Motor Functions of Central Nervous System PDF

Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- Motor Functions of Central Nervous System Sensory information are integrated at all levels of the central nervous system and cause the appropriat...

Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- Motor Functions of Central Nervous System Sensory information are integrated at all levels of the central nervous system and cause the appropriate motor response beginning in the spinal cord with simple reflexes, finally to the cerebral cortex where the most complicated responses are controlled. Motor Functions of Spinal Cord Each segment of the spinal cord contains several million neurons in the grey matter: Fig (53) I. Sensory Neurons: - Present in the dorsal horn. - Their functions discussed with sensations. II. Motor Neurons: - Present in the anterior (ventral) horn of spinal cord. - Their axons leave the spinal cord → skeletal muscle. - They are of 2 types. 1  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- A) Alpha-motor neurons (α-motor neurons) - Their axons are large and myelinated (A-α)→ large skeletal muscle fibers. - Each α-motor neuron + its axon + skeletal muscle fibers it supplies = motor unit. B) Gamma-motor neurons ( γ-motor neurons) - Are much smaller than α-motor neurons. - Transmit impulses along A-γ fibers → intrafusal muscle fibers of muscle spindles. III. The interneurons: - They are smaller and more numerous than anterior motor neurons. The interconnections between the interneurons and anterior motor neurons represent the integrative area for spinal cord reflexes. N.B.: Renshaw Cells: are small inhibitory interneurons present in the ventral horn of spinal cord. Motor functions of spinal cord: Spinal cord reflexes are group of simple reflexes: they are either: I. Monosynaptic reflex : only stretch reflex. II. Polysynaptic reflexes. 2  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- 1. Monosynaptic reflex (stretch reflex): Components of Stretch Reflex: Fig (54) -Stimulus: Stretch of the muscle. -Receptors: Muscle spindles. -Afferent neuron: in dorsal root ganglion. Afferent fiber: thick myelinated A- α fibers. -Center: in spinal cord-monosynaptic. -Efferent neuron: α-motor neuron. Efferent fibers: thick myelinated A- α fibers. -Response: contraction of skeletal muscle. Muscle spindle  Are encapsulated, spindle-shaped structures present in the fleshy part of skeletal muscle. Their pointed ends are attached to the surrounding extrafusal muscle fibers. 3  Central Motor Nervous System ----------------------------------------------------------------------------------------------------------------  The central part of muscle spindle is non-contractile and full of nuclei and called "the receptor area", while the peripheral parts are striated and contractile.  Muscle spindle is stimulated when its receptor area is stretched by: Fig (57): a-Stimulation of gamma efferents that contract the peripheral parts of intrafusal fibers. b-The whole muscle is stretched N.B.Maximal stimulation of muscle spindle occurs when the muscle is stretched + increased rate of discharge along γ-efferent motor fibers.  Conversely the muscle spindles are inhibited by: a- Active muscle contraction b- Passive muscle shortening. Types of Stretch Reflex; 1) Static stretch reflex:  Maintained stretch to the muscle → maintained muscle contraction.  It is the basis of muscle tone. 2) Dynamic stretch reflex:  Sudden stretch of the muscle →instantaneous strong contraction of the muscle followed by relaxation.  It is the basis of tendon jerks. 4  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- 3) Negative stretch reflex: Sudden shortening of a muscle —> inhibition of muscle spindles → reflex muscle relaxation. Conclusion: Stretch reflex resists changes in muscle length.The dynamic and static stretch reflexes resist stretching, while, negative stretch reflex resists shortening of the muscle. Functions of stretch reflex: -Maintains body posture erect against the effect of gravity, because static stretch reflex is the basis of muscle tone. -During performance of movements: 1-Makes muscle contraction smooth and not oscillating (damping or smoothing function of stretch reflex). Stretch reflex buffers changes of motor signal that reach spinal cord as a result of its passage through different neuronal pools. Fig (58) 5  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- 2-Whenever signals are transmitted from motor center to alpha-motor neurons, almost always γ-motor neurons are simultaneously stimulated "Coactivation". This is very important as it keeps the length of the receptor portion from changing → Keeps the muscle spindle from opposing the muscle contraction. 3-Servo-assist function of muscle spindle: as it a-Allows the brain to cause muscle contraction against a load without expending much nervous energy (load reflex), instead, the spindle reflex would provide most of the nervous energy. b-Adjusts the degree of muscle contraction to the heaviness of the load. c-Compensates for failure of the muscle to provide the proper contraction because of fatigue or other in muscle abnormalities. Supraspinal control of stretch reflex: -Supraspinal centers control the activity of stretch reflex through regulating the activity of gamma motor neurons. -Supraspinal centers are either facilitatory or inhibitory. 6  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- Facilitatory centers Inhibitory centers 1.Facilitatory reticular formation. 1. Inhibitory reticular formation 2. Motor area 4 2. premotor area 6 3. Caudate nucleus 3. Lentiform nucleus. 4. Vestibular nuclei 4. Red nucleus 5. Neocerebellum 5. Paleocerebellum Facilitatory reticular formation has its own intrinsic activity activity→ excitatory impulses along ventral reticulospinal tract → γ motor neurons. -All supraspinal facilitatory centers, stimulate facilitatory reticular formation → ventral reticulospinal tract → γ- motor neurons. -Vestibular nucleus sends also direct facilitatory impulses to spinal cord along vestibulospinal tracts.  Inhibitory reticular formation has no intrinsic activity, i.e. can not discharge by itself. -All inhibitory centers stimulate the inhibitory reticular formation → inhibitory signals travel along lateral reticulospinal tract → inhibition of γ motor neurons. - Red nucleus also send direct inhibitory signals to the spinal cord along the rubrospinal tract. Remember:  There are 2 supraspinal facilitatory tracts: 1- Ventral reticulospinal tract. 2- Vestibulospinal tracts. 7  Central Motor Nervous System ----------------------------------------------------------------------------------------------------------------  There are 2 supraspinal inhibitory tracts: 1- Lateral reticulospinal tract. 2- Rubrospinal tract.  Facilitatory and inhibitory centers do not affect alpha-motor neurons directly, but reflexly through affection of gamma motor neurons.  There is reciprocal innervation between facilitatory and inhibitory reticular formation. Clinical application of stretch reflex: 1) Muscle tone: -Static stretch reflex is the basis of muscle tone. -Functions: 1- Maintains erect posture of the body against the effect of 8  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- gravity by maintained reflex contraction of the muscles (muscle tone) especially the antigravity muscles. 2- Helps venous return and lymph flow. 3- Helps regulation of body temperature. 4- Keeps the viscera in position (specially in animals). 2) Tendon jerks or deep reflexes: -The dynamic stretch reflex is the basis of tendon jerks. N.B.Examination of tendon jerks is also a clinical method used to determine the sensitivity and integrity of stretch reflex and to localize the site of lesion in CNS (see practical). 3) Clonus: e.g. knee or ankle clonus: - Is rhythmic oscillation of the tendon jerk obtained by sudden maintained stretch of the muscle. It occurs only if the stretch reflex is supraspinally facilitated. -Mechanism : as stretch is maintained + supraspinal facilitation ---> the cycle of contraction and relaxation repeats itself. II. Polysynaptic spinal cord reflexes: A) Somatic reflexes. B) Autonomic reflexes. A) Polysynaptic somatic cord reflexes: 1) Golgi tendon reflex: (Inverse stretch reflex )Fig (60) -Contains 2 synapses -Stimulus: When the tension on the muscle and therefore 9  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- on the tendon becomes extreme as: a) When the muscle contracts strongly. b) When the muscle is overstretched. -Receptors: Golgi tendon receptors -Response: Inhibition of the muscle, i.e. relaxation (lengthening reaction).. Fig (60) Diagram illustrating the pathways responsible for stretch reflex and the inverse stretch reflex. -Is protective reflex to prevent tearing of the muscle or avulsion of the tendon from its bone attachment. So, muscle spindle detects changes in muscle length while Golgi tendon organs detect changes in muscle tension. 