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Related Concept Videos

Somatic Spinal Reflexes01:22

Somatic Spinal Reflexes

Somatic spinal reflexes are rapid, involuntary muscular responses to external stimuli that involve the somatic musculature and the spinal cord.
One of the most well-known somatic spinal reflexes is the stretch reflex, which is activated by the sudden stretching of a muscle. This reflex involves the activation of specialized sensory receptors called muscle spindles, which are located in the muscle tissue and detect changes in the length and speed of muscle contractions. When a muscle is suddenly...
Motor Unit Stimulation01:20

Motor Unit Stimulation

When the neuron of a motor unit fires an action potential, it triggers a series of events, leading to a twitch contraction in the muscle fibers. The process of excitation-contraction coupling is crucial in relaying the action potential to the muscle fibers.
The latent period of contraction marks the onset of excitation-contraction coupling, when the action potential propagates across the sarcolemma, preparing the muscle fibers for contraction. As the fibers enter the contraction phase, the...
Relaxation of Skeletal Muscles01:29

Relaxation of Skeletal Muscles

The period of muscle contraction primarily influences the duration of stimulation at the neuromuscular junction (NMJ), the presence of free calcium ions in the sarcoplasm, and the availability of energy or ATP to support contractions.
When an action potential reaches the axon terminal, it depolarizes the membrane and opens voltage-gated sodium channels. Sodium ions enter the cell, further depolarizing the presynaptic membrane. This depolarization causes voltage-gated calcium channels to open.
Muscle Stimulation Frequency01:22

Muscle Stimulation Frequency

The contraction strength of muscles is regulated by motor neurons, which modulate the frequency of action potentials dispatched to the motor units based on the body's requirements. This process of varying the muscle stimulation frequency allows muscles to contract with a force that is precisely tailored to the needs of the moment, whether lifting a feather or a heavy box.
Wave summation
At low firing rates, motor neurons induce individual twitch contractions in muscle fibers. These twitches...
Smooth Muscle Contraction01:25

Smooth Muscle Contraction

Smooth muscle contraction is a complex process vital for various bodily functions, from maintaining blood vessel tension to facilitating the movement of food through the digestive tract. Unlike striated muscles, smooth muscle contraction begins more slowly and lasts longer.
The onset of contraction is triggered by an increase in calcium ions within the sarcoplasm, similar to the process in striated muscle. However, smooth muscles have a relatively smaller reservoir of the sarcoplasmic...
The Micturition Reflex01:26

The Micturition Reflex

Urination, or micturition involves the coordination of the bladder's detrusor muscle and two sphincters to ensure controlled bladder emptying.
The process begins with bladder filling, where the bladder wall stretches as urine accumulates. This stretching activates the urine storage reflex, mediated by the sacral spinal segments and the pontine storage center. Efferent sympathetic impulses stimulate the detrusor muscle to relax and the internal urethral sphincter to contract, facilitating urine...

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Related Experiment Video

Updated: Jul 13, 2026

Methods to Quantify Pharmacologically Induced Alterations in Motor Function in Human Incomplete SCI
14:55

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Published on: April 18, 2011

Voluntary modulation of human stretch reflexes.

Daniel Ludvig1, Ian Cathers, Robert E Kearney

  • 1Department of Biomedical Engineering, McGill University, 3775 University Street, Montreal, QC, Canada H3A 2B4. daniel.ludvig@mail.mcgill.ca

Experimental Brain Research
|July 14, 2007
PubMed
Summary

The central nervous system (CNS) can independently control reflex stiffness, not just overall joint stiffness. This finding reveals the CNS

Area of Science:

  • Neuroscience
  • Biomechanics
  • Motor Control

Background:

  • The central nervous system (CNS) is thought to modulate joint mechanical properties via reflex pathways.
  • Previous evidence relied on indirect measures like H-reflexes and electromyography (EMG).
  • Direct evidence for independent control of reflex stiffness, separate from intrinsic stiffness, was lacking.

Purpose of the Study:

  • To investigate if the CNS can control reflex stiffness independently of intrinsic stiffness.
  • To provide direct evidence for the CNS's ability to tune joint mechanics through reflex pathways.

Main Methods:

  • Developed a novel algorithm to estimate intrinsic and reflex stiffness in real-time.
  • Utilized real-time biofeedback to train subjects in controlling stiffness components.

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Non-invasive Assessment of Changes in Corticomotoneuronal Transmission in Humans

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  • Measured ankle muscle electromyogram (EMG) to ensure constant contraction levels.

    • Main Results:

    • Subjects successfully learned to control reflex stiffness independently of intrinsic stiffness using biofeedback.
    • Reflex stiffness gain was modulated by a factor of 4 at low torque levels.
    • Constant elastic stiffness and torque were maintained, with stable EMG activity.

    Conclusions:

    • The CNS possesses the capability to independently control reflex stiffness.
    • This independent control offers significant flexibility in adapting joint mechanical properties for functional tasks.
    • Findings support the hypothesis of task-dependent tuning of joint mechanics by the CNS.