Dorsal root fibres

Dorsal root fibres

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How can dorsal root fibres be unmylinated though are responsible for conduction of pain and temperature? How is their conduction so fast without even being myelinated? Is presence of only one axon( indicating that a single axon travels from skin to dorsal root ganglion) enough for such fast conduction?

Dorsal Root Ganglion

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A ganglion is the collection of cell bodies of neurons located outside the central nervous system. A dorsal root ganglion is the one associated with the dorsal or posterior root of the nerves originating from the spinal cord.

All the posterior roots of spinal nerves contain a ganglion. As the dorsal or posterior root of a spinal nerve is primarily sensory, the dorsal root ganglion contains cell bodies of these sensory nerve fibers.

In this article, we will talk about the structure,
location, and connections of the dorsal root ganglion. We will also discuss the
functions and clinical conditions associated with the dorsal root ganglion.


It is evident from the name that a dorsal root ganglion is associated with the dorsal or posterior root of spinal nerves. One dorsal root ganglion is associated with each spinal nerve present in our body.

The neurons present in the dorsal root ganglion gives rise to all the fibers present in the dorsal root of a spinal nerve. It lies suspended via these fibers just lateral to each segment of the spinal cord. It is protected by different processes of a vertebra.

Responses of Single Dorsal Cord Cells to Peripheral Cutaneous Unmyelinated Fibres

IN the dorsal part of the dorsal horn there is a lamina of cells which respond to cutaneous stimulation and send their axons into the dorsolateral tract. In previous investigations 1 it was apparent that many different types of A fibres converged on these cells. It is, therefore, interesting to see whether C fibres also affect their firing. In a recent investigation 2 it was found that an afferent volley in the unmyelinated fibres led to a positive dorsal root potential as opposed to the well-known negative dorsal potential which is elicited by the large myelinated fibres. It was suggested that C fibres led to presynaptic hyperpolarization which would produce facilitation as contrasted with the presynaptic inhibitory effects of the A fibres. An investigation of the ventral root reflex (VRR, ref. 2) showed no late component which could be attributed to C fibres however, a tetanus in the C's was found to potentiate the VRR elicited by the A fibres in the same peripheral nerve. It was also known that a large stimulus to a peripheral nerve led to late discharges in various midbrain and forebrain structures 3 . With these factors in mind an investigation of the response of cells in the dorsolateral tract of the cat to C fibres was carried out.

Immunohistochemical correlation of human adrenal nerve fibres and thoracic dorsal root neurons with special reference to substance P

Applying a double-labelling immunofluorescence technique, six types of substance P-containing nerve fibres were distinguished in the human adrenal gland according to the immunohistochemical colocalization of (I) calcitonin gene-related peptide (CGRP), (II) cholecystokinin, (III) nitric oxide synthase, (IV) dynorphin, (V) somatostatin, and (VI) vasoactive intestinal polypeptide. Fibre populations I to IV in their mediator content resembled the respective subpopulations of primary sensory neurons in human thoracic dorsal root ganglia, while populations V and VI revealed no correspondence with dorsal root neurochemical coding. Nerve fibres with the combination substance P/nitric oxide synthase occurred only in the adrenal cortex, whereas all other fibre types were present in both cortex and medulla. As revealed by immuno-electron microscopy, substance P-immunolabelled axon varicosities (a) exhibited synaptic contacts with medullary chromaffin cells or with neuronal dendrites, (b) were directly apposed to cortical steroid cells and (c) were separated from fenestrated capillaries only by the interstitial space. These findings provide immunochemical support for an assumed sensory innervation of the human adrenal gland, and additionally suggest participation of substance P in efferent autonomic pathways. Furthermore, the results are indicative for a differentiated involvement of substance P in the direct and indirect regulation of neuroneuronal and neuroendocrine interactions.


