VBMS 212 Neurology Quiz 2 Flashcards

dorsal root
Terms Definitions
PERIPHERAL SENSORY FUNCTION
Enteroception- nociception- deep receptors- superficial receptorsProprioception- conscious- unconscious
NOCICEPTORS
Pain and Noxious StimuliRespond to potentially tissue damaging stimuli- Thermal- Mechanical- InflamatoryBare Nerve EndingsCell Body in Dorsal Root or Cranial GangliaPrimary Afferent axons are small with little or no myelination tf slowHigh Threshold ie not sensitive
THREE ACTIONS OF NOCICEPTORS
Direct Activation via cold or heat, Mechanical Damage, Chemical DamageDamage of surrounding tissue causes release of cellular contents (ie Histamine, Bradykinins etc) generating further stimulationOnce activated the receptor RELEASES Glutamate and Substance P, amplifiying inflamation and vasodilation
MINIMUM NUMBER OF NEURONS IN ENTEROCEPTION PATHWAYS
3
FOUR ENTEROCEPTION PATHWAYS KNOWN IN CATS AND DOGS AND PRESUMED IN OTHER VETERINARY SPECIES
Dorsal FunicularSpinothalamicSpinoreticularSpinocervical
FUNKY FACTS ABOUTDORSAL FUNICULAR PATHWAY
aka LemniscalPeripheral Sensory Enteroception3 NeuronsPrimary Sensory Afferents DIRECTLY enter dorsal funiculus via dorsal rootFasciculus Gracilis carries axons from Caudal regions and Hind LimbsFasiculus Cuneatus carries axons from Cranial regions and Fore LimbsPrimary sensory afferents synapse on Nuclei Gracilus and Cuneatus in caudal portion of MedullaAxons from Nuclei Gracilus and Cuneatus DECUSSATE and travel in the Contra Lateral MEDIAL LEMNISUCUS where they synapse on nuclei in the Rostral thalamusAxons from the nuclei in the thalamus travel to the SOMATO SENSORY CORTEX
FASICULUS GRACILUS
Medial Portion of Dorsal FuniculusCarries primary sensory afferents from caudal regions and hind limbs for- enteroception- Conscious Proprioception
FASICULUS CUNEATUS
Lateral Portion of Dorsal FuniculusCarries primary sensory afferents from cranial regions and fore limbs for- enteroception- Conscious Proprioception
SOMATOTOPIC ARRANGEMENT
Adjacent areas of the body are represented by axons which run adjacent to each other
SIZZILING SENSATIONS ABOUTSPINOTHALAMIC PATHWAY
Peripheral Sensory Enteroception3 NeuronsPrimary sensory afferents enter dorsal horn via dorsal root and SYNAPSE on nuclei of afferent interneuronsAxons of afferent interneurons cross Grey Commissure and travel in the CONTA LATERAL LATERAL FUNICULUSInterneurons synapse in the ThalamusAxons from the nuclei in the thalamus travel to the SOMATO SENSORY CORTEX
ROUSING REVELATIONS ABOUTSPINORETICULAR PATHWAY
Peripheral Sensory Enteroception3 OR 4 NeuronsPrimary sensory afferents enter dorsal horn via dorsal root and SYNAPSE on nuclei of afferent interneuronsAxons of afferent interneurons cross Grey Commissure and travel in the CONTA LATERAL LATERAL FUNICULUSInterneurons synapse in the Thalamus AND ALSO have COLATERAL neurons which synapse in various regions of brain stem.Axons from neurons (the 4th neurons) in the various regions in the brain stem synapse in the thalamus Axons from the nuclei in the thalamus travel to the SOMATO SENSORY CORTEX
CURIOSITIES ABOUTSPINOCERVICAL PATHWAY
Peripheral Sensory Enteroception4 OR 5 NeuronsPrimary sensory afferents enter dorsal horn via dorsal root and SYNAPSE on nuclei of afferent interneuronsAxons of afferent interneurons travel in the IPSO LATERAL LATERAL FUNICULUSAxons from the distal afferent interneurons synapse on LATERAL CERVICAL NUCLEI in the C1 - C2 spinal segments.Axons from the LATERAL CERVICAL NUCLEI decussate in the MEDIAL LEMNISCUS and then travel contralaterally to synapse in the Thalamus AND ALSO have COLATERAL neurons which synapse in various regions of brain stem.Axons from neurons (the 5th neurons) in the various regions in the brain stem synapse in the thalamus Axons from the nuclei in the thalamus travel to the SOMATO SENSORY CORTEX
NASTY NOTIONSNOCICEPTION PATHWAY
Peripheral Sensory EnteroceptionMinimum 3 NeuronsPrimary sensory afferents enter dorsal horn via dorsal root and SYNAPSE on nuclei of afferent interneuronsSensory Afferents travel via- Spinothalamic Pathway and Bilateral (decusation) PathwayMultiple multisynaptic bilateral pathways are SLOWER but more ROBUST tf absence of response to Deep Pain Stimulus indicates a severe lesion.
