Neuroanatomy: Descending Tracts Overview

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Questions and Answers

What is the primary function of upper motor neurons (UMNs)?

Control movement and inhibit muscle tone. (correct)

Receive sensory input from the body.

Directly innervate muscle tissue.

Facilitate voluntary movement without inhibition.

Which spinal cord tract is primarily responsible for sending signals from the brain to skeletal muscles?

Spinothalamic tract

Cuneate column

Corticospinal tract (correct)

Gracile column

What is the approximate length of the spinal cord in adults?

30 cm

45 cm (correct)

75 cm

60 cm

What type of paralysis is associated with upper motor neuron lesions?

Spastic paralysis Signup and view all the answers

Which section does the spinal cord end in adults?

L2 Signup and view all the answers

Where do the lateral corticospinal tracts decussate?

At the medulla (pyramids) Signup and view all the answers

What type of information is conveyed by the corticospinal (pyramidal) tract?

Motor information Signup and view all the answers

Which term describes the type of paralysis that results from lower motor neuron (LMN) lesions?

Flaccid paralysis Signup and view all the answers

What role do lower motor neurons (LMNs) play in the nervous system?

Control movement by innervating skeletal muscle directly. Signup and view all the answers

What structural feature is associated with the enlargement of the spinal cord?

Increased volume of motor cells Signup and view all the answers

What distinguishes the corticobulbar tract from the corticospinal tract?

It primarily controls facial and head muscles. Signup and view all the answers

Which of the following is NOT a meningeal layer surrounding the spinal cord?

Coronary layer Signup and view all the answers

How many pairs of spinal nerves are there in the human body?

31 Signup and view all the answers

Which of the following statements about motor neuron lesions is incorrect?

Both UMN and LMN lesions do not affect sensory input. Signup and view all the answers

What is the primary function of the spinal cord?

Carrying signals between the brain and the body Signup and view all the answers

Which tract is responsible for the transmission of pain and temperature sensations?

Spinothalamic tract Signup and view all the answers

Where do most corticospinal fibers decussate?

In the brainstem at the pyramids Signup and view all the answers

What is the primary function of the corticospinal tract?

To initiate voluntary skilled movements Signup and view all the answers

Which cranial nerves are associated with the corticonuclear tract?

CN III, IV, V, VI, VII, IX, X, XI, XII Signup and view all the answers

What occurs to axons in the anterior segment of the corticospinal tract?

They remain ipsilateral until they reach the spinal cord Signup and view all the answers

What role does the anterior corticospinal tract primarily serve?

Motor innervation to proximal portions of extremities Signup and view all the answers

What type of information does the spinothalamic tract primarily carry?

Pain, temperature, itch, and light touch sensations Signup and view all the answers

Which of the following statements about motor fibers of cranial nerves is NOT true?

They primarily carry sensory impulses. Signup and view all the answers

What do axons in the corticospinal tract primarily originate from?

The motor cortex of the brain Signup and view all the answers

What do the anterior (ventral) rootlets primarily transmit?

Motor messages Signup and view all the answers

Which structure is responsible for the transmission of sensory information to the CNS?

Dorsal root ganglia Signup and view all the answers

What is the significance of the Cauda Equina?

It contributes to lumbar punctures and spinal anaesthetics. Signup and view all the answers

What are the primary components of white matter in the spinal cord?

Axons and nerve fibers Signup and view all the answers

Which lamina is specifically associated with motor neurons to skeletal muscle?

Lamina IX Signup and view all the answers

Which fibers would be classified as ascending tracts in the spinal cord?

Pathways that relay pain and temperature sensations Signup and view all the answers

What type of grey matter structure is found in the spinal cord?

Butterfly ('H') shaped structure Signup and view all the answers

What are the three columns of white matter found in the spinal cord?

Dorsal, Ventral, Lateral Signup and view all the answers

Which tract is responsible for conveying proprioceptive information to the cerebellum?

Spinocerebellar tract Signup and view all the answers

Which sensory modalities are conveyed by the lateral pathway of the spinothalamic tract?

Pain and temperature Signup and view all the answers

Where do the dorsal column tracts decussate?

At the medulla Signup and view all the answers

What is the role of the Artery of Adamkiewicz?

Supplies the anterior spinal cord Signup and view all the answers

How many neurons are involved in the pathway for pain sensation from the primary afferent neuron to the somatosensory cortex?

3 Signup and view all the answers

What type of sensory information does the gracile tract carry?

Touch and vibration Signup and view all the answers

What is the primary anatomical feature of venous drainage in the spine?

Numerous and tortuous, valveless veins Signup and view all the answers

Which statement is true regarding spinal sensory pathways?