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Dorsal root fibres - Biology

Neurons & the Nervous System - Part 2

2 - Spinal nerves (31 pair) & their branches

Divisions of the nervous system



    2 - Visceral - supplies & receives fibers to & from smooth muscle, cardiac muscle, and glands. The visceral motor fibers (those supplying smooth muscle, cardiac muscle, & glands) make up the Autonomic Nervous System. The ANS has two divisions:
    • Parasympathetic division - important for control of 'normal' body functions, e.g., normal operation of digestive system
    • Sympathetic division - also called the 'fight or flight' division important in helping us cope with stress

    1 - Myelencephalon, which includes the medulla

    2 - Metencephalon, which includes the pons and cerebellum

    3 - Mesencephalon, which includes the midbrain (tectum and tegmentum)

    4 - Diencephalon, which includes the thalamus and hypothalamus

    5 - Telencephalon, which includes the cerebrum (cerebral cortex, basal ganglia, & medullary body)

    Human brain (coronal section). The divisions of the brain include the (1) cerebrum, (2) thalamus, (3) midbrain,
    (4) pons, and (5) medulla oblongata. (6) is the top of the spinal cord (Source: Wikipedia).

    Structures of the Brain:

      1 - continuous with spinal cord

    2 - contains ascending & descending tracts that communicate between the spinal cord & various parts of the brain

      • cardioinhibitory center, which regulates heart rate
      • respiratory center, which regulates the basic rhythm of breathing
      • vasomoter center, which regulates the diameter of blood vessels

      2 - Origin of four cranial nerves (V or trigeminal, VI or abducens, VII or facial, & VIII or vestibulocochlear)

      3 - contains pneumotaxic center (a respiratory center)

      The brain stem is the region between the diencephalon (thalamus and hypothalamus) and the spinal cord. It consists of three parts: midbrain, pons, and medulla oblongata. The midbrain is the most superior portion of the brain stem. The pons is the bulging middle portion of the brain stem. This region primarily consists of nerve fibers that form conduction tracts between the higher brain centers and spinal cord. The medulla oblongata, or simply medulla, extends inferiorly from the pons. It is continuous with the spinal cord at the foramen magnum. All the ascending (sensory) and descending (motor) nerve fibers connecting the brain and spinal cord pass through the medulla (Source:

        1 - Corpora quadrigemina - visual reflexes & relay center for auditory information.Two pairs of rounded knobs on the upper surface of the midbrain mark the location of four nuclei, which are called collectively the "corpora quadrigemina." These masses contain the centers for certain visual reflexes, such as those responsible for moving the eyes to view something as the head is turned. They also contain the hearing reflex centers that operate when it is necessary to move the head so that sounds can be heard better.

      2 - Cerebral peduncles - ascending & descending fiber tracts

      3 - Origin of two cranial nerves (III or oculomotor & IV or trochlear)

      1- posterior medullary velum, 2 - choroid plexus, 3 - cisterna cerebellodellaris of subarachnoid cavity, 4 - central canal,
      5 - corpora quadrigemina , 6 - cerebral peduncle, 7 - anterior medullary, 8 - ependymal lining of ventricle, & 9 - cisterna pontis of subarachnoid cavity
      (Source: Wikipedia).

        1 - Control of Autonomic Nervous System

      2 - Reception of sensory impulses from viscera

      3 - Intermediary between nervous system & endocrine system

      4 - Control of body temperature

      7 - Part of limbic system (emotions such as rage and aggression)

      8 - Part of reticular formation

        1 - portions located in the spinal cord, medulla, pons, midbrain, & hypothalamus

      2 - needed for arousal from sleep & to maintain consciousness

        1 - largest portion of the human brain

      • Cortex:
        • outer 2 - 4 mm of the cerebrum
        • consists of gray matter (cell bodies & synapses no myelin)
            • 'folded', with upfolded areas called gyri & depressions or grooves called sulci
            • consists of four primary lobes
                • functional areas include motor areas (initiate impulses that will cause contraction of skeletal muscles) (see A Map of the Motor Cortex), sensory areas (receive sensory impulses from throughout the body), and association areas (for analysis)

                'Forward' ( a ) and 'inverse' ( b ) model control systems for movement. According to 'instructions' from the premotor cortex (P), an area in the motor cortex (controller, or CT) sends impulses to the controlled object (CO a body part). The visual cortex (VC) mediates feedback from the body part to the motor cortex. The dashed arrow indicates that the body part is copied as an 'internal model' in the cerebellum. In the forward-model control system, control of the body part (CO) by the motor cortex (CT) can be precisely performed by referring to the internal feedback. In the inverse-model control system, feedback control by the motor cortex (CT) is replaced by the inverse model itself (Ito 2008).