SOMATOSENSORY CORTEX
Receives Enteroceptic Sensory AfferentsLocated in ventral rostral region of cerebral cortexRequired for- conscious perception of pain- localization of pain- pain related learning
NOCICEPTIONBRAIN STEM
Nociceptive information reaching Pons or Medulla is important for changing STATE OF AROUSAL
NOCICEPTIONMID BRAIN
Nociceptive information that reaches midbrain is transferred to structures of LIMBIC SYSTEM that are responsible for EMOTIONAL response to pain
NOCICEPTIONHYPOTHALAMUS
Cardiovascular and neural hormonal responses to pain
NOCICEPTIONSPINAL COLUMN - DORSAL HORN
Nociception afferent interneuron receives:- stimulation from nociceptor primary afferent both directly and via inhibition of inhibitory interneurons- inhibition and stimulation from non nociceptor primary sensory afferents- inhibition and stimulation from descending brain neurons- tf high level of control
GATE THEORY OF PAIN
Gating of nonnociceptive inputs blocks transmission of nociceptive transmission to brain at level of dorsal horn neuronsie pressure sensing neurons can have a net stimulatory effect on nociception inhibitory neurons in short term tf rub to alleviate painORlong term noxious stimulation (ie inflamation) creates hypersensitivity in Dorsal Horn Nociceptor Afferent Interneuron. As a result low levels of stimulation from non nociceptor primary sensory afferents result in net stimulation of nociception afferents tf sensitivity to pressure around wound
NEUROPATHIC PAIN
No source in peripheryDorsal Horn:- spontaneously hyperexcited- or remains hyperexcited after stimulationDifficult to controlCommon in spinal cord injurytf, in addition to general aneshtetics, use local anesthetics in dorsal horn when AMPUTATING
MIDBRAIN MODULATION OF PAIN
Periaquaductal Grey Matter- area around mesodermal aqueductNeurons in Periaqueductal Grey Matter INHIBIT activity in DORSAL HORN neuronsResponsive to OPTIATESStimulated by intense activities ie fighting
TWO OTHER AREAS OF PAIN MODULATION
Synapses in Pons and MedullaDorsal Horn Neurons- receptors for Opiods and NE inhibit tf use opiods or alpha agonists (xylazine) for epidurals
PROPRIOCEPTION
Spatial awareness of musculoskeletal systemsense of location and motion of all body segementsConscious - pathways end in Cerebral CortexUnconscious - pathways end in Cerebellum
PROPRIOCEPTIVE RECPTORSTHREE LITTLE PIGGIES
Muscle Spindles- length of muscles- speed of change of muscle length- Ia axons largest and fastestGolgi Tendon Organ- force in muscle- Ib axons large but not largest diameterStretch Receptors- joint Capsules- skin over joints- αβ axons mid size diameterSensor afferents that conduct information from prorioception receptors are amoungst largest in body
CONSCIOUS PROPRIOCEPTION PATHWAY
Primary sensory afferents DIRECTLY enter dorsal funiculusCaudal and hind limb afferents travel in Ipsolateral Funiculus GracilisCranial and fore limb afferents travel in Ipsolateral Funiculus CuneatusPrimary sensory afferents synapse on nuclei gracili and cuneati in Caudal MedullaAxons from nuclei Gracili and Cuneati decussate and travel in Contralateral Medial Lemniscus and synapse in Thalamus.Axons from nuclei in thalamus travel to Somatosensory Cortex
UNCONSCIOUS PROPRIOCEPTION PATHWAYCAUDAL AND HINDLIMBS
Primary Sensory afferents enter the dorsal horn and synapse in the dorsal grey columnsAxons from nuclei in the dorsal grey columns then ascend via two tracts:DORSAL SPINOCEREBELLAR TRACT- Ipsolateral in the Dorsal Spinocerebellar Tract of the Lateral Funiculus to the Cerebellum via the Caudal Cerebellar Peduncle.VENTRAL SPINOCEREBELLAR TRACT- Contralateral in the Ventral Spinocerebellar Tract of the (contralateral) Lateral Funiculus to the Cerebellum via the Rostral Cerebellar Peduncle.
