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Spinal Cord – Definition, Structure, Functions

What is Spinal cord?

  • The spinal cord plays a crucial role in the functioning of the central nervous system (CNS), which includes both the brain and the spinal cord. As an elongated and tubular structure, the spinal cord extends from the medulla oblongata in the brainstem down to the lumbar region of the vertebral column. Its length can vary, with an average of around 45 cm (18 in) in adult men and 43 cm (17 in) in adult women.
  • One of the primary functions of the spinal cord is to transmit nerve signals between the motor cortex in the brain and the rest of the body. Motor signals from the brain travel down the spinal cord to reach the muscles, allowing us to perform voluntary movements. Similarly, sensory signals from various parts of the body are transmitted via afferent fibers of sensory neurons to the sensory cortex in the brain, enabling us to perceive and interpret sensations.
  • In addition to its role in transmitting signals, the spinal cord also serves as a center for coordinating reflexes. Reflex arcs within the spinal cord can independently control certain reflex actions, providing swift and automatic responses to stimuli without involving the brain. These reflexes are essential for our safety and survival, allowing us to quickly withdraw from potentially harmful situations.
  • Moreover, the spinal cord contains groups of spinal interneurons, which form neural circuits known as central pattern generators. These circuits are responsible for generating and coordinating rhythmic movements, such as walking. By generating the appropriate motor instructions, the spinal cord contributes to the smooth and coordinated execution of rhythmic activities.
  • The spinal cord is well-protected by the bony vertebral column, which surrounds and shields it from external damage. It is further safeguarded by the meninges, a protective membrane, and cerebrospinal fluid that surrounds the spinal cord within the vertebral canal. These layers of protection ensure the spinal cord’s integrity and minimize the risk of injury.
  • The study of the spinal cord, its structure, function, and related disorders, falls under the field of neuroscience. Neuroscientists delve into understanding the intricacies of the spinal cord’s organization, the transmission of signals, and its involvement in various physiological processes. By gaining insights into the spinal cord, researchers can develop a deeper understanding of neurological conditions and explore potential treatments and interventions.
  • Overall, the spinal cord serves as a vital link between the brain and the body, facilitating the transmission of nerve signals and coordinating essential functions. Its role in motor control, sensory perception, reflexes, and rhythmic movements makes it an integral component of our nervous system, contributing to our ability to interact with and navigate the world around us.

Definition of Spinal cord

The spinal cord is a long, tubular structure made of nervous tissue that extends from the brainstem to the lower back. It is a vital part of the central nervous system, responsible for transmitting nerve signals between the brain and the rest of the body. It plays a crucial role in motor control, sensory perception, reflexes, and coordination of rhythmic movements.

General Features of Spinal cord

The spinal cord possesses several general features that contribute to its structure and function:

Diagram of the spinal cord showing segments
Diagram of the spinal cord showing segments | Cancer Research UK, CC BY-SA 4.0, via Wikimedia Commons
  • Location: The spinal cord is located within the vertebral canal, a hollow space formed by the vertebrae of the vertebral column (backbone). It extends from the base of the skull, specifically the medulla oblongata, down to the lower back region.
  • Size and Shape: The spinal cord has a long, thin, and tubular shape. Its length varies depending on the individual, with an average length of around 45 cm (18 inches) in adult men and 43 cm (17 inches) in adult women. The diameter of the spinal cord also varies along its length, being larger in the cervical and lumbar regions compared to the thoracic area.
  • Protective Coverings: The spinal cord is surrounded and protected by three layers of membranes called meninges. These membranes are the dura mater (outer layer), arachnoid mater (middle layer), and pia mater (inner layer). They provide cushioning and support to the delicate neural tissue of the spinal cord.
  • Spinal Canal and Cerebrospinal Fluid: The spinal cord runs through the spinal canal, which is formed by the stacked vertebrae. Within the spinal canal, the spinal cord is bathed in cerebrospinal fluid (CSF), a clear fluid that serves as a protective and nourishing medium for the spinal cord and brain.
  • Segments: The spinal cord is divided into segments, each corresponding to a specific region of the vertebral column. These segments are named after the vertebrae above them. The segments are cervical (C1-C8), thoracic (T1-T12), lumbar (L1-L5), sacral (S1-S5), and coccygeal (Co).
  • White Matter and Gray Matter: The spinal cord is composed of both white matter and gray matter. The white matter consists of myelinated nerve fibers that transmit signals up and down the spinal cord. The gray matter, located in the center of the spinal cord, contains cell bodies, dendrites, and unmyelinated fibers. It is involved in processing and integrating sensory and motor information.
  • Spinal Nerves: The spinal cord gives rise to 31 pairs of spinal nerves, which exit the spinal cord through spaces between the vertebrae. These spinal nerves carry sensory information from the body to the spinal cord (afferent fibers) and transmit motor commands from the spinal cord to the muscles and organs (efferent fibers).

These general features of the spinal cord provide the foundation for its role in transmitting nerve signals, coordinating reflexes, and facilitating communication between the brain and the body.

