Ivana Pavlinac Dodig, M.D., Ph.D. 1. Organization of the CNS 2. 3. Pathways of the spinal cord 1. Long ascending tracts 2. Long descending tracts 4. Spinal cord in cross sections

2 = Cell Body

White Matter = Myelinated axon

3 „ Cortex „ Nucleus (CNS) „ Ganglion (PNS); exception: Basal Ganglia

4 ƒ Nerve (PNS) ƒ Tract (CNS) ƒ Fasciculus/Funiculus = group of fibers with common origin and destination ƒ Lemniscus = ribbon‐like fiber tract ƒ Peduncle = massive group of fibers (usually several tracts)

5 „ Tracts are named with origin first, then destination ¾Corticobulbar tract ¾Corticospinal tract ¾ ¾Mammilothalamic tract

6 Pars cervicalis „ Spinal cord is SMALL! „ 40‐45 cm long Pars thoracica „ 1 cm wide at widest point „ Does not extend all the way to the bottom of the spinal column „ From foramen magnum to intervertebral disc (L1‐L2); Pars lumbalis continues as (to sacral canal)

Conus medullaris ƒ Upper 2/3 of the & filum terminale vertebral column

7 „ Pattern of grey/ is reversed in the cord „ White matter tracts on outside „ Grey matter on the inside „ Staining reverses this!!!

White matter (tracts of axons)

Grey matter (cell bodies)

8 White matter ‐ funiculi: ƒ Dorsal (posterior) ƒ Lateral ƒ Ventral (anterior)

Gray matter –buterfly shaped –horns: ƒ Anterior ƒ Posterior ƒ Intermediolateral cell column (IML)

9 „ Posterior (dorsal) horn „ Intermediate grey „ Anterior (ventral) horn

„ Laminar organisation „

10 „ Spinal cord is segmented anatomically „ Input and output occurs in groups of rootlets arranged in a series longitudinally along the cord „ Dorsal rootlets =Input (carry sensory information) „ Ventral rootlets =Output (motor neurons)

11 Dorsal and ventral roots

Common spinal nerve trunk (1‐2 mm)

Dorsal and ventral ramus

12 13 ƒ 31 pair of spinal nerves ƒ 8 cervical (C1 ‐ C8) ƒ 12 Thoracic (T1 ‐ T12) ƒ 5 Lumbar (L1 ‐ L5) ƒ 5 Sacral (S1 ‐ S5) ƒ 1 Coccygeal

14 „ The spinal cord is housed within the vertebral column „ Each cord segment has a corresponding vertebra of the same name (e.g., C3) „ Spinal nerves enter/exit underneath their corresponding vertebral segment

15 „ But wait! Something doesn’t add up! „How can spinal nerves exit below their corresponding vertebral segment if the cord is only 40cm‐45cm long? „Answer: Spinal nerves extend down to the appropriate vertebral segment forming the „ This means cord segments and vertebral segments don’t line up

16 Each set of rootlets forms a spinal nerve that innervates a corresponding segment of the body

Area of the skin supplied by the right and left dorsal roots of a single spinal segment.

Overlapping areas!

17 „ Cord is not of uniform thickness throughout its length. Why not?

„ Answer: „Segments of the cord innervate parts of the body that differ in complexity „There are fewer white matter tracts lower in the cord.

18 2 enlargements: ▪ Cervical (C5‐T1) C5 - T1 ▪ Lumbar (L1‐S2)

o C1‐C4 = plexus cervicalis o C5‐T1 = plexus brachialis o L1‐L4 = plexus lumbalis Lumbar enlargement L1 – S2 o L4‐S2 = plexus sacralis

19 ƒ Association ƒ Projection ƒ Commissural

20 ƒ Exteroceptive (from surface): touch, vibration, pain, temperature, localization ƒ Proprioceptive (deep, protopathic): locomotor system (periost, tendon and muscle spindles, joints); mostly nonconscious! ƒ Interoceptive: from visceral system; mostly nonconscious! Base for proper function of the autonomic reflexes, homeostasis, neuroendocrine system

21 ƒ Tractus spinothalamicus

ƒ Tractus spinocerebelaris

ƒ Fasciculus gracilis and cuneatus

22 1. Direct pathway (pain, temperature, simple tactile sensations) ▪ Neospinothalamic tract

2. Indirect pathways (affective, autonomic, endocrine, motor, and arousal components of pain, and simple tactile sensations) ▪ Paleospinothalamic ▪ Spinoreticular ▪ Spinomesencephalic tracts

