Problem 9 - Biology of Humans: Concepts, Applications, and Issues

Question

What type of contraction is characterized by a rapid, jerky response to a single stimulus? a. summation b. treppe c. tonic d. twitch

Step-by-Step Solution

Answer

d. twitch

Step 1: Identify the Question

The question is asking for the type of muscle contraction that is characterized by a rapid, jerky response to a single stimulus.

Step 2: Understand the Options

Review the provided options: summation, treppe, tonic, and twitch.

Step 3: Define Each Option

Summation refers to the additive effect of multiple stimuli on muscle contraction. Treppe, or the staircase effect, describes the gradual increase in muscular contraction following repeated stimulation. Tonic contractions maintain muscle tone and involve sustained tension. Twitch is a brief, rapid contraction in response to a single stimulus.

Step 4: Match the Definition

Compare the definitions to the description in the question. The rapid, jerky response to a single stimulus matches the definition of a twitch.

Step 5: Conclude the Answer

The type of contraction characterized by a rapid, jerky response to a single stimulus is a twitch.

Key Concepts

summation

Summation in muscle contractions occurs when multiple stimuli are applied to a muscle within a short period of time. This can result in the force of each individual contraction combining to produce a stronger overall contraction. There are two main types of summation:

• **Temporal (or wave) summation** - This happens when stimuli are delivered in rapid succession, causing the second stimulus to occur before the muscle has fully relaxed from the previous contraction. This leads to a stronger contraction.
• **Spatial summation** - This involves simultaneous stimuli from different locations, which can enhance the force of contraction.

Summation is critical for activities requiring sustained muscle contractions, such as lifting weights or maintaining posture.

treppe

Treppe, also known as the staircase effect, describes the phenomenon where a muscle responds to a series of stimuli with increasing strength of contractions. When muscles are stimulated consecutively, each contraction becomes slightly stronger than the previous, up to a certain point. This occurs because:

• **Increased Calcium Availability** - With each stimulus, more calcium ions are available, improving the muscle's ability to contract.
• **Enhanced Enzyme Activity** - Repeated stimulation increases the efficiency of enzymes involved in muscle contraction.

Treppe is often noticed when muscles initially start to work, such as in the warm-up phase before exercises.

tonic contraction

Tonic contractions are crucial for maintaining posture and muscle tone. These contractions are characterized by continuous, low-strength contractions that keep muscles ready for action. Key features include:

• **Sustained Tension** - Unlike rapid twitches, tonic contractions involve prolonged periods of tension without significant relaxation.
• **Postural Maintenance** - These contractions help keep our body upright and stable, crucial for activities involving balance and steady positions.

Tonic contractions are not usually associated with significant movements but are essential for functions like sitting and standing.

twitch

A muscle twitch is a single, rapid contraction followed by relaxation in response to a single stimulus. This kind of contraction is characterized by its brief, jerky motion. The sequence of a twitch involves:

1. **Latent Period** - The brief time between the application of the stimulus and the start of the contraction.
2. **Contraction Phase** - When the muscle fibers actively shorten, generating force.
3. **Relaxation Phase** - The period of returning to resting length after the peak of the contraction.

Twitches are fundamental in understanding how muscles respond to stimuli, but they represent only one type of muscle response, unlike prolonged contractions needed for endurance tasks.