Anatomy of Spinal Column

The anatomy of the spinal column encompasses the structure and organization of the vertebral column, as well as the divisions and functions of the spinal cord and spinal nerves within it.

The vertebral column, also known as the backbone or spine, is composed of a series of individual bones called vertebrae. These vertebrae provide support, stability, and protection for the spinal cord. The vertebral column is divided into four main regions:

  1. Cervical Region: The cervical region consists of seven vertebrae, designated as C1 to C7. This region is located in the neck area and is responsible for innervating the muscles of the neck, shoulders, arms, and hands. The cervical region also plays a crucial role in controlling the diaphragm, which is essential for breathing.
  2. Thoracic Region: The thoracic region comprises twelve vertebrae, labeled as T1 to T12. These vertebrae correspond to the upper and middle back region. Nerves from the thoracic region innervate the intercostal muscles between the ribs and the abdominal muscles. They also have connections to the autonomic nervous system, influencing the activity of internal organs during fight-or-flight responses.
  3. Lumbar Region: The lumbar region is composed of five vertebrae, known as L1 to L5. This region is located in the lower back and is responsible for transmitting motor commands to the hips, thighs, and knees. Afferent lumbar nerves detect sensory information from the ventral side of the legs.
  4. Sacral Region: The sacral region is situated at the posterior end of the vertebral column and consists of five fused vertebrae known as S1 to S5. The sacral spinal nerves control movements such as flexing the toes and transmit sensory information from the genital organs and the dorsal aspects of the legs. Additionally, parasympathetic nerves originating from the sacral region innervate the colon, bladder, and genital organs.

The spinal cord, a vital component of the central nervous system, is encased within the vertebral column. It extends from the base of the brainstem down to the lumbar region. The spinal cord’s length averages around 44 cm (17.5 inches). Although continuous, it can be divided into segments based on the overlying vertebrae. Each section is identified using a letter representing the vertebral section and a number indicating its position relative to the previous section.

Spinal cord
Spinal cord

Branching off from each section of the spinal cord are two pairs of nerves: the afferent (sensory) nerve roots and the efferent (motor) nerve roots. These nerves combine and form the spinal nerves, which exit the vertebral column and extend to various parts of the body. The spinal nerves are responsible for transmitting sensory information towards the central nervous system and carrying motor commands away from it.

Understanding the anatomy of the spinal column provides insights into how the spinal cord and spinal nerves function and interact with different regions of the body. It highlights the specialized roles of each vertebral region and their contributions to sensory perception, motor control, and autonomic regulation.

Cross Section of the spinal cord

A cross section of the spinal cord provides a detailed view of its internal structure and reveals several important features:

The spinal cord can be divided into white and gray matter.
The spinal cord can be divided into white and gray matter.
  1. Roots: The spinal cord is connected to the spinal nerves through two major roots:
    • Ventral Root (Anterior/Motor Root): This root enters the ventral side of the spinal cord and contains motor nerve axons. It carries nerve impulses from the spinal cord to skeletal muscles, enabling voluntary movements.
    • Dorsal Root (Posterior/Sensory Root): This root enters the dorsal side of the spinal cord and consists of sensory nerve fibers. It transmits sensory information from peripheral regions of the body to the spinal cord.
  2. Dorsal Root Ganglion: Located on the dorsal root, the dorsal root ganglion is a cluster of cell bodies of sensory neurons. It serves as a relay station for sensory information entering the spinal cord.
  3. Gray Matter: The central region of the spinal cord appears as an H shape or a pair of butterfly wings in cross-section. It is composed of gray matter, which primarily contains cell bodies, dendrites, and unmyelinated fibers.
    • Gray Commissure: The crossbar of the H shape is known as the gray commissure. It contains neural tissue and acts as a bridge connecting the left and right sides of the spinal cord.
    • Anterior (Ventral) Horns: Found at the front of each side of the H shape, the anterior horns consist of gray matter. They contain the cell bodies of motor neurons responsible for stimulating skeletal muscles, enabling voluntary movement.
    • Posterior (Dorsal) Horns: Located at the rear of each side of the H shape, the posterior horns are also composed of gray matter. These horns primarily consist of interneurons that receive sensory input and help process and transmit signals to the brain.
    • Lateral Horns: Present only in the thoracic and lumbar regions of the spinal cord, the lateral horns are small projections of gray matter. They contain cell bodies of motor neurons that are part of the sympathetic branch of the autonomic nervous system, which controls involuntary functions.
    • Central Canal: Situated in the center of the gray commissure, the central canal is a small hole that runs the length of the spinal cord. It is filled with cerebrospinal fluid (CSF) and connects with the fourth ventricle of the brain.
  4. White Columns (Funiculi): Surrounding the gray matter, there are six areas of white matter, three on each side of the H shape:
    • Anterior (Ventral) Columns: Located on the front side of the spinal cord, these columns contain nerve tracts responsible for transmitting motor information from the brain to the spinal cord and then to the muscles and glands.
    • Posterior (Dorsal) Columns: Situated on the back side of the spinal cord, these columns carry sensory information from various parts of the body to the brain.
    • Lateral Columns: Found on the sides of the spinal cord, the lateral columns contain a mix of ascending and descending nerve tracts.
  5. Fasciculi: Within the white columns, there are bundles of nerve tracts called fasciculi. These fasciculi consist of neurons with similar functions or destinations:
    • Ascending (Sensory) Tracts: These tracts transmit sensory information from different parts of the body to the brain, allowing for perception and awareness of sensory stimuli.
    • Descending (Motor) Tracts: These tracts carry nerve impulses from the brain to muscles and glands, enabling voluntary and involuntary motor control.

