EMG/NCS Basics: Understanding Your Nerves and Muscles

How Your Nervous System Works and What EMG and Nerve Conduction Tests Measure

Published: February 2026 Read Time: 7-9 minutes

To understand what EMG and nerve conduction studies measure, it helps to understand how your nervous system, nerves, and muscles work together. This article explains the basic anatomy and physiology in plain language so you'll understand what your test is evaluating.

The Peripheral Nervous System

[1] Your nervous system has two main parts:

• Central nervous system (CNS): Your brain and spinal cord
• Peripheral nervous system (PNS): All the nerves outside your brain and spinal cord

EMG and NCS test the peripheral nervous system—the nerves that run throughout your body carrying messages to and from your muscles.

What Are Nerves?

[2] Nerves are like biological electrical cables. Each nerve contains thousands of individual nerve fibers (axons) bundled together. These axons carry electrical signals at high speed. A single nerve might be thicker than a pencil but contain microscopic individual fibers.

Motor Nerves: Control Movement

Motor nerves carry signals FROM your brain and spinal cord TO your muscles.

How They Work

[1] Here's the motor pathway:

1. Brain decides: Your brain decides you want to move your arm
2. Signal generated: Neurons in your brain generate an electrical signal
3. Signal travels: The signal travels down a motor nerve at very high speed (up to 60 meters per second)
4. Reaches muscle: The nerve reaches the muscle and triggers contraction
5. Muscle contracts: The muscle contracts, producing movement

What Can Go Wrong

• Nerve damage: The nerve is injured or diseased
• Slow conduction: Signals travel slower than normal
• Lost axons: Nerve fibers die, reducing signal strength

NCS can detect all these problems by measuring how fast signals travel and how strong they are.

Sensory Nerves: Carry Sensation

Sensory nerves carry signals FROM your skin and body TO your brain.

How They Work

Sensory nerves detect:

• Touch: Pressure on skin
• Temperature: Hot and cold
• Pain: Tissue damage
• Position: Where your body parts are in space

When you touch something, sensory nerves detect the stimulus and send the signal back to your brain, which interprets it.

What Can Go Wrong

• Numbness (loss of sensation)
• Tingling (abnormal sensation)
• Pain (even without injury)

NCS can detect sensory nerve damage by measuring their function.

How Muscles Work

[3] Muscles are electrically active tissues. When nerve signals reach a muscle, the muscle generates its own electrical activity and contracts.

Muscle Structure

A muscle contains:

• Muscle fibers: Individual muscle cells
• Motor units: A nerve and all the muscle fibers it controls
• Neuromuscular junction: Where nerve meets muscle (see next section)

What Can Go Wrong

• Muscle weakness: Muscles don't have enough strength
• Muscle atrophy: Muscles shrink from disuse or disease
• Muscle disease: Primary muscle dysfunction

EMG can detect these problems by measuring muscle electrical activity.

The Neuromuscular Junction

The neuromuscular junction is where the nerve communicates with the muscle. [2]

How It Works

This junction uses chemical transmission:

1. Signal arrives: Electrical signal reaches the nerve ending
2. Chemical released: The nerve releases a chemical (acetylcholine)
3. Muscle activated: The chemical binds to muscle receptors
4. Muscle contracts: The muscle generates electrical activity and contracts

What Can Go Wrong

• Antibodies blocking: (myasthenia gravis) - antibodies block the chemical receptors
• Lack of chemical: Botulism and some medications prevent chemical release
• Receptor damage: Autoimmune diseases damage the muscle receptors

Special EMG testing (repetitive stimulation) can detect neuromuscular junction problems.

When Things Go Wrong: Neurological Disorders

[4] Disorders affecting nerves and muscles can occur at different levels:

Neuropathy (Nerve Problem)

Disease of the nerve fibers themselves

Examples: Diabetes, infections, toxins

EMG/NCS findings: Slowed conduction, reduced amplitude

Myelopathy (Myelin Problem)

Disease of the myelin (insulation around nerve fibers)

Examples: Multiple sclerosis, some inherited disorders

EMG/NCS findings: Significant slowing of conduction

Axonopathy (Axon Problem)

Damage to the actual nerve fiber

Examples: Toxic exposures, some neuropathies

EMG/NCS findings: Reduced amplitude with normal or mildly slowed conduction

Myopathy (Muscle Problem)

Primary disease of muscle tissue

Examples: Muscular dystrophy, inflammatory muscle disease

EMG findings: Characteristic muscle electrical patterns; NCS usually normal

Neuromuscular Junction Disorder

Problem at the connection between nerve and muscle

Examples: Myasthenia gravis, Lambert-Eaton syndrome

Special EMG testing: Shows characteristic fatigue pattern

What EMG and NCS Actually Measure

[4] Understanding this helps you understand your results:

NCS Measures

• Speed of conduction: How fast electrical signals travel (should be 40-60+ meters per second)
• Amplitude: How strong the nerve's electrical response is
• Latency: How long it takes for signal to travel a measured distance

EMG Measures

• Resting activity: What the muscle does when relaxed (should be silent)
• Contraction patterns: What the muscle does when you contract it
• Motor unit potentials: The pattern of electrical activity from groups of muscle fibers