The grey columns are three regions of the somewhat ridge-shaped mass of grey matter in the

spinal cord The spinal cord is a long, thin, tubular structure made up of nervous tissue that extends from the medulla oblongata in the lower brainstem to the lumbar region of the vertebral column (backbone) of vertebrate animals. The center of the spinal c ...

. These regions present as three columns: the anterior grey column, the posterior grey column, and the lateral grey column, all of which are visible in cross-section of the spinal cord. The anterior grey column is made up of

alpha motor neuron Alpha (α) motor neurons (also called alpha motoneurons), are large, multipolar neuron, multipolar lower motor neurons of the brainstem and spinal cord. They innervate extrafusal muscle fibers of skeletal muscle and are directly responsible for i ...

gamma motor neuron A gamma motor neuron (γ motor neuron), also called gamma motoneuron, or fusimotor neuron, is a type of lower motor neuron that takes part in the process of muscle contraction, and represents about 30% of ( Aγ) fibers going to the muscle. Like ...

s, and small neurons thought to be

interneuron Interneurons (also called internuncial neurons, association neurons, connector neurons, or intermediate neurons) are neurons that are not specifically motor neurons or sensory neurons. Interneurons are the central nodes of neural circuits, enab ...

s. It affects the skeletal muscles. The posterior grey column receives several types of sensory information regarding touch and sensation from receptors in the skin, bones, and joints, including fine touch,

proprioception Proprioception ( ) is the sense of self-movement, force, and body position. Proprioception is mediated by proprioceptors, a type of sensory receptor, located within muscles, tendons, and joints. Most animals possess multiple subtypes of propri ...

, and

vibration Vibration () is a mechanical phenomenon whereby oscillations occur about an equilibrium point. Vibration may be deterministic if the oscillations can be characterised precisely (e.g. the periodic motion of a pendulum), or random if the os ...

. It contains the cell bodies of second-order sensory neurons and their synapses with the pseudounipolar first-order sensory neurons (whose cell bodies are located within the sensory ganglia (a.k.a. dorsal root ganglia)). The lateral grey column is only present in the thoracic region and upper lumbar segments (T1-L2). It contains preganglionic cell bodies of the

autonomic nervous system The autonomic nervous system (ANS), sometimes called the visceral nervous system and formerly the vegetative nervous system, is a division of the nervous system that operates viscera, internal organs, smooth muscle and glands. The autonomic nervo ...

and sensory relay neurons.

Structure

Anterior grey column

The anterior grey column, (also known as the anterior horn of spinal cord and anterior cornu) is broad and of a rounded or quadrangular shape. Its posterior part is termed the base, and its anterior part the head, but these are not differentiated from each other by any well-defined constriction. It is separated from the surface of the spinal cord by a layer of white substance which is traversed by the bundles of the anterior nerve roots. In the thoracic region, the posterolateral part of the anterior column projects laterally as a triangular field, which is named the lateral grey column. It comprises three different types of neurons, two types of

lower motor neuron Lower motor neurons (LMNs) are motor neurons located in either the anterior grey column, anterior nerve roots (spinal lower motor neurons) or the cranial nerve nuclei of the brainstem and cranial nerves with motor function (cranial nerve lower ...

– large alpha motor neurons, and medium gamma motor neurons, and small neurons thought to be

interneurons Interneurons (also called internuncial neurons, association neurons, connector neurons, or intermediate neurons) are neurons that are not specifically motor neurons or sensory neurons. Interneurons are the central nodes of neural circuits, ena ...

. These neurons differ in both their morphology and in their patterns of connectivity. They are organized in the same manner as the muscles they innervate.

Alpha motor neurons

Alpha motor neurons are

s that innervate extrafusal muscle fibers to generate force at neuromuscular junctions at the start of a

muscle contraction Muscle contraction is the activation of Tension (physics), tension-generating sites within muscle cells. In physiology, muscle contraction does not necessarily mean muscle shortening because muscle tension can be produced without changes in musc ...

. They have large cell bodies and receive

proprioceptive Proprioception ( ) is the sense of self-movement, force, and body position. Proprioception is mediated by proprioceptors, a type of sensory receptor, located within muscles, tendons, and joints. Most animals possess multiple subtypes of propri ...

input. They have been shown to reduce in population, but not in size with age. Damage to these cell bodies can lead to severe muscle weakness and loss of reflexes, and is also associated with ALS.