Sensory modalities have their own distinct pathways and decussation points. Signup and view all the answers

Study Notes

Descending Tracts

Motor signals from the brain to lower motor neurons
Found in the white matter of the spinal cord, in the columns (anterior, lateral, posterior)
Corticospinal Tract
- Lateral Corticospinal Tract: Decussates (crosses over) in the medulla oblongata (pyramids), controls movement of distal extremities
- Anterior Corticospinal Tract: Decussates at the spinal cord segment, controls movement of axial muscles, ( trunk and proximal limbs)

Upper Motor Neurons

Located in the cerebral cortex and brainstem.
Responsible for planning, initiating, and controlling voluntary movement and regulating muscle tone.
Example: The motor cortex is an example of UMNs, which control muscle contraction through the corticospinal tract.

Lower Motor Neurons

Located in the anterior horn of the spinal cord and cranial nerve nuclei in the brainstem.
Directly innervate skeletal muscles.
Responsible for carrying the final signal to muscles for contraction.
Example: If a lower motor neuron is damaged, the muscle it innervates will become weak or paralyzed.

UMN and LMN Lesions

UMN Lesions: Result in spastic paralysis (increased muscle tone and hyperreflexia, no muscle wasting). Example: stroke.
LMN Lesions: Cause flaccid paralysis (decreased muscle tone and reflexes, long-term muscle wasting), Example: Spinal cord injury or nerve damage.
Spinal Cord and Brainstem Lesions: Damage both LMNs at the level of the lesion and UMNs of all levels below the lesion, also leading to loss of all sensory input at and below the level of the lesion.

Motor Decussations

Most motor tracts cross over to the opposite side of the body, called decussation.
The lateral corticospinal tract decussates in the medulla oblongata (pyramids).
The anterior corticospinal tract decussates at the level of the spinal cord segment.

Corticobulbar Tract

Controls voluntary movements of the head and face.
Synapses with nuclei of cranial nerves III, IV, V, VI, VII, IX, X, XI, and XII.
Example: The corticobulbar tract is responsible for facial expressions, chewing, and swallowing.

Spinothalamic Tract

Carries sensory information about pain, temperature, itch, and crude touch from the body to the brain.
Lateral Spinothalamic Tract: Perceives pain and temperature.
Anterior Spinothalamic Tract: Perceives crude touch.

Spinal Cord

An elongated cylindrical structure located in the vertebral canal.
Extends from the medulla oblongata to L2 in adults (L3 in newborns).
Enlargements: Cervical enlargement (for innervation of the upper limbs) and lumbosacral enlargement (for innervation of the lower limbs).

Meninges

Dura Mater: Outermost layer, tough and fibrous.
Arachnoid Mater: Middle layer, delicate and web-like.
Pia Mater: Innermost layer, thin and vascular, tightly adhered to the spinal cord.

Spinal Nerves

31 pairs of spinal nerves, each consisting of an anterior (ventral) root (motor) and a posterior(dorsal) root(sensory).
The anterior and posterior roots join to form a mixed spinal nerve, which exit the vertebral canal through intervertebral foramen.
Spinal nerves branch into ventral and dorsal rami, innervating different areas of the body.

Cauda Equina

Lower nerve roots extend downwards from the conus medullaris, resembling a horse's tail.
Important for lumbar punctures, epidural anaesthesia, and spinal anaesthesia.

Grey Matter

Located centrally in the spinal cord, resembling a butterfly or 'H' shape.
Contains cell bodies of neurons.
Dorsal Horns: Receive sensory information and relay it to the brain.
Ventral Horns: Contain motor neurons that send signals to muscles.

White Matter

Surrounds the grey matter in the spinal cord.
Contains bundles of axons, which transmit information to and from the brain.
Arranged into columns (anterior, lateral, posterior).
Ascending Tracts: Sensory pathways, carry information from the body to the brain.
Descending Tracts: Motor pathways, carry information from the brain to the body.

Spinal Cord Arterial Supply

Anterior Spinal Artery: Supplies the anterior two-thirds of the spinal cord.
Posterior Spinal Arteries: Supply the posterior one-third of the spinal cord.
Artery of Adamkiewicz: Largest segmental artery, supplies the lower spinal cord, a critical artery.

Spinal Cord Venous Drainage

Venous drainage is via the internal vertebral venous plexus.
Valveless, allowing for drainage in both directions (towards the heart and towards the brain).

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Description

This quiz explores descending tracts in neuroanatomy, focusing on motor signals from the brain to lower motor neurons. It highlights the corticospinal tract and distinguishes between upper and lower motor neurons, including their roles in muscle movement and control.