Clinical Neuroscience Week 4

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Questions and Answers

Which of the following correctly describes the function of Group Aα axons?

Innervate autonomic structures (presynaptic)

Innervate extrafusal muscle fibers (correct)

Innervate intrafusal muscle fibers

Innervate spindles

What is a dermatome?

A group of muscles that are innervated by a single nerve root

An area of skin innervated by axons that enter the spinal cord through a single dorsal root (correct)

A bundle of nerve fibers that extend from the spinal cord to various parts of the body

A single nerve root that produces a specific motion

Which of the following is a characteristic of a lower motor neuron (LMN) lesion?

Hyperactive reflexes

Global sensory loss

Muscle weakness in a specific region (correct)

Hypotonia

What type of axons are responsible for carrying sensory information from the spindles and Golgi tendon organs?

Group Ia; Ib (C) Signup and view all the answers

Which of the following is NOT a characteristic of the autonomic division of the peripheral nervous system?

Carries information from the skin to the brain (A) Signup and view all the answers

What type of axon is responsible for innervating intrafusal muscle fibers?

Group Aδ (D) Signup and view all the answers

Which of the following is a characteristic of a peripheral nerve lesion?

Specific sensory loss in a particular region (C) Signup and view all the answers

What is the function of Group C axons?

Innervate autonomic structures (postsynaptic) (C) Signup and view all the answers

Which of the following statements about myotomes is TRUE?

A myotome is a single nerve root that produces a specific motion (D) Signup and view all the answers

Which of the following is NOT a characteristic of upper motor neuron (UMN) lesions?

Hypotonia (D) Signup and view all the answers

Which of the following accurately describes the location of the substantia gelatinosa within the spinal cord?

It is located in the dorsal gray horn, involved in processing sensory information. (D) Signup and view all the answers

Which spinal cord region exhibits a greater amount of gray matter compared to the thoracic region, and why?

Cervical region; due to the need to accommodate for the arms and legs. (B) Signup and view all the answers

Which of the following tracts is NOT directly involved in transmitting sensory information to the brain?

Spinocerebellar tract (B) Signup and view all the answers

What is the primary function of the descending systems within the spinal cord?

Controlling and coordinating voluntary movements by sending signals to lower motor neurons. (A) Signup and view all the answers

Which of the following accurately describes the role of the basal ganglia in movement coordination?

They ensure the proper timing and initiation of movement sequences. (D) Signup and view all the answers

Which of the following accurately describes the relationship between the anterior spinal artery and motor function?

Damage to the anterior spinal artery is more likely to result in motor deficits. (A) Signup and view all the answers

Which of these spinal cord structures is specifically involved in the stretch reflex?

Muscle spindles (B) Signup and view all the answers

Which of the following is NOT a characteristic of the stretch reflex?

It is a polysynaptic reflex, requiring multiple synapses. (C) Signup and view all the answers

What is the primary reason for the decrease in white matter observed as you descend from the cervical to the sacral levels of the spinal cord?

The exit of tracts and their dispersal to target areas. (A) Signup and view all the answers

Which of the following accurately describes the role of the cerebellum in movement coordination?

It fine-tunes and coordinates ongoing movements based on sensory input. (A) Signup and view all the answers

What happens to the muscle when the sciatic nerve is injured?

Muscle begins to atrophy in a specific pattern. (B) Signup and view all the answers

What characterizes the reflexes when there is hyperreflexia?

Quick and exaggerated responses. (B) Signup and view all the answers

Which clinical application is specifically associated with progressive loss of muscle control?

Amyotrophic Lateral Sclerosis (ALS) (C) Signup and view all the answers

What is the typical prognosis for individuals diagnosed with ALS?

Only about 10% live more than ten years after diagnosis. (C) Signup and view all the answers

In the central nervous system, what happens to neurons after injury?

Scarring inhibits regeneration and contributes to neuronal death. (C) Signup and view all the answers

What is the primary role of Schwann cells in the peripheral nervous system after nerve injury?

To promote regrowth of the nerve and attract axons. (C) Signup and view all the answers

What defines Wallerian degeneration?

Degeneration of the distal part of the injured nerve. (B) Signup and view all the answers

In the context of nerve regeneration, what limits the effectiveness of central neuron recovery?