        Understanding the cross section of the spinal cord helps in comprehending the complex organization of neural pathways and the integration of sensory and motor functions within the central nervous system.

        The spinal cord is comprised of white and gray matter
        The spinal cord is comprised of white and gray matter

        Structure of Spinal Cord

        The structure of the spinal cord encompasses its length, divisions, protective layers, and the nerve projections that extend from it:

        1. Length and Divisions: The length of the spinal cord can vary slightly among individuals. On average, females have a spinal cord length of about 43 cm, while males have a length of about 45 cm. The spinal cord is divided into three main sections:
        • Cervical (Neck) Region: This is the uppermost section of the spinal cord, consisting of the cervical vertebrae and corresponding spinal nerves. It provides nerve supply to the neck, shoulders, arms, and hands.
        • Thoracic (Chest) Region: Located in the middle section of the spinal cord, the thoracic region corresponds to the thoracic vertebrae and associated spinal nerves. It innervates the trunk area and intercostal muscles between the ribs.
        • Lumbar (Lower Back) Region: Positioned in the lower section of the spinal cord, the lumbar region includes the lumbar vertebrae and the related spinal nerves. It provides nerve supply to the hips, thighs, and knees.
        1. Protective Layers: The spinal cord is enveloped by three layers of protective tissue called meninges:
        • Dura Mater: The dura mater is the outermost layer of the spinal cord’s meninges. It is a tough and durable protective layer.
        • Arachnoid Mater: Positioned between the dura mater and the innermost layer, the arachnoid mater provides additional protection to the spinal cord.
        • Pia Mater: The pia mater is the innermost layer of the meninges. It closely adheres to the surface of the spinal cord and provides nourishment to its tissues.
        1. Vertebral Column: The vertebral column, also known as the spinal bones or backbone, surrounds and protects the spinal cord and its meninges. Extending from the base of the skull to the sacrum, the vertebral column is composed of individual vertebrae.
        • Cervical Vertebrae: Most individuals have seven cervical vertebrae in the neck region.
        • Thoracic Vertebrae: The thoracic region consists of twelve thoracic vertebrae in the chest area.
        • Lumbar Vertebrae: In the lower back, there are typically five lumbar vertebrae.
        1. Nerve Projections: If a horizontal “slice” were taken through the spinal cord, a circular area covered by the protective layers of the meninges would be observed. From this central region, nerve projections extend outward. These projections consist of nerve fibers that radiate from the spinal cord to provide sensation and transmit nerve signals to various parts of the body.

        Understanding the structure of the spinal cord helps in recognizing its divisions, the importance of protective layers, and the distribution of nerve projections that play a crucial role in sensory perception and motor control throughout the body.

        Important area of the Spinal Cord

        The key areas of the spinal cord can be identified in a cross-section of this complex structure:

        1. Gray Matter: The gray matter is a prominent region in the cross-section of the spinal cord. It appears as a butterfly-shaped area consisting of nerve cell bodies. This region is responsible for integrating and processing incoming sensory information and initiating motor commands.
        2. White Matter: Surrounding the gray matter, the white matter forms the outer layer of the spinal cord. It consists of nerve fibers covered in myelin, a fatty substance that enhances the speed of nerve signal transmission. Unlike the gray matter, the white matter primarily contains axons and serves as a conduit for transmitting nerve impulses to and from different regions of the body.
        3. Posterior Root: The posterior root emerges from the posterior (dorsal) side of the spinal cord. In a cross-section, the top wings of the gray matter butterfly extend toward the spinal bones, while the bottom wings face the body’s internal organs. The posterior root contains sensory nerve fibers that carry sensory information from the peripheral areas of the body to the spinal cord.
        4. Anterior Root: The anterior root arises from the anterior (ventral) side of the spinal cord. It contains motor nerve fibers responsible for transmitting nerve signals from the spinal cord to the muscles and glands throughout the body, enabling voluntary movements and other motor functions.
        5. Spinal Ganglion: Located on the posterior root, the spinal ganglion is a collection of nerve cell bodies that house sensory neurons. These sensory neurons play a vital role in detecting various stimuli from the body’s external and internal environments and transmitting the information to the spinal cord for processing.
        6. Spinal Nerve: The spinal nerve is formed by the merging of the posterior and anterior roots. There are 31 pairs of spinal nerves originating from the spinal cord, each pair associated with a specific segment of the spinal cord. These spinal nerves play a crucial role in regulating both sensory perception and motor function throughout the body.

        It is important to note that while the spinal cord itself is not elongated, the spinal nerves extend beyond the spinal column, branching out to innervate different regions of the body, allowing for communication between the central nervous system (spinal cord) and peripheral tissues and organs.

