). • Axons in lateral corticospinal tract originate in region of primary motor cortex and supplementary motor area- control distal parts of limbs (arms, hands, fingers, lower legs, feet, toes). Form synapses with motor neurons in gray matter of spinal cord which control movement of distal limbs. • Corticospinal pathway controls hand/finger movement, important for moving fingers independently Corticobulbar Tract • Projects to medulla (can be called bulb) • This pathway terminates in the motor nuclei of 5 ,7 ,9 ,10 ,11 ,12 cranial nerves. These nerves control movements of face, neck, tongue and parts of extraoccular eye muscles. Rubrospinal Tract • It originates in red nucleus (nucleus rubber) of midbrain • Red nucleus receives inputs from motor cortex via corticorubral tract and from cerebellum • Axons of rubrospinal tracts terminate on motor neurons in the spinal cord that control independent movements of forearms and hands (independent of trunk, don’t control fingers either). -The ventromedial group consists of vestibulospinal tract, tectospinal tract, reticulospinal tract and ventral corticospinal tract. They control motor neurons in the ventromedial part of the spinal cord gray matter. They control automatic movement: example-posture and locomotion. Control movements of trunk and proximal muscles. Receive input from premotor cortex, & subcortical regions (amygdala, hypothalamus, basal ganglia). • Axons of ventral corticospinal tract originate in upper leg and trunk regions of primary motor cortex • Axons descend to appropriate region of spinal cord and divide, sending terminal buttons into both sides of gray matter • They control motor neurons that move the muscles of upper legs and trunks • Cell bodies of neurons located in vestibular nuclei • tectospinal tract: cell bodies in superior colliculus, involved in coordinating head/trunk/eye movements. • Reticulospinal tract: cell bodies in nuclei of brain stem and midbrain reticular formation-control automatic function (respiration, coughing, Etc) and neocortical control behaviour(walking). Planning and Initiating Movements: Role of motor association cortex -supplementary motor area+ premotor area plan movements & execute plans through connections with primary motor cortex (even imagining movements activate these regions). Get info from parietal and temporal cortex. Review of chap6: visual association cortex has 2 streams: ventral (what pathway-temporal lobe) for recognition and dorsal (where-parietal lobe… also organizes visually guided behavior “how pathway”). Parietal lobe gets info about spatial location, important for locomotion and arm/hand movement. -motor association cortex also for imitating behavior -posterior association cortex for perceptions/memories -frontal association cortex for plans of movements Supplementary Motor Area (SMA) -involved in learning/performing behavior with sequences of movement -damage to this area: can impair very simple and well-learnt sequences -neurons show little activity with visual cue stimuli, but very activated when performing sequences -neurons can be specific to certain parts of the sequences -even with inactivation of the supplementary motor area in monkeys with drug that stimulates GABA receptors and inhibits neural activity, monkeys can reach for object but CANNOT perform a sequence of 3 behaviors previously learnt. Same case with humans. -SMA involved in planning the elements that are yet to come in sequences of movement -execution of movement probably controlled by primary motor cortex -anterior to SMA is pre-SMA which seems to control spontaneous movements and perception of control, SMA and pre-SMA (frontal lobes) stimulation can make one want to perform movements, whereas stimulation of motor cortex can cause movement without causing a DESIRE for movement -pre-SMA can be active before people make spontaneous movement, so neural activity for decision to move begins before a person is even AWARE of making that decision -SMA’s most important input from parietal lobes: lesions to parietal lobe can make people start a movement (and actually know when they started the movement), while these people have no idea if they had an intention of making that movement before it occurred. -maybe prefrontal cortex disrupt people’s plans of voluntary movements, so if lesions there, patients can react to events while showing deficit in initiating that behaviour Premotor cortex -to imitate/understand and predict others’ responses -involved in learning/executing complex movements guided by sensory info -uses arbitrary stimuli to indicate what movements should be made, which