2)Flexor Reflex: (Withdrawal Reflex): Fig (61) -It is a polysynaptic reflex: Requiring at least 3 to 4 interneurons. So the central delay is more than 2 ms. -It can be produced by any type of cutaneous sensory stimulation, however, the classic form is elicited most 10  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- powerfully by stimulation of pain receptors, e.g. pin prick and burns. For that reason, it is called nociceptive reflex or pain reflex. ---> contraction of the flexor muscles of the limb ---> withdrawing it from the stimulus (flexor reflex). -The pattern of withdrawal reflex depends on the locality of the stimulus, e.g. when the injurious stimulus is applied to the inner aspect of the limb → flexion and abduction of the limb to withdraw it from such a stimulus. - Flexor reflex shows the following phenomena: A) Divergence: This allows spread of excitation to the motor neuronal pools of several muscles which are required to produce movement of the limb. B) Reciprocal Innervation: Contraction of muscles of a limb is accompanied by relaxation of their antagonistic muscles. C) Recruitment: Means the power of contracting muscles rises gradually. D)Tetanic contraction of muscles: -Means that muscles remain contracted for some time -Occurs as a result of successive stimulation of motor neuronal pools of muscles. E) After Discharge: -Means prolongation of action after stoppage of stimulation 11  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- 3) Crossed extensor reflex: -Application of an injurious stimulus to a limb → reflex withdrawal of ipsilateral limb and extension of the contralateral limb to support the body weight. Flexor reflex, crossed extensor refiex, and reciprocal innervation. -Properties: a- The latent period is longer than that of the flexor reflex as the impulses has to cross to the opposite side of the cord. b- It shows the phenomenon of reciprocal innervation. The extensors contract while the flexors relax. c- After discharge is longer than that of flexor reflex to hold the body away from the stimulus. 4) Scratch Reflex: -Initiated by itch and tickle sensation → scratch reflex (consist of to and fro scratching movements). 12  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- 5) Postural and locomotion spinal reflexes: 1- Positive supporting reaction: Application of a deep pressure to the sole of the foot → reflex contraction of both extensors and flexors of the limb. Thus the limb is changed into a rigid column to support the body weight. 2- Stepping reflex of a single limb: In spinal animal, forward flexion of a limb is followed by backward extension of the same limb. 3- Reciprocal stepping of the opposite limb: Forward flexion of a limb is accompanied by backward extension of the opposite limb. 4- Diagonal stepping of all 4 limbs: Fig (63) In a well recovered spinal animal, stretch of one limb produces stepping reflexes that involve all 4 limbs. Diagonal stepping movements exhibited by a spinal animal. 13  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- 6) Superficial skin reflexes: They are of clinical importance since they help to localize the site of the lesion in spinal cord. 1- Upper and lower abdominal reflexes: Stroking (Scratching) the skin of the abdomen→ reflex contraction of: -Upper abdominal muscle: The center in 7, 8, 9 and 10th thoracic segments. -Lower abdominal muscle: The center in 10, 11 and 12th thoracic segments. 2) Cremastric reflex: -Stroking the skin of the inner aspect of the thigh → reflex contraction of cremastric muscle and elevation of the testes. -Center: First lumbar segment. 3) Planter reflex: -Stroking the skin of the sole of the foot → planter flexion of the toes.-Center: First and second sacral segments. B) Autonomic Cord Reflexes: They include: 1) Micturition reflex. 2) Defecation reflex. 3) Changes in vascular tone resulting from localized skin heat and cold. 14  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- 4) Sweating which results from localized heating of the body. 5) intestino-intestinal reflexes that control some motor functions in the gut 6) Peritoneo-intestinal reflexes: peritoneal irritation →inhibition of gastric motility. Spinal Cord Lesions I. Hemisection of spinal cord (Brown-Sequard Syndrome): Discussed before with somatic sensations. II. Complete cord transection:  Cause: As a result of a bullet or an accident.  Effects: A) Sensations: Permanent loss of all sensations at and below the level of the lesion. B) Voluntary Movements: Permanent loss of all voluntary movements at and below the level of the lesion, so: * In upper cervical lesion: immediate death due to stoppage of respiration. * In lower cervical lesion: paralysis of the 4 limbs (quadriplegia). 15  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- * In mid-thoracic lesion: paralysis of both lower limbs (paraplegia). In all these conditions, muscle paralysis is either: * Lower motor neuron paralysis: occur at the level of the lesion on both sides. * Upper motor neuron paralysis: occurs below the level of the lesion on both sides. C) Reflexes: Spinal reflexes pass in 3 stages: 1) Stage of spinal shock. 2) Stage of recovery of spinal reflexes. 3) Stage of failure of spinal reflexes. i) Stage of shock of spinal reflexes: There is complete loss of all reflexes at and below the level of the lesion: 1- Loss of stretch reflexes and 2-flexor reflex 3- Loss of micturition, defecation and erection reflexes. The wall of the bladder is paralyzed, but the tone of internal urethral sphincter rapidly returns. Urine accumulates in the bladder till its pressure overcomes the tone of internal urethral sphincter → dribbling of urine "Retention with overflow" or “overflow dribbling”. 4- Drop of arterial blood pressure to a very low value (40 mmHg), due to interruption of the descending fibers from 16  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- the vasomotor center of the medulla to the LHCs. 5- As a result of muscle paralysis and loss of muscle tone, arteriolar and venular dilatation occurs → decreased venous return from the legs which become cold and blue with dry skin and very liable to be affected by bed sores. Cause of spinal shock; Is due to sudden cessation of supraspinal excitatory impulses → depression of spinal centers to the point of complete loss of function. Duration of spinal shock: Is proportional to the degree of encephalization of motor function in various species. So it is: * Few minutes in frogs. * Few hours in dogs and cats. * Several days in monkeys. * Weeks to months in humans. Complications of complete cord transection: 1) Like all immobilized patients, develop a negative nitrogen balance due to protein catabolism. 2) Catabolism of protein matrix of bone → mobilization of calcium → hypercalcemia and hypercalciuria and renal stones. Renal stones + paralysis of the bladder —> urinary stasis which predispose to urinary tract infection. 3) The weight of the body compresses the circulation to the skin over the bony prominences, so that unless the patient is moved frequently, the skin breaks down at these points → decubitus ulcers. These ulcers are prone to infection 17  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- and tissue destruction "bed sores". Management of patients during spinal shock: 1) Prevention of decubitus ulcers and bed sores by: * Frequent changing the position of the patients. * Rubbing of the skin with alcohol. 2) Prevent urinary tract infection by: * Frequent evacuation of urinary bladder. * Use of antibiotics. 3) Good attention to nutrition and fluid balance. Prognosis: Is very poor and death occurs from septicemia and uremia. ii) Stage of recovery of spinal reflexes As the spinal shock passes, reflex spinal activity graduially reappears. The first reflexes to return are the stretch reflexes: The tone appears first in the flexor muscles → paraplegia in flexion. This is followed by the appearance of more complex reflexes, e.g.: 1- Flexor reflex: see before 2- Mass reflex: application of minor noxious stimulus to the skin of the lower limbs or anterior abdominal wall below the lesion → widespread reaction consists of: 18  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- - Flexion of both lower limbs and contraction of abdominal muscles. - Evacuation of the bladder and rectum. - Profuse sweating from large areas of the body. - Rise of arterial blood pressure to maximal values, sometimes to a mean pressure over 200 mmHg. N. B.: Mass reflex can be used to give paraplegic patients a degree of bladder and bowel control. 3)Sexual reflexes: genital manipulation in a male spinal animal and humans ---> erection and even ejaculation. 4)Deep reflexes: appear later, e.g. knee and ankle jerks. 5) Autonomic reflexes: a) Autonomic (or automatic) bladder and rectum: Distention of bladder or rectum by accumulated urine or stools → stimulation of stretch receptors in their walls → impulses to the spinal cord centers→ contraction of urinary bladder or rectum and inhibition of their internal sphincters → evacuation of bladder or rectum. b) The spinal sympathetic vasomotor centers in LHCs below the transection regain their activity and send impulses to arterioles and veins. c) Local spinal autonomic reflexes: e.g. warming the skin → vasodilatation and sweating. The skin becomes more healthy and ulcers heal up. 19  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- Maximum degree of recovery occurs after 6 months and the following reflex activities develop: a) The tone of extensors becomes more than that of flexor, so the lower limbs become extended (paraplegia in extension). b) Flexor reflex is accompanied by crossed extensor reflex. c)Positive supporting reaction becomes well developed to the extent that the patient can stand without support for few minutes. d) Stepping reflexes appear, e.g. passive flexion of one limb → extension of the opposite limb. iii) Stage of failure of reflex activity - This occurs as a result of infection in the urinary tract and bedsores. - There is gradual failure of reflex spinal activities. - Finally the patient dies from uremia. 20  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- Motor Functions of Brain Stem Brain stem masters the following functions: Autonomic 1) Control of respiration. 2) Control of Cardiovascular system. 3) Control of gastrointestinal functions. Somatic 4) Control of erect posture against gravity. 5) Control balance during movement...equilibrium. 6) Control of stereotyped movements. 7) Control of locomotion … forward progression. 