DCML(dorsal column medial lemniscal):Rhomberg's test,posterior cord syndrome,Friedrich's Ataxia

Summary

The DCML (Dorsal Column Medial Lemniscal) system is a crucial pathway in the nervous system responsible for sensations such as fine touch, pressure, vibration, proprioception, stereognosis, and two-point discrimination. The system involves three neurons: first-order neurons carry signals from receptors to the medulla, second-order neurons cross to the opposite side and project to the thalamus, and third-order neurons send sensory signals to the somatosensory cortex. Disorders like posterior cord syndrome and Friedreich's ataxia, which involve loss of myelin and sensory coordination, highlight the importance of this pathway for movement and balance.

Takeaways

• 😀 The DCML (Dorsal Column-Medial Lemniscal) system is responsible for transmitting sensations like fine touch, pressure, proprioception, vibration, stereognosis, and two-point discrimination.
• 😀 Fine touch is primarily carried by the DCML system, distinguishing it from crude touch, which is handled by other sensory pathways.
• 😀 The DCML system starts at the receptors in the skin, with specific sensory receptors like Meissner's discs, Pacinian corpuscles, and muscle spindles, which detect various sensations.
• 😀 The first order neurons in the DCML system transmit sensory information from the receptors to the spinal cord, specifically to the posterior horn, and ascend to the medulla via the posterior column.
• 😀 The DCML system uses two types of fibers: gracile fibers for lower limb sensations and cuneate fibers for upper limb sensations.
• 😀 At the medulla, the fibers cross to the opposite side (decussate) and form the second order neurons, which then ascend to the thalamus, where they end at the VPN nucleus.
• 😀 The third order neurons in the DCML system project from the thalamus to the post-central gyrus of the cerebral cortex, allowing the brain to process sensory information.
• 😀 If there is damage to the DCML system, sensory coordination is lost, which can lead to difficulties with movement, balance, and fine touch recognition.
• 😀 The Rhomberg test is used to diagnose DCML disorders. A positive test suggests proprioceptive issues, which are indicative of DCML damage.
• 😀 Common disorders associated with DCML dysfunction include **posterior cord syndrome** and **Friedreich’s ataxia**, the latter being a genetic disorder that causes progressive ataxia and often presents with hypertrophic cardiomyopathy.

Q & A

What is the DCML system and why is it called 'dorsal column'?

The DCML system, or Dorsal Column Medial Lemniscal System, is a sensory pathway that transmits fine touch, pressure, proprioception, vibration, stereognosis, and two-point discrimination sensations. It's called 'dorsal column' because the sensory fibers travel through the dorsal column of the spinal cord.

What are the six functions of the DCML system?

The six functions of the DCML system are: 1) Fine touch, 2) Pressure, 3) Proprioception (joint sense), 4) Vibration, 5) Stereognosis (identifying objects by touch with eyes closed), and 6) Two-point discrimination.

What is the role of proprioception in the DCML system?

Proprioception is the sense that informs the brain of the position of joints and limbs in space. It helps coordinate movements by informing the brain about the body's posture, allowing for balance and motor control.

How does the DCML system transmit sensory information from the skin to the brain?

The sensory information from the skin is received by receptors such as Meissner's discs and Pacinian corpuscles. The first-order neurons carry the signals to the posterior horn of the spinal cord, ascend through the dorsal column, and terminate in the medulla in the gracile or cuneate nuclei. From there, second-order neurons cross to the opposite side and travel to the thalamus, where third-order neurons project to the somatosensory cortex in the brain.

What is the significance of the gracile and cuneate fibers in the DCML system?

Gracile fibers carry sensory information from the lower limbs, while cuneate fibers carry sensory information from the upper limbs. These fibers ascend through the spinal cord's dorsal column and eventually terminate in their respective nuclei in the medulla.

What happens to the fibers at the level of the medulla in the DCML system?

At the level of the medulla, the sensory fibers (gracile and cuneate) cross to the opposite side of the body, a process known as decussation. This crossing of fibers is essential for the system's function in transmitting sensations from the opposite side of the body to the brain.

How are the sensory fibers arranged in the DCML system?

In the DCML system, the fibers from the lower limbs are most medial, and those from the upper limbs are lateral. This organization is maintained throughout the spinal cord, medulla, and thalamus, reflecting the somatotopic arrangement of sensory input.

What clinical test is used to diagnose DCML involvement, and how is it conducted?

The Romberg test is used to diagnose DCML involvement. It tests a person's ability to maintain balance with their eyes closed. If the person loses balance when their eyes are closed, this suggests a loss of proprioceptive input, indicating a potential DCML disorder.

What are some common disorders associated with DCML dysfunction?

Common disorders associated with DCML dysfunction include posterior cord syndrome (due to damage or blockage of the posterior spinal artery) and Friedreich's ataxia, a genetic disorder that causes progressive demyelination in the spinal cord, affecting the posterior column and leading to sensory and motor coordination problems.

What is Friedreich's ataxia, and how is it related to the DCML system?

Friedreich's ataxia is an autosomal recessive genetic disorder caused by a defect in chromosome 9, leading to a deficiency of frataxin. This results in demyelination of nerve fibers in the spinal cord, particularly in the posterior column, which impacts the DCML system's ability to transmit sensory information effectively. It is often associated with hypertrophic cardiomyopathy.