are informations that aren’t directly related to the movements they signal. Ex: associations between stimuli and the movements they designate are arbitrary and need to be learnt -inactivating premotor cortex with injections of muscimol, ONLY nonarbitrary movements could be done (for monkeys). Similar situation with people who have damaged premotor cortex. Imitating and Comprehending Movements: Role of the Mirror Neuron System -neurons in area F5 (area of the rostral part of the ventral premotor cortex in the monkey brain) responded to sight or execution of particular movements. -these are mirror neurons and they are located in the ventral premotor cortex (connected to inferior parietal lobule-the IPL) -help imitation -humans have mirror neurons in inferior parietal lobule and in the ventral premotor area, they are the most activated when one watches a behaviour at which he is expert -mirror neurons can even be activated with the sound of familiar action, individual neurons (AUDIOVISUAL neurons) responded to sounds of particular actions and to their sight -audiovisual neurons connect quickly, and even if a behaviour is recently and newly learnt, these neurons can be activated just by hearing that behaviour -even by watching a silent video of a piano being played- mirror neurons/visual cortex and the auditory system were all activated. -so mirror neurons can help one understand behaviour of others, - we understand action because the motor representation of that action is activated in our brain, so it is as if neural circuits “resonate” to what we see/hear -helps understand recognition of actions -we even imitate facial expressions of others. Smiles are contagious for real  -mirror neurons can help understand others’ intentions Control of Reaching and Grasping -reaching controlled by vision (dorsal stream=location). -when you make a reaching movement or point- parietal reach region is activated -parietal cortex gives location of movement, & gives info about location to motor mechanism in frontal cortex - the anterior part of the intraparietal sulcus (aIPS) controls hand/finger movements in grasping target object -aIPS is really important for grasping, even stimulation of hand area of primary motor cortex and other parts of parietal lobes aren’t as good -aIPS’s visual input from Dorsal stream of visual system, so aIPS involved in recognition and execution of grasping -info about object activated ventral stream and info about shape of hand activated aIPS Deficits of Skilled Movements: The Apraxias -Apraxia: damage to frontal or parietal cortex on the left side of brain -apraxia means “without action”, but it differs from paralysis to weaknesses -apraxia: inability to imitate movements or to produce them even with verbal instructions. LIMB apraxia: problem with movements of arms/hands/fingers -movement of wrong part of limb/incorrect movement of correct part/correct movement but in incorrect sequences -at times, when we will ask patients to pretend they have a certain object and to act out according to that object, the patients won’t be able to do so accurately. Example: pretending the finger is the brush instead of pretending to hold a brush in your hand while acting out a scene of “brushing my teeth” -damaged left hemisphere causes apraxia because left is involved with one’s own body, left parietal lobe organizes movements that one would make in response to what one has seen (while the right hemisphere is more involved in extrapersonal space) - frontal lobe seems more important than parietal for recognizing meaning of hand gestures. So damage to the inferior forntal gyrus (but not the parietal cortex) can show deficit in comprehension of gestures CONSTRUCTIONAL apraxia: -difficulty in drawing/constructing objects, trouble with assembling objects from elements (toy building blocks) -lesions in right hemisphere, right parietal lobe -hard for ppl to perceive/imagine geometrical relations, so hard to draw lines/angles (NOT cause of difficulty controlling arms/hands) -trouble with spatial perceptions. Ex: using a map The Basal Ganglia -important for motor system -motor nuclei of basal ganglia: caudate nucleus, putamen, globus pallidus -receives input from cerebral cortex, especially primary motor cortex/primary somatosensory cortex and the substantia nigra -Primary output: primary motor cortex, supplementary motor area and premotor cortex (via thalamus) and motor nuclei of brain stem that contribute to the ventromedial pathways. -frontal, parietal and temporal cortex send axons to the caudate nucleus and the putamen, which then connect with the globus