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Cortical Motor Areas & Descending Pathways
- 1. CORTICAL MOTOR CENTER AND DESCENDING PATHWAYS
- 2. At the end of the session, the group should be able: 1. identify the different cortical motor centers and discuss their role in the control of movement and posture, 2. trace the corticospinal tract from the cerebral cortex to the motor neuron in the spinal cord, 3. explain the major function of the corticospinal tract as a direct activation pathway of the motor system in posture and movement, 4. describe the other descending tracts constituting the indirect activation pathway to the spinal cord, particularly the rubrospinal, reticulospinal, tectospinal and vestibulospinal tracts, 5. explain the role of the different tracts of the indirect activation pathway listed above in the execution of movement and maintenance of posture and; 6. differentiate between the clinical manifestations of upper motor neuron lesions and those of lower motor neuron lesions.
- 7. ATTENTION PLANNING DECISION MAKING PACQUIAO IN NEUROSCIENCE SKILLED MOVEMENTS POSTURAL ADJUSTMENTS
- 12. PRIMARY CORTEX AREA( M1) Located in the anterior lip of the central sulcus(fissure of Rolando)/pre-central gyrus Critical for the control of fractionated movements of the fingers and the recruitment of motor neurons for increasing force.
- 13. BETZ CELL Pyramidal cell Upper motor neuron that send their axons down to the spinal cord
- 17. NON-PRIMARY MOTOR AREA Includes the lateral pre- motor area and supplementary motor area Involved in visually guided movements, planning and programming motor movements
- 20. ANTERIOR CINGULATE MOTOR AREA Involved in motor responses initiated by emotional motivational cues.
- 24. Overview of motor pathway
- 25. MOTOR NEURONS 1. UPPER MOTOR NEURON 2. LOWER MOTOR NEURON UMN LMN Alpha motor neurons (α-MNs) Gamma motor neurons (γ-MNs)
- 27. MOTOR CONTROL
- 31. CORTICOSPINAL TRACT Travels from the cerebral cortex down to the spinal cord. CST actually consists of two separate tracts in the spinal cord: the lateral corticospinal tract and the anterior corticospinal tract. Contains mostly motor axons. Lateral CST Anterior CST
- 36. TRACT
- 41. RUBROSPINAL TRACT • Travels from the cerebral cortex down to the spinal cord via the red nucleus. • Its main role is the mediation of voluntary movement. It is responsible for large muscle movement such as the arms and the legs as well as for fine motor control. It facilitates the flexion and inhibits the extension in the upper extremities
- 44. TECTOSPINAL TRACT • The superior colliculus, located in the tectum of the midbrain. • It is involved with conjugated movements of the head, eyes and limbs toward contralateral space.
- 48. VESTIBULOSPINAL TRACT • Inputs originate from the labyrinthine system via the vestibular nerve and from the cerebellum. • The lateral vestibular nucleus give rise to the lateral vestibulospinal tract. • The medial and inferior vestibular nuclei give rise to the medial vestibulospinal tract. V
- 49. LATERAL VESTIBULOSPINAL TRACT MAINTENANCE OF POSTURE
- 51. RETICULOSPINAL TRACT • The tract is divided into two parts, the medial (or pontine -nuclei reticularis pontis caudalis ) and lateral (or medullary-nucleus reticularis gigantocellularis) reticulospinal tracts (MRST and LRST). • 1. Integrates information from the motor systems to coordinate automatic movements of locomotion and posture. • 2. Facilitates and inhibits voluntary movement, influences muscle tone. P M
- 56. DESCENDING PATHWAY LESIONS • An upper motor neuron lesion is a lesion of the neural pathway above the anterior horn cell or motor nuclei of the cranial nerves. • lower motor neuron lesion, which affects nerve fibers travelling from the anterior horn of the spinal cord to the relevant muscle(s). • Upper motor neuron lesions are indicated by: • Spasticity, increase in tone in the extensor muscles (lower limbs) or flexor muscles (upper limbs) • Clasp-knife response where initial resistance to movement is followed by relaxation • Weakness in the flexors (lower limbs) or extensors (upper limbs), but no muscle wasting • Increase Deep tendon reflex (DTR) • Presence of Babinski sign
- 57. • Damage to lower motor neurons, lower motor neurone lesions (LMNL) causes: • Decreased tone • Decreased strength And: • Decreased reflexes in affected areas. • These findings are in contrast to findings in upper motor neurone lesions. • LMNL is indicated by: • Abnormal EMG potentials, fasciculations, paralysis, weakening of muscles, and neurogenic atrophy of skeletal muscle.