Gamma motor neurons

Gamma motor neurons innervate intrafusal muscle fibers that control the sensitivity of

muscle spindles Muscle spindles are stretch receptors within the body of a skeletal muscle that primarily detect changes in the length of the muscle. They convey length information to the central nervous system via afferent nerve fibers. This information can be ...

to stretch. They have smaller cell bodies than alpha motor neurons and do not receive proprioceptive input. They have been shown to reduce in numbers but not size with age.

Small neurons

The physiology of the small neurons in the anterior column is not well understood. Their effects can be both excitatory and

inhibitory An inhibitory postsynaptic potential (IPSP) is a kind of synaptic potential that makes a Chemical synapse, postsynaptic neuron less likely to generate an action potential.Purves et al. Neuroscience. 4th ed. Sunderland (MA): Sinauer Associates, Inc ...

. They are suspected to be interneurons and have been shown to reduce in size but not numbers with age. Clinical significance It is these cells that are affected in the following diseases, –

amyotrophic lateral sclerosis Amyotrophic lateral sclerosis (ALS), also known as motor neuron disease (MND) or—in the United States—Lou Gehrig's disease (LGD), is a rare, Terminal illness, terminal neurodegenerative disease, neurodegenerative disorder that results i ...

, spinal and bulbar muscular atrophy, Charcot–Marie–Tooth disease, progressive muscular atrophy, all spinal muscular atrophies,

poliomyelitis Poliomyelitis ( ), commonly shortened to polio, is an infectious disease caused by the poliovirus. Approximately 75% of cases are asymptomatic; mild symptoms which can occur include sore throat and fever; in a proportion of cases more severe ...

, and

West Nile virus West Nile virus (WNV) is a single-stranded RNA virus that causes West Nile fever. It is a member of the family ''Flaviviridae'', from the genus ''Flavivirus'', which also contains the Zika virus, dengue virus, and yellow fever virus. The virus ...

. Pharmacological interaction The anterior grey column is the target for some spasmolytic medications.

Norepinephrine Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic compound, organic chemical in the catecholamine family that functions in the brain and human body, body as a hormone, neurotransmitter and neuromodulator. The ...

release here, (as induced by

cyclobenzaprine Cyclobenzaprine, sold under several brand names including, historically, Flexeril, is a muscle relaxer used for muscle spasms from musculoskeletal conditions of sudden onset. It is not useful in cerebral palsy. It is taken by mouth. Common ...

) reduces spasms by innervation (reducing nerve activity) of alpha motor neurons via interaction with gamma fibers.

Posterior grey column

The posterior grey column, also known as the posterior (or dorsal) horn of spinal cord, is subdivided into six layers known as Rexed laminae, based on the type of sensory information sent to each section. * Marginal nucleus of spinal cord (lamina I) * Substantia gelatinosa of Rolando (lamina II) * Nucleus proprius (laminae III, IV) * Spinal lamina V, the neck of the posterior horn * Spinal lamina VI, the base of the posterior horn. The other four laminae are located in the other two grey columns in the spinal cord. The function of the spinal dorsal horn is to process and integrate sensory information from the

peripheral nervous system The peripheral nervous system (PNS) is one of two components that make up the nervous system of Bilateria, bilateral animals, with the other part being the central nervous system (CNS). The PNS consists of nerves and ganglia, which lie outside t ...

. It receives inputs from primary afferent fibers and modulatory systems, and it projects to higher brain centers and

motor neurons A motor neuron (or motoneuron), also known as efferent neuron is a neuron whose cell body is located in the motor cortex, brainstem or the spinal cord, and whose axon (fiber) projects to the spinal cord or outside of the spinal cord to directly or ...

. The dorsal horn circuitry is involved in various aspects of sensory processing, including discrimination, integration, and modulation of nociceptive and non-nociceptive signals. Dysfunction of the dorsal horn circuitry has been implicated in chronic pain conditions and other neurological disorders. Laminae I and II receive information from afferent neurons that sense nociception, temperature, and itching, laminae III and IV are sent information from neurons that sense mechanical pressure, and laminae V and VI are sent information from proprioceptors. It is known to be the primary relay point for haptic and nociceptive messages. The posterior horn is also known as a partially layered structure because only laminae I and II are well defined. The column can also be separated by nociceptive and non-nociceptive senses. Laminae I and II are important in nociception, laminae III and IV are not involved nociception, and lamina V is involved in both nociception and non-nociception. The function of the spinal dorsal horn is to process and integrate sensory information from the

