What is an innervation ratio?

A number indicating the density of innervation (1) of a specified muscle by motor neurons, especially the average number of muscle fibres contacted by each motor neuron (the total number of muscle fibres contacted divided by the number of motor neurons), a low ratio being indicative of a lack of precise control, and a …

Which muscles have the highest innervation ratio?

Conversely, high innervation ratios (approximately 2000) occur in larger muscles such as the biceps of the upper arm where accuracy of movement is relatively insignificant. When a motor neuron fires, the neurotransmitter acetylcholine is released in the neuromuscular junction.

Which of the following muscles have the lowest innervation ratio?

Out of the above choices, _C_, the muscles that move the fingers would have motor units with the lowest innervation ratio.

Why is there a smaller muscle fiber to motor neuron ratio for muscles responsible for precision?

Why is there a smaller muscle fiber to motor neuron ratio for muscles responsible for precision? Because control of the individual muscle fibers increases. Once an action potential excites the sarcolemma, a series of actions take place in order to produce a muscle contraction.

Do alpha motor neurons release GABA?

One way they differ is that synapses between neurons typically use glutamate or GABA as their neurotransmitters, while the neuromuscular junction uses acetylcholine exclusively. Alpha motor neurons have Aα axons, which are large-caliber, heavily myelinated fibers that conduct action potentials rapidly.

How many motor units are in a muscle?

An individual muscle contains all three types of motor units. This provides each muscle with the ability to produce an increased force output from a low level to a high level, and it also provides each muscle with a certain degree of muscular endurance.

Where is motor neurons located?

Motor neurons (MNs) are neuronal cells located in the central nervous system (CNS) controlling a variety of downstream targets. There are two main types of MNs, (i) upper MNs that originate from the cerebral cortex and (ii) lower MNs that are located in the brainstem and spinal cord.

What are the steps of muscle contraction?

What are the 8 steps of muscle contraction?

1. action potential to muscle.
2. ACETYLCHOLINE released from neuron.
3. acetylcholine binds to muscle cell membrane.
4. sodium diffuse into muscle, action potential started.
5. calcium ions bond to actin.
6. myosin attaches to actin, cross-bridges form.

Which muscle has the largest motor units?

The best example is the large motor units of the thigh muscles or back muscles, where a single motor neuron will supply thousands of muscle fibers in a muscle, as its axon splits into thousands of branches.

Do alpha motor neurons contain Myofibrils?

Alpha (α) motor neurons (also called alpha motoneurons), are large, multipolar lower motor neurons of the brainstem and spinal cord. Alpha motor neurons are distinct from gamma motor neurons, which innervate intrafusal muscle fibers of muscle spindles.

What is the largest motor unit in the human body?

The sartorius muscle is the longest muscle in the human body. It is strap-like, up to 600 mm in length, and contains five to seven neurovascular compartments, each with a neuromuscular endplate zone. Some of its fibers terminate intrafascicularly, whereas others may run the full length of the muscle.

What is the smallest motor unit in human body?

The smallest motor units are in muscles that must produce very fine gradations of force:

• lumbricals: 100 fibers/unit.
• eye muscles: 5 fibers/unit.

Is the thyrohyoid muscle innervated by the ansa?

Thyrohyoid, unlike the other infrahyoid muscles, is not innervated by the ansa cervicalis. Instead, nerve fibers from the anterior rami of the first cervical spinal nerve (C1) reach the muscle via the hypoglossal nerve (CN XII).

Is the thyrohyoid muscle innervated by the C1 nerve?

It is innervated by thyrohyoid branch of C1 nerve. This nerve branches from the first cervical nerve as it joins the hypoglossal nerve (12th Cranial Nerve) for a short distance. This is the only exception in the infrahyoid muscles, or strap muscles, that is not innervated by ansa cervicalis .

What is the function of the thyrohyoid muscle?

The thyrohyoid muscle is an infrahyoid muscle of the neck that is innervated by the ventral ramus of C1. The primary function of the thyrohyoid muscle is to depress and fix the hyoid bone and larynx though it may also raise the larynx when the hyoid bone is fixed.

Is the thyrohyoid a part of the hyoid?

Thyrohyoid. For a brief stretch, the first cervical nerve also joins the hypoglossal nerve, which controls the movement of the tongue. The thyrohyoid muscle is not the only muscle attached to the hyoid. The middle pharyngeal constrictor, the digastric, the omohyoid, and other muscles are located in close proximity.