Week 6 Flashcards

Question

Vestibulo-Occular Reflex

Answer 1

Head movements illicit compensatory eye movements to maintain fixation – minimise motion on the retina • Loss of VOR – oscillopsia (“bouncing vision”) • Bilateral loss of VOR leaves the patient with the sensation that the world is moving whenever the head moves • Information about head movements signalled by the vestibular organs is unavailable • Compensatory eye movements are not made

Answer 2

Is comprised of three systems: • Exteroceptive system: senses external stimuli applied to the surface of the skin. • Proprioceptive system: senses the position of limbs via joint angles; body posture; vestibular senses. • Interoceptive system: senses the general conditions within the body such as temperature, blood pressure.

Answer 3

• 5 senses – touch • Different aspects – physical contact, temperature, pain • Many types receptors: • Mechanoreceptors (different for stroke, pressure, vibration, stretch, light stroke, erotic touch) • Temperature receptors (cool, warm, cold, hot) • Nociceptors (sharp, burn, freeze, slow burn) • Lots fibres – vary in diameter and myelination • Conduction speed can vary from 100m/s (large myelinated – most non-stroking mechano) down to 0.5 m/s (unmyelinated – erotic touch and slow burn nociceptors) • Typically touch and proprioception fast, thermal and nociception slower

Answer 4

``` Meissner corpuscles • Surface • Adapt quickly – no sustained response • Best response to lateral motion • Medium sensitivity Pacinian corpuscles • Deep • Respond rapidly, adapt quickly • Sudden displacement of the skin • Respond best to vibration • High sensitivity Merkel’s disks • Surface • Sustained response, slow adaptation • Gradual skin indentation • Best response to edges and points • Medium sensitivity Ruffini Endings • Deep • Sustained response, slow adaptation • Best response to skin stretch • Low sensitivity Free nerve endings • No specialised structure • Temperature and pain ```

Answer 5

• Sensory and motor systems rep info about state of muscles and limbs • Muscle length and speed, muscle stretch, muscle contraction, joint angle, excess stretch or force • A variety of receptors embedded in muscles, tendons, and joint capsules • Some involved in conscious sensation of muscle activity, some in unconscious monitoring of body for posture, some in reflexes • Patellar reflex – stretches muscle spindle in quadricep – spinal reflex to contract quad and relax hamstring

Answer 6

• Visceral sensations rep status of internal body organs • Drive behaviour for survival: respiration, hunger, thirst, nausea (food aversion), arousal • Loss of air – feeling of suffocation becomes all consuming goal – hold breath when needed knowing that signal will tell you when to stop • O2 and CO2 sensors in carotid bodies and in respiratory centres of medulla and hypothalamus • Ondine’s Curse – damage to medullary centres and loss of ‘air hunger’ – death and failure of auto breathing in sleep

Answer 7

• Somatosensory information ascends from each side of the body to the cortex via two major pathways • Dorsal Column-Medial Lemniscus carries information about touch and proprioception • Anterolateral System carries information about pain and temperature • Both fed by dorsal roots of spinal nerves (or trigeminal sensory nerves in the head)

Answer 8

``` • Afferent nerve fibres over a specific area of the body converge on specific dorsal roots in the spinal cord • Considerable overlap so damage or loss of one does not result in a large deficit in sensation of the dermatome • Quadruped setup ```

Answer 9

``` • Touch and proprioception (fast – large myelinated) • Ascend ipsilaterally in dorsal columns and synapse on dorsal column nuclei in medulla • Decussate then ascend via medial lemniscus to contralateral VPN ```

Answer 10

``` • Pain and temperature (slow – small myelinated and unmyelinated) • Synapse on cord entry • Decussate and ascend by contralateral anterior lateral spinal cord (some ascend ipsilaterally • Multiple tracts • Spinothalamic to thalamus (several nuclei) – main noxious, thermal and visceral • Others to various brainstem structures ```

Answer 11

``` • Primary (S1) and secondary (S2) somatosensory cortex (anterior parietal) • Sensory Homunculus – somatotopic organisation (map of the body) in S1 (contralateral) and S2 (bilateral) • S1 and S2 output to association cortex – posterior parietal • Damage to S1 is not marked by major deficits in sensation. This is probably due to the numerous parallel pathways in the two systems ```

Answer 12

• Pain is adaptive because it stops us from doing damage to ourselves • Encourages us to seek treatment or to treat ourselves • The cortical representation of pain is diffuse - no single structure is responsible • S1 and S2 respond to painful stimuli but are not necessary - removal does not reduce sensitivity to pain. • Full removal of an entire hemisphere has little effect

Answer 13

