Pyramida and extrapyramidal tracts

First MBBS Lecture

1. Motor Neurophysiology Dr Raghuveer Choudhary Associate Professor Dept. of Physiology Dr S.N.Medical College, jodhpur

2. OBJECTIVES Locate the various motor areas of cerebral cortex Describe the pathway of the pyramidal tract Describe the pathways and functions of major extrapyramidal tracts Express the function of brainstem in controlling motor functions of the body.

3. The human skeleton is a system of levers that are moved by contraction of skeletal muscles. The motor system is comprised of skeletal muscles and the neurons that control them. Muscle contraction only occurs in response to action potentials in alpha motor neurons , which originate in the ventral gray matter of the spinal cord (and brainstem nuclei) and constitute the final common path for motor control

4. hierarchy of motor control within the CNS is as follows:

5. Cortical motor areas Four areas Primary motor cortex Premotor area Suplementary motor area Parietal cortex

6. Inputs to Motor Cortex Subcortical fibers from other cortical areas : somatosensory , frontal, auditory, visual . Subcortical fibers from contralateral cortex through the corpus callosum . Somatosensory fibers from thalamic ventrobasal complex . Fibers from thalamic VL and ventroanterior nuclei – from cerebellum and basal ganglia . Fibers from thalamic intralaminar nuclei – arousal .

7. Motor Cortex 1. Primary motor cortex =4 Somatotopic arrangement > 1/2 area ---controls hands & speech More of neuron stimulate movements instead of contracting a single muscle

8. 2. Premotor area= 6 Anterior to lateral portions of primary motor cortex for 1-3 cm below supplemental area -topographical organization ---same Receive information from parietal and prefrontal areas Project to primary Motor cortex, Basal ganglion and Spinal cord For planning and coordination of complex planned movements

9. 3. Supplemental motor area= 6 -superior to premotor area lying mainly in the longitudinal fissure , but extends a few cm. into the superior frontal cortex -functions in concert with premotor area to provide bilateraly ;- attitudinal movements fixation movements positional movements of head & eyes background for finer motor control of arms/hands

10. DESCENDING MOTOR PATHWAYS traditionally subdivided into 1.Pyramidal tract OR lateral pathways ( i.e,corticospinal tract 80%) 2. Extrapyramidal pathways OR M edial pathways (everything else: basal ganglia, cerebellum, brain stem

11. Motor Control 1. Lateral motor system Lateral corticospinal tracts 80 % Rubrospinal tracts Controls more distal muscles of limbs 2. Medial motor system of the cord Reticulospinal , Vestibulospinal , Tectospinal Anterior corticospinal tracts– 20% Controls mainly the axial & girdle muscles

12. . Lateral motor system Lateral corticospinal tracts 80 % Rubrospinal tracts Controls more distal muscles of limbs 2. Medial motor system of the cord Reticulospinal , Vestibulospinal , Tectospinal Anterior corticospinal tracts– 20% Controls mainly the axial & girdle muscles

13. The motor pathways are divided into two groups Direct pathways (voluntary motion pathways) - the pyramidal tracts Indirect pathways (postural pathways) , essentially all others - the extrapyramidal pathways

14. Descending Spinal Tracts Pyramidal Corticospinal Extrapyramidal Rubrospinal Tectospinal Vestibulospinal Olivospinal Reticulospinal Descending Autonomic Fibers

15. Primary Motor Cortex Vertical Columnar Arrangement An integrative processing system + 50-100 pyramidal cells to achieve muscle contraction Pyramidal cells or Betz cells 35000 3% (2 types of output signals) Dynamic signal excessively excited at the onset of contraction to initiate muscle contraction Static signal fire at slower rate to maintain contraction

16. Corticospinal tract Originates Primary motor cortex- 30% PMA+SMA- 30% Somatic sensory areas- 40% Synapses with: Motor neurons controlling distal muscles (alpha and gamma motor neurons) Interneurons controlling motor neurons

17. Descends via the posterior limb of the internal capsule- (lies between caudate & putamen ) Forms the pyramids of medulla Most fibers cross midline & form lateral corticospinal tract axons decussate at the junction between medulla and spinal cord. Some fibers stay ipsilateral & form ventral corticospinal tract

18. Origin : motor and sensory cortices Axons pass through corona radiata , internal capsule , crus cerebri and pyramid of medulla oblongata In the caudal medulla about 75-90% of the fibers decussate and form the lateral corticospinal tract Rest of the fibers remain ipsilateral and form anterior corticospinal tract . They also decussate before termination

19. Distribution : 55% terminate at cervical region 20% at thoracic 25% at lumbosacral level Termination : Ventral horn neurons (mostly through interneurons , a few fibers terminate directly) Corticobulbar tracts end at the motor nuclei of CNs of the contralateral side

