Neuroanatomy 4 ASYNCHRONOUS Spinal Cord Reflexes PDF

Spinal Cord Reflexes (E-Learning Module) Presented By: Dr. M. Doroudi; [email protected] Link to this module recording Boucher Campus: https://ccnm.ca.panopto.com/Panopto/Pages/Viewer.aspx?id=ce5619e 0-834e-4dec-84e3-af58015d3a70&instance=Moodle Toronto Campus: https://ccnm.ca.panopto.com/Panopto/Pa...

Spinal Cord Reflexes (E-Learning Module) Presented By: Dr. M. Doroudi; [email protected] Link to this module recording Boucher Campus: https://ccnm.ca.panopto.com/Panopto/Pages/Viewer.aspx?id=ce5619e 0-834e-4dec-84e3-af58015d3a70&instance=Moodle Toronto Campus: https://ccnm.ca.panopto.com/Panopto/Pages/Viewer.aspx?id=87c4f17d -e286-41b5-abb3-af58015d4852&instance=Moodle Reflexes and Reflex Arcs vA reflex is a fast, involuntary, unplanned sequence of action that occurs in response to a particular stimulus and helps to maintain homeostasis. vReflexes may be spinal, cranial [somatic or autonomic (visceral)] Reflexes and Reflex Arcs The gray matter of spinal cord serves as an integrating center for spinal reflexes. Reflex Arc A pathway followed by nerve impulses that produce a reflex is called a reflex arc. Monosynaptic Vs. 5 components of a reflex arc Polysynaptic 1. Receptor reflexes 2. Sensory neuron 3. 4. 5. Integrating center Motor neuron Effector Somatic reflex Vs. Autonomic (Visceral) reflex Spinal Cord Reflexes q Somatic spinal reflexes include: ØStretch reflex ØTendon reflex ØFlexor (withdrawal) reflex ØCrossed extensor reflex All exhibit reciprocal innervation:(Contraction of one muscle and relaxation of its antagonist muscle or muscles) Stretch Reflex (Patellar Reflex) A feedback mechanism that controls muscle length by causing muscle contraction. – Prevents injury from overstretching because muscle contracts when it is stretched Monosynaptic, ipsilateral reflex arc Events of the stretch reflex –  to Reciprocal innervation: – (polysynapticinterneuron) – antagonistic muscles relax as part of the reflex The stretch reflex can also maintain posture. Tendon Reflex A feedback mechanism that controls muscle tension by causing muscle relaxation when muscle force becomes too extreme. Ipsilateral polysynaptic reflex Golgi tendon organs are in tendon – activated by stretching of tendon – inhibitory neuron is stimulated (polysynaptic) – motor neuron is hyperpolarized and muscle relaxes Both tendon & muscle are protected Reciprocal innervation (polysynaptic) Flexor (withdrawal) Reflex The flexor (withdrawal) reflex is ipsilateral and is a protective withdrawal reflex that moves a limb to avoid pain This reflex results in contraction of flexor muscles to move a limb to avoid injury or pain Flexor (withdrawal) Reflex Ø Step on a tack (pain fibres send signal to the spinal cord Ø Interneurons branch to different spinal cord segments, intersegmental reflex arch Ø Motor fibers in several segments are activated Ø More than one muscle group activated to lift the foot off of tack Crossed Extensor Reflex The crossed extensor reflex, which is contralateral, helps to maintain balance during the flexor reflex This is a balance-maintaining reflex that causes a synchronized extension of the joints of one limb and flexion of the joints in the opposite limb Crossed Extensor Reflex Lifting right foot requires an extension of the left leg to maintain one’s balance Pain signals cross to the opposite spinal cord Contralateral extensor muscles are stimulated by interneurons to hold up the body weight Reciprocal innervation - when extensors contract flexors relax, etc Clinical Considerations of reflexes Checking a patient’s reflexes may help to detect disorders/injury q Babinski's Reflex or Extensor Plantar Reflex: ü is a test for dysfunctional corticospinal tract [Upper Motor Lesion (UML)]. ü The test involves stroking the outside sole from heel to toe with a pointed object. ü The normal response: üDownward (flexor) movement of all toes (Image A) ü In infants under 1.5 years of age (incomplete myelination in children) and people with dysfunction in the corticospinal tract, this causes an upward (extensor) movement of the big toe, often with extension and abduction (“fanning”) of the other toes (Image B). http://www.merriam-webster.com/mw/art/dict/babinski.htm 14 q Achilles Reflex (Ankle Jerk Reflex): ü Tapping on the calcaneal tendon (Achilles Tendon) would cause plantar flexion of the ankle joint. ü This reflex checks if the S1 nerve root are intact and could be indicative of sciatic nerve pathology. ü This reflex is usually absent in disk herniation at the L5-S1 level. ü A reduction in the ankle jerk reflex is also indicative of peripheral neuropathy. 15 http://edinfo.med.nyu.edu/courseware/neurosurgery/Img0037.jpg