                The rate of change in cortical thickness in children and teens of varying intelligence. Positive values indicate increasing cortical thickness, negative values indicate cortical thinning. The point of intersection on the x axis (0) represents the age of maximum cortical thickness (5.6 yr for average, 8.5 yr for high, and 11.2 yr for the superior intelligence group).

                Cortex matures faster in youth with superior IQs -- Children and teens with superior IQ's are distinguished by how fast the thinking part of their brains thickens and thins as they grow up. Magnetic resonance imaging (MRI) scans showed that their brain&rsquos outer mantle, or cortex, thickens more rapidly during childhood, reaching its peak later than in their peers &mdash perhaps reflecting a longer developmental window for high-level thinking circuitry. It also thins faster during the late teens, likely due to the withering of unused neural connections as the brain streamlines its operations. Although most previous MRI studies of brain development compared data from different children at different ages, Shaw et al. (2006) controlled for individual variation in brain structure by following the same 307 children and teens, ages 5-19, as they grew up. Most were scanned two or more times at two-year intervals. The resulting scans were divided into three equal groups and analyzed based on IQ test scores: superior (121-145), high (109-120), and average (83-108). The researchers found that the relationship between cortex thickness and IQ varied with age, particularly in the prefrontal cortex, seat of abstract reasoning, planning, and other &ldquoexecutive&rdquo functions. The smartest 7-year-olds tended to start out with a relatively thinner cortex that thickened rapidly, peaking by age 11 or 12 before thinning. In their peers with average IQ, an initially thicker cortex peaked by age 8, with gradual thinning thereafter. Those in the high range showed an intermediate trajectory (see below). Although the cortex was thinning in all groups by the teen years, the superior group showed the highest rates of change. &ldquoBrainy children are not cleverer solely by virtue of having more or less gray matter at any one age,&rdquo explained co-author J. Rapoport. &ldquoRather, IQ is related to the dynamics of cortex maturation.&rdquo The observed differences are consistent with findings from functional magnetic resonance imaging, showing that levels of activation in prefrontal areas correlates with IQ, note the researchers. They suggest that the prolonged thickening of prefrontal cortex in children with superior IQs might reflect an &ldquoextended critical period for development of high-level cognitive circuits.&rdquo Although it&rsquos not known for certain what underlies the thinning phase, evidence suggests it likely reflects &ldquouse-it-or-lose-it&rdquo pruning of brain cells, neurons, and their connections as the brain matures and becomes more efficient during the teen years. &ldquoPeople with very agile minds tend to have a very agile cortex,&rdquo said co-author P. Shaw.

                  • Medullary body:
                    • the 'white matter' of the cerebrum consists of myelinated axons
                    • types of axons include:
                      • commissural fibers - conduct impulses between cerebral hemispheres (and form the corpus callosum)
                            • projection fibers - conduct impulses in & out of the cerebral hemispheres
                            • association fibers - conduct impulses within hemispheres
                            • masses of gray matter in each cerebral hemisphere
                            • important in control of voluntary muscle movements

                              1 - consists of a group of nuclei + fiber tracts

                            2 - located in part in cerebral cortex, thalamus, & hypothalamus

                            • aggression
                            • fear
                            • feeding
                            • sex (regulation of sexual drive & sexual behavior)

                            The spinal cord extends from the skull (foramen magnum) to the first lumbar vertebra. Like the brain, the spinal cord consists of gray matter and white matter. The gray matter (cell bodies & synapses) of the cord is located centrally & is surrounded by white matter (myelinated axons). The white matter of the spinal cord consists of ascending and descending fiber tracts, with the ascending tracts transmitting sensory information (from receptors in the skin, skeletal muscles, tendons, joints, & various visceral receptors) and the descending tracts transmitting motor information (to skeletal muscles, smooth muscle, cardiac muscle, & glands). The spinal cord is also responsible for spinal reflexes.


