Why Does The Size Of The Ventral Horns Of The Spinal Cord Vary Along Its Length?

Overview of the Spinal Cord

The spinal cord runs along the inside of the vertebral column and serves as the signaling conduit between the brain and the periphery.

Learning Objectives

Describe the features of the spinal cord

Primal Takeaways

Key Points

• The spinal cord extends from the occipital bone of the skull until information technology terminates well-nigh the second lumbar vertebra.
• The spinal cord is protected by iii layers of meninges: the dura mater, the arachnoid mater, and the pia mater.
• The central nervous arrangement (CNS) is fabricated up of the brain and spinal cord. The area between the arachnoid space and the pia mater contains cerebral spinal fluid (CSF).
• The spinal cord is divided into 31 segments that send nervus rootlets out into the torso through intervertebral foramen.
• Each segment of the spinal cord is associated with a pair of ganglia called dorsal root ganglia, which are situated just outside of the spinal cord and contain cell bodies of sensory neurons. These neurons travel into the spinal cord via the dorsal roots.
• Ventral roots consist of axons from motor neurons, which bring information to the periphery from cell bodies within the CNS. Dorsal roots and ventral roots come up together and exit the intervertebral foramina as they become spinal nerves.

Key Terms

• peripheral nervous system: The part of the nervous system that consists of the nerves and ganglia on the outside of the encephalon and spinal cord.
• efferent: The conduction of impulses outward from the brain or spinal cord.
• afferent: The conduction of impulses inwards to the brain or spinal cord.
• cauda equina: A bundle of nerve roots at the base of operations of the spinal column.
• spinal cord: A thick, whitish string of nerve tissue which is a major part of the vertebrate cardinal nervous organization. It extends from the brain stem downwardly through the spine, with nerves branching off to various parts of the body.

Examples

• A lumbar puncture (spinal tap) is an example of a medical process that direct targets the spinal cord.
• The birth defect spina bifida is a failure of the vertebral arch to close, exposing the spinal cord.

The spinal cord is a long, sparse, tubular bundle of nervous tissue and support cells that extends from the medulla oblongata of the encephalon to the level of the lumbar region. The brain and spinal cord together make up the central nervous arrangement (CNS). The spinal cord, protected by the vertebral cavalcade, begins at the occipital bone and extends down to the infinite between the beginning and 2d lumbar vertebrae. The spinal cord has a varying width, ranging from 0.v inch thick in the cervical and lumbar regions to 0.25 inch thick in the thoracic area. The length of the spinal cord is approximately 45 cm (eighteen in) in men and well-nigh 43 cm (17 in) long in women.

Spinal String and Vertebrae.png: Relationship between the spinal cord and vertebral column, delineating the cervical, thoracic, and lumbar sections.

Layers and Regions of the Spinal String

The spinal cord is protected by three layers of tissue called meninges and divided into three regions.

Spinal Cord Tissue Layers

The dura mater is the outermost layer of spinal cord tissue, forming a tough protective coating. The space between the dura mater and the surrounding bone of the vertebrae is called the epidural infinite. The epidural space is filled with adipose tissue and contains a network of claret vessels. The center layer is called the arachnoid mater. The pia mater is the innermost protective layer and is tightly associated with the surface of the spinal cord. The infinite betwixt the arachnoid and pia maters is called the subarachnoid space and is where the CSF is located. It is from this location at the level of the lumbar region that CSF fluid is obtained in a spinal tap.

Spinal Cord Regions

In cross-section, the peripheral region of the cord displays neuronal white thing tracts containing sensory and motor neurons. Internal to this peripheral region is the gray, butterfly-shaped fundamental region made up of nerve prison cell bodies. This central region surrounds the key canal, which is an anatomic extension of the spaces in the brain known equally the ventricles and like the ventricles, contains cerebrospinal fluid.

Spinal Cord Regions: Cross-sectional perspective of the spinal string regions

The spinal cord is divided into cervical, thoracic, and lumbar regions. The cervical region is divided into 8 levels that are related to different motor and sensory functions in the neck and the arms. The spinal nerves of the thoracic region supply the thorax and abdomen. The nerves of the lumbosacral spinal string supply the pelvic region, legs, and anxiety.

