1 - Anatomy

Question 1

Which part of the nervous system does the EDX study evaluate? 🔑🔑

Answer 1

Question 2

Draw Motor Unit. List 5 components 🔑

Answer 2

1. Anterior horn cell (motor nerve cell body)
2. Motor nerve axons
3. Peripheral nerve
4. NMJ
5. Muscle fibers

Cuccurollo 4th Edition Chapter 5 EDX pg333 Figure 5-2

Question 3

Draw a Neuron

Answer 3

Question 3

Draw a the Peripheral Nerve SystemDraw a Neuron

Answer 3

Question 4

Draw nerve connective tissue 🔑🔑 MOCK 2020

Answer 4

Cuccurollo 4th Edition Chapter 5 EDX pg332

Question 5

List 3 Types of Alpha Motor Neurons 🔑

Answer 5

💡 ABY: Alpha, Beta, Gamma

Outside to inside (Alpha Out - Beta Both - Gamma In)

Cuccurrollo 4th Editio Chapter 5 EDX pg333

Question 6

Compare innervation of type l and ll muscle fiber / alpha motor neuron . 4 marks. 🔑

Answer 6

Cuccurollo 4th edition Chapter 5 pg333

Question 7

Which nerve fiber is evaluated by EDX study?

Nerve fiber classifications?

Types of peripheral nerves?

Answer 7

💡 EDX studies evaluate only Ia (large, myelinated) fibers

Cuccurollo 4th Edition Chapter 5 EDX pg334 Tabkle 5-2

Question 8

Draw NMJ 🔑

List the main components

Quantal content vs response 🔑

Answer 8

NMJ Components

1- Presynaptic region (Storage & Release) “ACh Bank”

Storage compartments containing ACh

Quantal content: Number of ACh quanta released with each nerve depolarization

2- Synaptic cleft (Break down)

ACh crosses from the presynaptic region toward receptors on the postsynaptic region.

Contains an enzyme called acetylcholinesterase, which degrades ACh into acetate and choline as it crosses the cleft.

3- Postsynaptic region (Response)

ACh receptor requires two molecules of ACh to become activated.

Quantal response: Ability of the ACh receptors to respond to the ACh molecules

Cuccurollo 4th Edition Chapter 5 EDX pg338-339

Question 9

What are the states of NMJ physiology? 2 marks.

Answer 9

1- Resting State

During the periods of inactivation, a spontaneous release of a quanta occurs every 5 seconds. This results in production of one miniature endplate potential (MEPP).

2- Excited (Activation) state

Nerve depolarization opens voltage gated calcium (Ca++) channels, release of multiple quanta which generates a motor unit action potential (MUAP)

💡 Amplitude of an EPP must be high enough (four times more) to initiate an AP. EPP’s amplitude drops each time the EPP is created due to a drop in immediate available ACh (consumption of stored ACh).

Cuccurollo 4th Edition Chapter 4 EDX pg339

Question 10

What type of nerve fiber innervates the muscle? 1 mark 🔑🔑

Answer 10

An anterior horn motor neuron, called an alpha motor neuron, innervates the muscle

Neurology Secrets 6th Edition Chapter 2 pg13

Question 11

In the spinal cord, which nerve fibers synapse on the alpha motor neuron? 2 marks

Answer 11

1. Corticospinal tract
2. Afferent Ia sensory nerves

Both snapping on alpha motor neuron in the anterior horn of the spinal cord.

Neurology Secrets 6th Edition Chapter 2 pg13

Question 12

What is the muscle stretch reflex? What is the pathway?

Answer 12

Muscle stretch reflex

Reflex arc that responds to stretching of muscle fibers to keep the muscle in an appropriate state of tension and tone, ready to contract or relax as needed.

Sensory input (afferent)

Spindles and Golgi tendon organs.

Motor output (efferent)

Alpha motor neuron (contracts the muscle)

Neurology Secrets 6th Edition Chapter 2 pg13

Question 13

What is the function of the Ia sensory nerve fiber?
What is the function of the Ib sensory nerve fiber?

Answer 13

Muscle Stretch Reflex

• Maintains tone and tension in the muscle, by contracting it when it becomes too relaxed.

la sensory fibers (positive pathway)

• Arises from the muscle spindle, when it’s stretched (muscle relaxed), the Ia sensory nerve, through the dorsal root, monosynaptically stimulates the alpha motor neuron, which fires and contracts (shortens) the muscle.
• Monosynaptic arc, but initiates a polysynaptic inhibition of the antagonist muscle

lb sensory fibers (negative pathway)

• Originates from the Golgi tendon organ
• Polysynaptically inhibits the alpha motor neuron to prevent muscle contraction.
• Stimulates the gamma efferent nerve to the intrafusal fiber to reset the muscle spindle.

Neurology Secrets 6th Edition Chapter 2 pg13

Question 14

Muscle Fiber Classification 🔑🔑 MOCK 2020

Answer 14

Question 15

Answer 15

💡 A sarcomere runs from Z-line to Z-line. Its size changes during contraction.

