White Matter / Descending Pathways Flashcards
What areas do commisural fibres transmit impulses between? What is the largest of the commisural tracts?
- gyri of the opposite hemisphere
- corpus callosum
What areas do association fibres transmit impulses between?
gyri in the same hemisphere
Where do projection fibres transmit impulses between?
cerebrum and other parts of the CNS via ascending and descending pathways
What are the four afferent fibre types?
1a/1b, beta, A-delta, C-fibre
What are the two receptor types for 1a/1b fibres?
What is their stimulus?
What is their relative axon diameter?
Are they myelinated?
What is their relative conduction velocity?
- muscle spindle (1a), golgi tendon organ (1b)
- proprioception
- largest
- yes
- fastest
What is the receptor for A-delta fibres? What is their stimulus? What is their relative axon diameter? Are they myelinated? What is their relative conduction velocity?
- A-delta nociceptor
- tissue injury (mechanical, thermal)
- small
- yes
- slower (fast pain)
What is the receptor for C-fibres? What is their stimulus? What is their relative axon diameter? Are they myelinated? What is their relative conduction velocity?
- C-PMN nociceptor (polymodal)
- tissue injury (mechanical, thermal, alogogenic chemical)
- smallest
- no
- slowest (slow pain)
What are the 4 events between stimulus and experience? Describe them.
- transduction (stimuli converted to action potentials)
- transmission (signals enter and ascend the CNS)
- modulation (intensity is defined)
- perception (feeling)
What information does the dorsal column relay? Give 2 examples.
somatosensory information entering the spinal cord.
- proprioception
- vibratory sensations from the body (except face, mouth, head)
List 3 parallel ascending (sensory) tracts.
- dorsal column
- spinocerebellar tract
- spinothalamic tract
Where is somatosensory information from the face, mouth and head supplied from?
trigeminal nerve (CN V)
What information do the spinocerebellar tracts relay? (2)
- subconcious muscle
- joint position sense (proprioception)
What information does the spinothalamic tract relay? (2)
- pain
- temperature
What does crude touch imply?
that a person will not be able to localize where they were touched, only that they were touched
What are the two sub-divisions of the spinothalamic tract called?
- neospinothalamic
- paleospinothalamic
The neospinothalamic tract has ___ major neurons. The 1st order neuron is attached to a _______.
3 / A-delta nociceptor
What tract is associated with withdrawl reflexes and escape behaviour?
neospinothalamic tract
What information does the paleospinothalamic tract carry?
Via what?
Where to?
How is it interpreted?
- slow pain
- unmyelinated C-fibres
- contralateral side
- dull, ache, chronic pain
In the paleospinothalamic tract, the ______ neuron is attached to a _________.
unipolar / C-PMN nociceptor
What tract mediates reflexes and integrated responses (fear, memory) related to nociceptive impulses?
paleospinothalamic tract
Tracts of myelinated axons (white matter) in the CNS travel in ___ directions. What are they called, and what direction are they?
3
- association (anterior-posterior)
- commisural (lateral)
- projection (superior-inferior)
Where are lower motor neuron cell bodies located?
neuraxis
Motor (descending) pathways are divided into two main divisions called ______ and ______.
direct / indirect
Direct motor pathways travel from ______ directly to ______ via the ______ tract.
motor cortex / lower motor neurons / corticospinal (aka. direct motor)
Indirect motor pathways travel from the motor cortex to the lower motor neurons via the ______, ______, and ______ tracts.
rubrospinal / tectospinal / vestibulospinal
What does CN VII control?
facial muscle (expression)
What is the only direct connection between the motor cortex and the spinal cord?
corticospinal tract (aka. direct motor tract)
About ___% of the corticospinal tract axons _______ to the other side of the body in the distal _______.
90 / decussate / medulla
What separates the medulla from the spinal cord?
pyramidal decussation
What is the internal capsule?
What does is consist of?
- massive layer of white matter (8-10mm thick)
- ascending and descending projection fibres
What is the major route by which the cerebral cortex is connected to the brain stem and spinal cord?
internal capsule
Where is the most common stroke location?
part of the internal capsule which carries the corticospinal tract
What is the rubrospinal tract directed by?
What is it’s function?
- red nucleus in the brain stem
- alternative route for voluntary motor commands
What is the vestibulospinal tract directed by?
What is it’s function? (2)
- brain stem
- maintain correct position of head and neck
- mainaint upright posture by stimulating extensors (antigravity)
What is the tectospinal tract directed by?
What is it’s function?
- brain stem
- coordinates head and eye movement
What is divergence?
information in the CNS carried by neurons to many different neurons
What is convergence?
information in the CNS from many different sources sent to the same neuron/nucleus
What information does the neospinothalamic tract carry?
Where to?
How is the information interperated?
- fast pain (as well as crude touch)
- contralateral sensory cortex
- sharp, acute, localized pain