                            Reflex- rapid (and unconscious) response to changes in the internal or external environment needed to maintain homeostasis

                              1 - receptor - responds to the stimulus
                              2 - afferent pathway (sensory neuron) - transmits impulse into the spinal cord
                              3 - Central Nervous System - the spinal cord processes information
                              4 - efferent pathway (motor neuron) - transmits impulse out of spinal cord
                              5- effector - a muscle or gland that receives the impulse from the motor neuron & carries out the desired response
                            • Somatic afferent
                            • Somatic efferent
                            • Visceral afferent
                            • Visceral efferent

                            Somatic efferent neurons are motor neurons that conduct impulses from the spinal cord to skeletal muscles. These neurons are multipolar neurons, with cell bodies located in the gray matter of the spinal cord. Somatic efferent neurons leave the spinal cord through the ventral root of spinal nerves.

                            Visceral afferent neurons are sensory neurons that conduct impulses initiated in receptors in smooth muscle & cardiac muscle. These neurons are collectively referred to as enteroceptors or visceroceptors. Visceral afferent neurons are unipolar neurons that enter the spinal cord through the dorsal root & their cell bodies are located in the dorsal root ganglia.

                            • Visceral efferent 1 (also called the preganglionic neuron) is a multipolar neuron that begins in the gray matter of the spinal cord, which is where its cell body is located. This neuron leaves the cord through the ventral root of a spinal nerve, leaves the spinal nerve via a structure called the white ramus, then ends in an autonomic ganglion (either sympathetic or parasympathetic). In the ganglion, the visceral efferent 1 neuron synapses with a visceral efferent 2 neuron.
                            • Visceral efferent 2 (also called the postganglionic neuron) is also a multipolar neuron and it begins in the sympathetic ganglion (which is where its cell body is located). Visceral efferent 2 neurons may exit the ganglion through the gray ramus, then proceed to some visceral structure (smooth muscle, cardiac muscle, or gland).

                            The 4 types of peripheral neurons: somatic afferent (top right), somatic efferent (bottom right),
                            visceral afferent (top left), and visceral efferent (bottom left).

                              1 - entirely motor (consisting of the visceral efferent fibers)

                            • sympathetic neurons leave the central nervous system through spinal nerves in the thoracic & lumbar regions of the spinal cord
                            • parasympathetic neurons leave the central nervous system through cranial nerves plus spinal nerves in the sacral region of the spinal cord

                            Autonomic Nervous System - control of involuntary muscle

                            3 - impulses always travel along two neurons: preganglionic & postganglionic

                            4 - Chemical transmitters - all autonomic neurons are either cholinergic or adrenergic

                            Dorsal root fibres - Biology

                            The degeneration of cut, lumbosacral dorsal roots was traced by means of a silver method to the various sites of termination in the spinal cord of the cat. Particular attention was given to the pattern and distribution of dorsal root fibres terminating on motor cells. An attempt was made to correlate the synaptic organization of these monosynaptic pathways with the presence and distribution of short latency, direct excitation and inhibition (measured on the ventral roots) in comparable segments of the cord. Short latency excitation was found in the lower sacral segments to be correlated with dorsal root fibres terminating on cell bodies and dendrites of the motoneurons. Direct inhibition, largely or entirely uncontaminated by excitation, was identified in lower lumbar and upper and lower sacral segments. In these sites the terminal degeneration of the responsible dorsal root was limited to the dendrites and did not reach the cell bodies of the motoneurons. This consistent correlation between the spatial distribution of direct inhibition and terminals on motor dendrites suggests that this inhibition is monosynaptically and dendritically mediated, at least in part. Certain other interpretations are considered and relevant evidence obtained from intracellular microelectrodes placed in lower sacral motoneurones which were excited by ipsilateral and inhibited by contralateral dorsal root stimulation is discussed. Here, uncontaminated, monosynaptic excitation could be correlated with synaptic terminals on both cell bodies and dendrites of motoneurones.

