Med Neuro [Week 1] Flashcards
What sensations is the Dorsal Column/Medial Lemniscus composed of?
- light touch
- 2-point discrimination
- stereognosis
- graphesthesia - pressure
- vibration
- proprioception (limb position/motion sense)
Where are the cell bodies located for the sensory neurons?
Dorsal root ganglia (spinal ganglia)
What general things does the somatosensory system sense? (4)
- Touch - pressure against skin
- Temp of skin
- Proprioception
- Pain
Are sensory neurons are apart of the CNS or the PNS?
PNS
What are exteroceptive receptors?
Sense external world/skin - mechanoreceptors, thermoreceptors and nociceptors
What are proprioceptive receptors?
Sense muscle length, tension, joint angle - muscle, joint and tendon afferents, muscle spindles, golgi tendon organs
What are interceptive receptors?
Sense internal organs - visceral afferents and baroreceptors
Receptive field
Area in periphery where an adequate stimulus causes a response
Can receptive fields overlap?
Yes
Spatial summation code
The idea that the signal sent to the spinal cord is a summation of info from multiple neurons firing
Rate code
Frequency of AP firing
Increasing the diameter of an axon will _________ the conduction velocity.
Increase
What information can be determined from a “Compound AP” as a diagnostic tool?
- Nerve damage, nerve entrapment, trauma
2. Demyelinating diseases i.e. Guillain Barré
Where are the cell bodies of the neurons in the DC/ML system?
1st neuron = DRG
2nd neuron = nucleus cuneatus/gracilis (caudal medulla)
3rd neuron = VPL area of thalamus
Describe the peripheral and central processes of a 1st neuron in DC/ML system.
-peripheral process = info from mechanoreceptors (free nerve endings or encapsulated nerve endings)
-central process = transmit info from DRG and ASCENDS within IPSILATERAL dorsal columns
[descending branch = reflex pathway]
Which neuron in the DC/ML system is involved in decussation to the contralateral side of the body?
2nd neuron at the INTERNAL ARCUATE FIBERS (cross the white matter); the axon ASCENEDS as the medial lemniscus “ribbon”
Spatial resolution depends on what 2 things?
- Receptive field size
2. Innervation density
Name the characteristics of the cervical, thoracic, lumbar and sacral SC regions.
- cervical = has fasciculus gracilis/cuneatus; largest amount of white matter; NO lateral horn
- thoracic = has fasciculus gracilis; f.c. only above T7; has lateral horn in gray matter (ANS; T1-L2)
- lumbar = only fasciculus gracilis; large amount of white matters; some lateral horn (ANS; T1-L2)
- sacral = only fasciculus gracilis; smallest cross-section
The fasciculus _____ is more medial and corresponds to sensory of the _______ limbs whereas the fasciculus ______ is more lateral and corresponds to the _____ limbs.
- gracilis
- lower
- cuneatus
- upper
Fasciculus gracilis is located medially _______ T7, whereas fasciculus cuneatus is located laterally _____ T7.
- below
- above
The _____ separates the fasciculus gracilis from cuneatus.
posterior intermediate septum
Define somatotopy.
a map of the body that can be laid out at different spinal levels, depending on the nerve pathway
Which mechanoreceptors are slowly adapting?
- Merkel disks
2. Ruffini corpuscles
In the caudal medulla, describe the somatotopy.
“headless, hemisected man standing on a pyramid”
- sacral/lumbar are anterior (on pyramids of medulla)
- thoracic/cervical are posterior
In the pons, describe the somatotopy.
hemi-sected man WITH head! (this is where CN V comes in and adds facial sensory information)
- sacral/lumbar are anterior
- thoracic/cervical/head are posterior
The VPL receives ____ information while the VPM receives _______ information.
- body sensory
- facial sensory
How does the thalamus process sensory information?
NOT a simple relay; decides whether or not to send information
-ex: chased by a tiger, do not want to send pain info from cut on your foot (SNS)
In the thalamus (brain), describe the somatotopy.
in a coronal cross-section….
- face/cervical/thoracic more medial
- lumbar/sacral more lateral
The axons of the 3rd neurons of the DC/ML system pass through the _______ of the ______ made of white matter.