23 Neuron I Neuron II

Receptors in Dorsal root Dorsal horn (nucleus Dorsal root skin ganglion proprius)

Anterior white commissure

Ventral Postcentral Lateral white Capsula interna posterolateral gyrus (area 3,1,2) column nucleus of thalamus

Neuron III Tractus neospinothalamicus 24 ƒ Neurons located in the dorsal horn and intermediate gray matter ƒ Ascend contralaterally and ipsilaterally ƒ Synapses in ƒ Project in midline and intralaminar thalamic nuclei – diffuse projections to the cortex and limbic regions (cingulate gyrus)

25 ƒ Neurons located in the dorsal horn and intermediate gray matter ƒ Ascend contralaterally and ipsilaterally ƒ Synapses in medullary and pontine reticular formation ƒ Project in midline and intralaminar thalamic nuclei – diffuse projections to the cerebral cortex

26 ƒ Neurons located in the dorsal horn and intermediate gray matter ƒ Ascend to the midbrain (PAG) ƒ Descending projections to the spinal cord to inhibit pain sensations ƒ Transmission to the amygdala via parabrachial nuclei?

27 Neospinothalamic tract

28 ƒ Neospinothalamic tract – anesthesia, thermoanesthesia, loss of simple tactile sensations

ƒ Neospinothalamic tract – somatotopic organization

ƒ Sacral sparing – damage to the neospinothalamic tract leaves intact the pain, temperature, and simple tactile sensations in sacral dermatomes (lesion in the gray matter first affects thoracic and cervical fibers due to somatotopic organization of neospinothalamic tract)

29 ƒ Tactile sense: vibration, deep touch, two‐ point discrimination ƒ Kinesthetic sense: position and movement

ƒ Sacral and lumbar part = medial fasciculus gracilis (Goll’s fascicle)

ƒ Toracal and cervical part = lateral fasciculus cuneatus (Burdach’s fascicle)

30 Neuron I Neuron II

Receptors in Dorsal root dermis; Dorsal root Dorsal horn ganglion proprioceptors

Ventral posterolateral Medial Nucl. gracilis Ipsilateral nucleus of thalamus lemniscus and cuneatus dorsal columns

Postcentral Capsula gyrus (area Neuron III interna Fasciculus 3,1,2) gracilis and cuneatus

31 Dorsal (posterior) columns

32 ƒ Tractus spinocerebellaris anterior – information about whole limb movement and postural adjustments (lower limb) ƒ Tractus spinocerebellaris rostralis – upper limb ƒ Tractus spinocerebellaris posterior – status of individual muscles and groups of muscles + tractus cuneocerebellaris

ƒ All enter cerebellum ipsilaterally!!!

33 Neuron I Neuron II

Receptors in Dorsal root Dorsal root Dorsal horn tendons ganglion

Cerebellum Superior cerebellar Lateral (anterior lobe) peduncle funiculus

Tractus spinocerebellaris anterior

34 Neuron I Neuron II

Receptors in Dorsal root Dorsal root Dorsal horn tendons ganglion

Cerebellum Inferior cerebellar Lateral (anterior lobe) peduncle funiculus

Tractus spinocerebellaris rostralis

35 Neuron I Neuron II

Receptors in Dorsal horn Dorsal root joints, tendons Dorsal root (nucl. dorsalis of ganglion and muscles Clarke)

Cerebellum Inferior cerebellar peduncle Lateral (anterior lobe) (restiform body) funiculus

Tractus spinocerebellaris posterior

36 ƒ Nonconscious proprioception of upper limb

ƒ Rostral to C8 (no nucl. dors. of Clarke)

ƒ Ipsilaterally in the fasciculus cuneatus

ƒ Neuron II = accessory cuneate nucleus

37 Tractus Tractus Fasciculus gracilis et neospinothalamicus spinocerebelaris cuneatus Neuron I Dorsal root ganglion

Dorsal horn Dorsal horn Nucl. gracilis et Neuron II (nucl. dorsalis (nucleus proprius) cuneatus Clarke)

Neuron III thalamus thalamus

Nonconscious Discriminative touch Function Pain and temperature proprioception and kinesthesia

38 ƒ Corticospinal tract Flexor motor system, fine ƒ movements of the limbs

ƒ Antigravity muscles, ƒ posture, and balance ƒ Reticulospinal tract

39 ƒ Homunculus – precentral gyrus ƒ Primary motor cortex

40 Precentral gyrus Corona Capsula Crus (area 4) radiata interna cerebri

Neuron I Pyramids (upper motoneuron) Tractus Tractus corticospinalis corticospinalis lateralis (90%) anterior (10%) Anterior horn* Neuron II (lower motoneuron) Ventral root

