Somatosensory Pathways Flashcards
Loss of pain
Analgesia
Loss of touch
Anesthesia
Temporary mild pain, “pins and needles, tingling, burning, prickling”
Paresthesias
Chronic intense pain “shooting, stabbing or electric shock-like jolts”
Neuropathic Pain/Central Pain
Subsystem for processing different kinds of stimuli (physics/chemistry, receptor specificity and labeled line/pathway)
Modality
What are the three major long pathways in the CNS?
Corticospinal tract (CST), Dorsal Column-Medial Lemniscus System (DCMLS), and Spinothalamic Tract (STT)
The segregation of nerve cell axons that process the distinct stimulus attributes that comprise a particular modality
Parallel pathways
Responsible for fine touch, vibration, and proprioception
Dorsal Column-Medial Lemniscus System (DCMLS)
Responsible for pain, temperature, and crude touch
Spinothalamic Tract
Lowest stimulus strength a subject can detect
Sensory Threshold
Determined by the sensitivity of the receptors (i.e. minimum energy required to generate action potential)
Sensory Threshold
Slowly adapting
-Detects static qualities of stimulus
Tonic
Rapidly adapting
-Detects dynamic qualities of stimulus
Phasic
The minimal interstimulus distance required to perceive two simultaneously applied stimuli as distinct (spatial resolution)
Two point discrimination
Resolution is determined by
Density of receptors and receptive fields
The region in sensory space within which a specific stimulus elicits the greatest action potential response
Receptive fields
Area of skin innervated by a single dorsal root ganglion but differ among individuals
Dermatomes
Axons making up a dorsal root originate from several different peripheral nerves is a reason for
Overlap of Dermatomes
Detects muscle length
Muscle spindle
Detects muscle tension
Golgi Tendon Organ
A single dorsal root ganglion contains many types of
Sensory Neurons
Which receptor type is associated with proprioception
Muscle Spindle
Which receptor types are associated with touch?
Merkel, Meissner, Pacinian, and Ruffini Cells
Where is the termination of the DCMLS?
Postcentral gyrus (Primary somatosensory cortex)
What is the pathway relay #2 for DCMLS?
Thalamus (Ventral Posterolateral Nucleus (VPL))
What is the decussation of the DCMLS?
Caudal medulla (internal arcuate fibers)
What is the pathway of relay #1 for DCMLS?
Dorsal column nuclei (Internal arcuate fibers)
What is the modality of DCMLS?
Discriminative touch, vibration, and proprioception
Provides touch and vibration from the face to cortex
Trigeminal mechanosensory system
What type of organization is there for the DCMLS in the spinal cord?
Somatotropic Organization
Somatosensory Homunculus Parallels the
Motor homonucleus
Each of the 4 regions of the primary somatosensory cortex contains a separate and complete map of the
COntralateral body surface
Principle of cortical processing that allows the brain to find patterns common to stimuli of a particular class
Feature Detection
Posterior Parietal Cortex Connects to Motor Cortex for Association and is Involved in
Attention
Secondary Somatosensory Cortex (SII) Connects to Limbic System for
Tactile learning and Memory
In the epidermis and are responsible for pain and temperature
Nociceptors
Each thermoreceptive neuron only expresses a single type of
Temperature receptor
Thermoreceptors adapt. Cold and warm receptors fire mostly during changes of
Temperature
Free nerve endings are the receptors for
Pain and temperature
Unmyelinated free nerve endings are the receptors for
Pain, temperature, and itch
Crosses over to the opposite side as soon as it enters the spinal cord
Spinothalamic system
What is the point of termination for the spinothalamic tract?
Postcentral gyrus (primary somatosensory cortex)
What is the pathway relay #1 for spinothalamic system?
Spinal dorsal horn
What is pathway relay #2 for the spinothalamic system?
Thalamus (VPL and Reticular Formation)
Where is the decussation of the spinothalamic pathway?
-takes 2 levels to traverse
At segmental levels
What is the modality of the spinothalamic tract?
Pain, temperature, and crude touch
Where does the DCMLS cross over?
Medulla
Where does the STT cross over?
Spinal cord
Touch/proprioception from the body crosses over in the
Medulla
Pain/temperature from the body crosses over in the
Spinal cord
Touch/proprioception from the face crosses over in the
Pons
Pain/temperature from the face crosses over in the
Medulla
The spinocerebellar tract for proprioception involves
Large diameter sensory neurons
Goes from the lower limbs to ipsilateral cerebellum
Posterior spinocerebellar tract
Goes from upper limbs to ipsilateral cerebellum
Cuneocerebellar Tract
Goes from lower limbs (interneurons), decussates twice, to ipsilateral cerebellum
Anterior Spinocerebellar Tract
Goes from upper limbs (interneurons) to the ipsilateral cerebellum
Rostral Spinocerebellar Tract
Present as an ipsilateralloss of muscle coordination.
-However, the spinocerebellar pathways are unlikely to be damaged in isolation
Lesions of spinocerebellar tracts
Degeneration of dorsal columns causing impaired sensation and proprioception and progressive sensory ataxia
Tabes Dorsalis
Tabes dorsalis is caused by
Tertiary syphilis infection
Demyelination of dorsal columns, lateral corticospinal tracts, and spinocerebellar tracts causing ataxic gait, paresthesia, impaired position and vibration sense
Subacute combined degeneration from Vitamin B12 or E deficiency
Hemisection on the left side of the spinal cord at C5 is called
Brown-Sequard Syndrome
What is affected in Brown-Sequard Syndrome?
Pain/temp from right side and touch/vibration from left
Change position relative to eachother as they traverse the neuraxis
DCMLS and STT
If the touch/vibration and pain/temp symptoms are on the same side of body, than the lesion must be
Above the medulla
If the touch/vibration and pain/temp symptoms are on the opposite side of body, than the lesion must be
In the Spinal Cord
Cause sensory as well as motor deficits
Spinal Cord Lesions
Amputation causes change in
Cortical Representation
Reorganization of somatosensory cortex occurs in amputees so that neurons that used to be innervated by limb now respond to stimulation of other body parts. This is referred to as
Phantom Limbs and Phantom Pain