[SB3] IBS_PHYSIOLOGY_ Spinal Cord Motor Functions (09_11_2024).pdf

PHYSIOLOGY LECTURE | NEURO MODULE Spinal Cord Motor Functions & Cortical and Brain Stem Control of Motor Function DR. MARK DENEB ARMEÑA | 09/11/2024 |...

PHYSIOLOGY LECTURE | NEURO MODULE Spinal Cord Motor Functions & Cortical and Brain Stem Control of Motor Function DR. MARK DENEB ARMEÑA | 09/11/2024 | A. TYPES OF NEURONS TOPIC OUTLINE ANTERIOR MOTOR NEURON Located in anterior horns of gray matter I. Organization of the Spinal VI. Reflexes of Posture and 50 - 100% larger than most other neurons Cord for Motor Functions Locomotion Give rise to other nerve fibers A. Types of Neurons A. Postural and → Leave the cord via the anterior root II. Muscle Spindles Locomotive Reflexes of → Directly innervate the skeletal muscle fibers A. Receptor Function the Cord 2 Types of Anterior Motor Neurons: of the Muscle B. Stepping and Walking → Alpha Motor Neurons Spindle Movements Give rise to larger, Type Aα motor nerve fibers B. Muscle Stretch C. Scratch Reflex ○ Larger neuron size, faster impulse velocity. Reflex D. Autonomic Reflexes in Innervate the large skeletal muscle fibers directly C. Role of the Muscle the Spinal Cord Stimulation of a single fiber excites 3 to 100+ skeletal Spindle In Voluntary E. Spinal Shock fibers (Motor Unit) Motor Activity → Gamma Motor Neurons D. Clinical Application VII. Cortical and Brain Stem Located in the SC anterior horns III. Golgi Tendon Reflex Control of Motor Function Transmit impulses through smaller, Type Aγ motor A. Transmission of A. Motor Cortex and nerve fibers to intrafusal fibers (small, special skeletal Impulses Corticospinal Tract muscle fiber) B. Function 1. Primary Motor ○ Example of intrafusal fiber: Golgi tendon IV. Flexor Reflex and the Cortex Withdrawal Reflexes 2. Premotor Area A. Neuronal 3. Supplementary Mechanism of the Motor Area Flexor Reflex B. Specialized Area of B. Pattern of Motor Control Withdrawal During VIII. Transmission of Signal Flexor Reflex From the Motor Cortex to V. Crossed Extensor Reflex Muscles A. Neuronal A. Corticospinal Tract Mechanism B. Other Pathways from B. Reciprocal Inhibition Motor Cortex and Reciprocal IX. Red Nucleus Innervation X. Brain Stem XI. Vestibular Apparatus XII. References Figure 2. Sensory fibers and anterior motor neurons I. ORGANIZATION OF THE SPINAL CORD FOR MOTOR FUNCTION INTERNEURON 💬 Gray matter Present in all areas of the cord gray matter: butterfly H-shaped → Dorsal horns → Integrative area for the cord reflexes → Anterior horns → Path of sensory signals: → The intermediate areas between the dorsal and anterior horns Posterior/Dorsal root of the spinal cord (SC) 30x as numerous as the anterior motor neuron Two separate branches: Small, highly excitable ○ One terminates immediately in the gray matter → → Exhibits spontaneous activity Elicits local segmental cord reflexes and other → Capable of firing as rapidly as 1500x per second local effects Interconnections ○ Another transmits signals to higher levels of → Responsible for most of SC integrative function nervous system: Types of circuits found in interneurons: ○ Spinal Cord (SC), brain stem (BS), or cortex. → Diverging → Converging → Repetitive-discharge → Other types of circuits Connect one neuron to another OTHER TYPES Renshaw Cells → Large number of small neurons → Located in the anterior horns of the SC → In close association with the motor neurons → Inhibitory cells Transmits inhibitory signals to the surrounding motor neurons 💬spinal cord fine tunes movements Figure 1. Neurons of Spinal Cord → Lateral Inhibition Prepared by: SGD B3 | Mariscotes | Mesa | Ponce | Pron | Quimson | Rabadam | Ravalo | Reyes | Romasanta | Samarita | Silerio | PAGE 1 of 1 Tercero | Valenzuela | Yongco PHYSIOLOGY | LEC 3 Spinal Cord Motor Functions & Cortical and Brain Stem Control of Motor Function | Dr. Mark Deneb Armeña A stimulation of a motor neuron inhibits adjacent motor → Encircles the central portion of each intrafusal fiber neurons → Type la Fiber → Serves to focus/sharpen the signals 17 μm in diameter (average) Similar to sensory system principle Large size, large diameter, faster velocity; faster if ○ Allow unabated transmission of primary signal in myelinated desired direction → Transmits sensory signals to the SC at a velocity of 70–120 ○ Suppresses tendency for signals to spread laterally m/s, as rapidly as any type of nerve fiber in the entire body Propriospinal Fibers Secondary Ending → Run from one segment of the cord to another → Two smaller sensory nerve fibers → Sensory fibers → Type lI fibers Enter from posterior cord 8 μm in diameter (average) Bifurcate → Innervate the receptor region on one or both sides of the Branch both up and down the SC primary ending Some branches transmit signals to only one segment or → Sometimes encircles the intrafusal fibers in the same way that two and others transmit signals to many segments the Type la fiber does but often it spreads like branches on a → Provide pathways