Reflex Arc for Stretch Reflex Muscle Spindles Figure 13.2b, p. 419 - PowerPoint PPT Presentation

Reflex Arc for Stretch Reflex

Muscle Spindles Figure 13.2b, p. 419

Proprioceptors muscle spindle Golgi tendon organ Figure 16.9a Figure 16.11a Neuroscience, 2 nd Edition Neuroscience, 2 nd Edition (2001) (2001)

The Stretch Reflex in Action Figure 16.9b Neuroscience, 2 nd Edition (2001)

Reciprocal Innervation in the Stretch Reflex muscle spindle afferent directly excites somatic motor neuron to • same muscle • muscle spindle afferent excites an inhibitory interneuron that prevents activation of somatic motor neurons to antagonists muscle

What structure is hit with the reflex hammer? What muscles are stretched? What muscle action occurs as a consequence? Why do this test?

The Stretch Reflex is a Negative Feedback Loop to Maintain Muscle Length loss of descending inhibition from CNS in upper motor neuron disorders • hypertonia; hyperreflexia; clonus • • positive Babinski sign

Plantar Reflex: Babinski Sign normal adult response positive Babinski sign positive Babinski sign occurs in infants and in upper motor neuron disorders •

Stretch Reflexes to Test patellar tendon (knee jerk) • Achilles tendon (ankle reflex) • triceps tendon • finger flexors •

Patient B Diagnosis Is it peripheral neuropathy? • If so, what is the cause? •

Sensory Nerve Conduction Study: Recording Setup recording electrode stimulating electrode ground To determine conduction velocity: measure distance along nerve between negative pole of • stimulating electrode and positive pole of recording electrode • divide by time between stimulus and start of recorded response

Sensory Nerve Conduction Study recorded response stimulus artifact recorded response is due to the sum of all the action potentials in axons of the nerve under the recording electrode start of recorded response stimulus

Electromyography stimulate nerve and record from muscle What is the specific electrical activity in the muscle cells that is being measured in and EMG recording?

Motor Unit: Somatic Motor Neuron and all the Muscle Fibers it Innervates EMG signal: summed APs of all the muscle fibers in the motor unit

Peripheral Neuropathy polyneuropathy: multiple nerves affected; generalized disorder demyelinating: decreased conduction velocity example: Guillain-Barré axonal: decreased amplitude (fewer axons firing action potentials) example: diabetic neuropathy diabetic neuropathy: usually sensory-predominant, distal axonal polyneuropathy

Glove and Stocking Pattern Figure 36-14A in Principles of Neural Science (2000) 4 th edition

Terminology paresthesia: abnormal sensation allodynia: pain in response to a non-painful stimulus HbA1c: percentage of glycated hemoglobin used to monitor glycemic control • used to diagnose diabetes mellitus •

Examination

Treatments for Diabetic Neuropathy glycemic control • treat cardiovascular issues • pain medications to control symptoms •

Patient C Possible causes of weakness: CNS damage (upper motor neuron disorder) • peripheral neuropathy • myopathy • neuromuscular junction disorder •

Ptosis • due to weakness in skeletal muscles that retract the eyelid

Creatine Kinase: a Marker for Muscle Cells Figure 12.12 p. 389

Myasthenia Gravis autoimmune disorder • antibodies to nicotinic acetylcholine receptor at NMJ • most common cause, but can be caused by other autoantibodies decreases the size of the muscle EPSP • diagnosed by tests for antibodies, repetitive nerve • stimulation test

Decline in Amplitude of Muscle Response to Repetitive Nerve Stimulation Figure 1 in Lee, I., et al “Weak and Winded” NEJM 381 : 76-82

Repetitive Nerve Stimulation Test

Steps in Muscle Excitation

Muscle EPSP

Repetitive Nerve Stimulation Test

Treatment of Myasthenia Gravis pyridostigmine • • immunosuppressive drugs

Ice Pack Test “Diagnosing Myasthenia Gravis with an Ice Pack” NEJM (2016) 375 : e39 ice pack decreases acetylcholinesterase activity to improve symptoms •