6.2 Neuro Anatomy & Physiology - The Spinal Cord and Somatosensation

Question 1

What are the four kinds of sensation?

Answer 1

• Superficial/Exteroception
• Deep
• Visceral/Interoception
• Special Senses

Question 2

What is the most complex special sense?

Answer 2

Vision

Question 3

What are four kinds of superficial/exteroception?

Answer 3

• Pain
• Touch
• Temperature
• Two-point discrimination

Question 4

What is one kind of deep sensation?

Answer 4

Proprioception

Question 5

List the special senses

Answer 5

• Vision
• Olfactory sensation
• Hearing
• Balance
• Taste

(Replace touch with balance)

Question 6

What two kinds of sensation fall within somatosensation?

Answer 6

• Exteroception
• Deep sensation

Question 7

What four things are perceived through somatosensation?

Answer 7

• Touch
• Temperature
• Pain
• Body position

Question 8

Why can two identical action potentials result in two different sensations?

Answer 8

The type of the receptor being stimulated

Question 9

Which receptors mediate pain?

Answer 9

Nociceptors

Question 10

Which receptors mediate temperature?

Answer 10

Thermoreceptors

Question 11

Which receptors mediate touch, two-point discrimination, and proprioception?

Answer 11

Mechanoreceptors/proprioceptors

Question 12

What is the difference between nociception and pain?

Answer 12

Nociception is the transduction of signals that trigger pain, whereas pain itself is an unpleasant sensory and/or emotional experience associated with tissue damage

Question 13

What type of structures are nociceptors and where are they located?

Answer 13

Free nerve endings (dendrites) in the epidermis [this makes sense: detection]

Question 14

Which type of axons transfers fast and slow pain? (think: stubbing toe)

Answer 14

Fast: A delta
Slow: C

Question 15

Would it make sense for C fibres to be myelinated or unmyelinated? Why?

Answer 15

Unmyelinated; these axons transfer slow pain, meaning they are likely to not have myelin that would speed up the transduction

Question 16

Why is the onset of slow pain less obvious when hurting thumb than stubbing toe?

Answer 16

Thumb is faster to brain; delay of unmyelination is less pronounced

Question 17

What are the three types of C axons?

Answer 17

• Mechanical
• Thermal
• Polymodal (e.g. mechanical and chemical)

Question 18

How do local anaesthetics prevent perception of pain?

Answer 18

Block voltage-gated sodium channels, preventing depolarization

Question 19

What do skin mechanoreceptors help us to pick up on?

Answer 19

• Vibration
• Touch
• Pressure

Question 20

Give two examples of mechanoreceptors

Answer 20

• Meissner’s Corpuscle
• Pacinian Corpuscle

Question 21

What do meissner’s corpuscle detect?

Answer 21

Touch and vibration

Question 22

What do pacinian corpuscle detect?

Answer 22

Pressure (makes sense: located deeper in fatty layer of dermis)

Question 23

What are the three main somatosensory pathways of the body?

Answer 23

• Dorsal Column Medial-Lemniscus Pathway (DCML)
• Anterior spinothalamic tract
• Lateral spinothalamic tract

Question 24

What is the DCML responsible for? What areas of the spinal cord can it be associated with?

Answer 24

• Sensing touch and proprioception
• Associated with dorsal column white matter tract (sensory input)

Question 25

Describe the three orders of neurons in the DCML pathway

Answer 25

1st: Unipolar sensory neuron, carries information up the spinal cord in the caudal column 2nd: Synpases with 1st-order at ventral medulla, where it decussates and heads up through the foramen magnum into the brain\ 3rd: Synapses with second in the thamalus, and heads up into the cerebral cortex (post-central gyrus; primary somatosensory cortex)

Question 26

What is a name for the combination of the anterior and lateral spinothalamic tract?

Answer 26

Antero-lateral spinothalamic tract

Question 27

What is the anterior spinothalamic tract associated with?

Answer 27

Crude touch

Question 28

What is the lateral spinothalamic tract associated with?

Answer 28

Pain, temperature

Question 29

What is non-noxious stimuli?

Answer 29

Stimuli not picked up by nociceptors (i.e., pain receptors)

Question 30

Which of the two components of the antero-lateral spinothalamic tract deal with noxious and non-noxious mechanical stimuli?

Answer 30

Antero: Non-noxious Lateral: Noxious

Question 31

Describe the orders of neurons in the anterior spinothalamic tract

Answer 31

1st: Free nerve endings carry stimulus to second order neurons in the spinal cord 2nd: Synapses with first order neurons, and immediately crosses the spinal cord before heading up to the brain 3rd: Synapses with the second order neurons at the level of the thalamus, before heading out to the primary somatosensory cortex in the cerebral cortex

Question 32

In what part of the limbic lobe is emotional context added to pain responses?

Answer 32

The cingulate gyrus

Question 33

What is the biggest white matter tract in the brain?

Answer 33

Corpus callosum

Question 34

Describe the Gate Theory of Pain

Answer 34

A delta mechnoreceptor stimulation can excite inhibitory interneurons, thus preventing the relay of nociceptor action potentials through the lateral spinothalamic tract

Question 35

What type of pain regulation is associated with the Gate Theory of Pain

Answer 35

Afferent regulation (inhibition of afferent pain signals)

Question 36

Describe descending pain regulation

Answer 36

Nerves from the periaqueductal grey matter run through the raphe nuclei in the medulla and synapse on second order neurons in the lateral spinothalamic tract. Here, they secrete endogenous opioids (can be substituted with exogenous ones), thus modulating nociceptive input through the dorsal horn.

Question 37

What structure secretes endogenous opioids during descending pain regulation?

Answer 37

Raphe nuclei

Question 38

What are three kinds of sensory receptors (think of dog pictures)?

Answer 38

- Free nerve endings - Encapsulated nerve endings (pressure-sensitive) - Gustatory receptor

Question 39

Describe the basic mechanism of a gustatory receptor

Answer 39

Receptor potential triggers neurotransmitter release, which triggers action potential in afferent sensory neuron

Question 40

What are two ways in which primary afferent axons can vary?

Answer 40

- Myelination - Diameter