Grey column

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Grey column of spinal cord
Medulla spinalis - Section - English.svg
Cross section of the spinal cord. The three grey columns make up the butterfly-shaped shaded region
Details
Identifiers
Latin columnae griseae
TA98 A14.1.02.101
TA2 6063
FMA 77867
Anatomical terminology

The grey column refers to a somewhat ridge-shaped mass of grey matter in the spinal cord. [1] This presents 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.

Contents

The anterior grey column is made up of alpha motor neurons, gamma motor neurons, and small neurons thought to be interneurons. [2] The posterior grey column is divided into several of the Rexed laminae. [3] The lateral grey column is only present in the thoracic region and upper lumbar segments (T1-L2). The lateral grey column contains preganglionic cell bodies of the autonomic nervous system and sensory relay neurons.

Structure

Cross-sectional view of spinal cord Gray664.png
Cross-sectional view of spinal cord
Spinal nerve forming from grey column Gray675.png
Spinal nerve forming from grey column

Anterior grey column

The anterior grey column, also known as the anterior horn of spinal cord, comprises three different types of neurons: large alpha motor neurons, medium gamma motor neurons, and small neurons thought to be interneurons. [2] These neurons differ in both their morphology and in their patterns of connectivity. [4] They are organized in the same manner as the muscles they innervate. [5]

Alpha motor neurons

Alpha motor neurons innervate extrafusal muscle fibers that generate force at neuromuscular junctions at the start of muscle contraction. They have large cell bodies and receive proprioceptive input. [4] They have been shown to reduce in population, but not in size with age. [2] Damage to these cell bodies can lead to severe muscle weakness and loss of reflexes. [6]

Gamma motor neurons

Gamma motor neurons innervate intrafusal muscle fibers that control the sensitivity of muscle spindles to stretch. They have smaller cell bodies than alpha motor neurons and do not receive proprioceptive input. [4] They have been shown to reduce in numbers but not size with age. [2]

Small neurons

The physiology of the small neurons in the anterior column is not well understood. Their effects can be both excitatory and inhibitory. They are suspected to be interneurons and have been shown to reduce in size but not numbers with age. [2]

Posterior grey column

The posterior grey column, also known as the posterior (or dorsal) horn of spinal cord, is divided into several laminae, based on the type of sensory information sent to each section. [3] Laminae I and II are sent 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. [7] It is known to be the primary relay point for haptic and nociceptive messages. [8] 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. [9]

Laminae Medulla spinalis - Substantia grisea - English.svg
Laminae

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. [10] 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. [8] The CVLM receives nociceptive and cardiovascular responses. [11] The NTS receives cardio-respiratory inputs and affects reflex tachycardia from noxious stimulation. [12] The LPb projects to the amygdala and hypothalamus and is involved in the emotional response to pain. [13] The PAG develops ways to deal with pain and is a main target of analgesics. It projects to other parts of the brainstem. [14] The nuclei of the thalamus affect sensory and motivational aspects of pain. [15] The neurons of this lamina can be distinguished by their morphology as pyramidal, spindle, or multipolar. [16]

Lamina II

This layer is also known as the substantia gelatinosa of Rolando and has the highest density of neurons. [17] These neurons mediate the activity of nociceptive and temperature afferent fibers. [5] 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 as their main neurotransmitter and the inhibitory interneurons use GABA and/or glycine as their main neurotransmitter. The neurons of this layer are only C fibers and contain almost no myelin. [18]

Laminae III and IV

These laminae are also known as the nucleus proprius and contain a much smaller density of neurons than lamina II. [17] There are projection neurons scattered throughout these layers. [10] Mechanosensitive A beta fibers terminate in these layers. [9] The layers receive input from lamina II and also control pain, temperature, and crude touch. [5] C fibers that control nociception and temperature and sensory information from mechanoreceptors are relayed here. [19]

Lamina V

This lamina is also known as the neck of the posterior column and receives information from mechanoreceptors and danger information from nociceptors. [19] 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. [17]

Lamina VI

This lamina is only found in the cervical and lumbar regions of the spinal cord. It receives afferent input from muscle fibers and joints. [5]

Lateral grey column

The lateral grey column, or the lateral horn of spinal cord, is part of the sympathetic nervous system and receives input from brain stem, organs, and hypothalamus. 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 amyotrophic lateral sclerosis (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. [20]

Muscular atrophy 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. [21]

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 thalamus. The thalamus is known as the "gateway to the cortex". The third order neuron then goes to the cerebral cortex. 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. [10] C fibers that carry nociceptive signals can be divided into two types: fibers that contain neuropeptides, like substance P, and fibers that do not contain neuropeptides. [22] The two types terminate in very different areas. Non-peptidergic C fibers are linked to the skin, where they innervate the epidermis while peptidergic C fibers innervate other tissues and deeper parts of the skin. [10]

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 to help pinpoint the exact location of a stimulus. [23]

Affective

Affective nociceptive signals affect emotions. These signals go to the limbic system 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. [23]

Related Research Articles

Nociception is the sensory nervous system's process of encoding noxious stimuli. It deals with a series of events and processes required for an organism to receive a painful stimulus, convert it to a molecular signal, and recognize and characterize the signal in order to trigger an appropriate defense response.

