Vet Prep Reflexes PDF

Reflexes Devon Wallis Hague, DVM, DACVIM (Neurology) Rose Krupka Peters, DVM, DACVIM (Neurology) Learning objectives: 1) Understand why the neurologic exam is performed 2) Identify the 6 main parts of the neurological examination 3) Understand the difference between a “reflex” and a “response...

Reflexes Devon Wallis Hague, DVM, DACVIM (Neurology) Rose Krupka Peters, DVM, DACVIM (Neurology) Learning objectives: 1) Understand why the neurologic exam is performed 2) Identify the 6 main parts of the neurological examination 3) Understand the difference between a “reflex” and a “response” 4) Identify the anatomy assessed with withdrawal and patellar reflexes 5) Understand the difference between upper (UMN) and lower motor neuron (LMN) signs 6) Understand how we use reflex testing to help localize lesions Why do a neurologic exam? • Is the problem neurological? • Don’t be fooled by other problems like knee injuries, weakness from bleeding, fainting spells from heart disease, etc. • What is the lesion localization (where is the problem)? • CNS (brain, spinal cord) • PNS (neuromuscular system) • Multifocal? • Helps you to know what you are looking for and how to test for it • What disease could this be (differential diagnoses)? • Is it urgent or is there time for a slower approach? Components of the neurologic exam • 6 main parts: 1. Mentation Ø Assess behavioral responses to the environment and our focused tests 2. Gait and posture Ø Assess balance/ coordination and strength 3. Cranial nerve tests Ø Assess reflexes & responses of the head and face 4. Postural reactions Ø Assess proprioception & awareness of body position 5. Reflexes Ø Assess leg reflexes, skin reflex, and perineal reflexes 6. Sensation Ø Assessed in 2 ways: Does the patient hurt? Can the patient feel? Lesion localization • Use clues from the neuro exam to figure out where the problem is in the nervous system • It is like a logic puzzle! • Use normal and abnormal findings to help narrow things down Neurolocalization • Central nervous system • Peripheral nervous system • Brain • Cerebrum • Cerebellum • Brainstem • Spinal Cord • • • • • C1-C5 C6-T2 T3-L3 L4-S3 • Nerve • Muscle • Junction Let’s focus on the spinal cord üMentation and cranial nerves = NORMAL üPay attention to front leg function üHelps to determine where the problem is in the spinal cord üReflexes will help you to localize the spinal lesion Spinal functional segments • Higher cervical – C1-C5 • UMN! • Lower cervical – C6-T2 • LMN to the front and UMN to the rear • Thoracolumbar – T3-L3 • UMN to the rear • Lumbosacral - L4-S3 • LMN to the rear legs • Sacrocaudal – S1-caudal • LMN to the bladder, anus, and tail Look for the absent/ weak reflexes!! Some terms • Reflexes • A reflex is an automatic, involuntary reaction to a stimulus • Like pulling back your hand after touching something hot Reflex Arc includes: • Sensory receptors • Sensory neurons in the nerve • Segment of the spinal cord • Motor neurons in the nerve • Neuromuscular junction • Muscle or other end organ ** A problem anywhere in the reflex arc can cause a weak or absent reflex ** Some terms – Types of Reflexes • Monosynaptic reflex arc • Simple segmental reflexes • The reflex arc passes through a small segment of the nervous system • Tests a very specific area • Example: patellar reflex à When the reflex is abnormal, it means that you can localize the problem to a specific area in the nervous system Some terms – Types of Reflexes • Monosynaptic reflex arc • Simple segmental reflexes • The reflex arc passes through a small segment of the nervous system • Tests a very specific area • Example: patellar reflex à When the reflex is abnormal, it means that you can localize the problem to a specific area in the nervous system Some terms – Types of Reflexes • Polysynaptic reflex arc • Complex intersegmental reflexes • The reflex arc involves multiple segments in the nervous system • Tests broad area in the nervous system • Example: withdrawal reflex à When the reflex is abnormal, it means that you can localize the problem to any one of the multiple segments involved in the reflex. • We have to use additional clues from other tests to try to narrow things down further Some terms – Types of Reflexes • Polysynaptic reflex arc • Step on tack. Sensory fibers send signal to SC • Interneurons branch to different SC segments • Motor fibers in several segments are activated • More than one muscle group activated lift foot à When the reflex is abnormal, it means that you can localize the problem to any one of the multiple segments involved in the reflex. • We use additional clues from other tests to narrow things down Some terms Response • Responses • Conscious, behavioral responses to a stimulus • Requires the cerebrum (the part of our brain for conscious awareness) • This means the entire pathway can be long when we are talking about looking for conscious responses for tests in the back feet – involves the back leg, entire spinal cord, brainstem, and cerebrum! • Usually a manifestation of a learned behavior • Like yelling “OUCH!” when you touch something hot Reflex The withdrawal test • A reflex (pulling the leg toward the body away from an irritating stimulus) – the “Hot Coffee Reflex” • Indicates the local spinal cord segments and nerve are intact AND Test of nociception (deep pain) • A behavioral response (“Ouch!”) – the “Hot Coffee Response” • Look for turning the head to look at you, vocalizing, changes in breathing pattern, etc – something to indicate the pet is aware the toes are being pinched • Requires the entire spinal cord, brainstem, and cerebrum to function Testing reflexes AND responses • 6 main parts of the neurologic exam: • Mental state • Assess behavioral responses to the environment and our focused tests • Gait and posture • Assess balance and coordination reflexes and strength • Cranial nerve tests • Assess reflexes of the head and face and some responses to those tests • Proprioception • Assess balance and coordination reflexes • Leg and body reflexes • Assess leg reflexes, skin reflex, and perineal reflexes • Palpate for painful areas and the ability to feel a painful stimulus • Assess behavioral responses to the exam For example • Normal withdrawal • Pulling the leg to the body indicates functioning local reflex arc of the nerves, C6-T2 spinal cord segments, muscle and neuromuscular junction • Vocalizing and looking indicates the rest of the cervical spinal cord, brainstem, and cerebrum are working For example • Weak to absent withdrawal • Trouble pulling the leg to the body indicates a problem in the local reflex arc of the nerves or L4-S3 (back leg reflex arc) spinal cord segments • Loss of ALL reflexes makes us think of generalized neuromuscular disease instead of a focal lesion • Getting annoyed indicates the rest of the cervical spinal cord, brainstem, and cerebrum are working • It also tells us that the problem is not complete – there is enough function to still be able to feel the toes For example • Intact withdrawal but absent behavioral response • Pulling the leg to the body indicates the local reflex arc of the nerves and L4-S3 spinal cord segments are intact • Not reacting to a very painful pinch indicates that something is damaged severely somewhere in the rest of the thoracic and cervical spinal cord, brainstem, or cerebrum (essentially a problem cranial to L4) Main ideas • Reflexes help you to know WHERE the problem is in the nervous system • The degree of weakness or paralysis and the inability to feel the toes tells us HOW BAD the problem is • FIRST: Loss of proprioception and normal coordination • Loss of motor function • Mild – walking, but weak and wobbly • Moderate – unable to walk, but able to shuffle legs to try to stand • Severe – paralysis (inability to willfully move the legs) • Loss of superficial pain sensation (light fingernail pinch) • LAST: Loss of deep pain sensation (hemostat pinch) Main ideas • FIRST: Loss of proprioception and normal coordination • Loss of motor function • Mild – walking, but weak and wobbly • Moderate – unable to walk, but able to shuffle legs to try to stand • Severe – paralysis (inability to willfully move the legs) • LAST: Loss of deep pain sensation (hemostat pinch) UMN vs LMN • When using reflexes to localize a lesion, we also categorize as: • Lower motor neuron lesion (LMN) • Upper motor neuron lesion (UMN) • LMN • Motor neuron in the peripheral nervous system that connects directly to the effector muscle • Originates in the grey matter of the spinal cord in the reflex arc area • UMN • A neuron that communicates with the LMN to initiate motor movement • Originates in the brain and travels into the spinal cord to communicate with the LMN in the grey matter UMN vs LMN • Think of it like a TV that you want to turn on • Effector muscle • Turning on the TV screen