Somatic Pathways (Lec 21)

Question 1

Difference between sensation & perception

Answer 1

Sensation: DETECTION of changes of internal and external environment via sensory receptors

Perception: CONSCIOUS awareness & interpretation of sensations - process it in cerebral cortex

Not all sensations are perceived and conscious

Question 2

Various sensory modalities

Answer 2

• Somatic sensation (skin,muscles,joints)
  
  • tactile sensations (Arise from skin)
  • proprioceptive [position sense] sensations (arise from muscles/joints)
• Special senses (vision, hearing etc.)
• Visceral sensation (organ sensations)

Question 3

Receptors that detect somatic sensations

Answer 3

• Free nerve endings (pain, temp)
• Encapsulated nerve endings (pressure, vibration, proprioception)
• Separate cells (special senses)

Question 4

2 Main Somatic Sensory pathways

Answer 4

• Anterolateral pathway
  (Transmit signals from free nerve endings that lead to perceptions related to pain & temperature)
  - tracts in anterior/lateral columns
• Posterior column pathway
  (Transmit signals from encapsulated nerve endings that lead to perception related to touch, pressure, vibration, proprioception)
  - tract in posterior column

Question 5

2 main direct Somatic Motor pathways

Answer 5

Corticospinal pathway
- 90%
Upper motor neuron - cell body in primary motor area - decussate in brain stem (medulla oblongata) - lower motor neuron - travel down opposite side of spinal cord in the lateral corticospinal tract - cell body in anterior horn - skeletal muscle
- 10%
Upper motor neuron - cell body in the primary motor area - travel down same side of spinal cord in the anterior corticospinal tract - decussates at spinal cord - lower motor neuron - cell body in anterior horn - skeletal muscle

Question 6

Temperature and pain are received in response to stimulation of _______

Answer 6

Free nerve endings

Question 7

Touch pressure and vibration are perceived in response to stimulation of ________

Answer 7

Encapsulated nerve endings

Question 8

Motor tract =

Answer 8

From brain to body

Question 9

Sensory tract =

Answer 9

From body to brain

Question 10

Somatic sensory pathways consist of a 3 neuron relay system

Answer 10

• 1st order neuron
  
  • transmit sensory signals from receptor to spinal cord or brain stem
• 2nd order neuron
  (pathway always crosses to opposite side of body)
  
  • transmits signals from spinal cord/brain stem to thalamus
• 3rd order neuron
  
  • transmits signal from thalamus to primary somatosensory area in parietal lobe of cerebrum

Question 11

The posterior column pathway vs anterolateral pathway

Answer 11

Posterior is like a column, doesn’t switch til it’s up the spinal cord to the brain stem (1st order neuron change happens later)

Anterolateral switches over once entered to spinal cord (1st order neuron change happens sooner)

Question 12

Somatic Motor pathways consist of a 2-neuron relay system

Answer 12

• Upper motor neuron
  
  • transmits motor signals from primary motor area in frontal lobe of cerebrum to the spinal cord
• upper always cross to opposite side of body
• Lower motor neuron
  
  • transmits signals from spinal cord to skeletal muscle

Question 13

Decussation of pyramids is the ______

Answer 13

Site which neurons cross over in the somatic motor pathways