Neuroscience Flashcards
(111 cards)
Tabes Dorsalis
Consequence of syphilitic infection. Destruction of DRG cells with LARGE diameter MYELINATED AXONS.
LOSS OF TOUCH AND PROPRIOCEPTION (bilaterally?)
Nociception and T remain almost unaffected.
Phantom Limb Sensations
Reorganisation of cortical maps post- losing a limb.
Phantom limb sensations can be evoked by touching the face - perceived as pain from parts of phantom limb.
Touch pathways in the face form new circuits, connect with neurons that would have become useless for arm.
Hyperalgesia
Enhanced sensitivity and responsively to stimulation in area surrounding damaged tissue.
Due to sensitisation of nociceptors - bc of chemical substances released within the damaged area ie Prostaglandins, leukotrienes, substance P (signalling substance of primary afferent pain fibres) is
Allodynia
Normally non-noxious stimuli cause sensation of pain ie putting on a shirt after sunburn
Classifications of pain
Nociceptive - activation of nociceptors
Neuropathic - due to aberrant somatosensory processing ie phantom limb pain
Angina Pectoris Referred pain
Metabolic Products of ischemia stimulate visceral pain fibres. Pass through spinal nerve roots between C7 and T4, with cutaneous fibres. CONVERGENCE on a secondary sensory neuron within the spinal cord
Where would the ALS and Medial lemniscus likely be injured together?
Come close together at pons and midbrain, could be lesioned together here - ie impaired point discrim, pain, T from R side of body.
If loss of pain and thermal sensation on R side of face, where is the lesion?
Has to be at medulla or above because if it were below, would have BILATERAL loss of pain and thermal sensation, since the Trigminal pain path descends to the spinal trigeminal nucleus and then ascends through the medulla and pons.
Noxious substances released from damaged tissues that activate nociceptors
Blood - bradykinin
Mast cells - histamine
Potassium from damaged cells (ischemia, MI)
- activate nociceptors
Gate Control
In dorsal horn of spinal cord. Large myelinated fibres carrying touch sensations activate inhibitory interneurons within dorsal horn (interneuron releases ENKEPHALIN onto opioid receptors), reduce flow of nociceptive information through the gate between nociceptors (first order neurons of pain path) and their second order neurons.
Pain interventions
Inhibit sensitising agents ie prostaglandins
Inhibit pain pathway - ie block at DRG
Opioid drugs - increase interneurons activation inhibiting pain pathway ie codeine morphine, mimick enkephalin
Far Vision Accomodations
Light rays are ~ PARALLEL Cornea Refractive power 42 D (1/m) LENS refractive power 13 D (1/m), flattened CILIARY MUSCLE (circular): relaxed SUSPENSORY LIGAMENTS: tightened
Near Vision Accomodation
Light rays are NOT parallel. CILIARY MUSCLE (CIRCULAR) - CONSTRICTED SUSPENSORY LIGAMENTS - SLACK Cornea 42 D Lens, more convex, increases to about 26 D in young person.
Presbyopia
Lens looses its elasticity in ageing - reducing ability to focus on near objects. Focal length is too great (not converged fast enough)
Correct with a CONVEX LENS (Reading glasses)
Visual Acuity
Ability to distinguish two nearby points. Visual acuity is HIGH when two-point discrimination threshold is LOW (High spatial resolution)
Depends on density of photoreceptors, and proper function of optical apparatus of eye ie accommodation - if optical apparatus fails, objects appear blurry.
Emmetropia
Sharp picture of parallel rays entering the eye - refractive power of optical apparatus matches the length of the eyeball. Normal sightedness.
Myopia
(Nearsightedness)
Focus of parallel light rays is ANTERIOR to photosensitive elements of retinal photoreceptors.
Objects closer to the eye can be focused even without usual accommodation. Vision is best for NEAR objects.
CORRECT WITH: CONCAVE LENS
Hyperopia
(Farsightedness)
Focus of light rays is beyond the retina when ciliary muscle is relaxed and lens has its lowest refractive power.
Distant objects can be focused by activating mechanisms for near accomodation, increasing refractive power
Fails for close objects, vision best for far objects.
CORRECTED USING CONVEX (+D) LENS
Papilledema
Indicates increased ICP. Seen on inspection of ocular fundus. Increased ICP compromises venous drainage - dilation of retinal veins.
Optic disc is pushed forward and disc appears white.
Detached Retina
Retina separates from RPE and areas detached lose their function.
Focal lesion in defined region causes scotoma - an area of vision loss.
Detached part of retina will NOT regain its function even with surgery.
Age Related Macular Degeneration (AMD)
Poor central vision. Number of genetic, enviro, age, smoking, BMI can contribute to incidence.
Cells of RPE atrophy and outer segment waste removal becomes less efficient.
Diabetic Retinopathy
Initial small scotomas often unrecognised. Once macula is involved, visual loss is dramatic.
Defects caused by blood supply dysfunction, reduction of permeability of basal membranes of capillary endothelial cells and bv damage (aneurysms). Retina vulnerable.
Colour Blindness
6% of population, X linked recessive
Protagonist: L (red) cone absent
Deuteranopia: M (green) cone absent
Deficits in blue cone are rare
Nyctalopia (night blindness)
Vitamin A deficiency - secondary to dec ingestion, defective absorption etc. Precursor of visual pigments. RODS are first affected, hence night blindness issues.