Actin - Myosin - ZH - AI

Cuccurollo 4th Edition Chapter 5 EDX pg340

Question 16

Explain Muscle fiber contraction & relaxation

Answer 16

Muscle fiber contraction

Ca++ to be released from the sarcoplasmic reticulum. It binds to tropomyosin which exposes actin, then myosin heads, powered by ATP, bind with the active sites. The actin and myosin filaments slide over each other to shorten the muscle.

Muscle fiber relaxation

Ca++ is actively pumped back into the sarcoplasmic reticulum. This allows the tropomyosin to block actin’s active sites.

Cuccurollo 4th Edition Chapter 5 EDX pg340

Question 16

Define Innervation ratio (IR)

Answer 16

Definition: amount of muscle fibers belonging to an axon is the innervation ratio (IR).

Higher the IR, the greater the force generated by that motor unit, Example:

• Leg muscles can have a ratio of 600 muscle fibers to one axon (600:1)
• Eye muscles can be 1 muscle fiber to 1 axon (1:1).

Cuccurrollo 4th Editio Chapter 5 EDX pg332

Question 17

Henneman Size Principle

Answer 17

Smaller alpha motor neuron has a lower threshold of excitation, causing it to be recruited first during voluntary contraction.

Larger alpha motor neuron has a higher threshold of excitation and is recruited when moremotor units are needed to generate greater contractile force.

Cuccurrollo 4th Editio Chapter 5 EDX pg333

Question 18

Define Resting Membrane Potential 🔑🔑 EXAM

Answer 18

This is the voltage of the axon’s cell membrane at rest.

Normal resting membrane potential(RMP) is −70 to −90 mV egative potential is maintained by Na+–K+ ATP–dependent pump: (Two) K+ ions are imported.(Three) Na+ ions are exported.

Cuccurollo 4th Edition Chapter 5 EDx pg335

Question 19

Define Depolarization and Repolarization 🔑🔑 EXAM

Answer 19

Depolarization

Process of brining the membrane to less negative charge in response to stimulus

It is dependent on Na+ channel activation (Na+ go inside)

Thus generating action potential.

Repolirization

Process of bringing the depolarized membrane back to its more negative resting state.

It is dependent on Na+ channel inactivation and K+ channel activation (K+ go outside)

Cuccurollo 4th edition Chapter 5 EDX pg335 & 338

Question 20

Define All-or-none response 2 marks 🔑

Answer 20

A stimulus must be strong enough to reach threshold of activation. Once reached, the AP generated remains at a constant size and configuration.

Stimulus is below than the threshold will not result in AP.

Stimulus is greater than the threshold will not generate a larger potential.

Cuccurollo 4th Edition Chpater 5 EDX pg335

Question 21

Absolute refractory period vs Relative refractory period 🔑🔑 EXAM 2020-2021

Answer 21

Absolute refractory period:

Corresponds to depolarization and repolarization.

Time during which a second action potential cannot be elicited no matter how large a stimulus is repeatedly applied.

Relative refractory period:

This pertains to the period of time after the absolute refractory period.

At this time, an AP can be elicited with more intense stimulation.

Cuccurollo 4th Edition Chapter 5 EDX pg336

Question 22

Define Propagation 🔑🔑 EXAM

Answer 22

Saltatory conduction is the propagation of action potentials along myelinated axons from one node of Ranvier (which contains Na+ channels) to the next node, increasing the conduction velocity of action potentials.

Cuccurollo 4th Edition Chapter 5 EDX pg337

Question 23

How does demyelination affect electrophysiology of nerve cell. EDX findings of demyelination 🔑 🔑

Answer 23

**Pathophysiology** * Injury to the myelin sheath of the nerve * Axon remains intact **NCS** 1- Decreased conduction velocity 2- Increased distal latency 3- Increased temporal dispersion 4- Conduction block (acute or acquired conditions): Failure of an AP to propagate past an area of demyelination along axons 50% drop in CMAP amplitude between proximal and distal stimulation Amplitude may decrease secondary to temporal dispersion and phase cancellation **EMG** * Recruitment: Normal or decreased **Chronic Conditions** * Demyelination and remyelination occur repeatedly. * Myelin regeneration via Schwann cell proliferation. * This new myelin is thinner with shorter internodal distances. * CV improves but is usually slower than normal. Cuccurollo 4th Edition Chapter 5 EDX pg342

Question 24

What is conduction block? What is the significance of conduction block in peripheral neuropathy?

