Medsci L3: Sensory systems of the brain Flashcards
(24 cards)
What is discriminative and non-discriminative touch?
There are two kinds of sensory modalities when it comes to touch sensation. These are fine or discriminative touch, and crude or non-discriminative touch(pain & temperature). Fine touch enables a person to not only sense touch, but also localize it.
Spinal segmental level
location where 2 spinal nerves( right and left) exit the spinal cord
(looking at 1 cross-section of the spinal cord)
Dorsal Funiculi/ Columns
The biggest bundle of white matter
Within: Gracile fasciculus and cuneate fasciculus
Homuncular representation of the body( starting from toes up to the neck).
What information does gracile fasciculus carry?
lower limb
What information does cuneate fasciculus carry?
upper limb
What area of the spine only has gracile fasciculus?
Thoracic and lumbnar spinal cord levels
Lateral/Motor columns/ funiculi
responsible for carrying motor info from the brain down the spinal cord
Ventral Funiculi
Carry info about pain & temp
Where are pain & temp fibers found in the spinal cord?
area 1+ 2 in the grey matter
Proprioception
Ability to distinguish touch
Spatial feedback
What area is responsible for proprioception?
Area 3+4. Up to Nucleus proprius
Intermediate area function
Nervous supply to and from visceral organs( autonomic functions)
Heart, bladder etc
Helps maintain balance and posture. Returns the body to the midline after gesticulation.( swing arms during walking)
Motor neuron pool (8+9 area)
Lower motor neurons( drive muscle activity) localized within the spinal cord
2 step system for activating muscle:
upper motor neuron( starts in the primary motor cortex) which goes down to the spinal cord lvl where it can synapse with a lower motor neuron(localized in the motor neuron pool), which projects out to the muscle & activates it.
Ventral root
carries motor info to the muscle
Myotactic reflex
The brain is not aware of the activity
A sensory signal is carried through a sensory nerve, which then goes to the motor neuron pool and synapses with a motor neuron, which goes out the ventral root to the muscle
tract of lissaer
transparent
Area of the white matter that pain& temp neurons pass
What is the crossing(decussation) point of the pain& temp pathway?
anterior white commissure
thalamus
differentiates important information
associative sensory loss
the lesion on the right side of the brainstem causes loss of touch & pressure and pain& temp sensation on the left side
dissociative sensory loss
lesion in the lower part of spinal cord on the right side- no loss of touch & pain( discriminative) sensation on the left side, BUT loss on the right side and loss of pain& temp information on the left side and not on the right side.
The pathway of discriminative sensation( Dorsal column- medial lemniscal system)
The stimulus comes in from sensory nerve ending( e.g. C8-R.Arm)-> cuneate fasciculus( gracile for lower limbs)-> 1st neuron ascends up to lower medulla, where it connects to cuneate nucleus( gracile nucleus for lower limbs) synapses with a 2nd neuron, new cell body arises & crosses over to the other side in the Internal Arcuate fibers -> 2nd neuron fibers go to the pons through the midbrain and synapses with the 3rd neuron in the thalamus( differentiates information)-> 3rd neuron goes through the internal capsule up and is received in the arm area of the sensory homunculus.
Spinothalamic system( pain& temp pathway):
-Free nerve ending comes-> synapse in area 1+2 with a 2nd neuron after the tract of Lissauer to come into the dorsal area of the grey matter-> 2nd fiber crosses over the anterior white commissure-> goes up in the ventral funiculus through the medulla, pons, midbrain and synapses in the thalamus-> 3rd order neuron goes into the arm region of the sensory homunculus.
What part of the thalamus do the 2nd order neuron in the dorsal column-medial lemniscus pathway and the spinothalamic tract terminate?
VPL( ventral posterolateral nucleus of the thalamus)
