Motoric Action System Overview

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Questions and Answers

What is hypertonia commonly associated with?

Lower motor neuron lesions

Upper motor neuron lesions (correct)

Cerebellar dysfunction

Normal muscle tone

Which term describes the increased resistance to passive stretch in muscles?

Flaccidity

Hypotonia

Atrophy

Hypertonia (correct)

What characterizes spastic hypertonia?

Velocity-dependent increase in muscle tone (correct)

Flaccid paralysis

Non-speed dependent muscle tone

Decreased alpha motor neuron excitability

Which neural pathway lesion results in spasticity?

Corticospinal tract Signup and view all the answers

What is the clinical hallmark of upper motor neuron lesions?

Hyperreflexia Signup and view all the answers

What is the typical presentation of a lower motor neuron lesion?

Hypo- or atonia Signup and view all the answers

What defines the term 'spasticity' according to Lance's definition?

Velocity-dependent increase in tonic stretch reflexes Signup and view all the answers

In which scenario is the muscle tone described as being normal?

In the absence of neurological disorders Signup and view all the answers

What characterizes fasciculations in the context of LMN lesions?

They involve only a single motor unit and may be visible or not. Signup and view all the answers

What is the difference between hypertonia and hypotonia?

Hypertonia refers to increased muscle resistance, while hypotonia refers to decreased muscle resistance. Signup and view all the answers

Which statement accurately describes spastic hypertonia?

It leads to increased excitability of alpha motor neurons. Signup and view all the answers

What is a key feature of spasticity according to Lance's definition?

It involves a velocity-dependent increase in tonic stretch reflexes. Signup and view all the answers

In the context of muscle tone, what does a UMN lesion typically present as?

Hypertonia with increased resistance to passive stretch. Signup and view all the answers

How can 'rigid' hypertonia be characterized?

It is associated with basal ganglia dysfunction. Signup and view all the answers

Which of the following is a common feature of a lower motor neuron lesion?

Muscle atrophy and reduced tone. Signup and view all the answers

What is a common cause of spastic hypertonia?

Lesion in the descending motor pathways. Signup and view all the answers

What is the primary role of Upper Motor Neurons (UMN)?

To transmit signals from the brain and brainstem to lower motor neurons Signup and view all the answers

Which of the following statements about Lower Motor Neurons (LMN) is accurate?

LMNs exit the central nervous system to innervate muscles Signup and view all the answers

How does muscle weakness manifest in conditions affecting Upper Motor Neurons?

As contralateral weakness with increased muscle tone Signup and view all the answers

Which of the following best describes a typical presentation of LMN lesions?

Focal paralysis localized to specific muscle groups on the same side Signup and view all the answers

What is the relationship between neural activation and force production?

Neural activation determines the number and type of motor units recruited Signup and view all the answers

What condition results from a total loss of muscle function due to LMN damage?

Paralysis Signup and view all the answers

In terms of location, where do the axons of UMNs and LMNs differ?

LMN axons exit the CNS, while UMN axons remain within the CNS Signup and view all the answers

What is NOT a common feature associated with Upper Motor Neuron lesions?

Focal muscle weakness specific to a region Signup and view all the answers

What can result from an upper motor neuron (UMN) lesion in terms of motor control?

Loss of selective motor control Signup and view all the answers

Which of the following describes movements associated with abnormal coupling of related muscles after an UMN lesion?

Movements that cannot change with tasks Signup and view all the answers

What component is NOT included in the Fugl-Meyer assessment?

Strength Signup and view all the answers

What type of synergy might occur in an individual post middle cerebral artery stroke?

Abnormal flexor synergy Signup and view all the answers

Which behavior is indicative of abnormal synergies following an UMN lesion?

Loss of ability to move out of synergies Signup and view all the answers

Which tract is involved in activating lower motor neurons that produce abnormal synergy in the upper limb after a stroke?

Reticulospinal tract Signup and view all the answers

What is one of the maximal scores for the upper limb in the Fugl-Meyer assessment?

66 Signup and view all the answers

What is an expected characteristic of the movements in individuals with UMN lesions?

Movements become primitive and stereotyped Signup and view all the answers

What is the expected motor response in a patient with severe cerebral damage?

Spastic hypertonia Signup and view all the answers

Which type of rigidity is associated with severe lesions above the midbrain?

Decorticate rigidity Signup and view all the answers

What kind of motor function is typically observed in a patient with a spinal cord injury at the C6 level?

High tetraplegia Signup and view all the answers

For a patient with a traumatic spinal cord injury below the L1-L2 vertebrae, what type of paralysis is generally expected?

Flaccid paralysis Signup and view all the answers

Which type of paresis might appear in a patient with a traumatic injury between the cervical region and the lumbar transition L1-L2?

Mixed type (spastic and flaccid paresis) Signup and view all the answers

In the context of motor disorders, what can lesions in the basal ganglia lead to?

Dysfunction and dyskinesia Signup and view all the answers

Which statement about spasticity in patients with traumatic injuries is generally true?

