UNIVERSITY OF JORDAN FACULTY OF MEDICINE DEPARTMENT OF PHYSIOLOGY & BIOCHEMISTRY NEUROPHYSIOLOGY (MEDICAL), Spring 2014

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UNIVERSITY OF JORDAN FACULTY OF MEDICINE DEPARTMENT OF PHYSIOLOGY & BIOCHEMISTRY NEUROPHYSIOLOGY (MEDICAL), Spring 2014 Textbook of Medical Physiology by: Guyton & Hall, 12 th edition 2011 Eman

Spinal preparation; they transect the SC between medulla oblongata & SC. 2.

1 UNIVERSITY OF JORDAN FACULTY OF MEDICINE DEPARTMENT OF PHYSIOLOGY & BIOCHEMISTRY NEUROPHYSIOLOGY (MEDICAL), Spring 2014 Textbook of Medical Physiology by: Guyton & Hall, 12 th edition 2011 Eman Al-Khateeb, Professor of Neurophysiology No. 6 Motor Functions of the Spinal Cord: To study the motor functions of the Spinal Cord (SC) two types of experimental preparations is used: 1. Spinal preparation; they transect the SC between medulla oblongata & SC. 2. Decerebrate preparation; they transect at the mid or low mesencephalon (intercollicular lesion just above the pons) to block inhibitory signals from higher centers to pontine & vestibular nuclei leaving these nuclei tonically active to stimulate the SC motor activity. Below figure shows decerebrate and decorticate rigidity in human. There is no neural circuit anywhere in the brain that causes movements of the legs that is required in walking, instead the circuits for these movements are in the SC. 1

to the cerebral cortex. Each segment of the SC has several million neurons in its gray matter & these are: 1.Sensory neurons that are present within the dorsal root ganglia. 2.

2 Spinal Cord Reflexes: Sensory signals spinal cord (posterior roots) grey matter (motor neurons) motor nerve (ventral roots) skeletal muscle. Sensory signals enter the SC through the sensory (posterior) roots to go to the gray matter of the SC & elicit local reflexes or to transmit signals to higher levels in the cord, brainstem, or even to the cerebral cortex. Each segment of the SC has several million neurons in its gray matter & these are: 1.Sensory neurons that are present within the dorsal root ganglia. 2.Anterior motor neurons: larger than other cells & give rise to the nerve fibers that leave the SC by the anterior root & innervate the skeletal muscle fibers. They are of two types: a. The Alpha motor neurons: give rise to Aα motor nerve fibers that branch many times after they enter the muscle & they innervate the extrafusal muscle fibers. Each motor nerve fiber innervates from 3 - several hundred skeletal muscle fibers which are called the "Motor Unit". b. The Gamma motor neurons: much smaller cells & less in number than the alpha motor neurons they transmit impulses through type Aγ motor nerve fibers to the intrafusal fibers (Special muscle fibers that are part of the muscle spindle). 3.The Interneurons: they are small, highly excitable often have spontaneous activity & capable of firing at a rate up to 1500 AP / sec. They are present everywhere in gray matter & have many interconnections with one another, most of the incoming sensory signals are transmitted first through the interneurons where they are processed also many corticospinal fibers terminate on interneurons & then terminate on the anterior motor neurons. 4.The Renshaw cells: which are inhibitory interneurons that transmit inhibitory signals back to the surrounding motor neurons to cause lateral inhibition & to sharpen the signal. 2

The Golgi Tendon Organs: located in the muscle tendon & transmit information about muscle tension & the rate of change of tension. These two receptors are functioning entirely at subconscious level.

3 Muscle Sensory Receptors: 1.The Muscle Spindle: distributed throughout the belly of the muscle in between the extrafusal muscle fibers & send information to the CNS about the muscle length & the rate of change of its length. 2.The Golgi Tendon Organs: located in the muscle tendon & transmit information about muscle tension & the rate of change of tension. These two receptors are functioning entirely at subconscious level. The Muscle Spindle : it consists of 3-12 specialized muscle fibers enclosed in a capsule these fibers are called intrafusal muscle fibers. The central region of the intrafusal muscle fibers does not contract while the ends do. The central portion functions as a sensory receptor. The intrafusal fibers are in parallel with the extrafusal fibers & the capsule of the spindle is attached to the tendons on either ends of the muscle. The receptor portion of the muscle spindle is stimulated by stretch of the mid portion of the spindle this can occur as a result of: 1. Lengthening of the whole muscle. 2. Contraction of the end portions of the intrafusal fibers by increased stimulation of gamma motor neurons. There are two types of intrafusal fibers these are: 1. Nuclear chain fibers: which mediate the Static response of the spindle receptor i.e. the transmission of signals regarding the muscle length continues for as long as the receptor itself remains stretched. 3

