Neuro 13 descending tracts student

3,599 views

Published on

lecture 10-19-11

Published in: Education, Technology, Business
0 Comments
11 Likes
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total views
3,599
On SlideShare
0
From Embeds
0
Number of Embeds
1
Actions
Shares
0
Downloads
271
Comments
0
Likes
11
Embeds 0
No embeds

No notes for slide

Neuro 13 descending tracts student

  1. 1. DESCENDING TRACTS
  2. 2. Fiber Types <ul><li>A Fibers: </li></ul><ul><li>Somatic, myelinated. </li></ul><ul><li>Alpha ( α ): </li></ul><ul><li>Largest, also referred to as Type I. </li></ul><ul><li>Beta ( β ): </li></ul><ul><li>Also referred to as Type II. </li></ul><ul><li>Gamma ( γ ): </li></ul><ul><li>Delta ( δ ): </li></ul><ul><li>Smallest, referred to as Type IV. </li></ul>
  3. 3. Fiber Types <ul><li>B Fibers: </li></ul><ul><li>Lightly myelinated. </li></ul><ul><li>Preganglionic fibers of ANS. </li></ul><ul><li>C Fibers: </li></ul><ul><li>Unmyelinated. </li></ul><ul><li>Found in somatic and autonomic systems. </li></ul><ul><li>Also referred to as Type IV fibers. </li></ul>
  4. 4. Fiber Types <ul><li>Sensory fibers are either: </li></ul><ul><li>A- α or A- β fibers: </li></ul><ul><li>Conduction rate = 30-120 m/sec. </li></ul><ul><li>A- δ fibers: </li></ul><ul><li>Conduction rate = 4-30 m/sec. </li></ul><ul><li>C fibers: </li></ul><ul><li>Conduction rate is less than 2.5m/sec. </li></ul>
  5. 5. Fiber Types <ul><li>Nociceptors and thermoreceptors are related to C fibers or A- δ fibers. </li></ul>
  6. 6. Generalizations: Motor Paths <ul><li>Typical descending pathway consists of a series of two motor neurons: </li></ul><ul><li>Upper motor neurons (UMNs) </li></ul><ul><li>Lower motor neurons (LMNs) </li></ul><ul><li>Does not take into consideration the association neurons between UMNs and LMNs </li></ul>
  7. 7. Upper Motor Neurons <ul><li>Are entirely within the CNS. </li></ul><ul><li>Originate in: </li></ul><ul><li>Cerebral cortex </li></ul><ul><li>Cerebellum </li></ul><ul><li>Brainstem </li></ul><ul><li>Form descending tracts </li></ul>
  8. 8. Lower Motor Neurons <ul><li>Begin in CNS. </li></ul><ul><li>From anterior horns of spinal cord. </li></ul><ul><li>From brainstem cranial nerve nuclei. </li></ul><ul><li>Made up of alpha motor neurons (A- α ) . </li></ul><ul><li>Make up spinal and cranial nerves. </li></ul>
  9. 9. UMN Classification <ul><li>Classified according to where they synapse in the ventral horn: </li></ul><ul><li>Medial activation system: </li></ul><ul><li>Innervate postural and girdle muscles </li></ul><ul><li>Lateral activation system: </li></ul><ul><li>Associated with distally located muscles used for fine movements </li></ul><ul><li>Nonspecific activating system: </li></ul><ul><li>Facilitate local reflex arcs </li></ul>
  10. 10. Pyramidal System <ul><li>Characteristics: </li></ul><ul><li>Upper motor neurons: </li></ul><ul><li>75 – 85% Decussate in pyramids. </li></ul><ul><li>Remainder decussate near synapse with lower motor neurons. </li></ul><ul><li>Most synapse with association neurons in spinal cord central gray. </li></ul>
  11. 11. Pyramidal System <ul><li>Components: </li></ul><ul><li>Corticospinal Tract </li></ul><ul><li>Corticobulbar Tract </li></ul>
  12. 12. Corticospinal Tract Divisions <ul><li>Lateral corticospinal tract: </li></ul><ul><li>Made up of corticospinal fibers that have crossed in medulla. </li></ul><ul><li>Supply all levels of spinal cord. </li></ul><ul><li>Anterior corticospinal tract: </li></ul><ul><li>Made up of uncrossed corticospinal fibers that cross near level of synapse with LMNs. </li></ul><ul><li>Supply neck and upper limbs. </li></ul>
  13. 13. Corticospinal Tract Functions <ul><li>Add speed and agility to conscious movements: </li></ul><ul><li>Especially movements of hand. </li></ul><ul><li>Provide a high degree of motor control: </li></ul><ul><li>(i.e., movement of individual fingers) </li></ul>
  14. 14. Corticospinal Tract Lesions <ul><li>Reduced muscle tone </li></ul><ul><li>Clumsiness </li></ul><ul><li>Weakness </li></ul><ul><li>Not complete paralysis </li></ul><ul><li>Note: complete paralysis results if both pyramidal and extrapyramidal systems are involved (as is often the case). </li></ul>