for the multi-segmental reflexes bush Includes reflexes that coordinate simultaneous TYPES OF INTRAFUSAL FIBERS movements in the forelimbs and hindlimbs Nuclear Bag Muscle Fibers II. MUSCLE SPINDLES → 1 – 3 in each spindle Requirements for proper control of muscle fibers: → Several muscle fiber nuclei are congregated in expanded → Excitation of muscle themselves “bags” in the central portion of receptor area → Continuous feedback of sensory info via sensory receptors → Excites the primary sensory nerve ending ONLY Table 1.Comparison of Muscle Sensory Receptors Nuclear chain fibers → 3 – 9 in each spindle Muscle Spindle Golgi Tendon Organs → About half as large in diameter and length as nuclear bag fibers Distributed throughout Located in the muscle tendons → Nuclei aligned in a chain throughout receptor area belly of muscle Transmit info about tendon → Excites BOTH primary and secondary sensory nerve ending Send information to the tension or rate of change of nervous system about tension muscle length or rate of change A. RECEPTOR FUNCTION OF THE MUSCLE SPINDLE SENSORY INNERVATION OF MUSCLE SPINDLES 📖 Muscle spindle 📖📖 Built around 3 to 12 intrafusal muscle fibers Pointed at their ends Attached to glycocalyx of surrounding larger extrafusal muscle fibers → Central portion Receptor portion of the muscle spindle Central portion of intrafusal fibers has few to no actin and Figure 4. Nuclear bag and chains myosin filaments and does not contract; only ends contract STATIC AND DYNAMIC RESPONSES Stimulated by stretching of the spindle’s midportion Static Response 2 ways on how muscle spindles are excited: → Response of both the primary and secondary endings to → (1) Lengthening the whole muscle → Stretches the the receptor length midportion of spindle → Excites receptor → Whole stretches → Receptor portion of muscle spindle is stretched slowly → → (2) Contraction of the end portions of the spindle's Number of impulses transmitted from both endings increases intrafusal fibers → Stretches the midportion of the spindle → almost directly in proportion to degree of stretching →If the Excites receptor →Length of entire muscle may not change → muscle spindle is remains stretched: Periphery changes primary and secondary endings continue to transmit signals at least several minutes Dynamic Response → Response of the primary ending ONLY to the rate of change of receptor length 📖 Extremely active response Primary ending sends extremely strong, either positive or negative, signals to the spinal cord to apprise it of any change in length of the spindle receptor →Sudden increase in receptor length (even for a fraction of a micrometer for a fraction of a second) →Powerful stimulation of the primary ending → Primary endings transmit numerous excess impulses to the large 17μm sensory nerve fiber Exactly opposite sensory signals occur when the spindle 📖 receptor shortens Only occurs while the length is actually increasing ○ Length of the spindle receptor increases suddenly, Figure 3. Muscle spindle the primary ending (but not the secondary ending) is stimulated powerfully. TYPES OF SENSORY ENDINGS ○ When the spindle receptor shortens, exactly Primary Ending (Annulospiral Ending) opposite sensory signals occur. → Large sensory nerve fiber PHYSIOLOGY Spinal Cord Motor Functions Spinal Cord Motor Functions & Cortical and Brain Stem Control of PAGE 2 of 10 Motor Function PHYSIOLOGY | LEC 3 Spinal Cord Motor Functions & Cortical and Brain Stem Control of Motor Function | Dr. Mark Deneb Armeña ○ As soon as length stops increasing, extra rate of DAMPING MECHANISM discharge returns to the level of the much smaller “Smoothing” static response 💬 → Ability to prevent oscillation or jerkiness of body movements GAMMA MOTOR NERVES for fine tuning For the control of static and dynamic response intensity → Curve A Table 2. Comparison of Gamma Motor Nerves Graphically demonstrates the damping mechanism’s ability to smooth muscle contractions Gamma-dynamic (gamma-d) Gamma-static (gamma-s) Primary input signals to the muscle motor system may themselves be jerky Excites mainly the nuclear bag Excites mainly the nuclear intrafusal fibers chain intrafusal fiber Effect can also be called a signal averaging function of the muscle Dynamic response of muscle Static response enhanced spindle reflex spindle tremendously Dynamic response hardly enhanced affected Static response hardly affected CONTINUOUS DISCHARGE OF MUSCLE SPINDLES UNDER NORMAL CONDITIONS Gamma nerve excitation → Muscle spindles emit sensory nerve impulses continuously Muscle spindles stretching → Increases in the rate of firing Positive signals Figure 6. Muscle contraction in Curves A and B Muscle spindle shortening → Decrease in the rate of firing C. ROLE OF MUSCLE SPINDLES IN VOLUNTARY MOTOR Negative signals ACTIVITY B. MUSCLE STRETCH REFLEX (MSR) CO- ACTIVATION Muscle is stretched suddenly Gamma motor neurons are simultaneously activated when signals → Excitation of spindles → Reflex contraction of