8) Control eye movements because it contains nuclei of 3rd, 4th & 6th cranial nerves that cotrol movements of extraocular muscles. I)Control of static posture against gravity: Reticular formation (RF) -Is controlled by reticular formation of brain stem -RF is formed of large number of neurons present through the entire brain stem. It extends upward to the level of the thalamus and downward to be continuous with the interneurons of the spinal cord. -Some neurons of reticular formation are collected together to form specific nuclei, e.g.: 21  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- 1- Vestibular nucleus. 2-Red nucleus. 3-Subthalamic nucleus. 4- Interstitial nucleus. 5- Peristitial nucleus. 6- Substantia nigra. -RF is functionally divided into:  Pontine (Excitatory) Reticular Formation  Medullary (Inhibitory) Retcular Formation. Excitatory RF Inhibitory RF Site -In pons, but extends to -In the whole length of the midbrain. medulla oblongata. - Lies more laterally. -Lies more medially. Activity Has intrinsic activity Has no intrinsic activity. Connection Stimulated by : Stimulated by: 1. Vestibular nucleus. 1. Red nucleus. 2. Area 4 2.Area 4S. 3. Neocercbellum. 3. Paleocercbellum. 4. Caudate nucleus 4. Lentiform nucleus. Inhibited by: Inhibited by: 1. Red nucleus. 1. Vestibular. 2. Arca 4S. 2. Area 4 3. Paleocercbellum. 3. Neocerebellum. 4.Lentiform nucleus. 4. Caudate nucleus. Send 1. Motor neurons of spinal Motor neurons of spinal impulses to cord along ventral cord along lateral reticulospinal tract. reticulospinal tract. 2. All parts of cerebral cortex along reticular activating system (RAS). Function Stimulates the antigravity Inhibits the same muscles. antigraavity muscles. Stimulates all the cerebral cortex. 22  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- Reticular formation Functions of reticular formation: 1) Support body weight against effect of gravity: During standing, continuous facilitatory impulses pass from facilitatory RF and vestibular nucleus → motor neurons of the cord --> increased tone of antigravity muscles --> support the body weight against the effect of gravity. 2) Specific nuclei of reticular formation have the following Functions: a) Subconscious stereotyped movements: controlled by peristitial, interstitial and red nuclei. b) Forward progression: by subthalamus. c) Equilibrium: mainly controlled by vestibular nuclei. 23  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- 3) Reticular activating system (RAS): Fig (65) -Composed of the ascending branches of the large motor cells of the facilitatory RF. -The fibers of RAS ascend to reach all parts of cerebral cortex either directly or after relaying in the non-specific thalamic nuclei. Functions of RAS: 1- Produces diffuse stimulation of all parts of cerebral cortex → so it is responsible for the alert conscious state of the person. When it is depressed or destroyed → unconsciousness or coma occurs. b) Controls the overall level of electric activity of the cortex. Fig (65) Diagram of the ascending reticular activating system RAS is activated by: a) Impulses from sensory pathways : -Somatic sensory pathway. 24  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- -Auditory pathway. -Visual pathway. -Olfactory pathway. b) Impulses from cerebral cortex -From temporal and frontal lobes as in emotions. -From motor areas. c) Sympathomimetic Drugs: e.g. adrenaline and amphetamine. II)Maintenance of equilibrium (vestibular apparatus): -Vestibular Apparatus: is the organ that detects sensation of equilibrium. Fig (66) -Inner ear "labyrinth" is composed of:  A system of bony tubes and chambers in the petrous part of the temporal bone called "bony labyrinth"  Within this, a system of membranous tubes and chambers called the "membranous labyrinth", which consists of: a) Cochlear duct → for hearing. b) Vestibular apparatus (utricle + saccule + 3 semicircular canals) → concerned with equilibrium. Sense organs in vestibular apparatus: -Sense organ in utricles and saccules is called Macula. -Sense organ in semicircular canals is Crista ampullaris. 25  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- Macula - Is the sense organ in utricles and saccules. -Is a small sensory area about 2 mm in diameter, consisting of a ridge of supporting columnar epithelial cells and sensory hair cells. -Is covered by gelatinous layer in which many calcium carbonate crystals (statoconia or otoliths) are embedded. The cilia of the hair cells project up into this gelatinous layer. -The bases and sides of the hair cells are surrounded by the sensory endings of the vestibular nerve. -During rest, the hair cell emits a tonic discharge about 100 impulses/sec. -Under normal condition ,with erect posture of head in space , there is equal dicharge from both maculae in both sides 26  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- -Functions of maculae (otolithic organs): 1) Detection of changes in the orientation of the head in space. As the orientation of the head in space is changed, the weight of statoconia bends the cilia → signals are transmitted to the brain to inform malequilibrium. e.g.: if the head is tilted passively to left side → frequency of discharge from the left utericle is increased while that from the right utricle is decreased → unequal discharge to the brain → sense of bending the head to the left. 2) Detection of linear acceleration: -When the body is accelerated → The statoconia which have greater inertia than the surrounding fluids → bending of hairs in the opposite direction → stimulation of hair cells. *The macula of the utricle lies in horizontal plane → detects acceleration in horizontal plane. While that of the saccule lies in vertical plane → detects acceleration in vertical plane. 3) Are receptors for some postural reflexes. Semicircular canals: (SCCs) and Crista ampullaris:  There are 3 SCCs in each vestibular apparatus: anterior, posterior and horizontal. They are arranged at right angles to each other, representing all the planes in space.  When the head is bent forward 30°: 27  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- -The 2 horizontal canals are horizontal with respect to the surface of the earth. -The anterior canals are vertically placed and project 45° outward and forward, so: The posterior canals are vertically placed and project 45° outward and backward.  Each SCC has a dilated end called the ampuUa. The SCCs open into the utricle by 5 openings only, since the anterior and posterior canals unite at the non-ampullary ends and open by single opening into the utricle. One crista ampullaris is present in the ampulla of each SCC.  Crista ampullaris: -Is formed of a ridge of supporting columnar epithelial cells and specialized hair cells. The cilia are embedded in a gelatinous material called the cupula which projects from the crista to the opposite wall of the ampulla forming a movable partition that can be distorted by the movement of endolymph within the canals. - From the hair cells, signals are carried along the afferent fibers in the vestibular division of 8th cranial nerve. -During rest, the hair cell emits a tonic discharge about 100 impulses/sec. It is equal of both sides.  Function: 1) Detection of angular acceleration: i.e. Rotation: The crista ampullaris informs the central nervous system 28  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- about changes in the rate and direction of rotation of the head in the 3 different planes of space.  During rest: equal discharge of impulses from SCCs on both sides of the head.  During Rotation: for example to the right the following occurs: a) At start of rotation: Fig (68) The endolymph due to its inertia, moves relatively to the left → bends both cupulae to the left. - Right cupula bends toward utricle → stimulated. - Left cupula bends away from the utricle → inhibited. This unbalanced discharge leads to the sensation of rotation to the right. b) As Rotation continued: The endolymph moves at the same rate as its canal → The cupulae return to their normal position by their elasticity. So, after 20 seconds the sense of rotation disappears. fig (86) Movement of the cupula and its embedded hairs at the onset of rotation. 29  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- c) At the end of rotation: The endolymph, due to its momentum continues to move to the right → bending both cupulae to the right. So: *The right cupula moves away from utricle → inhibited. *The left cupula moves toward the utricle → stimulated. This unbalanced discharge → false sensation of rotation to the left = vertigo. N.B: *SCCs are stimulated at the beginning and at the of end of rotation and when change in rate of rotation is taking place. *At constant rotation, no stimulation of SCCs, e.g. we do not perceive the rotation of the earth. 2) predictive function of SCCs in maintenance of equilibrium: -If a person is running forward rapidly, and then suddenly begins to turn to one side, he will loose his balance and fall down within a fraction of a second unless appropriate correction is made. -The SCCs predict the malequilibrium before it occurs and cause the equilibrium centers to make the appropriate preventive adjustments → the person maintains his balance before he begins to change the situation. 30  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- Neuronal connections of vestibular apparatus: Fig (69) -Vestibular apparatus → vestibular division of 8th cranial nerve (mother cell in vestibular ganglion) → brain stem at the junction of the medulla and pons. -Some fibers pass directly through inferior cerebellar peduncle (ICP)→ folloculonodular lobe of cerebellum. -Other fibers pass to the vestibular nucleus → 1) Folloculonodular lobe of cerebellum through ICP. 2) Reticular formation of brain stem → reticulospinal tract → spinal cord. 3)Spinal cord along vestibulospinal tract. 