UNCONSCIOUS PROPRIOCEPTION PATHWAYCRANIAL AND HINDLIMBS
Primary Sensory afferents enter the dorsal horn and synapse AS WELL AS BRANCH in the dorsal grey columnsCUNEOCEREBELLAR TRACT- a branch of the primary sensory afferent directly enters the lateral most part of the Ipsolateral Funiculus Cuneatus and synapse in the LATERAL CUNEATE NUCLEUS in the medulla. Axons from neurons in the Lateral Cuneate Nucleus decussate and travel through the Caudal Cerebellar Peduncle to the Cerebellum.ROSTRAL SPINOCEREBELLAR TRACT- axons from nuclei in the dorsal grey columns then ascend ipsolateral in the Rostral Spinocerebellar Tract of the Lateral Funiculus to the Cerebellum.
BRAIN BASICSTELENCEPHALONDIENCEPHALONMESENCEPHALONMETENCEPHALONMYELENCEPHALON
Cerebrum- cerebral cortex- subcortical structures- Lateral VentriclesThe Thalamus Family- epithalamus- thalamus- hypothalamus- third ventricleMesencephalon- mesencephallic aqueductMetencephalon- pons- cerebellum- fourth ventricleMedulla- fourth ventricle as well
MIDBRAIN
Cerebral Peduncles- ventral portion- rostral caudal fibres- axons of Upper Motor Neurons- axons of Lower Motor NeuronsTementumTectum- Dorsally Located Colliculi- Rostral Colliculi coordination of Visual Reflexes- Caudal Colliculi coordination of auditory reflexesCranial Nerve III- Oculomotor Nerve- lower motor neurons- enervates Extrinsic Eye MusclesCranial Nerve IV- Trochlear Nerve- also enervates extrinsic eye muscles- thin
DIENCEPHALON
Epithalamus (Pineal Gland)HypothalamusThalamusCranial Nerve II- Optic Nerve
PONS
Fibres of Pons- lateral structure contains fibres which travel to cerebellumCranial Nerve V- Trigeminal Nerve- lower motor neurons- enervate muscles of mastication tf BIGCranial Nerve VI- Abducens Nerve- Lower Motor Neurons to extrinsic muscles of eye
MEDULLA
Nuclei CuneatusNuclei GracilisPyramids- contain Upper Motor Neurons ONLYCranial Nerve VII- Facial Nerve- Lower Motor Neurons to facial muscles- efferents to salivary and lacrimal glands- afferents for taste- Rostral MedullaCranial Nerve VIII- Vestibulocochlear Nerve- afferents from internal earCranial Nerve IX- Glossopharyngeal- Efferents/Afferents Pharynx- Afferents Taste- Autonomic Salivary GlandsCranial Nerve X- Vagus- Efferent/Afferents larynx, pharynx and visceraCranial Nerve XII- Hypoglossal- Lower Motor Neurons- enervates tongue
FOUR CRANIAL NERVES THAT HAVE CLINICAL RELEVANCE
III - MidbrainV - PonsVII - Rostral MedullaXII - Caudal MedullaClincially interesting for signs of Lower Motor Neuron Damage
CERVICAL SPINAL CORD
Cranial Nerve XI- Spinal Accessory Nerve- Lower Motor Neurons- enervates certain neck and thoracic limb muscles
RETICULAR FORMATION
All the matter of the brain stem less the muclei associated with cranial nervesBasically the brain stem is a big mess of neurons with extensive and complicated connections
FOUR FUNCTIONS OFRETICULAR FORMATION
Behavioral ArousalMotor ControlModulation of Pain SensationCoordination of Some Autonomic Functions- Respiratory Control- Cardiovascular Control- Vomition
RETICULAR FORMATIONBEHAVIOURAL AROUSAL
Ascending Reticular Activating System- required for maintenance of CONSCIOUSNESS ie powers up cerebral cortex- lesions in brain stem have potential to alter level of conciousnessAll inputs of cranial nerves I, II, V and VIII synapse in reticular formationNeurons in reticular formation synapse int the Thalamus which sends many neurons throughout the cerebral cortex resulting in DIFFUSE DISTRIBUTION
RETICULAR FORMATIONMOTOR CONTROL
Some Upper Motor Neurons are present in Reticular Formation
RETICULAR FORMATIONMODULATION OF PAIN SENSATION
Periaquaductal Grey matter resides in Reticular FormationNeurons with opiate receptors synapse in other regions of Reticular Formation. These neurons send axons to spinal cord which inhibit Dorsal Horn Neurons associated with pain
