Week 6 Flashcards

Question

Semicircular Canals- hyper polarisation and depolarisation

Answer 1

``` Hair cells deform one way for depolarisation (excitation), other for hyperpolarisation (inhibition) Excitation (or inhibition) as motion initiated • Baseline through most of the motion • Inhibition (or excitation) as motion stopped • Left and right act together as functional pairs ```

Answer 2

``` Hair cells into flat membrane covered in tiny ‘stones’ • Linear acceleration exerts force that moves the membrane, distorting the hair cells • Translational motion or gravity Otolith system cannot distinguish between tilt and linear acceleration • Use tilt to simulate G-force in VR Gravity is a constant linear acceleration • So head tilts illicit continuous activity above or below baseline firing rates ```

Answer 3

Most movements illicit complex patterns of vestibular stimulation • Individual organ signals may be ambiguous due to combined (complex) movement plus tilts and gravity • Integrate 3 canals + 2 otoliths + visual and somatosensory to interpret head and body movement and positions

Answer 4

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

Answer 5

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 6

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 7

``` Surface • Adapt quickly – no sustained response • Best response to lateral motion • Medium sensitivity ```

Answer 8

``` Deep • Respond rapidly, adapt quickly • Sudden displacement of the skin • Respond best to vibration • High sensitivity ```

Answer 9

* Surface * Sustained response, slow adaptation * Gradual skin indentation * Best response to edges and points * Medium sensitivity

Answer 10

Deep • Sustained response, slow adaptation • Best response to skin stretch • Low sensitivity

Answer 11

No specialised structure | • Temperature and pain

Answer 12

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 13

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 14

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 15

``` 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 16

``` 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 17

``` 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 18

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 19

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 20

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

Answer 21

``` Periaqueductal grey (PAG) has analgesic effects • Electric stimulation reduces pain • Receptors for opiate based pain drugs • Endorphins modulate PAG activity ```

Answer 22

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 23

• 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 24

``` 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 25

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 26

``` • 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 ```

Answer 27

ORNS (high convergence)-> 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 28

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 29

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 30

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 31

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 32

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

Answer 33

Auditory – transmit sound, transduce, transmit neural, process • Middle ear ossicles greatly amplify (impedance matching) • Basilar membrane vibrates, Organ of Corti transduces • Basilar membrane varies – tonotopic • Complex brainstem network from cochlear nucleus to MGN then A1 • Subcortical localisation – interaural time and intensity differences and SO 3 types of hearing loss • Vestibular – 5 organs to sense accelerations of the head • Semicircular canals (rotational), otolith organs (linear including gravity) • Vestibulo-occular reflex and oscillopsia • Somatosensory – extero-, proprio-, intero- • Dermatomes and pathways – DCML and ALS • S1 and S2 – centre-surround RFs • Olfaction – direct and ipsilateral then limbic and conscious • Gustatory