CNS Exam 2 - Tracts and Hindbrain

Where is the cervical enlargement of the spinal cord?

Cord level C5-6

What are the boundaries of the spinal cord?

Superior:

• General - foramen magnum

• Specific - most sup. ant. rootlet of C1

Inferior:

• General - conus medullaris

• Specific - L1-2 disc level

How many spinal nerves are there?

31 pairs

SAME DAVE

Sensory Afferent, Motor Efferent

Dorsal Afferent, Ventral Efferent

Which spinal nerve does NOT have a vertebra associated with it?

C8 nerve root

Where doe the S1-Co nerve roots exit the spinal column?

S1-Co correlate with the sacral foramina

S5 and Co exit via the sacral hiatus

Where is the cauda equina?

Begins at the L1-2 vertebral level

What are the two parts of the filum terminale?

Internum: pial part, L1-2 to S1-2

Externum: dural part, S1-2 to coccyx

What is quadriplegia? What are its characteristic symptoms?

Spinal cord injury to C8 or higher

Upper and lower extremity problems

What is paraplegia? What are its characteristic symptoms?

Lower extremity problems

What are the horns of the spinal cord?

Gray matter areas present at most levels of the cord

1. Anterior/ventral (motor)

2. Posterior/dorsal (sensory)

3. Lateral (autonomic, only present at T1-L2 and S2-4)

What are the Rexed laminae?

Specific areas of the gray horns which are not distinguishable through staining

Rexed lamina 1

Most dorsal tip of posterior horn (marginal zone)

Rexed lamina 2

Posterior horn, pain and temperature information (substantia gelatinosa)

Rexed lamina 3-6

Posterior horn, sensory information (touch & pressure)

Rexed lamina 7

Lateral horn, includes:

• Nucleus dorsalis (Clarke’s) at C8-L3

• Interomediolateral nucleus (sacral paranucleus) at T1-L2 and S2-4

  • Preganglionic ANS neurons via reticulospinal tracts

Descending axons synapse here

Rexed lamina 8

Medial side of anterior horn

Rexed lamina 9

Centers of anterior and lateral horns, skeletal muscle movement, class A motor neurons (fastest and largest MNs)

Rexed lamina 10

Bridge in center of gray surrounding the central canal (which is continuous with the 4th ventricle), contains unmyelinated gray commissures

What are the 3 funiculi of the spinal cord (bilateral)?

Anterior, posterior, lateral

What is found in the gray matter?

Cell bodies, dendrites, synapses, rich blood supply, unmyelinated fibers

What is found in the white matter?

Axons, less dense blood supply, myelinated fibers (if >1 micron diameter)

Tracts schematic (UNLABELED)

Tracts schematic (LABELED)

What is characteristic of ascending tracts?

3 neurons in the pathway, “spino___”

What is characteristic of descending tracts?

2 neurons in the pathway, “___spinal”

Gracilis (tract)

• Posterior funiculus (med. aspect)

• All cord levels (serves T6 and below)

• Cell body in dorsal root ganglion

• 1st neuron synapses in nucleus gracilis in M.O.

• NO cross over in cord

• 2 point touch discrim., vibratory and kinesthetic info

A$$ to Grass (med., lower extremity)

Serves the great toe

Cuneatus (tract)

• Posterior funiculus (lat. aspect)

• Cord levels T6 and up

• Cell body in dorsal root ganglion

• 1st neuron synapses in nucleus cuneatus in M.O.

• NO cross over in cord

• 2 point touch discrim., vibratory and kinesthetic info

Cuddle with cuneatus (lat., upper extremity)

Serves the carpals

Medial lemniscus (tract)

• Cell body in nucleus gracilis/cuneatus of M.O.

• 2nd neuron of pathway, synapses to VPL of thalamus

• Crosses over in M.O.

• 2 point touch discrim., vibratory and kinesthetic info

If there is a lesion in the gracilis or cuneatus tract, where will you lose sensation for vibration, kinesthesia, and 2 point touch discrimination?

On the SAME side as the lesion, BELOW it

• Cuneatus: in the upper extremity

• Gracilis: in the lower extremity

Anterior spinothalamic (tract)

• Anterior funiculus

• All cord levels

• Cell body in rexed lamina 3-6

• 1st neuron synapses in VPL of thalamus

• Cross over gradually in cord

• Light touch and pressure info (A-LTP)

Lateral spinothalamic (tract)

• Lateral funiculus

• All cord levels

• Cell body in rexed lamina 2

• 1st neuron synapses in VPL of thalamus

• Cross over immediately in cord

• Pain and temperature info (L-PT)

If there is a lesion in the ant. or lat. spinothalamic tract, where will you lose sensation for light touch/pressure or pain/temperature?