RETICULAR FORMATIONRESPIRATORY CONTROL
Maintains normal levels of CO2 and O2 via alveolar ventalation- respiration rate- respiration depthInputs- CO2, pH, O2 ReceptorsOutputs- motor neurons that enervate respiratory musclesPRE BOTZINGER COMPLEX- source of respiratory rhythm- located in MEDULLADORSAL RESPIRATORY GROUP- enervates Inspiratory neurons ONLY- located in Dorsal MEDULLAVENTRAL RESPIRATORY GROUP- enervates inspriatory and expiratory neurons- located in VENTRAL MEDULLAPONTINE RESPIRATORY GROUP- acts on Dorsal Respiratory Group to inhibit inspiration- located in PONSVoluntary Control Centre- located in SOMATOSENSORY CORTEXMechanical Regulation- Stretch Receptors in lung inhibit Dorsal Respiratory Centre via Vagus nerve
RESPIRATORY CENTRELESIONS
Respiratory muscles (abdominal, intercostals and diaphragm) are enervated by Phrenic Nerve tf Spinal Segments C5, C6, C7Lesion in Pons but not Medulla produces long slow inspiration and low respiration rateLesion in Voluntary Control Centre will not stop breathingLesion in Medulla will produce loss of rhythmicity and increase or decrease of rate and depth of respirationLesion in upper spinal cord will stop breathingChemo and Barrow receptors synapse in the Dorsal Respiratory Group- Aortic Body Receptors are enervated by Cranial Nerve IX- Carotid Body Receptors are enervated by Cranial Nerve XLesion in Vagus stops inhibition of Dorsal Respiratory Centre tf long inspiration and reduction of respiration rate
RESPIRATORY CENTRECHEMORECEPTOR EFFECTS
CO2-- has most significant effect- receptors in CNS detect CO2 changes via changes in in H+ because of BBB- H+ levels in CSF follow H+ levels in blood because low protein in CFS produces low buffering capacityO2- response only when pO2 < 60 mmHgAnimals under anesthesia have reduced response to changes in CO2 because receptors and respiratory centres are suppressed
CARDIOVASCULAR CENTRE
Located in Reticular Centre of Medulla- Pressor Centre- Depressor Centre
VOMITION CENTRE5 SENSORY PATHS
Located in Dorsal MedullaReceives Sensory Afferents from:- abdominal vagus nerve- cerebral cortex- vestibular nuclei- olfactory regions of brain- CHEMORECEPTOR TRIGGER ZONE(located in medulla near vomition centre)Blood Brain Barrier is compromised near chemorecptor trigger zone- tf sensitive to blood glc and drugs- apomophine, morphine stimulate - metaelopramide inhibitsSufficient stimulation from sensory afferents causes vomition centre to initiate a coordinated series of events resulting in regurgitation
THALAMUSFIVE FUNCTIONAL SOUND BITES
Composed of a large number of NucleiActs as a processing and relay system for information going up to the cerebral cortex from spinal system and brain stemMuch of the information from the cerebral cortex synapses in thalamus and is relayed to other parts of brainDiffusely distributes information received from Ascending Reticular Activating System to Cerebral CortexRole in reception of pain- animals without cerebral cortex still perceive pain in a general way
HYPOTHALAMUS6 FUNCITONS
Coordination and Regulation of Automomic SystemNeuroendocrine Regulation via AdenohypophysisCoordinates expression of STRONG EMOTIONS ie RAGERegulation of Temperature Regulation of FeedingRegulation of Circadian Rhythms
TEMPERATURE REGULATIONRECEPTORS
- Central located in the PREOPTIC AREA which is in the rostral most part of hypothalamus- Preoptic area is just rostral to the optic chiasm tf pituitary tumors can affect vision- Central recepetors are more sensitive to increases in temperature- Peripheral in skin and visceral- peripheral receptors are more sensitive to decreases in temperature- both central and peripheral receptors respond to increases or decreases in temperature
TEMPERATURE REGULATIONCOORDINATING CENTRESHOW MANY AND WHERE?
