Ascending and descending pathways of the spinal cord Flashcards
Give the simple explanation of what happens when a sensory input comes into the spinal cord
Sensory receptor in the muscle, skin or joint brings an electrical impulse into the dorsal horn of the spinal cord (grey matter).
The signals come from the integration of signals within the dorsal and ventral horns and are then transmitted up through ascending pathways through white matter towards the brain.
When a pain afferent comes through the dorsal root ganglia, it then synapses in the top part of the dorsal horn.
What is this part called?
The substantia gelatinosa
Why do tracts travel up and down the white matter?
White matter is myelinated so allowing for a faster conduction.
If an autonomic preganglionic axon is leaving the grey matter, at what part does it leave from?
The lateral grey matter.
Explain how the spinal reflex arc works
A hammer is used to depress the patella tendon on someones knee.
This causes an excitation into the spinal cord via the dorsal root ganglia.
Once in the spinal cord, the afferent fibre branches into two, one plays directly onto an excitatory motor neuron that causes contraction of the extensor muscles of the knee.
The other signal branch goes to an inhibitory interneuron which sends impulses to the flexor muscle to inhibit contraction.
How is the body organised for innervation?
The body is organised into dermatomes and each spinal nerve supplies a different section of the body.
We can work out where a problem is coming from in the spinal cord by seeing which dermatome is affected.
(same for sensory and motor fibres)
Why do we have cervical and thoracic enlargements?
To supply the nerves to the upper and lower limbs.
Explain why we have a caudal equina
The vertebral bones become out of sync with the spinal cord nerves.
The vertebral bone column is longer than the spinal cord.
e.g. the 10th vertebral bone is aligned with the 12th spinal cord.
Where do spinal nerve emerge out of the vertebrae?
They emerge between adjacent vertebrae through the intervertebral foramen.
Why do we have a cartilaginous disc between vertebrae?
The disc allows for flexibility and separation of the vertebrae to allow spinal nerves to enter and exit the cord.
What happens if a cartilaginous disc compresses?
The cartilage of this puts pressure on the spinal nerve which affects sensory information coming in and motor innervation exiting.
Typically occurs in the lumbar spine which gives arise to sciatica.
What are the names of the two conscious ascending sensory pathways? give details on where they cross and synapse
- Posterior column medial lemniscal
- Fine touch and proprioception
- Primary nerve comes into the dorsal root ganglion and branches into 2 connections. One into the dorsal horn of the spinal cord and the other runs up on the same side and it enters into the medulla
- Primary neuron synapses once in the medulla
- Second order neuron crosses the brain stem to the contralateral side
- Second order neuron goes into the ventral posterior nucleus in the thalamus
- Synapse onto third order neurons that runs from the thalamus to the somatosensory cortex - Spinothalamic
- Pain and temperature
- Sensory information in on the primary neuron
- Synapses to the secondary order neuron with the spinal cord and then travels up to the medulla on the opposite side
- Second order neuron travels to the ventral posterior nucleus of the thalamus
- Synapses with third order neuron from the thalamus to the somatosensory cortex
Where is the spinothalamic tract found in the spinal cord?
On the lateral-ventral section
Where in the white matter do we find the pathways for the dorsal column medial lemniscus pathway?
Dorsally
The fasciculus cuneatus is for T6 and above (signals from upper limb) and the fasciculus gracilis is for T6 and below (signals from lower limb).
The gracilis runs more medially.
Outline the descending pathways as to where they begin and what ‘stop-points’ they pass through
The neurons begin in the motor cortex where the information emerges and travels to the spinal cord.
Information from the motor cortex travels through the internal capsule and then through the brain stem there are stop off points including the red nucleus, the vestibular nucleus, the superior colliculus.
The pyramidal tract runs directly from the brain into the spinal cord and then connects with motor neurons that gives information at segmental levels to allow different muscles to contract.
