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Neuroanatomy (Spinal cord (Clinical signs by lesions in the C6-T2 spinal…

- - - - dorsal funiculus
        
        consists essentially of ascending tracts mainly involved in proprioception
      - Lateral funiculus
        
        contains both ascending (proprioception, touch, pressure, pain, temperature pathways) and descending (motor pathways) tracts
      - ventral funiculus
        
        only descending motor tracts
  - - - 2) motor function
        
        3) bladder function
        
        4) Nociception
  - - - reduced or absent cutaneous trunk reflex caudal to the level of the last intact dermatome
      - hypo/anaesthesia of the pelvic limbs, may be hyperaesthesia of thoracolumbar spine
  - - - decreased to absent pelvic limb withdrawal reflex (unilateral or bilateral)
      - normal in the thoracic limbs
      - decreased to absent perianal +/- perianal reflex
    - - flaccid/decreased pelvic limb and tail muscle tone
      - dilated anal sphincter
      - muscle atrophy in caudal thigh, hip and or distal pelvic limb muscles
      - hypoaesthesia in pelvic limb, perineal area and tail
      - may be hyperaesthesia in the lumbosacral spine/rectal palpation
      - urinary retention (LMN bladder), faecal incontinence
- - - - the very end of a branch of a nerve's axon, a long slender nerve fiber that conducts electrical signals to a nerve synapse
- - - - Limbic system
      - Olfactory nerve CN I
        
        Conscious perception of smell
        
        Cell bodies lie in olfactory epithelium on ethmoturbinate bones, rather than ganglion
        
        Axons pass through the cribriform plate to synapse with 2ry neurons in the olfactory bulb.
        
        2ry neurons pass to olfactory peduncle and olfactory tracts
        
        2ry neurons synapse with the 3rd order neurons in the olfactory tubercle
        
        These 3rd order neurons project to the piriform lobe in the olfactory region of the brain
    - - Mainly motor area
      - corticospinal and corticonuclear tracts
    - - mainly sensory-motor areas
    - - Auditory area
      - vestibular conscious perception
      - Pyriform lobe
        
        olfactory and limbic system
    - - visual conscious perception
      - Optic Nerve CN II
        
        Retinal ganglion cells, glial cells and meninges
        
        embryologically is an extension of the diencephalon
        
        first neutron represents the bipolar cells of the retina and receives visual info from the neuroepithelial cells of the retinal (rods and cones)
        
        2nd neuron corresponds to the ganglion cells of the retina. Its axon lies in the optic nerve and continues through the optic chiasm and proximal part of the optic tract on the opposite side.
        
        66% decussation in cats and 75% decussation in dogs
        
        The cell body of the 3rd neuron is located in the lateral geniculate nucleus in the diencephalon. Its axon projects to the visual cortex (mostly contralateral occipital cortex) in a band of fibres called the optic radiations
  - - - appetite, thirst, temperature, electrolyte and water balance, sleep and consciousness or wakefulness
    - - via CN I which projects to the hypothalamus and other parts of limbic system
    - - Extrapyramidal system is the main UMN system in dogs and cats.
  - - - altered (depression, delirium, dementia (confusion), stupor, coma)
      - Behavioural changes
    - - contralateral blindness
      - decreased/absent menace reaction
      - Normal PLR
    - - Normal gait
      - Abnormal movements and posture
      - Pleurothotonus (body turn towards lesion)
      - Head turn
      - Head pressing
      - Pacing
      - Wandering aimlessly
      - circling (usually ipsilateral)
    - - postural reaction deficits in contralateral limbs
    - - unaltered to increased in contralateral limbs
    - - unaltered to increased in contralateral limbs
    - - facial hypoalgesia to hypoaesthesia to contralateral half of body
    - - Seizures
      - Cervical hyperaesthesia
      - Hemi-Neglect syndrome
      - narcolepsy-cataplexy
      - movement disorders e.g. dyskinesias
- - - - ipsilateral menace deficit with normal vision and normal facial motor function, possibly vestibular signs, possibly anisocoria
    - - intention tremors of head and eyes
      - hypermetria with preservation of strength
      - truncal ataxia
      - Broad based stance
      - decerebellate rigidity
    - - Delayed initiation and then (exaggerated) dysmetric response
- - - - Cranial nerve II, optic nerve
    - - Cranial nerve VIII, vestibulocochlear nerve
- - - - only the oculomotor and trochlear arise from here.
        
        Oculomotor is motor and parasympathetic to the extra ocular muscles (dorsal, ventral and medial rectus and the ventral oblique). Also innervates the levator palpebrae superioris muscle and is responsible for sphincter pupillary muscle constriction.
        
