Sensory Pathways Flashcards
What are the 3 components of the analgesia system?
Periaquaductal gray and periventricular regions of the brainstem and third ventricle
Raphe magnus necleus and reticular nuclei in medulla
- raphe magnus is on either side of the midline of the brainstem
Pain inhibitory complex in dorsal horns of spinal cord
What are the types of receptors that discriminate thermal senesations?
Cold -A-delta myelinated fibers warmth -C-type fibers Pain
Referred Pain
Viseral pain fibers are stimulated and stimulate some of the pain fibers that conduct pain signals from the skin
Severe pain is when there is diffuse pain throughout the visera. Can be caused by ischema
Viseral pain from thoracic and abdominal cavities transferred by c pain fibers
Viseral pain fibers and skin pain fibers cross, at the vertebrae, so when one fires so does the other
Name the two alternative sensory pathways in the spine and brain?
Medial meniscal and (Lateral and Anterior) spinothalmatic tracts
Lateral Spinothalamic Tract
carries pain and temperature sensation
1˚ ascend or descend 1-2 spinal cord segments before synapsing
2˚ decussate immediately then travel up in the lateral column of the spinal cord, pass through the reticular formation and synapse in the ventral posterolateral (VPL) nucleus of the thalamus
3˚ go to the postcentral gyrus (form part of internal capsule)
Anterior Spinothalamic Tract
Carries light touch (crude touch), pressure, tickle, itch
1˚ ascend 8-10 spinal cord segments then synapsing (ventral spinothalamic tract)
2˚ immediately decussate and ascend to VPL nucleus of the thalamus
3˚ ascend through internal capsule and to the primary sensory cortex
Dorsal Column-Medial Lemniscal Pathway
Carries sensation for 2-point or fine touch, pressure and vibration
1˚ - ascend entire length of spinal cord and synapse in the medulla
2˚ - decussate and ascend to VPL in thalamus and synpase
3˚ - ascend through internal capulse and end in primary sensory cortex
Axons from below the midthorax level/or from lower limbs travel in the medial of the two dorsal columns - fasciculus gracilis
From the upper limbs or above midthoraxicc level travel the later column of the two dorsal columns - fasciculus cuneatus
Which of brodmann’s areas are the primary somatosensory areas?
And the somatosensory association area?
Areas 1, 2, and 3
Areas 5 and 7
Two-point discrimination, what is it? What is it’s function? Where does it occur?
Ability to discriminate between to touches, functions for fine touch and up to 2mm apart
Characteristics of fast pain
.0.1 seconds post stimulus
Not felt in deeper tissues
Generally from by mechanical and thermal stimuli
Typically carried Aδ pain fibers
Terminates in lamina I of the dorsal horns of the spinal cord
Travels neospinothalamic tract
Functions of Somatosensory Area I
Localize discrete sensations in different parts of the body
Judge degrees of pressure
Judge weight of objects
Judge shape or form
Judge texture
Somatosensory Area II functions
Gets signals from brain stem from both side of body and secondarily from the first area and the visual and auditory areas
Characteristics of slow pain
Begins about 1 second after and increases over several seconds
‘Aching, slow burning, throbbing, nauseous or chronic’
Mechanical, thermal or chemical stimuli
Carried by C type fibers and terminate in layers II and III of the dorsal horns of the spinal cord
Travels paleospinothalamic pathway
Brown-Sequard Syndrome
Hemisection of the spinal cord
No motor function on side of body with transection
Pain, head and cold sensation is lost on side not transection 2 to 6 sections below the cut
Loss of vibration sensation, kinesthetic and position sensation, discrete localization and two-point discrimination below transection
what stimulates a thermoreceptor?
Changes in their metabolic rates
