VBMS 212 Neurology Quiz 2
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- PERIPHERAL SENSORY FUNCTION
-
Enteroception
- nociception
- deep receptors
- superficial receptors
Proprioception
- conscious
- unconscious - NOCICEPTORS
-
Pain and Noxious Stimuli
Respond to potentially tissue damaging stimuli
- Thermal
- Mechanical
- Inflamatory
Bare Nerve Endings
Cell Body in Dorsal Root or Cranial Ganglia
Primary Afferent axons are small with little or no myelination tf slow
High Threshold ie not sensitive - THREE ACTIONS OF NOCICEPTORS
-
Direct Activation via cold or heat, Mechanical Damage, Chemical Damage
Damage of surrounding tissue causes release of cellular contents (ie Histamine, Bradykinins etc) generating further stimulation
Once 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 Funicular
Spinothalamic
Spinoreticular
Spinocervical -
FUNKY FACTS ABOUT
DORSAL FUNICULAR PATHWAY -
aka Lemniscal
Peripheral Sensory Enteroception
3 Neurons
Primary Sensory Afferents DIRECTLY enter dorsal funiculus via dorsal root
Fasciculus Gracilis carries axons from Caudal regions and Hind Limbs
Fasiculus Cuneatus carries axons from Cranial regions and Fore Limbs
Primary sensory afferents synapse on Nuclei Gracilus and Cuneatus in caudal portion of Medulla
Axons from Nuclei Gracilus and Cuneatus DECUSSATE and travel in the Contra Lateral MEDIAL LEMNISUCUS where they synapse on nuclei in the Rostral thalamus
Axons from the nuclei in the thalamus travel to the SOMATO SENSORY CORTEX - FASICULUS GRACILUS
-
Medial Portion of Dorsal Funiculus
Carries primary sensory afferents from caudal regions and hind limbs for
- enteroception
- Conscious Proprioception - FASICULUS CUNEATUS
-
Lateral Portion of Dorsal Funiculus
Carries 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 ABOUT
SPINOTHALAMIC PATHWAY -
Peripheral Sensory Enteroception
3 Neurons
Primary sensory afferents enter dorsal horn via dorsal root and SYNAPSE on nuclei of afferent interneurons
Axons of afferent interneurons cross Grey Commissure and travel in the CONTA LATERAL LATERAL FUNICULUS
Interneurons synapse in the Thalamus
Axons from the nuclei in the thalamus travel to the SOMATO SENSORY CORTEX -
ROUSING REVELATIONS ABOUT
SPINORETICULAR PATHWAY -
Peripheral Sensory Enteroception
3 OR 4 Neurons
Primary sensory afferents enter dorsal horn via dorsal root and SYNAPSE on nuclei of afferent interneurons
Axons of afferent interneurons cross Grey Commissure and travel in the CONTA LATERAL LATERAL FUNICULUS
Interneurons 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 ABOUT
SPINOCERVICAL PATHWAY -
Peripheral Sensory Enteroception
4 OR 5 Neurons
Primary sensory afferents enter dorsal horn via dorsal root and SYNAPSE on nuclei of afferent interneurons
Axons of afferent interneurons travel in the IPSO LATERAL LATERAL FUNICULUS
Axons 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 NOTIONS
NOCICEPTION PATHWAY -
Peripheral Sensory Enteroception
Minimum 3 Neurons
Primary sensory afferents enter dorsal horn via dorsal root and SYNAPSE on nuclei of afferent interneurons
Sensory Afferents travel via
- Spinothalamic Pathway and Bilateral (decusation) Pathway
Multiple 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 Afferents
Located in ventral rostral region of cerebral cortex
Required for
- conscious perception of pain
- localization of pain
- pain related learning -
NOCICEPTION
BRAIN STEM - Nociceptive information reaching Pons or Medulla is important for changing STATE OF AROUSAL
-
NOCICEPTION
MID BRAIN - Nociceptive information that reaches midbrain is transferred to structures of LIMBIC SYSTEM that are responsible for EMOTIONAL response to pain
-
NOCICEPTION
HYPOTHALAMUS - Cardiovascular and neural hormonal responses to pain
-
NOCICEPTION
SPINAL 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 neurons
ie pressure sensing neurons can have a net stimulatory effect on nociception inhibitory neurons in short term tf rub to alleviate pain
OR
long 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 periphery
Dorsal Horn:
- spontaneously hyperexcited
- or remains hyperexcited after stimulation
Difficult to control
Common in spinal cord injury
tf, in addition to general aneshtetics, use local anesthetics in dorsal horn when AMPUTATING - MIDBRAIN MODULATION OF PAIN
-
Periaquaductal Grey Matter
- area around mesodermal aqueduct
Neurons in Periaqueductal Grey Matter INHIBIT activity in DORSAL HORN neurons
Responsive to OPTIATES
Stimulated by intense activities ie fighting - TWO OTHER AREAS OF PAIN MODULATION
-
Synapses in Pons and Medulla
Dorsal Horn Neurons
- receptors for Opiods and NE inhibit tf use opiods or alpha agonists (xylazine) for epidurals - PROPRIOCEPTION
-
Spatial awareness of musculoskeletal system
