patho2test 3: Peripheral Nervous System mppt

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Questions and Answers

Which system is responsible for maintaining homeostasis?

Autonomic nervous system (correct)

Somatic nervous system

Peripheral nervous system

Central nervous system

What type of nerves primarily come from sensory receptors and travel into the central nervous system?

Motor neurons

Afferent nerves (correct)

Efferent nerves

Sensory neurons

Which type of pain is characterized as sharp, immediate, and acts as a warning signal to respond to a harmful stimulus?

Neuropathic pain

First pain (correct)

Chronic pain

Second pain

What protects the central nervous system from toxic injury?

Blood-brain barrier Signup and view all the answers

Which type of fibers carry general sensations such as light touch and vibration?

Faster fibers Signup and view all the answers

What is the function of the spinothalamic tract in the spinal cord?

Carries sensory information related to pain and temperature Signup and view all the answers

Which component of the peripheral nervous system provides movement and sensation to a specific region of the body?

Spinal nerves Signup and view all the answers

What is a characteristic of the somatic nervous system?

Regulated by conscious control Signup and view all the answers

What is the main structure that forms the superior boundary of the carpal tunnel?

Transverse carpal ligament Signup and view all the answers

Which of the following muscles is NOT supplied by the median nerve?

Flexor pollicis brevis (deep head) Signup and view all the answers

What is the characteristic feature of Charcot-Marie-Tooth Disease (CMT)?

Demyelination of peripheral nerves Signup and view all the answers

What is the primary pathogenic mechanism of Myasthenia Gravis?

Autoantibodies to the acetylcholine receptor Signup and view all the answers

What is the primary effect of acetylcholinesterase inhibitors in Myasthenia Gravis?

Block the breakdown of acetylcholine Signup and view all the answers

What is the characteristic symptom of Charcot-Marie-Tooth Disease (CMT) owing to muscular imbalance?

High arched feet Signup and view all the answers

What is the typical pattern of symptom progression in Charcot-Marie-Tooth Disease (CMT)?

Distal to proximal Signup and view all the answers

What is the primary goal of plasmapheresis in Myasthenia Gravis?

Remove autoantibodies from the blood Signup and view all the answers

What is the typical clinical feature of Myasthenia Gravis that improves with rest?

Generalized proximal limb weakness and fatigability Signup and view all the answers

What is the mechanism of action of IV immunoglobulin in Myasthenia Gravis?

Give other antibodies that block the anti-AChR antibodies Signup and view all the answers

Which of the following is NOT a risk factor for diabetic peripheral neuropathy?

Family history of diabetes Signup and view all the answers

What is the primary mechanism of nerve damage in diabetic peripheral neuropathy?

Ischemia due to microvascular damage Signup and view all the answers

What is the typical order of symptom progression in diabetic peripheral neuropathy?

Toes and feet, then hands and arms Signup and view all the answers

What is the most common preceding infection in Guillain-Barré syndrome?

Campylobacter jejuni Signup and view all the answers

What is the primary mechanism of autoimmune response in Guillain-Barré syndrome?

Molecular mimicry Signup and view all the answers

What is the main medication used to treat Guillain-Barré syndrome?

Intravenous immunoglobulin (IVIG) Signup and view all the answers

What is the typical timeframe for functional recovery in Guillain-Barré syndrome?

Weeks to months Signup and view all the answers

What is the primary cause of carpal tunnel syndrome?

Compression of the median nerve Signup and view all the answers

What is the most common compressive focal mononeuropathy seen in clinical practice?

Carpal tunnel syndrome Signup and view all the answers

What is the congenital predisposition that contributes to the development of carpal tunnel syndrome?

Smaller carpal tunnels Signup and view all the answers

Study Notes

Peripheral Nervous System

Direct extension of the central nervous system that monitors and reacts to external stimuli
Two components: autonomic nervous system (ANS) and somatic nervous system
Autonomic nervous system (ANS):
- Not regulated by conscious control
- Helps maintain homeostasis
- Automatically adjusts the activity of the sympathetic and parasympathetic nervous systems to match the body's needs
Somatic nervous system:
- Afferent (sensory) nerves: primarily come from sensory receptors and travel into the central nervous system
- Efferent (motor) nerves: travel from the CNS to primarily muscle for motor activation

Components of Peripheral Nervous System

Cranial nerves
Spinal nerves:
- Provide movement and sensation to a specific region of the body
- Carry sympathetic, parasympathetic, motor, and sensory information

