Comparison between tract and nerve

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  Comparison between tract and nerve Nerve Nerve contain bundle of axons (nerve fibers) in the peripheral nervous system (PNS) that transmits signals between the central nervous system (CNS) and other parts of the body. It is the most important part of peripheral nervous system Location: Peripheral nervous system. Structure: Made of axons, connective tissue layers (endoneurium: axon is surrounded by it , perineurium: bundle of axons are surrounded by it, epineurium: whole nerve trunk is surrounded by it), and blood vessels. It gets myelination by Schwann cell   Function: Carries sensory signals to the CNS (afferent) from peripheral part of body or motor signals carry from from the CNS (efferent) to target organs like skeletal muscle, cardiac muscle, smooth muscle or glands Example: Sciatic nerve, median nerve, except optic nerve (though optic nerve is technically part of CNS in develop...
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Difference between ventral and dorsal root of spinal nerve

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Difference between ventral and dorsal root of spinal nerve

The ventral and dorsal roots of spinal nerves are important  structures in the peripheral nervous system that connect the spinal cord to the body. They give motor and sensory supply of very large areas of body .

1. Ventral Root (Anterior Root) is composed of motor (efferent) fibers that originate from the anterior horn of the spinal cord which developed from basal plate of mantle layer of neural tube which carries impulses from the spinal cord to muscles and glands. It contain  two  functional components of motor parts : General somatic efferent give motor supply to the skeletal muscle and general visceral efferent give motor supply to smooth muscle cells of viscera and gland. This root controls voluntary and involuntary movements. Damage to the ventral root leads to motor deficits, such as paralysis.

2. Dorsal Root (Posterior Root) is composed of sensory (afferent) fibers that originate from sensory neurons in the dorsal root ganglion (DRG) which develops from alar plate of mantle layer of neural tube which transmits sensory information from the body to the spinal cord. It contain two functional components for sensory function general somatic afferent which collect sensory information from the skin and general visceral afferent collect sensory information or visceral pain from the viscera which includes sensations like pain, temperature, touch, and proprioception. Damage to the dorsal root results in sensory loss in the affected area.

Dorsal Root Ganglion (DRG) is ocated within the dorsal root.which contains cell bodies of sensory neurons and its functions as a relay center for sensory information.

Formation of Spinal Nerve

  • The ventral and dorsal roots unite at the intervertebral foramen to form a spinal nerve.
  • The spinal nerve is a mixed nerve, containing both motor and sensory fibers.
  • It later divides into the ventral and dorsal rami to supply different parts of the body.

Ventral root of spinal nerve
Dorsal root of spinal nerve
This root arises from the ventral horn of gray matter of  spinal cord
This root arises from the dorsal horn of gray matter of  spinal cord
It bears no ganglion
It bears posterior root ganglion
Functionally it is motor
Functionally it is sensory
Most of the ventral root contain general somatic efferent fibres but in thorocic and upper lumbar spinal nerves contain pre-ganglionic sympathetic fibres
Dorsal root contain general somatic afferent and general visceral afferent fibres. It contain no efferent fibres
Each ventral root is attached to the spinal cord by a series of rootlets that emerge from the ventrolateral sulcus of the spinal cord. Unlike the dorsal root fibers that are arranged in a neat line at their emergence from the spinal cord, ventral root fibers form an elliptical area named the anterior root exit zone (AREZ).
Each dorsal root is attached to the spinal cord by a series of rootlets arranged in a line at the dorsal root entry zone (DREZ). the length of the DREZ varies from 10.7 mm  to 12.7 mm
Ventral  roots are smaller  than the dorsal  roots
Dorsal roots are larger than the ventral roots, with thicker and more numerous fibers.
Nerve fibres mainly supply skeletal muscle of limb, ventolateral muscles of body wall , perineum, viscera of thorax and abdomen, gland 
The dorsal roots collect sensory information  from the skin, subcutaneous and deep tissues, and viscera of thorax and abdomen .

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