Scar formation and lack of growth factors. (B) Signup and view all the answers

What rehabilitation implication exists for individuals following peripheral nerve injury?

Muscle strengthening can occur depending on regeneration. (B) Signup and view all the answers

Which of the following factors may affect the onset of Amyotrophic Lateral Sclerosis (ALS)?

Genetic predisposition and environmental factors. (A) Signup and view all the answers

Which of these options correctly describes the location of the lateral horn in the spinal cord?

Exclusively found within the thoracic region. (C) Signup and view all the answers

What is the primary function of the dorsal column in the spinal cord?

Receiving sensory information from the body. (D) Signup and view all the answers

What is the significance of the enlargement of the grey matter in the cervical and lumbar regions of the spinal cord?

These regions are responsible for controlling more complex motor functions, requiring a larger number of motor neurons. (B) Signup and view all the answers

Which of the following statements accurately describes the anatomical relationship between spinal nerves and vertebrae in the thoracic, lumbar, and sacral regions?

Spinal nerves exit below their corresponding vertebrae in these regions. (C) Signup and view all the answers

Which of the following is NOT a characteristic of the cauda equina?

It is part of the spinal cord proper. (A) Signup and view all the answers

What is the main purpose of the gray commissure in the spinal cord?

To connect the left and right sides of the spinal cord. (B) Signup and view all the answers

Which spinal cord region is responsible for relaying sympathetic information to various organs?

Lateral horn (C) Signup and view all the answers

Which of the following is NOT a component of a typical three-order neural pathway?

Cauda equina (C) Signup and view all the answers

What is reciprocal inhibition's primary function?

To help prevent damage to muscles by inhibiting the antagonist muscle during a movement (A) Signup and view all the answers

What is the main difference between a stretch reflex and flexor withdrawal?

A stretch reflex activates only one spinal segment, while flexor withdrawal involves multiple segments (B) Signup and view all the answers

Which of the following is NOT a characteristic of muscle synergies?

They are independent of the central nervous system's control. (B) Signup and view all the answers

How do stepping pattern generators contribute to walking?

They activate lower motor neurons to produce alternating flexion and extension of the hips and knees. (B) Signup and view all the answers

Which model of walking suggests a significant role for sensory feedback?

Reflex Model (A) Signup and view all the answers

What is the main difference between upper motor neurons (UMNs) and lower motor neurons (LMNs)?

UMNs are located in the brain, while LMNs are located in the spinal cord. (D) Signup and view all the answers

What is the most likely consequence of a lesion to the brain or spinal cord?

Abnormal movement patterns and synergies (B) Signup and view all the answers

Which of the following is NOT a characteristic of a peripheral nerve?

It is part of the central nervous system. (C) Signup and view all the answers

What is the primary role of myotomes in motor control?

They control the activity of specific muscle groups. (D) Signup and view all the answers

Which of the following is an example of a pathological synergy?

A person with a stroke struggling to control their arm movements. (C) Signup and view all the answers

Study Notes

Spinal Cord Anatomy and Function

31 pairs of spinal nerves
Spinal cord ends at approximately L1/L2 in adults
Cervical and lumbar regions of grey matter are enlarged compared to thoracic
3-order neural pathway: information travels through 3 stops to reach destination
Cervical nerves exit superior (above) to their corresponding vertebral body. There are 8 cervical nerves and 7 cervical vertebrae.
Thoracic, lumbar, and sacral nerves exit inferior (below) to their corresponding vertebral body.
Cauda equina: the remaining spinal nerve fibers below L1/L2, located within the thecal sac.

Spinal Cord - Internal Structure

Gray matter:
- Dorsal horn: Sensory information enters the spinal cord.
- Lateral horn: Only in the thoracic region; houses sympathetic information relayed to organs.
- Gray commissure: Connects the two sides of the spinal cord.
- Ventral horn: Motor outputs and lower motor neuron cell bodies.
White matter:
- Dorsal column: Sensory information.
- Lateral column: Motor and autonomic functions.
- Anterior column: Motor outputs.

