Somatosensory System 1 Flashcards
Name 3 typical features of a Somatosensory neuron
- Pseudounipolar neurons
- Cell body (soma) is located in dorsal root ganglion (spinal cord) or cranial nerve ganglion
- Axon terminates in spinal cord or brian stem
Responses of receptors can either be tonic or phasic. Describe the two responses..
Tonic: Are slowly adapting receptors that respond for the duration of a stimulus
Phasic: Radidly adapt to a constant stimulus and turn off. Stop responding even if stimulus continues.
What are the 3 types of cutaneous receptors?
- Mechanoreceptors
- Thermoreceptors
- Nociceptors
Hair follicle receptors (RA1), name; class, receptive field, modality, ending, adaptation, location, skin type, innervation…
Class: mechanoreceptor
Receptive field: small
Modality: hair movement
Ending: non-encapsulated
Adaptation: rapid
Location: superficial
Skin type: hairy
Innvervation: A-beta
Meissner’s corpuscle (RA1), name; class, receptive field, modality, ending, adaptation, location, skin type, innervation…
Class: mechanoreceptor
Receptive field: small
Modality: touch, vibration (50 Hz)
Ending: encapsulated
Adaptation: rapid
Location: superficial
Skin type: glabrous
Innvervation: A-beta
Pacinian corpuscle (RA2), name; class, receptive field, modality, ending, adaptation, location, skin type, innervation…
Class: mechanoreceptor
Receptive field: large
Modality: pressure, vibration (250-300 Hz)
Ending: encapsulated
Adaptation: rapid
Location: deep
Skin type: all
Innvervation: A-beta
Merkel receptors (SA1); name; class, receptive field, modality, ending, adaptation, location, skin type, innervation…
Name: Merkel’s disk
Class: mechanoreceptor
Receptive field: small
Modality: light touch, pressure
Ending: non-encapsulated
Adaptation: slow
Location: superficial
Skin type: all
Innvervation: A-beta
Ruffini’s corpuscles (SA2); name; class, receptive field, modality, ending, adaptation, location, skin type, innervation…
Name: Ruffini’s corpuscles
Class: mechanoreceptor
Receptive field: small
Modality: stretch, pressure
Ending: encapsulated
Adaptation: slow
Location: deep
Skin type: all
Innvervation: A-beta
Free nerve endings (mechanoreceptors); name; class, receptive field, modality, ending, adaptation, location, skin type, innervation…
Name: Free nerve endings
Class: mechanoreceptor
Receptive field: small
Modality: light touch
Ending: non-encapsulated
Adaptation: slow
Location: superficial
Skin type: all
Innvervation: A-delta and C
Free nerve endings (thermoreceptors); name; class, modality, ending, adaptation, location, skin type, innervation…
Name: Free nerve endings
Class: thermoreceptor
Modality: Hot and cold temperature
Ending: non-encapsulated
Adaptation: rapid
Location: superficial
Skin type: all
Innvervation: C for hot and A-delta for cold
How do thermoreceptors transduce their adequate stimulus into a neural signal
Transduction: via temperature-sensitive transient receptor potential (TRP) ion channels. TRP channels are non-specific cation channels (Ca2+, Na+, Mg2+)
How do Nociceptors (pain) transduce their adequate stimulus into a neural signal?
Primary afferent neurons release both glutamate and substance P on to dendrites in the second order neurons in the spinal cord and brian.
How are “first” and “second” pain signals carried?
(what type of fibres)
First pain; carried by A-delta type fibres
Second pain; arrives by C type fibres
Describe the axon reflex
Axon reflex causes release of neuropeptides (e.g. substance P) from afferent endings that cause vasodilation of blood vessels around the injury site
What is Hyperalegsia?
Abnormally heightened sensitivity to noxious stimuli
What is Allodynia?
pain sensation in response to normally non-painful stimuli (e.g. touching, cooling/heating)
The Trigeminal nerve is the principle somatosensory nerve of the head. What are its 3 branches?
- Ophthalmic branch
- Maxillary nerve
- Mandibular nerve
What are the three trigeminal sensory nuclei?
- Mesencephalic trigeminal nucleus
- Pontine trigeminal nucleus
- Spinal trigeminal nucleus
What is the dermatome?
A sensory region on the surface of the body that sends afferents via a given spinal nerve.
Sensation of pain may be accompanied by:
- Relef withdrawl from stimulus
- Autonomic response
- Emotional response
Via which tract do secondary order neurons ascend to the thalamus?
via the lateral spinothalamic tract
Explain the gate-control theory
When you rub the skin around a painful area e.g. stubbed toe. It activates mechanoreceptors in the skin which excite inhibitory interneurons in the brain/spinal cord. This supresses the transmission of pain signals by inhibiting the second order neurons.
Explain Endogenous Analgesia
In response to stressful situations (e.g. fights) the brain can supress the transmission of pain signals.
Descending pathways from the midbrain release endogenous opioids such as enkephalin onto the synapse between the primary nociceptor afferents and the second order neurons in the dorsal horn of the spinal cord.
Explain Central Sensitization
Prolonged or intense release of glutamate from primary nociceptor afferent nerve terminals onto the dendrites of secondary afferent nerves in response to painful stimulus.
Columnar organisation
skin receptors in the same body region (i.e. have overlapping receptive fields).
Hierarchial organsation
Cortical neurons show increase in size of receptive field