        Spinal Nerves Types And Functions

        Because spinal nerves contain both sensory and motor fibers, they have sensory as well as motor functions. The spinal nerves receive sensory instructions from the skin, internal organs, and bones for sensory functions.

        These spinal nerves will then transmit this sensory information to the sensory roots before reaching the sensory fibres at the spinal cord’s hind end. The motor roots receive nerve instructions from the front of the spinal cord and then pass them to the spinal nerves to perform motor activities. This information will eventually be transmitted to little nerve branches, which will activate the muscles of the limbs and other body components.

        Cervical Nerves

        The cervical nerves play a crucial role in controlling various movements and sensory functions in the head, neck, shoulders, and upper extremities. Here are the key features of the cervical nerves:

        Cervical Nerves
        Cervical Nerves | Image Credit: www.simplypsychology.org
        1. C1, C2, and C3: These cervical spinal nerves are involved in controlling the movements of the head and neck. They contribute to the flexion, extension, rotation, and lateral bending of the neck.
        2. C4: The C4 cervical nerve assists in controlling the movement of the upper shoulder region. It also plays a role in powering the diaphragm, a critical muscle involved in respiration.
        3. C5: The C5 cervical nerve is responsible for controlling the deltoid muscles, which are located in the shoulders, as well as the biceps muscles of the upper arm. It enables movements such as shoulder abduction and elbow flexion.
        4. C6: The C6 cervical nerve contributes to the control of wrist extension and provides some innervation to the biceps muscles. It plays a role in movements involving wrist extension and helps stabilize the arm during activities such as lifting.
        5. C7: The C7 cervical nerve is primarily associated with the triceps muscles of the upper arm. It also provides motor control to the muscles responsible for wrist extension. C7 plays a crucial role in elbow extension and wrist stabilization.
        6. C8: The C8 cervical nerve is responsible for controlling the muscles of the hands, including finger flexors that contribute to hand grip strength. It plays a key role in fine motor control of the hands and fingers.

        The cervical nerves C1 to C5 can form a network known as the cervical plexus. This plexus arises from the merging of these nerves and gives rise to smaller nerves that carry sensory information and provide motor control to the muscles of the neck and shoulders.

        Additionally, the combination of the cervical nerves C5 to T1 forms the brachial plexus. This plexus branches into nerves that carry sensory messages and provide motor control to the muscles of the arms and upper back. It plays a vital role in the sensory and motor functions of the upper extremities.

        Overall, the cervical nerves are integral in coordinating movements and sensory perception in the head, neck, shoulders, and upper limbs, allowing for a wide range of functions and interactions with the environment.

        Thoracic Nerves

        The thoracic nerves, positioned below the cervical nerves, consist of 12 pairs (T1 to T12) located in the thoracic vertebrae of the spine. These nerves play a crucial role in innervating various regions of the chest, arms, hands, and abdomen. Here’s an overview of the functions of the thoracic nerves:

        Thoracic Nerves
        Thoracic Nerves | Image Credit: www.simplypsychology.org
        1. T1 and T2: The T1 and T2 thoracic spinal nerves supply the upper chest, arms, and hands. They contribute to sensory perception and motor control in these areas, enabling movements and providing feedback from the skin and muscles.
        2. T3, T4, and T5: These thoracic nerves supply the chest wall and play a role in aiding breathing. They innervate the intercostal muscles, which are responsible for the expansion and contraction of the ribcage during respiration.
        3. T6, T7, and T8: These thoracic nerves supply the chest region and extend into the abdomen. They contribute to motor control and sensory perception in these areas, playing a role in movements such as trunk rotation and stabilization.
        4. T9, T10, T11, and T12: These thoracic nerves primarily supply the abdomen and lower back. They innervate the abdominal muscles, providing motor control and enabling movements such as trunk flexion and lateral bending. They also contribute to sensory perception in these regions.

        The thoracic nerves play a critical role in transmitting sensory information, such as touch, temperature, and pain, from the chest, arms, hands, and abdomen to the central nervous system. They also provide motor control to the muscles in these regions, allowing for coordinated movements and functional activities.

        Understanding the functions of the thoracic nerves is essential in diagnosing and treating conditions that may affect these regions, such as chest pain, breathing difficulties, abdominal muscle weakness, and sensory abnormalities. Proper functioning of the thoracic nerves is crucial for maintaining optimal physical capabilities and overall well-being.

        Lumbar Nerves

        The lumbar nerves, located below the thoracic nerves, consist of five pairs (L1 to L5) situated in the lumbar vertebrae of the spine. These nerves play a crucial role in providing sensory perception and motor control to various regions of the lower body. Here’s an overview of the functions of the lumbar nerves:

        Lumbar Nerves
        Lumbar Nerves | Image Credit: www.simplypsychology.org
        1. L1: The L1 lumbar spinal nerves are responsible for providing sensations to the groin and genitals. They play a role in transmitting sensory information from these areas to the central nervous system.
        2. L2, L3, and L4: These lumbar nerves contribute to sensory perception and motor control in the front of the thighs and the inner side of the lower legs. They are involved in transmitting sensations from these regions and enabling movements of the hip and knee muscles.
        3. L5: The L5 nerves play a crucial role in providing sensations to the outer side of the lower legs and the upper foot. Additionally, they contribute to motor control, helping to regulate movements of the hips, knees, feet, and toes.