        Trochlear is motor to constrict the dorsal oblique
      - contains the red nucleus responsible for gait generation
      - Tectotegmentalspinal tract originates in midbrain
        
        sympathetic innervation to the eye
        
        The diencephalon has influence over this part of the midbrain
        
        3 neuron pathway
        
        Dysfunction of this pathway = HORNER'S SYNDROME
        
        Caused by lesions disrupting the sympathetic innervation to the eye
        
        components
        
        Miosis
        
        Enophthalmos
        
        Ptosis
        
        Prolapsed nictitans
        
        Causes
        
        first order (central)
        
        first order neurons originate in the hypothalamus and rostral midbrain and travel down the brainstem and cervical spinal cord to terminate at the preganglionic cell bodies in the thoracic spinal cord
        
        UMN lesions in brainstem or cervical spinal cord are relatively rare
        
        intracranial
        
        neoplasia
        
        infarct
        
        trauma
        
        inflammatory disease
        
        cervical spinal cord lesion
        
        intervertebral disc protrusion
        
        Neoplasm
        
        Fibrocartilaginous embolism
        
        Trauma
        
        Infectious inflammatory disease
        
        Granulomatous meningoencephalitis
        
        Ipsilateral hemiplegia and other concurrent neurologic abnormalities are expected
        
        Second order (Preganglionic)
        
        spinal cord lesion T1-T3 (trauma, neoplasia, fibrocartilaginous embolism, inflammation)
        
        Brachial plexus avulsion
        
        with this there will be complete LMN paralysis of the affected limb and an ipsilateral Horner syndrome that may be partial (miosis only) because of sparing of the T3 and sometimes T2 nerve roots.
        
        Thoracic spinal nerve root tumour
        
        Cranial mediastinal mass
        
        Cervical soft tissue neoplasia, trauma
        
        Skull base trauma
        
        The preganglionic cell bodies of the second order neurons are located in the lateral horn of the spinal cord gray matter at the level of the first 3 thoracic spinal cord segments (T1-T3)
        
        The 2nd order axons leave the spinal cord with the T1-T3 ventral nerve roots, but then leave the spinal nerves to form the thoracic sympathetic trunk, which courses cranially within the thorax
        
        1 more item...
        
        Affected animals will exhibit LMN signs in affected forelimb and UMN in the ipsilateral hindlimb + horners
        
        Third order (postganglionic)
        
        Most common
        
        Postganglionic axons for ocular sympathetic innervation course rostrally through the tympanooccipital fissure into the middle ear and enter the cranial cavity with the glossopharyngeal nerve (CN9)
        
        leaves the cranial cavity via orbital tissue for distribution to the smooth muscle of the orbit, the upper and lower eyelid and the iris muscles.
        
        Otitis media/interna
        
        Neoplasia in middle ear
        
        Retrobulbar injury, neoplasia
        
        Often accompanied by evidence of peripheral vestibular (CN8) disturbance and sometimes facial nerve (CN7) paralysis.
        
        Idiopathic
        
        50%
        
        Resolves spontaneously within 6m in most dogs
        
        1st neuron = tectotegmental spinal tract, 2nd neuron = cranial cervical ganglion 3rd neuron = typmano-occipital fissure, orbital tissue, trigeminal ganglion
        
        Pharmacologic testing to confirm diagnosis and localise cause of Horners syndrome
        
        when syndrome present for 2 weeks, denervation hypersensitivity will occur 2ry to loss of sympathetic innervation.
        
        sympathomimetic to confirm dx
        
        topical ophthalmic cocaine (6%)
        
        drop in normal and affected eye
        
        confirmation - no/poor dilation of affected pupil and dilation of normal side.
        
        wait 24-48h after cocaine test
        
        to localise add a drop of a very dilute concentration of a direct acting sympathomimetic (0.1% phenylephrine: stock 10% solution diluted 1:100 with saline in both eyes.
        
        pupil in normal eye should not dilate
        
        dilation of affected pupil will occur in 20min in animal with postganglionic lesion
        
        if no dilation within 20 min, a concentrated adrenergic (10% phenylephrine) can be applied to both pupils
        
        1 more item...
    - - Pons - metencephalon
        
        Only the trigeminal nerve arises from here.
        
        Ophthalmic branch (purple), maxillary branch (pink), mandibular branch (blue). All sensory, and mandibular has a motor component for the muscles of mastication (temporalis, masseter, pterygoid (lateral and medial), digastricus rostral)
      - Medulla oblongata - myelencephalon
        
        Abducens to the hypoglossal (6-12) arise from here.
    - - 1) CN deficits
        
        2) Proprioceptive deficits
        
        3)hemi/tetraparesis
        
        4)stupor/coma
        
        5)Abnormalities in respiratory and cardiovascular function
      - Clinical signs caused by lesions in brainstem
        
        mental status
        
        altered (depression, stupor, coma)
        
        CN abnormalities (III to XII)
        
        Posture/gait
        
        Paresis/paralysis of all 4 limbs (tetra paresis/plegia) or of ipsilateral thoracic and pelvic limbs (hemiparesis/plegia)
        
        possibly opisthotonus
        
        possibly decerebrate rigidity
        
        Postural reaction deficits in all 4 or in ipsilateral thoracic or pelvic limbs
        
        Spinal reflexes
        
        normal or increased in all 4 limbs or in ipsilateral thoracic or pelvic limbs.
        
        Muscle tone
        
        Normal to increased tone in all 4 limbs or in ipsilateral thoracic and pelvic limbs
        
        sensation
        
        unaltered, but can have cervical hyperaesthesia
        
        Can have cardiac or respiratory abnormalities
  - - - Ascending reticular activating system
      - Decreased ARAS activity -> sleep
    - - Medullary reticular formation
    - - also involved in voluntary excretion, swallowing, vomiting, muscle tone, voluntary movement