Transcript THE MOTOR CORTEX AND CORTICOSPINAL TRACT

Central Nervous System
Dr. Mohammad Alzoghiabi
Organization of the Nervous System
 Central nervous system
1. Brain
2. Spinal cord
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1.
2.
3.
Peripheral nervous system
Sensory receptors
Sensory nerves
Ganglia
Central Nervous System
Functions:
 Has information about environment
 Organizes reflexes
 Plans & execute voluntary movement
 Memories, thinking & learning
Central Nervous System
 Types of nerves
1. Sensory or afferent division
2. Motor or efferent division
Spinal cord
 The most caudal portion of CNS
 From the base of the skull to 1st lumbar
vertebra
 Contain 31 pairs of spinal nerves
Spinal cord and nerves
 Sensory verves:
carry information to spinal cord from different
organs via dorsal root and cranial nerve ganglia
 Motor nerves:
carry information from spinal cord to periphery,
include both:
 Somatic
 Autonomic
Brain Stem
 Medulla
breathing, blood pressure, swallowing, coughing
and vomiting reflexes
 Pons
participates with medulla in regulating breathing
gets information from cerebral hemispheres to
cerebellum
 Midbrain
Controls eye movements
contains neucli of auditory and visual system
Cerebellum
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i.
ii.
iii.
iv.
Functions:
Coordination of movements
Planning and execution of movements
Maintenance of posture
Coordination of head and eye movements
Thalamus and Hypothalamus
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Thalamus
processes all sensory and motor informations
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4.
Hypothalamus
contains centers to regulate
Body temp
Water balance
Pituitary gland
ADH and oxytocin
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Known as Diencephalon “between brain”
1.
2.
3.
Motor Cortex
 Anterior to the central cortical sulcus
divided into:
1- primary motor cortex
2- premotor area
3- supplementary motor area
Primary Motor Area (MI)
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Right front of the central sulcus
Laterally in the sylvian fissure
Superiorly to the top of the brain
Inferiorly to the longitudinal fissure
Topographical representations of the body
areas in an inverted manner
Primary Motor Area (MI)
 Main origin of the pyramidal tract
 More than half of motor area concerned with
the hands and muscle of speech
 Excitation of a single motor neuron causes
the excitation of a specific pattern of
movement but not a single muscle
 Contains upper motorneurons which project
directly to spinal cord
 Lesion in MI leads to flaccid paralysis
Premotor Area
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Anterior to the primary motor cortex
Superiorly to the longitudinal fissure
Inferiorly to the sylvian fissure
Same topographical organization as the
motor cortex
 Responsible for more complex patterns of
movement
Supplementary Motor Area
 Has another topographic organization
 Contraction often bilateral
- bilateral grasping movements (climbing)
- attitudinal movements
- fixation movements
- positional movements of head and eyes
Other Motor Regions
 Bronca’s Area: responsible for vocalization
 Voluntary eye movement field:
controls the eye movement to certain
objects and blinking
 Head rotation area
 Area of hand skills
destruction  motor apraxia
White Matter of Spinal Cord
 Posterior faniculus
 Anterior faniculus
 Lateral faniculus
Tract:
Composed of nerve fibers sharing a
common origin, destination and functions
Posterior funiculus
 Contains one ascending fibers concerned with two
modalities
- kinesthesia
- discriminative touch
 Lesion of this area causes loss of:
- vibration sense
- position
- two point discrimination
- fine touch (tested by piece of cotton)
- weight perception
Lateral & Anterior funiculi
Ascending Tracts:
 Dorsal spinocerebral tract
 Ventral spinocerebellar tract
 Spinocervical thalamic tract
 Lateral spionothalamic tract
 Anterior spinothalamic tract
Lateral & Anterior funiculi
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Desending Tracts
Corticospinal tract
Rubrospinal tract
Lateral vestibulospinal tract
Medial vestibularspinal tract
Reticulospinal tract
Descending autonomic pathway
Ascending Tracts
 Dorsal spinocerebellar tract:
conveys impulses from muscle spindle, golgi
organ via (DRG) to cerebellum
 Ventral spinocerebellar tract:
conveys impulses to cerebellum from golgi
organ
Ascending Tracts
 Spinocervical thalamic tract:
conveys impulses to thalamus; carries the
kinesthesia & discriminative touch
 Laeral spinothalamic tract:
transmits pain & temperature sensations
to thalamus
 Anterior spinothalamic tract:
transmits light touch sensations to brain
stem & thalamus
Descending Tracts
1. Corticospinal tract (pyramidal)
 From motor cortex to medulla as follow:
 30% from the motor cortex to the muscles
 30% from the premotor and supplementary
cortex to the muscles
 40% from somatosensory areas
 divided into:
1. Crossed (lateral corticospinal tract)
2. Uncrossed fibers (anterior corticospinal tract)
Corticospinal Pathway (pyramidal)
 From the cortex internal capsule  thru
brain stem  via medulla where majority of
the fibers cross in the lower medulla  lateral
coticospinal tract of the cord  interneurons
(few in dorsal horn and very few in anterior
motor neurons)
 N.B. also a few of fibers do not cross but
pass ipsilaterally in ventral corticospinal tract
Corticospinal tract (pyramidal)
 3% of pyramidal fibers with 16 m myelinated
 Originate from betz cells in the motor area
 Impulses conveyed are facilitatory to flexor
motor neurons
 Terminates in internurons laminae IV-VII
 Lesion:
 Homolateral paralysis
 Contralateral paralysis
In addition to: spasticity, hyperactive myotatic
reflexes and clonus
Descending Tracts
2. Rubrospinal tract
 Neuronal origin is in red nucleus (midbrain)
 Terminates similarly as pyramidal tract
 Indirect corticospinal tract
 Facilitates flexor motor neurons
3. Lateral vestibulospinal tract
 Neuronal origin lie in pons (lateral vestibular
nucleus)
 Terminates at laminae VII & VIII
 Facilitates extensor motor neurons
Descending Tracts
4. Medial vestibularspinal tract:
 From media vestibular nucleus in pons
 Terminates as latera tract
 Facilitates flexor motor neurons
5. Reticulospinal tract:
a. pontine reticulospinal tract
from pons
terminates at laminae VII & VIII
facilitates extensor motor neurons
b. medullary reticulospinal tract
terminates at VII & IX
facilitates flexor motor neurons
Descending Tracts
6. Descending autonomic pathway:
 Neuronal origin at hypothalamus
 Small caliber fibers
 Project into intermediolateral of column