Nerve Conduction Studies Quiz

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the consequence of not providing sufficient current for supramaximal nerve stimulation during a nerve conduction study?

It has no effect on the results of the study.

It results in higher CMAP amplitudes than expected.

It ensures accurate representation of nerve conduction velocity.

It leads to lower CMAP and SNAP amplitudes, causing false positive results. (correct)

Which of the following conditions would most likely result in reduced or absent CMAP and SNAP?

Normal nerve function

Radiculopathy

Neuropathy or plexopathy (correct)

Demyelinisation

What is the normal range for nerve conduction velocity in the fastest myelinated fibers?

1.6 m/s

19 m/s

61 m/s (correct)

100 m/s

During a repetitive nerve stimulation test, what is typically assessed to gauge neuromuscular transmission safety?

The response to a train of 10-20 stimuli Signup and view all the answers

Which of the following statements regarding distal motor latency (DML) is accurate?

DML is prolonged in cases of demyelinisation. Signup and view all the answers

What primarily controls fine motor tasks in the body?

Corticospinal tract Signup and view all the answers

Which tract is mainly involved in postural control and movements of the trunk?

Corticoreticulospinal tract Signup and view all the answers

What phenomenon describes the hypotonia after an upper motor neuron injury?

Spinal shock Signup and view all the answers

What is the role of the lateral system in motor control?

Control of distal muscles of the limbs Signup and view all the answers

What does the 'Babinski sign' indicate when the foot sole is stroked?

Extension of the big toe Signup and view all the answers

Which of the following is primarily coordinated by the vestibulospinal tract?

Posture and balance Signup and view all the answers

What is the main function of the medial premotor cortex?

Movements based on internal cues Signup and view all the answers

What best describes the relationship between multiple motor neurons and a single movement?

The average preferred movement direction determines the actual movement Signup and view all the answers

Which type of motor unit is characterized by a small twitch response and does not fatigue?

Slow (S) Signup and view all the answers

What is the primary function of the Golgi tendon organ reflex in motor control?

Inhibiting motor neuron responses Signup and view all the answers

Which category of neuromuscular disorders affects the spinal muscular atrophy?

Spinal cord/anterior horn cells Signup and view all the answers

What diagnostic tool is primarily used to assess nerve conduction studies?

Surface electrodes Signup and view all the answers

Which symptom is NOT commonly associated with neuromuscular disorders?

Hypertension Signup and view all the answers

What role does the H-reflex play in nerve conduction studies?

Assesses proximal nerve segments Signup and view all the answers

In the context of motor unit recruitment, which type of motor unit is recruited last due to its size?

Fast Fatigable (FF) Signup and view all the answers

Which test is used to evaluate autoimmune neuromuscular disorders like Myasthenia gravis?

Single fiber EMG Signup and view all the answers

What is the effect of muscle fibers being compromised on force generation?

They cannot exert any force Signup and view all the answers

Which condition is NOT typically classified under peripheral nerve disorders?

Amyotrophic lateral sclerosis (ALS) Signup and view all the answers

What is the primary function of the vestibulocerebellum?

Balance control and eye movement reflexes Signup and view all the answers

Which signs are associated with dysfunction in the spinocerebellum?

Hypotonia and dysmetria Signup and view all the answers

What type of fibers provides input to the middle cerebellar peduncle?

Afferent fibers from the pontine nuclei Signup and view all the answers

Which structure provides the output that is inhibitory (GABA) within the cerebellar circuitry?

Purkinje cells Signup and view all the answers

What occurs during simple spikes in cerebellar activity?

Only when many parallel fiber inputs are present Signup and view all the answers

What is the primary input source for the cerebrocerebellum?

Cerebral cortex Signup and view all the answers

Which fiber bundle transmits afferent fibers from the medulla?

Inferior cerebellar peduncle Signup and view all the answers

What common sign is associated with disturbances in the cerebrocerebellum?

Fine motor coordination issues Signup and view all the answers

What is one of the roles of mirror neurons in humans?

Involved in empathy Signup and view all the answers

Which of the following is a consequence of lesions in the temporal association cortices?

Inability to recognize faces Signup and view all the answers

What is the primary responsibility of the occipito-temporal network?

Object and face recognition Signup and view all the answers

In the context of spatial attention, what is a characteristic feature of hemi neglect syndrome?