4)The medial longitudinal bundles of both sides corrective movements of the eyes every time the head rotates. 5)Equilibrium center of the opposite side in the parietal lobe deep in the Sylvian fissure in apposition of auditory cortex in temporal lobe. N.B. -Equilibrium center is responsible for conscious perception of equilibrium. -To feel equilibrium equal discharge from vestibular apparatus of both sides should reach equilibrium centers of the brain. -Unequal discharge from vestibular apparatus of both sides to equilibrium centers → sense of malequilibrium. 31  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- -Vestibular nucleus is the center for reflexes that keep equilibrium. Effects of stimulation of SCCs: 1)Sense of rotation: -At start of rotation: True sense of rotation. -At end of rotation: False sensation of rotation, i.e. Vertigo. 2) Autonomic Responses: Include: nausea, vomiting, pallor, sweating, hypotension and increased respiratory rate due to connection of vestibular nucleus to RF of brain stem which contains the various autonomic centers. 3) Nystagmus: -Is oscillatory eye movements consisting of a slow and fast components. 32  Central Motor Nervous System ----------------------------------------------------------------------------------------------------------------  The slow component: - Is opposite to the direction of rotation. - Is due to connection of vestibular nucleus → medial longitudinal bundles → motor cranial nerve nuclei of the eye of both sides to fix objects during rotation.  The fast components: - Corrective impulses in the same direction of rotation by signals originate from reticular formation→ medial longitudinal bundles of both sides. 4) Changes in muscle tone: -Stimulation of SCCs → increased muscle tone in ipsilateral side and → decreased muscle tone in contralateral side. -This is done through vestibulospinal and reticulospinal tracts. 5) Past-pointing test of Baraney: After the end of rotation to the right, the person feels false sense of rotation to the left. So, if he is asked to touch a point on the wall while closing his eyes, he touches to the right of the point to compensate for the sense of vertigo to the left. 33  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- Motion Sickness: -Is due to excessive and repetitive labyrinthine stimulation due to motion of vehicle (car, train, ship or plane). -Is associated with vertigo, nausea and vomiting. -It can be treated by antiemetic drugs and tranquilizers. III) Stereotyped Movements: -Are simple movements, done subconsciously in a fixed pattern in all individuals. -Control: Interstitial, peristitial and red nuclei. IV) Locomotion: -Forward progression: subthalamus. -Purposeful locomotion: Thalamus + higher brain areas. Prove: a cat transected between the thalamus and subthalamus can walk normally, but when the animal comes to an obstruction it hits its head against the obstruction trying to keep on walking. Such animal lacks purposefulness of locomotion which requires the thalamus and higher brain centers. 34  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- Postural Reflexes Are reflexes which maintain body posture and equilibrium during rest and movement. Are classified according to their center into: I. Spinal postural reflexes. II. Medullary postural reflexes. III. Mid-brain postural reflexes. IV. Cortical postural reflexes. I. Spinal postural reflexes: - Studied in spinal animal - Include: 1) Stretch reflexes. 2) Crossed extensor reflex. 3) Positive supporting reaction (the only exception for reciprocal innervation). 4) Stepping reflexes. II. Medullary Postural Reflexes: -Studied in decerebrated animal, -Center is in medulla oblongata. -Receptors for the medullary positional reflexes are: Neck proprioceptors → tonic neck reflexes. Maculae of utricle and saccule → tonic labyrinthine 35  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- reflexes So, change in position of the head in space or in relation to the body → change in muscle tone in the 4 limbs to maintain posture. -Tonic Neck Reflexes: Receptors: neck proprioceptors. They are: 1-Turning the head of the animal to one side: → Extension of the jaw limbs and flexion of the skull limbs. 2-Turning the head of the animal up (dorsiflexion): -> Extension of the fore limbs and flexion of the hind limbs. e.g.: Posture adopted by normal animal looking upward at bird on a tree. 3) Turning the head of the animal down (ventroflexion):-> Flexion of the fore limbs and extension of the hind limbs. e.g.: Posture adopted by normal animal looking into a hole in the ground. B) Tonic Labyrinthine Reflexes. Receptors: maculae of the utricle and saccule (otolithic organs). They are: 1) If the animal is placed in its back ---> extention of 4 limbs 36  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- 2) If the animal is in the prone position ---> flextion of 4 limbs. N.B : When tonic labyrinthine and neck reflexes are simultaneously evoked, they produce algebraic sum of the separate responses. Thus, if the head is dorsiflexed in a decerebrate animal: * Labyrinthine impulses ---> extention of 4 limbs. * Neck impulses ---> extension of fore limbs and flexion of the hind limbs. so, the actual result observed is extension of the fore limbs and little or no change in hind limbs. This is important to keep the position of the body. II)Midbrain postural reflexes (Righting reflexes) -Studied in decorticated animal. -Center: for most of these, righting reflexes is in the midbrain. -Receptors for these reflexes are: a- The maculae of utricle and saccule. b-Neck proprioceptors c-Pressure receptors on the side of the body. d-Visual receptors. 37  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- - There are 4 midbrain righting reflexes:  Two reflexes correct the position of the head: a) Labyrinthine righting reflex on the head: - When the decorticated animal is held in air from its pelvis, the head stays level. -When the head is upside down → stimulation of otolithic organs → contraction of the neck muscles to keep the head level. b) Body righting reflex on the head: When the decorticated animal is put on its side, the side of the body in contact with the bench is stimulated, while the other side in contact with air is not. This asymmetric stimulation → reflex righting of the head.  Two reflexes correct the position of the body: a) Neck righting reflex on the body: If the head is corrected by one of the previous two reflexes and the body remains uncorrected → neck is twisted → stimulation of neck proprioceptors → correction of body position. b) Body righting reflex on the body: If The animal is put on its side → the asymmetric discharge from pressure receptors in both sides → reflex correction of the body position. 38  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- IV. Cortical Postural Reflexes: a) Visual Righting Reflex: -Studied in normal animal after denervation of the labyrinths and neck muscles. If the animal is dropped upside down in water, the eyes correct the position of the head and body, and the animal swims in water. If the animal is blind folded, it will sink. So the visual impulses from the retina right the head and body. -Center of this reflex is in the visual cortex. b) Placing reactions: - When a blind fold animal suspended in air is lowered toward a supporting surface, once the limbs touch that surface, the feet are placed firmly on the supporting surface to support the body. - The center of this reflex is in the cerebral cortex. c) Hopping Reactions: - If the animal is displaced laterally, it will hope by all 4 limbs to keep the limbs in position to support the body weight. - Pushing the animal → stretch of muscles → stimulation of muscle spindles → cerebral cortex (center) → motor signals → hopping reactions. 39  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- N.B.  Posture is determined by the degree and distribution of muscle tone, so it depends on the pattern of discharge of motor neurons which supply the muscles.  Orientation of the head in relation to the body is the function of neck receptors.  Orientation of the head in space is the function of otolithic organs.  A normal person keeps his balance with the eyes closed using the pressure receptors in the sole of the feet. Loss of these deep sensations (as in tabes dorsalis), the person can maintain his balance using his eyes. So when this person closes his eyes --> immediately he will fall down (+ve Romberg's sign).  Otolithic organs are very important for orientation when diving under deep water. Since, in these conditions the feet are not touching the ground, there is equal pressure all over the body and the visual impulses are not of help in determining the direction of the surface. Therefore, any person who have vestibular disorder should not go diving. 40  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- Motor Functions of Basal Ganglia Basal Ganglia consists of 3 large nuclear masses 1-Caudate nucleus 2-Putamen nucleus 3-Globus pallidus. -Caudate ＋ Putamen → corpus striatum -Globus pallidus＋Putamen → Lentiform nucleus Functionally related nuclei: Substantia nigra.and subthalamus. N.B.: The main afferent connection to basal ganglia terminates in corpus striatum, while the principal efferent output is from the globus pallidus. Neuronal connections of basal ganglia: 1-There are numerous free interconnections between the various nuclei of basal ganglia. 2-Two main circuits connecting the cerebral cortex with the basal ganglia:Caudate and Putamen Circuits. 