2. Nuclear bag fibers: which mediate the Dynamic response of the spindle receptor i.e. the transmission of signals regarding the rate of change in muscle length will be increased or decreased as the rate of change in muscle length is increased or decreased.

4 2. Nuclear bag fibers: which mediate the Dynamic response of the spindle receptor i.e. the transmission of signals regarding the rate of change in muscle length will be increased or decreased as the rate of change in muscle length is increased or decreased. There are two sensory endings within the receptor area of the muscle spindle: 1. Primary endings (The Annulospiral ending) it is type Ia fiber with a diameter = 17 mm & conduction velocity = m / sec. This ending is excited by both nuclear bag & nuclear chain fibers. 2. Secondary endings: it is type II fibers with a diameter = 8 mm & excited by nuclear chain fibers only & usually terminates on interneurons within the SC. Normally there is a slight amount of continuous gamma motor excitation consequently; the mid portion of the muscle spindle emits sensory nerve impulses continuously. Stretching the muscle spindles signal SC positively while unstretching (shortening) lead to negative signals send to SC. The γ motor nerve that innervates muscle spindle is divided to: 1. Gamma dynamic (gamma - d) mainly excite the nuclear bag intrafusal fibers& the dynamic response of the muscle spindle is enhanced. 2. Gamma static (gamma - s) mainly excite the nuclear chain intrafusal fibers & enhance the static response. Control of The Gamma motor neurons: 1. It is excited from the Bulboreticulr facilitatory region of the brainstem. 2. It is also excited by impulses trnsmitted to the bulboreticular area from cerebellum, basal ganglia, & even cerebral cortex. Anxiety increases the gamma neuron discharge. Alpha & gamma motor neurons are co-activated simultaneously this cause both the extrafusal & the intrafusal fibers to contract at the same time in order to: 1. Keep the muscle spindle reflex from opposing the muscle contraction. 2. To maintain proper sensitivity of the muscle spindle regardless of change in muscle length. The Stretch Reflex: (The Tendon reflex or the Deep reflex) 4

5 It is a reflex mediated by the muscle spindle, & it is the only Monosynaptic reflex in the body. When a skeletal muscle with an intact nerve supply is suddenly stretched it contract. the primary sensory endings enters the dorsal root of the SC & then it passes directly to the anterior horn of the gray matter & synapse directly with the anterior neurons that send nerve fibers back to the same muscle from where the muscle spindle fiber originated (Dynamic stretch reflex). The dynamic stretch reflex is over within a fraction of a second but then a weaker (static stretch reflex) continues for a prolonged period thereafter due to continuous static receptor signals by both primary & secondary endings, it causes the degree of muscle contraction to remain reasonably constant. Main functions of Stretch reflex: 1. Stretch reflex establishes the muscle tone (the resistance offered by the muscle to stretch). When the stretch reflex is interrupted (cutting the motor nerve to muscle), the muscle is flaccid. Hypotonic muscle: is the muscle with decreased resistance to stretch caused by low gamma efferent discharge. Hypertonic muscle: is the muscle with increased resistance to stretch caused by high gamma efferent discharge. 2. Stretch reflex prevents oscillation & jerkiness of the body movements leading to smoothing or damping function. 3. Enhancement of extrafusal muscle fiber contraction: when a muscle is contracted against a great load, extrafusal fibers might contract less than the intrafusal fibers. This mismatch in contraction would stretch the receptor portion of the spindle & therefore stretch reflex will take place & provides extra excitation of the extrafusal fibers. 4. Stabilization of body position during tense motor action (when high degree of delicate & exact positioning is needed). The facilitatory pontine reticular formation transmit excitatory signals through gamma fibers to intrafusal fibers on both sides of the joint, leading to tight & tense muscle opposing each other at the same joint. This will lead to stabilization of the major joints & aids in performing precise voluntary movements by fingers or other parts of the body. Reciprocal inhibition: When a stretch reflex occurs the muscles that antagonize the action of the muscle involved relax. The pathway is Bi-synaptic through collateral branch from the afferent neuron passes in the SC to an inhibitory interneuron that synapses directly on one of motor neurons supplying the antagonistic muscle. Clinical application of stretch reflex: 1. Knee jerk: tapping the patellar tendon lead to stretching of the quadriceps femoris muscle & excites the dynamic stretch reflex. 2. All the other muscle jerks. The purpose of performing stretch reflex on a patient is: To determine how much "Tone" (background excitation) the brain is sending to the SC. The Golgi Tendon Reflex: (The Inverse Stretch Reflex) When muscle tension is increased (by active muscle contraction), the Golgi tendon organs are stimulated & signals are send through type Iβ nerve fibers to the SC to synapse to an inhibitory interneurons that in turn inhibit the anterior alpha motor neuron innervated the same muscle from which the signals were originated. Interneuron releases the inhibitory neurotransmitter glycine that lead to hyperpolarization of the motor neuron. Strychnine (used for killing birds, rodents and for trapping fur-bearing animals) is a potent convulsant. It causes increased excitability in the spinal cord through inhibiting glycin. The initial symptoms are tightness and twitching of the muscles, agitation, and hyperreflexia. 5