Failure to respond to stimuli on one side of the body Signup and view all the answers

What do the left visual field and right primary visual cortex correlate to?

Object recognition pathways Signup and view all the answers

Which of these describes the ventral pathway in the visual processing system?

What-pathway for object recognition Signup and view all the answers

What is a core ability associated with cognition?

To attend to stimuli and make meaningful responses Signup and view all the answers

Which cognitive disorder is particularly associated with problems in the mirror neuron system?

Autism Signup and view all the answers

Study Notes

Muscle Force Production

Muscle force production is dependent on the length and health of the muscle.
If the muscle is stretched excessively, it cannot generate force.
If the muscle is compromised by injury or disease, it also cannot generate force.

Motor Units

Motor units are the basic functional units of the neuromuscular system.
Each motor unit consists of a single motor neuron and all the muscle fibers it innervates.
There are three types of motor units with varying force production capabilities and fatigue resistance:
- Slow (S): Small twitch response, generate minimal force, but have high fatigue resistance.
- Fatigue Resistant (FR): Produce more force than S units, with fatigue resistance between S and FF units.
- Fast Fatigable (FF): Generate the most force, but have low fatigue resistance.

Motor Unit Recruitment

Motor units are recruited according to their size, with smaller, slower units being recruited before larger, faster units for a given task.
This is known as the size principle.
Muscles often act redundantly across multiple joints, contributing to multiple degrees of freedom.

Reflexes

Stretch reflexes, also known as short-loop reflexes, are triggered by muscle stretch and mediated by the Ia afferent fibers.
Golgi tendon organ reflex senses force on the tendon via 1b afferent fibers, acting via an interneuron to inhibit the motor neuron.
Long loop reflexes involve ascending fibers that travel to the somatosensory cortex, then back to the motor cortex via descending pathways.

Neuromuscular Disorders (NMD)

NMDs affect the peripheral nervous system, affecting muscles, nerves or both.
Common symptoms include:
- Weakness (paresis)
- Delayed motor milestones
- Hypotonia (floppy infant)
- Low or absent muscle stretch reflexes
- Muscle atrophy
- Diminished cutaneous sensation (hypesthesia)
NMDs can be categorized by the affected structure:
- Spinal cord/anterior horn cells:
  - Spinal muscular atrophy (SMA)
  - Amyotrophic lateral sclerosis (ALS)
- Nerve roots:
  - Herniated nucleus pulposus (HNP)
  - Guillan-Barré syndrome (GBS)
  - Chronic inflammatory demyelinating polyneuropathy (CIDP)
- Brachial and lumbosacral plexus:
  - Neuralgic amyotrophy (Parsonage-Turner syndrome)
- Peripheral nerves:
  - Polyneuropathy
  - Carpal tunnel syndrome
- Neuromuscular junction:
  - Myasthenia gravis
  - Lambert-Eaton myasthenic syndrome (LEMS)
- Muscle:
  - Congenital or metabolic myopathies
  - Muscular dystrophies (Duchenne muscular dystrophy)

Spontaneous Muscle Activity in NMD

When nerve fibers or muscle fibers are no longer innervated, they can become spontaneously active:
- Fasciculations: Occur at the motor nerve fiber/motor unit level
- Fibrillations: Occur at the muscle fiber level

Diagnostic Approach to NMD

A comprehensive evaluation involves clinical investigation and lab testing:
- Clinical Investigation:
  - History taking: Symptoms of weakness, sensory abnormalities, age of onset, rate of progression, family history
  - Physical Examination: Severity and distribution of weakness, sensory involvement, tendon reflexes, muscle tone, contractures
- Laboratory Parameters:
  - Blood testing: CK level, auto-antibodies, lactate and other metabolic enzymes, thyroid function, electrolytes
  - Cerebrospinal fluid (CSF) testing: Increased protein levels, increased cells
  - Urine testing: Metabolic enzymes
  - Muscle imaging: Ultrasound, Computed Tomography (CT), Magnetic Resonance Imaging (MRI)

