Tracts Flashcards
What are tracts?
Organised nerve fibres sharing common origins, terminations and functions which run between the spinal cord and the brain
Define funiculi
Continuous area of white matter running the whole way down the spinal cord. Hold bundles of myelinated nerve fibres together (fascicles)
Where does the spinal cord finish?
At the conus medularis - L1/L2. Below this is the cauda equina
What type of matter is in the central part of the spinal cord?
Grey matter
Where does motor info exit the spinal cord?
Ventral root
Where does sensory info enter the spinal cord?
Cell body of the dorsal root ganglion
What are the descending tracts split into?
Extrapyramidal and pyramidal
What type of information do ascending/afferent tracts carry?
Carry impulses like pain, thermal, tactile, muscle and joint receptors to the brain and within spinal cord
Where do descending tract originate?
What type of information do descending/efferent tracts carry?
Name the 2 main descending tracts.
Originate from the cerebral cortex and brain stem.
Carry impulses controlling movement, muscle tone,
spinal reflexes, spinal autonomic functions and
modulate sensory transmission.
• Pyramidal/ direct/ Corticospinal
• Extrapyramidal/ indirect
Which is motor and which is sensory in descending/ascending tracts?
Descending = motor Ascending = sensory
What are the 3 areas of funiculi in the spinal cord?
Anterior, posterior funiculus and lateral funiculus
Name the 6 ascending tracts
Spinocerebellar - posterior + anterior
Spinothalamic - lateral + anterior
Dorsal white columns - fasciculus cuneatus + fasciculus gracilis
Name the function of
a) Spinocerebellar
b) spinothalamic
c) dorsal white columns
a) subconscious proprioception lower limb - ipsilateral
b) lateral: pain and temperature - contralateral
anterior: coarse touch - contralateral
c) Discriminative touch & conscious proprioception
Describe the posterior spinocerebellar tract
Runs: through spinal cord
Terminates: at cerebellum
Carries: afferent subconscious proprioception from
muscles spindles, Golgi tendon organs, joint proprioceptors in lower limb (ipsilateral)
1st order neurons: bring afferent nerve impulses through dorsal root ganglion, dorsal root and then synapses with 2nd order neuron
2nd order: transmits it to posterior part of lateral funiculi which then goes up the spinal cord through medulla and pons and then cerebellum
Describe the anterior spinocerebellar tract
Runs: through spinal cord
Terminates: at cerebellum
Carries: afferent subconscious proprioception from
muscles spindles, Golgi tendon organs, joint proprioceptors in lower limb (ipsilateral)
1st order neurons: bring afferent nerve impulses through dorsal root ganglion, dorsal root and then synapses with 2nd order neuron. Signal decassates (moves to opposite side of the spinal cord at which the movement occurred e.g. if movement occurred in left lower limb it would decasste to right hand side of spinal cord)
2nd order: transmits it to anterior part of lateral funiculi which then goes up the spinal cord through and pons (where it crosses back to the original side) and ends at cerebellum
Describe the lateral spinothalamic tract
contralateral
Runs: from spinal cord
Terminates: thalamus
Carries: info on pain and temperature i.e. signals from nociceptors and thermoreceptors across the body
1st order: impulses come in via 1st order through dorsal root and into dorsal horn.
2nd order neuron: 1st order synapses to 2nd. Signal crosses over in the lateral funiculus and stays on this side travelling up the spinal cord to the thalamus
3rd order: before going to cerebral cortex 2nd order synaposes to 3rd order
What part of the brain is the somatotopic representation of the body?
The somatosensory cortex on the post-central gyrus of the cerebral cortex
Describe the anterior spinothalamic tract
(similar to lateral spinothalamic)
1st order: via dorsal root ganglion 1st order neurons carry coarse touch and pressure info to 2nd order neurons. A synapse occurs into 2nd order neurons
2nd order: bring impulse to anterior funiculi through medulla, pons and midbrain before synapsing in thalamus
3rd order: bring it to an area on the contralateral side of the somatosensory cortex
Describe the type of information dorsal white columns relay
Fine discriminative touch • Vibration • Two point discrimination • Conscious proprioception • stereognosis
Describe the pathway of fasciculus cuneatus
Terminates: somatosensory cortex
Carries: info from the upper limbs
1st oder: enters via posterior dorsal root and organises to lateral part of dorsal white column without synapsing. It ascends to the nuclei cuneatus in the medulla as a 1st order neuron
2nd order: 1st order synapses to 2nd and crosses over to opposite side of thalamus
3rd order: goes to somatosensory cortex
Describe pathway of fasciculus gracilis
Carries: info from lower limbs/trunk enters spinal cord at dorsal root, dorsal horn.
1st order neurons: enter posterior horn via dorsal root and enters the medial aspect of posterior dorsal white column without synapsing. It ascends as a 1st order neuron to reach the nuclei gracilis in medulla and synapses to a 2nd order neuron
2nd order neuron: crosses over and travels to medial lemniscus tract, through pons and midbrain before synapsing at thalamus where it turns into a;
3rd order neuron goes to somatosensory cortex
What areas of the dorsal white column is responsible for upper and lower limb?
Medial = lower limb Lateral = upper limb
How are the upper limb signals differentiated from lower limb signals in the medulla?
Medulla is split into 4 medullary nuclei - 2 nuclei gracilis (medial 2) and 2 nuclei cuneatus (outer/lateral 2).
Upper limb signals ascend to the nuclei cuneatus
Lower limb signals ascend to the nuclei gracilis
Name the descending motor tracts
- Pyramidal (direct)
- corticospinal (lateral and anterior) - Extrapyramidal (indirect)
- rubrospinal
- tectospinal
- retuculospinal
- vestibulospinal
- olivospinal
Where do direct descending tracts come from?
Cortex
Where do indirect descending tracts come from?
Brainstem
What is Friedrich’s ataxia?
Degeneration of spinocerebellar tracts
Causes tremors difficulty in co-ordinating movement and damage to subconscious proprioception
