Ascending tracts in the spinal cord Flashcards
where are receptors for pain and temperature found
dermis and epidermis of skin / mucosa
where are cell bodies of sensory fibres situated
dorsal root ganglion
how do local anaesthetics like lignocaine work
block sodium channels on the axons and nerve conduction
what convey the sensation of pain and temperature
small myelinated (Aδ) and myelinated (C) fibres to the dorsal root
pathway of axons of pain transmission
enter at all levels and synapse in dorsal horn
cross into contralateral spinal cord via anterior white commissure
ascend through spinal cord and spinothalamic tract
where do fibres of the spinothalamic tract terminate
in the ventroposterior lateral nucleus of the thalamus
VPL projections
projects axons through the posterior limb of the internal capsule to reach the somatosensory cortex
functions of the spinothalamic tract
carries pain and temperature from body
also carries crude touch allowing sensation of touch without localisation
role of spinoreticular tract
carries pain and crude touch
polysynaptic relays of the spinoreticular tract
relays to the brainstem are in reticular formation
loose network of neurons between nuclei
these in turn projects via the non-specific thalamic nuclei
reticular activating system
example
reaches widespread areas of the cortex
required for arousal of higher CNS centres
increased wakefulness as a result of pain
what is the dorsal column medial lemniscus system responsible for
fine touch
conscious proprioception and vibratory sense
where are receptors for proprioception located
muscles, tendons and joints
dorsal column medial lemniscus system fibres
where are their cell bodies located
large, fast conducting fibres (Aβ)
pass towards the spinal cord in the peripheral nerves
dorsal root ganglion
fasciculus gracilis
ascending fibres from the legs and lower trunk
in the dorsal column
terminate in the nucleus gracilis in the medulla oblongata
fasciculus cuneatus
ascending fibres from the arms and upper trunk
in the dorsal column
terminate in the nucleus cuneatus in the medulla oblongata
nucleus gracilis and nucleus cuneatus axons pathways
decussate medulla (cross the contralateral)
ascend through the medulla, pons, and midbrain as the medial lemniscus
where do fibres of the medial lemniscus terminate
in the ventroposterior lateral nucleus of the thalamus
function of the medial lemniscus
carries fine touch, vibration and proprioception from arms, legs and trunk
effect of damage to the dorsal column medial lemniscus pathway
if before the decussation signs will be on the same side
if after the decussation the signs will be on the opposite side of the lesion
tabes dorsalis
due to syphilis
caused by demyelination by advanced infection
occurs if the primary infection is left untreated for 10-15 years
ataxia and staggering gait
trigeminal nerve afferents carry sensation from three non-overlapping segments of face
ophthalmic (V1)
maxillary (V2)
mandibular (V3)
where do axons in the trigeminal nerve terminate
spinal trigeminal nucleus
chief sensory nucleus
mesencephalic nucleus
spinal trigeminal nucleus
in the medulla oblongata and cervical spinal cord
receives pain and temperature from face through trigeminal and glossopharyngeal nerves
projects axons that cross contralateral and terminate in the VPM
chief sensory nucleus of V
located in pons
receives fine touch and vibration sensation from face via three branches of trigeminal
projects axons that join contralateral medial meniscus and terminate in the VPM
mesencephalic nucleus of V
located in the midbrain
contains cell bodies of axons of mandibular branch of trigeminal that carry proprioceptive input
projects axons to neurons of the trigeminal motor nucleus
ventroposterior medial nucleus of the thalamus
relays fine touch, pain and temperature input from contralateral face
projects axons through genu of internal capsule to reach somatosensory cortex
referred pain
pain sensation arising from a visceral structure can cause pain perception localised to predictable cutaneous regions
pain is referred to dermatomes supplied by the same posterior roots as the organ
where is referred pain experienced from:
parietal pleura and diaphragm
appendix
ureters
gallbladder
parietal pleura and diaphragm: shoulder near root of neck
appendix: umbilicus then right iliac fossa
ureters: flank and inguinal area
gallbladder: below the ribs and shoulder
neuropathic pain
continuous, intractable and frequently excruciating
burning pain with or without peripheral nerve damage
results from damage to sensory pathways not nociceptor activation
phantom limb pain
common causes
pain from limb that no longer exists
stimulus applied anywhere along the nerve fibre experienced as from the skin area supplied by that nerve
fibres at the stump are frequently squeezed by scar tissue
may also result from plasticity changes in the somatosensory cortex
gate control theory
small fibres activate posterior horn neurons that transmit pain centrally (open the gate)
large myelinated fibres activate interneurons that inhibit neurons in the posterior horn that transmit pain (close the gate)
supraspinal antinociception
periaqueductal grey activates serotonergic neurons in medullary raphe nuclei
project to enkephalin interneurons in dorsal horn and suppresses pain transmission from first to second order neurons