<span class="mw-page-title-main">Motor neuron</span> Nerve cell sending impulse to muscle

A motor 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 indirectly control effector organs, mainly muscles and glands. There are two types of motor neuron – upper motor neurons and lower motor neurons. Axons from upper motor neurons synapse onto interneurons in the spinal cord and occasionally directly onto lower motor neurons. The axons from the lower motor neurons are efferent nerve fibers that carry signals from the spinal cord to the effectors. Types of lower motor neurons are alpha motor neurons, beta motor neurons, and gamma motor neurons.

<span class="mw-page-title-main">Medulla oblongata</span> Structure of the brain stem

The medulla oblongata or simply medulla is a long stem-like structure which makes up the lower part of the brainstem. It is anterior and partially inferior to the cerebellum. It is a cone-shaped neuronal mass responsible for autonomic (involuntary) functions, ranging from vomiting to sneezing. The medulla contains the cardiac, respiratory, vomiting and vasomotor centers, and therefore deals with the autonomic functions of breathing, heart rate and blood pressure as well as the sleep–wake cycle.

<span class="mw-page-title-main">Afferent nerve fiber</span> Axonal projections that arrive at a particular brain region

Afferent nerve fibers are the axons carried by a sensory nerve that relay sensory information from sensory receptors to regions of the brain. Afferent projections arrive at a particular brain region. Efferent nerve fibers are carried by efferent nerves and exit a region to act on muscles and glands.

<span class="mw-page-title-main">Reflex arc</span> Neural pathway which controls a reflex

A reflex arc is a neural pathway that controls a reflex. In vertebrates, most sensory neurons do not pass directly into the brain, but synapse in the spinal cord. This allows for faster reflex actions to occur by activating spinal motor neurons without the delay of routing signals through the brain. The brain will receive the input while the reflex is being carried out and the analysis of the signal takes place after the reflex action.

<span class="mw-page-title-main">Nociceptor</span> Sensory neuron that detects pain

A nociceptor is a sensory neuron that responds to damaging or potentially damaging stimuli by sending "possible threat" signals to the spinal cord and the brain. The brain creates the sensation of pain to direct attention to the body part, so the threat can be mitigated; this process is called nociception.

<span class="mw-page-title-main">Spinothalamic tract</span> Sensory pathway from the skin to the thalamus

The spinothalamic tract is a part of the anterolateral system or the ventrolateral system, a sensory pathway to the thalamus. From the ventral posterolateral nucleus in the thalamus, sensory information is relayed upward to the somatosensory cortex of the postcentral gyrus.

The withdrawal reflex is a spinal reflex intended to protect the body from damaging stimuli. The reflex rapidly coordinates the contractions of all the flexor muscles and the relaxations of the extensors in that limb causing sudden withdrawal from the potentially damaging stimulus. Spinal reflexes are often monosynaptic and are mediated by a simple reflex arc. A withdrawal reflex is mediated by a polysynaptic reflex resulting in the stimulation of many motor neurons in order to give a quick response.

<span class="mw-page-title-main">Dorsal root ganglion</span> Cluster of neurons in a dorsal root of a spinal nerve

A dorsal root ganglion is a cluster of neurons in a dorsal root of a spinal nerve. The cell bodies of sensory neurons known as first-order neurons are located in the dorsal root ganglia.

<span class="mw-page-title-main">Posterior grey column</span>

The posterior grey column of the spinal cord is one of the three grey columns of the spinal cord. It receives several types of sensory information from the body, including fine touch, proprioception, and vibration. This information is sent from receptors of the skin, bones, and joints through sensory neurons whose cell bodies lie in the dorsal root ganglion.

<span class="mw-page-title-main">Spinocerebellar tract</span>

The spinocerebellar tract is a nerve tract originating in the spinal cord and terminating in the same side (ipsilateral) of the cerebellum.

<span class="mw-page-title-main">Gate control theory</span>

The gate control theory of pain asserts that non-painful input closes the nerve "gates" to painful input, which prevents pain sensation from traveling to the central nervous system.