to watch a movie • Like making the muscle contract/ work • LMN • The power cable that is part of the TV • The part that works directly to carry electricity to the TV to make it work • If you cut the power cord with scissors, the TV is not going to work anymore • UMN • The electrical outlet that you plug the power cord into • The part that sends the signal to the power cable to make it work • If the outlet doesn’t work, the TV is still functional, you just have to plug into a different outlet UMN vs LMN • LMN • The power cable that is part of the TV • The part that works directly to carry electricity to the TV to make it work • If you cut the power cord with scissors, the TV is not going to work anymore • Similarly if you damage the LMN, the muscle won’t be able to contract anymore. Nerve damage and reflex arc spinal cord segment injury are more likely to be permanent UMN vs LMN • UMN • The electrical outlet that you plug the power cord into • The part that sends the signal to the power cable to make it work • If the outlet doesn’t work, the TV is still functional, you just have to plug into a different outlet • Similarly if you damage the UMN, the segmental reflex arc is still intact and can still function if a new neuron connection can form with a different UMN in the spinal cord. UMN injuries are more likely to recover compared to a similarly severe LMN lesion UMN vs LMN • Signs • UMN • There may be some tone to the muscle, even in paralyzed legs • Muscle tone is sometimes exaggerated • Reflexes are intact and can sometimes be brisk or exaggerated • LMN • There is flaccid muscle tone and legs can feel loose and floppy • Reflexes are weak to absent UMN versus LMN Images from Small Animal Atlas and Textbook and BSAVA Manual of Canine and Feline Neurology, 4th ed UMN versus LMN X X Images from Small Animal Atlas and Textbook and BSAVA Manual of Canine and Feline Neurology, 4th ed UMN versus LMN X X Images from Small Animal Atlas and Textbook and BSAVA Manual of Canine and Feline Neurology, 4th ed UMN versus LMN X X Images from Small Animal Atlas and Textbook and BSAVA Manual of Canine and Feline Neurology, 4th ed UMN versus LMN X X Images from Small Animal Atlas and Textbook and BSAVA Manual of Canine and Feline Neurology, 4th ed Clues to UMN vs LMN disease • Localizing spinal cord lesions: • Mental state • Assess behavioral responses to the environment and our focused tests • Gait and posture • Assess balance/ coordination and strength • Cranial nerve tests • Assess reflexes and some responses of the head and face • Postural reactions • Assess proprioception & awareness of body position • Leg and body reflexes • Assess leg reflexes, skin reflex, and perineal reflexes • Palpate for painful areas and the ability to feel a painful stimulus • Assessed in 2 ways: Does the patient hurt? Can the patient feel? Lesion localization • FIRST question: • Are only the back legs affected OR are the front legs affected, too? Back legs = T3-L3 OR L4-S3 Front AND back legs = C1-C5 OR C6-T2 Lesion localization • Second question: • Are the leg reflexes intact or weak/absent? • Back legs • T3-L3 = front legs normal function, back legs affected BUT intact hindleg reflexes • L4-S3 = front legs normal function, back legs affected BUT weak to absent hindleg reflexes T3-L3 L4-S3 Lesion localization • Second question: • Are the leg reflexes intact or weak/absent? • Front AND back legs = C1-C5 OR C6-T2 • C1-C5 = all four legs affected, ALL legs have intact reflexes • C6-T2 = all four legs affected, reduced to absent reflexes in the FRONT legs and intact reflexes in the back legs C1-C5 C6-T2 Lesion localization If all four legs are affected and have weak to absent reflexes, then we think of generalized neuromuscular disease INSTEAD of spinal cord disease Summary • Neurologic exam helps • Confirm neurologic disease • Localize the lesion • Reflex = involuntary, unconscious reaction to a stimulus • i.e. patellar reflex • Response = conscious response to a stimulus and requires a functioning cerebrum (forebrain) • Reflexes are the key to localizing lesions in the spinal cord • LMN lesions cause weakening or loss of reflexes, loose muscle tone, and can be harder to recover from • LMN signs in the front legs are associated with C6-T2 • LMN signs in the rear legs are associated with L4-S3 • LMN signs in ALL FOUR legs are associated with generalized neuromuscular disease Questions? • [email protected]