Motor Pathways in Neuroscience

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Questions and Answers

What is the primary function of the basal ganglia in motor control?

Providing intention of movement

Acting as a gateway for translating intention into movement (correct)

Regulating balance and posture

Transmitting motor signals directly to skeletal muscles

Which neurotransmitter is primarily associated with lower motor neurons?

Glutamate

Serotonin

Acetylcholine (correct)

Dopamine

Which of the following muscles is not directly supplied by the corticospinal tract?

Skeletal muscles of the trunk

Extremities muscles

Facial muscles (correct)

Muscles of the head

What is the main function of cerebellum in motor control?

Determining sequence of movement commands Signup and view all the answers

Which area of the cerebral motor cortex is primarily involved in the control of voluntary muscle movement?

Primary motor cortex Signup and view all the answers

How does the flexor reflex function when a painful stimulus is applied? (select 3)

It triggers immediate muscle contraction from the neuronal pool in the spinal cord without brain involvement Signup and view all the answers

What is the role of muscle spindles in muscle control?

Detecting muscle length and rate of change of length Signup and view all the answers

Which areas are mainly involved in the mirrored tasks and patterns of movement?

Premotor area Signup and view all the answers

Which motor pathway decussates predominantly in the lower medulla?

Lateral corticospinal tract Signup and view all the answers

What occurs when a motor neuron injury happens below the decussation?

Paralysis occurs on the same side Signup and view all the answers

Which symptom is indicative of lower motor neuron disease?

Flaccid paralysis Signup and view all the answers

Which condition is characterized by ipsilateral loss of motor and proprioception and contralateral loss of temperature and pain?

Brown-Sequard syndrome Signup and view all the answers

What reflex mechanism helps maintain balance by extending the opposite limb in response to a painful stimulus?

Crossed extensor reflex Signup and view all the answers

What is a characteristic feature of amyotrophic lateral sclerosis (ALS)?

Progressively worsening condition from proximal to distal Signup and view all the answers

Which of the following best describes symptoms associated with cerebral palsy? (select 2)

Not progressive Signup and view all the answers

Which type of spinal cord injury leads to sensory dysfunction below the injury and impaired motor function primarily in upper extremities?

Central cord syndrome Signup and view all the answers

What result occurs in a complete transection of the spinal cord?

Loss of sensation and motor function below the injury Signup and view all the answers

Which of the following symptoms are associated with anterior cord syndrome? (Select all that apply)

Impaired motor function (ventral position of descending path) Signup and view all the answers

What are symptoms of posterior cord syndrome?

Loss of touch, proprioception, and vibration with intact motor function Signup and view all the answers

Which neurotransmitter is primarily associated with upper motor neurons?

Glutamate Signup and view all the answers

What is the most populous neuron in the corticospinal/pyramidal tract?

Interneurons Signup and view all the answers

What are the two types of anterior motor neurons (lower motor neurons)?

Alpha motor neurons and gamma motor neurons Signup and view all the answers

Which motor neuron innervates skeletal muscle?

Alpha motor neurons Signup and view all the answers

What do gamma motor neurons innervate?

Intrafusal fibers of the muscle spindle Signup and view all the answers

What area of the cortex is involved in bilateral movements?

Supplementary motor area Signup and view all the answers

Damage to what area causes motor apraxia?

Area for hand skills Signup and view all the answers

What structures are controlled by the anterior corticospinal tract?

Neck and trunk muscles Signup and view all the answers

Axons from the ____ synapse with the cranial nerve nuclei.

corticobulbar tract Signup and view all the answers

What type of information do Golgi tendon organs transmit?

Torsion and tension Signup and view all the answers

What are the symptoms of upper motor neuron disease? Select all that apply.

Hyperreflexia Signup and view all the answers

Which type of neurons are affected by Amyotrophic Lateral Sclerosis (ALS)?

Both upper and lower motor neurons Signup and view all the answers

Axons travel from cortex ->thru the internal capsule -> midbrain (basis pedunculi) -> medulla -> lateral corticospinal tract (aka PYRIMADAL TRACT) -> SPINAL CORD

True Signup and view all the answers

Where do nerve fibers decussate from the anterior corticospinal tract?

In the spinal cord before synapsing with lower motor neurons in the ventral horn Signup and view all the answers

Why does hypertonia occur in upper motor neuron injury?

Upper motor neurons lose their ability to inhibit lower motor neurons Signup and view all the answers

Which area is involved in the planning and coordination of complex movements?

Premotor area Signup and view all the answers

What type of motor neuron innervates muscle spindles?

Gamma motor neurons Signup and view all the answers

Extrafusal muscle fibers are innervated by what type of motor neuron?

