BBA #4

Can motor units change their properties with training?

Yes. Motor-unit and muscle-fibre properties can change in response to the neural signals they receive and to training.

What determines the properties of muscle fibres?

The neurons that innervate them influence their properties.

What did Buller, Eccles, and Eccles (1960) demonstrate?

Reversing the innervation of slow- and fast-twitch motor units caused the properties of the muscle fibres to reverse.

What does the firing rate of an alpha motor neuron influence?

It provides an instructive signal that influences muscle-fibre properties.

What changes occurred after resistance training of the tibialis anterior in humans?

The rate of force generation increased, the rate of EMG signal generation increased, and neural firing rates increased.

What does resistance training suggest about neural adaptation?

Resistance training can produce neural adaptations that change force generation.

What is a motor unit?

A single alpha motor neuron and all the skeletal muscle fibres it innervates.

What happens when an alpha motor neuron fires?

All the muscle fibres in its motor unit contract together.

What determines motor-unit size?

The number of muscle fibres innervated by a single alpha motor neuron.

How does motor-unit size affect movement?

Smaller motor units allow greater dexterity, while larger motor units support greater power.

What is electromyography (EMG)?

A graphical representation of the electrical activity of skeletal muscle.

What does an EMG signal estimate?

Muscle activation.

What produces the electrical activity measured by EMG?

Electrical activity associated with motor-unit activation and motor end-plate potentials.

What are the two main methods of EMG recording?

Surface EMG and intramuscular EMG.

What is surface EMG?

Recording muscle electrical activity using electrodes placed on the skin.

What is intramuscular EMG?

Recording muscle electrical activity using electrodes inserted into the muscle.

What does surface EMG measure?

Electrical activity from multiple motor units beneath the skin.

Why does surface EMG appear noisy?

Motor units do not fire synchronously, and the skin and tissues filter the amplitude and frequency contributions of individual motor units.

What is the relationship between motor-unit activity and EMG?

EMG is a combined signal resulting from the activity of multiple motor units.

What is the relationship between EMG amplitude and muscle force?

EMG amplitude is related to muscle activation and can be associated with force, but the relationship is influenced by other factors.

Why can EMG amplitude not directly determine muscle force?

Muscle length, fatigue, and other factors affect force generation, so the relationship is not one-to-one.

What is the goal of EMG data collection?

To increase the signal and decrease noise.

Why should the skin be cleaned before surface EMG recording?

Skin debris can act as a resistor and interfere with the voltage signal.

Where should surface EMG electrodes be placed?

Over the muscle of interest.

What is a limitation of surface EMG electrode placement?

It primarily records activity from muscles immediately beneath the skin surface.

Where is the ground electrode usually placed?

Over a bony process.

What is the role of a differential amplifier in EMG recording?

It amplifies differences between electrode signals and subtracts common signals, helping reduce noise.

What assumption does the differential amplifier use?

The unwanted signal is assumed to be present at both electrodes at the same time.

What is raw EMG?

The original recorded electrical signal from muscle activity.

What is rectified EMG?

The absolute value of the raw EMG signal, with negative values converted to positive values.

What is integrated EMG?

The area under the rectified EMG signal over a period of time.

Why is EMG processing performed?

To obtain useful measures of the timing and amplitude of muscle-activation bursts.

What does EMG activation timing tell us?

Whether a muscle is active or inactive during a particular activity and when activation occurs.

How can EMG be used to study muscle activity during walking?

It can identify when particular muscles activate and deactivate during different phases of the walking cycle.

What example of hip-muscle activity during walking is discussed in the lecture?

The swing phase can be driven by momentum and gravity rather than active hip-flexor contraction.

How can EMG be used clinically to assess nerve conduction?

It can help measure nerve conduction speed and identify signs of motor-neuron diseases.

What motor-neuron disease is mentioned in the lecture as an example of clinical EMG use?

Amyotrophic lateral sclerosis (ALS).

What upper-limb nerve conduction speed is given as normal in the lecture?

Greater than 50 m/s.

What lower-limb nerve conduction speed is given as normal in the lecture?

Greater than 40 m/s.

What does latency mean in nerve conduction testing?

The time delay between stimulation and the recorded response.

What is maximal voluntary contraction (MVC)?

The maximum muscle contraction a person can voluntarily produce.

Why is EMG normalized to MVC?

To express muscle activation relative to that muscle's maximum voluntary activation.

What is %MVC?

Muscle activation during a task expressed as a percentage of EMG amplitude during maximal voluntary contraction.

How is %MVC calculated?

%MVC = (EMG amplitude during the task / EMG amplitude during MVC) × 100.

If task EMG amplitude is 0.5 mV and MVC EMG amplitude is 2.0 mV, what is %MVC?

25%.

Why does %MVC make EMG comparisons more useful?

It provides a muscle-specific reference and allows comparisons across muscles or individuals.

What are the two major uses of EMG listed in the lecture?

Research to measure and test hypotheses about muscle activation, and clinical testing to help diagnose or rule out diseases.

What is the sensorimotor system?

The system involving the close relationship between sensory information and movement.

How does the CNS monitor the body during movement?

The brain and spinal cord send and receive signals to monitor muscle position, length, and tone.

Why does the CNS continuously monitor muscles?

To keep the body prepared to act and to adjust movements using sensory information.

