Lecture 5 Corticospinal Tracts & Motor Pathways PDF

CORTICOSPINAL TRACTS AND - OTHER MOTOR PATHWAYS LECTURE 5.1 PTY 214 LEARNING the At the end of this lectures the students starts atord should be able to identify: OBJECTIVE seind...

CORTICOSPINAL TRACTS AND - OTHER MOTOR PATHWAYS LECTURE 5.1 PTY 214 LEARNING the At the end of this lectures the students starts atord should be able to identify: OBJECTIVE seind The upper and lower motor neurons Histology of cerebral cortex S umN Most common cells found within cerebral cortex The pathway of pyramidal tracts (corticospinal and corticobulbar tracts) The lateral and ventral and corticospinal tracts CNS Functional role of corticospinal and corticobulbar tracts Static and dynamic signals of pyramidal tracts The extrapyramidal tracts as rubrospinal, Vestibulospinal, reticulospinal and tectospinal tracts  THE DESCENDING MOTOR SYSTEMS FOR VOLUNTARY MOUVEMENTS TO OCCUR WE NEED 2 NEURONES : UPPER MOTOR NEURONES : THEIR CELL BODIES LIE IN THE HIGHER MOTOR CENTERS IN THE BRAIN AND BRAIN STEM, AND THEIR AXONS CONSTITUE THE DESCENDING E MOTOR PATHWAYS LOWER MOTOR NEURONES : CELL BODIES LIE IN THE SPINAL VENTRAL HORN OR THE CORRESPONDING MOTOR CRANIAL NUCLEI AND INCLUDE MNALPHA AND GAMMA. THEIR AXONS PROCEED THROUGH THE PERIPHERAL SOMATIC NERVE TO INNERVATE SKELETAL MUSCLE  INTRODUCTION “DESCENDING FIBERS ARE THAT FIBERS THAT TRAVEL DOWNWARDS FROM THE BRAIN TO THE SPINAL CORD” One way ticket always way a  CLASSIFICATION OF DESCENDING MOTOR SYSTEMS THE DESCENDING MOTOR WAYS IS DIVIDED INTO PYRAMIDAL AND · EXTRAPYRAMIDAL TRACTS WHY? BECAUSE THE MOTOR TRACT WHICH ORIGINATE FROM THE CEREBRAL CORTEX AND DESCENDS TO THE SPINAL CORD (CORTICO SPINAL TRACT) PASS THROUGH THE PYRAMID OF THE MEDULLA THEREFORE HAS BEEN CALLED “ THE PYRAMIDAL TRACT” THE REST OF THE DESCENDING MOTOR PATHWAYS DO NOT TRAVEL THROUGH THE MEDULLARY PYRAMIDS, AND THEREFORE ARE COLLECTIVELY GATHERED UNDER THE HEADING: “ THE EXTRA-PYRAMIDAL TRACTS”  DESCENDING MOTOR TRACTS THERE ARE 5 IMPORTANT SETS OF DESCENDING MOTOR TRACTS NAMED ACCORDING TO THE ORIGIN OF THEIR CELL BODIES AND THEIR FINAL DESTINATION: 1. THE CORTICOBULBOSPINAL TRACT PYRAMIDAL TRACT 2. THE RUBRO SPINAL TRACT, 3. - THE RETICULO SPINAL TRACTS EXTRAPYRAMIDAL TRACT 4. THE VESTIBULOSPINAL TRACTS 5. THE TECTOSPINAL TRACT MIND MAP HOM  UPPER MOTOR NEURON AND LOWER MOTOR NEURON DIFFERENCES wed S · bred x ga. PYRAMIDAL TRACTS Corticospinal tract Corticobulbar tract DESCENDING TRACT tem ~ brains (smallest wack - Corticospinal ①medullo tracts = pyramidal UPPER MOTOR TRACTS Control-face - neck  80% 20% CORTICOSPINAL TRACT FOR FINE SKILLS MOUVEMENT # FUNCTIONS OF CORTICOSPINAL TRACTS  CORTICOSPINAL TRACT e ORIGIN: 30% PRIMARY MOTOR CORTEX 30% PRE-MOTOR AREA AND SUPPLEMENTARY MOTOR AREA 40% PARIETAL CORTEX “SOMATOSENSORY CORTEX” PREMOTOR AREA (MOTOR ASSOCIATION AREA) ITS STIMULATION PRODUCES COMPLEX COORDINATED MOVEMENTS, SUCH AS SETTING S THE BODY IN CERTAIN POSTURE TO PREFORM A SPECIFIC TASK SUPPLEMENTARY CORTEX THIS AREA (6) CONCERNS MAINLY WITH PLANNING, PROGRAMMING MOTOR SEQUENCES AND BIMANUAL ACTIVITY  UMNS CONTROL LMNS THROUGH 2 DIFFERENT PATHWAY Pyramidal tracts Extra Pyramidal tracts - There is more than million of fibers in each corticospinal tract - 97 % of these fibers are small and conduct background tonic signals to the spinal cord - Only 3 % of these fibers are large - These fibers originate from giant Betz cells - These cells are found only in the primary motor cortex - These are about 34000 of these large Betz cells fibers in each corticospinal tract The Betz cells fibers transmit The axons from Betz cells send short 3% of the corticospinal tract nerve impulses to the spinal collateral back to the cortex itself to are large myelinated cord at a velocity of about inhibit adjacent regions of the cortex pyramidal Betz cells in motor 70m/sec. when the Betz cells discharge, thereby area 4 “sharpening” the excitatory signal  DIFFERENCES ?? Sing Cresla  RECAP: COURSE AND TERMINATION Differences between the 2 tracts  TYPES OF CEREBRAL CORTEX NEOCORTEX 2. ARCHICORTEX NEWEST IN EVOLUTION HIPPOCAMPAL FORMATION, X LIMBIC SYSTEM ABOUT 90% OF TOTAL 3 LAYERS 6 LAYERS, MOST COMPLEX MOST PRIMITIVE MOST SUPERFICIAL MESOCORTEX ALLOCORTEX CINGULATE GYRUS, INSULAR 1. PALEOCORTEX CORTEX ASSOCIATED WITH OLFACTORY TRANSITIONAL BETWEEN SYSTEM, THE PARAHIPPOCAMPAL ARCHICORTEX AND GYRUS, UNCUS NEOCROTEX FEWER THAN 6 LAYERS  NEOCORTEX writing something I know THE WORDS USED TO DESCRIBE THE HIGHER MENTAL CAPACITIES · OF ANIMALS WITH A LARGE NEOCORTEX INCLUDE: CONSCIOUSNESS FREE WILL " INTELLIGENCE - INSIGHT ANIMALS WITH MUCH SIMPLER BRAIN LEARN WELL, SO LEARNING SHOULD NOT BE AMONG THESE CAPACITIES (MACPHAIL 1982) A SPECIES COULD HAVE GENETICALLY DETERMINED MECHANISMS, ACQUIRED THROUGH EVOLUTIONARY SELECTION, FOR TAKING ADVANTAGE OF THE REGULAR FEATURES OF THE ENVIRONMENT, OR THEY COULD HAVE LEARNED THROUGH DIRECT EXPERIENCE  HISTOLOGY OF THE CEREBRAL CORTEX NEOCORTEX HAS 6 LAYERS DESIGNATED I, II, III, IV, V AND VI PYRAMIDAL CELLS PREDOMINATE IN LAYERS III AND V X GRANULE (STELLATE) CELLS IN LAYERS II AND IV Schematic illustration of the six horizontal layers of Neocortex: I = molecular layer; II = outer granular layer; III = outer pyramidal layer; IV = inner granular layer; V = inner pyramidal layer; and VI = multiform layer.  