Corticospinal tract (Pyramidal tract)

here i am to explain the Anatomy and physiology of part of the Pyramidal tract, that is the corticospinal tract. I also added the clinical significance of corticospinal tract. The course of the corticospinal tract are well explained.

1. CORTICO SPINAL TRACT AJITH C STUDENT OF DEPARTMENT OF PHYSICAL MEDICINE AND REHABILITATION COIMBATORE

2. Tractus corticospinalis (or) Fasciculus cerebrospinalis LATIN:

3. Introduction about descending tracts Introduction about pyramidal tract Introduction about Corticospinal tract Fibres of the Corticospinal tract Origin of the Corticospinal tract Course of the Corticospinal tract Lateral Corticospinal tract Anterior Corticospinal tract Functions of the Corticospinal tract Clinical significance (or) Applied Anatomy of the Corticospinal tract References.

4. INTRODUCTION ABOUT DESCENDING TRACT : Descending pathway are considered with, SOMATIC & VISCERAL Motor activities.

5. Somatic motor pathway of brain and spinal cord are divided into two types. These tracts are functionally different. Clinically these tracts are considered together because lesions within the cortex always almost involve both of them. Pyramidal tract Extra pyramidal tract

6. Both these system control the motor activities of body through lower motor neurons (LMN). Have their cells of origin in the cerebral cortex (or) in the brainstem. It is otherwise called as motor pathway.

7. INTRODUCTION ABOUT PYRAMIDAL TRACT: Conventionally, the term pyramidal tract refers specifically to a group of corticospinal fibres ( corticospinal tract) which occupies the pyramid of the Medulla Oblengata , however clinically. or (the pyramidal tracts derive their name from the medullary pyramids of the medulla oblengata , which they pass through). This is the longest tract starting from the motor cortex and reaching up to the last segment of the spinal cord & carry motor impulses from cortex to the spinal cord. This is the main Voluntary motor pathway. 80% - 90% of the fibres in the pyramidal system are small diameter is 1µm diameter.

8. It consists of two neurons, the upper and lower motor neurons. Previously mentioned that the pyramidal tract are control the motor activities of body through Lower motor neuron (LMN). It is present in the higher animals and man where cerebrum has developed. All the pyramidal fibres, 55% end in the Cervical 20% in the Thoracic 25% in the Lumbosacral Region

9. Pyramidal tract are considered with, Corticospinal tract Corticonuclear tract Corticospinal tracts - Supplies the musculature of the axial & Extremity. Corticobulbar tracts - Supplies the musculature of the head & neck.

10. Upper motor neurons arise in the cerebral cortex Descend to Brainstem & relay in the Motor nuclei of the cranial nerves ( Corticonuclear tract) Anterior horn cells of the spinal cord ( Corticospinal tract) Pass through cranial and spinal nerves to supply the skeletal muscles.

11. Corticonuclear fibres otherwise called as Corticobulbar tract . That Motor Cranial Nuclei (Particularly 4, 7, 12) This is a pathway that begins in the cerebral cortex and ends in the brain stem. Bulbar means pertaining to the brainstem where all motor cranial nuclei are located. Throughout the brainstem, the corticobulbar fibres are crossing to reach the motor cranial nuclei of the opposite side INTRODUCTION ABOUT CORTICOBULBAR TRACT:

12. CORTICOSPINAL TRACT

13. The corticospinal tract are not the sole pathway for serving voluntary movement. Rather, they form the pathway that confers speed and agility to voluntary movements and is thus used in performing rapid skilled movements. Many of the simple, basic voluntary movements are mediated by other descending tracts. The corticospinal tract are the pathway concerned with voluntary, discrete, skilled movements, especially those of the distal part of the limbs. Corticospinal tract has approximately 1 Million nerve fibres with an avarage conduction velocity of approximately 60m/s using glutamate as their transmitter substance.

14. GROWTH OF CORTICOSPINAL TRACT IN FETUS: 1 st corticospinal axons, less than 0.5 microns in diameter. MYELINATION:- The myelination of the pyramidal fibres is incomplete at birth & gradually progresses in Cranio -caudal (from head to feet) direction and thereby progressively gaining functionality. Most of the myelination complete by 2 years of the age (that’s why under 2 years baby have babinski sign negative). Myelination commences between postnatal days 10-12. Myelinate largerly during the 1 st & 2 nd years after birth. It progressively slowly in Carnio -caudal direction upto 12the year of the age. The rate of extension of corticospinal axons are not constant.

