Student Reflexes, Senses & Pain PDF

Neurology: Reflexes Senses & Pain Dr. Jacqueline Mobley AHS 2202 Today we will learn about… 3 spinal reflexes and how they travel How the brain from receiving The general senses modulates reflexes stimulus to...

Neurology: Reflexes Senses & Pain Dr. Jacqueline Mobley AHS 2202 Today we will learn about… 3 spinal reflexes and how they travel How the brain from receiving The general senses modulates reflexes stimulus to delivering an action Reflexes Autonomic reflex Reflex Somatic reflex A reflex that A reflex that involves smooth A rapid, automatic involves contraction muscle, cardiac response to stimuli of skeletal muscles muscle, and endocrine glands The reflex arc ▪ Sensory receptor initiates an impulse ▪ Nerve impulse reaches the grey matter of the spinal cord or brainstem ▪ Sensory neuron synapses with interneuron(s) ▪ Interneurons integrate the sensory impulse with other impulses from other sensory neurons ▪ Interneuron synapses with a motor neuron ▪ The motor sends the integrated response from the spinal cord or brainstem to target organ (muscle or endocrine gland) Motor Neuron Target Somatic motor neuron Contracts or inhibit skeletal muscle Autonomic motor neuron Innervates an organ, blood vessel, cardiac muscle or endocrine gland Types of somatic reflexes Stretch Withdrawal Extensor reflex reflex reflex Stretch reflex Simple, monosynaptic or two-neuron reflex arc Stretch reflex has only one synapse, involving two neurons No interneuron! The stretch receptor Stretch receptor is a muscle spindle The muscle spindle stretches and sends a signal via the somatic sensory neuron to the spinal cord Sensory neurons synapse with the motor neurons of the same muscle Motor neurons cause the muscle to contract What’s the point of this reflex? Prevents overstretching/harm to the muscles Maintains tension and tone of the muscle for coordinated muscle function The patellar reflex ▪ Patellar reflex ▪ Commonly used as part of the neuro exam ▪ Helps diagnose spinal cord trauma, peripheral nerve damage or muscle disease ▪ How does it work? ▪ Reflex hammer taps the patellar ligament ▪ Quadriceps femoris is stretched, activating the reflex arc ▪ Quadriceps contracts This Photo by Unknown Author is licen se d under CC BY-SA ▪ Leg extends Stretch + relaxation We have already learned that stretched muscles contract due to the stretch reflex BUT….the reflex also causes opposing muscles to relax Afferent somatic sensory neuron branches will synapse with an inhibitory interneuron This synapse results in opposing muscle relaxation So in the case of the patellar reflex 1) Afferent sensory neuron synapses with the motor neuron of the same muscle 2) Afferent sensory neuron also synapses with an inhibitory interneuron in the spinal cord 3) Inhibitory neurotransmitters are released at the synapse with the semitendinosus & semimembranosus 4) Quadriceps is allowed to contract without antagonism of other muscles Withdrawal reflex (Flexor Reflex) Occurs when a strong (painful) stimulus is received Classic example: touching a hot stove and withdrawing hand Withdrawal reflex involves synapses with several interneurons Some interneurons synapse with motor neurons to contract muscles Some interneurons synapse with opposing muscle group and release inhibitory neurotransmitters The reflex is complex but does not involve the brain Crossed extensor reflex If you step on something painful, this reflex communicates with the opposite leg to prevent you from falling over In this reflex Afferent sensory impulse crosses to the other side of the spinal cord to extend muscles of the opposite limb The crossed extensor reflex is an example of a contralateral reflex (opposite side) The stretch reflex is an ipsilateral reflex (same side) Brain’s role in moderating reflexes The reflex arc exists primarily in the spinal cord But…the brain plays a role in dampening how dramatic the reflex is If the spinal cord is injured above the area of the reflex, the brain does not dampen it This results in a more dramatic reflex Example: if an injury to the spinal cord occurs at L1-L2, this reflex still occurs Patellar stretch → synapse at the spinal cord → motor impulse to contract quadriceps But the brain does not PERCEIVE the stretch, and does not dampen the strength of the contraction Result: Patellar reflex is more dramatic, i.e. leg kicks out with more force This excessively strong reflex is called Hyperreflexive Spinal injury at the level of the reflex ▪ Injury at the level of the spinal reflex will make a reflex absent or decreased ▪ Hyporeflexive: decreased reflex intensity ▪ Relevance: If a dog has a spinal cord injury and we check patellar reflex ▪ The patellar reflex synapse occurs at L2, L3, L4 ▪ If the injury is at L2-L4: patient is hyporeflexive ▪ If the injury is above L2-L4: patient is hyperreflexive ▪ If the injury is below L2-L4: patient has normal patellar reflex Other reflexes: Palpebral ▪ Palpebral reflex ▪ How it’s done: Tapping the inner corners of the eyelid skin ▪ What it evaluates: ▪ Sensory neurons in CN V (trigeminal n.) to the pons (brainstem) ▪ Pons synapse to with motor CN VII (facial n.) to muscles that causing