Download ANPS 019 Beneyto-Santonja 11-09

ANPS 019 Beneyto-Santonja 11/09/12
Dorsal Spinocerebellar pathway
 Function: Provides cerebellum with info about muscle length and tension (unconscious
proprioception) – “what am I doing”
 Receptors: Muscle spindles and Golgi tendon organs
 Ascending pathway
o Primary afferent neuron synapse within the dorsal horn gray matter
o Second order neuron enters ipsilateral cerebellum via inferior cerebellar peduncle
o After synapsing in cerebellum, info exits to contralateral red nucleus & thalamus;
therefore, INFO FROM THIS PATHWAY CROSSES IN CEREBELLUM!
Cuneocerebellar Pathway
 Uses the same receptors and conveys the same info as Dorsal Spinocerebellar Pathway
except for arm
Dorsal Column-Medial Lemniscus Pathway
 Function: Touch (Pressure, vibration); Conscious proprioception (sense of body in space)
 Receptors
o Cutaneous mechanoreceptors
o Muscle spindles, Golgi tendon organs
 Ascending pathway
o Primary afferent ascends in dorsal white matter
 Without synapsing in Spinal cord
 First synapse is in Medulla
o Leg info synapses in N. gracilis
o Arm info synapses in N. cuneatus
o Second order neuron crosses and synapses in thalamus
o INFO FROM THIS PATHWAY CROSSES IN MEDULLA!
Have you ever felt Pain?
 Pain has been defined as an ‘unpleasant sensory and emotional experience associated
with actual or potential tissue damage, or described in terms of such damage.’
 Nociceptive pain  “normal” pain caused by tissue damage
Two Anterolateral Pathways exist to convey Different types of Somatic Pain
 Acute Pain
o Derived from skin
o Has 2 components controlled by different afferents:
 Sharp and localizable initial pain
 Delayed pain (dull or burning)
 Chronic Pain
o Derived from muscles, joints, bones, or connective tissue
o Poorly localized, dull pain which tends to radiate into surrounding tissues
NEOspinothalamic Tract
 Function: Acute pain (sharp, critical); Temperature; Crude touch
 Receptors: Myelinated nociceptors
 Ascending pathway
o Primary afferent synapses in dorsal gray matter
o Second order neuron crosses in spinal cord, then synapses in thalamus
o INFO FROM THIS PATHWAY CROSSES IN THE SPINAL CORD!
PALEOspinothalamic Tract
 Function: Chronic pain (dull); Temperature; Crude touch
 Receptors: Unmyelinated nociceptors

Ascending pathway
o Same as Neospinothalamic tract except second order neuron sends info to Raphe
nucleus and Periaqueductal gray. These structures are involved in modulation of
chronic pain
o INFO FROM THIS PATHWAY CROSSES IN THE SPINAL CORD!
Central Pain Modulation
1. Opiates inhibit the activity of inhibitory interneurons in the PAG. This increases the
activity of neurons whose axons descend to the raphe nucleus
2. The activity of axons that descend from the PAG excites raphe nucleus neurons whose
axons descend in the dorsal columns of the spinal cord.
3. The activity of descending dorsal column axons excites inhibitory spinal interneurons
that block incoming pain signals.
Neuropathic Pain  pain that persists long after all tissue injury is healed
 Hyperalgesia: an exaggerated painful response to a normally noxious stimulus
 Allodynia: a painful response to a normally non-noxious stimulus (e.g., cloths touching
sunburned skin)
Referred Pain
 Visceral pain
o Generally dull and diffuse
o Can be produced by multiple stimuli
 Cessation of blood flow
 An irritant chemical
 Tissue stretching
 Muscle spasms within an organ
o Often accompanied by autonomic responses
o Since most viscera is not mapped in the somatosensory cortex, pain is localized
(‘referred’) to nearby somatic area
Mechanisms of referred pain
 Axons carrying organ pain info and axons carrying skin pain info synapse on the same
spinal cord neuron – brain cannot distinguish where pain is coming from.
Phantom Limb Pain
 Up to 80% of amputees have some phantom sensation
 Pain is usually neuropathic
 Etiology unclear