20. Corticospinal Tracts Concerned with voluntary, discrete, skilled movements, especially those of distal parts of the limbs (fractionated movements) Innervate the contralateral side of the spinal cord Provide rapid direct method for controlling skeletal muscle

21. Motor Pathways Contain a sequence of TWO neurons from the cerebral cortex or brain stem to the muscles Upper motor neuron : has cell body in the cerebral cortex or brain stem, axon decussates before terminating on the lower motor neuron Lower motor neuron : has cell body in the ventral horn of the spinal cord, axon runs in the ipsilateral ventral root of the spinal nerve and supply the muscle. UMN LMN

22. Upper motor neuron Lower motor neuron extrapyramidal tracts pyramidal tracts alpha motor neurone gamma motor neurone

23. Biceps Spinalcord EFMF Muscle spindal Alpha Motor Neuron Gamma Motor Neuron Gogi tendon Organ Lower Motor Neuron Injury UMN Injury

24. Lower motor neuron lesion causes flaccid paralysis Upper motor neuron lesion causes spastic paralysis

25. Lower motor neuron lesion muscle weakness flaccid paralysis muscle wasting (disuse atrophy) reduced muscle tone ( hypotonia ) reflexes: reduced or absent spontaneous muscle contractions ( fasciculations ) plantar reflex: flexor superficial abdominal reflexes: present

26. Upper motor neuron lesion muscle weakness spastic paralysis increased muscle tone ( hypertonia ) reflexes: exaggerated Babinski sign: positive superficial abdominal reflexes: absent muscle wasting is very rare

27. Babinski sign when outer border of the sole of the foot is scratched upward movement of big toe fanning out of other toes

28. positive Babinski sign

29. positive Babinski sign dorsiflexion of big toe fanning out of other toes

30. Babinski sign feature of upper motor neuron lesion extensor plantar reflex seen in infants during 1st year of life (becuase of immature corticospinal tract)

31. clonus rhythmical series of contractions in response to sudden stretch feature of upper motor neuron lesion

32. superficial abdominal reflexes light scratch of the abdominal skin brisk unilateral contraction of the abdominal wall upper motor neuron lesion causes reduced or loss of these reflexes

33. Different types of lesions monoplegia only 1 limb is affected either UL or LL, lower motor neuron lesion hemiplegia on half of the body including UL and LL lesion in the Internal capsule paraplegia both lower limbs thoracic cord lesion quadriplegia ( tetraplegia ) all 4 limbs are affected cervical cord or brain stem lesion

34. Site of lesions Cortex Internal capsule Brain stem Spinal cord Anterior horn cell Motor nerve Neuromuscular junction Muscle

35. Cortex Internal capsule Brain stem Spinal cord Anterior horn cell Motor nerve Neuromuscular junction Muscle muscle disorders myopathy muscle wasting muscle weakness mostly hereditary

36. Cortex Internal capsule Brain stem Spinal cord Anterior horn cell Motor nerve Neuromuscular junction Muscle neuromuscular disorders myasthenia gravis muscle fatigue snake poisoning insecticide poisoning

37. Cortex Internal capsule Brain stem Spinal cord Anterior horn cell Motor nerve Neuromuscular junction Muscle motor nerve peripheral neuropathy (eg. diabetic neuropathy) muscle weakness sensory features lower motor neuron lesion

38. Cortex Internal capsule Brain stem Spinal cord Anterior horn cell Motor nerve Neuromuscular junction Muscle anterior horn cell disorders motor neuron disease fasciculations (eg. tongue) muscle weakness lower motor neuron lesion

39. Cortex Internal capsule Brain stem Spinal cord Anterior horn cell Motor nerve Neuromuscular junction Muscle spinal cord injuries spinal shock spinal root compression spinal cord compression sensory loss muscle weakness upper motor neuron lesion

40. Cortex Internal capsule Brain stem Spinal cord Anterior horn cell Motor nerve Neuromuscular junction Muscle brain stem brain stem lesion muscle weakness upper motor neuron lesion bulbar palsy (cranial nerve palsy) brain stem transection at pons level decerebrate rigidity at midbrain level righting reflexes

41. Cortex Internal capsule Brain stem Spinal cord Anterior horn cell Motor nerve Neuromuscular junction Muscle internal capsule cortical level stroke ( cerebrovascular accident) upper motor neuron lesion

42. Rubrospinal Tract Controls the tone of limb flexor muscles, being excitatory to motor neurons of these muscles Origin : Red nucleus Axons course ventro -medially, cross in ventral tegmental decussation , descend in spinal cord ventral to the lateral corticospinal tract Cortico - rubro -spinal pathway ( Extrapyramidal )