1. Somatosensory I Flashcards
dorsal (posterior) column - medial lemniscal pathway: function
(aka dorsal white columns) fine touch, vibration, proprioception of trunk & extremities, decussate in caudal medulla (sensory decussation)
trigeminal correlate of DC-ML pathway: function
fine touch, vibration, and proprioception for face
decussate
crosses over (X)
anterolateral (ventrolateral) pathway: function
Pain, Temperature and crude touch for trunk and extremities, decussate 2-3 segments above dorsal root entry zone
other name for anterolateral (ventrolateral) pathway
Spinothalamic tract
Trigeminal correlate of anterolateral pathway: function
Pain, Temperature and crude touch for face
list 5 neuroanatomical pathways
- Dorsal (posterior) column – medial lemniscal pathway
- Trigeminal correlate of DC-ML pathway
- Anterolateral (ventrolateral) pathway
- Trigeminal correlate of anterolateral pathway
- Descending pain modulatory pathways
attentional systems:
(lobes involved)
frontal, parietal
comprehension systems
(lobes involved)
- parietal
- occipital
- temporal
behavioral choice systems
(lobes involved)
frontal
somatic sensory system
(senses)
- touch
- proprioception (position sense)
- pain
- temperature
- itch
touch:
tests
- tactile movement:
- 2-point discrimination
- stereogenesis
- vibration
tactile movement:
tests what
discriminatory sensory test to check parietal lobe function
two point discrimination:
tests what
- the ability to discern that two nearby objects touching the skin are truly two distinct points, not one
- often tested with two sharp points during a neurological examination and is assumed to reflect how finely innervated an area of skin is.
stereognosis:
tests what
- the ability to perceive and recognize the form of an object in the absence of visual and auditory information, by using tactile information to provide cues from texture, size, spatial properties, and temperature, etc
- Typically, these tests involved having the patient identify common objects (e.g. keys, comb, safety pins) placed in their hand without any visual cues
romberg test:
tests what
proprioception
- test used in an exam of neurological function for balance adn DUI
- based on the fact that a person requires at least 2/3 senses to maintain balance while standing:
- proprioception (the ability to know one’s body position in space);
- vestibular function (the ability to know one’s head position in space);
- and vision (which can be used to monitor and adjust for changes in body position).
what are the 3 senses (that you need 2 of) to maintain balance?
- proprioception (the ability to know one’s body position in space);
- vestibular function (the ability to know one’s head position in space);
- vision (which can be used to monitor and adjust for changes in body position).
Fast pain:
define, and test
- sharp, pricking type pain; well-localized;
type of nociceptive (noxious) or pain sensation
- test: by alternately touching the tip and head of a safety pin to the surface of the skin –> normally, the pt should be able to distinguish sharp tip from dull head
Slow pain:
define, and test
- dull, burning type, diffuse
- indicative of tissue injury
itch:
define
- thought to occur via a separate group of very slow conducting nonmyelinated fibers w/ histamine receptors
- previously thought to be associated w/ pain conducting nerve fibers
temperature:
test
temeprature sensation cold to cool to warm to hot;
tested by touching the skin with test tubes filled with either cold or warm water
what are the ascending pathways (trunk & extremities)
- Information from receptors –>
- To the spinal cord –>
- Ascends thru the spinal cord –>
- Ascend thru brainstem –>
- To thalamus (think: grand central station where info is relayed)–>
- To cortex
touch:
- sensation
- path from limbs/trunk
- path from head
- incl. pressure and vibration
- limbs/trunk –> cortex: via dorsal column/medial lemniscus pathway
- head –> cortex: via trigeminal nerve & trigeminalthalamic pathway
meissner corpuscle:
info conveyed, & location
tactile shapes and surfaces, low frequency vibration, flutter, and two-point touch
pacinian corpuscle:
info conveyed, & location
vibrations;
found in deeper areas of dermis
ruffini’s corpuscles:
info conveyed, & location
shapes & stretching, joint rotation;
found in deeper areas of dermis
merkel’s discks:
info conveyed, & location
- tactile indentations, edges, and shapes
- found in subdermal areas, slowly adapting
free nerve endings:
info conveyed, & location
- temperature and tissue damage, some touch
- subdermal areas; slowly adapting
proprioception:
includes the body knowing…
- static position of the limbs
- movement of the limbs (kinesthesia)
- muscular effort
what are the key sources of proprioceptive information?
- muscle spindles, &
- golgi tendon organs
what are some proprioceptors (in addition to muscle spindles and golgi tenodn organs)?
