Sensory Pathways Flashcards
Sensation of posteiror column-medial leminiscal pathway
Proprioception
Vibration
Fine, discriminative touch
Sensation of anterolateral pathway
Pain
Temp
Crude touch
Sensations of trigeminothalamic tract
All sensation from face and upper scalp
1st order neuron cell bodies of sensory pathways
In the dorsal root ganglion
What does each dorsal root ganglion cell do
Bifurcates and sends a peripheral process that conveys sensory info from the skin and internal body structures/infor from the spinal cord through dorsal nerve roots
A peripheral region innervated by sensory fibers from a single nerve root level called a _______
Dermatome
What is the only sensory that does not synapse in the thalamus
Olfactory
Levels that sense light Bruch’s
Hair follicles
Cells that sense dynamic deformation
Meissner corpuscle
Cells that sense indentation depth
Merkel
Cells that sense stretch
Ruffini
Cells that sense touch
C-fibrre LTM
Cells that sense injurious force
Mechano-nociceptor polydermal nociceptor
Central axons of the posterior column-medial lemnicus pathways
Enter the ipsilateral posterior columns to ascend all the way to the posterior column nuclei in the caudal medulla
What are the two parts of the dorsal column?
Fasciculus gracilis
Fasciculus cuneatus
What info does the fasciculus gracilis carry
Info from the legs and lower trunk
What info does the fasciculus cuneatus carry
Info from the upper trunk above about T6, the arms, and neck
How do fibers add onto the dorsal column as it ascends the spinal cord
Laterally
Second order axons of the posterior column-medial lemniscus pathway
Decussate at caudal medulla as arcuate fibers and form the medial lemniscus on the other side of the medulla
Where does the medial lemniwscus ascend
Through the brainstem
Where do the second order neurons in the posterior column-medial lemniscus synapse
VPL of the thalamus
Which has bigger axons, anterolateral or posterior column-medial lemniscus
Posterior column-medial lemniscus
Carries info for pain and temp
Anterolateral pathway
Where do the central axons of the anterolateral pathway enter spinal cord
Via the dorsal root
Where is the first synapse of the anterolateral pathway?
In the gray matter of dorsal horn
After the primary neuron synapses in the anterolateral tract, how does the secondary neuron run?
Cross over in the spinal cord anterior commissure to ascend in the anterolateral white matter
The anterolateral pathway crosses over at the spinal cord level. Is it the first or second order neuron that does the crossing over
Second order. The first order synapses on the dorsal horn on the ipsilateral side that it comes in on and then the second order neuron cross the anterior commissure
Sensory distribution in the anterolateral pathway
Most neurons move up 2-3 levels and then cross over so sensory loss is a little different, loss is a couple levels down
You will have a block where there is all loss of sensation ipsilateral for about 2-3 dermatome levels, and then you will have level down contralteral pain and temp loss
Somatotoic organization of anterolateral pathway
Arms more medial
Legs more lateral
This map is preserved as it passes through the brainstem
Location and intensity of the pain stimulus is detected in this tract
Spinothalamic tract
Where does the spinothalamic tract project to
VPL nucleus of the thalamus
This tract conveys the emotional and arousal aspects of pain
Spinoreticular tract
Where does the spinoreticular tract terminate
On the reticular formation
Where does the spinoreticular tract project to
The inralaminar thalamic nuclei
How does the spinoreticular tract project to the cerebrum
Diffusely
This tract participates in central modulation of pain
Spinomesecephalic tract
Where does the spina mesencephalic tract project to
The midbrain periaqueductal gray matter
Somatosensory pathways from the spinal cord relay in the ______ nucleus
VPL
Somatosensory pathways from the cranial nerves relay in the _______ nucleus
VPM
Where do the VPL and VPM project to
The primary somatosensory cortex
Visual info is relayed in the ____ nucleus
LGN
Auditory info is relayed in the _____ nucleus
MGN
Mnemonic for remembering the nuclei in which visual and auditory stimuli terminate on
Lateral light (vision), medial music (auditory)
What does the internal capsule look like in a horizontal brain section
Internal capsule
What structures are medial to the internal capsule
Thalamus and caudate nucleus
What structures are lateral to the internal capsule
Globes pallidus and putamen
What are the 3 parts to the internal capsule
Anterior limb
Posterior limb
Genu
Where in the internal capsule does the corticospinal tract lie
In the posterior limb of the internal capsule
Somatotopic map in the internal capsule
Face most anterior
Arm and leg are progressively more posterior
Despite the somatotopic arrangement, the fibers of the internal capsule are compact enough that lesions at this level often produce sensory (or motor) deficits of the entire contralateral body, however, occasionally capsular lesions can also produce more selective motor deficits
Where do sensory tracts that ascend go in the internal capsule
Posterior limb of the internal capsule
Where is somatosensory info from the VPL and VPM conveyed t
The primary somatosensory cortex in the postcentral gyrus
How is the primary somatosensory cortex organized
Somatotopically, with the face represented most laterally and the legs most medially
Integrates all sensation from body and face, communicates with the association motor cortex
Association sensory cortex
The primary somatosensory cortex sends projections to the secondary somatosensory association cortex located within the _______ in the _____ lobe
Sylvia’s fissure
Parietal
What do the primary somatosensory cortex and the somatosensory association cortex have extensive connections with
The motor cortex
Medial part of the sensory cortex blood supply
ACA
Legs
Lateral part of the sensory cortex blood supply
MCA
Head
Strokes involving the MCA and their effect on the sensory cortex
Contralteral hemiparesis and sensory loss predominantly in the face and upper extremity
(Face and upper extremity is a give away!!)