. It receives inputs from primary afferent fibers and modulatory systems, and it projects to higher brain centers and

Medulla spinalis - Substantia grisea - English

Lamina I

Lamina I is also known as the marginal nucleus of spinal cord. The majority of posterior column projection neurons are located in lamina I, however most neurons in this layer are interneurons. The main areas these neurons innervate are the caudal ventrolateral medulla (CVLM), the nucleus of the solitary tract (NTS), the lateral parabrachial area (LPb), the periaqueductal grey matter (PAG), and certain regions in the

thalamus The thalamus (: thalami; from Greek language, Greek Wikt:θάλαμος, θάλαμος, "chamber") is a large mass of gray matter on the lateral wall of the third ventricle forming the wikt:dorsal, dorsal part of the diencephalon (a division of ...

. The CVLM receives nociceptive and

cardiovascular In vertebrates, the circulatory system is a system of organs that includes the heart, blood vessels, and blood which is circulated throughout the body. It includes the cardiovascular system, or vascular system, that consists of the heart a ...

responses. The NTS receives cardio-respiratory inputs and affects reflex tachycardia from noxious stimulation. The LPb projects to the

amygdala The amygdala (; : amygdalae or amygdalas; also '; Latin from Greek language, Greek, , ', 'almond', 'tonsil') is a paired nucleus (neuroanatomy), nuclear complex present in the Cerebral hemisphere, cerebral hemispheres of vertebrates. It is c ...

and

hypothalamus The hypothalamus (: hypothalami; ) is a small part of the vertebrate brain that contains a number of nucleus (neuroanatomy), nuclei with a variety of functions. One of the most important functions is to link the nervous system to the endocrin ...

and is involved in the emotional response to pain. The PAG develops ways to deal with pain and is a main target of analgesics. It projects to other parts of the brainstem. The nuclei of the thalamus affect sensory and motivational aspects of pain. The neurons of this lamina can be distinguished by their morphology as pyramidal, spindle, or multipolar.

Lamina II

This layer is also known as the substantia gelatinosa of Rolando and has the highest density of neurons. These neurons mediate the activity of nociceptive and temperature afferent fibers. It is almost entirely made up of interneurons which can be further divided by their morphology. The four main morphological classes, based on the shape of their dendritic structure, are islet, central, vertical, and radial cells. The interneurons can also be divided by their function: excitatory or inhibitory. The excitatory interneurons release

glutamate Glutamic acid (symbol Glu or E; known as glutamate in its anionic form) is an α-amino acid that is used by almost all living beings in the biosynthesis of proteins. It is a Essential amino acid, non-essential nutrient for humans, meaning that ...

as their main

neurotransmitter A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a Chemical synapse, synapse. The cell receiving the signal, or target cell, may be another neuron, but could also be a gland or muscle cell. Neurotra ...

and the inhibitory interneurons use

GABA GABA (gamma-aminobutyric acid, γ-aminobutyric acid) is the chief inhibitory neurotransmitter in the developmentally mature mammalian central nervous system. Its principal role is reducing neuronal excitability throughout the nervous system. GA ...

and/or

glycine Glycine (symbol Gly or G; ) is an amino acid that has a single hydrogen atom as its side chain. It is the simplest stable amino acid. Glycine is one of the proteinogenic amino acids. It is encoded by all the codons starting with GG (G ...

as their main neurotransmitter. The neurons of this layer are only C fibers and contain almost no

myelin Myelin Sheath ( ) is a lipid-rich material that in most vertebrates surrounds the axons of neurons to insulate them and increase the rate at which electrical impulses (called action potentials) pass along the axon. The myelinated axon can be lik ...

Laminae III and IV

These laminae are also known as the nucleus proprius and contain a much smaller density of neurons than lamina II. There are projection neurons scattered throughout these layers. Mechanosensitive A beta fibers terminate in these layers. The layers receive input from lamina II and also control pain, temperature, and crude touch. C fibers that control nociception and temperature and sensory information from mechanoreceptors are relayed here.

Lamina V

This lamina is also known as the neck of the posterior column and receives information from mechanoreceptors and danger information from nociceptors. It has different neurons in different regions. In the medial region it contains medium-sized triangular neurons and the lateral region contains medium-sized multipolar neurons.