- 59. At the end of the session, the group should be able: 1. identify the different cortical motor centers and discuss their role in the control of movement and posture, 2. trace the corticospinal tract from the cerebral cortex to the motor neuron in the spinal cord, 3. explain the major function of the corticospinal tract as a direct activation pathway of the motor system in posture and movement, 4. describe the other descending tracts constituting the indirect activation pathway to the spinal cord, particularly the rubrospinal, reticulospinal, tectospinal and vestibulospinal tracts, 5. explain the role of the different tracts of the indirect activation pathway listed above in the execution of movement and maintenance of posture and; 6. differentiate between the clinical manifestations of upper motor neuron lesions and those of lower motor neuron lesions.
Editor's Notes
- Movements are the major way in which humans interact with the world. Most activities— including running, reaching, eating, talking, writing, and reading—ultimately involve motor acts. Thus motor control is a major task of the central nervous system (CNS), and from an evolutionary perspective, it is probably the reason that nervous systems first arose. Not surprisingly, a large amount of the CNS is devoted to motor control, which can be defined as the generation of signals to coordinate contraction of the musculature of the body and head, either to maintain a posture or to make a movement (transition between two postures).
- Immediately rostral to the lateral premotor area is the frontal eye field (area 8),which contains neurons involved in the generation of spontaneous and visually guided rapid eye movements called saccades
- the main contributor to generating neural impulses that pass down to the spinal cord and control the execution of movement.
- Nerve fibres in the corticospinal tract originate from pyramidal cells in layer V of the cerebral cortex. Fibres arise from the primary motor cortex (about 30%), supplementary motor area and the premotor cortex (together also about 30%), and the somatosensory cortex, parietal lobe, and cingulate gyrus supplies the rest
- The powerful direct cortical projections from the primary motor cortex to the motor neurons that innervate the distal muscles allow individual movements of the digits.
- .The head area is located above the fissure of Sylvius, the representation of the upper extremity is next (with the thumb and index finger in proximity to the face),the trunk is interposed between the shoulder and hip areas high on the convexity of the hemisphere,and the lower limb area extends onto the paracentral lobule in the longitudinal fissure.The size of the cortical representation varies with the functional importance and dexterity of the part represented.Thus,the lips,jaw,thumb,and index finger each have a large representation;the forehead,trunk,and proximal portions of the limbs have a small one.Input from different neurons within specific territories (face,arm, leg) of the primary motor cortex converge in the spinal cordtocontrol individual motor units,and individual cortical neurons within each territory project to motor neurons that innervate different but functionally related muscles.An important feature of the motor (as well as thesensory)cortexis the plasticityof cortical representation:thearearepresentingagivenareaofthebody maybeenlargedorreducedinresponsetoinjuryor acquisition of specific motor skills.
- visually guided movements like reaching ang grasping We have the ability to prepare for the next movements before it occurs
- The lateral premotor cortex, supplementary motor area ,and primary motor cortex receive input from the parietal lobe and participate in programming and executing movements in response to sensory stimuli. The supplementary motor area, through the pre-supplementary motor area ,and the anterior cingulate motor cortex receive input from the prefrontal cortex and are involved in planning and programming goal- or emotion-driven movements .By way of the thalamus ,all cortical motor areas receive inputs from the ipsilateral basal ganglia and contralateral cerebellum.