        The lumbar nerves L1 to L4 have the potential to combine and form the lumbar plexus. This plexus further divides into smaller nerves that carry sensory messages and provide motor control to the muscles of the abdomen and legs. It plays a significant role in coordinating movements and maintaining sensory perception in these areas.

        Understanding the functions of the lumbar nerves is essential in diagnosing and treating conditions that may affect these regions, such as leg pain, muscle weakness, and sensory abnormalities. These nerves play a crucial role in enabling movements, providing sensations, and ensuring the overall functionality of the lower body.

        Proper functioning of the lumbar nerves is vital for activities such as walking, standing, and maintaining balance. If any issues arise, medical professionals can evaluate and address the underlying causes to ensure optimal functioning and promote the well-being of individuals.

        Sacral Nerves

        The sacral nerves, situated below the lumbar nerves, consist of five pairs (S1 to S5) located in the sacrum of the spine. These nerves play a crucial role in transmitting sensory information and controlling motor functions in various regions of the lower body. Here’s an overview of the functions of the sacral nerves:

        1. S1: The S1 sacral nerves primarily affect the hips and the groin area. They contribute to sensory perception and motor control in these regions, playing a role in transmitting sensations and enabling movements.
        2. S2: The S2 nerves specifically affect the back of the thighs. They are involved in transmitting sensory information and providing motor control to this area, allowing for movements and maintaining sensation.
        3. S3: The S3 nerves affect the medial buttock area. They play a role in sensory perception and motor control in this region, assisting in movements and facilitating the transmission of sensations.
        4. S4 and S5: These nerves primarily affect the perineal area, which includes the genitals and the area between the anus and the genitals. They contribute to sensory perception and motor control in this region, playing a crucial role in transmitting sensations and enabling appropriate muscle movements.

        The spinal nerves from lumbar L4 to sacral nerves S4 have the potential to merge and form the sacral plexus. This plexus further divides into smaller nerves that carry sensory messages and provide motor control to the muscles of the legs. It plays a significant role in coordinating movements, maintaining balance, and ensuring sensory perception in the lower limbs.

        Understanding the functions of the sacral nerves is essential in diagnosing and addressing conditions that may affect these regions, such as hip pain, muscle weakness, and sensory disturbances. These nerves contribute to the overall functionality of the lower body, facilitating movements, and ensuring appropriate sensory feedback.

        Medical professionals can assess and address any issues related to the sacral nerves, ensuring optimal functioning and promoting the well-being of individuals. Proper functioning of the sacral nerves is vital for activities such as walking, sitting, and maintaining bladder and bowel control.

        Coccygeal Nerves

        Coccygeal Nerves
        Coccygeal Nerves | Image Credit: www.simplypsychology.org
        • Located at the very base of the spine, there is a single pair of coccygeal nerves, commonly referred to as the CO1 nerves. These nerves play a specific role in providing sensory innervation to the skin surrounding the coccygeal region, including the area around the tailbone.
        • The CO1 spinal nerves transmit sensory information from the skin in this region, allowing individuals to perceive touch, pressure, temperature, and pain sensations. They are responsible for relaying these sensory signals from the coccygeal area to the spinal cord and ultimately to the brain for processing and interpretation.
        • The skin around the coccyx, or tailbone, can be sensitive to various stimuli. The CO1 nerves play a vital role in detecting and conveying these sensory experiences to ensure appropriate responses and reactions. Sensations in the coccygeal region may include touch, discomfort, or pain, depending on the specific stimuli encountered.
        • Understanding the innervation provided by the coccygeal nerves is important in diagnosing and managing conditions or injuries that may affect this area. Trauma, inflammation, or other factors can lead to discomfort or pain in the tailbone region. By assessing the function and sensitivity of the CO1 nerves, medical professionals can better diagnose and address these issues, providing appropriate treatment and management strategies.
        • The coccygeal nerves represent the terminal branches of the spinal cord and serve a specific localized function in the sensory innervation of the coccygeal region. While they may not be as extensively studied or discussed as the other spinal nerves, their role in conveying sensory information from the tailbone area is significant for maintaining overall sensory perception and well-being.