Alpha motor neurons Signup and view all the answers

What type of neuron innervates Golgi tendon organs?

A-beta sensory neurons Signup and view all the answers

Which part of the nervous system are upper and lower motor neurons a part of?

Somatic nervous system Signup and view all the answers

Study Notes

Motor Pathways Overview

Motor pathways transmit signals from the brain to muscles via corticospinal and reticulospinal tracts, which are descending.
The extrapyramidal pathway, reliant on dopamine, is located in the brainstem and is associated with antipsychotic medications and conditions like Parkinson’s disease and neuroleptic malignant syndrome.

Primary Motor Structures

Primary motor cortex is situated in the precentral gyrus of the frontal lobe and is crucial for the intention of movement.
Basal ganglia function as a gateway translating movement intentions into actual movements, utilizing both excitatory and inhibitory signals.
The cerebellum organizes command sequences to achieve coordinated movement.

Motor Response Origins

Simple reflexes originate in the spinal cord, general movement from the brainstem, and complex movements are governed by the cerebrum.
Motor pathways consist of two neurons: upper motor neurons, transmitting signals from the brain to the spinal cord, and lower motor neurons, relaying signals from the spinal cord to muscles and glands.

Neuron Types and Functions

Upper motor neurons primarily use glutamate as their neurotransmitter.
Lower motor neurons use acetylcholine (ACh) and innervate skeletal muscles.
Interneurons in gray matter play a significant role, with a higher number than motor neurons, particularly in the corticospinal tract.

Motor Neuron Classification

Anterior motor neurons, the largest neurons, innervate skeletal muscle and are located in the anterior horns of gray matter.
Two types of anterior motor neurons:
- Alpha motor neurons innervate large skeletal muscles.
- Gamma motor neurons innervate intrafusal fibers of muscle spindles, helping maintain muscle tone.

Corticospinal Tracts

Corticospinal tract supplies voluntary control to trunk and extremities.
Cranial nerves control voluntary muscles of the head and neck.
Cerebral motor cortex is located anterior to the central sulcus, engaging in all voluntary muscle movement, with major areas dedicated to hands and speech.

Key Motor Cortex Areas

Primary motor cortex controls voluntary muscle contractions.
Premotor area focuses on movement patterns and mirroring tasks.
Supplementary motor area governs bilateral movements.
Specialized motor areas include Broca’s area for speech, voluntary eye movement fields, and a region for head rotation directing head movements.

Tract Pathways

Lateral corticospinal tract originates from the precentral gyrus; fibers decussate mainly at the lower medulla.
Anterior corticospinal tract consists of 10% of axons that do not decussate and cross at neck/thorax levels.
Corticobulbar tracts are responsible for controlling eye, tongue, chewing, facial expressions, and speech.

Sensory Structures in Muscle Regulation

Muscle spindles detect muscle stretch and send sensory information regarding muscle length.
Golgi tendon organs detect tension and provide feedback about tendon torsion.

Reflex Mechanisms

Flexor reflex is a protective withdrawal response activated by pain stimuli.
Reciprocal inhibition circuits prevent antagonist muscles from contracting simultaneously.
Crossed extensor reflex extends the opposite limb for balance when one limb withdraws from a painful stimulus.

Upper and Lower Motor Neuron Disease Symptoms

Upper motor neuron lesions present with:
- Increased deep tendon reflexes and muscle tone.
- Positive Babinski sign, spastic paralysis.
Lower motor neuron lesions present with:
- Decreased deep tendon reflexes and muscle tone.
- Negative Babinski sign, flaccid paralysis, muscle atrophy.

Injury Implications

Motor neuron injuries above decussation result in contralateral paralysis, while those below result in ipsilateral paralysis.
Cerebral palsy arises from upper motor neuron damage during the perinatal period, presenting with altered movement and coordination but is non-progressive.
ALS is a rapidly progressing disease affecting both upper and lower motor neurons, potentially linked to glutamate toxicity and oxidative stress.

Spinal Cord Injury Syndromes

Complete transection results in loss of sensation and motor function below the injury.
Central cord syndrome leads to upper extremity motor function loss with sensory dysfunction below.
Anterior cord syndrome impairs motor function, pain, and temperature sensation while preserving proprioception.
Brown-Sequard syndrome, a hemisection of the spinal cord, causes ipsilateral motor and proprioceptive loss and contralateral pain and temperature sensation loss.

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Description

This quiz explores the concepts of motor pathways, including the corticospinal and reticulospinal tracts. It covers the roles of dopamine and the effects of antipsychotic medications, as well as the functions of the primary motor cortex and basal ganglia in movement intention and execution.