Contraction, Advanced Terminology, Reflexes

What is a muscle twitch?

The response of a muscle to a single stimulation.

What are the three periods of a muscle twitch?

1. Latent

2. Contraction

3. Relaxation.

What is muscle fatigue?

The reduced ability of a muscle to produce force after prolonged or intense activity.

What causes muscle fatigue during high-intensity exercise?

K⁺ accumulation in T-tubules and ADP + Pi accumulation.

What causes muscle fatigue during low-intensity (long-duration) exercise?

Fuel depletion, electrolyte loss, and central fatigue.

What are the two main types of muscle contractions?

Isometric and isotonic contractions.

What is an isometric contraction?

The muscle develops tension but does not change length (no movement).

What is an isotonic contraction?

The muscle changes length while maintaining tension.

What are the two types of isotonic contractions?

Concentric and eccentric.

What is a concentric contraction?

The muscle shortens as it contracts (like lifting a weight).

What is an eccentric contraction?

The muscle lengthens while contracting (like lowering a weight).

What are the two types of muscle attachments?

Origin and insertion

What is the origin of a muscle?

The “stable” attachment point of a muscle, usually on the proximal (closer to the body) segment.

What is the insertion of a muscle?

The “moveable” attachment point of a muscle, usually on the distal (farther from the body) segment.

What is an agonist muscle?

The prime mover of a joint during contraction; it produces the main movement.

What is an antagonist muscle?

The muscle that opposes the prime mover (agonist).

How do agonist and antagonist muscles work together?

The agonist contracts to move the joint, while the antagonist relaxes to allow the movement.

What is a synergist muscle?

A muscle that assists the prime mover during movement.

What is a fixator muscle?

A muscle that prevents movement by stabilizing or “fixating” a bone.

What are the three components of a lever system?

Load, effort, and fulcrum.

What is a first-class lever?

he fulcrum is between the load and the effort. Example: lifting your head (neck joint acts as fulcrum).

What is a second-class lever?

The load is between the fulcrum and the effort. Example: standing on your tiptoes (ball of foot is fulcrum).

What is a third-class lever?

The effort is between the load and the fulcrum. Example: flexing your arm at the elbow (biceps).

Which class of lever is most common in the body?

Third-class levers.

What is an inborn (intrinsic) reflex?

An unlearned, unpremeditated, and involuntary reflex that can be somatic or visceral.

What is a learned (acquired) reflex?

A reflex developed through practice or repetition that becomes automatic.

What are the two main types of reflexes?

Inborn (intrinsic) and learned (acquired).

What are the five essential components of a reflex arc?

• Receptor

• Sensory neuron

• Integration center

• Motor neuron

• Effector

What are the four main properties of reflexes?

1. Require stimulation
2. Are quick
3. Are involuntary
4. Are stereotyped

What are the two main types of reflexes based on what they control?

Somatic (involving skeletal muscles) and visceral (involving internal organs or glands).

What are muscle spindles?

Modified muscle fibers that detect and signal changes in muscle length (body movement).

What is the main function of muscle spindles?

To sense how much a muscle is stretched and help regulate muscle tone and movement.

Where are muscle spindles typically found?

Near the musculotendinous junction (where the muscle meets the tendon).

What type of receptor are muscle spindles?

Proprioceptors

What are intrafusal fibers?

Muscle fibers located within the muscle spindle that detect changes in muscle length.

What type of motor neurons control intrafusal fibers?

Gamma motor neurons.

What type of sensory fibers are associated with intrafusal fibers?

Primary and secondary afferent (sensory) fibers.

What are extrafusal fibers?

The “regular” muscle fibers responsible for generating force and movement.

What type of motor neurons control extrafusal fibers?

Alpha motor neurons.

What is the stretch reflex?

A reflex that helps the nervous system smoothly coordinate skeletal muscle movement.

What information does the stretch reflex rely on?

The length of the muscle and how fast it’s changing.

What receptors detect muscle length for the stretch reflex?

Muscle spindles.

What two things do muscle spindles tell the nervous system during the stretch reflex?

How much (degree) the muscle is stretched and how fast (rate) it’s stretching.

What are Golgi tendon organs?

Small bundles of loose collagen fibers innervated by one or more nerve fibers that detect muscle tension.

Where are Golgi tendon organs located?

In the tendons, near the musculotendinous junction.

What do Golgi tendon organs detect?

The amount of tension or force a muscle is generating.

What type of receptor are Golgi tendon organs?

Proprioceptors

What is the tendon reflex?

A reflex that helps prevent muscles and tendons from tearing during excessive stretching or force.

What does the tendon reflex monitor?

The tension of the muscle, detected by Golgi tendon organs.

What type of reflex is the tendon reflex — monosynaptic or polysynaptic?

Polysynaptic reflex.

What is the result of the tendon reflex?

Muscle relaxation of the contracting muscle to reduce tension.

What are the two main steps of the tendon reflex?

1. Afferent impulse is sent to the cerebellum.

2. The contracting muscle is inhibited, and the antagonist muscle is activated.