Spinal nerve 41 ƒ 90% fibers cross at pyramidal decussation → lateral funicle (tractus corticospinalis lateralis) → apendicular muscles

ƒ 10% fibers descend ipsilaterally (tractus corticospinalis anterior) and cross at lower motoneuron → axial muscles

42 Lower motor neuron paralysis: Upper motor neuron paralysis: •loss of voluntary movement, •loss of voluntary movement, •flaccid paralysis, •spasticity, •loss of muscle tone, •increased deep tendon reflexes, •atrophy of muscles, •loss of superficial reflexes, •loss of all reflexes •Babinski sign

43 ƒ monoplegia ƒ hemiplegia ƒ diplegia ƒ paraplegia ƒ quadriplegia (tetraplegia)

44 Tractus corticospinalis

Neuron I Precentral gyrus (area 4) (upper motoneuron)

Neuron II Spinal cord: anterior horn (lower motoneuron)

*Plexus brachialis: C5-Th1 Plexus lumbosacralis: L1-S5

45 46 ƒ Motor response to afferent stimulation ƒ Automatic reactions – fast response to pain and noxious stimuli

ƒ Reflex arc –spinal segment: ƒ Aferent neuron ƒ = Renshaw’s cell ƒ Eferent neuron ƒ Efector (muscle)

47 ƒ Tractus rubrospinalis ƒ Tractus tectospinalis ƒ Tractus vestibulospinalis (medialis and lateralis) ƒ Tractus reticulospinalis ƒ Fasciculus longitudinalis medialis

ƒ Fasciculi proprii – intrinsic reflex mechanisms of the spinal cord

48 Sensorimotor Nucleus cortex ruber

Ventral tegmental decussation

Inferior olive

Ventral horn

• Facilitation of flexor motor neurons • Inhibition of extensor motor neurons

49 Colliculus Upper cervical superior segments

• Aid in directing head movements in response to auditory and visual stimuli

50 Cerebellum - Nucl. vestibularis Motor Extensor Interneurons lateralis neurons muscles + Vestibular apparatus

• Facilitation of ipsilateral extensor muscles • Maintaining upright posture and balance

51 Nucl. vestibularis Ventral horn medialis

• Adjustment of head position in response to changes in posture (i.e. while walking)

52 ƒ Motor functions ƒ Medullary (lateral) reticulospinal tract – supresses extensor spinal reflexes ƒ Pontine (medial) reticulospinal tract – facilitates extensor spinal reflexes ƒ Autonomic functions (ventrolateral medulla – IML of thoracolumbar cord) ƒ Modulation of pain (enkephalinergic) ƒ Midbrain PAG → nucl. raphe magnus → dorsal horn interneurons → spinothalamic system

53 Reticular formation

Nucl. vestibularis Ipsilateral upper cervical MLF - medialis motor neurons

Colliculus superior

• Mainly ascending fibers!!! • Head position control in response to excitation by the labyrinth

54 55 Posterior intermediate sulcus

Posterior median sulcus

Tract of Lissauer

Anterior white commisure

Anterior median fissure

56 „ Segments of the spinal cord have a similar organization, but vary in appearance. „ Always know where you are in the cord (i.e., cervical, thoracic, lumbar, sacral)

57 „ Cervical cord is wide, flat, almost oval in appearance.

58 „ What’s different about the cervical enlargement?

Cervical

Cervical Enlargement

59 „ Less white matter than cervical „ Rounder appearance „ Less prominent ventral horns than cervical enlargement

60 „ Less white matter than Lumbar thoracic „ Rounder appearance „ Larger ventral horns, especially in lumbar enlargement

Lumbar Enlargement

61 „ Not much white matter „ Mostly grey, although not much of that either

62 ƒ IML = T1‐L2 ƒ Clarke’s nucleus = C8‐L3 ƒ Fasciculus cuneatus = above T6

63 „ Corticospinal tract „ Voluntary movement

„ Dorsal columns „ Discriminative touch „ Conscious proprioception

„ Spinocerebellar tract (dorsal and ventral) „ Unconscious proprioception Corticospinal tracts Dorsal Columns „ „ Pain/temperature Spinothalamic tracts Spinocerebellar tracts

64 65