        Development of Spinal cord

        • The development of the spinal cord involves a series of intricate processes that transform the neural tube into a fully functional structure. The following stages outline the key steps in the development of the spinal cord: neural plate, neural fold, neural tube, and the spinal cord.
        • It all begins with the neural plate, which forms during the early stages of embryonic development. The notochord, a structure that runs along the midline of the embryo, releases a signaling molecule called Sonic hedgehog (SHH). SHH triggers the secretion of more SHH by the floor plate of the neural tube. This event induces the basal plate to develop motor neurons, which will eventually control muscle movements.
        • Simultaneously, the ectoderm located above the neural tube secretes a protein called bone morphogenetic protein (BMP). This protein stimulates the roof plate of the neural tube to produce BMP, initiating the development of sensory neurons in a region called the alar plate. The balance and concentration of molecules like SHH and BMP along the dorsal-ventral axis of the neural tube determine the different domains of dividing cells, leading to the formation of distinct neuronal populations.
        • Dorsal root ganglion neurons, responsible for transmitting sensory information, differentiate from neural crest progenitors. The lateral walls of the neural tube thicken and create a groove known as the sulcus limitans. This elongates the spinal cord into dorsal and ventral portions. As the cells in these regions continue to divide, the lumen of the neural tube narrows, forming the central canal of the spinal cord.
        • The sulcus limitans separates the alar plate, involved in sensory neuron development, from the basal plate, responsible for motor neuron development. In addition to SHH and BMP, the floor plate also secretes netrins. These netrins act as chemoattractants, guiding the decussation (crossing over) of pain and temperature sensory neurons from the alar plate through the anterior white commissure. From there, these neurons ascend towards the thalamus, a crucial relay station in the brain.
        • After the closure of the caudal neuropore and the formation of the brain’s ventricles, the central canal of the caudal spinal cord becomes filled with cerebrospinal fluid. This fluid helps protect and nourish the developing spinal cord and brain.
        • Research conducted by Viktor Hamburger and Rita Levi-Montalcini in chick embryos discovered the significance of programmed cell death (PCD) in the proper assembly of the nervous system. Subsequent studies have confirmed their findings, highlighting the importance of neuronal cell elimination through PCD during development.
        • While spontaneous embryonic activity has been found to play a role in neuron and muscle development, it appears to be less involved in the initial formation of connections between spinal neurons. The precise mechanisms underlying these connection formations continue to be an active area of research.
        • Overall, the development of the spinal cord is a complex and dynamic process, involving the coordinated action of various molecular signals and cellular interactions. These processes ultimately give rise to the intricate neural network responsible for transmitting sensory information and controlling motor functions throughout the body.

        Blood supply in Spinal cord

        • The blood supply to the spinal cord is essential for its proper functioning and viability. There are three main longitudinal arteries that supply blood to the spinal cord: the anterior spinal artery, and the right and left posterior spinal arteries. These arteries travel along the length of the spinal cord in the subarachnoid space and send branches into the spinal cord. They form connections, or anastomoses, through the anterior and posterior segmental medullary arteries, which enter the spinal cord at various points along its length.
        • However, the blood flow from these longitudinal arteries is not sufficient to sustain the spinal cord beyond the cervical segments. The major contribution to the blood supply of the spinal cord in regions below the cervical region comes from the posterior and anterior radicular arteries. These arteries run alongside the dorsal and ventral nerve roots and provide significant anastomoses to supplement the blood flow to the spinal cord. They arise from the aorta and include intercostal and lumbar radicular arteries.
        • Of particular importance is the artery of Adamkiewicz, also known as the anterior radicularis magna (ARM) artery. This artery, the largest of the anterior radicular arteries, typically arises between the first lumbar (L1) and second lumbar (L2) vertebrae. However, it can also originate anywhere from the ninth thoracic (T9) to the fifth lumbar (L5) vertebrae. The artery of Adamkiewicz plays a crucial role in supplying blood to the lower spinal cord and can be vulnerable during surgical procedures involving the aorta, such as aortic aneurysm repair. Impaired blood flow through these critical radicular arteries, especially when there is a sudden disruption of blood flow through the aorta, can lead to spinal cord infarction and result in paraplegia.
        • The intricate network of arteries supplying the spinal cord ensures the delivery of oxygen and nutrients necessary for its proper functioning. The understanding of this blood supply is crucial in clinical settings to minimize the risk of spinal cord complications during surgical procedures and to address any potential impairments to blood flow that could lead to serious neurological consequences.

        What do you mean by Gray Horns?

        The gray matter of the spinal cord is organized into distinct regions known as horns, which can be visualized in cross-section as a mirrored “H” shape. These horns play important roles in sensory processing, motor control, and autonomic functions.

        The posterior horn of the gray matter is responsible for sensory processing. It receives incoming sensory information from peripheral nerves and relays it to higher centers in the central nervous system for interpretation. This region plays a crucial role in transmitting sensations such as touch, temperature, pain, and proprioception.

        On the other hand, the anterior horn of the gray matter is involved in motor control. It contains multipolar motor neurons, which are some of the largest neurons in the spinal cord. These motor neurons send out axons that extend to skeletal muscles, allowing them to contract and generate movement. For instance, the motor neurons located in the anterior horn of the sacral spinal cord can activate the muscles responsible for the movement of the big toe. Due to the long distances these axons need to travel, the neuronal cell bodies in the anterior horn can be relatively large, reaching several hundred micrometers in diameter. This makes them among the largest cells in the body.

