motor unit
Unit
they are connected with the rope in the body
neuromuscular junction
The all-or-none law applies to individual muscle fibers within a skeletal muscle. This means that when a muscle fiber is stimulated by a motor neuron, it will either contract maximally or not at all, depending on whether the stimulus reaches the threshold for activation.
Electrical excitation of a muscle fiber. Skeletal muscle fibers (cells) can be stimulated either by amotor neuron in the body or by a voltage stimulator in the lab. Stimulation given by either method results in a depolarization of the sarcolemma. If the depolarization reaches threshold, an action potential (electrical signal) is initiated.
sarcoplasmic reticulum
The structures within the muscle fiber that shorten to cause skeletal muscle contraction are called myofibrils. Myofibrils are composed of repeating units called sarcomeres, which contain thick and thin filaments made of proteins (actin and myosin). When the muscle fiber is stimulated by a nerve impulse, the myosin heads interact with the actin filaments to generate the force required for muscle contraction.
Smooth muscle forms a functional syncytium due to the presence of gap junctions that allow electrical signals to pass from one cell to the next, enabling coordinated contractions. Skeletal muscle, on the other hand, does not form a functional syncytium as each skeletal muscle cell (fiber) is innervated individually by a motor neuron and must be stimulated independently.
Skeletal
Each muscle cell is only innervated by a single motor neuron, but each motor neuron innervates any number of muscle cells. When an action potential travels down the axon of an alpha motor neuron, it will depolarize several muscle cells at the same time, a phenomenon known as summation.
A motor endplate is a large special synaptic contact between motor axons and each skeletal muscle fiber. Each muscle fiber forms one endplate. Its function is to transmit impulses from nerves to muscles.
synapse
The chemical used at the junction with a skeletal muscle is acetylcholine (ACh). It is released from the motor neuron at the neuromuscular junction and binds to receptors on the muscle fiber's membrane, triggering muscle contraction. This process is essential for voluntary movement and is part of the overall neuromuscular signaling mechanism.