Motor neuron
Section through the spinal cord. Motor neuron projection through ventral root is shown in red. In Anatomy and Neurology, the ventral root (or anterior root) is the efferent motor root of a Spinal nerve.
Location	Ventral horn of the spinal cord
Function	Excitatory projection (to NMJ)
Neurotransmitter	UMN to LMN: glutamate; LMN to NMJ: ACh
Morphology	Projection neuron
Presynaptic connections	M1 via the Corticospinal tract
Postsynaptic connections	Muscle fibers and other neurons

In vertebrates, the term motor neuron (or motoneuron) classically applies to neurons located in the central nervous system (CNS) that project their axons outside the CNS and directly or indirectly control muscles. The spinal cord is a long thin tubular bundle of Nerves that is an extension of the Central nervous system from the brain and is enclosed in and protected A neuromuscular junction ( NMJ) is the Synapse or junction of the Axon terminal of a Motoneuron with the motor end plate, the Glutamic acid (abbreviated as Glu or E) is one of the 20 Alpha Amino acids It is not among the human Essential amino acids Its A neuromuscular junction ( NMJ) is the Synapse or junction of the Axon terminal of a Motoneuron with the motor end plate, the The Chemical compound acetylcholine (often abbreviated ACh) is a Neurotransmitter in both the Peripheral nervous system (PNS and Central The term morphology in Biology refers to the outward appearance ( Shape, Structure, Colour, Pattern) of an Organism The primary motor cortex (or M1) works in association with pre-motor areas to plan and execute movements The corticospinal or pyramidal tract is a massive collection of Axons that travel between the Cerebral cortex of the Brain and the Spinal Skeletal muscle is a type of Striated muscle, which usually attaches to tendons Neurons (ˈnjuːɹɒn also known as neurones and nerve cells) are responsive cells in the Nervous system that process and transmit information Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes Neurons (ˈnjuːɹɒn also known as neurones and nerve cells) are responsive cells in the Nervous system that process and transmit information In Vertebrates the central nervous system ( CNS) is the part of the Nervous system which is enclosed in the Meninges. An axon or nerve fiber is a long slender projectionof a nerve cell or Neuron, that conducts electrical impulses away from the neuron's Cell Muscle (from Latin musculus, diminutive of mus "mouse" is contractile tissue of the body and is derived from the Motor neuron is often synonymous with efferent neuron, primary neuron, or alpha motor neuron. In the Nervous system, efferent nerves – otherwise known as motor or effector Neurons – carry nerve impulses away from the

Contents 1 Anatomy and physiology 2 Function 3 Somatic motoneurons 4 Motor units 5 See also 6 References

Anatomy and physiology

Branch of NS	Position	Neurotransmitter
Somatic	n/a	Acetylcholine
Parasympathetic	Preganglionic	Acetylcholine
Parasympathetic	Ganglionic	Acetylcholine
Sympathetic	Preganglionic	Acetylcholine
Sympathetic	Ganglionic	Norepinephrine*
*Except fibers to sweat glands and certain blood vessels Motoneuron neurotransmitters

According to their targets, motoneurons are classified into three broad categories:

"Somatic motoneurons", which directly innervate skeletal muscles, involved in locomotion (such as muscles of the limbs, abdominal, and intercostal muscles). The skin contains two different groups of sweat glands: Apocrine sweat glands and Merocrine sweat glands. The blood vessels are part of the Circulatory system and function to transport Blood throughout the body Skeletal muscle is a type of Striated muscle, which usually attaches to tendons Intercostal muscles are several groups of Muscles that run between the Ribs, and help form and move the Chest wall.

“Special visceral motoneurons” — also called “branchial motoneurons”— which directly innervate branchial muscles (that motorize the gills in fish and the face and neck in land vertebrates). Special visceral efferent ( SVE) refers to Efferent nerves which supply muscles which derived from the Branchial arches. Branchiomeric muscles are striated muscles of the head and neck A gill is an anatomical structure found in many aquatic organisms Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes

