Sensorimotor Systems

• Where are primary sensory neuron cell bodies located?

  Dorsal root ganglia
• Fill in the blanks

  A) Muscle spindle

  B) Inhibitory interneuron

  C) Alpha motor neurons

  D) Antagonist muscle

  
• Different classes of sensory neuron project to different layers of the dorsal horn (or ventral horn -> proprioceptors).
• Where do mechanoreceptors project?

  Into dorsal horn locally AND up through dorsal columns
• What is a funiculus?

  Big chunk of white matter
• What is a fasiculus?

  particular axon tract
• Almost every sensory circuit to the cortex involves going via the thalamus.
• Fill in the blanks

  A) Lateral corticospinal

  B) Reticulospinal

  C) Vestibulospinal

  D) Tectospinal

  E) Medial longitudinal

  F) Ventral corticospinal

  G) Ventral spinocerebellar

  H) Dorsal spinocerebellar

  I) Cuneate fasciculus

  J) Gracile fasiculus

  
• Cuneate fasciculus conducts information from upper limb.

  Gracile fasciculus conducts information from lower limb.
• What is the thalamus part of?

  The diencephalon
• What do extrafusal muscle fibres do?

  Cause muscle tension/contraction
• What do intrafusal muscle fibres do?

  Sense tension
• Where do proprioceptors project?

  Into ventral horn locally & up through dorsal columns
• Proprioceptive signalling travels through the dorsal & ventral spinocerebellar tracts (lower body) and cuneate fasciculus (upper body).
• Fill in the blanks

  A) Primary motor cortex

  B) Somatosensory cortex

  C) Posterior parietal cortex

  D) Visual cortex

  E) Supplementary motor cortex

  F) Premotor area

  G) Prefrontal cortex

  H) Inferotemporal cortex

  I) Auditory cortex

  J) Gustatory cortex

  
• The primary somatosensory cortex is split into 4 Brodmann areas. What are they?


  1 - nociceptive signals

  2

  3a - proprioceptive & nociceptive signals

  3b - mechanoreceptive & nociceptive signals
• A topographic map of the body exists in the primary somatosensory cortex.
• What is the reticular formation?

  Huge 'reticulum' of nuclei & tracts in the brainstem

  Acts as a huge crossroads (think Birmingham spaghetti junction)
• What is the difference between discriminative pain & affective pain?

  Discriminative pain -> where the pain is, spinothalamic tract

  Affective pain -> how the pain makes you feel, spinoreticular tract
• Where does the spinothalamic pathway project to in the thalamus?

  Ventral posterolateral nucleus
• Where does the spinotreticular pathway project to in the thalamus?

  Medial thalamic nuclei
• Fill in the blanks

  A) Ventral posterior lateral nucleus

  B) Reticular formation

  C) PAG

  D) Superior colliculus

  E) Hypothalamus

  F) Amygdala

  G) Medial thalamic nuclei

  H) Anterior cingulate cortex

  I) insula

  
• Fill in the blanks

  A) Corpus callosum

  B) Cingulate gyrus

  C) Parahippocampal gyrus

  
• What do the vestibulospinal tracts do?

  Send vestibular motor signals
• What do tectospinal tracts do?

  Send motor signals to coordinate with eye & head movements
• What do reticulospinal tracts do?

  Send motor signals to coordinate (esp. in upright postural control)
• What do pyramidal tracts do?

  Control voluntary movements
• How does touch sensation travel from the upper limb?

  Mechanoreceptors -> dorsal horn -> into cuneate tract to cuneate nucleus -> decussates? -> up to medial leminiscus -> project to ventral posterior lateral nucleus of the thalamus -> projects to somatosensory cortex
• How does sensation travel up from lower limb?

  Mechanoreceptors -> dorsal horn -> into gracile tract -> up to gracile nucleus -> decussates? -> medial leminiscus -> projects to ventral posterior lateral nucleus of thalamus -> project to somatosensory cortex
• How does touch sensation from the head travel to the brain?

  Touch sensation in head is detected by somatosensory neurons in trigeminal ganglion -> projects to trigeminal sensory nucleus (in brainstem) -> projects across midline to thalamus (vental posterior medial nucleus) -> somatosensory cortex
• How can we inhibit pain signals?

  1 - Through reticular formation nuclei (e.g. PAG) -> sends projections down the spinal cord, via raphe nuclei -> send projections into dorsal horn -> active local inhibitory interneurons (that inhibit pain transmission) 

  2 - Mechanoreceptors (rubbing it better) -> stimulating touch sensation -> synapse with inhibiting interneurons -> inhibits second order ‘pain’ neurons