        In addition to the posterior and anterior horns, the gray matter of the spinal cord also contains a lateral horn. However, the lateral horn is only present in specific regions of the spinal cord, including the thoracic, upper lumbar, and sacral regions. The lateral horn is particularly important as it serves as the central component of the sympathetic division of the autonomic nervous system. This region controls involuntary processes, such as regulating blood pressure, heart rate, and other vital functions.

        Overall, the gray horns of the spinal cord represent specialized regions involved in sensory processing, motor control, and autonomic functions. They showcase the complex organization and diverse functions of the spinal cord in orchestrating sensory and motor activities throughout the body.

        Cross-section of Spinal Cord
        Cross-section of Spinal Cord

        What do you mean by White Columns?

        The white matter of the spinal cord is organized into distinct columns that play a crucial role in transmitting sensory and motor information between the brain and the rest of the body. These columns are comprised of ascending and descending tracts of nervous system fibers, each serving a specific function.

        The posterior columns, located between the two posterior horns of gray matter, consist of axons that form ascending tracts. These tracts carry sensory information from the peripheral nerves to the brain. They transmit sensations such as touch, proprioception (awareness of body position), vibration, and fine discriminative touch. The sensory information is relayed through these ascending tracts to higher centers in the brain for processing and interpretation.

        On the other hand, the anterior columns are situated between the two anterior horns of gray matter. They are bounded by the axons of motor neurons emerging from the gray matter. The anterior columns contain both ascending and descending tracts. The descending tracts carry motor commands from the brain to the spinal cord, enabling the control of voluntary movements. These tracts transmit signals that initiate muscle contractions and coordinate precise movements throughout the body.

        Adjacent to the anterior columns are the lateral columns, which extend between the posterior horn and the axons of the anterior horn neurons. Similar to the anterior columns, the lateral columns consist of various groups of axons that include both ascending and descending tracts. These tracts serve a wide range of functions, including motor control, sensory integration, and coordination of reflex responses.

        The white columns of the spinal cord form continuous bands of white matter running along its length. They facilitate the communication between different regions of the spinal cord and the brain. Through the ascending tracts, sensory information is transmitted to the brain for perception and interpretation, while the descending tracts carry motor commands from the brain to the spinal cord, allowing for voluntary movements and motor coordination.

        The organization of the white columns highlights the intricate network of nerve fibers that facilitate the transmission of sensory and motor signals, playing a vital role in maintaining the body’s sensory perception, motor control, and overall functionality.

        Clinical Aspects

        Spinal cord disorders encompass a range of problems or disorders that can affect the spinal cord, resulting in long-term and often permanent damage. These conditions impact the regular functioning of the spinal cord, and unfortunately, there is currently no known replacement for it. Here are some common clinical aspects and conditions associated with spinal cord disorders:

        1. Multiple Sclerosis (MS): MS is a demyelinating condition that can affect both the brain and the spinal cord. When the spinal cord is affected, it can lead to symptoms such as weakness, loss of sensation, tingling, and pain. MS is a chronic autoimmune disease where the immune system mistakenly attacks the protective covering of nerve fibers, known as myelin, leading to disruptions in nerve signal transmission.
        2. Spinal Cord Compression: Spinal cord compression occurs when there is pressure on the spinal cord, leading to weakness and loss of sensation. This compression can result from various causes, including spinal fractures, herniated discs, spinal tumors, or spinal stenosis (narrowing of the spinal canal). It is essential to alleviate spinal cord compression promptly to prevent further damage and preserve neurological function.
        3. Meningitis: Meningitis refers to the infection or inflammation of the meninges, the protective membranes surrounding the brain and spinal cord. When meningitis affects the spinal cord, it is called spinal meningitis. This condition can cause symptoms such as headaches, stiff neck, fever, and vomiting. Bacterial, viral, or fungal infections can lead to meningitis, and prompt diagnosis and treatment are crucial to prevent complications.
        4. Polio: Polio, also known as poliomyelitis, is a highly contagious viral infection that primarily affects the spinal cord. Polio can be prevented through vaccination, but in rare cases where infection occurs, it can lead to muscle paralysis in the areas controlled by the affected regions of the spinal cord. Polio is now relatively rare due to widespread vaccination efforts.
        5. Spinal Cord Cancer: While spinal cord cancer is not a common disease, tumors can develop in any part of the spinal cord. Meningeal carcinomatosis refers to the spread of cancer cells throughout the meninges and cerebrospinal fluid (CSF). Spinal cord tumors can cause various symptoms depending on their location and size, such as pain, weakness, sensory changes, or difficulty with motor function. Timely diagnosis, treatment, and management are crucial in addressing spinal cord cancer.

        In all these clinical aspects, it is essential to consult with healthcare professionals who specialize in neurology or spinal cord disorders. Treatment approaches may involve a combination of medical interventions, rehabilitation, physical therapy, and supportive care to manage symptoms, improve quality of life, and maximize functional abilities.

