What generates force and feedback?

Description of molecular muscle mechanism - actin and myosin coupling to shorten muscle fibers.

A muscle model with parallel and series springs are made to explain the active and passive forces generated by the muscle fiber. The force curve peaks around rest-length and decreases as a muscles stretches or contracts. Explains why isometric force is the greatest, i.e. force output when muscle length is not changing.

Covered how to convert forces applied by the muscle on joints to torques around those joints. Assuming constant force, this is done by relating joint angles, bone and muscle lengths. Equating angular work with linear work \[ \tau\Delta\theta = f\Delta\lambda \], we can derive the Jacobian \( \mathbf{J}=\mathbf{\frac{d\lambda}{d\theta}} \), where \( \mathbf{\theta} \) can be a vector. Using this, \( \mathbf{\tau}=-\mathbf{J^T}f \).

Muscle afferents including golgi tendon organs and muscle-spindle afferents which act as mechanical force sensors for the muscle. The muscle-spindles are innervated with \( \gamma \)-neurons at the poles. The primary muscle spindle afferents in the central nuclear bag correspond somewhat to muscle force velocity. Secondary muscle spindle afferents in the poles correspond to muscle length. \( \gamma \)-neurons innervate the poles to change length (co-activated with \( \alpha \)-neurons for the extrafusal muscles) as a type of target muscle activation. Perfect muscles length would result in 0 change in the primary afferent firing rates.

The \( \alpha \)-\( \gamma \) afferents monosynaptic connection is important in motor feedback.

This section is important for proprioception, motor movements, and motor feedback.