What are afferent signals?

Signals travelling from peripheral sensory receptors toward the CNS.

What are efferent signals?

Signals travelling from the brain toward spinal motor neurons and the periphery.

What is a sensory receptor?

A receptor or specialized neuron that responds to and encodes information.

What are exteroceptors?

Receptors that respond to information from outside the body.

What sensory information can exteroceptors detect?

External stimuli such as light, sound, and touch.

How is visual information converted into neural signals?

Light is converted into chemical energy in photoreceptors, leading to action potentials.

How is auditory information converted into neural signals?

Air-pressure waves produce mechanical stimulation that is converted into action potentials.

How is touch information converted into neural signals?

Mechanical pressure stimulates receptors that produce action potentials.

What are interoceptors?

Receptors that respond to information from within the body.

What internal conditions can interoceptors detect?

Conditions such as blood pressure, glucose levels, and oxygen and carbon dioxide levels.

What are proprioceptors?

Sensory receptors that provide information about the body's configuration, posture, and movement.

What is proprioception?

The ability to perceive the position and movement of the body without relying on vision.

What is kinesthesis?

The sense of movement of a body part.

What is the difference between proprioception and kinesthesis?

Proprioception refers to sensing limb position in space, while kinesthesis refers to sensing movement.

Can proprioception work without vision?

Yes. Sensory information from the body provides information about position and movement even when the eyes are closed.

Where are proprioceptive mechanoreceptors located?

In muscles, tendons, joints, and skin.

What information does proprioception provide?

Information about joint range of motion, body position, and movement effort.

How is proprioceptive information used?

It is sent to the brain and used to adjust movements.

Does proprioception always require conscious awareness?

No. Proprioceptive information can be used without conscious awareness.

Who was Ian Waterman, also known as Patient IW?

A man who lost touch and proprioception from the neck down following a viral infection in 1972.

What happened to Ian Waterman's sensory system?

Large group Ia afferent peripheral neurons carrying touch and proprioceptive information were damaged.

Could Ian Waterman still move his limbs?

Yes. His upper and lower motor neurons remained functional, but he could not accurately control or track movements without looking.

How did Ian Waterman relearn movement?

Over approximately three years, he relearned to move by consciously controlling and visually monitoring his actions.

Why must Ian Waterman keep his limbs in sight when voluntarily moving?

He lacks the normal touch and proprioceptive information needed to monitor limb position and movement without vision.

What does Ian Waterman's case demonstrate about proprioception?

Normal movement control depends heavily on sensory feedback, especially information from large muscle-related afferents.

What are the four sources of sensory information contributing to proprioception described in the lecture?

Joint afferents, skin receptors, muscle spindles, and Golgi tendon organs.

What are joint afferents?

Sensory nerve endings in the joint capsule that respond particularly to extreme joint positions and capsule deformation.

What type of afferents are joint afferents described as in the lecture?

Small-diameter, unmyelinated Type III afferents that conduct relatively slowly.

How do tactile receptors in the skin contribute to proprioception?

They provide information about skin stretch, particularly in areas such as the hands.

What type of afferents carry information from tactile receptors involved in proprioception?

Medium-diameter, myelinated Type II afferents.

What are the two major types of muscle afferent receptors?

Muscle spindles and Golgi tendon organs.

What do muscle spindles detect?

Muscle stretch and changes in muscle length.

Where are muscle spindles located?

Within muscles, arranged in parallel with ordinary muscle fibres.

What are ordinary muscle fibres also called?

Extrafusal muscle fibres.

What are intrafusal muscle fibres?

Specialized muscle fibres within muscle spindles that contribute to sensing muscle stretch.

What happens to muscle spindles when a muscle stretches?

The spindles stretch, increasing sensory firing.

What type of sensory afferents carry signals from muscle spindles?

Large-diameter, myelinated Type Ia afferents and medium-diameter, myelinated Type II afferents.

What are Golgi tendon organs (GTOs)?

Sensory receptors at the muscle-tendon junction that detect force.

Where are Golgi tendon organs located?

At the muscle-tendon junction, arranged in series with ordinary muscle fibres.

What type of sensory afferents carry signals from Golgi tendon organs?

Large-diameter, myelinated Type Ib afferents.

How do Golgi tendon organ firing rates change with muscle force?

Firing rates increase as muscle force increases.

What is the main difference between muscle spindles and Golgi tendon organs?

Muscle spindles signal muscle stretch and length, while Golgi tendon organs signal muscle force.

What are the two types of intrafusal muscle fibres in muscle spindles?

Nuclear bag fibres and nuclear chain fibres.

What are nuclear bag fibres?

Intrafusal fibres with a central, enlarged bag-like region surrounded by contractile tissue.

What information do nuclear bag fibres signal?

Muscle length and changes in muscle length, meaning position and movement.

Which sensory afferents wrap around nuclear bag fibres?

Large-diameter Type Ia sensory neurons.

What are the two types of nuclear bag fibres mentioned in the lecture?

Dynamic and static nuclear bag fibres.

What are nuclear chain fibres?

Intrafusal fibres with a narrow, chain-like central region surrounded by contractile tissue.

What information do nuclear chain fibres signal?

Muscle length or position.

Which sensory afferents are associated with nuclear chain fibres?

Type Ia and medium-diameter Type II sensory neurons.