<span class="mw-page-title-main">Vestibulospinal tract</span>

The vestibulospinal tract is a neural tract in the central nervous system. Specifically, it is a component of the extrapyramidal system and is classified as a component of the medial pathway. Like other descending motor pathways, the vestibulospinal fibers of the tract relay information from nuclei to motor neurons. The vestibular nuclei receive information through the vestibulocochlear nerve about changes in the orientation of the head. The nuclei relay motor commands through the vestibulospinal tract. The function of these motor commands is to alter muscle tone, extend, and change the position of the limbs and head with the goal of supporting posture and maintaining balance of the body and head.

<span class="mw-page-title-main">Substantia gelatinosa of Rolando</span>

The apex of the posterior grey column, one of the three grey columns of the spinal cord, is capped by a V-shaped or crescentic mass of translucent, gelatinous neuroglia, termed the substantia gelatinosa of Rolando, which contains both neuroglia cells, and small nerve cells. The gelatinous appearance is due to a very low concentration of myelinated fibers. It extends the entire length of the spinal cord and into the medulla oblongata where it becomes the spinal nucleus of the trigeminal nerve.

<span class="mw-page-title-main">Rexed laminae</span>

The Rexed laminae comprise a system of ten layers of grey matter (I–X), identified in the early 1950s by Bror Rexed to label portions of the grey columns of the spinal cord.

<span class="mw-page-title-main">Alpha motor neuron</span>

Alpha (α) motor neurons (also called alpha motoneurons), are large, multipolar lower motor neurons of the brainstem and spinal cord. They innervate extrafusal muscle fibers of skeletal muscle and are directly responsible for initiating their contraction. Alpha motor neurons are distinct from gamma motor neurons, which innervate intrafusal muscle fibers of muscle spindles.

<span class="mw-page-title-main">Group C nerve fiber</span> One of three classes of nerve fiber in the central nervous system and peripheral nervous system

Group C nerve fibers are one of three classes of nerve fiber in the central nervous system (CNS) and peripheral nervous system (PNS). The C group fibers are unmyelinated and have a small diameter and low conduction velocity, whereas Groups A and B are myelinated. Group C fibers include postganglionic fibers in the autonomic nervous system (ANS), and nerve fibers at the dorsal roots. These fibers carry sensory information.

<span class="mw-page-title-main">Spinal cord</span> Long, tubular central nervous system structure in the vertebral column

The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spinal cord, which contains cerebrospinal fluid. The brain and spinal cord together make up the central nervous system (CNS). In humans, the spinal cord begins at the occipital bone, passing through the foramen magnum and then enters the spinal canal at the beginning of the cervical vertebrae. The spinal cord extends down to between the first and second lumbar vertebrae, where it ends. The enclosing bony vertebral column protects the relatively shorter spinal cord. It is around 45 cm (18 in) long in adult men and around 43 cm (17 in) long in adult women. The diameter of the spinal cord ranges from 13 mm in the cervical and lumbar regions to 6.4 mm in the thoracic area.

Group A nerve fibers are one of the three classes of nerve fiber as generally classified by Erlanger and Gasser. The other two classes are the group B nerve fibers, and the group C nerve fibers. Group A are heavily myelinated, group B are moderately myelinated, and group C are unmyelinated.

<span class="mw-page-title-main">Spinal interneuron</span>

A spinal interneuron, found in the spinal cord, relays signals between (afferent) sensory neurons, and (efferent) motor neurons. Different classes of spinal interneurons are involved in the process of sensory-motor integration. Most interneurons are found in the grey column, a region of grey matter in the spinal cord.