Spinal Cord Nerve Branches

Thirty-one pairs of spinal nerves (sensory and motor) branch from the human being spinal string. Each spinal nerve is formed from the combination of nervus fibers from its posterior and inductive roots. The posterior root is the sensory (afferent) root that carries sensory data to the brain from other areas of the body. The inductive root is the motor (efferent) root that carries motor information to the body from the brain.

The spinal nervus emerges from the spinal column through the opening (intervertebral foramen) between adjacent vertebrae. An exception is the starting time spinal nerve pair (C1), which emerges between the occipital bone and the atlas (the get-go vertebra). The swelling found in the posterior root is the posterior (dorsal) root ganglion, which contains the cell bodies of sensory neurons. The anterior (ventral) root contains axons of motor neurons that conduct nerve impulses from the CNS to other parts of the body such as the muscles.

The cauda equina ("horse'due south tail") is the name for the collection of fretfulness in the vertebral column that extends beyond the cord. The fretfulness that etch the cauda equina supply the pelvic organs and lower limbs, including motor innervation for the hips, knees, ankles, anxiety, and internal and external anal sphincters. In addition, the cauda equina extends to sensory innervation of the perineum.

Master Spinal Cord Role

The spinal cord functions primarily in the transmission of neural signals betwixt the encephalon and the rest of the body, just it also contains neural circuits that can independently control numerous reflexes and central pattern generators. The three major functions of the spinal string are the conduction of motor information traveling down the spinal cord, the conduction of sensory data in the opposite management, and acting equally the center for conducting certain reflexes. The spinal string is the main pathway for information connecting the encephalon and peripheral nervous system.

The Spine

The spine encases the spinal cord for protection and support.

Learning Objectives

Describe the vertebral column, the protective structure of the spinal cord

Key Takeaways

Key Points

• The human spine consists of 24 articulating vertebrae grouped into cervical, thoracic, and lumbar regions. Nine more vertebrae brand up the sacrum and coccyx.
• Typical vertebrae consist of the anterior vertebral torso and the posterior department, which contains the vertebral foramen through which the spinal cord passes.
• There are four master curves of the spine: cervical, thoracic, lumbar, and pelvic.
• Facets of the vertebrae restrict range of move to forbid shearing of the spinal string.
• Blood vessels and nerves leave the spinal column at intervertebral foramina.
• There are 4 chief curves of the spine: cervical, thoracic, lumbar and pelvic.

Key Terms

• vertebrae: The bones that make up the spinal column.
• laminae: Plates of bone that course the posterior walls of each vertebra.
• pedicle: A segment of bone connecting the lamina to the vertebral body.
• vertebral foramen: Formed by the vertebral torso and vertebral arch and containing the spinal cord.
• vertebral column: The series of vertebrae that protect the spinal cord; the spinal column.

Examples

• Kyphosis is an exaggerated concave (kyphotic) curvature of the thoracic vertebral column; it is commonly known every bit "humpback."
• Lordosis is an exaggerated convex (lordotic) curvature of the lumbar region; it is ordinarily known every bit "swayback."
• Scoliosis is an abnormal lateral curvature of the vertebral column.

Number of Vertebrae

Vertebral Column: The sections of the vertebral cavalcade.

In homo anatomy, the vertebral cavalcade (backbone or spine) commonly consists of 24 articulating vertebrae and 9 fused vertebrae in the sacrum and the coccyx. Situated in the dorsal attribute of the torso and separated by intervertebral discs, it houses and protects the spinal cord in its spinal canal. There are normally 33 vertebrae in humans, including the five that are fused to form the sacrum, the four coccygeal bones that form the tailbone, and the others separated by intervertebral discs. The upper 3 regions incorporate the remaining 24, and are grouped as cervical (seven vertebrae), thoracic (12 vertebrae) and lumbar (v vertebrae).