ligaments and joint capsules
proprioception:
flow of information from trunk/extremities
- proprioceptive information from trunk & extremities –>
- ascends the CNS via the dorsal column-medial lemniscus pathway
dorsal column-medial lemniscal system (DC-ML):
function
- fine touch
- vibration
- position sense from trunk and extremities
dorsal column-medial lemniscal system (DC-ML):
pathway
- trunk and extremities
- cervical cord
- caudal medulla
- left pons
- left thalamus, VPL
- Left postcentral gyrus, primary somatosensory cortex (SI), trunk and extremities area
characteristics of:
A-alpha sensory axons
- Group I axons from muscles
- fastest conduction (80-120 m/sec)
- largest diameter (13-20 micrometer)
- proprioceptors of skeletal muscle
characteristics of:
A-beta sensory axons
- Group II axons from muscles
- Medium diameter (micrometer)
- Second fastest conduction velocity
- Mechanoreceptors of skin
Alpha gamma sensory axons:
characteristics
- Group III axons from muscles
- smaller diameter (1-5 micrometer)
- slower conduction velocity
- pain, temperature
group C axons:
characteristics
- Group IV axons from muscles
- No myelin ensheathing
- Smallest diameter (0.5-2 micrometer)
- Slowest conduction speed
- Temperature, pain, and itch
pathway of information:
from proprioceptors
- tactile information from receptors –>
- interacts w/ the first order neuron –>
- 1st order neuron has its cell body in the dorsal root ganglion –>
- central processes goes to the spinal cord
dorsal column-medial lemniscus (DC-ML) system in the spinal cord
- These axons are:
- located in the dorsal funiculus of the spinal cord
- are central processes of the DRG neurons that are the primary afferents of this system
- ascend to the medulla where they synapse on the next neuron in the pathway.
- DRG neurons - these are primary afferent neurons that transmit information from peripheral receptors into the spinal cord.
overall function of:
dorsal column-medial lemniscus pathway?
- a sensory pathway of the CNS that conveys sensations of fine touch, vibration, two-point discrimination, and proprioception (position) from the skin and joints
- transmits information from the body to the primary somatosensory cortex in the postcentral gyrus of the parietal lobe of the brain
where are the cell bodies of axons at dorsal root entry zone in the fasicuclus gracilis located?
in the dorsal root ganglion
somatotopic organization
- Spinal cord - from the lower extremity –> as you ascend, the fibers add to the outside of the nerve fibers –> leading to somatotopic organizations
- w/ lateral limbs more lateral, and medial limbs are more medial
which is more medial?
fasiculus gracilis? or fasiculus cuneatus?
fasiculus GRACILIS is more medial
*pathway of axons in
dorsal columns of the anterolateral system
- axons ascend in the dorsal funiculus
- ascend in a somatotopic way
- lower limb –> medially, upper limb –> laterally organized
what does “funiculus” mean?
“ropes”
where do first order neron of the PWC/Medial lemniscus pathway ascends?
ascends to the dorsal column nuclei, where is synapses w/ the 2nd order neuron;
3rd neurons projects to primary somesthetic cortex (located in the postcentral gyrus) via the posterior limb of the internal capsule
syanpses in the DC-ML pathway
- 1st synapse (w/in nucleus gracilis or n. cuneatus):
- b/w primary afferent neuron and 2nd order neuron
- 2nd synapse
- second order neurons’ axons cross the midline and ascend to the thalamus
- these axons form discrete bundle called the medial lemniscus
- ALS (anterolateral system) ascends the brainstem, making synaptic connections @ multi. sites in brainstem and thalamus
- ventral posterior lateral nucleu sof the thalamus - where 2nd order neurons synapses on 3rd order neurons
- 3rd order neurons project to primary somesthetic cortex (via the posterior limb of the internal capsule)
path of 2nd order neurons in medial lemniscus
ascend in the contralateral tegmentum of the pons and midbrain as they head toward the thalamus
thalamus:
key function, input and output
- major relay nucleus; to localize stimulation to a particular site ont eh both (proprioception and fine touch)
- ventral posterior lateral nucleus:
- inputs: DC-ML
- output: to primary somatic sensory cortex
where are the VPL, MD, and VPM relative to one another in coronal section?
MD: medial and superior/dorsal
VPM: medial and inferior
VPL: lateral
3 subsections of cortex
PSS, SSS, PP
- Primary somatic sensory cortex
- Secondary somatic sensory cortex
- Posterior parietal cortex
Which Brodmann’s areas are found in:
primary somatic sensory cortex?
1, 2, 3
which Brodmann’s areas are found in the:
posterior parietal cortex?
5, & 7
what does a homunculus represent?
map of density of sensory fibers - and drawn to proportion accordingly
cortex: sensory information of the
deep mechanoreceptors?
- joints and muscles
- course body representation
- limb position and shape detection
cortex: sensory information of the
superficial mechanoreceptors?
- skin
- complete and detailed body representation
- texture representation (to detect and understand the environment)
list the 2 other cortical areas mentioned?
- unimodal association cortex
- heteromodal association cortex
unimodal association cortex:
define, and fxn
- a constituent neurons respond predominantly to inputs from a single sensory modality (in post-central gyrus)
- initial synaptic relays
- fxn: encode perceptual character of sensory experience
example of unimodal cortex;
What can you differentiate about an object w/ eyes closed? What can you not?
- only detects one modality of sensation, so w/ eyes closed…
- You CAN ONLY tell if the 2 objects are same or different
- CAN’T TELL what they are or what they’re used for – this requires a diff’t cortex
heteromodal association cortex:
define
- multiple sensory systems have input into these cortical areas
- allows interpretation of an object
part of brain involved in object recognition?
temporal lobe
(where visual cortex is located; visualizing what it looks like based on our touch sensation)
part of brain for perception of body image?
posterior parietal cortex;
our body image in space; aspect of proprioception;
posterior parietal area is important for integrating all sensory information (heteromodal cortex)
somatic sensory system:
function
provides info to the body about its position in space and the impact of the environment on the body
(examples)