References

  1. ↑ Henry Gray; Susan Standring; Harold Ellis; B. K. B. Berkovitz (2005), Gray's anatomy, p. 255
  2. 1 2 3 4 5 Terao S, Sobue G, Hashizume Y, Li M, Inagaki T, Mitsuma T (Aug 1996). "Age-related changes in human spinal ventral horn cells with special reference to the loss of small neurons in the intermediate zone: a quantitative analysis". Acta Neuropathologica. 92 (2): 109–14. doi:10.1007/s004010050497. PMID   8841655. S2CID   19467756.
  3. 1 2 Cagle, MC; Honig, MG (July 2013). "Parcellation of Cblns 1, 2, and 4 among different subpopulations of dorsal horn neurons in mouse spinal cord". Journal of Comparative Neurology. 522 (2): 479–97. doi:10.1002/cne.23422. PMC   3855892 . PMID   23853053.
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  6. ↑ Haines, Duane (2012). Fundamental Neuroscience for Basic and Clinical Applications. Saunders. ISBN   978-1437702941.
  7. ↑ Brown, AG (1981). Organization in the Spinal Cord: The Anatomy and Physiology of Identified Neurones. Berlin: Springer-Verlag.
  8. 1 2 Gauriau, Caroline; Bernard, Jean-François (2004). "A comparative reappraisal of projections from the superficial laminae of the dorsal horn in the rat: The forebrain". The Journal of Comparative Neurology. 468 (1): 24–56. doi:10.1002/cne.10873. PMID   14648689. S2CID   26117604.
  9. 1 2 Kato G, Kawasaki Y, Koga K, Uta D, Kosugi M, Yasaka T, Yoshimura M, Ji RR, Strassman AM (April 2009). "Organization of intralaminar and translaminar neuronal connectivity in the superficial spinal dorsal horn". The Journal of Neuroscience. 29 (16): 5088–5099. doi:10.1523/JNEUROSCI.6175-08.2009. PMC   2777732 . PMID   19386904.
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  11. ↑ Lima D, Albino-Teixeira A, Tavares I (Mar 2002). "The caudal medullary ventrolateral reticular formation in nociceptive-cardiovascular integration. An experimental study in the rat". Experimental Physiology. 87 (2): 267–74. doi: 10.1113/eph8702354 . PMID   11856973. S2CID   13605412.
  12. ↑ Boscan P, Pickering AE, Paton JF (Mar 2002). "The nucleus of the solitary tract: an integrating station for nociceptive and cardiorespiratory afferents". Experimental Physiology. 87 (2): 259–66. doi: 10.1113/eph8702353 . PMID   11856972. S2CID   22373004.
  13. ↑ Gauriau, C; Bernard, J. F. (Mar 2002). "Pain pathways and parabrachial circuits in the rat". Experimental Physiology. 87 (2): 251–8. doi:10.1113/eph8702357. PMID   11856971. S2CID   42574814.
  14. ↑ Heinricher MM, Tavares I, Leith JL, Lumb BM (Apr 2009). "Descending control of nociception: Specificity, recruitment and plasticity". Brain Research Reviews. 60 (1): 214–225. doi:10.1016/j.brainresrev.2008.12.009. PMC   2894733 . PMID   19146877.
  15. ↑ Gauriau, C.; Bernard, J. F. (Jan 2004). "Posterior triangular thalamic neurons convey nociceptive messages to the secondary somatosensory and insular cortices in the rat". Journal of Neuroscience. 24 (3): 752–61. doi: 10.1523/JNEUROSCI.3272-03.2004 . PMC   6729251 . PMID   14736861.
  16. ↑ Han ZS, Zhang ET, Craig AD (Jul 1998). "Nociceptive and thermoreceptive lamina I neurons are anatomically distinct". Nature Neuroscience. 1 (3): 218–25. doi:10.1038/665. PMID   10195146. S2CID   21222047.
  17. 1 2 3 Paxinos, George (2004). The Human Nervous System. Academic Press. ISBN   978-0125476263.
  18. ↑ Grudt, T. J.; Perl, E. R. (Apr 1, 2002). "Correlations between neuronal morphology and electrophysiological features in the rodent superficial dorsal horn". The Journal of Physiology. 540 (Pt 1): 189–207. doi:10.1113/jphysiol.2001.012890. PMC   2290200 . PMID   11927679.
  19. 1 2 Muthayya, NM (2002). Human Physiology. New Delhi: Jaypee Brothers Medical Publishers.
  20. ↑ Terao S, Sobue G, Hashizume Y, Mitsuma T, Takahashi A (Feb 1994). "Disease-specific patterns of neuronal loss in the spinal ventral horn in amyotrophic lateral sclerosis, multiple system atrophy and X-linked recessive bulbospinal neuronopathy, with special reference to the loss of small neurons in the intermediate zone". Journal of Neurology. 241 (4): 196–203. doi:10.1007/bf00863768. PMID   8195817. S2CID   23011881.
  21. ↑ Terao S, Sobue G, Li M, Hashizume Y, Tanaka F, Mitsuma T (Jan 1997). "The lateral corticospinal tract and spinal ventral horn in X-linked recessive spinal and bulbar muscular atrophy: a quantitative study". Acta Neuropathologica. 93 (1): 1–6. doi:10.1007/s004010050575. PMID   9006650. S2CID   12023369.
  22. ↑ Snider, W. D.; McMahon, S. B. (Apr 1998). "Tackling pain at the source: new ideas about nociceptors". Neuron. 20 (4): 629–32. doi: 10.1016/s0896-6273(00)81003-x . PMID   9581756. S2CID   18001663.
  23. 1 2 Price, Donald (Oct 2002). "Central neural mechanisms that interrelate sensory and affective dimensions of pain". Molecular Interventions. 2 (6): 392–403, 339. doi:10.1124/mi.2.6.392. PMID   14993415.
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