Vertebral Shape

A typical vertebra consists of the vertebral body and vertebral curvation. These parts together enclose the vertebral foramen that contains the spinal cord. The vertebral arch is formed by a pair of pedicles and a pair of laminae. Two transverse processes and one spinous process are posterior to (behind) the vertebral body. The spinous process projects toward the posterior direction, while one transverse process projects to the left and the other to the right. The barbed processes of the cervical and lumbar regions can exist felt through the pare. Facet joints are located above and below each vertebra. These restrict the range of movement. Between each pair of vertebrae are two small openings chosen intervertebral foramina through which the spinal nerves go out.

Vertebrae: Oblique view of cervical vertebrae.

Vertebral Curvature

When viewed laterally, the vertebral column presents several curves corresponding to the different regions of the column: cervical, thoracic, lumbar, and pelvic.

Cervical and Thoracic Curves

The cervical curve convexes forrard and begins at the noon of the odontoid (molar-like) process. It ends at the heart of the 2d thoracic vertebra. The thoracic curve convexes dorsally, begins at the middle of the second thoracic vertebra, and ends at the middle of the 12th thoracic vertebra.

Lumbar and Pelvic Curves

The lumbar curve, which is more pronounced in women than in men, begins at the middle of the concluding thoracic vertebra and ends at the sacrovertebral angle. It is convex anteriorly with the lower three vertebrae much more than convex than the upper two. This curve is described as a lordotic curve. The pelvic curve begins at the sacrovertebral articulation and ends at the point of the coccyx; its concavity is directed downward and forward.

Principal and Secondary Curves

The thoracic and sacral curvatures are termed principal curves considering they are nowadays in the fetus and remain the same in the adult. Equally the child grows, lifts the caput, and begins to assume an upright position, the secondary curves (cervical and lumbar) develop. The cervical bend forms when the infant is able to hold upwardly his or her head (at three or four months) and sit upright (at ix months). The lumbar curve forms between twelve to eighteen months when the child begins to walk.

Spinal String Gray Matter and Spinal Roots

The grey thing of the spinal cord contains neuronal cell bodies, dendrites, axons, and nerve synapses.

Learning Objectives

Depict the gray matter and spinal roots of the spinal cord

Cardinal Takeaways

Cardinal Points

• Each segment of the spinal cord is associated with a pair of ganglia called dorsal root ganglia, situated only outside of the spinal string.
• The dorsal root ganglia contain the prison cell bodies of sensory neurons. Axons of these sensory neurons travel into the spinal cord via the dorsal roots.
• The grey matter in the center of the cord contains interneurons and the prison cell bodies of motor neurons, axons, and dendrites.
• Projections of the grey matter (the "wings") are called horns. Together, the grey horns and the grayness commissure class the H-shaped gray matter.
• The dorsal root ganglia develops in the embryo from neural crest cells. The spinal ganglia can thus exist regarded every bit grey matter of the spinal cord that was translocated to the periphery.

Key Terms

• neural crest: A strip of ectodermal material in the early on vertebrate embryo inserted between the prospective neural plate and the epidermis.
• grey matter: A major component of the central nervous organization consisting of neuronal cell bodies, neuropil (dendrites and unmyelinated axons), glial cells (astroglia and oligodendrocytes), and capillaries.
• neural tube: The embryonic forerunner to the primal nervous system (CNS).

Examples

• The spine acts equally the conduit to relay information to and from the encephalon from the rest of the body.
• Impairment to the grey matter (eg, the ventral gray horn) may pb to tingling and muscle weakness.

The spinal cord is the main pathway for information connecting the brain and peripheral nervous organisation. The spinal cord is much shorter in length than the bony spinal column. The human spinal string extends from the foramen magnum of the occipital bone of the skull and continues to the conus medullaris near the second lumbar vertebra, terminating in a fibrous extension known as the filum terminale.

Spinal Cord Topography and Roots

Cross-Section of Spinal Cord, Mid-Thoracic Level: Note the commissure, rendered in grey.

The spinal string is compressed dorsoventrally, giving information technology an elliptical shape. The string has grooves in the dorsal and ventral sides. The posterior median sulcus is the groove in the dorsal side, and the inductive median scissure is the groove in the ventral side.