sense of location and motion of all body segements
Conscious - pathways end in Cerebral Cortex
Unconscious - pathways end in Cerebellum -
PROPRIOCEPTIVE RECPTORS
THREE LITTLE PIGGIES -
Muscle Spindles
- length of muscles
- speed of change of muscle length
- Ia axons largest and fastest
Golgi Tendon Organ
- force in muscle
- Ib axons large but not largest diameter
Stretch Receptors
- joint Capsules
- skin over joints
- αβ axons mid size diameter
Sensor afferents that conduct information from prorioception receptors are amoungst largest in body - CONSCIOUS PROPRIOCEPTION PATHWAY
-
Primary sensory afferents DIRECTLY enter dorsal funiculus
Caudal and hind limb afferents travel in Ipsolateral Funiculus Gracilis
Cranial and fore limb afferents travel in Ipsolateral Funiculus Cuneatus
Primary sensory afferents synapse on nuclei gracili and cuneati in Caudal Medulla
Axons 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 PATHWAY
CAUDAL AND HINDLIMBS -
Primary Sensory afferents enter the dorsal horn and synapse in the dorsal grey columns
Axons 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 PATHWAY
CRANIAL AND HINDLIMBS -
Primary Sensory afferents enter the dorsal horn and synapse AS WELL AS BRANCH in the dorsal grey columns
CUNEOCEREBELLAR 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 BASICS
TELENCEPHALON
DIENCEPHALON
MESENCEPHALON
METENCEPHALON
MYELENCEPHALON -
Cerebrum
- cerebral cortex
- subcortical structures
- Lateral Ventricles
The Thalamus Family
- epithalamus
- thalamus
- hypothalamus
- third ventricle
Mesencephalon
- mesencephallic aqueduct
Metencephalon
- pons
- cerebellum
- fourth ventricle
Medulla
- fourth ventricle as well - MIDBRAIN
-
Cerebral Peduncles
- ventral portion
- rostral caudal fibres
- axons of Upper Motor Neurons
- axons of Lower Motor Neurons
Tementum
Tectum
- Dorsally Located Colliculi
- Rostral Colliculi coordination of Visual Reflexes
- Caudal Colliculi coordination of auditory reflexes
Cranial Nerve III
- Oculomotor Nerve
- lower motor neurons
- enervates Extrinsic Eye Muscles
Cranial Nerve IV
- Trochlear Nerve
- also enervates extrinsic eye muscles
- thin - DIENCEPHALON
-
Epithalamus (Pineal Gland)
Hypothalamus
Thalamus
Cranial Nerve II
- Optic Nerve - PONS
-
Fibres of Pons
- lateral structure contains fibres which travel to cerebellum
Cranial Nerve V
- Trigeminal Nerve
- lower motor neurons
- enervate muscles of mastication tf BIG
Cranial Nerve VI
- Abducens Nerve
- Lower Motor Neurons to extrinsic muscles of eye - MEDULLA
-
Nuclei Cuneatus
Nuclei Gracilis
Pyramids
- contain Upper Motor Neurons ONLY
Cranial Nerve VII
- Facial Nerve
- Lower Motor Neurons to facial muscles
- efferents to salivary and lacrimal glands
- afferents for taste
- Rostral Medulla
Cranial Nerve VIII
- Vestibulocochlear Nerve
- afferents from internal ear
Cranial Nerve IX
- Glossopharyngeal
- Efferents/Afferents Pharynx
- Afferents Taste
- Autonomic Salivary Glands
Cranial Nerve X
- Vagus
- Efferent/Afferents larynx, pharynx and viscera
Cranial Nerve XII
- Hypoglossal
- Lower Motor Neurons
- enervates tongue - FOUR CRANIAL NERVES THAT HAVE CLINICAL RELEVANCE
-
III - Midbrain
V - Pons
VII - Rostral Medulla
XII - Caudal Medulla
Clincially 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 nerves
Basically the brain stem is a big mess of neurons with extensive and complicated connections -
FOUR FUNCTIONS OF
RETICULAR FORMATION -
Behavioral Arousal
Motor Control
Modulation of Pain Sensation
Coordination of Some Autonomic Functions
- Respiratory Control
- Cardiovascular Control
- Vomition -
RETICULAR FORMATION
BEHAVIOURAL 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 conciousness
All inputs of cranial nerves I, II, V and VIII synapse in reticular formation
Neurons in reticular formation synapse int the Thalamus which sends many neurons throughout the cerebral cortex resulting in DIFFUSE DISTRIBUTION -
RETICULAR FORMATION
MOTOR CONTROL - Some Upper Motor Neurons are present in Reticular Formation
-
RETICULAR FORMATION
MODULATION OF PAIN SENSATION -
Periaquaductal Grey matter resides in Reticular Formation
Neurons 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 FORMATION
RESPIRATORY CONTROL -
Maintains normal levels of CO2 and O2 via alveolar ventalation
- respiration rate
- respiration depth
Inputs
- CO2, pH, O2 Receptors
Outputs
- motor neurons that enervate respiratory muscles
PRE BOTZINGER COMPLEX
- source of respiratory rhythm
- located in MEDULLA
DORSAL RESPIRATORY GROUP
- enervates Inspiratory neurons ONLY
- located in Dorsal MEDULLA
VENTRAL RESPIRATORY GROUP
- enervates inspriatory and expiratory neurons
- located in VENTRAL MEDULLA
PONTINE RESPIRATORY GROUP
- acts on Dorsal Respiratory Group to inhibit inspiration