  15. 15. Corticobulbar Tract <ul><li>Innervates the head </li></ul><ul><li>Most fibers terminate in reticular formation near cranial nerve nuclei. </li></ul><ul><li>Association neurons: </li></ul><ul><li>Leave reticular formation and synapse in cranial nerve nuclei. </li></ul><ul><li>Synapse with lower motor neurons. </li></ul>
  16. 16. Extrapyramidal System <ul><li>Includes descending motor tracts that do not pass through medullary pyramids or corticobulbar tracts. </li></ul><ul><li>Includes: </li></ul><ul><li>Rubrospinal tracts </li></ul><ul><li>Vestibulospinal tracts </li></ul><ul><li>Reticulospinal tracts </li></ul>
  17. 17. Rubrospinal Tract <ul><li>Begins in red nucleus. </li></ul><ul><li>Decussates in midbrain. </li></ul><ul><li>Descends in lateral funiculus (column). </li></ul><ul><li>Function closely related to cerebellar function. </li></ul><ul><li>Lesions: </li></ul><ul><li>Impairment of distal arm and hand movement. </li></ul><ul><li>Intention tremors (similar to cerebellar lesions) </li></ul>
  18. 18. Vestibulospinal Tract <ul><li>Originates in vestibular nuclei: </li></ul><ul><li>Receives major input from vestibular nerve: </li></ul><ul><li>(CN VIII) </li></ul><ul><li>Descends in anterior funiculus (column). </li></ul><ul><li>Synapses with LMNs to extensor muscles: </li></ul><ul><li>Primarily involved in maintenance of upright posture. </li></ul>
  19. 19. Reticulospinal Tract <ul><li>Originates in various regions of reticular formation. </li></ul><ul><li>Descends in anterior portion of lateral funiculus (column). </li></ul><ul><li>Thought to mediate larger movements of trunk and limbs that do not require balance or fine movements of upper limbs. </li></ul>
  20. 20. BASAL NUCLEI
  21. 21. Basal Ganglia Functions <ul><li>Compare proprioceptive information and movement commands. </li></ul><ul><li>Sequence movements. </li></ul><ul><li>Regulate muscle tone and muscle force. </li></ul><ul><li>May be involved in selecting and inhibiting specific motor synergies. </li></ul>
  22. 22. Basal Ganglia Functions <ul><li>Basal ganglia are vital for normal movement but they have no direct connections with lower motor neurons. </li></ul><ul><li>Influence LMNs: </li></ul><ul><li>Through planning areas of cerebral cortex. </li></ul><ul><li>Pedunculopontine nucleus of midbrain. </li></ul>
  23. 23. Basal Ganglia Functions <ul><li>Basal nuclei set organism’s level of responsiveness to stimuli. </li></ul><ul><li>Extrapyramidal disorders are associated with basal nuclei pathology: </li></ul><ul><li>Negative symptoms of underresponsiveness: </li></ul><ul><li>Akinesias </li></ul><ul><li>i.e. Parkinson disease </li></ul><ul><li>Positive symptoms of over-responsiveness: </li></ul><ul><li>Choreas, athetoses, ballisms </li></ul><ul><li>i.e. Huntington’s chorea </li></ul>
  24. 24. Basal Nuclei Components <ul><li>Corpus striatum </li></ul><ul><li>Substantia nigra (within the midbrain) </li></ul><ul><li>Subthalamic nuclei (diencephalon) </li></ul><ul><li>Red nucleus (?) </li></ul><ul><li>Claustrum (?) </li></ul><ul><li>Nucleus accumbens (?) </li></ul>
  25. 25. Corpus Striatum <ul><li>Composed of caudate nucleus + lentiform nucleus: </li></ul><ul><li>Striatum = caudate nucleus + putamen. </li></ul><ul><li>Pallidum = globus pallidus. </li></ul><ul><li>Putamen + globus pallidus = lentiform nucleus. </li></ul><ul><li>Controls large subconscious movements of the skeletal muscles. </li></ul><ul><li>The globus pallidus regulates muscle tone. </li></ul>
  26. 26. Corpus Striatum Corpus Striatum (Telencephalon) Striatum Pallidum Caudate Nucleus Putamen Globus Pallidus
  27. 27. Substantia Nigra Subdivisions <ul><li>Dorsal pars compacta: </li></ul><ul><li>Has melanin containing neurons and dopaminergic neurons. </li></ul><ul><li>Ventral pars reticularis: </li></ul><ul><li>Has iron-containing glial cells. </li></ul><ul><li>Has serotonin and GABA (no melanin). </li></ul>
  28. 28. Substantial Nigra Substantia Nigra Mesencephalon Dorsal Pars compacta Ventral Pars reticularis Melanin containing neurons Dopaminergic neurons Iron-containing glial cells Serotonin and GABA