Lamina VI

This lamina is only found in the cervical and

lumbar In tetrapod anatomy, lumbar is an adjective that means of or pertaining to the abdominal segment of the torso, between the diaphragm (anatomy), diaphragm and the sacrum. Naming and location The lumbar region is sometimes referred to as the lowe ...

regions of the spinal cord. It receives afferent input from muscle fibers and joints.

Lateral grey column

The lateral grey column, or the lateral horn of spinal cord, is part of the

sympathetic nervous system The sympathetic nervous system (SNS or SANS, sympathetic autonomic nervous system, to differentiate it from the somatic nervous system) is one of the three divisions of the autonomic nervous system, the others being the parasympathetic nervous sy ...

and receives input from

brain stem The brainstem (or brain stem) is the posterior stalk-like part of the brain that connects the cerebrum with the spinal cord. In the human brain the brainstem is composed of the midbrain, the pons, and the medulla oblongata. The midbrain is co ...

, organs, and

. The lateral column is only present in the thoracic region and upper lumbar segments. The lateral grey column contains preganglionic cell bodies of the autonomic nervous system and sensory relay neurons.

Clinical significance

Neurons in the anterior column have been shown to be affected by

(ALS). The number of large alpha motor neurons and medium gamma motor neurons was greatly reduced and the number of small neurons was either slightly or greatly reduced depending on the type of ALS.

Muscular atrophy Muscle atrophy is the loss of skeletal muscle mass. It can be caused by sedentary lifestyle, immobility, aging, malnutrition, medications, or a wide range of injuries or diseases that impact the musculoskeletal or nervous system. Muscle atrophy le ...

has also been shown to have an effect on neurons of the anterior column. A large loss of large alpha motor neurons, medium gamma motor neurons, and small neurons was recorded in cases of muscular atrophy. Damage to the lateral column can result in Horner's syndrome. Multiple system atrophy (MSA), has also been linked to the lateral grey column. MSA has been shown to reduce the cell count in the lateral column by over 50%. The posterior column has a prominent role in the pain system, it is the first central relay in the nociceptive pathway. The first-order afferent neuron carries sensory information to the second order neuron in the dorsal horn. The axon of the second order neuron, if it is a projection neuron and not an interneuron, then goes to the third order neuron in the

. The thalamus is known as the "gateway to the cortex". The third order neuron then goes to the

cerebral cortex The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. It is the largest site of Neuron, neural integration in the central nervous system, and plays ...

. The afferent neurons are either A fibers or C fibers. A fibers are myelinated allowing for faster signal conduction. Among these there are A beta fibers which are faster and carry information about non-painful touch and A delta fibers which are slower and thinner than the A beta fibers. The C fibers are not myelinated and therefore slower. C fibers that carry nociceptive signals can be divided into two types: fibers that contain

neuropeptides Neuropeptides are chemical messengers made up of small chains of amino acids that are synthesized and released by neurons. Neuropeptides typically bind to G protein-coupled receptors (GPCRs) to modulate neural activity and other tissues like the ...

, like substance P, and fibers that do not contain neuropeptides. The two types terminate in very different areas. Non-peptidergic C fibers are linked to the skin, where they innervate the

epidermis The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and Subcutaneous tissue, hypodermis. The epidermal layer provides a barrier to infection from environmental pathogens and regulates the ...

while peptidergic C fibers innervate other tissues and deeper parts of the skin. There are two main types of nociceptive signals: sensory and affective.

Sensory

Sensory nociceptive signals provide information about what kind of stimulus (heat, mechanical, etc.) is affecting the body and also indicates where on the body the stimulus is. Sensory nociceptive neurons have a small

receptive field The receptive field, or sensory space, is a delimited medium where some physiological stimuli can evoke a sensory neuronal response in specific organisms. Complexity of the receptive field ranges from the unidimensional chemical structure of od ...

to help pinpoint the exact location of a stimulus.

Affective

Affective nociceptive signals affect emotions. These signals go to the

limbic system The limbic system, also known as the paleomammalian cortex, is a set of brain structures located on both sides of the thalamus, immediately beneath the medial temporal lobe of the cerebrum primarily in the forebrain.Schacter, Daniel L. 2012. ''P ...

and tell the body to react to the danger stimulus (i.e. removing a hand from a hot stove). These neurons have larger receptive fields because the emotional reaction to most pain stimuli is similar.

References

{{Authority control Spinal cord