Neuroanatomy 2 - Tracts

Question 1

What is the origin of the corticospinal tract?

Answer 1

pyramidal neurons in the primary motor cortex (precentral gyrus), premotor cortex, and supplementary motor area of the frontal lobe

Question 2

Describe the pathway of corticospinal fibres through the brain.

Answer 2

From the cortex (precentral gyrus/primary motor cortex)
corona radiata
posterior limb of internal capsule
anterior parts of brainstem = crus cerebri of midbrain → basilar pons → pyramids of medulla

90% of fibres decussate at the medulla - form the lateral C tract
10% of fibres don’t decussate - continue as the anterior/ventral CS tract

Question 3

Where does the corticospinal tract decussate?

Answer 3

At the pyramidal decussation in the caudal medulla:

90% cross → Lateral corticospinal tract

10% remain uncrossed → Ventral corticospinal tract

Question 4

Where do corticospinal tract fibers synapse with lower motor neurons?

Answer 4

In the anterior horn (ventral horn) of the spinal cord at the target segment.

Question 5

What is the difference between the lateral and ventral corticospinal tracts?

Answer 5

Lateral: Controls limbs; decussates in medulla; located in lateral funiculus.

Ventral: Controls trunk/proximal muscles; decussates at spinal level; in anterior funiculus.

Question 6

UMN vs LMN (upper/lower motor neurons)—where do they begin and end?

Answer 6

UMN: Cortex → spinal cord (synapse in anterior horn)

LMN: Anterior horn → target muscle

Question 7

UMN lesion signs?

Answer 7

Spastic paralysis, hyperreflexia, Babinski sign, no fasciculations

Question 8

LMN lesion signs?

Answer 8

Flaccid paralysis, hyporeflexia, fasciculations, muscle atrophy.

Question 9

Which tract is responsible for voluntary motor control of limbs?
A) Rubrospinal
B) Corticospinal
C) Spinothalamic
D) DCML

Answer 9

B) Corticospinal

Question 10

Where do most corticospinal fibers decussate?
A) Midbrain
B) Pons
C) Medulla
D) Spinal cord

Answer 10

C) Medulla

Question 11

The dorsal column pathway transmits:
A) Pain and temperature
B) Pressure and vibration
C) Proprioception and fine touch
D) Motor impulses

Answer 11

C) Proprioception and fine touch

Question 12

What sensations are carried by the DCML pathway?

Answer 12

fine touch
vibration
proprioception

Question 13

DCML - receptors?

Answer 13

sensory receptors - Messner’s/ Merkel’s/ muscle spindles, golgi tendon organs

Question 14

DCML pathway - 1st, 2nd & 3rd order neurons?

Answer 14

1st = sensory neuron - dorsal root ganglion - ascends ipsilaterally via fasciculus gracilis (below T6 sensation) or cuneatus (above T6) - reach medulla & synapse in nucleus gracilis/cuneatus

2nd = nucleus gracilis/cuneatus (medulla) - decussate - ascend as medial lemniscus (brainstem) - synapse at VPL nucleus (thalamus)

3rd = from VPL nucleus (thalamus) - posterior limb of internal capsule - post-central gyrus/ primary somatosensory cortex

Question 15

clinical testing of DCML?

Answer 15

Vibration: Tuning fork (128 Hz) on bony prominences

Proprioception: Move joint → ask direction

Fine touch: 2-point discrimination

Question 16

lesion effects of DCML - spinal cord lesion, brainstem lesion?

Answer 16

SC lesion (below decussation) = Ipsilateral loss of fine touch/proprioception

Brainstem/thalamic/cortical lesion: Contralateral sensory loss (after crossing-over)

Question 17

spinothalamic tract - receptors? modalities?

Answer 17

receptors = free nerve endings; nociceptors and thermoreceptors

modalities
- lateral ST = pain & temperature
- anterior ST = crude touch & pressure

Question 18

spinothalamic tract - 1/2/3 order neurons?

Answer 18

First order - dorsal root ganglia
Second order - Substantia gelatinosa
(Dorsal grey horn)
Third order - Thalamus

Question 19

spinothalamic tract - clinical testing?

Answer 19

Pain: Pinprick
Temperature: Cold/ethyl chloride spray
Crude touch: Cotton wool

Question 20

spinothalamic tract - spinal cord & central lesions?

Answer 20

Spinal cord lesion: Contralateral pain/temp loss starting 1–2 levels below

Central cord (e.g., syringomyelia): Bilateral loss of pain/temp at affected levels (cape-like)

Question 21

corticospinal tract (pyramidal) - upper motor neurons?