Heat Loss Centre- Rostral Hypthalamus- stimulation produces loss of heat- vasodilation, sweating, shade seeking- lesions produce chronic hyperthermiaHeat Retention Centre- Caudal Hypthalamus- stimulation produces retention of heat- vasoconstriction, piloerection, shivering, shelter seeking- chronic stimualtion of cold receptors will result in release of thyroid hormones via release of TSH. Produces increased cellular metabolism over several weeks- lesions not noticeable until animal exposed to cold, results in chronic hypothermiaDeviation from temperature setpoint results in stimulation/suppresion of both centres tf responses driven by net output of both centresPeriphery may have local response which is independent of central centres
PYREXIA
aka FeverIncrease in body termperature above normalPyrogens released in pathological conditions (LPS, IL-1 etc)- increase firing rate of cold sensitive neurons in pre optic area- same effect as cooling hypothalamusHalothane and Isoflurane reduce senstivity of temperature sensitive neurons- tf thermoregulation operates over a wider termperature zone
TEMPERATURE REGULATIONINHALATION ANESTHETICS
Holothane and Isoflurane reduce senstivity of termperature sensitive neurons- tf thermoregulation operates over a wider termperature zone
APPETITE REGULATIONCENTRESHORMONES
FEEDING CENTRE- lateral regions of middle hypothalamus- stimulation produces eating or searching for food- bilateral lesions result in starvation (note will eat if food placed in mouth)SATIETY CENTRE- ventral medial region of middle hypothalamus- stimulation stops eating- chronic stimulation results in starvation- bilateral lesions result in continuous eating and EXTREMELY AGGRESSIVE BEHAVIOUR- tf satiety centre inhibits aggressive behaviourInputs to centres are received from:- Cerebral Cortex conscious control- olfactory systemOutputs of both centres go to Pons and Medulla which regulate the mechanics of eatingHormonal Influences- GHRELIN is released from stomach prior to feeding.- Activity in hypothalus is likely in Feeding Centre- LEPTIN is released from Adipocytes after feeding.- Activity in hypothalamus is likely in Satiety Centre
CENTRE
Area of CNS that is FUNCTIONALLY DEFINED by electrical sitmualtion and lesioningMay contain axons or cell bodies tf response of centre may be due to stimulation of either
REGULATION OF CIRCADIAN RHYTHM
Intrinsic Pacemaker (major of several) is located in SUPRACHIASMATIC NUCLEUS- nuclei active on 24 hour cycle- afferents from retina and other external inputs- light cycle maintains 24 hour period- continous light increases or decreases period depending on species- synchronizes many other functions- important role in reproduction via outputs to Pineal Gland which produces melatoninNote Pineal Gland and Retina are major pacemakers in birdsCircadian Rhythms have significance effects on physiology and pharmacology-
CORPUS CALLOSUM
Connects left and right halves of Cerebrum
CEREBRUMANATOMICAL REFERENCES
Relative to Skull BonesFrontal CortexParietal CortexOccipital CortexTemporal Cortex(Olfactory)
CEREBRUMFUNCTIONAL REFERENCESFive
Visual AreaMotor AreaAuditory AreaSomatosensory AreaPrefrontal Area
CREBRUMTOPOGRAPHICAL REPRESENTATION
Structures of cortex relate to distinct areas of bodyRight body is represented in Left cortex and visa versaSomatosensory Cortex- somatotopic map has disproportionate representation of body areas- areas with large amounts of receptors ie whiskers have larger representation in somatosensory cortexMotor Cortex- representation of muscles is proportionate to enervation ratio- fine control muscles (extrinsic eye 1:10 motor unit:myocyte) have more representation than coarse control muscles (back 1:1000)Visual Cortex (Occipital)- map of visual field - left eye is represented in right cortex and visa versa- retnotopic map ie adjacent areas of retina are represented in adjacent areas of cortexAutitory Cortex (Temporal)- several maps- left AND right auditory fields are represented on each side to allow sound location via timing differences of sound arrival between earsNOTE major map is in Caudal Colliculus
PRORIOCEPTIONSIGNS OF LOSS
Loss of Unconscious Proprioception- cereballar malfunction- uncoordinated movements- dysmetriaConscious Proprioception- commonly reffered to as Proprioceptive Deficits- loss of position sense- involvement of cerebral cortex- KNUCKLING RESPONSE via correction of weight bearing on dorsum of paw- HOPPING REFLEX via maintaining leg under body when dangled so that weight is borne on one paw and animal is subjected to rapid lateral movements- BLIND FOLDED WALKING
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