large skeletal are transmitted from the motor cortex or any other area of the brain to muscle fibers → Stretched muscle and closely allied the alpha motor neurons synergistic muscles affected Causes both extrafusal skeletal muscle fibers and the muscle spindle → E.g. biceps and triceps intrafusal muscle fibers to contract at the same time Purposes: NEURONAL CIRCUITRY 📖 Monosynaptic pathway → Type 1a proprioceptor from the muscle spindle → Keeps muscle spindle reflex from opposing muscle contraction → Maintains proper damping function of the muscle spindle, → Enters dorsal root 💬 regardless of any change in muscle length → Goes to anterior horn of gray matter and synapses with flex biceps while triceps antagonize anterior motor neurons BULBORETICULAR SYSTEM → Send signals to motor fibers back to the same muscle from Region in the brainstem that excites the gamma efferent system which muscle spindle fiber originated Secondarily receives impulses from the ff.: → Shortest possible time → Cerebellum 📖 → No delay → Basal ganglia Type 2 proprioceptors terminate on multiple interneurons in gray → Cortex matter which delays signal to anterior motor neurons Concerned with antigravity contractions → Antigravity muscles are mostly made up of muscle spindle fibers → Antigravity muscle movements are important for damping movements such as walking and running D. CLINICAL APPLICATION KNEE JERK REFLEX Done by tapping the patellar tendon using a reflex hammer Instantaneously stretches the quadriceps muscle and excites a dynamic stretch reflex that causes the lower leg to “jerk” forward Sudden stretch of muscle spindles → Requirement to elicit a dynamic stretch reflex Most frequently used in determining the presence or absence of Figure 5. Neuronal circuit of stretch reflex muscle spasticity caused by: COMPONENTS OF MSR → Lesions in motor areas of the brain → Diseases that excite the bulboreticular facilitatory area of the DYNAMIC STRETCH REFLEX brain stem Elicited by the potent dynamic signal transmitted from primary sensory endings of muscle spindles Caused by rapid stretch or unstretch When a muscle is suddenly stretched or unstretched, a strong signal is transmitted to the spinal cord → Instantaneous strong reflex contraction (or decrease in contraction) of same muscle from which the signal originated Reflex functions to oppose sudden changes in muscle length STATIC STRETCH REFLEX Elicited by continuous static receptor signals transmitted by both primary and secondary endings Causes the degree of muscle contraction to remain reasonably constant except when NS wills otherwise Figure 7. Myograms from knee jerk PHYSIOLOGY Spinal Cord Motor Functions Spinal Cord Motor Functions & Cortical and Brain Stem Control of PAGE 3 of 10 Motor Function PHYSIOLOGY | LEC 3 Spinal Cord Motor Functions & Cortical and Brain Stem Control of Motor Function | Dr. Mark Deneb Armeña CLONUS Oscillation of muscle jerks Occurs only when stretch reflex is highly sensitized by facilitatory impulses from the brain Example: Decerebrate Posture 💬 low GCS score → Stretch reflexes are highly facilitated; clonus develops readily Determining the degree of facilitation of SC → Neurologists test patients for clonus by suddenly stretching a muscle and applying a steady stretching force to it Clonus occurs 💬 → Degree of facilitation is certain to be high Decorticate position → seen in elderly and fetus Figure 9. Golgi Tendon Reflex IV. FLEXOR REFLEX AND THE WITHDRAWAL REFLEXES FLEXOR REFLEX → Flexor muscles of the limb contract when a cutaneous sensory stimuli is applied in a decerebrate individual. → Elicited most powerfully by stimulation of pain endings. E.g. pinprick, heat, wound, nociceptive reflex or pain reflex → Stimulation of touch receptors can also elicit a weaker and less prolonged flexor reflex. Figure 8. Decerebrate Posturing WITHDRAWAL REFLEX III. GOLGI TENDON REFLEX → Elicited if some part of the body other than one of the limbs is A. TRANSMISSION OF IMPULSES painfully stimulated Exhibited by the golgi tendon organ → Encapsulated sensory receptor → Body parts will similarly be withdrawn from the stimulus. → Provides the nervous system with instantaneous information → Reflex may not be confined to flexor muscles on the degree of tension in each small segment of each A. NEURONAL MECHANISM OF THE FLEXOR REFLEX muscle Table 3. Major Differences in Excitation of Golgi Tendon vs. Muscle Spindle Golgi Tendon Muscle Spindle Detects muscle tension as Detects muscle length and reflected by the tension in changes in muscle length itself Signals from tendon organ are transmitted through large, rapidly conducting type 1b nerve fibers Via spinocerebellar tract pathway → Local cord signal excites a single inhibitory interneuron that inhibits the anterior motor neuron 💬 Exhibits negative feedback mechanism (especially during increase in tension) seen on weightlifters LENGTHENING REACTION Inhibitory effect observed in muscle and tendon when tension is stimulated at extreme levels