Answer 21

Origin: Primary motor cortex (precentral gyrus)

Pathway:
- corona radiata → Posterior limb of internal capsule
- anterior parts of brainstem = Crus cerebri (midbrain) > basilar pons > pyramids (ventral medulla)

Decussation:
- 90% cross at pyramidal decussation → Lateral corticospinal tract
- 10% uncrossed → Ventral corticospinal tract, cross at spinal level

Question 22

corticospinal tract (pyramidal) - lower motor neurons?

Answer 22

Lower Motor Neuron (LMN):
Cell body: Anterior horn of spinal cord

Axon: Exits via ventral root → peripheral nerve → skeletal muscle

Question 23

corticospinal tract (pyramidal) - clinical testing?

Answer 23

Muscle strength, tone, reflexes
Plantar reflex (Babinski)

Question 24

corticospinal tract - lesion effects above & below decussation at medulla?

Answer 24

Above decussation (brain/capsule) → Contralateral motor weakness

Below decussation (spinal cord) → Ipsilateral weakness

Question 25

A patient has loss of proprioception and vibration on the right side of the body below T10. Where is the most likely site of the lesion? A. Left medial lemniscus B. Right dorsal column at T8 C. Right spinothalamic tract at T8 D. Left dorsal column at T12

Answer 25

B. Right dorsal column at T8 - DCML pathway ascends ipsilaterally in the spinal cord. A lesion at T8 on the right affects fibres from T10 and below.

Question 26

hich of the following structures contains the decussating fibres of the corticospinal tract? A. Posterior limb of internal capsule B. Midbrain tegmentum C. Pyramids of the medulla D. Ventral white commissure

Answer 26

C. Pyramids of the medulla - Corticospinal tract fibres cross in the pyramidal decussation at the caudal medulla

Question 27

Which of the following pathways decussates at the level of the spinal cord rather than in the brainstem? A. Dorsal column-medial lemniscus B. Corticospinal tract C. Spinothalamic tract D. Tectospinal tract

Answer 27

C. Spinothalamic tract - Spinothalamic fibres cross within 1–2 spinal segments of entry.

Question 28

A patient with a stroke in the left internal capsule would most likely have which of the following findings? A. Left-sided spastic paralysis B. Right-sided flaccid paralysis C. Right-sided spastic hemiparesis D. Bilateral proprioception loss

Answer 28

C. Right-sided spastic hemiparesis

Question 29

A lesion of the fasciculus cuneatus would most likely affect: A. Proprioception from the lower limb B. Crude touch from the upper limb C. Vibration sense from the upper limb D. Pain from the upper limb

Answer 29

C. Vibration sense from the upper limb - Fasciculus cuneatus → upper body DCML sensations (fine touch, vibration, proprioception).

Question 30

Which tract is responsible for transmitting crude touch? A. Dorsal column B. Lateral spinothalamic C. Anterior spinothalamic D. Corticospinal

Answer 30

C. Anterior spinothalamic

Question 31

A lesion in the right medial lemniscus in the pons would lead to: A. Loss of crude touch on the left B. Loss of proprioception on the right C. Loss of proprioception on the left D. Loss of pain and temperature on the right

Answer 31

C. Loss of proprioception on the left

Question 32

Which of the following signs would you expect with a lower motor neuron lesion? A. Spasticity and hyperreflexia B. Muscle wasting and fasciculations C. Positive Babinski reflex D. Clonus

Answer 32

B. Muscle wasting and fasciculations - LMN damage = flaccid paralysis, atrophy, fasciculations

Question 33

Which sensory deficit would result from a lesion of the medial lemniscus in the midbrain? A. Ipsilateral loss of proprioception and vibration B. Contralateral loss of pain and temperature C. Contralateral loss of proprioception and vibration D. Ipsilateral loss of pain and temperature

Answer 33

C. Contralateral loss of proprioception and vibration - DCML decussates in medulla → medial lemniscus carries contralateral sensations upward to thalamus.

Question 34

A patient cannot distinguish two-point touch discrimination on the left hand. Where is the most likely site of the lesion? A. Right anterior spinothalamic tract B. Left fasciculus gracilis C. Right fasciculus cuneatus D. Left lateral corticospinal tract

Answer 34

C. Right fasciculus cuneatus - Left hand = upper limb = fasciculus cuneatus. Deficit is contralateral → lesion in right cuneate

Question 35

A lesion damaging the anterior horn cells of the spinal cord would affect which neurons? A. First-order sensory neurons B. Second-order sensory neurons C. Upper motor neurons D. Lower motor neurons

Answer 35

D. Lower motor neurons - Anterior horn = LMNs → flaccid paralysis, areflexia.

Question 36

Which of the following is a classic sign of upper motor neuron lesion? A. Muscle atrophy B. Hyperreflexia C. Fasciculations D. Hypotonia

Answer 36

B. Hyperreflexia UMN lesion = spasticity, hyperreflexia, Babinski. LMN = atrophy, fasciculations.