blinking ▪ What is a normal response: Patient blinks when you tap the inner corner of the eyes Other reflexes: PLR ▪ Pupillary light reflex (PLR) ▪ How it’s done: Shining a bright light into the eyes ▪ What it evaluates: Retina, CN II (optic n.), diencephalon, and motor neurons of CN III (oculomotor n.) ▪ What is normal response: Both eyes constrict simultaneously in response to light ▪ PLR does not assess “vision” This Photo by Unknown Author is licen se d under CC BY-NC-ND Clinical Case: Intervertebral Disc Disease (IVDD) ▪ IVDD – neurologic disease in which the intervertebral disc bulges or ruptures, causing swelling around the spinal cord ▪ Spinal cord swelling can cause permanent death to the neurons (paralysis) ▪ Clinical signs: Ataxia or paralysis, decreased pain or absent pain with toe pinch, abnormal spinal reflexes ▪ Diagnosis: ▪ Radiographs *might* show abnormalities such as calcified material in the disc or narrow intervertebral disc spaces. Rads rule out spinal fracture, bone tumor, osteomyelitis. ▪ MRI or CT will determine exact spinal segment when disc is injured This Photo by Unknown Author is licen se d under CC BY ▪ Treatment: ▪ Surgical decompression vs. medical management ▪ Prognosis: ▪ Good if prompt treatment SENSES General Senses The general senses include Visceral sensations Touch Temperature Pain Proprioception What’s is the point of the senses? Keeps the brain informed of what’s happening outside and inside the body Hunger Thirst Stretch of hollow organs resulting in pain Visceral Gas in GI tract sensations Stones in a ureter Urinary bladder overextension Peritoneum and pleura If becomes inflamed, results in pain Touch AKA “tactile sense” Sensation of something in contact with the body Pressure Sensation of something pressing on the body Touch & Types of sensations with touch Pressure Light contact Deep pressure Vibration Hair movement Once physical contact is initially sensed, it fades away though the contact continues Temperature ▪ Temperature receptors detect increases and decreases in body temp ▪ Hypothermia ▪ Hyperthermia ▪ 2 types of temperature receptors ▪ Superficial ▪ Central ▪ Superficial receptors ▪ Located in the skin and detect fluctuation in skin temp ▪ Heat receptors send impulses when it’s warmer ▪ Cold receptors send impulses when it’s colder  Central temperature CNS response to receptors temperature variations Keep track of the core Blood flow to the skin temperature Sweating Located in the hypothalamus Piloerection We accurately assess core Shivering temperature by taking rectal Thyroid hormone production temp Temperature  Pain ▪ Nociceptors = pain receptors ▪ The most common and widely distributed sensor receptors inside and on surface of body ▪ Except NOT in the brain! ▪ Simple, free nerve endings ▪ Specialized structures that detect mechanical force, temp ▪ Purpose of pain receptors: protect the body from injury ▪ Nociception: the process of perceiving pain ▪ Nociception is a complex process Nociception 1) Transduction Conversion of painful stimulus to a nerve impulse at the sensory nerve ending 2) Transmission Nerve impulse traveling up the afferent sensory nerve fibers to the spinal cord Nerve impulse can be amplified or suppressed 3) Modulation Occurs at the dorsal horns of the spinal cord Conscious perception occurs in the cerebral cortex 4) Perception Other areas of the brain can be involved Classifications of pain Superficial Deep Visceral pain Affects muscles Involves organs Affects skin & SQ & joints Acute Chronic Sharp, intense Dull and aching Wind up pain ▪ Pain is still experienced even when a patient is under general anesthesia ▪ Spinal cord receives pain signal and amplifies it ▪ When patient awakes, they are in severe pain (wind-up) ▪ Wind-up must be prevented ▪ It is easier to prevent pain than it is to treat it ▪ Multi-modal pain control ▪ Medications can be administered to block perception of pain at different parts of the pain pathway ▪ Transduction, transmission, modulation, perception This Photo by Unknown Author is licen se d under CC BY-NC-ND Challenges with assessing pain in animals Animals often seem Ability to assess pain to carry on and Hiding pain is a is critical for complain less than survival mechanism providing good care people We do not worry Pain is about “masking” counterproductive pain to healing Old school, outdated & unethical! Proprioception ▪ Proprioception is the sense of the body and its limbs in space ▪ Involves the vestibular system ▪ Involves stretch receptors in skeletal muscles, tendons, ligaments & joint capsules ▪ How is conscious proprioception (CP) evaluated during neurologic exam? ▪ Turn paw over so pet is standing on its knuckles ▪ Normal response: patient returns leg to normal standing position This Photo by Unknown Author is licensed under CC BY-NC-ND Clinical Scenario: Old dog vestibular disease Clinical signs: rolling, Disease involving the nystagmus (coocoo clock vestibular system (brain & movement of the eyes), inner ear) of older dogs ataxia, vomiting, anorexia, drooling Treatment: Hospitalization Diagnostics: Labs, rads, BP, if needed for IV fluids, ear exam & cytology motion sickness meds (meclizine) THE END