Instantaneous relaxation of the muscles Prevents excessive tension in the muscles Figure 10. Flexor reflex, crossed extensor reflex, and reciprocal EQUALIZING FORCE inhibition Golgi tendon organs equalize contractile forces through the following The left-hand portion of Figure 10 shows the neuronal pathways mechanisms: → Inhibition of muscle fibers that exert excess tension for the flexor reflex. → Excitation of muscle fibers that exert too little tension → Painful stimulus is applied to the hand, causing the upper Prevents overloading areas of muscles arm's flexor muscles to become excited and withdraw the B. FUNCTION hand from the painful stimulus. Muscle spindles and Golgi tendon Pattern of Withdrawal During Flexor Reflex [Guyton and Hall, → control of high motor function 2017] → apprise the higher motor control centers Withdrawal that results when the flexor reflex is elicited depends → Golgi tendon organs direct sensation to the cerebellum at on which sensory nerve is stimulated conduction velocities approaching → E.g. Painful stimulus on the inward of arm not only contracts 120 m/sec, the most rapid conduction anywhere in the brain flexor muscles but also the abductor muscles to pull arm outward or spinal cord. Integrative centers contract muscles that most effectively remove the pained part from the stimulus → Occurs on any part of body but most applicable to highly developed limb PHYSIOLOGY Spinal Cord Motor Functions Spinal Cord Motor Functions & Cortical and Brain Stem Control of PAGE 4 of 10 Motor Function PHYSIOLOGY | LEC 3 Spinal Cord Motor Functions & Cortical and Brain Stem Control of Motor Function | Dr. Mark Deneb Armeña 📖 Basic types of circuits involved: → Neuronal circuit that causes this reciprocal relation. → Diverging circuits Reciprocal relations often exist between the muscles on the two spread the reflex to the necessary muscles for sides of the body withdrawal → exemplified by the flexor and extensor muscle reflexes → Reciprocal inhibition circuits inhibit the antagonist muscles → Circuits to cause afterdischarge lasting many fractions of a second after the stimulus is over. Figure 13. Myogram of a flexor reflex showing reciprocal inhibition caused by an inhibitory stimulus from a stronger flexor reflex on the opposite side of the body. A moderate but prolonged flexor reflex is elicited from one limb of the body; while this reflex is still being elicited, a stronger flexor reflex is elicited in the limb on the opposite side of the Figure 11. Myogram of the flexor reflex showing rapid onset of the body. reflex, an interval of fatigue and, finally, afterdischarge after the input stimulus is over. VII. REFLEXES OF POSTURE AND LOCOMOTION A. POSTURAL AND LOCOMOTIVE REFLEXES OF THE CORD → Flexor is appropriately organized to withdraw a pained or Positive Supportive Reaction otherwise irritated part of the body from a stimulus. → The duration of afterdischarge depends on the intensity of the Pressure on the footpad of a decerebrate animal causes the limb to sensory stimulus that elicited the reflex extend against the pressure applied to the foot. → Because of afterdischarge, the reflex can hold the irritated Involves a complex circuit in the interneurons similar to the circuits part away from the stimulus for 0.1 to 3 seconds after the responsible for the flexor and cross extensor reflexes irritation is over. Magnet Reflexes → During this time, other reflexes and actions of the central → Pressure on one side causes extension in that direction nervous system can move the entire body away from the CORD “RIGHTING” REFLEXES painful stimulus. When a spinal animal is laid on its side, it will make uncoordinated V. CROSSED EXTENSOR REFLEX movements trying to raise itself to the standing position. A. NEURONAL MECHANISM Demonstrates that some relatively complex reflexes associated with posture are integrated in the spinal cord → Occurs after a stimulus elicits a flexor reflex in one limb, the opposite limb begins to extend. (about 0.2 to 0.5 second) B. STEPPING AND WALKING MOVEMENTS → The extension of the opposite limb can push the entire body RHYTHMICAL STEPPING MOVEMENTS OF A SINGLE LIMB away from an object. Each hindlimb can still perform individual stepping functions even → Many interneurons are involved in the circuit between the when the lumbar portion of the spinal cord is separated from the incoming sensory neuron and the motor neurons of the remainder of the cord to block neuronal connections between the opposite side of the cord responsible for the crossed two sides of the cord and between the two limbs. extension. Forward flexion of the limb is followed by a second or so later by → Longer period of afterdischarge than does the flexor reflex. backward flexion. → Presumably, prolonged afterdischarge results from STUMBLE REFLEX reverberating circuits among the interneuronal cells. Elicited when the foot encounters an obstruction during forward thrust → forward thrust will stop temporarily → (rapid