Ascending and descending tracts Flashcards
What are the boundaries of the spinal cord?
Foramen magnum to L1/2
Where is a lumbar puncture carried out and why?
At cauda equina, below L2 to minimise risk of damage.
What is grey matter composed of?
Cell bodies
What is white matter composed of?
Myelinated axons organised into tracts
Which has more tracts, sensory or motor?
Sensory - more going in than coming out
Which matter requires more blood supply?
Grey due to the activity of the cell bodies. Has larger arteries than white matter.
Which type of matter is more likely to have a vascular block?
White as lumen is narrower.
What is the function of the
a) Dorsal horn
b) Lateral horn
c) Ventral horn
a) Sensory
b) Autonomic motor - preganglionic sympathetic and S2-4 parasympathetic
c) Somatic motor
Which end of the spinal cord has more white matter?
More in rostral than caudal = descending tracts and ascending joining
e.g. C5 contains all white matter from S5 upwards
What results from a transection at
a) C3
b) C4
c) C5?
a) C3 - Require a ventilator with no BP control
b) C4 - no movement but respiratory control with little shoulder and elbow flexion, loss of diaphragm
c) C5 - Phrenic N intact = breathe and speak
What is the function of an ascending vs descending tract?
Ascending = Sensory Descending = Motor
What is somatotopic organisation?
Spatial organisation in the brain with specific cortex regions linked to different areas of the body
Why does sensory and motor loss occur together with lack of blood supply?
In close proximity and share blood supply
Which spinal arteries dominate, anterior or posterior?
Anterior as it supplies the ventral and lateral horn.
Posterior supplies the dorsal horn.
Anastamosed together
What is the pre central gyrus?
Primary motor cortex
What is the post central gyrus?
Primary sensory cortex
Where are short association fibres located?
Between gryus
Where are projection fibres located?
From cortex to spinal cord through the internal capsule to cerebral peduncle
Where are long association fibres located?
Between lobes
Where are the commisural fibres located?
Between hemispheres
What is the difference between cerebral peduncle and crus cerebri?
Cerebral peduncles are large bundles of nerves passing out from the pons to connect the cerebral hemispheres and cortex.
Crus cerebri are tracts of nerve fibres at the base of the midbrain linking the pons to cerebral hemisphere. It forms the anterior portion of cerebral peduncles, containing the motor tracts.
What is the inferior colliculus and what is its function?
Part of the midbrain acting as the main auditory centre
How many neurons are involved in an ascending pathway? What are their paths?
3: Primary from receptor to spinal cord with cell body in DRG. Secondary decussate and synapses in thalamus. Tertiary arises in thalamus and terminates in primary sensory cortex.
What is the fucntion of the spinothalamic tract?
Pain, temperature and crude touch
What is the function of the trigeminothalamic tract?
Pain, temperature and crude touch via CN V
What is the function of the dorsal column / medial lemniscus pathway?
Fine touch and proprioception
Why is the spinocerebellar pathway unique and what is its function?
Only has 2 neurons despite being an ascending apthway.
For unconscious proprioception from spine to cerebellum
How many neurons from a descending motor pathway? What is their path?
2: Upper motor neuron from primary motor cortex to spinal cord where it decussates. Synapses with interneuron or LMN. Lower motor neuron from the ventral horn
What can damage the CNS?
Ischaemia from cerebrovascular incidents of stroke or haemorrhage.
Trauma from direct damage or compression from tumour or haemotoma.
Disease e.g. PD, AD
What can damage the PNS?
Direct trauma or indirect compression
MND, myasthenia gravis
What is myasthenia gravis?
AI neuromuscular disease causing skeletal muscle weakness. Antibodies produced against ACh receptors in the synapse
