Ascending Spinal Tracts Overview

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Questions and Answers

What are the three types of neurones involved in ascending spinal tracts?

First-order, second-order, and third-order neurones.

Where does the first-order neurone enter the spinal cord?

Through the dorsal root of a spinal nerve.

What is the role of the second-order neurone in the sensory pathway?

It decussates to the opposite side of the CNS and ascends to the thalamus.

Identify the two main tract systems in the spinal cord that follow the three-neurone pattern.

<p>The dorsal columns and the spinothalamic tracts.</p> Signup and view all the answers

What sensations are primarily carried by the dorsal columns?

<p>Proprioception and fine touch.</p> Signup and view all the answers

Where are the fasciculus gracilis and the fasciculus cuneatus located?

<p>Between the dorsal median sulcus and the dorsal horn.</p> Signup and view all the answers

Which part of the central nervous system does the third-order neurone connect to?

<p>The somatosensory cortex in the parietal lobe.</p> Signup and view all the answers

Which sensory modality does the first-order neurone transmit to the spinal cord?

<p>Pain, thermal, tactile, muscle, and joint sensations.</p> Signup and view all the answers

What is the role of the fasciculus cuneatus in the nervous system?

<p>The fasciculus cuneatus conveys information from the upper limb to the brain and is involved in proprioception.</p> Signup and view all the answers

Describe the pathway taken by first-order neurones from the fasciculus cuneatus.

<p>First-order neurones enter through the upper thoracic and cervical dorsal roots, ascend uninterrupted to the medulla oblongata.</p> Signup and view all the answers

What happens to second-order neurones after they receive signals in the medulla?

<p>They decussate as internal arcuate fibres and ascend through the brainstem as the medial lemniscus.</p> Signup and view all the answers

Explain the impact of tabes dorsalis on proprioception.

<p>Tabes dorsalis causes loss of proprioception, leading to a high steppage and unsteady gait.</p> Signup and view all the answers

How does subacute combined degeneration of the spinal cord manifest?

<p>It results in sensory ataxia and weakness due to degeneration of the dorsal columns and lateral columns.</p> Signup and view all the answers

What is the function of the spinothalamic tract?

<p>The spinothalamic tract carries information related to pain, thermal sensations, and non-discriminative touch.</p> Signup and view all the answers

What are the consequences of damage to the fasciculus cuneatus in multiple sclerosis?

<p>Damage leads to loss of proprioception in the hands and fingers, causing decreased dexterity.</p> Signup and view all the answers

Where do third-order thalamocortical neurones project in the nervous system?

<p>They project to the somatosensory cortex located in the postcentral gyrus of the parietal lobe.</p> Signup and view all the answers

What is referred pain and how does it relate to visceral and somatic pain?

<p>Referred pain is a phenomenon where pain originating from visceral structures is perceived in other body parts. It occurs due to the convergence of somatic and visceral afferents on the same dorsal horn neurons, leading to misinterpretation of the pain source.</p> Signup and view all the answers

Describe the organization of the spinocerebellar tracts and their role in the nervous system.

<p>The spinocerebellar tracts consist of four pathways, with two carrying information from the lower limb and two from the upper limb. They relay proprioceptive and tactile information to the cerebellum for posture and movement coordination.</p> Signup and view all the answers

Identify the two main types of spinocerebellar tracts and their locations in the spinal cord.

<p>The two main types are the dorsal spinocerebellar tract and the ventral spinocerebellar tract. The dorsal tract is located at the dorsolateral surface, while the ventral tract is at the ventrolateral surface of the spinal cord.</p> Signup and view all the answers

Where do the fibres of the dorsal spinocerebellar tract originate, and how do they ascend?

<p>Fibres of the dorsal spinocerebellar tract originate from Clarke's column in the thoracic nucleus at spinal levels T1–L2 and ascend ipsilaterally to the cerebellum via the inferior cerebellar peduncle.</p> Signup and view all the answers

What is the primary function of the spinocerebellar system?

<p>The primary function of the spinocerebellar system is to convey information about body position and movement from sensory receptors to the cerebellum, facilitating balance and coordination.</p> Signup and view all the answers

Explain the difference between the ascending pathways of the dorsal and ventral spinocerebellar tracts.

<p>The dorsal spinocerebellar tract ascends ipsilaterally while the ventral spinocerebellar tract decussates and ascends contralaterally. This distinction affects how proprioceptive information is processed in relation to body coordination.</p> Signup and view all the answers

What role do mechanoreceptors like Golgi tendon organs play in the spinocerebellar tracts?

<p>Mechanoreceptors such as Golgi tendon organs provide sensory information about muscle tension and joint position to the spinocerebellar tracts. This information is crucial for the cerebellum's role in motor control and coordination.</p> Signup and view all the answers

Discuss the significance of somatotopic organization in the localization of pain.

<p>Somatotopic organization allows for precise localization of somatic pain due to distinct pathways in the ascending neural structures. In contrast, the poor localization of visceral pain is attributed to this organization being less defined.</p> Signup and view all the answers

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Flashcards

Dorsal Columns (aka Posterior Columns)

Carries sensory information about touch, pressure, vibration, and proprioception from the body to the brain.

Fasciculus Cuneatus

The part of the dorsal column responsible for carrying sensory information from the upper body and limbs.