Spinal Cord - Sensory and Motor Information

Sensory (afferent) information enters through dorsal horn, motor (efferent) from ventral horn.
Information travels from the periphery (sensory nerves) to the spinal cord, then to nerve roots and ultimately to the nerves themselves

White Matter Pathways

Anterolateral system:
- Lateral spinothalamic tract
- Anterior spinothalamic tract
Spinocerebellar tracts: transmit sensory information to the cerebellum
Dorsal column-medial lemniscus system:
- Fasciculus gracilis
- Fasciculus cuneatus

Spinal Cord Longitudinal Organization

Regional differences in spinal cord structure: Cervical and lumbar regions have more gray matter due to increased need for arm/leg function.
Thoracic region has lateral horns for containing sympathetic nervous system.
White matter decreases as tracts disperse during descent from cervical to sacral regions.

Spinal Cord Blood Supply

Anterior spinal artery: Supplies the anterior two-thirds of the spinal cord.
Posterior spinal arteries: Supply the posterior one-third.
Anterior spinal artery injuries often lead to motor deficits; posterior artery stroke impacts sensory tracts more.

Spinal Cord Movement Coordination and Reflexes

Reflexes: Basic, withdrawal, and reciprocal inhibition reflexes.
Stepping pattern generators: Spinal circuits that generate rhythmic movements like walking.
Descending systems (Upper Motor Neurons): Plan, initiate, and direct voluntary movements.
Stretch reflex (monosynaptic): Quick response to tendon tap (e.g. knee-jerk), involves muscle spindles and alpha motor neurons. -Involves reciprocal inhibition: Relaxation of the opposing muscle.

Reciprocal Inhibition

Antagonist muscle opposition is inhibited through inhibitory interneurons (e.g., during a stretch reflex).
Muscle synergies: Coordinated action of functionally linked muscles.
Lesions or diseases, such as amyotrophic lateral sclerosis (ALS), can lead to abnormal synergies and movement patterns.

Flexor Withdrawal Reflex

Protective reflex involving flexion of a limb in response to a noxious stimulus.
Involves multiple spinal segments (polysynaptic).
Persistence even after spinal cord injury.

Stepping Pattern Generators

Adaptable networks of spinal interneurons generating alternating flexion/extension of limbs.
Responsible for rhythmic, stereotypical movements (walking).
Spinal cord can generate rhythmic movement patterns in the absence of higher-level brain input, although cortex is needed for complex behaviors like balance coordination and preventing unwanted movements.

Peripheral Nervous System

Upper Motor Neurons (UMN) vs. Lower Motor Neurons (LMN):
- UMN lesions cause global weakness, hypertonia, hyperreflexia.
- LMN lesions result in focal weakness, hypotonia, hyporeflexia, atrophy.
Peripheral nerves:
- Located outside brain and spinal cord.
- Contain myelinated (Schwann cells) and unmyelinated axons.
- Lesions lead to focal weakness or sensory loss (compared to diffuse loss associated with CNS lesions).
Peripheral nerve classification:
- Size and myelination of axon determine conduction velocity.
- Carry sensory, motor, or both functions (somatic or autonomic).

Dermatomes

Area of skin innervated by axons entering the spinal cord through a single dorsal root.
Help specify location and extent of nerve damage, specifically after spinal cord or traumatic vertebral column injuries.

Myotomes

Specific spinal nerves responsible for specific muscle actions.

Amyotrophic Lateral Sclerosis (ALS)

Progressive neurodegenerative disease, unknown cause.
Loss of muscle strength/motor neuron control.
Symptoms of both UMN and LMN disease.
Fatal, with few living more than a decade post-diagnosis.
Supportive treatments, some medications.

Spinal Cord Regeneration

Peripheral nerves: Can regenerate, with Schwann cells promoting regrowth.
Central nervous system (CNS): Regeneration is limited due to glial scarring, lack of suitable growth factors.
CNS has poor ability to regenerate when injured, in contrast to the peripheral nervous system.

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Description

Test your knowledge on the anatomy and function of the spinal cord. This quiz covers essential concepts, including spinal nerve pairs, the structure of gray and white matter, and the organization of the spinal cord. Understand how information travels through the spinal cord and its significance in the nervous system.

Clinical Neuroscience Week 4 - The Spinal Cord

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