41  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- The Caudate Circuit: -Cerebral cortex → caudate nucleus → globus pallidus ---> ventroanterior and ventrolateral thalamic nuclei --> prefrontal, promoter and supplemental motor areas of cerebral cortex. -Is concerned with pattern of movements instead of individual muscle movement. The Putamen Circuit: Cerebral cortex → putamen nucleus → ventroanterior and ventrolateral thalamic nuclei → primary motor cortex, premotor and supplemental areas. Is concerned with execusion of the pattern of simple movements. Functionally, in close association with the putamen circuit there are 3 additional neuronal circuits connecting the basal ganglia with the subthalamus and substantia nigra. N.B.: All these circuits are negative-feedback circuits which inhibit the motor cortex → prevent any unwanted movements during rest. 3) Brain stem and spinal cord: From Globus pallidus: → 1) Reticular formation → reticulospinal tract. 2) Red nucleus → rubrospinal tract. 3) Vestibular nucleus → vestibulospinal tract. 4) Inferior olivary nucleus → olivospinal tract. 42  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- 43  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- Neurotransmitters in basal ganglia: (Fig. 69) - Fibers from cerebral cortex → corpus striatum secrete acetylcholine. - Fibers from substantia nigra → corpus striatum secrete dopamine. - Fibers from brain stem to basal ganglia secrete norepinephrine, serotonin and enkephalin. - Fibers from corpus striatum → globus pallidus and substantia nigra secrete GABA. Acetylcholine and noradrenaline are excitatory transmitters, while GABA, dopamine, serotonin and enkephalin are inhibitory transmitters. A balance between all these transmitters is essendal for proper funcdoning of the basal ganglia. 44  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- Functions of basal ganglia: 1) Control of muscle tone: Lentiform nucleus → inhibition of motor cortex and stimulation of inhibitory reticular formation → inhibition of muscle tone. Caudate nucleus → stimulaton of vestibular nucleus and inferior olivary nucleus → stimulation of muscle tone. However, diffuse stimulation of basal ganglia → inhibition of muscle tone, i.e. the inhibitory effect is stronger than the stimulatory effect. 2) Corpus Striatum is the center of all gross intentional movements of the body which are performed subconsciously except stereotyped movements , through 2 pathways: 3) Role of basal ganglia in voluntary movements: a)Globus pallidus controls the axial and girdle movements which provide background positioning of the body and proximal limbs and fix them, so that more discrete motor functions of the hand and foot can be performed. b)Planning and programming of movements since the neurons of basal ganglia are found to discharge before the movements begin. 45  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- c)Execusion of the pattern of simple movements e.g. writing of letters of alphabet, cutting paper with scissors, or hammering nails because the program of such movements is stored in basal ganglia. This is mainly a function of putamen circuit. d)Transformation of thoughts generated in mind to motor activities. This is called the cognitive control of motor activity, which determines the pattern of movements will be used together and in what sequence to achieve a complex goal. e)Timing and scaling of movements, it is mainly a function of caudate circuit. Diseases of basal ganglia: All diseases of basal ganglia are characterized by: A) Involuntary movements during rest: -Caused by interruption of the negative feedback stability circuit between basal ganglia and motor cortex. -The pattern of such abnormal movements is dependent on which part of basal ganglia is damaged. -They are inhibited by sleep and performance of voluntary movements and exaggerated by emotions and stress. B) Hypertonia: Present in all diseases of basal ganglia except chorea, because the caudate nucleus is specifically facilitatory to stretch reflex. C) All the manifestations appear on the opposite side of the body and involve the whole side of the body. 46  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- - Diseases of basal ganglia are : chorea, athetosis, hemibalismus and Parkinson's disease. 1) Chorea:  Caused by degeneration of the caudate nucleus.  Is characterized by: a) Rapid purposeless involuntary "dancing" movements during rest. They might be superimposed on voluntary movements leading to their disruption. b) Hypotonia because the caudate nucleus is exceptionally facilitatory to stretch reflex.  Types: A) Sydenham's Chorea: Is a complication of rheumatic fever. It occurs early in life (5-15 years). More common in females than males. B) Huntington 's Chorea: Is a hereditary disease. It occurs in the third or fourth decade of life. There is spontaneous damage of cholinergic and GABA-ergic neurons in corpus striatum → dementia and chorea. 2) Athetosis:  Is due to lesion in the lentiform nucleus.  Is characterized by: a) Involuntary continuous slow spasmodic writhing (snake-like) 47  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- movements of one or more limbs particularly the hands. b) Hypertonia. 3) Hemibalismus:  Caused by damage of the subthalamic nuclei.  Characterized by: a) Involuntary sudden and strong spasmodic movements involving: -An entire leg suddenly jerks to full flexion → falling of the body during walking. -An arm may be pulled upward suddenly with great force. -The body twists explosively sideways. b) Hypertonia. 4) Parkinson’s disease: "Paralysis agitans"  Caused by degeneration of the dopaminergic neurons in the substantia nigra. Normally, there is steady loss of dopamine and dopamine receptors with age. Acceleration of these losses by the following factors precipitates Parkinsonism: a) Atherosclerosis → decreased dopamine secretion in the corpus striatum. b) Use of tranquilizers that block the dopamine receptors. In this case an imbalance between dopamine (from nigral projection fibers) and acetylcholine (from cortical projection fibers) occurs in the corpus striatum. 48  Central Motor Nervous System ----------------------------------------------------------------------------------------------------------------  Manifestations (Rigidity, Tremors and Akinesia) 1) Rigidity: -Occurs in both flexors and extensors, but more in flexors → bending forward the body of the patient. -Caused by: a) Facilitation of gamma motor neurons due to loss of the supraspinal inhibitory effect of basal ganglia ---> facilitation of stretch reflex. b) Facilitation of alpha-motor neurons: loss of the inhibitory effect of substantia nigra on corpus striatum, the latter becomes overly active → continuous output of excitatory signals to motor cortex → corticospinal tract → facilitation of alpha motor neurons -Rigidity in Parkinson's disease is lead-pipe or cog-wheel type while that of UMNL or decerebrate rigidity is clasp-knife type which is due to facilitation of gamma motor neurons only. 2) Tremors: "Static Tremors" -Are involuntary, rhythmic, oscillating movements due to alternating contraction and relaxation of antagonistic muscles leading to e.g, alternating flexion and extension, pronation and supination or pill-rolling movements. - It occurs at a rate of 4 - 8 cycles/sec. -Occurs during waking hours during rest and disappears during 49  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- sleep and performance of voluntary movement. During voluntary movements → increased discharge to both alpha and gamma motor neurons → stimulate stretch reflex → damping of such involuntary movements. - Mechanism: damage of dopaminergic neurons → rapid on-off inhibition of the motor cortex → alternate activation and inactivation of the antagonistic muscles. 3) Akinesia: - Means general poverty of movements and the patient looks like a statue. - Mechanism: rigidity of antagonistic muscles → difficult initiation and progression of motor activity. -Manifested by: a) Difficulty in initiation of voluntary motor activities → the person appears as if he is paralyzed. That is they Parkinson's disease is also called paralysis agitans or false paralysis. b) Loss of subconscious positioning movements of the proximal joints during performance of voluntary motor skilful acts by the distal ones. So these positioning movements should be done voluntarily which require much nervous effort to overcome rigidity of the muscles. c) Loss of habitual associating movements, e.g. swinging the arm during walking. 50  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- d) Mask face due to lack of automatic facial expressions related to emotional content of thought and speech. e) Speech: Slow, monotonus and low volume speech. f) Shuffling gait: The patient walks in a short steps without lifting his legs from the ground. Treatment of Parkinson's disease: A) Medical Treatment: Reestablishment of balance between the output of cholinergic and dopaminergic neurons in the corpus striatum by either:  Anticholinergic drugs or better by,  L-dopa: unlike dopamine, this dopamine precursor crosses the blood brain barrier and helps to repair the dopamine deficiency. B) Surgical Treatment: Since almost all feedback from basal ganglia to cerebral cortex pass through ventrolateral and ventroanterior thalamic nuclei, destruction of these nuclei by electrocoagulation will prevent these feedback circuits which are responsible for tremors and other symptoms of Parkinson's disease. 51  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- Cortical Control of Motor Functions All voluntary movements involve conscious activity of the motor cortex. Motor cortex: Fig (73) -It lies anterior to the central sulcus occupying approximately the posterior 1/3 of the frontal lobe. -It is further divided into 3 separate areas: I. The primary motor cortex. II. The promoter area. III. The supplemental motor area. I. Primary motor cortex Lies just anterior to the central sulcus. This area is the same as area 4 in Brodmann's classification: Body representation in primary motor cortex: Fig (74)  Crossed: Electrical stimulation of primary motor cortex → contraction of the muscles in the opposite side of the body.  