It is not always present in traumatic brain injuries. Signup and view all the answers

What defines an upper motor neuron (UMN) lesion in terms of reflexes?

Hyperactive reflexes Signup and view all the answers

Study Notes

Motoric Action System - Introduction

The motoric action system is composed of the upper motor neuron (UMN) and the lower motor neuron (LMN).
The UMN is located in the brain and brainstem and its axons remain within the central nervous system (CNS).
The LMN is located in the brainstem and spinal cord and its axons leave the CNS.
The LMN synapse with muscle fibers.
The UMN synapses with the LMN.
The UMN controls the LMN.
The LMN controls muscle contractions.
The LMN is also known as the peripheral motor neuron.
The UMN is also known as the central motor neuron.
There are 31 spinal nerves that cluster to form peripheral nerves such as the tibialis nerve and the radial nerve.
There are also cranial nerves such as the facial nerve, the trigeminal motor nerve, and the hypoglossal nerve.

### UMN-LMN Lesion: Clinical Features

An UMN lesion results in a widespread paresis or paralysis, either contralaterally or ipsilaterally, depending on the location of the lesion above or below the pyramidal decussation.
An LMN lesion results in a focal paresis or paralysis on the ipsilateral side, affecting either a specific segment or peripheral nerve.
UMN lesions involve the corticospinal tract, cortico-reticulo-spinal tract, and the basal ganglia.
UMN lesions cause increased excitability of the alpha motor neurons, leading to increased muscle tone, exaggerated tendon reflexes, and abnormal synergy patterns.
LMN lesions involve the peripheral nerves, causing muscle weakness, fasciculations, and fibrillations.

### Muscle Weakness

Weakness refers to the inability to generate normal levels of force.
Paresis refers to a mild or partial loss of muscle strength.
Paralysis – or plegia, refers to a total loss of strength.

### Muscle Tone

Muscle tone is defined as the resistance to passive stretch, and it is normally present in muscles.
Hypotonia is low muscle tone, commonly observed in LMN lesions and cerebellar lesions.
Hypertonia is excessive muscle tone, commonly observed in UMN lesions and basal ganglia dysfunction.

### Spasticity

Spasticity is a velocity-dependent form of hypertonia, most commonly a result of an UMN lesion.
Spasticity is characterized by muscle stiffness and increased reflexes.
Spasticity results from increased alpha motor neuron excitability, leading to increased muscle tone, exaggerated tendon reflexes, and abnormal synergy patterns.

### Rigidity

Rigidity is a non-velocity-dependent form of hypertonia, most commonly associated with basal ganglia dysfunction.
Rigidity is characterized by steady resistance to passive movement throughout the range of motion.

Voluntary Movements

Voluntary movements are also known as fractionation or individuation.
The term “fractionation” means the ability to selectively activate a single muscle or muscle group without causing movements in other muscles.
UMN lesions can impair voluntary movements, resulting in abnormalities in the coordination of synergistic muscles known as synergy patterns.

Abnormal Synergies

Abnormal synergies are stereotyped movement patterns, which are highly predictable and commonly observed after an UMN lesion.
Abnormal synergies are often observed as a result of the descending signals from the reticulospinal tract activating lower motor neurons to proximal muscles.
Examples of abnormal synergies include:
- Flexion synergy: The arm flexes at the shoulder, elbow, and wrist, and the forearm is pronated.
- Extension synergy: The arm extends at the shoulder and elbow, and the forearm is supinated.

The Fugl-Meyer Assessment

The Fugl-Meyer assessment is a standardized instrument for assessing motor function after stroke.
The Fugl-Meyer assessment is used to measure motor impairment in the upper and lower limbs.
It measures reflexes, movement in and out of synergy patterns, selective movements, coordination, and sensory function.

Clinical Manifestations: UMN & LMN Lesions

Cerebrovascular Accident (CVA) or Stroke: results in UMN lesions.
Spinal Cord Injury (SCI): can result in both UMN and LMN lesions.
Traumatic Brain Injury (TBI): results in UMN lesions.

Tone and Reflexes in Various Pathologies with UMNL and LMNL

LMN lesions are characterized by hypotonia and hyporeflexia.
UMN lesions are characterized by hypertonia and hyperreflexia.
Basal ganglia dysfunction is characterized by rigidity and resting tremor.
Cerebellar lesions are characterized by hypotonia, ataxia, and dysmetria.

### Pathologies and Locations of Possible Motor Impairments

Severe cerebral damage:
- Severe lesions above the midbrain: Decorticate rigidity, characterized by neck and leg extension, plantar flexion, and arm flexion.
- Severe lesions in the midbrain: Decerebrate rigidity, characterized by extension in the trunk and all limbs, internal rotation, and plantar flexion.
Stroke, TBI, MS: result in UMN lesions.
SCI: can lead to both UMN and LMN lesions.

### Spinal Cord Injury (SCI)

Motor Level: describes the lowest intact spinal cord segment with normal muscle function.
Tetraplegia: involves paralysis of all four limbs.
Paraplegia: involves paralysis of the lower limbs.