Ascending & Descending Tracts

Question 1

Nuclei

Answer 1

Clusters of neuronal cell bodies within the CNS

Question 2

Ganglia

Answer 2

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

Question 3

Grey matter

Answer 3

Areas occupied by neuronal cell bodies

Question 4

White matter

Answer 4

Dense collections of myelinated fibres

Question 5

Nerves

Answer 5

Bundles of axons covered by CT sheath -> PNS

Question 6

Tracts

Funiculus

Fasciculus

Answer 6

Bundles of axons in the CNS

e.g. ascending and descending tracts

Question 7

How does the CNS communicate with peripheral body structures

Where do they travel

Answer 7

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

Question 8

Principal fibre tracts of spinal cord (composite)

Answer 8

Question 9

How do ascending and descending tracts differ in their naming convention

Answer 9

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

Question 10

Precentral gyrus

Answer 10

Primary motor cortex

Question 11

Post-central gyrus

Answer 11

Primary somatosensory cortex

Question 12

What do the superior peduncles connect

Answer 12

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

SUPERIOR

MIDDLE

INFERIOR

Question 13

What are pathways composed of

Answer 13

Paired tracts

Question 14

How many neurons are involved in SENSORY pathways

Answer 14

3

Primary

Secondary

Tertiary

S ≈ 3

Question 15

How many neurons are there in motor pathways

Answer 15

2

Upper motor neuron

Lower motor neuron

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

Question 16

Name the main descending spinal tract

Answer 16

To distinguish posterior from anterior (spinal cord) -

H of grey matter reaches posterior aspect of SC

Anterior median sulcus

Question 17

Where would an upper motor neuron be located

Answer 17

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

Question 18

Where would a lower motor neuron usually be located

Answer 18

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

Question 19

Where do motor neurons usually decussate

Answer 19

At the medulla

Question 20

What tract is responsible for the conscious control of muscle

Answer 20

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

Question 21

What do the corticospinal tracts form

Answer 21

A thick pair of anterior bulges in the medulla

• PYRAMIDS

Question 22

DECUSSATION of corticospinal tracts

Answer 22

Question 23

Pathway of the lateral corticospinal tracts

What do these tracts control

Answer 23

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

Question 24

Pathway of the anterior corticospinal tracts

What do these tracts innervate

Answer 24

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

Question 25

Decussation of CSTs

Answer 25

80% of pyramids decussate

Question 26

Areas of 1. forebrain 2. midbrain 3. spinal cord that innervate the legs, trunks, arms and face

Answer 26

Question 27

What do sensory pathways conduct information about

Answer 27

Limb position Sensation of touch Temperature Pressure Pain

Question 28

Name the 3 types of somatosensory pathways

Answer 28

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

Question 29

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

Answer 29

Fasciculus gracilis Fasciculus cuneatus

Question 30

Name the 2 tracts of the spinocerebellar pathway

Answer 30

Posterior spinocerebellar tract Anterior spinocerebellar tract

Question 31

Name the 2 tracts of the anterolateral pathway

Answer 31

Lateral spinothalamic tract Anterior spinothalamic tract

Question 32

Name the 2 tracts of the anterolateral pathway

Answer 32

Lateral spinothalamic tract Anterior spinothalamic tract

Question 33

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

Answer 33

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

Question 34

What does the posterior column - medial lemniscus pathway sense

Answer 34

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

Question 35

Collective name for the sensory tracts in the spinal cord

Answer 35

The posterior funiculus

Question 36

Collective name for the tracts within the brainstem

Answer 36

Medial lemniscus

Question 37

Where can the fasciculus gracilis be found What spinal nerves is it responsible for

Answer 37

Throughout the cord length Responsible for sacral, lumbar and lower 6 thoracic spinal nerves

Question 38

Where can the fasciculus cuneatus be found

Answer 38

T6 and above Also cervical cord segments

Question 39

Path of the PC-MLP

Answer 39

* 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

Question 40

Primary somatosensory cortex

Answer 40

Question 41

Where is the spinothalamic/anterolateral pathway located Name the 2 tracts this pathway is composed of What does the pathway sense

Answer 41

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)

Question 42

What is the anterior spinothalamic tract responsible for

Answer 42

Light/crude touch and pressure

Question 43

What is the lateral spinothalamic tract responsible for

Answer 43

Pain and temperature

Question 44

Path of the spinothalamic pathway

Answer 44

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**

Question 45

What sort of info does the spinocerebellar pathway conduct

Answer 45

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

Question 46

Name the 2 tracts that compose the spinocerebellar pathway

Answer 46

Anterior & posterior SC tracts

Question 47

Path of the spinocerebellar pathway

Answer 47

* 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

Question 48

Anterior vs posterior SC tract

Answer 48

Question 49

What could cause hemisection of segments T6-T8

Answer 49

Fracture dislocation of VC Bullet Stab wound Expanding tumour

Question 50

What does syringomyelia cause

Answer 50

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