Inverted (Upside Down): The face represented in the lower area while the legs and feet are represented in the upper part and the medial surface of the cerebral hemisphere.  Area of representation: Is dependent on the motor function of the part e.g. large area for hands and muscles of speech and small area for the trunk. 52  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- Function of primary motor cortex: 1) Initiation of voluntary, fine, discrete (separate) movements of the distal parts of the body, e.g. hands and fingers. 2) Facilitation of stretch reflex (facilitation of skeletal muscle tone and tendon jerks). 53  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- Effect of lesion of primary motor cortex: 1) Paralysis of the opposite side of the body (usually monoplegia). Later on there is recovery of gross movement involving proximal joints, but the fine movements of fingers never recover. 2) Hypotonia of the affected part. 3) Positive Babiniski’s sign in the opposite side (will be discussed later). II. The Premotor area (premotor area 6) - Lies immediately anterior to the primary motor cortex.. - The topographic organization of the premotor cortex is roughly the same as the of the primary motor cortex. -Premotor cortex is connected to primary motor cortex either directly or indirectly via basal ganglia and thalamus. - Functions: 1) Initiation of gross movements that involve groups of muscles. These movements are either done voluntarily or subconsciously to support and facilitate fine movements, e.g. fix the shoulders and arms at a certain position, so that the hands and fingers can do skilled movements. 2) Inhibition of stretch reflex and grasp reflex. 3) Located in the premotor area some specialized areas of motor control, they are: Fig (75) a) Broca's area of speech: (Word formation area [area 44])  Lies immediately anterior to the primary motor cortex and immediately above the Sylvian fissure. 54  Central Motor Nervous System ----------------------------------------------------------------------------------------------------------------  In this area, the memory for words is stored. So, damage of this area does not prevent the person from vocalization, but it makes him impossible to speak the whole words other than simple words such as "Yes" or "No". b) Voluntary eye movement field: (Area 8)  Lies immediately above Broca's area.  Damage of this area prevents the person from voluntarily moving the eyes toward different objects.  This area also controls the eye lid movements such as blinking. c) Head rotation area:  This area is closely associated with the eye movement field.  It is concerned with voluntary directing the head toward objects. d) Area for hand skills:  Lies immediately anterior to the primary motor cortex for the hand and fingers.  In this area, the memory for hand skills are stored.. Lesion in this area, the hand movements become incoordinated and non- purposeful "motor apraxia". Exner's center is the center for writing skills. III. The Supplemental Motor Area - Lies immediately superior and anterior to premotor area. - The leg area lies most posteriorly and the face most anteriorly. 55  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- -Functions: 1) It functions together with the premotor area to provide attitudinal movements, fixation movements of the different segments and positional movements as a background for the finer motor control of the hands and feet by the primary motor cortex. 2) It may be involved in programming motor sequences since it shows electrical activity one second before the beginning of movement. Connection of motor cortex: I ) Afferent Connection: A) From other cortical areas: Same side: from sensory (somatic , visual, auditory) areas and frontal area. Opposite side: from contralateral motor cortex to connect corresponding points of both sides. B) From Thalamus: Sensory : ventrobasal complex (VPMNT and VPLNT). Motror: VL and VA thalamic nuclei which receive impulses from cerebellum and basal ganglia. Non-specific thalamic nuclei (midline and intralaminar nuclei) which discharge to all areas of cerebral cortex. II ) Efferent connections: Motor signals are transmitted from the cortex to the spinal cord either: a) Directly: Through the pyramidal tract, or 56  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- b) Indirectly: Through multiple pathways that involve the basal ganglia, cerebellum and various brain stem nuclei (extrapyramidal system). F1g (75):Representation of the different muscles of the body in the motor cortex and location of other cortical areas responsible for specific types of motor movements. PYRAMIDAL TRACT Consists of 3 descending tracts: A) Corticonuclear Tract:  The part of pyramidal tract that controls voluntary movement of extraocular muscles.  Originates from voluntary eye movement field → terminate around the cranial nerve nuclei of extraocular muscles (III, IV and VI).  Functions: 1) Voluntary movement of eyes. 2) Facilitatory to stretch reflex of occulomotor muscles. 57  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- B) Corticobulbar Tract:  Is the part of pyramidal tract that controls the movements of the head,  These fibers terminate around the nuclei of cranial nerves V, VII, IX, X, XI and XII.  Functions: 1) Voluntary movements of the head muscles. 2) Facilitatory to stretch reflex of these muscles. C) Corticospinal Tract:  Is the part of pyramidal tract that reaches the spinal cord.  Origin: - 30% from primary motor cortex. - 30% from premotor and supplementary motor areas. - 40% From the somatic sensory areas.  Pathway: -After leaving the cortex, the fibers forms the corona radiata to pass through the internal capsule occupying the genu and the anterior 2/3 of the posterior limb. -Then the fibers descend in the brain stem: In Medulla oblongata: It occupies the pyramid of the medulla, that is why it is called the pyramidal tract. In lower part of medulla: * 90% of fibers cross to the opposite side (motor decussation) → lateral column of the spinal cord → lateral (crossed) corticospinal 58  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- tract. *10% of fibers pass ipsilaterally down in the ventral column of the spinal cord→ ventral (direct) corticospinal tract. Many of these fibers also cross to the opposite side of the cord at termination. Only 2% of the fibers terminate in the ipsilateral side.  Termination: The corticospinal fibers terminate around the intemeurons which then discharge to AHCs. Functions of corticospinal tract: - Mainly in the opposite side of the body: 1) Initiation of fine discrete voluntary movements of the distal parts of the body, e.g. fingers and hands. 2) Facilitation of lower motor neurons and stretch reflex. Functions of uncrossed fibers: these fibers are concerned with : 1- Provide bilateral innervation of some muscles as respiratory and abdominal muscles. 2- Bilateral positioning movements controlled by supplementary motor area. 3- Partial recovery of movements after injury of contralateral corticospinal tract 59  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- 60  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- Extrapyramidal System Extrapyramidal system includes all parts of the brain and brain stem that contribute to motor control and are not part of pyamidal tract. 1) Motor cortex 2) Basal ganglia: It receives afferent fibers from the motor cortex → corpus striatum → globus pallidus → several brain stem nuclei, e.g. subthalamus, substantia nigra, red nucleus, tectum of the midbrain, reticular formation, vestibular nucleus and inferior olive. 3) Red nucleus:  Located in the midbrain. a- Receives fibers directly from motor cortex, from corticospinal tract as it passes through the midbrain or from basal ganglia. b-Gives rise to rubrospinal tract → that follow the course parallel to the corticospinal tract → the lateral column of spinal cord and terminate at AHCs either directly or through interneurons (mainly).  Functions : 1) The cortico-rubro-spinal pathway serves as an accessory route for transmission of discrete signals from motor cortex. So: -Destroying corticospinal tract → discrete movements can still occur, wrist movements are present, but movement of fingers and hand are greatly impaired. 61  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- -Destroying corticospinal tract + corticorubrospinal tract —-> loss of all discrete movements including that of the wrist. 2) Red nucleus is a supraspinal inhibitory center for stretch reflex. 4) Tectum of midbrain:  Lateral tectospinal tract: - Originates from the superior colliculus (center for visual reflexes) and terminates in the cervical spinal cord. - It is concerned with directing the eyes and turning the head to the opposite side toward a light source (visuospinal reflexes).  Ventral tectospinal tract: - Originate from the inferior colliculus (center for auditory reflexes) and terminates also in the cervical spinal cord. -It is concerned with turning the head to the opposite side toward a sound (auditory spinal reflex). 5) Reticular formation:( discussed before) 6) Vestibular nucleus: Lateral and Ventral Vestibulospinal Tracts: concerned with: 1) Facilitation of stretch reflex. 2) Mediation of some postural and equilibrium reflexes. 7) Inferior olive:  Give rise to olivospinal and olivocerebellar tracts.  Functions of inferior olive: 1) Facilitation of stretch reflex. 2) Mediation of motor signals from the cortex and cerebellum to the spinal cord.(discussed with cerebellum). 