Clinical Methods for NMD

Electrodiagnostic testing plays a crucial role:
- Nerve conduction studies:
  - Useful for localization of the lesion to the nerve root, plexus, or peripheral nerve.
  - Helpful in differentiating between mono- and polyneuropathy or monoradiculopathy and polyradiculopathy.
  - Delineate type of pathology, such as axonal vs demyelinating damage.
  - Involve surface electrodes and supramaximal nerve stimulation.
  - Measure motor nerve conduction velocities (NCVs), sensory nerve action potentials (SNAPs), and parameters like amplitude, latency, and dispersion.
- Needle electromyography (EMG):
  - Examination of muscle activity.
  - Contraindications include open wounds, inaccessible limbs, and blood coagulation disorders.
- Stimulated single fiber EMG (SFEMG) and repetitive nerve stimulation (RNS):
  - Used for assessing neuromuscular junction disorders.
  - RNS tests the safety threshold of neuromuscular transmission.

Nerve Conduction Studies (NCS)

NCS measures the electrical activity of nerves.
NCS parameters include:
- Compound Muscle Action Potential (CMAP): Electric signal generated by a muscle in response to nerve stimulation.
- Sensory Nerve Action Potential (SNAP): Electric signal generated by a sensory nerve in response to stimulation.
- Distal Motor Latency (DML): Time taken for a nerve signal to travel from the stimulation site to a specific muscle.
Normal nerve conduction velocities:
- Fastest myelinated fibers: 61 m/s
- Smallest myelinated fibers: 19 m/s
- Unmyelinated fibers: 1.6 m/s

Repetitive Nerve Stimulation (RNS)

RNS tests the safety threshold of neuromuscular transmission by delivering a train of stimuli to a nerve.
Used in conditions like:
- Myasthenia gravis
- Lambert Eaton myasthenic syndrome
If transmission fails (e.g., in myasthenia gravis), the amplitude of the evoked muscle action potentials progressively decreases with each stimulus in the train.

Movement Control

Movements are controlled by complex interactions between the central nervous system and the muscles.
Unilateral control: Independent control of distal muscles in arms and legs allows for separate control of left and right limbs.
Direct pathways: Responsible for fine voluntary movements in distal limbs with high precision.
Indirect pathways: Responsible for movements of the core body and coarse motor control.
Lateral system: Controls the distal muscles of the limbs, responsible for fine motor tasks.
Ventromedial system: Controls the axial muscles of the trunk and proximal limb muscles, responsible for walking and posture.

Lateral System

Corticospinal tract: Responsible for fine voluntary movements of body and limbs.
(Cortico)rubrospinal tract: Also involved in voluntary movements, mainly in the limbs but less important than the corticospinal tract.

Ventromedial System

(Cortico)reticulospinal tract: Controls movements and postural control in the trunk and proximal limbs.
Vestibulospinal tract: Maintains head and eye coordination, posture and balance, and conscious awareness of orientation and motion.
Tectospinal tract: Coordinates hand and eye movements.

Single Motor Neuron Function

Studies on monkeys demonstrate that a single motor neuron in the motor cortex controls a particular movement direction but can be imprecise on its own.
Many neurons working together contribute to an actual observed movement.

Premotor Cortex

Lateral premotor cortex (PMC): Plans movements based on external events.
Medial PMC: Plans movements based on internal cues.

Spinal Shock

Spinal shock is a temporary loss of reflexes and muscle tone that occurs after an upper motor neuron injury (e.g., spinal cord injury).
It is caused by decreased activity of spinal circuits due to the lack of input from the motor cortex and brainstem.

Symptoms of Upper Motor Neuron Lesions

Babinski sign: Stroking the sole of the foot causes extension of the big toe and fanning of the other toes (instead of flexion of the big toe).
Spasticity : increased muscle tone, hyperactive stretch reflexes, and clonus (rhythmic, involuntary muscle contractions).
Hyporeflexia / superficial reflexes: Decreased vigor of superficial reflexes.
Loss of fine motor skills: Unable to perform intricate movements.

Muscle Tone

Muscle tone is the resting level of tension in a muscle.
It depends on the resting discharge levels of alpha motor neurons.
Muscle tone allows for optimal responsiveness to voluntary and reflexive commands.