                            The distribution of dorsal root fibres on motor cells in the lumbosacral spinal cord of the cat, and the site of excitatory and inhibitory terminals in monosynaptic pathways

                            The degeneration of cut, lumbosacral dorsal roots was traced by means of a silver method to the various sites of termination in the spinal cord of the cat. Particular attention was given to the pattern and distribution of dorsal root fibres terminating on motor cells. An attempt was made to correlate the synaptic organization of these monosynaptic pathways with the presence and distribution of short latency, direct excitation and inhibition (measured on the ventral roots) in comparable segments of the cord. Short latency excitation was found in the lower sacral segments to be correlated with dorsal root fibres terminating on cell bodies and dendrites of the motoneurons. Direct inhibition, largely or entirely uncontaminated by excitation, was identified in lower lumbar and upper and lower sacral segments. In these sites the terminal degeneration of the responsible dorsal root was limited to the dendrites and did not reach the cell bodies of the motoneurons. This consistent correlation between the spatial distribution of direct inhibition and terminals on motor dendrites suggests that this inhibition is monosynaptically and dendritically mediated, at least in part. Certain other interpretations are considered and relevant evidence obtained from intracellular microelectrodes placed in lower sacral motoneurones which were excited by ipsilateral and inhibited by contralateral dorsal root stimulation is discussed. Here, uncontaminated, monosynaptic excitation could be correlated with synaptic terminals on both cell bodies and dendrites of motoneurones.

                            Use of In Vivo Single-fiber Recording and Intact Dorsal Root Ganglion with Attached Sciatic Nerve to Examine the Mechanism of Conduction Failure

                            Single-fiber recording is an effective electrophysiological technique that is applicable to the central and peripheral nervous systems. Along with the preparation of intact DRG with the attached sciatic nerve, the mechanism of conduction failure is examined. Both protocols improve the understanding of the peripheral nervous system's relationship with pain.

                            Single-fiber Recording plays an important role in recording the activities of nerve fibers. Especially activities transmitting peripheral sensation from receptive fields to neurons in dorsal root ganglion. In wavel of fiber recording, provides length of duration time with capacity to record responses to nature stimuli, and was later disturbance of the intercellular environment.

                            In a single fiber recording requires neutron automatic good for the situation. Therapist calls the requirement for the preparation of integrated DRG tests the sciatic nerve is integrated. The result of demo situation shows almost all the details of nerves in good, physical decal stage.

                            And third, entire DRG preparation as are integrated. To begin this procedure, prepare and disinfect all surgical instruments prior to surgery. Then prepare one to two liters of normal Ringer's extracellular solution and store at four degrees Celsius until use.

                            To expose the sciatic nerve trunk for recording, first, cut open the anesthetized rat's skin and muscles on the dorsal part of the thigh. Then, perform a blunt dissection along the femoral biceps. Carefully isolate the sciatic nerve trunk using ophthalmic scissors and a glass separation needle, and keep the tissue moist using Ringer's solution.

                            Next, fix the animal on a home-made metal hoop by sewing the skin into the slot around it. Pull the skin up slightly to establish a fluid bath. Expose one centimeter of sciatic nerve trunk at the proximal side.

                            Place a small, brown platform under the nerve trunk to enhance the contrast in order to observe the fine nerve trunk clearly. Subsequently, apply some warm liquid paraffin on the top of the nerve trunk to prevent drying of the fiber surface. Remove the fluid if there is an exudation around the nerve trunk.

                            To perform recording, select the platinum filament as the recording electrode. Eat and create a small hook at the very end. Afterward, attach the electrode to a micromanipulator.

                            In the bath, place a reference electrode next to the subcutaneous tissue. Split the spinal dura and the Pia mater and obtain the sciatic nerve. Under a stereo-microscope at 25%magnification, pick up a fine fascicle and suspend the approximal end of the axon on the hook of the recording electrode.

                            Identify the receptive field of a single, nonconceptive c fiber using a mechanical simulis and thermal stimulus. If the firing of the nerve fiber responds to the mechanical stimuli and hot water, then consider it as a polymoto, nonconceptive c fiber. Next, insert two needle stimulus electrodes with a two millimeter interval into the skin of the identify field for the delivery of the electrical stimuli.