Each segment of the spinal cord is associated with a pair of ganglia chosen dorsal root ganglia, situated simply exterior of the spinal cord. These ganglia comprise cell bodies of sensory neurons. Axons of these sensory neurons travel into the spinal string via the dorsal roots.

The grey thing, in the center of the cord, is shaped like a butterfly and consists of cell bodies of interneurons and motor neurons, besides as neuroglia cells and unmyelinated axons. Projections of the grey matter (the "wings") are called horns. Together, the grey horns and the grey commissure form the H-shaped grey matter.

Dorsal and Ventral Roots

The dorsal root ganglia prevarication forth the vertebral column by the spine. The dorsal root ganglia develops in the embryo from neural crest cells, not the neural tube. Hence, the spinal ganglia tin be regarded as grey matter of the spinal string that became translocated to the periphery.

The axons of dorsal root ganglion neurons are known as afferents. In the peripheral nervous system, afferents refer to the axons that relay sensory data into the central nervous system. These neurons are of the pseudo-unipolar type, meaning that they have an axon with 2 branches that human action as a single axon, ofttimes referred to as distal and proximal processes. Ventral roots consist of axons from motor neurons, which bring information to the periphery from cell bodies inside the CNS. Dorsal roots and ventral roots come together and exit the intervertebral foramina equally they get spinal nerves.

The nerve endings of dorsal root ganglion neurons have a multifariousness of sensory receptors that are activated by mechanical, thermal, chemical, and baneful stimuli. In these sensory neurons, a group of ion channels thought to exist responsible for somatosensory transduction has been identified. Compression of the dorsal root ganglion by a mechanical stimulus lowers the voltage threshold needed to evoke a response and causes activity potentials to be fired. This firing may even persist afterwards the removal of the stimulus.

Impulse Transmission

The dendrite receives data from another neuron's axon at the synapse, and the axon sends information to the next neuron's dendrites. Different the majority of neurons found in the CNS, an action potential in a dorsal root ganglion neuron may initiate in the distal process in the periphery, bypass the prison cell body, and continue to propagate along the proximal process until reaching the synaptic last in the dorsal horn of the spinal string.

The distal section of the axon may either be a blank nerve ending or encapsulated by a construction that helps relay specific information to nervus. For instance, a Meissner's corpuscle or a Pacinian corpuscle may encapsulate the nerve catastrophe, rendering the distal process sensitive to mechanical stimulation, such equally stroking or vibration.

Ion Channels

Two distinct types of mechanosensitive ion channels have been establish in the dorsal root ganglia, broadly classified every bit either high-threshold (HT) or depression-threshold (LT). As their names suggest, they take unlike thresholds equally well as different sensitivities to pressure. These are cationic channels whose action appears to be regulated by the proper functioning of the cytoskeleton and cytoskeleton-associated proteins. The presence of these channels in the dorsal root ganglion gives reason to believe that other sensory neurons may contain them besides.

High-threshold channels have a possible office in nociception. These channels are plant predominantly in smaller sensory neurons in the dorsal root ganglion cells and are activated by college pressures, two attributes that are characteristic of nociceptors. Too, the threshold of HT channels was lowered in the presence of PGE2 (a compound that sensitizes neurons to mechanical stimuli and mechanical hyperalgesia), which further supports a role for HT channels in the transduction of mechanical stimuli into nociceptive neuronal signals.

Spinal Cord White Matter

The white matter of the spinal cord is composed of bundles of myelinated axons.

Learning Objectives

Draw the office and compositon of spinal string white affair

Key Takeaways

Key Points

• White thing is one of the ii components of the key nervous system and consists mostly of glial cells and myelinated axons.
• The white thing is white because of the fatty substance ( myelin ) that surrounds the nerve fibers. Myelin acts as an electric insulation. It allows the letters to pass quickly from place to place.
• Cognitive and spinal white matter practice not incorporate dendrites, which can simply be establish in grey matter along with neural cell bodies, and shorter axons.
• White affair modulates the distribution of action potentials, acting every bit a relay and coordinating communication betwixt unlike encephalon regions.
• White matter in the spinal cord functions as the "wiring"; primarily to carry information.