Cerebellum and Movement Coordination

The cerebellum plays a crucial role in coordinating movement and maintaining balance.
Three main subdivisions:
- Vestibulocerebellum:
  - Inputs: Vestibular system, visual system
  - Output: Vestibular nuclei
  - Function: Balance control and compensatory eye movement reflexes.
  - Signs: Ataxia, imbalance with eyes closed, nystagmus (involuntary eye movements).
- Spinocerebellum:
  - Inputs: Somatosensory, proprioceptive, acoustic, visual
  - Output: Lateral and medial motor systems
  - Function: Muscle tone and fine-tuning of movement execution.
  - Signs: Hypotonia, dysmetria (poorly coordinated movements).
- Cerebrocerebellum:
  - Inputs: Cerebral cortex (copy of motor commands)
  - Output: Back to motor and premotor cortex
  - Function: Initiation, timing, and planning of skilled movements.
  - Signs: Clumsiness, tremor, slow movement initiation, timing problems.

Cerebellar Peduncles

These fiber bundles carry inputs and outputs to and from the cerebellum.
Inferior cerebellar peduncle:
- Afferents: From the medulla
- Efferents: To the vestibular nuclei
Middle cerebellar peduncle:
- Afferents: From the pontine nuclei
Superior cerebellar peduncle:
- Efferents: From the cerebellar nuclei
- Afferents: From the spinocerebellar tract

Cerebellum and Ipsilateral Control

The cerebellum receives inputs from and sends outputs to the ipsilateral side of the body.
Cerebellar outputs to the red nucleus and thalamus cross on their way to the motor cortex and premotor cortex, so the cerebellum modulates movements on the ipsilateral side while the cortex controls the contralateral side of the body.

Cerebellar Circuit Elements

Mossy fibers: Input from lower brain stem
Granule cells: Most numerous neurons in the brain, receive mossy fiber input
Parallel fibers: Axons of granule cells, project to Purkinje cells
Purkinje cells: Large, inhibitory neurons in the cerebellar cortex, receive input from parallel fibers and climbing fibers
Climbing fibers: Input from the inferior olive, important for motor learning
Deep cerebellar nuclei: Output nuclei of the cerebellum, receive input from Purkinje cells and other sources

Cerebellar Circuit Pathways

Direct pathway: Deep cerebellar nuclei project directly to motor systems.
Indirect side-loop: Involves mossy fibers, granule cells, parallel fibers, Purkinje cells, and deep cerebellar nuclei.
Climbing fiber input: From the inferior olive to Purkinje cells, plays a role in motor learning and reflexes.

Cerebellar Output

The cerebellum primarily uses GABAergic (inhibitory) output, mainly from Purkinje cells.

Simple Spike

Simple spikes are Purkinje cell action potentials that are generated when there is sufficient parallel fiber input.

Mirror Neurons

Located in the premotor cortex, mirror neurons fire when an individual performs an action or observes another individual performing the action.
Proposed functions:
- Understanding goals and intentions
- Facilitation of learning
- Involved in empathy
- Human self-awareness
Problems with the mirror neuron system may be associated with cognitive disorders, particularly autism.

Cognition

The ability to attend to stimuli, identify their significance, and make meaningful responses.
Five association cortices are responsible for this complex processing:

Occipito-temporal Network

Involved in object and face recognition.
Retino-cortical pathway: Pathway from the eye to the brain, crucial for perception.
Left visual field: Projected to the right primary visual cortex.
Two cortical pathways:
- Spatial vision pathway:
- Object recognition pathway (ventral pathway or WHAT pathway):

Lesions of Temporal Association Cortices

Agnosia: Unable to identify objects despite recognizing their presence.
Prosopagnosia: Inability to recognize faces.

Parieto-frontal Network

Involved in spatial attention and processing of information about location.
WHERE-pathway: Processes information about the location of objects relative to the individual's body.

Parietal Lobe Function

Processes categorical relations (e.g., the mouse is to the right of the keyboard).
Processes metric or coordinate relations (e.g., distance in centimeters):
Hemi-neglect syndrome: Patients fail to attend to or respond to stimuli presented on the side opposite their brain lesion (usually the right hemisphere).

Visual Field Processing

Both the left and right eyes have a left visual field and a right visual field.
Neglect is not related to eye movement, as patients can neglect stimuli regardless of whether they are looking with one or two eyes.

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Test your knowledge on nerve conduction studies with this quiz. It covers key concepts such as maximal nerve stimulation and typical parameters assessed during various tests. Ideal for students and professionals in neurology and physiology.