        Function of the Spinal Cord 

        The spinal cord is a long, thin, tubular bundle of nerves that extends from the base of the brain down through the vertebral column. It is a crucial part of the central nervous system (CNS) and serves several important functions:

        1. Transmission of sensory information: The spinal cord acts as a conduit for sensory information traveling from the body to the brain and vice versa. Sensory neurons carry signals related to touch, temperature, pain, pressure, and proprioception (awareness of body position) from various parts of the body to the spinal cord. From there, the signals are transmitted to the brain for interpretation and processing.
        2. Motor control: The spinal cord is responsible for transmitting motor signals from the brain to the muscles and glands throughout the body. Motor neurons in the spinal cord receive instructions from the brain and relay them to the target muscles, enabling voluntary movements. This coordination allows us to perform various actions, such as walking, grasping objects, and speaking.
        3. Reflex arcs: The spinal cord plays a critical role in mediating reflex actions. Reflexes are involuntary responses to certain stimuli that help protect the body and maintain balance. When a specific sensory receptor in the body detects a stimulus, such as pain or heat, the sensory signal travels to the spinal cord, which quickly generates a motor response without involving the brain. Examples of reflex actions include the withdrawal of a hand upon touching something hot or the knee jerk reflex.
        4. Autonomic functions: The spinal cord also controls numerous automatic or involuntary functions of the body through the autonomic nervous system (ANS). The ANS regulates vital processes such as heart rate, blood pressure, digestion, and respiration. Nerve fibers in the spinal cord connect with the ANS to facilitate these functions.

        Overall, the spinal cord acts as a vital relay system between the brain and the rest of the body, enabling communication, coordination, and control of sensory and motor functions.

        FAQ

        What is the spinal cord?

        The spinal cord is a long, thin bundle of nerves that extends from the base of the brain down the vertebral column. It is a vital part of the central nervous system.

        What is the function of the spinal cord?

        The spinal cord serves multiple functions, including transmitting sensory information from the body to the brain, relaying motor signals from the brain to muscles, coordinating reflex actions, and regulating autonomic functions.

        Can the spinal cord regenerate if injured?

        In general, the spinal cord has limited regenerative capacity. However, researchers are actively studying ways to promote regeneration and repair damaged spinal cord tissue.

        What are some common causes of spinal cord injury?

        Spinal cord injuries can result from traumatic events like car accidents, falls, or sports injuries. Other causes include diseases, infections, tumors, and degenerative conditions of the spine.

        What are the symptoms of spinal cord injury?

        Symptoms vary depending on the severity and location of the injury. Common symptoms include paralysis or weakness, loss of sensation, changes in reflexes, pain, difficulty breathing, and changes in bowel or bladder control.

        How is a spinal cord injury diagnosed?

        Diagnostic methods may include a physical examination, medical history review, imaging tests (such as MRI or CT scans), and neurological assessments to determine the extent and location of the injury.

        What are the treatment options for spinal cord injuries?

        Treatment depends on the severity and type of injury. It may involve immobilization, surgery to stabilize the spine, rehabilitation (including physical therapy and occupational therapy), assistive devices, and medications to manage symptoms.

        What are some common spinal cord disorders?

        Common spinal cord disorders include multiple sclerosis (MS), spinal stenosis, herniated discs, spinal tumors, spinal cord compression, and syringomyelia.

        Can spinal cord disorders be prevented?

        While some spinal cord disorders are not preventable, adopting a healthy lifestyle, practicing proper body mechanics, using protective gear during physical activities, and avoiding risky behaviors can reduce the risk of spinal cord injuries.

        Are there any ongoing advancements or research in spinal cord treatment?

        Yes, there is ongoing research focused on spinal cord injury treatments, including stem cell therapies, neuroprotection techniques, electrical stimulation, and advancements in rehabilitation strategies. These efforts aim to improve outcomes and enhance functional recovery for individuals with spinal cord disorders.

        References

        • https://courses.lumenlearning.com/suny-ulster-ap1/chapter/spinal-cord/
        • https://openbooks.lib.msu.edu/introneuroscience1/chapter/spinal-cord-structure/
        • https://open.oregonstate.education/aandp/chapter/14-4-the-spinal-cord/
        • https://www.simplypsychology.org/spinal-nerves-anatomy.html
        • https://www.cliffsnotes.com/study-guides/anatomy-and-physiology/the-nervous-system/the-spinal-cord
        • http://courses.washington.edu/pbio375/spinal-cord/sc-anatomy.html
        • https://collegedunia.com/exams/spinal-cord-biology-articleid-6268
        • https://www.biologydiscussion.com/human-beings/spinal-cord/human-spinal-cord-structure-and-functions/70628
        • https://openstax.org/books/anatomy-and-physiology-2e/pages/12-1-basic-structure-and-function-of-the-nervous-system
        • https://overallscience.com/structure-and-functions-of-spinal-cord/
        • https://www.kenhub.com/en/library/anatomy/the-spinal-cord
        • https://nba.uth.tmc.edu/neuroscience/m/s2/chapter03.html
        • https://www.physio-pedia.com/Spinal_cord_anatomy
        • https://www.verywellhealth.com/spinal-cord-anatomy-4780787
        • https://www.getbodysmart.com/spinal-cord/
        • https://www.geeksforgeeks.org/spinal-cord-anatomy-functions-and-clinical-aspects/
        • https://www.vedantu.com/evs/spinal-cord

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