                            Display the wave form of an action potential on the oscilloscope, and employ computer a d-board with a signal sampling rate of 20 kilohertz. Then, record the spikes using data acquisition software and analyze it later with professional software. To measure conduction failure, deliver the repetitive electrode stimuli in different frequencies to a c fiber for 60 seconds.

                            Allow a 10 minute interval for the fiber to relax between stimuli. Then, calculate the ratio of the number of failures to the number of delivered repetitive stimulus pulses and multiply by 100%to obtain the degree of conduction failure. To expose the dorsal root ganglion, first cut open the skin from the midline of the back at the l4 to l5 segment.

                            Next, remove the muscles spine process vertebral bor and transverse process using a bone rongeur, and expose the spinal cord NDRG body. Cover the exposed spinal cord, NDRG, with cotton soaked with normal Ringer's extracellular solution to maintain neural activity. Stop the bleeding and remove the blood as necessary.

                            Subsequently, using ophthalmic scissors, remove l4 to s1 bone structure above the vertebral foramen in order to expose the DRG and connected spinal nerve. Make a cut on the skin to expose the sciatic nerve at the middle thigh. Separate and disconnect the sciatic nerve from the distal end of the nerve where it goes inside the muscle.

                            And ligate the nerve trunk with surgical line at the end of the nerve prior to cutting. Then, separate the sciatic nerve from the underlying connective tissue by lifting the nerve ligation point. Remove for dura from the spinal cord, and separate the DRG from the underlying connective tissue until it reaches the adjacent part of the sciatic nerve.

                            Thus, isolate the whole preparation of DRG with an attached sciatic nerve. To clear the surface of the DRG, at 4x magnification, carefully remove the spinal dura on the surface of l4 to l6 DRG using tweezers. Place the DRG with attached sciatic nerve in a glass tube containing one milliliter of mixed enzymes.

                            Digest in a 37 degree Celsius water bath for 15 minutes. After 15 minutes, lift the end of the surgical line and move the preparation to a dish filled with normal Ringer's extracellular solution to wash out the enzyme. Then, transfer the digested DRG to a container filled with oxygenated Ringer's extracellular solution for recording.

                            To perform recording, prepare intracellular solution, and store it at zero degree Celsius until use. Using a slice anchor, stabilize the ganglia and connect the nerve end to a suction stimulating electrode. At 40x magnification, visualize and select a DRG neuron with a water emersion objective.

                            Fold an electrode and fill it with intracellular solution. Attach the electrode on the holder, and apply positive pressure in the pipet with a final resistance of four to seven megaohms. Next, bring the electrode to the cell surface.

                            Then, apply negative pressure to the pipet to form a seal. Once a gigaohm seal is reached, set the membrane potential at about minus 60 millivolts and establish all cell recording mode. Subsequently, deliver repetitive stimuli of 5 to 50 hertz to the sciatic nerve the through the suction electrode to screen for conduction failure.

                            Measure the amplitude of AHP from baseline to peak and the 80%AHP duration. This figure shows the original consecutive recordings of single c5 re-firings from rats in response to 10 hertz electrical stimulation. Every twentieth sweep is shown and displayed top to bottom.

                            The insert shows a representative action potential. Here are the recordings of single c fibers from CFA injected rats in response to the same stimulation as the previous panel. This figure shows the continuous recordings of series firing responses to five hertz stimulation under control conditions, or administration of different concentration of ZD7288 in a small diameter DRG neuron from CFA rated rats.

                            The insets show expanded traces for the specified recording periods. Dark spots represent spike failures. The AHP showed a bigger rising slope in the control.

                            While a smaller rising slope was observed after 125 micromolars at ZD7288 application. When a time single fiver recording, I think it's important to cut the fiber will maintaining the animals is good any safety condition. And microenvironment around the neutron.

                            The combination of single fiber recording and application of intact DRG attached with the sciatic nerve, improved our understanding of the peripheral nervous system pertaining to pain.


  1. Diramar

    I will not begin to speak on this theme.

  2. Kazizilkree

    The post is good, I read and saw many of my mistakes, but did not see the main one :)

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