Fasciculus Gracilis

The part of the dorsal column that carries sensory information from the lower body and limbs.

Nucleus Cuneatus

Located in the medulla oblongata; the second-order neurons in this nucleus receive information from the fasciculus cuneatus.

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Nucleus Gracilis

Located in the medulla oblongata; the second-order neurons in this nucleus receive information from the fasciculus gracilis.

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Tabes Dorsalis

A neurological disorder that affects the dorsal columns, impairing proprioception and leading to ataxia.

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Subacute Combined Degeneration of the Spinal Cord

A neurological disorder caused by vitamin B12 deficiency, impacting both the dorsal and lateral columns.

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Spinothalamic Tract

Carries sensory information about pain, temperature, and crude touch from the body to the brain.

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Ascending Spinal Tracts

Ascending spinal tracts carry sensory information from the body to the brain. They're like roads that deliver messages to the brain about touch, pain, temperature, and more.

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First-Order Neuron

These neurons are the first in the chain of sensory information transmission. They receive sensory input from the body and carry it to the spinal cord.

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Second-Order Neuron

These neurons carry sensory information from the spinal cord or brainstem to the thalamus, a relay center in the brain.

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Third-Order Neuron

These neurons are the last link in the chain, carrying information from the thalamus to the cerebral cortex, the brain region responsible for conscious sensory perception.

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Dorsal Columns

The dorsal columns are bundles of nerve fibers located in the spinal cord. They carry proprioception (sense of joint position and movement) and fine touch information.

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Proprioception

This is the ability to perceive the position and movement of our body parts without looking at them. It involves our sense of joints, muscles, and tendons.

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Referred pain

The phenomenon where visceral pain is experienced in a different part of the body, often a somatic area.

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Spinocerebellar tracts

Ascending pathways that carry sensory information from the body to the cerebellum for the control of posture and coordination.

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Clarke's column

A group of cells in the spinal cord that receive sensory information from the lower limb and relay it to the cerebellum.

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Dorsal spinocerebellar tract

The ascending pathway that carries sensory information from the lower limb to the cerebellum on the same side of the body.

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Ventral spinocerebellar tract

The ascending pathway that carries sensory information from the lower limb to the cerebellum on the opposite side of the body.

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Inferior cerebellar peduncle

The part of the cerebellum that receives sensory information from the dorsal spinocerebellar tract.

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Superior cerebellar peduncle

The part of the cerebellum that receives sensory information from the ventral spinocerebellar tract.

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Posture and coordination control

Sensory information that reaches the cerebellum via the spinocerebellar tracts is used for...

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Study Notes

Ascending Spinal Tracts

  • Carry sensory information from pain, temperature, tactile, muscle, and joint receptors to the brain.
  • Some information goes to conscious areas (cerebral cortex), while some goes to subconscious areas (e.g., cerebellum).
  • Pathways to conscious levels have similar characteristics.
  • The pathways consist of three neurons:
    • First-order neuron: Enters spinal cord via dorsal root, cell body in dorsal root ganglion. Central process branches extensively, forming connections for spinal reflexes and coordination.
    • Second-order neuron: Cell body in spinal cord or medulla oblongata. Axon crosses over (decussates) to the opposite side and ascends to the thalamus.
    • Third-order neuron: Cell body in the thalamus; axon projects to somatosensory cortex in the parietal lobe of the opposite cerebral hemisphere.

Dorsal Columns

  • Located between the dorsal median sulcus and dorsal horn.
  • Composed of fasciculus gracilis (medial) and fasciculus cuneatus (lateral).
  • Carry information about proprioception (movement/joint position) and discriminative touch.
  • Axons of primary afferent neurons enter the cord through dorsal roots.
  • Fasciculus gracilis carries information from lower limbs, fasciculus cuneatus from upper limbs.
  • Impulses travel to spinal cord without interruption (ipsilateral).
  • Synapse in medulla oblongata.
  • Axons decussate, forming the medial lemniscus.
  • Medial lemniscus terminates in ventral posterior (VP) nucleus of the thalamus.
  • Third-order neurons then project to somatosensory cortex.

Spinothalamic Tract

  • Also known as the anterolateral system.
  • Lies lateral and ventral to the ventral horn of the spinal gray matter.
  • Carries information related to pain, temperature, and non-discriminative (crude) touch and pressure.
  • Second-order neurons lie in the contralateral dorsal horn.
  • Axons cross over (decussate) in the ventral white commissure.
  • Ascends in the spinothalamic tract.
  • Terminates in the ventral posterior (VP) nucleus of the thalamus.
  • Third-order neurons project to the somatosensory cortex.
    • Organised somatotopically for high accuracy in locating sensory input.

Spinocerebellar Tracts

  • Carry sensory information from muscle spindles, Golgi tendon organs, and tactile receptors to the cerebellum for posture and movement coordination.
  • Mostly consist of two neurons:
  • First order neurons terminate in the dorsal horn
  • Second order neurons ascend to cerebellum, (mostly ipsilateral for dorsal tracts, and contralateral for ventral tracts).
  • Includes dorsal and ventral spinocerebellar tracts (lower limbs), and cuneocerebellar and rostral spinocerebellar (upper limbs).
  • Terminate in the cerebellar cortex as mossy fibers, mainly in the vermis and paravermal areas.

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