CNS 3

Question 1

Sensory function is dependent on:

Answer 1

• Intact afferent cellular circuits
  
  • damage to peripheral nerves, spinal cord, lower brainstem, or thalamus, message wont be received by brain

Question 2

sensory “pathway”

Answer 2

1. sensory receptors transduce changes in environmental energy into electronic signals
2. receptors connect to primary afferent neurons which bring this “information” to the spinal cord and brain via action potentials
3. Primary afferent neuron cell bodies housed in dorsal root and cranial nerve ganglia two processes
   
   1. peripheral process that extends distally within a peripheral nerve to appropriate sensory recepters.
   2. a central process that enters the spinal cord/brain through a dorsal root or cranial nerve.

Question 3

afferent

Answer 3

toward the CNS

Question 4

Dermatomes:

T1, C7-C8

Answer 4

• related to hands and medial FA
• *when administering block, numb hands could mean you block is migrating up
• will affect phrenic nerve, airway control, and cardiac accelerants

Question 5

What does the Phrenic nerve innervate?

Answer 5

the diaphragm

*provides only innervation to diaphragm

Question 6

Exteroceptive information

Answer 6

• interaction of the skin with the environment
• Two types
  
  • Fine, discriminatory touch
    
    • A(alpha)
  • Pain and temperature
    
    • A(delta)

Question 7

Dermatome:

T3, 4, and 5

Answer 7

Cardiac accelerator fibers

*person with T4 spinal injury or block, they are more likely to go into shock; unable to compensate by increasing HR

Question 8

Dermatome:

T 10

Answer 8

Umbilicus

Question 9

Proprioceptive information

Answer 9

Where your body/limb is positioned “in space”

Question 10

Enteroceptive information

Answer 10

internal status of the body

Question 11

Types of receptor activation

Answer 11

• Mechanoreceptor- compression or stretch
• Chemicoreceptor
• Thermoreceptors- expand and contract with different temperatures (different receptors for each change)
• nociceptors (pain)-detect physical or chemical damage
• electromagnetic (detect photons)- used for sight
  
  • open in the dark, allows flux of ions, close when they see light

Question 12

Fine Discriminatory touch

Mechanosensitive afferent fibers

Answer 12

• Fast adaptive tactile fibers
  
  • quickly stop noticing
• Slow adaptation tactile fibers
  
  • keep noticing stimulus for a while (pain)
• Type 1- small receptive field, higher density of fibers
• Type 2 fibers- large receptive field

Question 13

Meissner’s corpuscles

Answer 13

• Type of mechanoreceptor
• Fast adaptive
• right beneath the non-hairy skin
• senses change in pressure and velocity
• can discriminate precisely where the stimulus is because it is located so shallowly in the skin

Question 14

Labeled line principle

Answer 14

1. Each nerve tract terminates at a specific point in the CNS and carries a selective sensory modality
2. sensation is perceived when a specific stimulated nerve leads to specific areas in the CNS
3. alteration of the specific nerve tracts activity will only change the intensity of the stimulus (quantitative) vs changing the type of stimulus perceived (qualitative)

Question 15

Dorsal Column

Medial Lemniscal pathway

How does it work?

Answer 15

• primary afferent neurons have cell bodies in the dorsal root.
• Their axons ascend to the medulla where they encounter the dorsal column nuclei:
  
  • Nucleus gracilis (lower body/leg)
  • Nucleus cuneatus (upper body/arm)
• 2nd order neuron axons then cross to the other side of medulla and project to the thalamus via the medial lemniscus

Question 16

The Anterolateral System

Spinothalamic

Answer 16

• Enters the spinal cord from the dorsal spinal nerve roots, immediately synapses in the dorsal horns
• dessucates to the other side of the cord
• travels upward through anterior and lateral white columns
• tracts terminate at all levels of the lower brain stem and in the thalamus

Question 17

Spinocerebellar

Proprioceptive Pathway

Answer 17

• Perception of position, awareness of body movements and local reflexes
• Carries both cutaneous and proprioceptive information to cerebellum and cerebral cortex

Question 18

Dorsal Column Nuclei

Answer 18

• Contains the second order neurons
  
  • gracile and cuneate nuclei
• in the medulla

Question 19

How the dorsal column neurons differ from primary afferent neurons

Answer 19

1. receptive fields cover a greater area
   
   1. multiple primary afferent fibers synapse on each dorsal column neuron
2. Several types of primary afferent neurons (different sensory modalities) converge on the second-order neurons allowing a greater diversity in sensory responses
3. Dorsal column neurons often modulated by adjacent interneurons that provide inhibition to the served receptive fields.

Question 20

Thalamus

Third order neurons

Answer 20

• these neurons project to the somatosensory cortex
  
  • inhibitory and excitatory
  • sleep/wake cycle and anesthesia will influence excitability

Question 21

Parts of the Basal ganglia (5)

Answer 21

1. caudate nucleus
2. putamen
3. globus pallidus
4. substantia nigra
5. subthalamic nucleus

Question 22

lesions of the basal ganglia cause _______

Answer 22

abnormal movement and posture

Question 23

Pacinian corpuscle

Answer 23

• type of mechanoreceptor
• Fast adaptive
• onion-like structure in the subcutaneous skin (surrounding unmyelinated nerve endings)
• sensation: vibration; tapping

Question 24

Ruffini corpuscle

Answer 24

• type of mechanoreceptor
• slow adapting
• encapsulated
• Senses pressure

Question 25

Merkel disk

Answer 25

* Type of mechanoreceptro * slow adaptive * transducer is on epithelial cells * senses location

Question 26

Dorsal column somatosensory system What does it sense?

Answer 26

1. fine touch 2. pressure 3. two-point discrimination 4. vibration 5. proprioception