Somatosensory System Flashcards
Neostriatum
Largest part of basal ganglia
= caudate nucleus + n. accumbens + putamen
Amygdala connections
Hippocampal formation, dorsomedial thalamus, medial prefrontal cortex
input: nociceptive pathways
Axial section through the internal capsule is
a very important site of strokes
How are sensory axons in peripheral nerves classified?
according to their diameter and conduction speed
Characteristics of sensory axons in skin
Aβ-15μm, 70m/sec
• Aδ-3μm, 20m/sec
• C-unmyelinated
Characteristics of sensory axons in muscle + tendon
I- up to 20μm,100m/sec
• II- < 10μm, 50 m/sec
• IV- unmyelinated, 1μm, 1m/sec
c-fibres
Nociceptive unmyelinated primary afferents
Sensory receptors are classified as
Rapidly Adapting or Slowly Adapting. RA receptors signal
stimulus changes; SA receptors signal prolonged stimulus contact.
Name 4 cutaneous receptors
- Meissner’s corpuscles (RA) important for two point
discrimination- concentrated in skin of fingers and around
mouth etc. - Merkel’s discs (SA) also important for discriminative touch
- Ruffini endings (SA) Skin stretch
- Pacinian corpuscles (RA)- vibration
Cutaneous receptors are all innervated by
Aβ fibres
Muscle stretch is detected by
Muscle spindles - Ia afferents -> also receive type II (Ab afferents)
Tension is detected by
Golgi tendon organs 1b afferents
Pain and temperature is detected by
c fibres plus A gamma
The central axons of primary afferents _____ on entering the cord and innervate several ______
bifurcate, segments
C-fibres run up and down…
Lissauer’s tract
myelinated afferents run up and down in the _______
Dorsal columns
DRG contains
cell bodies of sensory neurones
C-fibres end in _____..
A Delta fibres end in _____
Ia afferents end in_______
Aβ afferents end in….
laminae II, laminae I and V, laminae IX
Clarke’s column
thoracic nucleus
C-fibres mainly end in _____ but _____ is mainly populated
by interneurons- ______ neurons are not found in
_____
lamina II, spinothalamic tract, lamina II
Major nociceptive pathway in experimental animals
the spino-parabrachial pathway
Chronic pain is ______- not physiological. It involves changes in the _______ and
_______ (as well as the neurons) of the spinal cord
pathological, microglia, astrocytes
The modality of the stimulus is denoted by
the axons that are activated
altered-allodynia occurs when
mechanoceptive fibres activate
nociceptive pathways in the spinal cord
Periaqueductal grey function
Sends axons to the nucleus raphe magnus in the medulla and the locus ceruleus.
Stimulation of PAG
extremely powerful analgesic effect throughout
the body
Raphe nuclei function
These send serotonergic (5HT) fibres all over the CNS. Receives input from PAG and modulates nociceptive transmission in dorsal horn of spinal cord
Nucleus raphe Magnus
Raphe-spinal axons project down to superficial dorsal horn of spinal cord - they can turn the gain on the nociceptive pathways up or down
Locus ceruleus
Largest noradrenergic nucleus -> descending noradrenergic fibres -> analgesic effect
Syringomyelia
Destruction of crossing fibres leads to loss of pain and temperature over affected segments, which are usually cervical. Sensation from below the lesion is unaffected
A syrinx
fluid-filled cavity
Ventrolateral cordotomy
Performed to relieve pain in right leg -> disrupts left spinothalamic tract
Which cranial nerves are different?
- II -> optic nerve = cns tissue
2. I -> olfactory have cell bodies in mucus membrane and different glial cells
Cranial nerves containing somatosensory fibres
- V - Trigeminal -> face, cornea, nasal cavity, mouth
- IX - Glossopharyngeal -> back of tongue
- X - Vagus -> somatic afferents to ear, larynx
The main somatosensory cranial nerve is ______. It has 3 branches:
V trigeminal
- Opthalmic
- Maxillary
- Mandibular
Trigeminal neuralgia
a neuropathic pain that feels as if it is coming from part of the territory supplied by the trigeminal nerve
Which relationship can give rise to trigeminal neuralgia?
Superior cerebellar artery near trigeminal roots
Post herpetic neuralgia follows
Shingles
The large primary afferent in the _____ ___ has function of _____ with cell body in _____ _____
Upper pons, discriminative touch, trigeminal ganglion
Trigeminal nuclei extend through …..
most of the brainstem
Trigeminal sensory nuclei extends from x to y
X - midbrain
Y- spinal cord
Effects of a Posterior Inferior Cerebellar
Artery (PICA) lesion
PICA supplies dorsolateral medulla
so…
Visceral afferent fibres carry
taste or other information from the viscera including the carotid sinus and body. They all end in the nucleus of the solitary tract
Vestibular and cochlear fibres end in X and Y
end in the vestibular and cochlear nuclei
Nucleus of the solitary tract receive _____. It’s important for ____
visceral afferent (taste and general visceral afferent) information. It is an important centre for autonomic control and parts of it form the dorsal inspiratory respiratory centre.