Key Terms

• myelin: A white, fatty, cloth composed of lipids and lipoproteins, that surrounds the axons of nerves.
• white thing: A region of the fundamental nervous system containing myelinated nervus fibers and no dendrites.
• cognitive ventricles: Interconnected cavities in the brain where the cerebrospinal fluid is produced.
• glial cell: A type of cell, in the nervous system, that provides support for the neurons.

White matter is one of the two components of the central nervous system. It consists more often than not of glial cells and myelinated axons and forms the bulk of the deep parts of the brain and the superficial parts of the spinal string. Information technology is the tissue through which messages laissez passer betwixt dissimilar areas of grey matter inside the nervous arrangement.

Limerick of White Matter

White matter is equanimous of bundles of myelinated nervus jail cell processes (or axons). The axons connect various grey affair areas (the locations of nerve cell bodies) of the brain to each other and deport nerve impulses between neurons. The axonal myelin acts as an insulator and increases the speed of transmission of all nerve signals. White matter does not contain dendrites, which are only found in gray affair along with neural prison cell bodies and shorter axons.

In a freshly cutting brain, the tissue of white matter appears pink white to the naked eye because myelin is composed largely of lipid tissue that contains capillaries. In nonelderly adults, 1.7-3.six% of the white matter is blood. Myelin is establish in almost all long nerve fibers and acts equally electrical insulation. This is important because it allows the letters to laissez passer quickly from place to place.

Spinal Cord Columns

The spinal string white matter is subdivided into columns. The dorsal columns conduct sensory information from mechanoreceptors (cells that respond to mechanical pressure or baloney). The axons of the lateral columns ( corticospinal tracts ) travel from the cerebral cortex to contact spinal motor neurons. The ventral columns carry sensory hurting and temperature information and some motor information.

Part of White Matter

Long idea to be passive tissue, white thing actively affects how the brain learns and functions. While grey affair is primarily associated with processing and cognition, white affair modulates the distribution of action potentials, acting equally a relay and analogous communication between different brain regions. The brain in full general (and especially a child'due south brain) can adapt to white-matter damage by finding culling routes that featherbed the damaged white-thing areas; therefore, it can maintain proficient connections betwixt the various areas of greyness affair. Using a calculator network as an illustration, the gray matter tin can be thought of as the actual computers themselves, whereas the white thing represents the network cables connecting the computers together.

Axon Tracts

Within white matter, there are three different kinds of tracts or bundles of axons that connect i role of the encephalon to another and to the spinal string:

1. Projection tracts extend vertically betwixt higher and lower brain and spinal cord centers. They carry information between the cerebrum and the residual of the body. The corticospinal tracts, for example, carry motor signals from the cerebrum to the brainstem and spinal string.
2. Commissural tracts cross from one cerebral hemisphere to the other through bridges called commissures. Commissural tracts enable the left and correct sides of the cerebrum to communicate with each other.
3. Association tracts connect dissimilar regions within the same hemisphere of the encephalon. Amongst their roles, association tracts link perceptual and memory centers of the brain.

White Thing-Grey Matter Interactions

White matter forms the bulk of the deep parts of the brain and the superficial parts of the spinal cord. Aggregates of grey thing, such as the basal ganglia and brain stem nuclei, are spread inside the cerebral white matter. The cerebellum is structured in a similar manner as the cerebrum, with a superficial mantle of cerebellar cortex, deep cerebellar white thing (called the "arbor vitae"), and aggregates of grey affair surrounded by deep cerebellar white thing (dentate nucleus, globose nucleus, emboliform nucleus, and fastigial nucleus). The fluid-filled cognitive ventricles (lateral ventricles, third ventricle, cerebral aqueduct, and fourth ventricle) are too located deep within the cognitive white matter.

White matter in spinal cord: The spinal cord diagram showing location of the white thing surrounding grayness matter.

Why Does The Size Of The Ventral Horns Of The Spinal Cord Vary Along Its Length?,

Source: https://courses.lumenlearning.com/boundless-ap/chapter/the-spinal-cord/

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