“General visceral motoneurons” — "visceral motoneurons" for short — which indirectly innervate smooth muscles of the viscera (like the heart, and the muscles of the arteries): they synapse onto neurons located in ganglia of the autonomic nervous system (sympathetic and parasympathetic), located in the peripheral nervous system (PNS), which themselves directly innervate visceral muscles (and also some gland cells). The general visceral efferent fibers ( GVE or sympathetic efferent fibers) probably arise from cells in the Lateral column or the base of the anterior column Smooth muscle is a type of non- Striated muscle, found within the Tunica media layer of large and small Arteries and Veins, the bladder In Anatomy, a viscus (ˈvɪskəs ( Plural: viscera /ˈvɪsərə/ is an internal organ of an animal (including humans in particular an internal The heart is a muscular organ in all Vertebrates responsible for pumping Blood through the Blood vessels by repeated rhythmic Arteries are Blood vessels that carry blood away from the Heart. Chemical synapses are specialized junctions through which Neurons signal to each other and to non-neuronal cells such as those in Muscles or Glands In Anatomy, a ganglion (pl ganglia) is a tissue mass. Neurology In neurological contexts ganglia are composed mainly of &trade The autonomic nervous system ( ANS) (or visceral nervous system) is the part of the Peripheral nervous system that acts as a Control The Sympathetic Nervous System ( SNS) is a branch of the Autonomic nervous system along with the Enteric nervous system and Parasympathetic nervous The parasympathetic Nervous system ( PSNS) is a division of the Autonomic nervous system (ANS along with the Sympathetic nervous system The peripheral nervous system ( PNS) resides or extends outside the Central nervous system (CNS which consists of the Brain and Spinal cord.

In other words:

• the motor command of skeletal and branchial muscles is monosynaptic (involving only one motoneuron, respectively, somatic and branchial, which synapses onto the muscle). Skeletal muscle is a type of Striated muscle, which usually attaches to tendons
• the command of visceral muscles is disynaptic (involving two neurons: the “general visceral motoneuron” located in the CNS, which synapses onto a ganglionic neuron, located in the PNS, which synapses onto the muscle). Smooth muscle is a type of non- Striated muscle, found within the Tunica media layer of large and small Arteries and Veins, the bladder

It could be argued that, in the command of visceral muscles, the ganglionic neuron — parasympathetic or sympathetic — is the real “motoneuron”, being the one that directly innervates the muscle (whereas the “general visceral motoneuron” is, strictly speaking, a “preganglionic” neuron). The parasympathetic Nervous system ( PSNS) is a division of the Autonomic nervous system (ANS along with the Sympathetic nervous system In the Autonomic nervous system, fibers from the CNS to the ganglion are known as preganglionic fibers. But, for historical reasons, the term motoneuron is reserved for the CNS neuron.

All motoneurons are cholinergic, that is, they release the neurotransmitter acetylcholine. A receptor is cholinergic if it uses Acetylcholine as its Neurotransmitter. The Chemical compound acetylcholine (often abbreviated ACh) is a Neurotransmitter in both the Peripheral nervous system (PNS and Central Parasympathetic ganglionic neurons are also cholinergic, whereas most sympathetic ganglionic neurons are noradrenergic, that is, they release the neurotransmitter noradrenaline. Norepinephrine ( INN) (abbreviated norepi or NE) or noradrenaline ( BAN) (abbreviated NA or NAd) is a Norepinephrine ( INN) (abbreviated norepi or NE) or noradrenaline ( BAN) (abbreviated NA or NAd) is a (see Table)

Function

The interface between a motoneuron and muscle fiber is a specialized synapse called the neuromuscular junction. Chemical synapses are specialized junctions through which Neurons signal to each other and to non-neuronal cells such as those in Muscles or Glands A neuromuscular junction ( NMJ) is the Synapse or junction of the Axon terminal of a Motoneuron with the motor end plate, the Upon adequate stimulation, the motoneuron releases a flood of neurotransmitters that bind to postsynaptic receptors and triggers a response in the muscle fiber. See Chemical synapse for an introduction to concepts and terminology used in this article In Biochemistry, a receptor is a Protein molecule embedded in either the Plasma membrane or Cytoplasm of a cell to which a mobile signaling

• In invertebrates, depending on the neurotransmitter released and the type of receptor it binds, the response in the muscle fiber could be either excitatory or inhibitory. An invertebrate is an Animal lacking a Vertebral column. The group includes 98% of all animal Species — all animals except those in the Chordate