- posterior limb
- internal capsule
Describe what can happen to the thalamus due to a massive MCA stroke.
CONTRALATERAL loss of sensation from the body/head
In a coronal cross section of the brain, describe the somatotopy of the S1 cortex.
- feet/genital sensory info most medial
- arms, face most lateral
You’re sitting Kerrigan listening to a lecture and the room is at a surprisingly comfortable temperature (physiological zero). Are your cooling receptors firing?
Yes at a rate of ~1 Hz
In the middle of lecture you suddenly feel very chilly. How are your cooling and warming receptors responding to this?
- Cooling receptors will fire at an increased rate which will gradually come back down
- Warming receptors will stop firing and gradually begin again
Describe the etiology of POSTERIOR CORD SYNDROME. What disease could cause this as well as trauma?
- lesion in only the posterior (DC/LM) part of spinal cord
- tertiary neuro-syphilis
Describe a posterior cervical spinal cord injury.
- loss of light touch, pressure, vibration/proprioception
- other sensory/motor functions INTACT (can feel pain, temperature, and can move!)
__________ receptors have a very small RF and infrequent distribution.
Cooling
Describe a large central cord lesion
- loss of light touch, pressure, vibration/proprioception
- loss of other sensory/motor functions
- SPARED SACRAL REGION (in genitals)
In large central cord lesions, as you increase in SC levels in the cervical spinal cord, there tends to be _____ sacral region sparing because ________.
- more
- sacral fibers tend to be more dorsal
A-mechanonociceptors respond to __________________ and are ____________ adapting.
- Intense force, heat (53˚C)
2. slowly adapting
What acute pathology can cause a loss of all sensorimotor information on the contralateral side of a person’s body?
medial medullary syndrome = caused an anterior vertebral artery aneurysm
Suppose a patient gets a lesion at the base of the corona radiata and another patient gets a lesion at the periphery of the corona radiata. Which is worse? Why?
the base; all fibers from VPL and VPM from the thalamus originate at the base and fan out, like a deck of cards, and eventually innervate the SI cortex; therefore a lesion at the base would affect ALL fibers, whereas a lesion at the periphery would only affect those fibers in that part of the SI cortex
Which nociceptor encodes “fast pain” that is easy to localize? i.e. sharp, shooting, electrical pricking pain?
A-mechanonociceptor
In the DC/ML system, what are the 4 major Brodmann areas in the SI cortex? Where are they located?
3a = most medial, post-central gyrus lining central sulcus 3b = medial, lining central sulcus 1 = vertex of post-central gyrus 2 = most lateral; part of post-central gyrus lining the post-central sulcus
What are the functions of Brodmann areas 3a, 3b, 1 and 2?
3a = limb movement/proprioception 3b = basic tactile information (edges/texture) 1 = motion and direction of movement of objects 2 = limb position; shapes of objects
Which nociceptor encodes “slow pain” that is difficult to localize? i.e. long-lasting, burning, aching pain
C polynodal nociceptors
Parietal association cortices are located ________. Describe what information they process.
- along intraparietal sulcus
- receive sensory info and project to motor cortex
Which area is associated with HAND-EYE COORDINATION/perception?
parietal association cortices = super marginal gyrus, angular, superior parietal lobule
Describe a UNIMODAL lesion in the parietal association cortices.
ONE piece of sensory information is lost; i.e visual, auditory, somatosensory
What is an agnosia?
inability to recognize an object or a property of an object; due to lesion in parietal association corties
Describe a MULTIMODAL lesion in the parietal association cortices.
problem putting together lots of information; ex. combining sensation with motivation, attention, relevance, etc.
What is contralateral neglect?
aka hemi-neglect; disregarding information on the contralateral side of the body as the lesion; due to multimodal lesion in the parietal association cortices
A right shift on a compound AP implies what?
Slowed conduction velocity
A lower peak on a compound AP readout implies what?
Decreased number of neurons
Rapidly adapting neurons encode ____________ stimuli.
Changing/dynamic - impact and motion - fires at onset and offset
Slowly adapting neurons encode ____________ stimuli.
Static - pressure shape of object
Spatial resolution depends on what 2 things?
- Receptive field size
2. Innervation density