Lecture 5: General Sensory Mechanisms II

Question 1

What are the three physiological types of somatic senses?

Answer 1

• mechanoreceptive somatic senses
  
  • include both tactile and position senses that are stimulated by mechanical displacement of some tissue of the body
• thermoreceptive senses
• pain sense

Question 2

Where do somatic sence receptors collect sensory information from?

Answer 2

From all over the body.

Question 3

What does special senses refer to?

Answer 3

• vision
• hearing
• smell
• taste
• equilibrium

Question 4

What is a exteroreceptive sensation?

Answer 4

A sensation from the surface of the body.

Question 5

What does a proprioceptive sensation refer to?

Answer 5

Refers to physical state of the body.

• position sensations
• muscle and tendon sensations
• pressure sensations
• equilibrium

Question 6

What type of sensations are deep sensations?

Answer 6

• deep pressure
• pain
• vibrations

Question 7

Where do primary sensory neurons come from, travel through, and synapse?

Answer 7

• From external receptors
• Travel through dorsal roots of spinal cord
• Synapse with secondary neurons

Question 8

What do secondary sensory neurons make up?

Answer 8

Make up tracts in spinal cord and brainstem.

Question 9

In what anatomical structure do secondary sensory neurons usually terminate?

Answer 9

Thalamus

Question 10

What neurons do secondary neurons synapse with?

Answer 10

Synapse with tertiary neurons.

Question 11

What anatomical structure does tertiary neurons travel through?

Answer 11

Travel through the internal capsule.

Question 12

Where are teritary neurons coming from and going to?

Answer 12

From thalamus to the primary sensory cortex.

Question 13

What are the two systems that control conscious perception?

Answer 13

• Spinothalamic system
• Medial Lemniscal system

Question 14

What are the four ascending pathways that control unconscious perception?

Answer 14

• Spinocerebellar
• Spino-olivary
• Spinotectal
• Spinoreticular

Question 15

What are the two tracts of the spinothalamic system that are involved with conscious perception?

Answer 15

• Lateral Spinothalamic Tract
• Anterior Spinothalamic Tract

Question 16

What type of afferent sensory signals are carried by the lateral spinothalamic tract?

Answer 16

Carries pain and temperature.

Question 17

True or False:

In the lateral spinothalamic tract tertiary fibers ascend or descend 1-2 spinal cord segments before synapsing with secondary fibers.

Answer 17

False - primary fibers ascend or descend 1-2 spinal cord segments before synapsing with secondary fibers.

Question 18

In which column of the spinal cord do secondary axons of the lateral spinothalamic tract travel in?

Answer 18

Lateral column of the spinal cord.

Question 19

What do secondary axons in the lateral spinothalamic tract decussate through?

Answer 19

Anterior gray and white commissures.

Question 20

What does decussate mean?

Answer 20

Crossing-Over

Question 21

In the brainstem, which fibers join the secondary fibers of the lateral spinothalamic tract?

Answer 21

Fibers of the trigeminothalamic tract.

**carry pain and temperature from the face and teeth**

Question 22

You know that secondary fiber collaterals from the lateral spinothalamic tract project to reticular formation. What do they stimulate?

Answer 22

• Wakefulness
• Consciousness

Question 23

Where do secondary fibers from the lateral spinothalamic tract synapse with tertiary fibers at?

Answer 23

Ventral Posterolateral (VPL) nucleus of thalamus.

Question 24

Where do the tertiary fibers (corticopetal fibers) of the lateral spinothalamic tract synapse at?

Answer 24

Postcentral Gyrus

**somatic sensory areas 3, 1, 2**

Question 25

True or False: Tertiary fibers form part of the internal capsule.

Answer 25

True

Question 26

True or False: Secondary fibers project to ventral posterolateral (VPL) nucleus of the thalamus.

Answer 26

True

Question 27

What do afferent sensory neurons of the anterior spinothalamic tract carry?

Answer 27

* Light Touch (crude touch) * Pressure * Tickle * Itch

Question 28

How far can primary neurons of the anterior spinothalamic tract ascend in the spinal cord before synapsing with secondary neurons?

Answer 28

Primary neurons may ascend 8-10 spinal cord segments before synapsing with secondary neurons.

Question 29

True or False: Secondary fibers from both the anterior spinothalamic tract and lateral spinothalamic tract synapse with tertiary fibers in the VPL nucleus of thalamus.

Answer 29

True

Question 30

In the anterior spinothalamic tract, do tertiary fibers ascend through internal capsule to the primary sensory cortex?

Answer 30

Yes

Question 31

What afferent sensroy signal does the medial lemniscus system (posterior column system) carry?

Answer 31

* sensations for two-point sensation (fine touch) * pressure * vibration

Question 32

Where do primary fibers of the medial lemniscus system (posterior column system) ascend and synapse with secondary neurons at?

Answer 32

Primary fibers ascend entire length of spinal cord and synapse with secondary neurons in the medulla. * fasciculus gracilis * fasciculus cuneatus

Question 33

In the medial lemniscus system, where do fibers of the fasciculus gracilis synapse?

Answer 33

In nucleus gracilis.

Question 34

You know that in the medial lemniscus system fibers of the fasciculus gracilis synapse in the nucleus gracilis. What sensations does this route convey?

Answer 34

Convey sensations from below midthoracic level.

Question 35

In the medial lemniscus system, where do fibers of the fasciculus cuneatus synapse at?

Answer 35

In nucleus cuneatus.

Question 36

You know that in the medial lemniscus system fibers from the fasciculus cuneatus synapse in the nucleus cuneatus. What sensations does this route convey?

Answer 36

* Convey sensations from above the midthoracic level. * Also covenys proprioceptive sensation from arms to cerebellum.

Question 37

Do secondary fibers in the medial lemniscus system decussate?

Answer 37

Yes

Question 38

Where do secondary fibers ascend to and synapse?

Answer 38

With tertiary fibers in the VPL of thalamus.

Question 39

True or False: Tertiary fibers ascend through the internal capsule to the primary sensory cortex in the medial lemniscus system.

Answer 39

True

Question 40

What Brodmann's areas make up the primary somatosensory area?

Answer 40

Brodmann's areas 1, 2, and 3.

Question 41

Which Brodmann's areas make up the somatosensory association area?

Answer 41

Brodmann's areas 5 and 7.

Question 42

What does widespread bilateral excision of the somatosensory area I cause?

Answer 42

* loss of ability to localize discretely the different sensations in the different parts of the body; crude localization is still possible. * loss of ability to judge critical degrees of pressure against the body. * loss of ability to judge weights of objects * loss of ability to judge shapes or forms (astereognosis). * loss of ability to judge texture of materials. \*\*NOTE: pain and temperature sense is still preserved but poorly localized\*\*

Question 43

Where does the somatosensory area II receive signals from?

Answer 43

* brainstem * transmitted upward from both sides of the body * secondarily from somatosensory area I * other sensory areas of the body * including visual and auditory \*\*NOTE: projections from somatosensory area I are required for function of somatosensory area II \*\*NOTE: removal of somatosensory II has NO apparent effect on response of neurons in somatosensory area I

Question 44

Where do layers I and II of the somatosensory cortex receive input signals from?

Answer 44

lower brain centers

Question 45

Where do layers II and III of the somatosensory cortex send information through and to?

Answer 45

Send information through **corpus callosum** to **opposite hemisphere**.

Question 46

What distant areas do large neurons in layer V of the somatosensory cortex project to?

Answer 46

* basal nuclei * brainstem * spinal cord

Question 47

Where do axons from layer VI of the somatosensory cortex project to?

Answer 47

thalamus