Somatic Pathways

Question 1

What is sensation?

Answer 1

• the detection of changes in our internal environment and/or external environment
• involves sensory receptors and the neurons that convey the signals from those receptors to the CNS

Question 2

What is perception?

Answer 2

• the conscious awareness and interpretation of sensations

- involves the processing of sensory information in the cerebral cortex

Question 3

What are somatic sensations?

Answer 3

• tactile sensations that arise from the skin (e.g., touch,
  pressure, vibration, temperature, pain)
• proprioceptive (position sense) sensations that arise
  from the muscles and joints

Question 4

What are special sensations?

Answer 4

• vision, hearing, taste, smell, balance

Question 5

What are visceral sensations?

Answer 5

• sensations that arise from the visceral organs (e.g.,

pressure, stretch, chemical concentrations)

Question 6

What are the three types of sensory receptors?

Answer 6

• free nerve endings
• encapsulated nerve endings
• separate cells

Question 7

Which type of sensory receptor is responsible for pain and temperature?

Answer 7

• free nerve endings

Question 8

Which type of sensory receptor is responsible for pressure and vibration?

Answer 8

• encapsulated nerve endings

Question 9

Which type of sensory receptor is responsible for special senses?

Answer 9

• separate cells

Question 10

Which proprioceptive sensory receptors are found in muscle?

Answer 10

• muscle spindles, tendon organs

Question 11

Which proprioceptive sensory receptors are found in joints?

Answer 11

• ruffini corpuscles, pacinian corpuscles

Question 12

What are the five types of tactile sensory receptors?

Answer 12

• free nerve ending
• merkel disc
• meissner corpuscle
• ruffini corpuscle
• pacinian corpuscle

Question 13

What do proprioceptive sensory receptors do in relation to sensation in the muscles?

Answer 13

• muscle spindle = muscle length

- tendon organ = muscle tension

Question 14

What do the sensory pathways of the somatic nervous system do?

Answer 14

• transmit somatic sensory signals from peripheral receptors to the brain

Question 15

What do the motor pathways of the somatic nervous system do?

Answer 15

• transmit motor signals from the brain to skeletal muscles

Question 16

Are tracts sensory and motor?

Answer 16

• tracts are either sensory OR motor, they are never mixed

Question 17

What is the 3-neuron relay system?

Answer 17

• first, second, and third order neurons are in between each step
• sensory receptor, spinal cord or medulla oblongata, thalamus, primary somatosensory area

Question 18

Why is the second-order neuron important?

Answer 18

• always decussates (cross over to the opposite side of the body)

Question 19

What are the two main somatic sensory pathways?

Answer 19

• anterolateral pathway

- posterior column pathway

Question 20

What is the anterolateral pathway?

Answer 20

• carries signals related to temperature and pain

- uses tracts in the anterior and lateral columns

Question 21

What is the posterior column pathway?

Answer 21

• carries signals related to touch, pressure, vibration, and proprioception
• uses tracts in the posterior column

Question 22

In the anterolateral pathway, where is the cell body located in the first-order neuron?

Answer 22

• posterior root ganglion

Question 23

In the anterolateral pathway, where is the cell body located in the second-order neuron?

Answer 23

• posterior horn

- crosses in the spinal cord

Question 24

In the anterolateral pathway, where is the cell body located in the third-order neuron?

Answer 24

• thalamus

Question 25

In the posterior column pathway, where is the cell body located in the first-order neuron?

Answer 25

- posterior root ganglion

Question 26

In the posterior column pathway, where is the cell body located in the second-order neuron?

Answer 26

- medulla oblongata | - crosses in the brain stem

Question 27

In the posterior column pathway, where is the cell body located in the third-order neuron?

Answer 27

- thalamus

Question 28

Is the spinothalamic tract contralateral or ipsilateral?

Answer 28

- contralateral

Question 29

Is the posterior columb tracts contralateral or ipsilateral?

Answer 29

- ipsilateral

Question 30

What is the 2-neuron relay system of the somatic motor pathways?

Answer 30

- upper motor neuron, and lower motor neuron | - primary motor area, spinal cord, skeletal muscle

Question 31

Which neuron pathway crosses in the somatic motor pathways?

Answer 31

- first neuron crosses

Question 32

What are the two ways somatic motor pathways are classified?

Answer 32

- direct or indirect

Question 33

What are direct motor pathways?

Answer 33

- carry signals originating in the cerebral cortex

Question 34

What are indirect motor pathways?

Answer 34

- carry signals originating in the brain stem

Question 35

What is the main direct motor pathways?

Answer 35

- the corticospinal pathway

Question 36

90%

Answer 36

- 90% of the upper motor neurons decussate in the medulla oblongata and travel down the contralateral side of the spinal cord (lateral corticospinal tract)

Question 37

10%

Answer 37

- 10% of the upper motor neurons travel down the ipsilateral side of the spinal cord (anterior corticospinal tract) and decussate at their target spinal segment

Question 38

What is syringomyelia?

Answer 38

- fluid-filled (CSF) cyst can form within the central canal of the spinal cord - pain/temperature affected - touch/ pressure/ vibration/ proprioception unaffected

Question 39

What is brown-séquard syndrome?

Answer 39

- caused by an injury to one half of the spinal cord (hemisection) - affects the ipsilateral anterior, lateral, and posterior column