6 Convulsions and hyper-reactivity to stimuli are characteristic of strychnine poisoning. The patient is conscious and has intense pain. The tendon organ like the primary receptors of the muscle spindle has both dynamic & static response. This reflex has the benefit of: 1. Prevents tearing of the muscle or avulsion of the tendon from its attachment to the bone through the "lengthening reaction". 2. Equalize the contractile forces of the separate muscle fibers. When the tension becomes too little, impulses from the tendon organ cease & the loss of inhibition lead to activation of alpha motor neurons again. This reflex is entirely inhibitory & provides negative feedback mechanism that prevents the development of too much tension on the muscle. Control of the Golgi Tendon Reflex: From the golgi tendon organs impulses go through spinocerebellar tract (conduction velocity = 120 m / sec.) directly to cerebellum. Additional pathway also goes to the reticular region & cerebral cortex. The brain sends signals to the target muscle through alpha motor neurons to cause muscle contraction at a required tension & signals to the inhibitory interneurons of the SC to inform them of the tension required as detected by the feedback from the golgi tendon organs, the inhibitory interneurons automatically inhibit the muscle contraction to prevent additional tension. In this way the muscle tension is adjusted to set point dictated by the brain. Clinical application: In a hypertonic muscle, if passive & sustained muscle stretch is applied this will lead to: 1. Clasp - knife reflex: in a hypertonic muscle, moderate passive stretch will lead to muscle contraction, however stronger passive stretch will lead to relaxation due to excitation of the golgi tendon organs & reflex inhibition i.e. in a hypertonic muscle sustained stretch lead to resistance followed by relaxation. 2. Clonus: regular rhythmic contraction of a hypertonic muscle that is subjected to sudden sustained passive stretch. It is due increased gamma efferent discharge. Best example is Ankle Jerk when dorsiflex the foot there will be rhythmic planter flexion at the ankle (the stretch reflex - inverse stretch reflex sequence may contribute to this response). 6

Ankle clonus test: Place patient's knee bent, thigh externally rotated. Dr lifts patient's heel in Dr's cupped hand. Dr quickly dorsiflexes patient's ankle and holds it flexed for 3 seconds.