62  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- 8) Cerebellum Functions of extrapyramidal system:(collectively) 1) Mediation of gross movements that involve a group of muscles (voluntary or involuntary). 2) Provides a weaker alternative to pyramidal system for mediation of some discrete movements (via corticoru-brospinal pathways), 3) Mediation of fixation and positioning movements which accompany other fine movements. 4) Adjustment of skeletal muscle tone (facilitation or inhibition). 5)Mediation of muscular coordination of voluntary and involuntary movements.(cerebellum) Upper and Lower motor neurons `To do voluntary movements, signals start in the cerebral cortex and reach skeletal muscle through 2 levels of neurons: 1) Upper motor neuron: - Are neurons of pyramidal and extra-pyramidal tracts in CNS. - Extend from the cortex down to the AHCs or corresponding cranial nerve nuclei - Is a single neuron in pyramidal tract, but multiple in extra- pyramidal system. 2) Lower Motor Neuron: - They are the AHCs + their axons + their axon terminals. 63  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- - Corresponding cranial nerve nuclei. Upper And Lower Motor Neuron Lesion Manifestations: 1) Muscle Paralysis:  In both UMNL and LMNL the muscle will be paralyzed (i.e. inability to do voluntary movements).  Extent of paralysis: - In UMNL: paralysis is widespread, e.g. lesion in internal capsule → hemiplegia. - In LMNL:paralysis is localized to the muscle or group of muscles affected.  Side of paralysis: - UMNL: at opposite side if above motor decussation at same side if below motor decussation - LMNL: always at the same side 3) Reflexes: LMNL: all reflexes (stretch reflexes, deep reflexes or tendon jerks and superficial reflexes) are lost due to interruption of their reflex arc. UMNL:  Stretch reflex and muscle tone: there is hyper or hypotonia depending on which portion of its supraspinal control is damaged; -Lesion of both pyramidal and extra-pyramidal systems at the 64  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- level of internal capsule → hypertonia due to loss of the strong inhibitory effect of the extra-pyramidal system on stretch reflex above lesion → facilitation of gamma motor neurons → clasp knife rigidity or spasticity. -Pure lesion in area 4 or pure pyramidal tract lesion → hypotonia.  Deep reflexes and tendon jerks: - Are exaggerated in cases of hypertonia and clonus may appear, e.g. ankle clonus or patellar clonus due to supraspinal facilitation. -Are inhibited in hypotonia.  Superficial Reflexes: - Loss of superficial reflexes. - Appearance of Babiniski sign. Babiniski Sign: -Means: Scratching of the lateral border of the sole of the foot ---> dorsiflexion of the big toe and fanning of other toes. 65  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- -Causes: 1) Lesion of corticospinal system: Babiniski sign is used clinically to detect damage specifically in the corticospinal tract. 2) When the corticospinal tract is inhibited in the following conditions: deep coma and general anaesthesia. 3) In infants below 1 year (pyramidal tract is not yet myelinated, i.e. non-functioning). 3) Muscle atrophy: LMNL: atrophy of the paralyzed muscles because they can not contract either voluntarily or reflexly (disuse atrophy). UMNL: no atrophy because the muscles still contract reflexly. 4) Response of paralyzed muscles to electric stimulation: -Healthy muscle respond to both faradic and galvanic currents. In galvanic current stimulation: cathodal closing contraction > anodal closing contraction (CCC > ACC) LMNL: -Decreased blood supply to the muscle → Muscle degeneration. -In degenerating muscle → Reaction of degeneration. A)1- No response to faradic current. 2- Response to galvanic current is reversed, i.e. ACC > CCC. 3- Prolonged chronaxie. B) After complete degeneration → no response to either faradic or galvanic current. UMNL: normal response of paralyzed muscle to electric stimuli.. 66  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- Internal Capsule Is a mass of white fibers lying between the basal ganglia and the thalamus. It is limited laterally by the lenticular nucleus and medially by the caudate nucleus and thalamus. In horizontal section, it is V shaped and the point of V (genu) looks medially. Internal capsule lesion: (best common example of UMNL) Caused by thrombosis or haemorrhage of lenticulostriate artery which supplies the posterior limb of the internal capsule. Clinical picture: The patient passes by 2 stages: I. Acute stage (stage of shock): - Is a state of shock which lasts for 2 - 4 weeks. -During this stage there is complete flaccid hemiplegia hemianaesthesia and loss of reflexes on the opposite side. 67  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- - The case then passes into the chronic stage. II. Chronic stage (stage of recovery): is characterized by: A) Motor disturbances: 1) Paralysis: -Loss of voluntary movements due to paralysis of muscles of the opposite half of the body "contralateral hemiplegia". -However, after sometime a considerable improvement occurs in the legs and the patient may walk. A good power returns to the arm and face. There is permanent loss of voluntary movements of the hands and fingers. The recovery is due to: a) Ipsilateral corticospinal fibers. b) Extra-pyramidal tract fibers that originate from levels lower than internal capsule especially the red nucleus. 2) Reflexes: a) Stretch Reflex and Muscle Tone: - The tone is increased in antigravity muscle, so the upper limbs is flexed and the lower limb is extended. - Cause: loss of strong inhibitory effect of extra-pyramidal system on muscle tone → activation of facilitatory reticular formation → stimulate gamma motor neurons → clasp knife rigidity. b) Deep reflexes: - Are exaggerated due to hypertonia. - Clonus appears due to supraspinal facilitation. c) Superficial reflexes: 68  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- - Loss of superficial reflexes (abdominal and cremastric). -Appearance of Babiniski sign. d) Tonic neck reflexes: - Rotation of the head toward the hemiplegia side --> The spastic arm moves into extension and abduction. - Rotation of the head toward the healthy side → The spastic arm moves into increased flexion and adduction. 3)No atrophy: because of hypertonia and reflex muscle contraction. 4) No reaction of degeneration. B) Sensory disturbances: 1- There is recovery of pain, temperature and crude mecha- noreception, but fine mechanoreception never recovers. 2-Crossed homonymous hemianopia, i.e. loss of corresponding halves of the visual fields on both sides (left or right). See the physiology of vision, 3- Decreased auditory acuity in both ears, because the auditory pathway from each cochlea takes bilateral course. 69  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- The Cerebellum The cerebellum is also called the silent area because electrical stimulation of the cerebellum does not cause any sensation or any motor movement. It is concerned with coordination of all motor activities in the body. The cerebellum is connected to brain stem by 3 pairs of cerebellar peduncles: superior, middle and inferior. Functional division of the cerebellum: Fig (78) Functionally the cerebellum is divided into 3 parts: 1) Archicerebellum (or vestibulocerebellum):  Consists of the nodule of the vermis + the flocculi in the hemispheres …flocculonodular lobe.  Is the oldest part of the cerebellum.  Functions with the vestibular system and RF to control poisture and equilibrium. Fig (78) Functional parts of the cerebellum 2) Paleocerebellum (or spinocerebellum):  Includes: rest of vermis + the adjacent medial portions of the hemispheres (the intermediate zone of the cerebellum)  Topography: -The axial portion of the body is represented in the vermis. 70  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- -Limbs and facial region lie in the intermediate zone. N.B.: There are 2 separate representation for the body in spinocerebellum. Note that the lateral zones do not have any topographic representation for the body Body representation in spinocerebellum 3) Neocerebellum:  Is the lateral zones of the cerebellar hemispheres.  Is the newest part of the cerebellum.  Does not have any topographic representation for the body.  Is connected with the corresponding association areas of motor and sensory cortex.  Operates at a much more remote level since it is concerned with overall planning and programming of all the sequential motor movements. Neuronal connections of cerebellum.: I)Afferent Fibers: Input to cerebellum. Fig (80) A)From brain: from all motor centers in the brain. B)From Periphery: Fig (81) Mainly through dorsal and ventral spinocerebellar tracts:  Dorsal spinocerebellar tract: reach epsilateral cerebellar hemisphere -Receives information from: 1. Musice spindles. 71  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- 2. Golgi tendon organs. 3. Joint receptors. 4. Large tactile receptors. Fig (80) principal afferent tracts to the cerebellum Principal efferent tracts from the cerebellum. -Inform the cerebellum about. 1. State of the muscle contraction. 2. State of muscle tension. 3. Position and rate of movement. 4. Forces acting on the surface of the body. 72  Central Motor Nervous System ----------------------------------------------------------------------------------------------------------------  Ventral spinocerebellar tract: reach both cerebellar hemisphere -Receives information from: 1. Motor signals reaching the spinal cord along corticospinal and rubrospinal pathways. 2-Less information from the periphery. -Inform the cerebellum about the motor signal indeed arrived the spinal cord (efference copy).  