Bulbar muscles, often referred to as the brainstem muscles, are a collection of muscles in the head and neck that receive commands from motor neurons located in the lower part of the brainstem, sometimes called the bulb. This group of muscles coordinates many fundamental and complex voluntary movements. Proper function of these muscles is necessary for both communication and nutrition. Understanding their function and the signs of their decline is important for recognizing certain neurological conditions.
Location and Essential Roles
Bulbar muscles are situated in the face, jaw, tongue, pharynx, and larynx, controlling the coordinated actions required for oral function. They are innervated by several lower cranial nerves that emerge directly from the brainstem. These nerves transmit signals allowing for intricate movements of the tongue, lips, and vocal cords.
Swallowing
Swallowing, or deglutition, is a primary function, involving manipulating food in the mouth and safely propelling it into the esophagus. The muscles of the tongue and pharynx work in a precise sequence to form a food bolus and initiate the swallowing reflex. This process also protects the airway to prevent food or liquid from entering the lungs.
Speaking and Respiration
Speaking requires bulbar muscles for articulation and vocalization. They control the fine movements of the lips, tongue, and soft palate necessary to produce distinct speech sounds. Muscles in the larynx adjust the tension of the vocal cords to create voice and regulate pitch. The respiratory system is also tied to these muscles, as they contribute to airway protection through the cough reflex.
Identifying Signs of Weakness
When bulbar muscles fail, the resulting symptoms are categorized into two main clinical manifestations affecting communication and eating.
Dysphagia (Difficulty Swallowing)
Dysphagia is the medical term for difficulty with swallowing. Common signs include coughing or choking during or immediately after eating, especially with thin liquids. Individuals may notice food or liquid leaking from the mouth due to poor lip closure, or a sensation that food remains in the throat after swallowing. Difficulty manipulating food inside the mouth, such as forming a cohesive bolus or chewing dense textures, is another sign. This weakness can also lead to drooling or the pooling of saliva because the muscles cannot clear oral secretions effectively.
Dysarthria (Slurred Speech)
Dysarthria refers to slurred or unclear speech due to muscle weakness. Speech may become slow, effortful, or sound nasal because the soft palate cannot properly block air from entering the nasal cavity. As weakness progresses, the tongue may become visibly atrophied or show involuntary twitching, further impairing the ability to form clear consonants. The voice itself may change, becoming harsh, hoarse, or breathy due to poor control over the laryngeal muscles.
Major Health Conditions Affecting Bulbar Muscles
The most common conditions affecting bulbar muscles involve damage to the motor neurons that control them.
Motor Neuron Diseases
Bulbar Palsy, also called Progressive Bulbar Palsy (PBP), is a motor neuron disease defined by the progressive degeneration of lower motor neurons in the brainstem. This results in flaccid weakness, atrophy, and fasciculations (twitching) in the affected muscles of the face, tongue, and throat. Amyotrophic Lateral Sclerosis (ALS), often known as Lou Gehrig’s disease, frequently involves these muscles, particularly in the bulbar onset form. In bulbar onset ALS, motor neuron damage begins in the brainstem region before affecting the limbs, leading to dysarthria and dysphagia as initial symptoms. This form tends to progress more quickly than other variants of ALS.
Other Neurological Causes
Other neurological diseases can cause bulbar muscle dysfunction by disrupting the neural signals or the muscles themselves. Myasthenia Gravis (MG) is an autoimmune condition where the body attacks the connections between nerves and muscles, causing weakness that worsens with activity and improves with rest. Bulbar symptoms in MG include difficulty chewing and fatigable speech. A brainstem stroke can also directly damage the cranial nerve nuclei, leading to sudden onset of severe bulbar weakness.
Managing Impaired Function
Management of impaired bulbar function focuses on supportive care to ensure safety and maintain quality of life, regardless of the underlying disease. Speech-Language Pathologists (SLPs) are central to this process, assessing both swallowing and speech abilities. They can recommend exercises to maintain muscle strength and help with compensatory swallowing strategies, such as the chin-tuck posture to protect the airway.
Swallowing Safety and Diet
Dietary modifications are a common intervention to reduce the risk of aspiration, which is when food or liquid enters the lungs. This often involves altering the texture of foods to be softer or pureed, and thickening liquids to slow their movement for safer swallowing. The goal is to maximize nutritional intake while minimizing the risk of choking or developing aspiration pneumonia.
Communication Support
For communication difficulties, SLPs may teach techniques such as speaking slower, taking a full breath before speaking, and using larger lip movements. When speech intelligibility declines significantly, alternative methods become necessary. These can range from low-tech communication boards to high-tech assistive communication devices that generate speech through a computer.