Week 4 Physiology

Monosynaptic reflexes

  • Knee reflex
  • Stretch receptor in tendon –> stretch–> afferent to spinal cord –> synapse directly to efferent –> motor neuron –>  contraction of extensor.
  • Doesn’t have cortical input
  • Fast


Polysynaptic reflexes

  • Afferent and efferent neuron separated by at least one interneuron.
  • Withdrawal reflex
  • Pain leads to ipsilateral leg contraction and contralateral leg extension


Organisation of the spinal cord

  • Midbrain, pons, medulla
  • Conscious tracts – Comprised of the dorsal column-medial lemniscal pathway, and the anterolateral system.
    • Dorsal column – vibration, proprioception, fine touch.
    • Dorsal column–> medial leminiscus(brain stem).
    • UL travel in fasciculus cuneatus.
    • LL travel in fasciculus gracillis.
    • Decuss in medulla as second order neuron which goes to thalamus(ventral posterolateral nucleus).
    • Third order neuron: Thalamus–> internal capsule–> sensory cortex.
    • Anterolateral spinothalamic tract – crude touch, pressure.
    • Lateral spinothalamic tract  – pain, temperature
    • Both enter and ascend 1-2levels then terminate in dorsal horn(substantia gelatinosa).
    • 2nd order decusses, separate into the two tracts and rises to thalamus(ventral posterolateral nucleus)
    • Then third neuron–> internal capsule to sensory cortex.
  • Unconscious tracts – Comprises of the spinocerebellar tracts. – balance
  • Descending tracts
    • Cortex –> internal capsule(between thalamus and basal ganglia)–> crus of cerebri–> midbrain/pons/medulla–> divides into lateral and anterior corticospinal tracts–> terminate in ventral horn at synapse with lower motor neuron.
    • Lateral tract decuss at medulla while anterior spinal tract descends to cervical/thoracic level then decuss.


Sensory homonculus

  • Sensation of various parts of the body occupies different amount of the sensory cortex reflecting the depth of sensory detail in each body part- this is the visual representation.


Visual pathways and lesions


Ganong's Review of Medical Physiology, 24th Edition

Ganong’s Review of Medical Physiology, 24th Edition

LP – lower quadrant is via Parietal radiation. Upper is Temporal radiation.


Pupillary reflexes

  • Sensory – CN 2 –> CN3 leads to pupillary constriction in both eyes.
  • Accomodation is also via CN3

Overview of anatomy and auditory pathways.

External ear captures sound and funnels it –> tympanic membrane vibrates–> transmitted by the stapes, incus and malleus(who act as step down with help from stapedius and tensor tympani) to oval window of inner ear –> hair cells in cochlea activate at different frequencies –> change sound energy to electrical energy and transmit to brain via CN 8.


Tuning fork tests

  • Webber – place tuning fork in middle
    • Normal – hear it equal on both sides
    • In sensory deafness –> hear it louder in normal ear
    • In conductive deafness  -> increase bone conduction–> hear it in the affected ear
  • Rinne –  placed on mastoid process then near ear canal
    • Sensory deafness – can hear it after placed near canal if partial loss
    • In conductive deafness  -> increase bone conduction–> cant hear it after placing next to ear canal

Vestibular function is worth a quick look too (particularly nystagmus and caloric stimulation)

Mediated by the three semi-lunar canals via CN 8




  • Tell me about the stretch reflex
  • Explain the sensory and motor tracts o the spinal cord
  • What is the effect of various lesions to the visual pathways
  • How does the pupillary reflex work