Fibers of the spinocerebellar tracts are thick and myelinated. They transmit impulses at a rate of 120 m/sec., which is the most rapid rate of conduction in the CNS. This is very important for the instantaneous informing the cerebellum about the changes in the peripheral motor system. II)Efferent fibers: "Output from cerebellum" Fig (82)  Originates only from cerebellar nuclei.  Three main pathways lead out of the cerebellum. 73  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- 1) Efferent fibers originate in the neocerebellum → dentate nucleus → opposite cerebral cortex. -Responsible for coordination of sequential motor activities initiated by cerebral cortex. -Cerebellar hemisphere of one side coordinates the voluntary movements of the SAME side of the body. 2)Efferent fibers originate in the intermediate zone → nucleus interpositus→ opposite cerebral cortex, basal ganglia, red nucleus and RF of brain stem. -These fibers are responsible for coordination of movements of the peripheral portions of the body especially hands and fingers. 3) Efferent fibers originate in the vermis and flocculonodular lobe → fastigial nucleus → medullary and pontile regions of brain stem. -These fibers function in close association with: a) Equilibrium apparatus → control equilibrium. b) Reticular formation of brain stem → control the body posture. Neuronal circuit of Cerebellum: Fig (83) - The human cerebellar cortex is a large folded sheet, each fold is known as folium. -The cerebellar cortex is formed of 3 layers: a) Molecular layer. b) Purkinje cell layer: contain Purkinje cells. c) Granule cell layer: contain granular cells. Cerebellar nuclei are located beneath these layers. 74  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- -Each time the input signal reaches the cerebellum, it divides and goes in 2 directions: a) Directly to deep nuclei. b) To the cerebellar cortex over the deep nucleus → the deep nucleus itself. Thus all the input signals entering the cerebellum end in the deep nuclei. -Afferent fibers to the cerebellum are of 2 types: a) Climbing Fibers:  All the climbing fibers originate from the inferior olive.  These fibers, after sending collaterals to the deep nuclei, → project directly to the molecular layer to synapse with the dendrites of Purkinje cells.  Inferior olive receives information from: a- The corticospinal tract and motor centers in brain stem → gives idea about the intention of the movement. 75  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- b- Sensory nerve endings in the muscle and surrounding tissues → give idea about the performance that actually occurs. So the inferior olive compares the intention with the performance: -If they match → no change in firing rate of climbing fibers. -If they mismatch, the climbing fibers becomes stimulated or inhibited until no mismatch occurs. b) Mossy Fibers: -All afferent fibers to the cerebellum beside those coming from the inferior olive are of mossy type. -These fibers send collaterals to stimulate the deep nuclei → pass to granular cell layer where it synapses with granular cells which send axons to molecular layer → synapse with the dendrites of Purkinje cells. -When the Purkinje cells are stimulated, they send inhibitory signals to the deep nuclear cells. So the nuclear cells receive. *Direct excitatory impulses from the input fibers and *Indirect inhibitory impulses from Purkinje cells. -During performance of rapid movement: 1- Stimulation of the deep nuclei: the output fibers cause potentiation of the start of movement, i.e. turning on the agonist muscles. 2- Few msec. later, the deep nuclei will be inhibited by Purkinje cells → damping function to stop the muscle movement from overshooting its mark i.e. turning off the agonist muscle. -Also, at the onset of movement there is turning off the antagonist muscle, while at the end of movement there is turning on of these muscles. This mainly caused by the reciprocal innervation of agonist and antagonist muscle circuits at the spinal cord. 76  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- N.B. There is no reverbratory pathways in the cerebellar neuronal circuits → prevent signal prolongation, so the input and output signals are very rapid and transient. Functions of cerebellum: The cerebellum is concerned with control of motor activities initiated elsewhere in the CNS. 1) Control of body posture and equilibrium:  This function is exerted by the flocculonodular lobe and vermis of cerebellum.  Receives impulses from non-auditory labyrinth either directly or through the vestibular nucleus and from RF.  Discharges to the vestibular nucleus and RF through the fastigial nucleus.  Removal of flocculonodular lobes of cerebellum → extreme disturbances of posture and equilibrium. 2) Regulation of muscle tone:  It is found that: Stimulation of paleocerebellum → inhibition of muscle tone. Stimulation of neocerebellum → stimulation of muscle tone. Overall stimulation of cerebellum stimulates muscle tone. 3) Role of cerebellum in voluntary movements: A) Servocomparator function: Fig (S4) During performance of voluntary movement, the intermediate zone of the cerebellum receives 2 types of information: a) Direct information from motor cortex and red nucleus → telling the cerebellum about the intended plane of movements for the next few fractions of a second. 77  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- b) Feedback information from the peripheral parts of the body through the dorsal and ventral spinocerebellar tracts → telling the cerebellum what actual signal reaches the LMN and the performance of effector oorgans ( movements). Intermediate zone compares the intention with perfonnance. then sends corrective output signals: a) Back to motor cortex → corticospinal tract → spinal cord. b) Back to red nucleus → rubrospinal tract → spinal cord. N.B.: Similar comparation occurs in the inferior olive. However, the inferior olive and climbing fiber activities are increased during learning a new movement. B) Damping function of cerebellum: -Almost all body movements are pendular because each movement has a momentum → overshooting of the movement. - If the cerebellum is not intact, the cerebral cortex detects the overshoot after its occurrence and initiates corrective movements in the opposite direction occurs. But each corrective movement has a momentum, so the 78  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- arm oscillates back and forth past its intended point for several cycles before it finally fixes on that point. This is called intention tremors or kinetic tremors. -If the cerebellum is intact, it prevents the overshoot by automatic inhibition of the agonist with stimulation of antagonist muscles at the end of movement. C) Cerebellar control of ballistic movements: - Many rapid (ballistic) movements of the body such as typing occur, so rapidly that it is not possible to receive:  Feedback information either from the periphery to the cerebellum or  From the cerebellum back to the motor cortex before these movements are over. - So the entire movement is controlled by the cerebellum in the following way:  When the cerebral cortex first initiates the movement, it immediately sends signals to the intermediate zone of cerebellum at the same time → excitation of deep nuclei (nucleus interpositus) → excitatory signals to cerebral cortex → gives force to the onset of movement.  Few msec. later, the signal entering the cerebellum has to go through a specific delay circuit in the cerebellar cortex to return to Purkinje cells → inhibition of deep cerebellar nuclei → turning off the agonist muscle and turning on the antagonist muscle → stoppage of ballistic movement.  The delay time in the circuit determines the duration of the ballistic movement. D) Planning function of cerebellum: -The plane for the sequential movements is transmitted from the association areas of the cortex → lateral zone of cerebellar hemispheres. Two-way traffic between cerebellum and cortex is necessary to provide appropriate transition from one movement to the next. 79  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- - Since the dentate nuclei of neocerebellum show the activity pattern of the next movement at the same time the present movement is occurring. Thus the lateral hemispheres appear to be involved with what will happen in the next moment. E) Timing function of cerebellum: -It is the function of the lateral zone of the cerebellar hemispheres. -The timing function of the cerebellum is to provide appropriate timing for each movement. Without this timing function, the person becomes unable to control the beginning of the next movement, it may begin too early or too late. - Therefore, in extensive cerebellar lesion, complex movements, e.g. writing, typing and talking become completely incoordinated. N.B.: Planning and timing functions are performed by the lateral zones of the cerebellar hemispheres. This zone: a) Receives No direct input information from the peripheral parts of the body. b) Is not connected with the primary motor cortex itself, but with the association areas. 4) Role of cerebellum in involuntary movements: -Signals for involuntary movements, e.g. habitual, emotional and background positioning movements are initiated in: a)Premotor & supplementary) motor areas → cerebellum. b)Basal ganglia → inferior olive→ cerebellum. c) RF → cerebellum. -Also, the cerebellum receives feedback information from the spinal cord and periphery mainly through the ventral and dorsal spinocerebellar tracts → inform the cerebellum about the performance. -The cerebellum compares the intention with the performance. If there is 80  Central Motor Nervous System ---------------------------------------------------------------------------------------------------------------- an error, it corrects it by acting