Somatosensory Pathways

What is the Dorsal Column: Medial Lemniscus Pathway?

Ascending sensory path that carries discriminative touch, stretch, vibrations, and proprioception to the brain

What does a Meissner’s Corpuscle detect?

Light touch and vibrations

What does a Merkel Disc detect?

Light touch, pressure, texture

What does a Pacinian Corpuscle detect?

High-frequency vibrations and deep pressure

What does a Peritrichial Nerve Ending detect?

Movement of hair

What do Ruffini Corpuscles detect?

Sustained pressure and skin stretch

What do Muscle Spindles detect?

Changes in muscle length and speed of stretch

What do Golgi Tendon Organs (GTOs) detect?

Changes in muscle force

What do Joint Receptors detect?

Proprioception

What is the 1st Order neuron of the DCML pathway?

Dorsal Root Ganglion

What is the next step after the 1st Order neuron in the LE DCMLP?

Enters SC through dorsal gray horn, goes into fasciculus gracilis without synapsing

What is the next step after the 1st Order neuron in the UE DCMLP?

Enters SC through dorsal gray horn, goes into fasciculus cuneatus without synapsing

What is the 2nd Order neuron of the DCMLP?

Nucleus Gracilis/Nucleus Cuneatus

What is the next step after the 2nd Order neurons of the DCMLP?

Fibers merge, cross over using Internal Arcuate Fibers in dorsal medulla and pons, becoming the medial lemniscus

Where does the Medial Lemniscus go to?

Runs upwards to the Ventral Posterior Lateral (VPL) nucleus in the thalamus

Where do the 3rd Order fibers run in the DCMLP?

Run up through the Corona Radiata to the postcentral gyrus

What does the Anterior Spinothalamic Tract carry?

Light touch and Pressure

What does the Lateral Spinothalamic Tract carry?

Pain, Temperature

What is the first step of the Spinothalamic Tract?

The sensation is picked up by receptors and is carried through the DRG into the SC, specifically the dorsal gray horn. The different axons then synapse into the lamina. The new fibers then cross over through the Anterior White Commissure in the same level.

What happens after the crossing through the AWC in the Spinothalamic Tract?

The axons travel up the SC. Crude touch and pressure go through the Ventral Spinothalamic Tract. Pain, Temperature, and Slow Pain go through the Lateral Spinothalamic Tract

Where does the Ventral Spinothalamic Tract run to?

Ventral Posterior Lateral nucleus in Thalamus

Where does the Lateral Spinothalamic Tract run to?

85% of C fibers go into the Reticular Formation. The rest go to non-specific nuclei in thalamus. The A-delta fibers go to the VPL nucleus in thalamus.

What do Alpha motor neurons provide in the spinal laminated IX?

Voluntary movement

What are Fast-Adapting fibers?

Sensory nerve cells that fire signals when a stimulus starts and stops, but stop firing when the stimulus stays the same

What are Slow-Adapting fibers?

Sensory nerve cells that fire continuously for the entire duration of a steady touch or pressure.

What are examples of Fast-Adapting Fibers?

Meissner Corpuscles and Pacinian Corpuscles

What are examples of Slow-Adapting Fibers?

Merkel Discs and Ruffini Endings

What is High Threshold?

Respond to intense, potentially harmful pressure

What is Low Threshold?

Respond to gentle, harmless touch

What are examples of high threshold?

Free nerve endings (Nociceptors)

What is the difference between thoracic and lumbar gray matter?

The difference is the amount of gray matter across these regions, where lumbar has more due to more muscles to control, whereas thoracic has less because it only manages the thin muscles of the torso and ribs.

What is a myotatic reflex?

An involuntary, automatic contraction of a muscle in response to it being stretched. The fastest reflex in the human body, to prevent tearing due to over-stretching.

What are the 3 nuclei of the Trigeminal nerve?

Mesencephalic nucleus, Pontine trigeminal nucleus, and nucleus of spinal tract

What do the Nucleus of spinal tract carry?

PainW

What does the Pontine trigeminal nucleus carry?

Discriminatory touch “Chief nucleus”W

What does the Mesencephalic nucleus carry?

Proprioception

If there was a midbrain stroke, what symptoms would present when specifically focusing on the Trigeminal nuclei?

Proprioception, discriminatory touch, and pain loss

If there was a pontine stroke, what symptoms would occur when specifically focusing on the Trigeminal nuclei?

Discriminatory touch and pain

What is the epidural potential space?

Potential space between the inner surface of the skull and dura mater

What typically occurs when there is a epidural hematoma?

