6.2 Neuro Anatomy & Physiology - The Spinal Cord and Somatosensation Flashcards
What are the four kinds of sensation?
- Superficial/Exteroception
- Deep
- Visceral/Interoception
- Special Senses
What is the most complex special sense?
Vision
What are four kinds of superficial/exteroception?
- Pain
- Touch
- Temperature
- Two-point discrimination
What is one kind of deep sensation?
Proprioception
List the special senses
- Vision
- Olfactory sensation
- Hearing
- Balance
- Taste
(Replace touch with balance)
What two kinds of sensation fall within somatosensation?
- Exteroception
- Deep sensation
What four things are perceived through somatosensation?
- Touch
- Temperature
- Pain
- Body position
Why can two identical action potentials result in two different sensations?
The type of the receptor being stimulated
Which receptors mediate pain?
Nociceptors
Which receptors mediate temperature?
Thermoreceptors
Which receptors mediate touch, two-point discrimination, and proprioception?
Mechanoreceptors/proprioceptors
What is the difference between nociception and pain?
Nociception is the transduction of signals that trigger pain, whereas pain itself is an unpleasant sensory and/or emotional experience associated with tissue damage
What type of structures are nociceptors and where are they located?
Free nerve endings (dendrites) in the epidermis [this makes sense: detection]
Which type of axons transfers fast and slow pain? (think: stubbing toe)
Fast: A delta
Slow: C
Would it make sense for C fibres to be myelinated or unmyelinated? Why?
Unmyelinated; these axons transfer slow pain, meaning they are likely to not have myelin that would speed up the transduction
Why is the onset of slow pain less obvious when hurting thumb than stubbing toe?
Thumb is faster to brain; delay of unmyelination is less pronounced
What are the three types of C axons?
- Mechanical
- Thermal
- Polymodal (e.g. mechanical and chemical)
How do local anaesthetics prevent perception of pain?
Block voltage-gated sodium channels, preventing depolarization
What do skin mechanoreceptors help us to pick up on?
- Vibration
- Touch
- Pressure
Give two examples of mechanoreceptors
- Meissner’s Corpuscle
- Pacinian Corpuscle
What do meissner’s corpuscle detect?
Touch and vibration
What do pacinian corpuscle detect?
Pressure (makes sense: located deeper in fatty layer of dermis)
What are the three main somatosensory pathways of the body?
- Dorsal Column Medial-Lemniscus Pathway (DCML)
- Anterior spinothalamic tract
- Lateral spinothalamic tract
What is the DCML responsible for? What areas of the spinal cord can it be associated with?
- Sensing touch and proprioception
- Associated with dorsal column white matter tract (sensory input)
Describe the three orders of neurons in the DCML pathway
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)
What is a name for the combination of the anterior and lateral spinothalamic tract?
Antero-lateral spinothalamic tract
What is the anterior spinothalamic tract associated with?
Crude touch
What is the lateral spinothalamic tract associated with?
Pain, temperature
What is non-noxious stimuli?
Stimuli not picked up by nociceptors (i.e., pain receptors)
Which of the two components of the antero-lateral spinothalamic tract deal with noxious and non-noxious mechanical stimuli?
Antero: Non-noxious
Lateral: Noxious
Describe the orders of neurons in the anterior spinothalamic tract
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
In what part of the limbic lobe is emotional context added to pain responses?
The cingulate gyrus
What is the biggest white matter tract in the brain?
Corpus callosum
Describe the Gate Theory of Pain
A delta mechnoreceptor stimulation can excite inhibitory interneurons, thus preventing the relay of nociceptor action potentials through the lateral spinothalamic tract
What type of pain regulation is associated with the Gate Theory of Pain
Afferent regulation (inhibition of afferent pain signals)
Describe descending pain regulation
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.
What structure secretes endogenous opioids during descending pain regulation?
Raphe nuclei
What are three kinds of sensory receptors (think of dog pictures)?
- Free nerve endings
- Encapsulated nerve endings (pressure-sensitive)
- Gustatory receptor
Describe the basic mechanism of a gustatory receptor
Receptor potential triggers neurotransmitter release, which triggers action potential in afferent sensory neuron
What are two ways in which primary afferent axons can vary?
- Myelination
- Diameter