15. On the day after birth, labelled corticospinal axons have crossed in the pyramidal decussating and extended into the dorsal column of the upper cervical spinal cord level. Postnatal day-3 Corticospinal tract reach the thoracic segments Postnatal day-6 It reach Lumbar segments Postnatal day-9 It reach the sacral segments

16. FIBERS OF THE CORTICOSPINAL TRACT: Are usually 90% between 1 – 4 micro in diameter. Are usually 67% myelinated . With diameters greater than 20 micra , represent 4% of the tract’s population. These are the axons of the Giant cells of Betz (these Betz cells are found in the precentral gyrus and in the anterior paracentral lobule). Betz cells  are pyramidal  cell  neurons located within the 5 th layer of the primary motor cortex. They are some of the largest in the central nervous system, sometimes reaching 100 µm in diameter and send their axons down the corticospinal tracts to the anterior horn  cells  of the spinal cord.  They are named after Ukrainian scientist Vladimir  Betz , who described them in his work published in 1874. (Functions of the Betz cells are see further more in the functions of the corticospinal tract)*.

17. The Archicortex consists of the hippocampus, which is a three-layered cortex. The Neocortex represents the great majority of the cerebral cortex. It has six layers  and contains between 10 and 14 billion neurons. TYPES OF CORTEX: Archicortex Paleocortex Neocortex

18. INTRODUCTION ABOUT CORTICOSPINAL TRACT: Corticospinal tract are considered with, Lateral Corticospinal tract Anterior Corticospinal tract Physiologically, the anterior pathways are old, whereas the lateral pathways are new.

19. ORIGIN OF CORTICOSPINAL TRACT: Fibres of the corticospinal tract arise as axons of pyramidal cells situated in the 5 th layer of the cerebral cortex. 1/3 rd of the fibres originate primary motor cortex (Area 4). 1/3 rd originate from the Secondary motor cortex (Area 6). 1/3 rd originate from the These fibres do not control motor activity but influence sensory input to the nervous system. Primary Somato sensory cortex ( postcentral gyrus ) (Area 3, 1 and 2).

20. PRIMARY SOMATOSENSORY CORTEX (Post central gyrus ) PRIMARY MOTOR CORTEX ( Precentral gyrus )

21. SUPPLEMENTAL MOTOR AREA PRE MOTOR AREA PRE FRONTAL CORTEX SECONDARY MOTOR CORTEX

22. Electrical stimulation of different part of the precentral gyrus produces movements of different parts of the opposite side of the body, we can represent the parts of the body in the areas of the cortex, Such a Homunculus. Note that the region controlling the face is situated inferiorly and the region controlling the lower limb is situated superiorly and on the medial surface of the hemisphere. The Homunculus is a distorted picture of the body, with the various parts having a size proportional to the area of the cerebral cortex devoted to their control. It is intresting to find that the majority of the corticospinal fibres are myelinated and are relatively slow-conducting small fibres.

23. COURSE OF THE CORTICOSPINAL TRACT: These descending fibres converge in the Corona radiata to reach Internal capsule. (Located between the Thalamus and the basal ganglia) IN THE INTERNAL CAPSULE: then pass through the posterior limb of the Internal capsule. Where they occupy in the genu and the anterior 2/3 rd of the posterior limb.

24. INTERNAL CAPSULE INTERNAL CAPSULE

25. The motor fibres passes through the posterior limb of the internal capsule where they are organized in the sequence of “fibres of UPPER EXTREMITY, TRUNK, LOWER EXTREMITY”. This is clinically important, as the internal capsule is particularly susceptible to compression from haemorrhagic bleeds , known as a ‘ capsular stroke ‘.  Such an event could cause a lesion of the descending tracts.

26. CAUDATE NUCLEUS PUTAMEN

27. THALAMUS GLOBUS PALLIDUS

28. IN THE MIDBRAIN: The tract then continues through the middle 3/5 th of the ( Crus cerebri of Cerebral peduncle) or basis pedunculi of the midbrain ventral to the substantia nigra . The middle fifth carries the pyramidal tract and medial frontopontine and lateral temporopontine fibres.

29. IN THE PONS: And then passes through the base (Basilar part) of the pons . In the pons the corticospinal tracts are become scattered.