Blunt trauma that leads to fracture of the skull, tearing of the middle meningeal arteryW

What are the symptoms of an epidural hematoma?

Swift presentation of symptoms: Severe headache, vomiting, altered conscious state, hemiparesis

What is a subdural potential space?

Potential space between the inner layer of the dura mater and the arachnoid mater

What typically occurs when there is a subdural hematoma?

Venous bleeding (usually Superior Cerebral Vein) due to a shearing force leading to tear

What are symptoms of a subdural hematoma?

Slow presentation of symptoms: increasing headache, vomiting, dizziness, altered state (usually later in the day)

What is the Foramen of Lushka?

Lateral foramen in 4th ventricle where CSF flows out and surrounds SC

What is the Foramen of Magendie?

Medial foramen in 4th ventricle where CSF flows out and surrounds SC and brain

What is a Caudate nucleus?

A basal ganglia that helps control voluntary movement, learning, memory, and goal-directed behavior; related to pathology that results in Parkinson’s or Huntington’s

What is the Putamen?

A round subcortical structure of gray matter located at the base of the forebrain that regulates voluntary movement and motor skills

What is the Crus cerebri?

The front portion of the midbrain's cerebral peduncles that carries massive bundles of descending motor nerve fibers from the cerebral cortex to the brainstem and spinal cord

What is Obstructive (Non-communicating) Hydrocephalus?

A physical blockage within the ventricular system stops the normal flow of fluid

What is Communicating Hydrocephalus?

Fluid flows through the ventricles freely, but it is either overproduced or poorly reabsorbed by blood vessels

What is Ex vacuo Hydrocephalus?

A condition where the ventricles inside the brain look larger on scans, but the pressure of the fluid is normal

What type of hydrocephalus does the kid in the photo have?

Obstructive Hydrocephalus

What is Senile Normal Pressure Hydrocephalus?

Usually in older adults, where CSF accumulates and enlarges the ventricles, but the measured CSF pressure can be normal or only intermittently elevated.

What are symptoms of Senile Normal Pressure Hydrocephalus?

Urinary problems, impaired gait, dementia, can mimic Alzheimers and Parkinson’s disease

What is a Subfalcine herniation?

Occurs when increased intracranial pressure pushes the cingulate gyrus underneath the falx cerebri, toward the opposite side.

What are symptoms of a Subfalcine herniation?

Contralateral leg weakness, sensory loss; incontinence problems

What is a Central herniation?

Brain is pushed into the tentorial notchW

What are symptoms of Central herniation?

Impairment of CN III, lead to dilation of eye, and CN IV, eye movement

What is an Uncal transtentorial herniation?

The uncus is pushed through the tentorial notch, compressing structures in the midbrain

What are symptoms of Uncal transtentorial herniation?

Contralateral Hemiplegia; Ipsilateral “Blown pupil”, loss of consciousness due to reticular system, eye goes “Down and out”

What is a Tonsillar herniation?

The tonsils of the cerebellum are pushed through the foramen magnum, compressing the medulla

What are symptoms of Tonsillar herniation?

Affects respiration, BP, HR

When having visceral pain, where do the sensations go?

Intensity of the visceral pain goes through the DCML, Location of the pain goes through the ALS

What are examples of innocuous stimuli?

Itching (histamine response), Muscle soreness (due to release of lactic acid), sensual touch, thermal (mild temps), nondiscriminatory touch

What is fast pain?

Stimulation of Aδ fibers: 5-40 m/s; tingling, burning, or sharp sensation; identify location of tissue damage; Stimulate glutamate (excitatory)

What is slow pain?

Stimulation of C fibers: (0.5-2 m/s); dull, long-lasting sensation; emotional and cognitive response to damaged tissue; release of multiple neuropeptides

What is primary chronic pain?

Pain is the disease (Fibromyalgia, chronic back pain, IBS)Wha

What is secondary chronic pain?

Pain is a symptom (Arthritic pain, cancer pain, myofascial pain

What is Nociceptive chronic pain?

Persistent pain caused by ongoing or repeated activation of nociceptors due to actual tissue damage or inflammation.

What is neuropathic pain?

Caused by actual damage or disease of the somatosensory nervous system—the nerve, spinal cord, or brain itself is involved

What is hyperalgesia?

Increase pain response of nociceptors

What is Allodynia?

Perception of innocuous stimuli as painfulW

What is spontaneous pain?

Pain is unprovoked

What is Temporal summation

“Wind-up”; amplified output of 2nd order neurons

How does the hypothalamus affect modulation of pain?

It releases endorphins (peptides), longer lasting than normal neuroreceptors