• For vertebrates, however, the response of a muscle fiber to a neurotransmitter can only be excitatory, in other words, contractile. Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes See Chemical synapse for an introduction to concepts and terminology used in this article Muscle relaxation and inhibition of muscle contraction in verterbrates is obtained only by inhibition of the motorneuron itself. Although muscle innervation may eventually play a role in the maturation of motor activity. This is why muscle relaxants work by acting on the motoneurons that innervate muscles (by decreasing their electrophysiological activity) or on cholinergic neuromuscular junctions, rather than on the muscles themselves. This article refers to skeletal muscle relaxants For information on Smooth muscle relaxants see Antispasmodic. Electrophysiology (from Greek grc ἥλεκτρον ēlektron, "amber" the [[Electron#Etymology|etymology of "electron"]] grc φύσις The Chemical compound acetylcholine (often abbreviated ACh) is a Neurotransmitter in both the Peripheral nervous system (PNS and Central A neuromuscular junction ( NMJ) is the Synapse or junction of the Axon terminal of a Motoneuron with the motor end plate, the

Somatic motoneurons

Somatic motoneurons are further subdivided into two types: alpha efferent neurons and gamma efferent neurons. (Both types are called efferent to indicate the flow of information from the central nervous system (CNS) to the periphery. In Vertebrates the central nervous system ( CNS) is the part of the Nervous system which is enclosed in the Meninges. The peripheral nervous system ( PNS) resides or extends outside the Central nervous system (CNS which consists of the Brain and Spinal cord. )

• Alpha motoneurons innervate extrafusal muscle fibers (typically referred to simply as muscle fibers) located throughout the muscle. Alpha motor neurons ( α-MNs) are large Lower motor neurons of the Brainstem and Spinal cord. Extrafusal muscle fibers are a class of Muscle fiber innervated by Alpha motor neurons They generate tension do mechanical work and allow for movement by contracting Their cell bodies are in the ventral horn of the spinal cord and they are sometimes called ventral horn cells.
• Gamma motoneurons innervate intrafusal muscle fibers found within the muscle spindle. Gamma motoneurons ( γ-motoneurons) also called gamma motor neurons, are a component of the Fusimotor system, the system by which the Central Intrafusal fibers are Muscle fibers that comprise the Muscle spindle and are innervated by the gamma motor neurons ( Gamma motoneuron) Muscle spindles are Sensory receptors within the belly of a Muscle, which primarily detect changes in the length of this muscle

In addition to voluntary skeletal muscle contraction, alpha motoneurons also contribute to muscle tone, the continuous force generated by noncontracting muscle to oppose stretching. In Physiology, Medicine, and Anatomy, muscle tone (aka residual muscle tension or tonus) is the continuous and passive partial When a muscle is stretched, sensory neurons within the muscle spindle detect the degree of stretch and send a signal to the CNS. Sensory neurons are Neurons that are activated by sensory input (vision touch hearing etc Muscle spindles are Sensory receptors within the belly of a Muscle, which primarily detect changes in the length of this muscle The CNS activates alpha motoneurons in the spinal cord, which cause extrafusal muscle fibers to contract and thereby resist further stretching. This process is also called the stretch reflex. A stretch reflex is a muscle contraction in response to stretching within the muscle

Gamma motoneurons regulate the sensitivity of the spindle to muscle stretching. With activation of gamma neurons, intrafusal muscle fibers contract so that only a small stretch is required to activate spindle sensory neurons and the stretch reflex.

Motor units

A single motoneuron may synapse with one or more muscle fibers. The motoneuron and all of the muscle fibers to which it connects is a motor unit. A motor unit is a single α-motor neuron and all of the corresponding muscle fibers it innervates.

See also

• Neuromuscular junction
• Muscle spindle
• Motor unit
• Motor neurone disease
• Motor nerve
• Efferent nerve

References

• Sherwood, L. A neuromuscular junction ( NMJ) is the Synapse or junction of the Axon terminal of a Motoneuron with the motor end plate, the Muscle spindles are Sensory receptors within the belly of a Muscle, which primarily detect changes in the length of this muscle A motor unit is a single α-motor neuron and all of the corresponding muscle fibers it innervates. The motor neurone diseases (or motor neuron diseases) (MND are a group of progressive neurological disorders that destroy Motor neurones the cells that control voluntary Motor nerves allow the Brain to stimulate muscle contraction A motor Nerve is an Efferent nerve that exclusively contains the Axons of somatic In the Nervous system, efferent nerves – otherwise known as motor or effector Neurons – carry nerve impulses away from the (2001). Human Physiology: From Cells to Systems (4 ed. ). California: Brooks/Cole.
• Marieb, E. N. , Mallatt, J. (1997). Human Anatomy (2 ed. ). California: Benjamin/Cummings.

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