``` Anterior Cingulate Cortex • Implicated in mediating the perception of pain • PET studies showed increase in activity when participants touched very hot or very cold objects • Likely involved in the emotional response to pain • Prefrontal lobotomy results in reduced emotional response to pain but no change in pain threshold Descending control Periaqueductal grey (PAG) has analgesic effects • Electric stimulation reduces pain • Receptors for opiate based pain drugs • Endorphins modulate PAG activity ```

Answer 14

No Pain – Congenital Insensitivity to Pain (CIP) • Miss C. - the woman who felt no pain • Normal university student had never felt pain • Bit the tip of her tongue off while chewing; burnt her legs on a heater; felt no electric shock • No sneezing or coughing; no corneal reflex • Not even autonomic reaction to pain (e.g. no increased heart rate) • Had multiple health problems - bad joints (lack of protection) • Died age 29 of massive infection • Genetic – mutation in gene for subunit of a sodium channel found in nociceptors – extremely rare

Answer 15

• Chemicals in the environment are cues • General state of the local environment – toxins, pH, ionic, etc • Food (constituent and emitted); predator/prey scent; mate scent; kin identification • Volatile chemicals – odours • Non-volatile chemicals – tastes • Single cells react and respond to local chemical environment • Chemical senses evolved very early • Multiple responses – identification; affective; initiate physiological changes

Answer 16

``` • Receptors in upper nasal passage embedded in olfactory mucosa • Olfactory receptor neuron (ORN) • Dendrites in nasal passage • Axons pass through cribriform plate into olfactory bulbs • Synapse then project via olfactory tracts to brain ```

Answer 17

• Olfactory receptors (OR) – G-protein coupled receptors located on cilia on the ORN dendrite • ~400 OR types (~1000 genes but most broken) • Only 1 OR type per ORN • Each OR responds in varying degrees to many odours – component processing – odours identified by pattern of activity across many receptor types • Intensity changes the perceived smell as lower affinity receptors come online • Rapid turn over of ORNs (1-2 months) – continually replaced from basal stem cells • Human 10M ORNs (dog 200M)

Answer 18

``` • Different receptor types scattered throughout olfactory mucosa • Same receptor types project to same general spot in olfactory bulb • Some type of topographic layout but not based on similarity of smell • Large convergence at olfactory bulb – 100 times ORNs-> olfactory bulb (Olfactory tract - bulb to cortex directly (not via thalamus) and mostly ipsilateral): (Each olfactory tract projects to several structures in medial temporal lobe) - 2 main pathways from amygdala/piriform ->amygdala->hypothalamus and other limbic structures (Limbic: motivational responses, autonomic, emotional) ->piriform cortex (primary olfactory)->thalamus->orbital frontal cortex (Thalamic-orbitofrontal: conscious perception of odours, memory, attention) ```

Answer 19

• 5 primary tastes: salty, sweet, sour, bitter, umami • More complex taste from higher level cortical processing of combined input • Information provided • Umami – protein • Sweet – carbs/high caloric • Salty – ion/water balance • Bitter and sour – warning system (detect bitter 1000 times better than salty) • Maybe 6th taste of fat – usually thought of as texture/feel – some evidence for tastebud response – fat is important • Taste receptors – tongue and oral cavity – clusters of 50-100 in taste buds • Taste buds located on small protuberances – papillae

Answer 20

• Few taste buds on centre tongue • Receptors not neural but synapse like connection to neuron • Multiple receptors feed each neuron • Non-taste papillae – secretory and somatosensory - mouthfeel, temperature and nociception (irritants like capsaicin, CO2, acetic acid) • Receptor for each of the 5 primary tastes – 1 receptor protein in each receptor cell • High receptor turnover (10-30 days) drops with age especially after 70 • 33 gustatory receptor proteins – 1 umami, 2 sweet, 30 bitter • Sour and salty act directly on ion channels

Answer 21

``` • 3 gustatory afferents • Solitary nucleus in medulla then project to ventral posterior medial (VPM) nucleus of thalamus • VPM projects to primary gustatory cortex (superior lip of lateral fissure near face area of somatosensory homunculus) ```

Answer 22

• 25% super (and 25% nontasters) • Taste buds vary individually – 120 to 670 per cm2 – women more than men • Super-tasters experience much more intense taste (especially bitter) and more pain to irritants • Young children very sensitive to bitter – protection from accidental poisoning (put everything in their mouths!) • More papillae seems to be the underlying cause (more densely packed)

Answer 23

Anosmia - the inability to smell • Common cause: blow to the head such that the brain shifts in the skull and the axons from the olfactory receptors are sheared off where they enter the skull (cribriform plate) Ageusia - the inability to taste • Very rare • Probably due to the diffuse afferent tracts from the taste receptors