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CNS > Ascending & Descending Tracts > Flashcards

Ascending & Descending Tracts Flashcards

1
Q

Nuclei

A

Clusters of neuronal cell bodies within the CNS

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2
Q

Ganglia

A

Collection of neuronal cell bodies outside the CNS e.g. dorsal root ganglia

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3
Q

Grey matter

A

Areas occupied by neuronal cell bodies

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4
Q

White matter

A

Dense collections of myelinated fibres

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5
Q

Nerves

A

Bundles of axons covered by CT sheath -> PNS

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6
Q

Tracts

Funiculus

Fasciculus

A

Bundles of axons in the CNS

e.g. ascending and descending tracts

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7
Q

How does the CNS communicate with peripheral body structures

Where do they travel

A

Through pathways

They conduct either sensory or motor info

Pathways travel through the white matter of the brainstem and/or the spinal cord as they connect various CNS regions with cranial and spinal nerves

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8
Q

Principal fibre tracts of spinal cord (composite)

A
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9
Q

How do ascending and descending tracts differ in their naming convention

A

ASCENDING - “spino…” as they’re carrying impulses from pain, tactile, thermal, muscle and joint receptors

DESCENDING - “cortico…” as they carry motor info from the cerebral cortex and brainstem

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10
Q

Precentral gyrus

A

Primary motor cortex

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11
Q

Post-central gyrus

A

Primary somatosensory cortex

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12
Q

What do the superior peduncles connect

A

The midbrain to cerebellum, allowing info to travel from spinal cord to cerebellum

SUPERIOR

MIDDLE

INFERIOR

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13
Q

What are pathways composed of

A

Paired tracts

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14
Q

How many neurons are involved in SENSORY pathways

A

3

Primary

Secondary

Tertiary

S ≈ 3

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15
Q

How many neurons are there in motor pathways

A

2

Upper motor neuron

Lower motor neuron

Located in ventral horn of grey matter (vent of car)

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16
Q

Name the main descending spinal tract

A

To distinguish posterior from anterior (spinal cord) -

H of grey matter reaches posterior aspect of SC

Anterior median sulcus

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17
Q

Where would an upper motor neuron be located

A

Cell body located either within the cerebral cortex or a nucleus within the brainstem

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18
Q

Where would a lower motor neuron usually be located

A

Within the anterior grey matter of the spinal cord or within a brainstem cranial nerve nucleus

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19
Q

Where do motor neurons usually decussate

A

At the medulla

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20
Q

What tract is responsible for the conscious control of muscle

A

The corticospinal tract/pyramidal pathway

Originates in the cerebral cortex

Axons descend through the internal capsule, enter the cerebral peduncles and form descending motor tracts

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21
Q

What do the corticospinal tracts form

A

A thick pair of anterior bulges in the medulla

  • PYRAMIDS
22
Q

DECUSSATION of corticospinal tracts

A
23
Q

Pathway of the lateral corticospinal tracts

What do these tracts control

A

Decussate within the pyramids of the medulla and then form the lateral corticospinal tracts in the lateral funciuli of the spinal cord

Axons of the lower motor neurons innervate skeletal muscles that control skilled movements in the limbs

24
Q

Pathway of the anterior corticospinal tracts

What do these tracts innervate

A

The tracts descend the spinal cord in the anterior white funiculi

Axons decussate and synapse either with interneurons or lower motor neurons in the anterior grey matter of the spinal cord

Axons of the lower motor neurons innervate axial skeletal muscle

25
Q

Decussation of CSTs

A

80% of pyramids decussate

26
Q

Areas of

  1. forebrain
  2. midbrain
  3. spinal cord

that innervate the legs, trunks, arms and face

A
27
Q

What do sensory pathways conduct information about

A

Limb position

Sensation of touch

Temperature

Pressure

Pain

28
Q

Name the 3 types of somatosensory pathways

A
  1. Posterior column - medial lemniscus pathway
  2. Spinothalamic (anterolateral pathway)
  3. Spinocerebellar pathway
29
Q