On the OPPOSITE side as the lesion, BELOW it

Anterior spinocerebellar (tract)

• Lateral funiculus (periphery)

• All cord levels

• Cell body in lumbosacral gray horn

• 1st neuron synapses in cerebellum via the superior cerebellar peduncle (AS)

• Cross over twice (1st in cord, 2nd as entering M.O.)

• Gross lower-body anticipatory and proprioceptive movement

Posterior spinocerebellar (tract)

• Lateral funiculus (periphery)

• Cord levels L3 and up

• Cell body in multiple places

  • Above C8 - lateral cuneate nucleus via cuneocerebellar tract

  • C8-L3 - in rexed lamina 7 (Clarke’s nucleus)

  • Below L3 - in gracilis tract (to go up to Clarke’s nucleus)

• 1st neuron synapses in cerebellum via inferior cerebellar peduncle

• NO cross over

• Fine proprioceptive movement info:

  • Lower extremity = below L3

  • Upper extremity = above C8

If there is a lesion in the anterior spinocerebellar tract, where will you lose sensation for gross lower-body anticipatory proprioceptive movement?

OPPOSITE side of lesion, BELOW it

(Remember, this tract crosses twice: once in the cord, once in the M.O.)

If there is a lesion in the posterior spinocerebellar tract, where will you lose sensation for fine movement proprioception?

SAME side as the lesion, BELOW it

Anterior corticospinal (tract)

10% of info!

• Anterior funiculus

• Cord levels T6 and up

• Cell body in precentral gyrus of cerebral cortex

• 1st neuron synapses in the anterior horn (lamina 7 to lamina 9)

• Cross over in cord

• Control of axial muscles of neck and shoulder

• pyramidal aka voluntary

Lateral corticospinal (tract)

90% of info!

• Lateral funiculus (post. half)

• All cord levels

• Cell body in precentral gyrus of cerebral cortex

• 1st neuron synapses in the anterior horn (lamina 7 to lamina 9)

  • Giant Betz cells go directly to lamina 9

• Cross over in pyramids of M.O.

• Control of skilled voluntary movements of distal extremities (hands/feet)

• pyramidal aka voluntary

Tectospinal (tract)

• Anterior funiculus

• Cord level C4-5 and up

• Cell body in tectum of midbrain (superior colliculus)

• 1st neuron synapses to C.N. XI to control traps/SCM

• Crosses over

• Postural reflexes related to visual/auditory acuity (in traps/SCM)

• EXTRApyramidal aka INvoluntary

Rubrospinal (tract)

• Lateral funiculus

• All cord levels

• Cell body in tegmentum of midbrain (nucleus Ruber/red nucleus)

• 1st neuron synapses to anterior horn

• Crosses over in midbrain

• Contralateral flexors and inhibits extensors

• EXTRApyramidal aka INvoluntary

Backup to corticospinal tracts

Bros flex!

Vestibulospinal (tract)

• Anterior and lateral funiculi

• All cord levels

• Cell body in M.O. (lateral vestibular nucleus (Dieter’s))

• 1st neuron synapses to anterior horn (lamina 7 to lamina 9)

• NO cross over

• Ipsilateral extensors and inhibits flexors, proper orientation when falling

• EXTRApyramidal aka INvoluntary

Extend your arms to keep your balance!

Medial reticulospinal (tract)

• Anterior funiculus

• All cord levels

• Cell body in pons tegmentum

• 1st neuron synapses to the interomediolateral nucleus (in lamina 7)

• NO cross over

• ANS control (HR, BP, resp.), alternative to pyramidal tracts

Lateral reticulospinal (tract)

• Lateral funiculus

• All cord levels

• Cell body in M.O.

• 1st neuron synapses to the interomediolateral nucleus (in lamina 7)

• NO cross over

• ANS control (HR, BP, resp.), alternative to pyramidal tracts

Propriospinal (not a true tract, spinospinal)

• All cord levels

• Cell body and synapse in gray matter of cord

• 1st neurons to be myelinated

• Conduct the spinal reflexes

Dorsolateral tract of Lissauer (not a true tract, spinospinal)

• All cord levels

• Cell body between lamina 1 and post. sulcus of cord

• Synapse in posterior cord (lamina 2)

• Many contralateral branches

What are the characteristics of upper motor neurons (UMNs)? What happens when there are UMN lesions?