30. Great Motor Decussation IN MEDULLA OBLONGATA : While coming out of the pons , the scattered corticospinal fibres are reunited and enter the medulla as a thick bundle. The bundles are become grouped together in the upper part of medulla & along the anterior border to form a swelling known as the pyramid or Medulla Oblongatary Pyramids ( Cervicomedullary Junction) (hence the alternative name pyramidal tract).

31. Pyramid of the Medulla Oblangata Olivary Nuclei

32. Olivary Nuclei Pyramid of the Medulla Oblangata

33. The majority of the fibres cross (Decussate) to the opposite side & enter the lateral white column as the Lateral Corticospinal Tract of spinal cord . The remaining fibres about do not cross in the decussation & enter the anterior white column as Anterior corticospinal tract of spinal cord.

34. LATERAL CORTICOSPINAL TRACT

35. In the lower part of medulla(junction between the medulla oblongata and the spinal cord) the majority of the fibres (75-90%) cross to the opposite side & descend in the spinal cord occupying the posterior part of lateral white column as the Lateral Corticospinal Tract of spinal cord . It extend throughout the spinal cord. At each segment some fibres leave the tract, turn inward and end round the anterior grey horn cells (Motor neurons) either directly or through interneuron's. They are also called as “ CROSSED CORTICOSPINAL TRACT” .

36. The Lateral Corticospinal Tract (Betz cells fibres) descend in the Lateral funiculus of the spinal cord to terminate mainly in the lumbosacral region of the spinal cord.

37. TERMINATION OF THE LATERAL CORTICOSPINAL TRACT: It terminates via Interneurons on ventral horn motor neurons and sensory neurons of the dorsal horn till the lumbosacral region of the spinal cord.

38. ANTERIOR CORTICOSPINAL TRACT

39. The remaining fibres about (10-25%) do not cross in the decussation & enter the anterior white column near the median fissure and descend down as Anterior corticospinal tract of spinal cord. They are also called as “ UNCROSSED CORTICOSPINAL TRACT”. As a rule, the direct pyramidal tract does not crossed beyond the Lower cervical (or) Mid thoracic region.

40. The Anterior Corticospinal Tract descend in the Anterior funiculus of the spinal cord to terminate mainly in the anterior horn grey matter of the cervical and upper thoracic spinal cord levels.

41. Near their termination, fibres of the anterior corticospinal tract cross the midline (decussate to the opposite side) to end round the anterior horn cells of the opposite side & instead synapse directly with lower motorneurons .

42. FUNCTIONS OF THE CORTICOSPINAL TRACT:

43. Thought of the Movement in Prefrontal cortex (Example: Flexion of Biceps) ORIGIN: (BETZ cells) ~Primary motor cortex - pre motor cortex ~Secondary motor cortex - Supplemental Area ~Primary Somatosensory cortex Basal Ganglia (Blue print of the movement) Special checking mechanism: ~Low/high/perfect intensity of the movement Cerebellum This is the planned motor movements What type of movement can be perform? Muscle Receptors ( Proprioception ) Pontine nuclei (Conveying the information ) Spinal cord 1 2 3 4 5 5 5 6 6

44. ~Primary motor cortex -pre motor cortex ~Secondary motor cortex -pre frontal cortex -Supplemental Area ~Primary Somatosensory cortex Internal Capsule (Special white matter) Corona radiata Crus Cerebri of the Cerebro peduncle Pontine Nuclei Fibres are scattered (leg/arm/trunk) Continue

45. Scattered fibres are reunited Lower part of meduul oblengata (Pyramidal decussation ) Lateral Corticospinal tract Anterior Corticospinal tract Continue Lateral Funiculus Anterior Funiculus Synapse with the same side cell bodies of Ventral or Anterior grey horn Synapse (via Anterior commusure ) with the opposite side cell bodies of Venral or Anterior grey horn Alpha motor neuron Gamma motor neuron Stimulate Extrafeusal fibres (Maintain the contractions) Stimulate the Muscle Spindles (Maintain the length and Tone)

46. The corticospinal tract has many functions which include the, Control of afferent inputs:– (These fibres that originate from the sensory cortex ( somatosensory cortex) terminate in the dorsal horn of the spinal cord where they synapse with interneurns that receive input from somatosensory receptors and are thought to regulate information pheripheral receptors within the spinal cord). Spinal reflexes:– (the 1 st order afferent sensory fibres transmitting sensory information from the muscle spindles also from synapses with the inhibitory interneurons (that synapse with the Lateral corticospinal tract) to mediate reflex activity. Motor neuron activity.