LAYERS OF NEOCORTEX 6 LAYERS OF CEREBRAL CORTEX X MOLECULAR LAYER (I) EXTERNAL GRANULAR LAYER (II) EXTERNAL PYRAMIDAL LAYER (III) INTERNAL GRANULAR LAYER (IV) INTERNAL PYRAMIDAL LAYER (V) MULTIFORM (FUSIFORM) LAYER (VI) EXCITATION OF THE SPINAL CORD MOTOR AREAS BY THE PRIMARY MOTOR CORTEX AND RED NUCLEUS X THE MOTOR CORTEX IS ARRANGED INTO THOUSANDS VERTICAL COLUMNS, EACH COLUMN HAS SIX DISTINCT LAYERS OF CELLS. LAYER 5 (FROM CORTICAL SURFACE) GIVEN ORIGIN FOR THE PYRAMIDAL CELLS THAT GIVE RISE TO THE CORTICOSPINAL FIBERS THE INPUT SIGNALS ENTER CORTEX BY WAY OF LAYERS 2 AND 4 LAYER 6 GIVES RISE TO FIBERS THAT COMMUNICATE WITH OTHER REGIONS OF THE CEREBRAL CORTEX  FUNCTIONAL DIVISION OF THE LAYERS OF NEOCORTEX 3 PARTS: 1. SUPRAGRANULAR CELLS MOLECULAR LAYER (I); EXTERNAL GRANULAR LAYER (II); X EXTERNAL PYRAMIDAL LAYER (III) PRIMARY ORIGIN AND TERMINATION OF INTRACORTICAL CONNECTIONS WHICH ARE EITHER: ASSOCIATION COMMISSURAL HIGHLY DEVELOPED IN HUMANS AND PERMITS COMMUNICATION BETWEEN ONE PORTION OF THE CORTEX AND OTHER REGIONS  FUNCTIONAL DIVISION OF THE LAYERS OF NEOCORTEX 3 PARTS: 2. INTERNAL GRANULAR LAYER (IV) RECEIVES THALAMOCORTICAL CONNECTIONS MOST PROMINENT OM THE PRIMARY SENSORY CORTEX X  FUNCTIONAL DIVISION OF THE LAYERS OF NEOCORTEX 3 PARTS: X 3. INFRAGRANULAR LAYERS INTERNAL PYRAMIDAL LAYER (V); MULTIFORM (FUSIFORM) LAYER (VI) CONNECT THE CEREBRAL CORTEX WITH SUBCORTICAL REGIONS MOSTLY DEVELOPED IN MOTOR CORTICAL AREAS LAYER V GIVES RISE TO ALL OF THE PRINCIPAL CORTICAL EFFERENTS PROJECTIONS (TO BASAL GANGLIA, BRAINSTEM AND SPINAL CORD) LAYER VI (MULTIFORM OR FUSIFORM LAYER) PROJECTS PRIMARILY TO THE THALAMUS  · CELLS OF THE CORTEX large 6 ells Pyramidal cells Fusiform cells Stellate (granulate) cells  PYRAMIDAL CELLS MAIN CELL TYPE WITHIN LAYERS III AND IV EXTREMELY LARGE IN LAYER V OF THE MOTOR CORTEX GIVING RISE TO MOST CORTICOBULBAR AND CORTICOSPINAL FIBERS PYRAMIDAL CELLS ARE THE PRIMARY OUTPUT CORTICAL NEURON (BETZ CELLS) THESE CELLS ARE PYRAMIDAL IN SHAPE, WITH AN APICAL DENDRITE THAT EXTENDS ALL THE WAY TO LAYER I OF THE CORTEX HAVE LONG AXIS THAT LEAVES THE CORTEX AND ENTERS THE SUBCORTICAL WHITE MATTER, THEY ARE DESTINED TO BE: COMMISSURAL (FORM CORPUS CALLOSUM) ASSOCIATION (PROJECT TO IPSILATERAL ASSOCIATION AREAS) PROJECTION (LEAVE THE CORTEX AND PROJECT TO DIFFERENT REGIONS OF THE CNS – THALAMUS, SPINAL CORD, ETC)  FUSIFORM CELLS DEEPEST CORTICAL LAYER X FUNCTIONS ARE SIMILAR TO THAT OF PYRAMIDAL CELLS DENDRITES EXTEND FROM EACH END OF THE CELL BODY BRANCHING INTO DEEPER AND MORE SUPERFICIAL LAYERS ALSO COMMISSURAL, ASSOCIATION OR PROJECTED (+) ORIENTED STELLATE (GRANULAR) CELLS MOST PROMINENT IN LAYER IV THEIR AXONS REMAIN IN THE CORTEX PROCESSES VERY SHORT AND PROJECT X LOCALLY IN THE CORTEX (THEY DO NOT LEAVE THE CORTEX) MAIN INTERNEURONS OF THE NEOCORTEX MODULATE THE ACTIVITY OF OTHER CORTICAL NEURONS SPINY (DENDRITES WITH SPINES) LAYER IV (RELEASE GLUTAMATE) EXCITATORY INTERNEURONS ASPINY (DENDRITES WITHOUT SPINES) RELEASE GABA INHIBITORY INTERNEURONS  INTERCONNECTION OF CORTEX AFFERENT FIBERS SYNAPSE HIGH (SUPERFICIAL) IN THE CORTEX WITH DENDRITES OF EFFERENT NEURON X EFFERENT FIBERS TYPICALLY THE AXONS OF PYRAMIDAL CELLS TEND TO GIVE OFF BRANCHES THESE BRANCHES PASS BACK INTO SUPERFICIAL LAYERS TO COMMUNICATE WITH THEIR OWN DENDRITES THIS CAN BE VIA INTERNEURONAL CONNECTIONS OR INVOLVING OTHER CORTICAL CELLS TYPES  Interconnection of cortex - radial for PY AFFERENT INPUT EFFERENT OUTPUT ASSOCIATION NUCLEI (THALAMUS) CORTICOTHALAMIC FIBERS OTHER CORTICAL AREAS CORTICOCORTICAL FIBERS INTRALAMINAR NUCLEI CORTICOSTRIATE FIBERS TO (THALAMUS) BRAINSTEM AND SPINAL CORD  DYNAMIC AND STATIC SIGNALS ARE TRANSMITTED BY THE PYRAMIDAL NEURONS IF A STRONG SIGNAL IS SENT TO A MUSCLE TO CAUSE INITIAL RAPID CONTRACTION, THEN A MUCH WEAKER CONTINUING SIGNAL CAN MAINTAIN THE CONTRACTION FOR LONG PERIODS THEREAFTER. CTO DO THIS, EACH COLUMN OF CELLS EXCITES 2 POPULATION OF PYRAMIDAL CELL NEURONS (1) DYNAMIC NEURONS – THE DYNAMIC NEURONS ARE EXCITED AT A HIGH RATE FOR A SHORT PERIOD AT THE BEGINNING OF A CONTRACTION, CAUSING THE INITIAL RAPID DEVELOPMENT OF FORCE maintain (2) STATIC NEURONS – THEY FIRE AT A MUCH SLOWER RATE AN CONTINUE FIRING AT THIS SLOW RATE TO MAINTAIN THE FORCE OF CONTRACTION AS LONG AS THE CONTRACTION IS REQUIRED  LESIONS OF THE PRIMARY CORTEX (AREA PYRAMIDALIS) CASE 1 REMOVAL OF THE PRIMARY CORTEX AREA WITHOUT DAMAGE TO PREMOTOR AND SUPPLEMENTARY AREA FUNCTIONAL LOST – LOSS OF VOLUNTARY CONTROL OF DISCRETE MOVEMENTS OF THE DISTAL SEGMENTS OF THE LIMB, ESPECIALLY OF THE HANDS AND FINGERS FUNCTION PRESERVED – GROSS POSTURAL AND LIMB “FIXATION” MOVEMENT CAN STILL OCCUR PRIMARY MOTOR CORTEX (AREA PYRAMIDALIS) IS ESSENTIAL FOR: - VOLUNTARY INITIATION OF FINE CONTROLLED MOVEMENTS ESPECIALLY OF THE HANDS AND FINGERS RESULTS IN < HYPOTONIA  T LESIONS OF THE PRIMARY CORTEX CASE 2 REMOVAL OF THE PRIMARY CORTEX AREA WITH DAMAGE TO THE OTHER PART OF THE BRAIN (EX. BASAL GANGLIA). (MOST LESIONS SUCH AS THAT CAUSED BY STROKE) RESULTS IN MUSCLE SPASTICITY THE REASON FOR MUSCLE SPASTICITY: DAMAGE TO ACCESSORY NON-PYRAMIDAL PATHWAYS ACTIVATION OF VESTIBULAR AND RETICULAR BRAIN STEM MOTOR NUCLEI (NORMALLY THEY ARE INHIBITED) EXCESSIVE SPASTIC TONE IN THE INVOLVED MUSCLES ↑ EXTRAPYRAMIDAL TRACTS > I  EXTRAPYRAMIDAL TRACTS IT’S PATHWAY EXTRAPYRAMIDAL SYSTEM FUNCTIONS: 1- SETS THE POSTURAL BACKGROUND NEEDED FOR PERFORMANCE OF SKILLED MOVEMENTS 2 – CONTROLS SUBCONSCIOUS GROSS EXTRAPYRAMIDAL TRACTS TYPE MOVEMENTS RUBROSPINAL TRACT VESTIBULOSPINAL TRACT VESTIBULOSPINAL TRACTS balance head-neck  VESTIBULOSPINAL TRACTS VESTIBULOSPINAL TRACT DIVIDE INTO: (1) LATERAL VESTIBULOSPINAL TRACT (2) MEDIAL VESTIBULOSPINAL TRACT skip  ROLE OF THE VESTIBULAR NUCLEI TO EXCITE THE ANTI-GRAVITY MUSCLES ALL THE VESTIBULAR NUCLEI FUNCTION IN ASSOCIATION WITH THE PONTINE RETICULAR NUCLEI TO CONTROL THE ANTIGRAVITY MUSCLES THE VESTIBULAR NUCLEI TRANSMIT STRONG EXCITATORY SIGNALS TO THE ANTIGRAVITY MUSCLES BY THE LATERAL AND MEDIAL VESTIBULOSPINAL TRACT IN THE ANTERIOR COLUMN OF THE SPINAL CORD WITHOUT THIS SUPPORT THE PONTINE RETICULAR SYSTEM WOULD LOSE MUCH OF ITS EXCITATORY OF THE AXIAL ANTIGRAVITY MUSCLES THE SPECIFIC ROLE OF THE VESTIBULAR NUCLEI, ITS TO SELECTIVELY CONTROL THE EXCITATORY SIGNALS TO THE ANTIGRAVITY MUSCLES TO MAINTAIN EQUILIBRIUM IN RESPONSE TO SIGNALS FROM THE VESTIBULAR APPARATUS  TECTOSPINAL TRACT nearech TECTOSPINAL TRACT  RETICULOSPINAL TRACT LATERAL RETICULOSPINAL TRACT DIVIDE INTO: (1) PONTINE (MEDIAL) RETICULOSPINAL TRACT (2) MEDULLARY (LATERAL) RETICULOSPINAL TRACT 3x MEDIAL RETICULOSPINAL TRACT (increases dicreas or X X OLIVO SPINAL TRACT  FUNCTION OF EACH TRACT CORTICOSPINAL TRACT “INITIATION OF FINE, DISCRETE SKILLED VOLUNTARY MOVEMENTS” RUBROSPINAL TRACT “ACCESSORY ROUTE FOR TRANSMISSION OF RELATIVELY DISCRETE SIGNALS FROM THE MOTOR CORTEX TO THE SPINAL CORD” VESTIBULOSPINAL TRACT “CONTROLS POSTURAL & RIGHTING REFLEXES” TECTOSPINAL TRACT “MEDIATE/FACILITATE TURNING OF THE HAD IN RESPONSE TO VISUAL OR AUDITORY STIMULI” RETICULOSPINAL TRACT 1. “INFLUENCE MOTOR FUNCTIONS AS VOLUNTARY AND REFLEX MOVEMENT” 2. “EXCITATORY OR INHIBITORY TO MUSCLE TONE” divo7 X X THANK YOU