White Matter Flashcards
What’s the word for when a neuron crosses the midline of the spine?
decussates
Which part of the spinal column relays somatosensory information entering the spinal cord to the brain? (except for face, mouth, head)
posterior aka dorsal column
Somatosensory information from the face, mouth and head is supplied primarily by ___ ___ axons of the ___ nerve?
afferent unipolar; trigeminal nerve (CN V)
The posterior column is made up of the ___ ___ (lower limb) and the ___ ___ (upper limb)
gracile (slender) fasciculus; cuneate (wedge shaped) fasciculus
What do gracile, cuneate, and fasciculus mean?
slender; wedge-shaped; tract
Which tracts transmit impulses for subconscious muscle and joint position sense (proprioception) to the cerebellum?
spinocerebellar tracts
Where is proprioceptive information obtained?
by golgi tendon organs and muscle spindles
What kind of information is relayed by the spinothalamic tract?
relays pain, temperature and crude touch
Which tract carries first aka fast aka discriminative aka well localized pain as well as crude touch directly to the sensory cortex?
neospinothalamic tract
The neospinothamic tract has 3 major neurons. The 1st order neuron is attached to a(n) ___ ___
A-delta nocicptor
Which tract is associated with superficial cutaneous and withdrawal reflexes and escape behaviour?
neospinothalamic tract
Does the signal in the neospinothalamic tract decussate?
yes
What kind of information does the paleospinothalamic tract carry?
carries second aka slow pain aka poorly localized pain via unmyelinated C-fibres
What kind of receptor is the unipolar neuron in the paleospinothalamic tract attached to?
C_PMN nociceptor
The paleospinothalamic tract consists of more than _ neurons in relaying signals from the dorsal horn to the ___, ___, ___, and ___ system.
3; brain stem; hypothalamus; thalamus; limbic-forebrain
Which tract mediates reflexes and integrated responses (fear, memory) related to nociceptive impulses?
paleospinothalamic tract
What are the ascending tracts from the spinal cord?
-posterior coloumn aka dorsal column (DC) -spinocerebellar tracts -spinothalamic tract (neospinothalamic and paleopinothalamic) -cranial nerve V (trigeminal nerve) from head
What are the three principle directions in which white matter runs?
- Projection fibres form tracts that transmit APs between the cerebrum and other parts of the CNS (ascending or descending) 2. Association fibres connect and transmit impulses between gyri in the same hemisphere 3. Commissural fibres transmit impulses from the gyri in one cerebral hemisphere to the corresponding gyri in the opposite cerebral hemisphere. (corpus callosum is largest)
What are the names and receptor types of fibres in the ascending tracts?
1a, 1b: MS (1a), GTO (1b) beta: Meissner’s, Pacinian corpuscle A-delta: A delta nociceptor C fibre: C-PMN nociceptor
What stimuli are associated with each fibre type in ascending tracts?
1a, 1b: proprioception beta: touch (fine), pressure A-delta: mechanical or thermal tissue injury C fibre: tissue injury by mechanical, thermal, algogenic chemicals in interstitial fluid
What’s the diameter, myelination and conduction velocity of each fibre type in ascending tracts?
1a, 1b: largest, myelinated, fastest beta: large, myelinated, fast A-delta: small, myelinated, slower (fast pain) C fibre: smallest, unmyelinated, slowest (slow pain)
APs in C-nerve fibres travel and the speed of ___, A-delta at speed of ___, 1a/1b at speed of ___
slow walk; fast sprint; near airplane
When you stub your toe, you first feel sensation carried by ___ nerve fibres, then you feel sharp pain carried by ___ fibres, then dull throb of ___ fibres
beta; A-delta; C
What are the four complex electrical and chemical events between stimulus and experience?
- transduction 2. transmission (nn signals enter and ascend CNS in various pathways) 3. modulation (process by which accompanying neural activity from other ascending inputs or signal descending from the brain can modify sensory transmission – in this way, the intensity of sensory input to cerebral cortex can be controlled) 4. perception (combination of transmission and modulation that results in final subjective feelings – can be altered by emotions such as fear, rage or depression)
Where are LMN cell bodies located?
in the neuraxis
What are the two motor pathway divisions of the descending pathways of the direct (aka pyramidal aka corticospinal aka voluntary) tracts?
direct pathways: motor cortex directly to LMN (corticobulbar [head] and corticospinal [body]) indirect pathways: motor cortex via other tracts to the LMN (rubrospinal, tectospinal, vetibulospinal)
What’s the only reason we call an UMN “upper”?
it bosses around a LMN
What are the akas for the pyramidal tract?
direct, corticospinal, voluntary
The corticospinal (aka direct aka pyramidal aka voluntary) tract is a pathway consisting of:
UMNs from the motor cortex and LMNs from the SC or brainstem (CN V, VII) that innervate skeletal muscle
The direct (aka pyramidal aka corticospinal aka voluntary) tract controls:
voluntary movements of our body (it’s the only direct connection between the motor cortex and the spinal cord)
What % of corticospinal (aka direct aka pyramidal aka voluntary) tract axons decussate in the distal medulla?
90%
What is the elevated area of decussation of the voluntary (aka direct aka pyramidal aka corticospinal) tract called?
pyramidal decussation
What separates the medulla from the spinal cord?
the pyramidal decussation
This massive layer (8 to 10mm thick) layer of white matter is the major route by which the cerebral cortex is connected to the brainstem and spinal cord.
internal capsule
Which part of the internal capsule is the most common stroke location?
that which carries the corticospinal tract
Terms denoting paralysis an entire side of the body
hemiplegia; hemiparesis
Referencing the 2 neuron system of the pyramidal tract, where are UMNs located?
brainstem
What does bulbar refer to?
medulla oblongata
What are the bulbar muscles?
muscles of mouth and throat responsible for speech and swallowing
Projection fibres from the ___ and ___ also influence the LMNs but they do so indirectly.
basal ganglia and cerebellum (via extrapyramidal descending tracts)
Persons with ___ disorders, for example Parkinson disease, frequently have problems with balance and may experience frequent falls.
extrapyramidal/indirect
What does the rubrospinal pathway innervate and what is it directed by?
Innervates: it’s an alternative by which voluntary motor commands can be sent to the spinal cord. although it is relatively minor in humans it is an important pathway for the recovery of some voluntary motor function after damage to the corticospinal tract Directed by: red nucleus in brainstem
What does the vestibulospinal pathway innervate and what is it directed by?
Innervates: a) vestibular reflexes maintain the correct position of head and neck b) they also maintain upright and balanced posture mainly by stimulating extensors (antigravity) muscles Directed by: brainstem
What does the tectospinal pathway innervate and what is it directed by?
Innervates: coordinates head and eye movements Directed by: brainstem
The largest of the Commissural Tracts is the ___ ___.
Corpus Callosum