47. MOTOR NEURON ACTIVITY ANTERIOR CORTICOSPINAL TRACT This mediates the execution of rapid, skilled , voluntary and Fine movements of the distal musculature of upper and lower limbs. i.e., The intrinsic and extrinsic muscles of the hand and foot, especially the muscles of the hand. LATERAL CORTICOSPINAL TRACT Control of Axial muscles (Neck, Shoulder, and Trunk) proximal upper limb (girdle) musculature. And they are associated with the maintenance of upright posture.

48. Betz cells are capable of faster nerve impulse transmission to the spinal cord. The rapid conduction rate is 70m/sec. Betz cells Synapse only in the lumbosacral levels of the spinal cord Synapse directly with the lower motor neuron That innervates the musculature of lower limbs, (these monosynapstic connections of betz cells with the Lower motor neuron innervating the muscles of the lower limbs are actually fewer in number than the monosynapstic connections To lower motorneurons innervating the hand).

49. CLINICAL SIGNIFICANSE:

50. INTRODUCTION: 1) The resulting deficiencies associated with lesions to the respective tracts will depend on the location of the lesions. A lesion proximal to the decussation of the pathway will result in a contralateral defect. In contrast, a lesion distal to the decussation will result in ipsilateral signs and symptoms. Injury to the corticospinal tract caudal to the decussation may present with varying types of paresis or paralysis of the upper and lower limbs. Unilateral lesions present with ipsilateral hemiparesis , hemiplegia or Monoplegia . While bilateral lesions may result quadriplegia, or bilateral paresis.

51. 2) The lesion types are deviding into two. Upper Motor Neuron Lesion Lower Motor Neuron Lesion

52. 1) UPPER MOTOR NEURON LESIONS: The pyramidal tracts are susceptible to damage, because they extend almost the whole length of the central nervous system. As mentioned previously, they particularly vulnerable as they pass through the  internal capsule  – a common site of cerebrovascular accidents (CVA) - (haemorrhagic bleeds , known as a ‘ capsular stroke ‘). (Additionally, lesions of the cortex (cortical lesions) or within the internal capsule (capsular lesions) may present with both corticospinal and corticobulbar findings. That is, contralateral muscle weakness in addition to cranial nerve abnormalities.)

53. If there is only a unilateral lesion(upper to the decussation ) of the left or right corticospinal tract, symptoms will appear on the contralateral side of the body. ( Corticospinal tract syndrome) The Cardinal signs of an upper motor neurone lesion are: Hypertonia  – an increased muscle tone Hyperreflexia  – increased muscle reflexes Clonus –  involuntary, rhythmic muscle contractions (an oscillatory motor response to muscle stretching) Babinski sign  – extension of the hallux in response to blunt stimulation of the sole of the foot. Muscle weakness.

54. When the Babinski reflex is present in a child older than 2 years or in an adult, it is often a sign of a central nervous system disorder. The central nervous system includes the brain and spinal cord. Disorders may include: Amyotrophic lateral sclerosis (Lou Gehrig disease) Brain tumor or injury Meningitis (infection of the membranes covering the brain and spinal cord) Multiple sclerosis Spinal cord injury , defect, or tumor Stroke.

55. 1. THE BABINSKI SIGN : The normal response in an  adult  to stroking the sole of the foot is flexion of the big toe, and often the other toes. Following damage to descending upper motor neuron pathways, however, this stimulus elicits extension of the big toe and a fanning of the other toes. A similar response occurs in human infants before the maturation of the corticospinal pathway and presumably indicates incomplete upper motor neuron control of local motor neuron circuitry.

56. 2. SAPSTICITY ( Hypertonia ): Spasticity is increased muscle tone. Spasticity is probably caused by the removal of inhibitory influences exerted by the cortex. It predominates in the Antigravity muscles. Spasticity is also eliminated by sectioning the dorsal roots. The form and intensity of spasticity may vary markedly, depending on the extend and site of the Central Nervous System(CNS) system damage. It is typically manifested as increased resistance to passive movements. 3. SPINAL REFLEXES ( Hyperreflexia ): Spasticity is also eliminated by sectioning the dorsal roots, suggesting that it represents an abnormal increase in the  gain  of the spinal cord reflex due to loss of descending inhibition.

