Upper Motor Neuron vs Lower Motor Neuron | UMN vs LMN - ASLPclick

 UMN v/s LMN

The Central Nervous System (CNS) –

-       The Central Nervous system (CNS) consists of the brain in the spinal cord and the upper motor neurons are higher up in the CNS whereas lower motor neurons are located at the lower regions of the CNS.

-       Also known as motoneuron, a motor neuron is a neuron having a cell body located in the motor cortex, spinal cord, or the brainstem, and whose axon fiber projects to the spinal cord or outside of the spinal cord to control effector organs directly/indirectly like muscles and glands. The spinal cord is the place where communication between upper and lower motor neurons takes place.

 

Ø What is Upper Motor Neuron –

Upper motor neurons (upper nerve cells) are present in the cerebral cortex and brainstem carries information down to activate interneurons and also lower motor neurons which ultimately signal muscles to contract or relax.

 

Ø What is Lower Motor Neuron –

It is the nerve cell that goes from the spinal cord to the muscle  Its cell body is in the spinal cord and its termination takes place in a skeletal muscle.

 

Ø Different b/w UMN & LMN –

 

Upper Motor Neurons	Lower Motor Neurons
These are the neurons located within the brain or brainstem. Innervates Alpha and Gamma motor neurons in ventral horn	These are the alpha and gamma motor neurons located in the ventral horn of the spinal cord.
Axon travels down the spinal cord.	Axon travels peripherally to innervate the muscle.
It is the motor system restricted to the Central Nervous System.  The upper motor neuron is responsible for effectively managing voluntary movement, maintenance of muscle tone for supporting the body against gravity, and also provides regulation of postures to provide a stable background upon which it is needed to initiate the voluntary activity.	It is the efferent neuron of the peripheral nervous system (PNS) that connects the CNS with the muscle to be innervated. It is the nerve cell present in the spinal cord and its termination is in skeletal muscle.
UMNs have numerous regulatory functions. They can modulate the activity of α- and γ-LMNs either directly (mono synaptically) or indirectly (via interneurons).	The entire function of the CNS is manifested through this neuron.
The cell bodies of the upper motor neuron are bigger as compared to the lower motor neuron cell bodies.	The cell bodies of the lower motor neurons are comparatively smaller.
These transmit motor impulses from the brain to the synapses of the lower motor neuron.	These neurons collect the transmitted motor impulses from the upper motor neuron to the muscles in the body.
Diseases related to its dysfunction include spinal cord injury, multiple sclerosis, and stroke. A motor neuron disease where only the upper motor neuron is affected is primary lateral sclerosis.	Its loss leads to body weakness, fasciculation or twitching of muscle, and loss of muscle mass called muscle atrophy.
The diseases associated with upper motor neurons are a heterogeneous group of disorders in which a degeneration of motor neurons of the cortex and tronco encefalico motor nucleus occurs. Symptoms include weakness, spasticity, motor clumsiness, and hyperreflexia.	The General Somatic Efferent fibers present here involve all neurons that innervate striated voluntary skeletal muscle (which is derived from somite’s and somatic mesoderm in the limb buds of the wall and from somitomeres in the head). The lower motor neurons are located in all of the spinal nerves and all of the cranial nerves except I, II, and VIII.
These are classified based on the pathways they travel.	Their classification is based on the muscle fiber type they innervate.
These form synapses with the lower motor neurons.	These form synapses with the muscles in the body.

Ø LMN vs UMN Lesion –

The difference between upper and lower motor neuron lesion is such that an upper motor neuron lesion is the lesion that occurs in the neural pathway above the anterior horn of the spinal cord or cranial nerves motor nuclei; whereas a lower motor neuron lesion affects the nerve fibers that travel from the anterior horn of the spinal cord to the associated muscle.

 

Ø Upper and Lower motor neuron : what’s the difference?

The upper motor neuron is the motor component of the central nervous system that transmits impulses from the brain to lower motor neuron synapses, whereas the lower motor neuron is the motor component that connects with the muscles. 

The motor part of the somatic nervous system is made up of upper and lower motor neurons. They are responsible for the voluntary movement of muscles. The motor cortex, a posterior part of the frontal lobe of the brain, initiates and coordinates voluntary muscular movements. 

Ø Upper Motor Neuron –

The upper motor neuron is a type of motor neuron that originates in the cerebral cortex's motor region or in the brainstem. It is responsible for transmitting nerve impulses from the brain to lower motor neurons. As a result, it isn't involved in nerve impulse transmission to the muscles. A neurotransmitter called glutamate transmits nerve impulses from upper motor neurons to lower motor neurons through glutamatergic receptors.   

The corticospinal tract, corticobulbar tract, colliculospinal tract, rubrospinal tract, vestibulospinal tract, and reticulospinal tract are the six pathways of the upper motor tract. 

 

Ø Lower Motor Neuron –

The lower motor neuron transmits nerve impulses from the upper motor neurons to the effector's muscles. It could come from the brainstem, the anterior grey column, anterior nerve roots, or cranial nerve nuclei of the cranial nerves. Lower motor neurons' primary function is to connect the spinal cord or brainstem to the muscles. As a result, the cranial and spinal nerves are the lower motor neurons. 

 

Ø UMN & LMN Neurons have similarities too –   

• The somatic nervous system includes upper and lower motor neurons.   
• They help the brain send nerve impulses to the muscles.
• They are both in charge of voluntary muscular movements.

 

Ø Definition –

Upper Motor Neuron: A motor neuron that originates in the cerebral cortex's motor region or in the brainstem. 

Lower Motor Neuron: A motor neuron that transmits nerve impulses from the upper motor neurons to the effector muscles is known as a lower motor neuron. 

 

Ø Significance –

Upper Motor Neuron: A type of motor neuron that is found near the central nervous system. 

Lower Motor Neuron: This type of neuron is found near muscles. 

 

Ø Transmission –

Upper Motor Neuron: Sends nerve impulses from the brain to lower motor neuron synapses. 

Lower Motor Neuron: Sends nerve impulses from upper motor neurons to the muscles via the lower motor neuron. 

 

Ø Bodies of Cells –

The upper motor neuron is larger and is found in the cortex of the brain. 

Lower Motor Neurons are small motor neurons that are found in the grey matter of the spinal cord and the brainstem. 

Ø Based on the Classification –

Upper Motor Neuron Pathway: They travel in this direction. 

Lower Motor Neuron: They innervate a specific type of muscle fiber. 

 

Ø Classification –   

There are six pathways in the upper motor neuron. 

Lower Motor Neuron: Nerves of the skull and spine 

 

Ø Damage signs & Symptoms -

UMN: Increased muscle tone and hyperactive deep reflexes in the upper motor neuron 

LMN: Muscle atrophy, hyperactive deep reflexes, and decreased muscle tone.