VP MKehl Reflexes Spring 2024.pdf

Vet Prep Structural and Functional Biology Dr. Melissa Kehl Reflexes Learning Objectives 1. Describe how a reflex arc works and its parts. 2. Differentiate between monosynaptic and polysynaptic reflexes. 3. Differentiate between response and reflex. 4. Describe examples of reflexes and what nerves a...

Vet Prep Structural and Functional Biology Dr. Melissa Kehl Reflexes Learning Objectives 1. Describe how a reflex arc works and its parts. 2. Differentiate between monosynaptic and polysynaptic reflexes. 3. Differentiate between response and reflex. 4. Describe examples of reflexes and what nerves are involved. Reflex is a simple, involuntary reaction to a stimulus Reflex arc includes: Sensory receptors Sensory neurons Segment of spinal cord Motor neurons Neuromuscular junction Muscle or other end organ Monosynaptic reflex – small segment of nervous system, tests a very specific area, ex – patella reflex Polysynaptic reflex – broad area, multiple segments, ex - withdrawal Interneuron Stimulus – a change in the environment Receptor – the end of a sensory neuron that response to a stimulus Sensory (afferent) neuron – sends sensory impulses to the CNS Interneuron – located in the spinal cord, connect a sensory neuron to a motor neuron Motor (efferent) neuron – carries an impulse (info) to an organ/muscle The monosynaptic reflex Most simple, uncommon, rapid Also called stretch reflex 1. The stretch on the tendon 2. stimulates muscle spindles 3. send information via the afferent (sensory) neuron to the spinal cord. 4. The impulse is then transmitted 5. to the efferent (motor) neuron whose axon innervates 6. the quadriceps muscle NO interneuron! Patellar Reflex = monosynaptic reflex A stretch reflex that tests the femoral nerve. When the patellar ligament is struck, there should be a contraction of the quadricep muscle. The Polysynaptic Reflex May involve motor neurons to several muscles May involve inhibition of muscle contraction 1. Skin receptor 2. Sensory neuron 3. Synapse on Interneuron 4. Synapse at motor neuron 5. Muscle 6. Spinal cord. Interneuron in spinal cord Withdrawal Reflex = polysynaptic reflex Flexion of all joints of pinched limb Coordinated contraction of many flexor muscles across several joints Message to opposite leg to extensor muscles The skin between the toes are pinch and there should be a flexion of the joints. Use a minimum amount of force to elicit a withdrawal reflex. If too much force, then you are testing pain. Reflex vs Response A reflex only involves the spinal cord. It is an automatic reaction to a stimulus that does not involve conscious thought. They will be present even if the spinal cord is severed cranial to the reflex. A response carries sensory information to the brain for interpretation. LMN and UMN LMN = (Lower motor neuron) motor neuron in the peripheral nervous system that connects directly to the muscle; originates in the grey matter of the spinal cord in the reflex arc area TV cord LMN damage more likely to be permanent Flaccid muscle tone, loose and floppy; reflexes weak to absent UMN = ( upper motor neuron) located totally in the CNS; a neuron that communicates with the LMN to initiate motor movement; originates in the brain and travels within the spinal cord to communicate with the LMN in the gray matter Electrical outlet UMN damage more likely to recover. Need to find a new neuron connection. Some tone in muscles, muscle tone many be exaggerated Spinal Functional Segments Higher Cervical C1-C5 – UMN Lower Cervical C6-T2 – LMN to 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 Menace Response Blinking in response to a potentially harmful object advancing toward the one eye The opposite eye must be covered Positive response is blinking Not seen in puppies/kittens under 16 wks old Learned response Travels up the spinal cord to the cerebrum Pupillary Light Reflex Involves CN II (optic nerve) and CN III (oculomotor nerve) Does not assess vision With bright light, pupil will constrict Panniculus Reflex Patient is lightly touched along the dorsal surface of the back. The muscle along the back is the cutaneous trunci. A stimulus to the trunk causes the cutaneous trunci muscle to twitch. Ascending sensory tracts extend up the spinal cord to the cell body of the lateral thoracic nerve in spinal cord segment C8. The lateral thoracic nerve supplies motor innervation to the cutaneous trunci. This response is not found over the sacral or cervical areas. Palpebral Reflex Touching the eyelid sends sensory information over the trigeminal nerve (CN V) to synapse with the facial nerve (CN VII) in the brain stem. Motor fibers of the facial nerve cause the orbicularis oculi muscle to contract. Often used to evaluate depth of anesthesia. Perineal Reflex Tested by touching the sides of the perineal area Positive test causes contraction of the anal sphincter and flexion of the tail Mediated by the pudendal nerve, with roots from S1-S3. 1. Which of the following is an example of a monosynaptic reflex? A) B) C) D) E) Patella reflex Withdrawal reflex Menace response Panniculus reflex Perineal reflex 2. The image shows a reflex arc. The arrow labelled #5 is showing a ______ neuron. A) B) C) D) Motor visceral Motor somatic Sensory somatic Sensory visceral 3. An injury in the which area of the spinal cord would affect lower motor neurons (LMN) to the front limb? A) C6 – T2 B) T3 – L3 C) L4- S-3 D) S1 - Cd Practice Question Answers 1. A 2. B 3. A