Sensory Receptors

General sensation: light touch and vibration
- Carried by the dorsal columns in the spinal cord
- We adapt to these sensations more rapidly than heat and pain because they are carried by faster fibers
Pain:
- Highly subjective
- Carried by the spinothalamic tract in the spinal cord
- "First pain" - sharp, immediate, a "good" thing that acts as a warning signal to respond to a harmful stimulus
- "Second pain" - delayed, longer-lasting sensation, chronic "bad" pain that comes from damage or pathology that remains even after the stimulus is gone
Temperature:
- Carried by the spinothalamic tract in the spinal cord
- Interestingly, both pain and temperature can be sensed by the same receptors
- Extreme heat or extreme cold can trigger the sensation of pain

Diabetic Peripheral Neuropathy

Most common complication of diabetes
Duration and severity of hyperglycemia and metabolic syndrome are the 2 most important risk factors in patients with type 1 or type 2 diabetes
Distal symmetric polyneuropathy:
- Can involve sensory, motor, and autonomic neurons
- Sensory neurons are more susceptible to damage than motor neurons because most sensory neurons are unmyelinated
Pathophysiology:
- Distal portions of long sensory axons degenerate
- Ischemia due to microvascular damage from hyperglycemia
- Buildup of advanced glycation end products (AGEs) contributes to oxidative stress and damages nerves
Clinical manifestations:
- Progressive loss of sensation
- Negative symptoms (numbness, loss of balance)
- Positive symptoms (tingling, pain)
- Symptoms start distally in the toes and feet, and positive symptoms are usually worse at night

Guillain-Barré Syndrome

Autoimmune destruction of the schwann cells surrounding peripheral nerves
Post-infectious autoimmune neuropathy
~ 70% of patients have a preceding infection
Campylobacter jejuni is a common organism that can trigger GBS
Molecular mimicry:
- One of the main mechanisms through which infectious (or chemical) agents produce an autoimmune response
- Similarities between foreign peptides and "self" peptides cause activation of T/B cells
Clinical manifestations:
- Symmetric, ascending weakness is the hallmark, typically begins in the legs
- Numbness
- Tingling
- Weakness that can progress to paralysis
- Symptoms generally progress over a period of 2 weeks
Diagnosis:
- Typically, a clinical diagnosis (preceding infection with characteristic presentation, etc.)
- EMG and nerve studies can be helpful if unclear
Treatment:
- Start with supportive care
- Monitor for progression
- Monitor respiratory status
- Monitor blood pressure and heart rate
- DVT prophylaxis
- Pain control
- Main medication for GBS is IVIG (Intravenous immunoglobulin)

Carpal Tunnel Syndrome

Common condition causing numbness, tingling, and pain in the hand and forearm
Really an anatomic issue, not a "physiologic" one
Median nerve is compressed as it travels through the wrist (the carpal tunnel)
Compression of the median nerve leads to ischemia and mechanical disruption
Presents as pain, paresthesia, and less commonly, weakness in the median nerve distribution
Traversing the carpal tunnel:
- The carpal tunnel is formed by the transverse carpal ligament superiorly with the carpal bones inferiorly
- As the median nerve crosses the wrist, it passes through the carpal tunnel along with nine flexor muscle tendons

Charcot-Marie-Tooth Disease (CMT)

Group of hereditary disorders that cause peripheral neuropathy in both sensory and motor neurons
Often abnormalities in the axons or production/maintenance of the myelin sheath
The "demyelinating" disorder of the peripheral nervous system
Over time, neurons degenerate leading to muscle weakness/atrophy
Affects longer nerves first
Symptoms typically begin in the feet/lower legs and then the fingers, hands, and arms
High arched feet due to muscular imbalance (from atrophy)

Myasthenia Gravis

Autoimmune disorder of the neuromuscular junction that manifests as progressive skeletal muscle weakness and fatigability
Pathogenesis:
- The body makes autoantibodies to the acetylcholine receptor
- The antibodies bind to the receptor and interfere with neurotransmitter function
- There are fewer acetylcholine receptor sites available when an action potential arrives
Clinical manifestations:
- Generalized proximal limb weakness and fatigability with repeated activities → this improves with rest
- Drooping of eyelids (ptosis)
- Double vision (diplopia)
- Flattened smile
- Difficulty chewing and/or swallowing
- If severe: difficulty breathing
Treatment:
- Acetylcholinesterase inhibitors
- Block the enzyme that's breaking down Ach = more Ach around to bind to receptors that are still functional
- It is also used to diagnose MG by showing improvement of muscle weakness with use
- Immunosuppressants like corticosteroids
- Plasmapheresis to remove autoantibodies from the blood
- IV immunoglobulin: give other antibodies that block the anti-AChR antibodies

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Description

Learn about the peripheral nervous system, its components, and functions in maintaining homeostasis and reacting to external stimuli.