Spinal cord and periphery Flashcards
In a cross section of the spinal cord, which horn is dorsal and which is ventral?
Dorsal root is pointed and more medial, ventral root is wider and more lateral. This is the grey matter of the spinal cord.
Where do axons of sensory fibres enter the spinal cord?
Via the dorsal root into the dorsal horn.
Where are the cell bodies of motor neurons?
Ventral horn.
Which neurons are affected in MND?
The motor neurons in the ventral horn of the spinal cord - these are LMN’s. The neuron dies, and as a result the muscle it supplies atrophies.
What is white matter made of?
Tracts - axons transmitting information between higher centres in the brain to peripheral nerves.
Ascending pathways are sensory, descending pathways are motor.
Describe an ascending spinal tract.
There are 3 neurons between peripheral receptor and cortex:
- 1st order neuron: carries information from the receptor, goes through the dorsal root/CRN ganglion and enters the dorsal horn
- 2nd order neuron: starts in the grey matter of the spinal cord or the medulla, ascends and crosses over to the contralateral side in the spinal cord or medulla
- 3rd order neuron: has its nucleus in the contralateral thalamus and goes to the contralateral parietal cortex (primary somatosensory cortex)
Which senses are carried in the posterior/dorsal column?
Fine touch, vibration sense, tactile localisation and proprioception.
Describe upper and lower MN’s.
UMN’s start in the cortex. They tell a LMN to tell a muscle to start contracting, and also when to tell the muscle to stop contracting.
LMN’s are the direct messengers that tell muscles to start contracting.
What happens if there is a LMN lesion?
The LMN cannot tell the muscle to start contracting and so this results in weakness of that muscle.
What happens if there is an UMN lesion?
There can be weakness as the UMN cannot tell the LMN to start contracting.
But also cannot tell the LMN to stop contracting so the muscle continues to spastically contract–> this results in spasticity which is the characteristic feature of an UMN lesion.
Spastic paralysis with hyperreflexia.
Which fibres are carried in the lateral spinothalamic tracts and where do these decussate?
Pain and temperature. These decussate at the point of entry to the spinal cord.
Which fibres are carried in the posterior/dorsal columns/medial lemniscus and where do they decussate?
Vibration sense, propriosension, fine touch and tactile localisation. These travel up the spinal cord on the ipselateral side of entry ad decussate in the cuneate and gracile nuclei of the medulla.
Where is the damage if a patient can feel temperature but not vibration at a certain spinal level?
As temperature is carried in the spinothalamic tract this crosses over as soon as it enters the spinal cord. Vibration is carried in the dorsal columns and so the damage must be on the ipselateral side above the level of that nerve root.
Which senses are carried in the right lateral spinothalamic tract?
Pain and temperature from the left side of the body.
Which senses are carried in the right dorsal column?
Vibration, proprioception and fine touch from the right side of the body.