succession) foot will be lifted higher → proceed forward to be placed over the obstruction. RECIPROCAL STEPPING OF OPPOSITE LIMBS If the lumbar bar spinal cord is not split down its center → Every time stepping occurs in the forward direction in one limb, the opposite moves backwards → Results from reciprocal innervation between the two limbs. DIAGONAL STEPPING OF ALL FOUR LIMBS — “MARK TIME” REFLEX Figure 12..Myogram of a crossed extensor reflex showing slow onset Walking pattern where stepping occurs diagonally between the but prolonged afterdischarge. forelimbs and hindlimbs Animals held up from the floor and its legs are allowed to dangle → Relatively long latency before reflex begins and the long → stretch on the limbs occasionally elicits stepping reflexes that afterdischarge at the end of the stimulus. involve all four limbs. → Prolonged afterdischarge is of benefit in holding the pained Involves diagonal coordination of fore and hind limbs area of the body away from the painful object until other Example: The air paddling mechanisms of dogs whenever their pet nervous reactions cause the entire body to move away. owners lift them on their torso and hold them above the water B. RECIPROCAL INHIBITION AND RECIPROCAL INNERVATION surface. GALLOPING REFLEX RECIPROCAL INHIBITION Both forelimbs move backward in unison while both hind limbs → When a stretch reflex excites one muscle, it often move forward simultaneously inhibits the antagonist muscles. Occurs when almost equal stretch or pressure stimuli are applied to the limbs on both sides of the body at the same time. RECIPROCAL INNERVATION Unequal stimulation elicits the diagonal walking reflex PHYSIOLOGY Spinal Cord Motor Functions Spinal Cord Motor Functions & Cortical and Brain Stem Control of PAGE 5 of 10 Motor Function PHYSIOLOGY | LEC 3 Spinal Cord Motor Functions & Cortical and Brain Stem Control of Motor Function | Dr. Mark Deneb Armeña Forelimb stimulation=Hindlimb stimulation → (3) The arterial pressure often rises to maximal values, → When the animal strikes the ground during galloping sometimes to a SBP well over 200 mmHg, C. SCRATCH REFLEX → (4) Large areas of the body break out into profuse sweating. Initiated by itch or tickle sensation Two functions: F. SPINAL CORD TRANSECTION AND SPINAL SHOCK → (1) A positive sense that allows the paw to find the point of Reaction that happens when the spinal cord is suddenly irritation on the surface of the body transected. ◆ Highly developed function All cord functions, including the cord reflexes, immediately become ◆ Example: Flea on the shoulder. Hind paw can locate a depressed to the point of total silence. flea’s position and it requires precise contraction of 19 muscles simultaneously. Effects Of Spinal Shock On Spinal Cord Functions → (2) To-and-fro scratching movement → (1) At onset of spinal shock, the arterial BP falls instantly and ◆ Stepping movements of locomotion involves reciprocal drastically to as low as 40 mmHg innervation circuits that cause oscillation. → (2) Skeletal muscle reflexes integrated in the cord are blocked. D. SPINAL CORD REFLEXES THAT → (3) Sacral reflexes such as bowel and bladder control are CAUSE MUSCLE SPASM suppressed. In many instances, localized pain is the cause of local spasm. MUSCLE SPASM RESULTING FROM A BROKEN BONE VII. CORTICAL AND BRAIN STEM CONTROL OF MOTOR Occurs in muscles surrounding the fracture FUNCTION Spasm results from pain impulses initiated from broken bone Most “voluntary” movements initiated by the cerebral cortex are edges, which cause the muscles that surround the area to achieved when the cortex activates “patterns” of function stored in contract tonically. lower brain areas - the cord, brain stem, basal ganglia, and Pain relief methods: cerebellum. → Local anesthesia at the broken bone edges These lower centers, in turn, send specific control functions to the → Deep general anesthetic (e.g. ether anesthesia) muscles. ABDOMINAL MUSCLE SPASM IN PERSONS WITH PERITONITIS A. MOTOR CORTEX AND CORTICOSPINAL TRACT Caused by irritation of the parietal peritoneum by peritonitis. Contains 3 subareas Relevance in surgical procedures: → (1) The Primary Motor Cortex → Can complicate abdominal surgeries as pain impulses from → (2) The Premotor Areas parietal peritoneum cause abdominal muscles to contract → (3) The Supplementary Motor Area extensively. → May cause intestinal extrusion through surgical wounds THE PRIMARY MOTOR CORTEX → Necessitates deep anesthesia for intra-abdominal operations Lies in first convolution of frontal lobes anterior to central sulcus. MUSCLE CRAMPS One half of the entire primary motor cortex is concerned with Mechanism: controlling the muscle of the hands and the muscles of speech. → (1) Initial sensory signals sent to spinal cord Point stimulation in these hand and speech motor areas on rare → (2) Reflex feedback causes muscle contraction occasion causes contraction of a single muscle; → (3) Contraction stimulates more sensory receptors