- Hierarchical: 3 major types Reflexes Spinal cord circuits Postural adjustments Spinal & Brain stem Voluntary movements Spinal cord, Brain stem, and cortex
- Upper motor neurons originate in the motor region of the cerebral cortex of the brain stem and carry motor information down to the final common pathway, that is, any motor neurons that are not directly responsible for stimulating the target muscle. Lower motor neurons (LMNs) are the motor neurons connecting the brainstem and spinal cord to muscle fibers, transmitting nerve impulses from the upper motor neurons to the muscles. A lower motor neuron's axon terminates on an effector (muscle). Lower motor neurons are classified based on the type of muscle fibre they innervate: Alpha motor neurons (α-MNs) innervate extrafusal muscle fibers, the most numerous type of muscle fibre and the one involved in muscle contraction. Gamma motor neurons (γ-MNs) innervate intrafusal muscle fibers, which together with sensory afferents compose muscle spindles. These are part of the system for sensing body position (proprioception).
- DP- is monosynaptic IP- multisynaptic
- Pyramidal tracts – These tracts originate in the cerebral cortex, carrying motor fibres to the spinal cord and brain stem. They are responsible for the voluntary control of the musculature of the body and face. Extrapyramidal tracts – These tracts originate in the brain stem, carrying motor fibres to the spinal cord. They are responsible for the involuntary and automatic control of all musculature, such as muscle tone, balance, posture and locomotion
- The TRACT is a bundle of nerve fibers (within CNS) having the same origin, course, destination & function The name of the tract indicates the origin and destination of its fibers The axons within each tract are grouped according to the body region innervated
- The corticospinal tracts begin in the cerebral cortex, from which they receive a range of inputs: Primary motor cortex Premotor cortex Supplementary motor area
- Concerned with voluntary, discrete, skilled movements, especially those of distal parts of the limbs (fractionated movements
- The corticobulbar tracts arise from the lateral aspect of the primary motor cortex. They receive the same inputs as the corticospinal tracts. The fibres converge and pass through the internal capsule to the brainstem
- Transmit motor information to control: eye movements (via CN III, IV, and VI) cranial, facial, pharyngeal, and laryngeal muscles (via CN V, VII, IX, and X) some superficial muscles of the back and neck (via CN XI) intrinsic and extrinsic tongue muscles (via CN XII)
- Axons course ventro-medially, cross in ventral tegmental decussation, descend in spinal cord ventral to the lateral corticospinal tract. The movement is not discrete as compare to the corticospinal tract
- Rubrospinal neurons receive both direct excitatory and indirect inhibitory (via interneurons) inputs from the motor cortex.
- It receives input from the frontal eye fields and visual and motor cortices and participates in orienting responses.
- Axons course ventro-medially around the periaqueductal gray matter, cross in dorsal tegmental decussation, descend in spinal cord near the ventral median fissure, terminate mainly in cervical segments
- The superior colliculus is the source of the crossed tectospinal tract, which projects primarily to the cervical segments ,synapsing on motor neurons that control neck movements , and to areas of the reticular formation that control eye movements. Rubrospinal and tectospinal pathways (both are bilateral ,but are shown unilaterally).The rubrospinal tract arises in the red nucleus on the opposite side and reaches the cervical spinal cord to activate flexor movements of the arm. The tectospinal tract arises in the contralateral superior colliculus and ,together with the medial vestibulospinal tract (not shown),coordinates movements of the head with those of the eyes.
- located in the dorsolateral portion of the medulla and pons( receives little input from the cerebral cortex)
- axons descend uncrossed through medulla and through the length of spinal cord. The lateral vestibulospinal tract arises in the lateral vestibular nucleus, which receives inputs from the labyrinth, cerebellum, and neck proprioceptors, but not the cerebral cortex. This pathway descends in the anterior quadrant of the spinal cord and activates extensor reflexes necessary for maintaining posture w/c keep the body upright against the pull of gravity.
- Axons descend bilaterally in the ventral funiculus(only in cervical and thoracic region), with the medial longitudinal fasciculus (which descends together with the tectospinal tract in the ventral quadrant of the spinal cord to synapse on motor neurons that control the neck muscles).
- involved in control of breathing
- The pontine reticular formation gives rise to the medial (pontine) reticulospinal tract, which descends ipsilaterally in the ventral portion of the spinal cord. The medullary reticular formation gives rise to the lateral reticulospinal tract and dorsolateral reticulospinal tract, which occupy the lateral portions of the spinal cord.