Answer 24

**Conduction block** * Focal abnormality across a nerve segment that results in failure to conduct an action potential typically due to focal disruption of the myelin sheath. * In conduction block, a compound muscle action potential (CMAP) drop of 30% to 50% is recorded between the distal and proximal stimulation sites. * Distal to the block, conduction is preserved. **It indicates reversible conditions like** 1. Acute reversible ischemic injury 2. Compression-induced demyelination (Neuropraxia) 3. Acquired demyelinative neuropathies Neurology Secrets 6th Edition Chapter 6 Peripheral Neuropathy pg79

Question 25

Mention 2 types of axonal degeneration, what is the clinical significant?🔑🔑

Answer 25

**Wallerian degeneration** * Separation of axon from neuron cell body * A nerve injury that begins in a anterograde fashion (proximal to distal degeneration) * For the distal motor axons, the degeneration is generally complete in 7 days. * For the distal sensory axons, the degeneration is generally complete in 11 days. **Axonal degeneration** * Dying back, likely to worsen over time (ie radial n. starts dying from wrist up to elbow) * A nerve injury that begins in a retrograde fashion (distal to proximal degeneration) **EDX Study** * Postponed by 10-14 days after incident/injury, other wise it will be normal. Cuccurollo 4th Edition Chapter 5 EDX pg343

Question 26

List 4 causes for Axonal injury 🔑 Three weeks post elbow trauma. You think there is an axonal injury to the ulnar nerve. What are four findings on NCS/EMG? (EDX findings of Axonal injury) 🔑🔑

Answer 26

**Axonal Injury** 1. Focal Crush 2. Stretch 3. Peripheral Neuropathies 4. Transection **NCS** * Temporal dispersion: Normal * Conduction velocity: Mild slowing (largest and fast conducting axons are lost) * Distal latency: Mild slowing (largest and fast conducting axons are lost) * Amplitude: Decreased **EMG** 💡 **Axonal damage result in muscle de-innervation, which shows in EMG study** * Insertional activity: Abnormal * Resting activity: Fibrillation potentials, Positive sharp waves * Recruitment: Decreased * MUAP: Abnormal Cuccurollo 4th Edition Chapter 5 EDX pg343-344

Question 27

Is it possible to recover from axonal injury? 🔑🔑 Recovery after muscles have lost their innervation. What would happen?

Answer 27

**1- Collateral sprouting** **Motor Unit 1 from 12 to 16+ muscle fiber** Process where an intact motor unit sprouts axon and innervates denervated muscle fibers of an injured motor unit. Muscle fibers become part of the new motor unit athus increasing the size of its territory. Result in motor units with poor firing synchronicity, secondary to the immature terminal sprouts. 💡 **EMG: Polyphasic (Immature NMJ) & increased amplitudes (More muscle fibers)** **2- Axonal regrowth** Axon will regrow down its original pathway toward its muscle fibers (1 inch per month) **Decreased diameter, thinner myelin, and shorter internodal distance.** 💡 **EMG: Low-amplitude, long-duration, and polyphasic potentials** Cuccurollo 4th Edition Chapter 5 EDX pg344-345

Question 28

What is neuroma?

Answer 28

Neuroma can form with failure of axonal regeneration (re-growth) to reach the final end organ. Cuccurollo 4th Edition Chapter 5 EDX pg344

Question 29

Sunderland Classification 🔑🔑

Answer 29

Cuccurollo 4th Edition Chapter 5 EDX pg345

Question 30

Seddon Classification 🔑🔑

Answer 30

**NEUROPRAXIA** * Conduction block for 10-14 Days **AXOTOTMESIS** * Conduction block for 10-14 Days * Conduction failure for 1 week * Recovery after months **NEUROTMESIS** * Conduction block for 10-14 Days * Conduction failure for life Neurology Secrets 6th Edition Chapter 6 pg78 Cuccurollo 4th Edition Chapter 5 EDX pg345

Question 31

EMG findings after 1) Neuropraxia 2) Axonotmesis 3) Neurotmesis. Go back to basics.

Answer 31

**Neuropraxia** * Compression only, Axon is intact → Muscle isn’t de-innervated → **Normal EMG** * Active Demyelination → Abnormal insertional activity **Axonotmesis & Neuropraxia** * Axonal damage → Muscle is dying/de-innervation → **Abnormal EMG** 1. Abnormal insertional activity 2. Abnormal resting activity 3. Abnormral spontansous activity → Fibs and PSW 4. MUPA: Neurogenic Large amplitude, Long duration (LALD), polyphasic

Question 32

3 DDx for generalized weakness with preserved motor and sensation. 🔑

Answer 32

1. Fibromyalgia 2. Myofascial pain syndrome 3. Polymyalgia rheumatica Cuccurollo 4th Edition Chapter 5 EDX pg449 Braddom 6th Edition Chapter 8 EDX Medicine pg116 Fig. 8.1

Question 32

6 DDx for motor weakness with reduced sensation. 🔑

Answer 32

**BRAIN - CORTICOSPINAL TRACT - ROOT** 1. Bain Tumor 2. MS 3. Syrinx / Myelopathies 4. Lumbar stenosis **PERIPHERAL NERVE NERVE** 1. Cauda equina syndrome 2. Radiculopathy 3. Plexopathy 4. Polyneuropathy 5. Peripheral Neuropathy 6. Entrapment neuropathy

Question 33

4 DDx for motor weakness with preserved sensation. 🔑

Answer 33

1. Anterior Horn Cell → Motor neuron disease 2. Multiple Motor Units → Multifocal motor neuropathy 3. NMJ → Neuromuscular disorders 4. Muscle → Myopathies 5. Radiculopathy 6. Mononeuropathy 7. Myofascial pain syndrome