topic 19- Nervous system pathways

Question 1

Ascending Spinal Pathways (Sensory)

Answer 1

• conduct impulses from general sense receptors into brain
• 3 successive neurons from receptor to cortex:
  First Order neuron
  Second Order neuron
  Third order neuron
• axons of 1st or 2nd order neurons form ascending spinal tracts:
• pathways (= neurons from receptor to brain) are named for the location of the tracts (projection tracts in white matter of spinal cord)

Question 2

First order neuron

Answer 2

• unipolar sensory neuron with receptor

- signal from receptor to spinal cord (PNS)

Question 3

Second order neuron

what type of polar

where is the cell body

where does it terminate, does it cross over?

Answer 3

• interneuron, multipolar (CNS)
• cell body in dorsal horn of spinal cord or medulla (CNS)
• decussates (crosses over) in spinal cord or medulla
• axon terminal in thalamus

Question 4

Third order neuron

where is cell body?

where does it impulse to?

Answer 4

• interneuron, multipolar

- cell body in thalamus – impulses to postcentral gyrus (sensory cortex) (CNS)

Question 5

3 ascending pathways

Answer 5

posterior (dorsal) column pathway/tract
Spinothalamic Pathway/Tracts
Spinocerebellar Pathway/Tracts

Question 6

Posterior (Dorsal) Column Pathway /Tracts

Answer 6

• sensations can be precisely located (touch)

- receptors = free nerve endings, Meissner’s etc

Question 7

Spinothalamic Pathway/Tracts

what type of receptors?

Answer 7

• non-specific, difficult to localize

- receptors = temperature, pain

Question 8

Spinocerebellar Pathway/Tracts

what are the receptors

what neurons are involved

crossing over? conscious?

Answer 8

• ascending tracts from spinal cord to cerebellum
• receptors = proprioceptors
• 2nd order neuron directly to cerebellum (no 3rd order)
• no conscious perception
• no decussation

Question 9

somatic descending motor pathways

what are the two types of neurons

Answer 9

• conduct impulses from brain to effector (skeletal muscle)
  2 neurons in pathway:
  a) Upper Motor Neuron (CNS):
• multipolar interneurons
• cell bodies in cortex or brainstem nuclei
  b) Lower Motor Neuron = a motor neuron (cell bodies in ventral horn (CNS) and axons in PNS)

Question 10

axons of upper motor neurons form descending spinal tracts:

Answer 10

• • pathways (brain to effector) are named for the location of the descending tracts (projection tracts in spinal cord)

Corticospinal Pathway/tract
Indirect pathways/tract

Question 11

Corticospinal Pathways/Tracts

cell bodies where

decussate?

Answer 11

• cell bodies in cerebral cortex

- tracts mainly decussate in medulla

Question 12

Indirect Pathways/Tracts

where are the cell bodies

receive impulses from where

Answer 12

• cell bodies in brainstem nuclei

- receive impulses from motor cortex, basal nuclei, cerebellum