7 Ankle clonus test: Place patient's knee bent, thigh externally rotated. Dr lifts patient's heel in Dr's cupped hand. Dr quickly dorsiflexes patient's ankle and holds it flexed for 3 seconds. Clonus if sustained movement afterwards. The Withdrawal (Flexor)Reflex: It is a polysynaptic reflex (3-4 neurons pathway), the painful or other sensory stimulus pass into a group of interneurons & then to the anterior motor neurons to elicit muscle contraction & usually withdrawal of the affected limb. In the interneurons, the signal will stimulate the necessary muscles for withdrawal& inhibit the antagonistic muscles (reciprocal inhibition circuits) & circuits to cause the "After Discharge" through a recurrent pathways that initiate oscillation in reverberating interneuron circuits these in tern transmit impulses to anterior motor neurons for seconds after the incoming signal is over thus the flexor reflex is to withdraw the irritated part of the body from the stimulus & the after discharge can hold that part for sec after the irritation is over, during this time other actions from the CNS can move the entire body away from the stimulus.. Also there is crossing to the other side of the SC to cause opposite reflex in the opposite limb (crossed extensor reflex) i.e. extend the opposite limb & push the entire body away from the object causing the painful stimulus. This reflex has even longer after discharge than the flexor reflex. Clinical applications for polysynaptic reflexes: 1. Abdominal reflex. 2. Cremasteric reflex. CUTANEOUS (SUPERFICIAL) REFLEXES (CR) There are three diagnostically useful CR, plantar, abdominal, and cremasteric reflexes. They are related to upper motor neuron lesions. 7

8 1.The plantar reflex(s1,s2): is elicited by scratching or lightly stroking the sole of the foot, especially at the lateral aspect, using a blunt instrument. Most students and some clinicians erroneously apply deep pressure that causes injury. Plantar-flexion of the toes, especially the great toe (big toe), represents the normal response. In upper motor neuron lesions (pyramidal tract lesions) plantar-flexion is replaced by dorsiflexion and is called Babinski response or reflex (after the name of the neurologist who discovered it). It is misleading to say Babinski positive and Babinski negative because there is one Babinski response. These confusing terms can be avoided by using down-going toe for the normal response and up-going toe for the abnormal response. Dorsiflexion of the big toe may be accompanied by dorsiflexion and abduction of the other toes (fanning), and often by dorsiflexion of the foot and flexion at the knee and hip. This indicates that the Babinski reflex is part of a wider withdrawal (nociceptive) reflex. Planter reflex, upper normal, middle upgoing, lowers equivocal The Babinski reflex is the most sensitive, consistent, and pathognomonic sign of pyramidal tract lesion. When there is a lesion, the reflex is obtainable after one or two trials, and in the absence of such a lesion, frantic stroking will not by an act of magic elicit a reflex. The receptive field becomes restricted to the most lateral aspect of the sole in mild lesions, and may extend to the leg or even to the thigh in spinal cord lesions (some cases of spastic paraplegia) but not in cerebral lesions. Elicitation of the reflex from areas other than the sole of the foot is given various names (Oppenheim, Gordon, Chaddock s reflexes). These reflexes are present only when the Babinski reflex is present, hence they are not helpful. The Babinski reflex may be obtained in children up to 2 years of age (incomplete myelination of the pyramidal tracts), during sleep and general anesthesia, coma, alcohol intoxication, and generalized epileptic seizure. In these conditions there is interruption of function (physiological) of the pyramidal system and not a structural damage and the reflex is bilateral. 2.The abdominal cutaneous reflex: (T 8 12) is elicited by stroking the skin with a blunt instrument causing contraction of the abdominal muscles. It is equivalent to the withdrawal reflex of a limb after a pinprick. This reflex can be obtained independently from the four quadrants of the abdomen. This reflex is lost especially in acute lesions of the pyramidal system (stroke, spinal cord injury, acute attack of multiple sclerosis). In chronic lesions as 8