Stimulation contracts a group of muscles instead. → (4) Positive feedback loop develops, wherein a small amount of initial irritation causes more and more contraction until a full-blown cramp ensues. Triggers: → Local irritating factor → Metabolic abnormality of a muscle → Examples: severe cold, lack of blood flow, overexercise E. AUTONOMIC REFLEXES IN THE SPINAL CORD (1) Changes in vascular tone resulting from changes in local skin heat. (2) Sweating, which results from localized heat on the surface of the body. (3) Intestinal reflexes that control some motor functions of the gut. (4) Peritoneo-intestinal reflexes that inhibit gastrointestinal motility in response to peritoneal irritation. (5) Evacuation reflexes for emptying the full bladder or the colon. Figure 14. Degree of representation of the different muscles of the body in the motor cortex. (Modified from Penfield W, Rasmussen T: MASS REFLEX The Cerebral Cortex of Man: A Clinical Study of Localization of Excessive activity of the spinal cord causing massive discharge of Function. New York: Hafner, 1968.) impulses. Usual cause: strong pain stimulus to the skin or excessive filling of THE PREMOTOR AREA a viscus, such as overdistention of the bladder or the gut. Lies 1-3 cm anterior to the primary motor cortex Characteristics: Extends inferiorly into the sylvian fissure and superiorly into the ➔ Can last for minutes longitudinal fissure ➔ Involves activation of numerous reverberating circuits Mouth and Face areas located most laterally ➔ Similar mechanism to epileptic seizures, but in spinal cord As one moves upward, the hand, arm, trunk, and leg areas are Effects: encountered. → (1) Strong flexor spasm of skeletal muscles. Nerve signals generated in the premotor area cause much more → (2) The colon and bladder are likely to evacuate; complex “patterns” of movement than the discrete patterns generated in the primary motor cortex, PHYSIOLOGY Spinal Cord Motor Functions Spinal Cord Motor Functions & Cortical and Brain Stem Control of PAGE 6 of 10 Motor Function PHYSIOLOGY | LEC 3 Spinal Cord Motor Functions & Cortical and Brain Stem Control of Motor Function | Dr. Mark Deneb Armeña MIRROR NEURONS → Special class of neurons that become active when a person performs a specific motor task or when he or she observes the same task performed by others. → Important for understanding the actions of other people and for learning new skills by imitation. THE SUPPLEMENTARY MOTOR AREA Function in Concert with the premotor area to: → provide body-wide attitudinal movements → fixation movements of the different segments of the body → positional movements of the head and eyes, → background for the finer motor control of the arms and hands by the premotor area and primary motor cortex Contractions stimulated in this area are often bilateral rather than unilateral. SPECIALIZED AREA OF MOTOR CONTROL Figure 16.Corticospinal (pyramidal) tract. OTHER PATHWAYS FROM THE MOTOR CORTEX Other Pathways from the Motor Cortex The Axons from the giant Betz cells. ○ send short collaterals back to the cortex itself. ○ collaterals are believed to inhibit adjacent regions of the cortex when the Betz cells discharge, thereby “sharpening” the boundaries of the excitatory signal. ○ Caudate Nucleus and Putamen - Mainly to control body postural muscle contractions Figure 15. Representation of the different muscles of the body in the ○ Red Nuclei of the midbrain motor cortex and location of other cortical areas responsible for - Additional fibers pass down the cord through specific types of motor movements. the rubrospinal tract. Broca’s Area Reticular substance and vestibular nuclei of the → for expressive language brain stem → damage to this area does not prevent a person from ○ Signals go to the cord the cord by way of vocalizing but makes it impossible for the person to speak reticulospinal and vestibulospinal tracts, whole words rather than uncoordinated utterances or an ○ Others go to the cerebellum by way of occasional simple word such as “no” or “yes” (expressive reticulocerebellar and vestibulocerebellar tracts. aphasia) Pontile nuclei “Voluntary” Eye Movement Field ○ give rise to the pontocerebellar fibers → locus for controlling voluntary eye movements. ○ carrying signals into the cerebellar hemispheres. → prevents a person from voluntarily moving the eyes toward Inferior Olivary nuclei different objects. instead, the eyes tend to lock involuntarily ○ secondary olivocerebellar fibers transmits signals onto specific objects. to multiple areas of the cerebellum. Head and Rotation Area **basal ganglia, brain stem, and cerebellum all receive → elicits head rotation strong motor signals from the corticospinal system every → closely associated with the eye movement field and it directs time a signal is transmitted down the spinal cord to cause a the head toward different objects. motor activity. Hand Skills Area INCOMING SENSORY FIBER PATHWAYS TO THE MOTOR CORTEX → when tumors or other lesions cause destruction