  29. 29. Input Nuclei <ul><li>Striatum </li></ul><ul><li>Caudate nucleus </li></ul><ul><li>Putamen </li></ul><ul><li>Nucleus accumbens </li></ul><ul><li>Receive widespread input from: </li></ul><ul><li>Neocortex </li></ul><ul><li>Intralaminar nuclei </li></ul><ul><li>Substantia nigra </li></ul><ul><li>Dorsal raphe nucleus </li></ul>
  30. 30. Input Nuclei <ul><li>Striatum projects to: </li></ul><ul><li>Globus pallidus </li></ul><ul><li>Substantia nigra </li></ul><ul><li>Pars reticularis </li></ul><ul><li>Via gabaminergic fibers </li></ul><ul><li>Motor and sensory cortices project to putamen. </li></ul><ul><li>Association areas of all lobes project to caudate nucleus. </li></ul>
  31. 31. Output Nuclei <ul><li>Globus pallidus (medial part) </li></ul><ul><li>Substantia nigra: </li></ul><ul><li>Pars reticularis </li></ul><ul><li>Ventral pallidum </li></ul><ul><li>Fibers project to: </li></ul><ul><li>VA/VL nuclei </li></ul><ul><li>Mostly inhibitory </li></ul>
  32. 32. General Core Circuit <ul><li>Cerebral cortex to: </li></ul><ul><li>Striatum to: </li></ul><ul><li>Globus pallidus to: </li></ul><ul><li>Thalamus to: </li></ul><ul><li>Portions of motor cortex to: </li></ul><ul><li>Upper motor neurons </li></ul>
  33. 33. Thalamic Fasciculi <ul><li>Ansa lenticularis: </li></ul><ul><li>Consists of fibers from dorsal portion of globus pallidus. </li></ul><ul><li>Loops under internal capsule. </li></ul><ul><li>To VA/VL complex. </li></ul>
  34. 34. Thalamic Fasciculi <ul><li>Lenticular fasciculus: </li></ul><ul><li>Consists of fibers from ventral portion of globus pallidus. </li></ul><ul><li>Passes across the internal capsule. </li></ul><ul><li>To VA/VL complex. </li></ul>
  35. 35. Dopamine Neuronal System <ul><li>Consists of nigrostriatal fibers </li></ul><ul><li>From pars compacta of substantia nigra </li></ul><ul><li>To striatum </li></ul><ul><li>Dopaminergic </li></ul>
  36. 36. Direct Basal Ganglia Circuit <ul><li>Motor cortex projects to putamen: </li></ul><ul><li>Excitatory (glutamate) </li></ul><ul><li>Putamen projects to output nuclei (globus pallidus internus and substantia nigra reticularis): </li></ul><ul><li>Inhibitory (GABA and substance P) </li></ul>
  37. 37. Basal Ganglia Connections Red = excitatory; Black = Inhibitory Motor areas of cerebral cortex Ventrolateral thalamus Putamen Globus pallidus externus Output nuclei Subthalamic nuclei Substantia nigra compacta Lateral Activation pathways Pedunculo- Pontine nuclei Reticulospinal and Vestibulospinal pathways
  38. 38. Direct Basal Ganglia Circuit <ul><li>Output nuclei project to motor thalamus (VA-VL) and pedunculopontine nuclei: </li></ul><ul><li>Inhibitory (GABA) </li></ul><ul><li>Ventrolateral (VA-VL) thalamus projects to motor cortex: </li></ul><ul><li>Excitatory </li></ul><ul><li>Therefore: </li></ul><ul><li>Increasing input to putamen increases activity in corticofugal fibers </li></ul>
  39. 39. Direct Basal Ganglia Circuit <ul><li>Pedunculopontine nuclei project to reticulospinal and vestibulospinal pathways. </li></ul><ul><li>Stimulation of pedunculopontine nuclei elicit rhythmical behaviors such as locomotor patterns. </li></ul>
  40. 40. Indirect Basal Ganglia Circuit <ul><li>Motor cortex to putamen: </li></ul><ul><li>Excitatory (glutamate) </li></ul><ul><li>Putamen to globus pallidus externus: </li></ul><ul><li>Inhibitory (GABA and enkephalins) </li></ul><ul><li>Globus pallidus externus to subthalamic nuclei: </li></ul><ul><li>Inhibition (GABA) </li></ul>
  41. 41. Indirect Basal Ganglia Circuit <ul><li>Subthalamic nuclei to output nuclei (substantia nigra reticularis) </li></ul><ul><li>Excitatory (glutamate) </li></ul><ul><li>Output nuclei to VA-VL complex (motor thalamus) </li></ul><ul><li>Inhibitory (GABA) </li></ul>
  42. 42. Indirect Basal Ganglia Circuit <ul><li>VA-VL complex to motor cortex: </li></ul><ul><li>Excitatory </li></ul><ul><li>Therefore: decrease in corticofugal pathways. </li></ul>
  43. 43. Input from Substantia Nigra Compacta <ul><li>Projects to putamen: </li></ul><ul><li>Excitatory (dopamine) </li></ul><ul><li>Two kinds of receptors in basal ganglia circuit: </li></ul><ul><li>D1: facilitates activity in direct pathway </li></ul><ul><li>D2: inhibits activity in indirect pathway </li></ul>

×