A&P Chapter 16 - Sensory and Motor Pathways

  1. ascending tracts
    • always sensory and afferent
    • carry info from receptors up to brain and spinal cord
    • begin at a sensory receptor that is acted on by a stimulus
    • AP travels to spinal cord, up to cerebrum or cerebellum
  2. descending tracts
    • always motor and efferent
    • carry info from brain out out effectors
    • begin in frontal lobe motor cortex
    • AP travels down cord out to muscle or gland
  3. tracts
    • all fibers in a tract have similar origins, destinations, functions
    • fibers usually decussate in tract
    • if they cross, response is contralateral
  4. sensory pathways
    • every sensory tract contains 3 neurons: FON, SON, TON
    • 3 specific pathways: posterior column medial lemniscus/fasciculus gracilis, fasciculus cuneatus
  5. first order neuron
    • begins at sensory receptor, ends at brain stem or spinal cord
    • BS: sensations from mouth, teeth, eyes (via cranial nerves)
    • SC: sensations from posterior head, neck, everywhere else (via spinal nerves)
  6. second order neuron
    • begins at BS/SC, ends at thalamus
    • decussation in medulla pyramids
  7. third order neuron
    begins at thalamus, ends at cerebrum (rarely cerebellum)
  8. posterior column medial lemniscus pathway
    • sensory pathway
    • conveys sensations of touch to the cerebrum
    • contralateral
    • discriminative touch, stereognosis, proprioception, weight discrimination, vibration, kinesthesia
  9. fasciculus gracilis
    • part of posterior column medial lemniscus pathway
    • conveys info from lower part of body
  10. fasciculus cuneatus
    • part of posterior column medial lemniscus pathway
    • conveys info from upper part of body
  11. stereognosis
    ability to perceive the form of an object by using the sense of touch
  12. proprioception
    awareness of the position of the body without looking
  13. kinesthesia
    awareness of the movement of the body without looking
  14. anterolateral spinothalamic pathway
    • sensory pathway
    • anterior: conveys sensations of itch, tickle, pressure, and crude touch
    • lateral: conveys sensations of pain and temperature
  15. anterior posterior spinocerebellar pathway
    • sensory pathway
    • balance, posture, muscle tone, skilled body movements
  16. motor pathways
    • always begin in frontal lobe of brain and end in muscle or gland
    • 2 types: direct and indirect
  17. direct motor pathways
    • aka pyramidal
    • 2 neurons: upper motor neuron and lower motor neuron
    • produces precise, voluntary contraction of a muscle
    • almost all fibers decussate (95%)
    • 3 pathways: lateral corticospinal, anterior corticospinal, corticobulbar
  18. upper motor neuron
    • begins in motor cortex, ends in BS/SC
    • synapses with lower motor neuron
  19. lower motor neuron
    begins in BS/SC, ends in muscle or gland
  20. lateral corticospinal pathway
    • direct motor pathway
    • all fibers decussate
    • voluntary movement of the arms, hands, legs, feet
  21. anterior corticospinal pathway
    • direct motor pathway
    • 90% of fibers decussate
    • voluntary movement of the neck, trunk, axial skeleton
  22. corticobulbar pathway
    • direct motor pathway
    • all fibers decussate
    • voluntary contraction of the muscles of the head, face, neck
  23. indirect motor pathways
    • aka extrapyramidal
    • more complicated than direct (extra neuron)
    • begins in motor cortex with association neuron -> UMN -> LMN
    • produces involuntary responses
    • 5 tracts: tectospinal, rubrospinal, vestibulospinal, lateral reticulospinal, medial reticulospinal
  24. tectospinal pathway
    • indrect motor pathway
    • involuntary movement of the eyes and head in response to rapid auditory, visual, or tactile stimulation
  25. rubrospinal pathway
    • indirect motor pathway
    • involuntary movement of fingers and toes
  26. vestibulospinal pathway
    • indirect motor pathway
    • no fibers cross
    • muscle tone, posture, balance
  27. lateral reticulospinal pathway
    • indirect motor pathway
    • controls reflexes associated with pain (withdrawal reflex)
  28. medial reticulospinal pathway
    • indirect motor pathway
    • inhibits withdrawal reflex
  29. sensation
    a conscious or subconscious awareness of internal or external stimulus
  30. perception
    the way a sensation is interpreted
  31. sensory modality
    • a unique sensations (such as taste, smell, etc)
    • a neuron can carry only one modality
    • 2 classes: general senses, special senses
  32. general senses
    touch, pressure, temperature
  33. special senses
    vision, hearing, taste, smell
  34. free nerve endings
    • sensory receptors
    • exposed dendrites that respond to pain, temp, itch, tickle, light touch
  35. encapsulated nerve endings
    • sensory receptors
    • dendrites enclosed in connective tissue capsule (pressure receptors)
  36. separate cells
    • sensory receptors
    • hearing and vision receptors
  37. exteroceptors
    receptors on body surface that respond to external stimuli
  38. interoceptors
    • aka visceroceptors
    • receptors inside body around blood vessels that respond to stretch, pressure, and pain
  39. proprioceptors
    receptors in muscles, tendons, joints, inner ear that respond to body position, movement, balance
  40. thermoreceptors
    temperature receptors
  41. photoreceptors
    light receptors
  42. chemoreceptors
    chemical receptors
  43. nociceptors
    pain receptors
  44. chronic pain
    long term and constant pain
  45. phantom pain
    pain perceived in a structure that was amputated
  46. referred pain
    deep pain projected to a surface site that shares the same spinal nerve
  47. sensory adaptations
    • long lasting stimulus will cause a sensation to decrease until it is no longer perceived
    • 2 receptors: phasic and tonic
  48. phasic receptors
    rapidly adapting receptors (temp, smell, touch)
  49. tonic receptors
    slowly adapting receptors (pain, chemical)
  50. baro receptors
    • heart and blood vessels
    • respond to changes in BP
  51. hair cell receptors
    • inner ear
    • maintain balance
  52. muscle spindle cells
    • muscles
    • prevent muscle damage if muscle has been stretched
  53. root hair plexus
    • hair follicle
    • makes hair sensitive to touch
  54. meissner's corpuscles
    touch receptors in the dermis
  55. pacinian corpuscles
    • pressure receptors in the dermis
    • respond to heavy and continuous touch
Card Set
A&P Chapter 16 - Sensory and Motor Pathways
A&P Chapter 16 - Sensory and Motor Pathways