Name the 2 fasciculi of the posterior fasciculus - medial lemniscus pathway

A

Fasciculus gracilis

Fasciculus cuneatus

30
Q

Name the 2 tracts of the spinocerebellar pathway

A

Posterior spinocerebellar tract

Anterior spinocerebellar tract

31
Q

Name the 2 tracts of the anterolateral pathway

A

Lateral spinothalamic tract

Anterior spinothalamic tract

32
Q

Name the 2 tracts of the anterolateral pathway

A

Lateral spinothalamic tract

Anterior spinothalamic tract

33
Q

Name the structures the posterior column - medial lemniscus pathway passes through

A

Projects through the spinal cord, brainstem and thalamus before terminating within the cerebral cortex

34
Q

What does the posterior column - medial lemniscus pathway sense

A

Conducts sensory stimuli concerned with PROPRIOCEPTIVE info about limb position, discriminative touch, precise pressure and vibration sense

35
Q

Collective name for the sensory tracts in the spinal cord

A

The posterior funiculus

36
Q

Collective name for the tracts within the brainstem

A

Medial lemniscus

37
Q

Where can the fasciculus gracilis be found

What spinal nerves is it responsible for

A

Throughout the cord length

Responsible for sacral, lumbar and lower 6 thoracic spinal nerves

38
Q

Where can the fasciculus cuneatus be found

A

T6 and above

Also cervical cord segments

39
Q

Path of the PC-MLP

A
  • Fibres ascend ipsilaterally
  • Synapse with neurons in gracile nucleus and cuneate nucleus of medulla
  • 2nd order neurons cross the midline - sensory decussation
  • ML ascends to pons, midbrain and synapse at ventral posterolateral (VPL) nucleus of thalamus

Posterior limb internal capsule -> corona radiata -> postcentral gyrus

40
Q

Primary somatosensory cortex

A
41
Q

Where is the spinothalamic/anterolateral pathway located

Name the 2 tracts this pathway is composed of

What does the pathway sense

A

in the anterior and lateral white funiculi of the spinal cord

Anterior & lateral spinothalamic tract

Conducts stimuli related to light/crude touch and pressure (anterior) as well as pain and temp (lateral)

42
Q

What is the anterior spinothalamic tract responsible for

A

Light/crude touch and pressure

43
Q

What is the lateral spinothalamic tract responsible for

A

Pain and temperature

44
Q

Path of the spinothalamic pathway

A

Synapse with cells of posterior grey matter

Axons of secondary neurons cross over to the opposite side of the spinal cord before ascending to the brainstem

Synapse with 3rd order neuron in ventral posterolateral (VPL) nucleus

posterior limb of internal capsule -> corona radiata -> primary sensory cortex

*** THESE NEURONS CROSS OVER FIRST AND THEN ASCEND

45
Q

What sort of info does the spinocerebellar pathway conduct

A

Proprioceptive info to cerebellum (so not conscious info) for processing to co-ordinate body movement

46
Q

Name the 2 tracts that compose the spinocerebellar pathway

A

Anterior & posterior SC tracts

47
Q

Path of the spinocerebellar pathway

A
  • Axons enter the posterior grey column and synapse
  • Axons of the posterior SC tract ascend on same side to medulla
  • Inferior cerebellar peduncle transmits the axons to the cerebellar cortex - synapse at Clark’s Column
  • Majority of axons of anterior SC tract cross before ascending
  • Superior cerebellar peduncle transmits axons to cerebellum
  • Fibres cross back again
48
Q

Anterior vs posterior SC tract

A
49
Q

What could cause hemisection of segments T6-T8

A

Fracture dislocation of VC

Bullet

Stab wound

Expanding tumour

50
Q

What does syringomyelia cause

A

This developmental abnormality causes loss of pain and temperature senses

Interruption of lateral spinothalamic tracts (pain and temp)

NOTE:

Tactile sensation and proprioception - ascending tracts in posterior white columns remain unaffected - not close to region where syringomyelia is affecting the spinal cord

CNS (36 decks)

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