Spinal Cord and Processing Two Flashcards
What brain regions are involved in processing somatosensory information?
A number of brain regions are involved in recieving, relaying and processing somatosensory input
What is the role of the thalamus in somatosensory processing?
Its VPN (ventroposterior nucleus) receives input from second order neurons in the posterior column medial lamincus pathway and the spinothalamic tracts. It then projects (relays) up to the primary somatosensory area.
The sensory pathways innervate different parts of the thalamus depending on what information they are carrying. (it is mapped very precisely)
What is the role of the somatosensory cortex one (primary)?
Receives inputs from the thalamus.
How is the somatosensory cortex one divided?
Into broadmanns area
3a, 3b, 1 , 2
- Based on its cytoarchitecture and function
- Somatotopically organized
What does the broadmanns areas implicate?
- Different areas receive different information
- The cortical layers project between one another.
- Important for the co-ordination of movement
what cortical layer does the thalamus project to?
It projects to cortical layer four (4)
Where do fibers of the VPN in the thalamus project to?
Mostly to the 3B of S1
3B projects onto S2
Whats the role of S2?
Somatosensory information intergration
Where does S2 project to?
S1 (regulation)
Association Cortex
Motor Cortex
Amygdala and hippocampus (Tactile learning)
What is the role of the somatosensory association cortex?
- Higher order processing
- Input from visual cortex
- Projects to motor cortices (voluntary movement)
- Learning complex associations
What is somatosensory plasticity?
Changes in cortical representation occur following injury or due to experience (training)
How fast can somatosensory plasticity occur?
- Can be instantaneous, transient
What causes somatosensory plasticity to occur?
- Due to training or change in behavior from normal. Cortical map will return to normal if task not continued.
- Over time stable enlargement of the cortical representation can occur (structural plasticity)
What anatomical feature allows structural plasticity to occur?
Overlapping projection zones allow for changes in fields. (i.e growth in a tonotopic zone)
- Can occur due to injury or training
- With injury, neural inhibition is lost, can be rapid
- “Use dependent” synaptic strengthening takes days or weeks
What does loss of input (i.e nerve death) lead to?
permanent re-organization of the cerebral cortex
What may cortical changes (caused by loss of input) also result in?
Subcortical modification
- Branching of axons from one zone to another, i.e when they fire you can cause phantom pain
Whats an example of somototopical plasticity that occurs because of learning?
i. e Learning brail
- Very detailed info at finger tips
- Enlargement of finger tip representation at cortex
Do changes in the S1 area correlate with braile ability?
No, they dont and lesions in S1 dont degrade braile ability suggesting other cortical inputs
Why does braile result in enlarged cortical representation?
input undergoes re-organisation and redistribution to allow the processing of fine spatial and temporal details.
= Cross modal plasticity (recruitment of de-afferented areas to undertake the increased input/ task)
Where can damage occur that results in somatosensory impairment?
- Peripheral Nerve
- Spinal Cord
- Thalamus
- Cortex
What does peripheral nerve affect?
The somatic area it innervates (not below or above it)
What are the types of peripheral nerve damage?
Partial (some fibers)
Full (all fibers)
Mononeuropathy
Polyneuropathy
Acute (transient, pins and needles)
Chronic (death of neuron)
What are the causes of peripheral nerve damage?
Trauma
Infection
Ischemia
Disease
What can peripheral nerve damage be due to?
Axon Dieback
Demyelonation
nerve cell death
What is polyneuropathy?
When one cause affects many neurons, can be all around the body
What is a cause of polyneuropathy and why?
Diabetes, as the arteries become calcified and the neurons become ischemic
What are the causes of spinal cord injury?
Trauma
Infection
Inflammation
Damage to blood vessels
What does spinal cord injury result in?
Full or partial loss of somatosensory function below the level of injury (depends on type of injury)
What are the examples of spinal cord injury?
Posterior cord syndrome
Anterior cord syndrome
Brown-Sequard syndrome
Central Cord Syndrome
What is posterior cord syndrome?
Damage to the posterior portion of the spinal cord, or interruption to the posterior spinal cord artery
Loss of fine touch, vibration (posterior column, medial laminscal pathway)
What is anterior cord syndrome?
Damage to the anterior portion of the spinal cord or the interruption of the anterior spinal cord artery
Loss of crude touch, temperature probably motor function too
What is Brown-Sequard syndrome?
Hemisection loss of spinal cord.
- Dissociative sensory loss (as lose different sensations on different sides of the body- due to decussation rules)
i. e lose pain+temp one side and touch+vibration on the other
What is central cord syndrome?
Loss of propioception and sense of vibration below the level of injury
- Loss of motor movement in the arms and far lesser so to the legs, (inverse paraplagia)
What causes thalamus injury?
Mainly stroke
What is the result of thalamus injury?
Damage to VPN will result in loss of all somatosensory modalities (relay nuclie) only for the area lesioned, often mutliple areas affected though.
What will damaged to the cortex result in?
Damage will be contralesional to the side that is affected.
Damage to the Primary somatosensory area will result in loss of vibration, propioception and discriminative sensation.
Lose ability to localize pain
Can be more complex
What causes a complex cortex damage?
Damage to the parietal lobe
- Can be one or more of the somatosensory areas
What are some examples of complex cortical injuries?
Hemineglect
Agraphthesia
Somatosensory Agnosia
What is hemieglect?
The inability to be aware of half of your body
What is agraphthesia?
Cant recognize cutaneous orientation i.e cant distinguish cross from circle drawn on the hand
What is somatosensory agnosia?
Inability to identify and object without visual input