Strokes involving the MCA affecting the internal capsule
Contralateral sensory loss for all types of sensation
Usually contralateral hemiparesis
Strokes involving the ACA main symptoms
- Contralteral hemiparesis in the lower extremities
- Contralateral sensory loss predominantly in the lower extremity
- Urinary incontinence
GIVE AWAYS!
Ascending nocicpetive signals reach and activate periaquductal grey (PAG) neurons via an ______ pathway
Enkephalinergic
Emotional areas of the brain
Cingulate gyrus, insula, amygdala
Ascending nociceptive signals project through
Pulvinar and intralaminar nuclei in the thalamus to various cerebral cortical regions
Injury to tissue
Leads to release of NT that are excitatory at specific membrane receptors on the pain fibers
What are the NT that activate pain fibers
- bradykinin
- prostaglandins
- serotonin (platelets)
- leukotrienes
When pain fibers get activated, what do they do
They also release NT onto dorsal horn
What are the NT that the pain fibers release onto the dorsal horn neurons
Glutamate
Substance P
CGRP neuropeptide
Inflammatory cells in injured tissue
Can cause a release of histamine from mast cells, which causes edema, which causes pain. This starts the cycle over again
Pain and suffering and received by ___ brain regions
Separate
What pathway is involved in the localization of painful stimuli
Neospinothalamic
_____ pathways that access the hypothalamus and limbic system via the reticular formation and PAG are involved in the suffering component of the pain experience
Paleospinothalamic pathways
What does the periaqueductal gray mater receive
Inputs from the hypothalamus, amygdala, and cortex
What does the periaqueductal gray do
Inhibits pain transmission in the dorsal horn via the rostral ventral medulla (RVM)
End result of central modulation of pain
Activation of inhibitory interneuron in the dorsal horn that releases enkephalin (Enk), an endogenous opioids, that binds an inhibitory receptor on the projection neuron
What is the NT that inhibits pain
Enkephalin
What exerts their analgesic effects through receptors found on peripheral nerves and neurons in the spinal dorsal horn
Opiate medications such as morphine
Where enkephalin, B-endorphin, and dynorphin found
In high concentrations at key points in the pain modulators pathways
These alleviate all pain and cause euphoria
What are these: morphine, heroin, codeine, oxy
Opioids
Addiction signs of opioid
- tolerance
- physical dependence
- withdrawal syndrome
- preoccupation to obtain and take opioids
- using more than intended despite social and professional consequences
Addiction to opiates mechanisms
- brain adjusts and becomes irresponsive to normal doses
- reward/pleasures
Withdrawal symptoms of opioids
- agitation
- diarrhea
- dilated pupils
- goose bumps
Treatment for opioids addiction
Replacement with methadone
Naloxone in treatment of opioid overdose
Lesions of the somatosensory pathways
Negative symptoms of sensory loss
Abnormal positive sensory phenomenon called paresthesias
Lesions of the posterior column
Medial lemniscal pathways , patients commonly described a tingling, numb sensation
Lesions of the anterolateral pathways
Sharp burning or searing pain
Lesions of the thalamus
Severe contralateral pain called Dejerine-Roussy syndrome
Lesions of the cervical spine
Electricity like sensation running down the back and into the extremities upon neck flexion
Lesions of nerve roots
Radical are pain that radiates down the limb in a dermatomal distribution, is accompanied by numbness an tingling, and is provoked by movements that stretch the nerve root
Peripheral nerve lesions
Pain, numbness, and tingling in the sensory distribution of the nerve
Thalami nuclei after damage
Can undergo changes that can occur directly as a result of damage to the ascending pathways or secondarily as a result of removal of sensory inputs
Can cause chronic pain or phantom limb pain
Receptive fields
Area of skin innervated by branches of a sensory afferent fiber
Greatest density of cutaneous tactile receptors
Fingertips
Least dense region of tactile receptor is found
Back
Lesion to thalamic ventral posteiror lateral (VPL) and VPM nuclei
Deficit is contralteral to the lesion
Lesion of the primary sensory cortex
A clinical pearls for damage to primary cortex: mild or “uneven” sensory loss!
Heineglect syndrome
Sensory association cortex
Lesion of the right parietal or right frontal lobes