in this area, 1. Subcortical fibers from adjacent regions of the cerebral hand movements become uncoordinated and non purposeful, cortex, especially from: a condition called motor apraxia. a. Somatosensory areas of the parietal cortex VIII. TRANSMISSION OF SIGNAL FROM THE MOTOR b. Adjacent areas of the frontal cortex anterior to the CORTEX TO MUSCLES motor cortex CORTICOSPINAL TRACT c. Visual and auditory cortices Corticospinal (Pyramidal) Tract 2. Subcortical fibers that arrive through the corpus callosum → most important output pathway from the motor cortex from the opposite cerebral hemisphere - connect → originates about 30% from the primary motor cortex, 30% corresponding areas of the cortices in the two sides of the from the premotor and supplementary motor areas, and 40% brain. from the somatosensory areas posterior to the central sulcus. 3. Somatosensory fibers that arrive directly from the vertebral Pyramidal Cells of Betz complex of the thalamus - relay mainly cutaneous tactile ○ population of large myelinated fibers originating signals and joint and muscle signals from the peripheral from giant pyramidal cells. body. ○ transmit nerve impulses to the spinal cord at a 4. Tracts from ventrolateral and ventroanterior nuclei oif the velocity of about 10 m/sec, the most rapid rate of thalamus - receives signals from the cerebellum and basal transmission of any signals from the brain to the ganglia; provide signals that are necessary for coordination cord. PHYSIOLOGY Spinal Cord Motor Functions Spinal Cord Motor Functions & Cortical and Brain Stem Control of PAGE 7 of 10 Motor Function PHYSIOLOGY | LEC 3 Spinal Cord Motor Functions & Cortical and Brain Stem Control of Motor Function | Dr. Mark Deneb Armeña among the motor control functions of the motor cortex, basal ganglia, and cerebellum. 5. FIbers from the intralaminar nuclei of the thalamus - control the general level of excitability of the motor cortex in the cerebrum; control the general level of excitability of the most other regions of the cerebral cortex. IX. RED NUCLEUS ALTERNATIVE PATHWAY FOR TRANSMITTING CORTICAL SIGNALS TO THE SPINAL CORD → Location: in the mesencephalon → Receives: large number of direct fibers from the primary motor cortex through corticorubral tract, as well as branching fibers from the corticospinal tract. Figure 18. Convergence of different motor control pathways on the Red Nucleus Pathway fibers synapse in the lower portion of the red nucleus, the anterior motor neurons magnocellular portion, which contains large neurons similar in Cervical Enlargement of the Cord size to the Betz cells. → Hands and fingers are represented Large neurons then give rise to the rubrospinal tract, which → Large numbers of both corticospinal and rubrospinal fibers also crosses to the opposite side in the lower brain stem. terminate directly on the anterior motor neurons Rubrospinal fibers terminate mostly on the interneurons of the → Allows direct route from the brain to activate muscle contraction intermediate areas of the cord gray matter, Has close connections with the cerebellum EFFECTS OF LESION IN THE MOTOR CORTEX OR IN THE CORTICOSPINAL PATHWAY - STROKE Magnocellular portion of the red nucleus has somatographic Results in loss of blood supply to the cortex or corticospinal tract representation of all the muscles of the body. → Passes through the internal capsule between the caudate, nucleus, and the putamen Removal of Primary Motor Cortex (Area pyramidalis) → Causes varying degrees of paralysis of the represented muscles → Undamaged sublying caudate nucleus and adjacent premotor and supplementary motor areas → Gross postural and limb fixation Movements still occur Apparent loss of voluntary control of discrete movements ○ Hands and fingers ○ Distal segments of lungs Muscle Spasticity Figure 17. The corticorubrospinal pathway for motor control. (Guyton → Caused by lesions that damage large areas near the motor and Hall, 2017) cortex → Results in hypotonia Less fine and less developed than motor cortex → Almost invariably occurs in affected muscle areas on the Damaged, but the corticorubrospinal pathway is intact opposite side of the body → discrete movements can still occur → Mainly results from damage to accessory pathways that → Except, movements for fine control of the fingers and hands normally inhibit vestibular and reticular brainstem motor nuclei are considerably impaired. Corticospinal & Rubrospinal Tracts X. BRAIN STEM → lie in the lateral columns of the spinal cord, along with the → Consists of medulla, pons, and mesencephalon/ midbrain. corticospinal tract → It performs motor and sensory functions for the face and head → terminates on the interneurons and motor neurons that control regions. the more distal muscles of the limbs (Lateral Motor System of → Serves as a way station for “command signals” from higher the Cord) neural centers. Medial Motor System CONTROL OF MOTOR FUNCTIONS BY THE BRAIN STEM → vestibulo reticulospinal system → Control of respiration → In contrast to corticospinal and rubrospinal tracts which → Control of Cardiovascular system compromise the lateral motor system of the cord → Partial control of GI function → Control of many stereotyped movements of the body EXTRAPYRAMIDAL SYSTEM → Control of equilibrium All portions of the brain and brain stem that contribute to motor → Control of eye movements control but are not part of the direct corticospinal-pyramidal system RETICULAR AND VESTIBULAR NUCLEI → Basal ganglia → Support of the body against gravity → Reticular formation of the brain stem → Reticular nuclei → Vestibular nucleI 2 Major groups: → Red nuclei ○ Pontine reticular nuclei ○ Slightly posteriorly and laterally in the pons and extending into the mesencephalon ○ Medullary reticular nuclei ○ Extends through the entire medulla, lying ventrally and medially near the midline PHYSIOLOGY Spinal Cord Motor Functions Spinal Cord Motor Functions & Cortical and Brain Stem Control of PAGE 8 of 10 Motor Function PHYSIOLOGY | LEC 3 Spinal Cord Motor Functions & Cortical and Brain Stem Control of Motor Function | Dr. Mark Deneb Armeña These 2 nuclei groups function antagonistically to each other ○ Pontine reticular nuclei= exciting the antigravity muscles ○ Medullary reticular nuclei= relaxing the antigravity muscles Table 3. Comparison of the Pontine and Medullary Reticular System PONTINE RETICULAR MEDULLARY RETICULAR SYSTEM SYSTEM → Transmits excitatory → Transmits inhibitory signals downward into the signals to the same cord through the pontine antigravity anterior motor reticulospinal tract in the neurons via the medullary anterior column of the cord. reticulospinal tract located → Causes powerful in the lateral column of the excitation of antigravity cord. muscles throughout the → Counterbalances the Figure 20. Comparison of Decorticate and Decerebrate Posturing body. excitatory signals from the retrieved from Cleveland Clinic → Have a high degree of pontine reticular system. XI. VESTIBULAR APPARATUS natural excitability. → Receive strong input Sensory organ for detecting sensations of equilibrium → Receive strong excitatory collaterals from: Encased in a system of bony tubes and chambers signals from: Corticospinal tract Located in the petrous portion of the temporal tube Vestibular nuclei Rubrospinal tract ○ Bony labyrinth Deep nuclei of the Other motor pathways → Contains membranous tubes and chambers cerebellum ○ Membrane Bony labyrinth Functional part of the vestibular apparatus 💬 “Maculae” for equilibrium Utricle and saccule’s sensory organs For detecting orientation of the head with respect to gravity Figure 19. Vestibulospinal and reticulospinal tracts descending in the spinal cord Solid lines represent excitation of anterior motor neurons Dashed lines represent inhibition of motor neurons Controls the body’s axial musculature VESTIBULAR NUCLEI Transmit strong excitatory signals to the antigravity muscles Via lateral and medial vestibulospinal tracts in the spinal cord’s anterior columns Selectively control excitatory signals to the different antigravity muscles → Maintain equilibrium in response to signals from the vestibular apparatus. Decerebrate Rigidity → Damage below mesencephalon Figure 21. Membranous labyrinth and organization of the crista ampullaris and → With intact pontine and medullary reticular system the macula Does not occur in all muscles of the body and in antigravity muscles PHYSIOLOGY Spinal Cord Motor Functions Spinal Cord Motor Functions & Cortical and Brain Stem Control of PAGE 9 of 10 Motor Function PHYSIOLOGY | LEC 3 Spinal Cord Motor Functions & Cortical and Brain Stem Control of Motor Function | Dr. Mark Deneb Armeña Figure 22. Hair cell of the equilibrium apparatus (left) and Movement of Cupula (right) 💬for homeostasis andUTRICLE AND SACCULE equilibrium Maintain static equilibrium when the head is in near-vertical position Statoconia Have greater mass inertia than the surrounding fluid Falls backward on the hair cell cilia Then, information of disequilibrium is sent into the nervous centers Causes person to feel as though they were falling backward SEMICIRCULAR DUCTS For angular acceleration, when head suddenly begins to rotate in any direction Endolymph in the semicircular ducts tends to remain stationary while the semicircular ducts turn. Due to its inertia Causes relative fluid flow in the ducts in the direction opposite to head rotation XII. REFERENCES Armeña, M. (2023). Nervous System Physiology: Motor Functions of Spinal Cord, Cord Reflexes, Cortical and Brainstem Control of Motor Function [PowerPoint Slides]. PHY-1A.S1.L04-Motor Functions of the Spinal Cord. Batch 2027 Trans Berne, R., Levy, M., & Koeppen, B. (2019). Physiology 10th edition. Elsevier, Inc. Hall, J., & Hall, M. (2021). Guyton and Hall Textbook Medical Physiology 14th Edition. Elsevier, Inc. PHYSIOLOGY Spinal Cord Motor Functions Spinal Cord Motor Functions & Cortical and Brain Stem Control of PAGE 10 of 10 Motor Function