- located in PONS
Voluntary Control Centre
- located in SOMATOSENSORY CORTEX
Mechanical Regulation
- Stretch Receptors in lung inhibit Dorsal Respiratory Centre via Vagus nerve -
RESPIRATORY CENTRE
LESIONS -
Respiratory muscles (abdominal, intercostals and diaphragm) are enervated by Phrenic Nerve tf Spinal Segments C5, C6, C7
Lesion in Pons but not Medulla produces long slow inspiration and low respiration rate
Lesion in Voluntary Control Centre will not stop breathing
Lesion in Medulla will produce loss of rhythmicity and increase or decrease of rate and depth of respiration
Lesion in upper spinal cord will stop breathing
Chemo 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 X
Lesion in Vagus stops inhibition of Dorsal Respiratory Centre tf long inspiration and reduction of respiration rate -
RESPIRATORY CENTRE
CHEMORECEPTOR 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 capacity
O2
- response only when pO2 < 60 mmHg
Animals 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 CENTRE
5 SENSORY PATHS -
Located in Dorsal Medulla
Receives 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 inhibits
Sufficient stimulation from sensory afferents causes vomition centre to initiate a coordinated series of events resulting in regurgitation -
THALAMUS
FIVE FUNCTIONAL SOUND BITES -
Composed of a large number of Nuclei
Acts as a processing and relay system for information going up to the cerebral cortex from spinal system and brain stem
Much of the information from the cerebral cortex synapses in thalamus and is relayed to other parts of brain
Diffusely distributes information received from Ascending Reticular Activating System to Cerebral Cortex
Role in reception of pain
- animals without cerebral cortex still perceive pain in a general way -
HYPOTHALAMUS
6 FUNCITONS -
Coordination and Regulation of Automomic System
Neuroendocrine Regulation via Adenohypophysis
Coordinates expression of STRONG EMOTIONS ie RAGE
Regulation of Temperature
Regulation of Feeding
Regulation of Circadian Rhythms -
TEMPERATURE REGULATION
RECEPTORS -
- 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 REGULATION
COORDINATING CENTRES
HOW MANY AND WHERE? -
Heat Loss Centre
- Rostral Hypthalamus
- stimulation produces loss of heat
- vasodilation, sweating, shade seeking
- lesions produce chronic hyperthermia
Heat 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 hypothermia
Deviation from temperature setpoint results in stimulation/suppresion of both centres tf responses driven by net output of both centres
Periphery may have local response which is independent of central centres - PYREXIA
-
aka Fever
Increase in body termperature above normal
Pyrogens released in pathological conditions (LPS, IL-1 etc)
- increase firing rate of cold sensitive neurons in pre optic area
- same effect as cooling hypothalamus
Halothane and Isoflurane reduce senstivity of temperature sensitive neurons
- tf thermoregulation operates over a wider termperature zone -
TEMPERATURE REGULATION
INHALATION ANESTHETICS -
Holothane and Isoflurane reduce senstivity of termperature sensitive neurons
- tf thermoregulation operates over a wider termperature zone -
APPETITE REGULATION
CENTRES
HORMONES -
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 behaviour
Inputs to centres are received from:
- Cerebral Cortex conscious control
- olfactory system
Outputs of both centres go to Pons and Medulla which regulate the mechanics of eating
Hormonal 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 lesioning
May 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 melatonin
Note Pineal Gland and Retina are major pacemakers in birds
Circadian Rhythms have significance effects on physiology and pharmacology
- - CORPUS CALLOSUM
- Connects left and right halves of Cerebrum
-
CEREBRUM
ANATOMICAL REFERENCES -
Relative to Skull Bones
Frontal Cortex
Parietal Cortex
Occipital Cortex
Temporal Cortex
(Olfactory) -
CEREBRUM
FUNCTIONAL REFERENCES
Five -
Visual Area
Motor Area
Auditory Area
Somatosensory Area
Prefrontal Area -
CREBRUM
TOPOGRAPHICAL REPRESENTATION -
Structures of cortex relate to distinct areas of body
Right body is represented in Left cortex and visa versa
Somatosensory Cortex
- somatotopic map has disproportionate representation of body areas
- areas with large amounts of receptors ie whiskers have larger representation in somatosensory cortex
Motor 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 cortex
Autitory 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 ears
NOTE major map is in Caudal Colliculus -
PRORIOCEPTION
SIGNS OF LOSS -
Loss of Unconscious Proprioception
- cereballar malfunction
- uncoordinated movements
- dysmetria
Conscious 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