Originate in higher brain center (cortex, brainstem) and influence LMNs

Lesions lead to hyperreflexia, increased muscle tone, clonus, the sign of Babinski

Ex.: cortico___ tracts

What are the characteristics of lower motor neurons (LMNs)? What happens when there are LMN lesions?

Originate in spinal cord, innervate skeletal muscle

Lesions lead to hyporeflexia, hypotonia, atrophy, muscle fibrillations/fasciculations, lack of movement

Ex.: cranial nerves

What are the traits of pyramidal UMNs?

Cell body in cerebral cortex, initiate skilled voluntary movements, conscious control (cortico___ fibers)

What are the traits of extrapyramidal UMNs:

Cell body in brainstem, reflexes and involuntary movements, below consciousness (e.g. tectospinal)

Do EXTRA to smoothen movements!

What is multiple sclerosis?

A CNS demyelinating disease, leads to asymmetrical splotches in the white matter

What is a cord hemisection (Brown-Sequard syndrome)?

Total loss of one side of the cord, loss of function below lesion

What is Guillen-Barre syndrome?

A PNS demyelinating disease, damages one peripheral nerve

What are the parts of the rhombencephalon (midbrain)?

Metencephalon (pons, cerebellum), myelencephalon (M.O.)

What are the parts of the brain stem?

Pons, M.O., midbrain

Where is the medulla oblongata (M.O.)?

Anterior/ventral to cerebellum, inferior to pons, superior to brainstem

Inferior border is the most superior anterior rootlet of C1

What are the functions of the medulla oblongata (M.O.)?

Corticospinal fibers run through, relay via nuclei gracilis and cuneatus, location of cranial nuclei V and VII-XII

What is the decussation of the M.O.?

Where the pyramids meet and pyramidal axons cross

What is contained in the pyramids of the M.O.?

Pyramidal (voluntary) axons, from the corticospinal tracts

What are the olives of the M.O.? The inferior olivary nuclei?

Ventral structures lateral to the pyramids, overlaying the inferior olivary nuclei (internal)

Inferior olivary nuclei relay information to the cerebellum

What is the obex?

The inferior tip of the 4th ventricle, continuous with the central canal; seen at the bottom of the rhomboid fossa of the M.O.

What are the nuclei gracilis and cuneatus?

Gray structures in the M.O. which hold the cell bodies of 2nd order sensory neurons (in gracilis and cuneatus tracts), connecting to the arcuate fibers of the medial lemniscus

What are arcuate fibers?

Found in the M.O., originate in nuclei gracilis/cuneatus, cross the midline and rise through the medial lemniscus (tract) to the VPL of the thalamus

What are the fissures and sulci of the M.O.?

1. Anterior median fissure

2. Anterolateral sulcus (between pyramids and olives)

3. Medullopontine sulcus

4. Posterior median sulcus

5. Posterolateral sulcus

What is an apparent origin?

Where a cranial nerve attaches to the CNS

Where are the apparent origins of C.N. IV-VIII and XII?

IV-VI: Posterolateral sulcus of M.O.

VI-VIII: Medullopontine sulcus, moving lateral from the midline

XII: Anterolateral sulcus

What is the apparent origin of CN III?

In the midline at the superior border of the pons

What is a nucleus of origin?

Where lower motor neurons (LMNs) of cranial nerves have their cell bodies

What is a nucleus of termination?

Where 2nd order sensory neurons synapse into the CNS

What are the nuclei for CN III (oculomotor)?

Origin: Oculomotor nucleus (Oc)

Origin: Accessory oculomotor (EW) - parasympathetic

What is the nucleus for CN IV (trochlear)?

Origin: Trochlear nucleus (Tr)

What are the nuclei for CN V (trigeminal)?

Origin: Trigeminal motor nucleus (mT)

Termination: Spinal nucleus of the trigeminal nerve (spT)

Termination: Mesencephalic nucleus (mes)

Termination: Main sensory nucleus (msT)

What is the nucleus for CN VI (abducens)?

Origin: Abducens nucleus

What are the nuclei for CN VII (facial)?

Origin: Facial motor nucleus (Fa)

Origin: Superior salivary nucleus (Ss) - parasympathetic

Termination: Solitary nucleus (Sol)

Termination: Spinal trigeminal nucleus

What are the nuclei for CN VIII (vestibulocochlear)?

