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Without this connection, voluntary and involuntary (reflex) muscle control is impossible. Voluntary muscle control is lost because α-MNs relay voluntary signals from upper motor neurons to muscle fibers. Loss of involuntary control results from interruption of reflex circuits such as the tonic stretch reflex.
The muscle fibers belonging to one motor unit can be spread throughout part, or most of the entire muscle, depending on the number of fibers and size of the muscle. [2] [3] When a motor neuron is activated, all of the muscle fibers innervated by the motor neuron are stimulated and contract. The activation of one motor neuron will result in a ...
The motor unit: a single motor neuron and the muscle fibers that it innervates. A motor pool consists of all of the motor neurons that innervate a single muscle. Distinct skeletal muscles are controlled by groups of individual motor units. Such motor units are made up of a single motor neuron and the muscle
The soleus muscle is composed of "red" muscle which was revealed to indicate that muscle fibers were fatigue-resistant but created small forces when contracting. The gastrocnemius muscle is heterogeneous, composed of both "red" and "pale" muscle, and thus containing fast-twitch high force fibers.
The compound muscle action potential (CMAP) size is found using supramaximal stimulation of the motor nerve to the muscle or muscle group (similar to a nerve conduction study). It is recorded using surface electrodes. This is representative of the sum of the surface detected motor unit action potentials from muscles innervated by that nerve.
Signal transmission from nerve to muscle at the motor end plate. The neuromuscular junction is the synapse that is formed between an alpha motor neuron (α-MN) and the skeletal muscle fiber. In order for a muscle to contract, an action potential is first propagated down a nerve until it reaches the axon terminal of the motor neuron.
[6] [7] The maximal force depends on the contractile properties of the muscle fibers. Within a motor unit, all the muscle fibers are of the same type (e.g. type I (slow twitch) or Type II fibers (fast twitch)), and motor units of multiple types make up a given muscle. Motor units of a given muscle are collectively referred to as a motor pool.
Cardiac muscle cells are joined to neighboring cells by intercalated discs, and when joined in a visible unit they are described as a cardiac muscle fiber. [8] Smooth muscle cells control involuntary movements such as the peristalsis contractions in the esophagus and stomach. Smooth muscle has no myofibrils or sarcomeres and is therefore non ...