57. 4. HYPOREFLEXIA OF SUPERFICIAL REFLEXES: The initial stage of lesion, the superficial reflexes are Areflexia or Hyporeflexia . That mechanism of diminishment of superficial reflexes is not well understood. Further signs are the decreased vigor (and increased threshold) of superficial reflexes such as the, Corneal reflex, Superficial abdominal reflex (tensing of abdominal muscles in response to stroking the overlying skin), and The cremasteric reflex in males (elevation of the scrotum in response to stroking the inner aspect of the thigh).

58. 5. A loss of the ability to perform fine movements:   If the lesion involves the descending pathways that control the lower motor neurons to the upper limbs, the ability to execute fine movements (such as independent movements of the fingers) is lost. 6. MUSCLE WEAKNESS: Weakness may range in severity from mild paresis to total paralysis, depending on the extent of the lesion. Types of weakness or paralysis: Hemiplegia /paresis Monoplegia /paresis Paraplegia/paresis Triplegia /paresis Tetraplegia (or) Quadriplegia/paresis

59. Types of Weakness Definition Common causes Hemiplegia / Hemiparesis Paralysis/Weakness of muscles of the arm, leg &sometimes face on one side of the body. Lesion at the Internal capsule, cerebral hemispheres, pontine bleed, rarely a high spinal cord injury . Monoplegia / Moparesis Paralysis/Weakness of all the muscles of the limbs, either Upper extremity & Lower extremity. Lesion at the cerebral hemisphere and spinal cord & peripheral Neuropathy. Paraplegia/ Paraparesis Paralysis of muscles in both legs Spinal cord lesions & Peripheral Neuropathy. Triplegia / Triparesis Hemiplegia paresis combined with paralysis of one limb on the opposite side of the body. High cervical spinal cord lesion or multiple lesion. Tetraplegia / tetraparesis Paralysis/Weakness of all four limbs. Lesion: high cervical spinal cord, brainstem or Cerebral Hemispheres, and Acute polyneuropathy , Radiculopathy , Myopathy

60. PARTS ARTERIAL SUPPLY Motor cortex Leg area Face, Trunk & Arm areas Anterior cerebral artery Middle cerebral artery Internal capsule Branches of middle cerebral artery Midbrain ( Crus cerebri ) Posterior cerebral artery Pons Pontine branches of basilar artery Medulla Oblangata Anterior spinal branches of vertibral artery Spinal cord Segmental branches of Anterior & posterior spinal artery

61. TRISOMY 18 (or) EDWARDS SYNDROME: A condition that causes severe developmental delays due to an extra chromosome 18 . This is exhibit various developmental abnormalities in the CNS. Dominant trisomy- 18 syndrome is uncrossed pyramidal tract. The symptoms are, Cleft palate Clenched fists Deformed feet (Rocker-Bottom feet) Feeding problems Small head ( microcephaly ) Small jaw ( micrognathia ) Weak cry.

62. TAKE HOME MESSAGES

63. REFERENCE: B.D.Chourasia (Human Anatomy) Sembulingam (Medical Physiology) A.K.Jain (Textbook of Physiology) James D.Fix ( NeuroAnatomy ) Christoper M.Fredericks ( Pathophysiology of the motor system) Eric R.Kandel (Principles of neural science) Snell’s (Clinical NeuroAnatomy ) Vichram Singh (Clinical NeuroAnatomy ) Harold Ellis (Clinical Anatomy)

64. 10. Shumway –Cook and Woolcott M.H. (2007) . (Motor control. Translating research into clinical practice). 11. Crossman, A.R. and Neary , D. (2015) ( Neuroanatomy ) 12. Bear MF, Connors BW, Paradiso . (Brain and Neuroscience). 13. Stiner CM, Barber PA, Petoe M, Anwar S, (Functional potential in chronic stroke patients depends on corticospinal tract integrity). 14. Dale Purves , George J Augustine, David Fitzpatrick, Lawrence C Katz, Anthony-Samuel LaMantia , James O McNamara, and S Mark Williams (Neuroscience-2 nd edition). Karen J.Jones ( Neuro Assessment a Clinical Guide). Pictures from KEN HUB (Licensed Anatomy page on the internet). Susan B. O’Sullivan (Physical Rehablitation ). Gray’s atlas of Human Anatomy. Mlyata H. ( Neuro Physiology)

65. THANK YOU