Termination: Vestibular nucleus (Ves)

Termination: Cochlear nucleus (C)

What are the nuclei for CN IX (glossopharyngeal)?

Origin: Nucleus ambiguus (Am)

Origin: Inferior salivary nucleus (Is) - parasympathetic

Termination: Solitary nucleus (Sol)

Termination: Spinal nucleus of the trigeminal

What are the nuclei for CN X (vagus)?

Origin: Dorsal nucleus of vagus (dV) - parasympathetic

Origin: Nucleus ambiguus (Am)

Termination: Solitary nucleus (Sol)

Termination: Spinal nucleus of the trigeminal

What is the nucleus for CN XI (spinal accessory)?

Origin: Spinal nucleus of accessory nerve (Ac)

What is the nucleus for CN XII (hypoglossal)?

Origin: Hypoglossal nucleus (Hy)

Oculomotor nucleus

Origin, CN III, serves ciliary and sphincter pupae muscles

Accessory oculomotor nucleus (Edinger-Westphal’s)

Where cell bodies of preganglionic parasympathetic nerves live, which synapse in the ciliary ganglion

Trochlear nucleus

Origin, CN IV, serves the superior oblique

Trigeminal motor nucleus

Origin, CN V, serves muscles of mastication

Spinal nucleus of trigeminal nerve

CN V, VII, IX, X, nucleus of termination for pain & temperature, extends into cervical cord (part of spinotrigeminal pathway)

Solitary nucleus

CN VII, IX, X, nucleus of termination for taste

Nucleus ambiguus

CN IX and X, nucleus of origin

Which CNs have parasympathetic functions?

(Nuclei have preganglionic parasympathetic fibers)

III - Oculomotor

VII - Facial

IX - Glossopharyngeal

X - Vagus

Which CNs are involved in eye musculature?

III - Oculomotor

IV - Trochlear

VI - Abducens

Spinotrigeminal (tract)

1st order cell body = CN V ganglion (spinal nucleus of trigeminal)

2nd order = from spinal nucleus to VPM of thalamus

3rd order = from VPM to post. central gyrus of cerebrum

What happens in a lateral medullary stroke?

Affects the posterior inferior cerebellar artery

Lose pain & temperature sensation on:

• Same side of face (spinal nucleus of V)

• Opposite side of body (spinothalamic tract)

What are corticobulbar fibers?

UMNs from the cerebral cortex to the M.O., pyramidal (cell body in cortex)

What is the relative location of the pons?

Part of the brainstem; ventral to cerebellum, inferior to midbrain, superior to M.O.

What are the functions of the pons?

Fiber conduction (spinothalamic, corticospinal), home of CN nuclei V-VIII, relay information to cerebellum

Pontine reticular formation: med. reticulospinal tract

What are the external features of the pons?

Anterior bulge (where the basilar artery lies on the ventral surface)

Superior part of rhomboid fossa (4th ventricle)

Middle cerebellar peduncle (pons → cerebellum)

What are the internal structures of the basilar/anterior division of the pons?

Corticospinal fibers (descending pyramidal axons)

Medial lemniscus (post., somatic sensory)

Pontine nuclei (take info from cortex and send to cerebellum via middle cerebellar peduncle)

What are the internal structures of the tegmentum of the pons?

CN nuclei V-VIII (pons = 4 letters = 4 nuclei)

Other extrapyramidal tracts:

• Spinothalamic

• Ant. spinocerebellar

• Tectospinal, rubrospinal

• Lateral lemniscus (auditory, most ant. in tegmentum)

What are the 3 pairs of cerebellar peduncles? How do they move information?

Superior: midbrain to cerebellum

• Mostly efferent (from cerebellum), some afferent (to cerebellum)

Middle: pons to cerebellum

• ONLY afferent

Inferior: M.O. to cerebellum

• Mostly afferent, some efferent

SAME DAVE

What are the functions of the cerebellum?

Integrate sensory input, output influences motor neurons

How does the ipsilateral orientation of the cerebellum dictate how it influences the tracts?

Red nucleus (of Ruber): crosses, so R cerebellum affects L nucleus

Lateral vestibular nucleus: NO cross, so R cerebellum affects R nucleus

Cerebral cortex: crosses, so R cerebellum influences L cerebral cortex

What are the 3 lobes of the cerebellum? What is between them?

Anterior and posterior lobes (separated by primary fissure; post. is largest), flocculonodular lobe

Separated by the vermis