9 motor neuron disease and long-standing hemiplegia, it may remain intact or return increased after a period of loss. The reflex may become unobtainable in obese individuals and after multiple pregnancies without a lesion of the pyramidal system. Although loss of the abdominal cutaneous reflex is a characteristic sign of pyramidal system lesion, it may remain intact. 3.The cremasteric cutaneous reflex: (genitofemoral nerve, L1, L2)is obtained by stroking the skin of the thigh in proximity of the testicles causing ascend (withdrawal) of the testicle on the same side. This reflex is lost in lesions of the pyramidal system but usually ignored by clinicians. Reflexes of posture & locomotion: 1. Positive supportive reaction: pressure on the foot pad causes the limbs to extend even in decerbrated animal. The locus of pressure will determine the direction of limb extension "The Magnet Reaction" 2. Cord Righting reflex. 3. Stepping & walking reflexes. Spinal Reflexes that cause Muscle Spasm: 1. Muscle spasm from a broken bone. 2. Abdominal muscle spasm in peritonitis & during surgical operations due to irritation to parietal peritoneum. 3. Muscle cramps due to severe cold, lack of blood flow or severe exercise can cause reflex muscle spasm. Autonomic reflexes in the SC: 1. Changes in vascular tone resulting from changes in local skin heat. 2. Sweating. 3. Intestinointestinal reflex. 4. Peritoneointestinal reflex. 5. Evacuation reflexes for emptying the bladder & colon. 6. Mass reflex: can be initiated by strong pain stimulus. It leads to strong flexor reflex spasm, evacuation of colon & bladder & profuse sweating. It involves the activation of many reverberating circuits within the SC & in this it is similar to what happens in epileptic seizure where many reverberating circuits are activated in the brain. Spinal cord injury (SCI) & Transection: SCIs (in USA) occur more often in the summer months, on Saturdays, and during daylight hours. Not surprisingly, motor vehicle accidents (48%) account for the majority of SCI, while falls (21%), violent crimes (15%), sports (14%; mostly diving accidents), and medical tumors (2%) account for the remainder. Men (82%) are much more likely to suffer from SCI. Regardless of gender; substance abuse and alcohol intoxication are substantial risk factors for SCI. Regardless of the mechanism, spinal-cord injuries have the following three common abnormalities that lead to tissue damage: Destruction from direct trauma Compression by bone fragments or disk matter Ischemia secondary to impingement of the spinal arteries When synaptic connections are suddenly interrupted, the following events rapidly ensue: 1. The impact of force damages nerve cells. 2. There is a loss of normal blood flow, swelling of tissue, breakdown of cell structure, and loss of myelin sheathing. 3. The flow of ionic current is disrupted when the higher concentrated calcium ions on the exterior of the nerve cells leak interiorly and flood the neuron. 9

Cord functions immediately depressed (Spinal Shock) due to interruption of excitatory fibers from higher centers as the reticulospinal, vestibulospinal & corticospinal tracts, arterial blood pressure

10 Cord functions immediately depressed (Spinal Shock) due to interruption of excitatory fibers from higher centers as the reticulospinal, vestibulospinal & corticospinal tracts, arterial blood pressure falls & all skeletal muscle reflexes are blocked & sensation is lost. Some reflexes may eventually become hyper excitable, particularly if a few facilitatory pathways remain intact, then after two weeks to several months in human the spinal neurons regain excitability. The first reflexes to return are the stretch reflexes followed by others. Sacral reflexes for evacuation are also suppressed but in most cases they eventually return. A person who may have a spinal cord injury should not be moved. Treatment of SCI begins with immobilization. This strategy prevents partial injuries of the cord from severing it completely. Use of splints to completely immobilize suspected SCI at the scene of the injury has helped reduce the severity of spinal cord injuries in the last two decades. Intravenous methyl prednisone, a steroidal anti-inflammatory drug, is given during the first 24 hours to reduce inflammation and tissue destruction. Rehabilitation after spinal cord injury seeks to prevent complications, promote recovery, and make the most of remaining function. Rehabilitation is a complex and long-term process. Poliomyelitis Poliomyelitis results from a relatively selective destruction of lower motorneurons in the ventral horn by the poliovirus. The disease causes a flaccid paralysis of muscles with the accompanying hyporeflexia and hypotonia. Some patients may recover most functions whereas others progress to muscle atrophy and permanent disability. Amyotrophic lateral sclerosis (ALS) - Lou Gehrig Disease ALS is a relatively pure motor system disease that affects both upper and lower motorneurons. The disease typically begins at cervical levels of the cord and progresses either up or down the cord. Patients present with bilateral flaccid weakness of the upper limbs and bilateral spastic weakness of the lower limbs. Lower motorneurons in the brain stem nuclei may be involved later. 10

Stretch reflex and Golgi Tendon Reflex. Prof. Faten zakareia Physiology Department, College of Medicine, King Saud University 2016

Stretch reflex and Golgi Tendon Reflex Prof. Faten zakareia Physiology Department, College of Medicine, King Saud University 2016 Objectives: Upon completion of this lecture, students should be able to