pallidus. -globus pallidus sends info back to the motor cortex via the ventral anterior and ventrolateral nuclei of the thalamus -so basal ganglia can monitor somatosensory info and is informed of movements being planned and executed by the motor cortex -info is presented somatotopically (projections from neurons in motor cortex that cause movements in particular parts of body project to particular parts of putamen-this is like this all the way to the motor cortex). -input to basal ganglia from substantia nigra of midbrain is also important 1. complexities of cortical-based ganglia loop -links in loops are made by excitatory (glutamate secreting neurons) and inhibitory (GABA secreting neurons_ -caudate nucleus and putamen receive excitatory input from cerebral cortex -inhibitory axons sent to external and internal divisions of the globus pallidus (GPi and GPe). -Pathway for GPi known as direct pathway (neurons in send inhibitory axons to ventral anterior and ventrolateral thalamus which are VA/VL thalamus), which send excitatory projections to the motor cortex) -net effect of loop is excitatory cause contains 2 inhibitory links -so excitatory input to caudate nucleus and putamen causes these tructures to inhibit neurons in the GPi. This inhibition removes inhibitory effect of connections between GPi on the VA/VL thalamus, so VA/VL become more excited, and this excitation is passed on to motor cortex. -Pathway of GPe is the INDIRECT pathway. Neurons in GPe send inhibitory input to the subthalamic nucleus, which sends excitatory input to the GPi. This loop has an inhibitory effect on thalamus and frontal cortex. -Global pallidus also sends axons to various motor nuclei in the brain stem that contribute to the ventromedial system Parkinson’s Disease -symptoms: muscular rigidity, slowness of movement, resting tremor, postural instability, can’t easily pace back and forth across a room, movements start with delay, individual components of movement not well coordinated, postural movements are impaired -also produces a resting tremor: vibratory movements of the arms/hands that diminish somewhat when the individual makes postural movements -normal movements need balance between direct (excitatory) and indirect (inhibitory) pathway -caudate nucleus and putamen consist of 2 diff zones which receive input from dopaminergic neurons of the substantia nigra -one zone contains D1 dopamine receptors (produce excitatory effect),where neurons send axons to GPi -the other zone contains neurons with D2 receptors, so inhibitory effects, which send axons to GPe- circuit has excitatory effect on behavior. -the 2ndcircuit begins with an inhibitory input to the caudate nucleus and putamen, and goes through 4 inhibitory synapses in the following pathway: substantia nigra>caudate/putamen>GPe>substantia nucleus>GPi> VA/VL thalamus, so this pathway is also excitatory and so dopaminergic input to caudate nucleus and putamen facilitate movements. -GPi also sends axons to ventromedial system -treatment for Parkinson: L-DOPA (precursor of dopamine) -when an increased amount of L-DOPA is present, the remaining of nigrostriatal dopaminergic neurons will produce and release more dopamine in Parkinson;s patient -but dose of L-DOPA can cause dyskinesias and dystonias (involuntary movements), and L-DOPA is not the perfect cure Huntington’s Disease: -caused by degeneration of caudate nucleus and putamen, especially of GABAergic and acetylcholinergic neurons -causes uncontrollable jerky movements, can cause death -starts at 30s or 40s, but can begin at early 20s -first signs of neural degeneration in caudal nucleus and putamen -The loss of inhibition provided by GABAsecreting neurons increases the activity of the GPe, which then inhibits the subthalamic nucleus---so activity level of GPi decreases and excessive movements occur -patient can due of immobility cayse no more neurons in putamen and caudaus nucleus -it’s hereditary (dominant gene on chromosome 4) and has no treatment -gene has repeated sequence with an elongated stretch of glutamine The Cerebellum: -important for motor system, has more neurons than cerebral cortex -damage causes uncoordinated movements -looks like a cerebrum in miniature -medial part of cerebellum is phylogenetically older than lateral part, so it controls ventromedial system -The flocculonodular lobe receives input from vestibular system and projects axons to vestibular nucleus (involved in posture reflex) -the vermis (worm) in midline receives auditory and visual info from tectum and cutaneuous and kinesthetic info
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