Week 2: Upper and Lower Motor Neurons

What are upper motor neurons?

Neurons in descending motor tracts that carry motor commands from the cerebral cortex to the brainstem and spinal cord.

Where do upper motor neurons terminate for speech and swallowing?

They terminate on the motor nuclei of cranial nerves, where they synapse with lower motor neurons.

What do lower motor neurons do?

They carry motor impulses from the cranial nerve nuclei to the muscles of the head, neck, and face.

Why are pyramidal tracts susceptible to damage?

They extend through the entire central nervous system, making them vulnerable to strokes and other injuries.

What happens if upper motor neurons are damaged?

Motor plans cannot be effectively transmitted to lower motor neurons, impairing voluntary movement.

What are extrapyramidal tract impairments associated with?

Disorders affecting reflexes, posture, and muscle tone, commonly seen in Parkinson’s disease and motor neuron disease.

Why is understanding upper and lower motor neurons important for speech pathologists?

It helps diagnose and assess neurological impairments in clients with speech and swallowing disorders.

How do upper motor neurons transmit information?

Through the pyramidal and extrapyramidal tracts, carrying signals from the cerebral cortex to the spinal cord and brainstem.

What is the role of contralateral innervation in motor function?

Each hemisphere of the brain largely controls motor function on the opposite side of the body.

How is motor speech system innervation different?

In most cases, innervation is bilateral, meaning both hemispheres contribute to motor control.

Why is bilateral innervation protective?

It prevents severe impairments in speech and swallowing from unilateral brain damage, such as a stroke.

What are the exceptions to bilateral innervation?

The lower face and tongue, which receive purely contralateral innervation.

What happens when there is unilateral upper motor neuron damage?

Contralateral lower face and tongue movement is affected due to lack of alternative neural pathways.

What is decussation?

The crossing of motor pathways in the brainstem.

How does upper motor neuron damage present?

It results in contralateral impairments, affecting the opposite side of the body from the damage site.

How does lower motor neuron damage present?

It causes ipsilateral impairments, affecting the same side as the damage.

Why does the upper face behave differently in motor neuron damage?

The upper face has bilateral innervation, so damage to one hemisphere doesn’t completely disrupt function.

What happens when lower motor neurons are damaged?

Both upper and lower face muscles on the same side as the damage are affected.

How do speech pathologists determine the location of brain damage?

By examining face and tongue movement to assess if impairments are ipsilateral or contralateral.

What is the role of the brainstem?

• Controls automatic survival behaviors

• Relays sensory and motor signals.

Why is the brainstem crucial for speech and swallowing?

It houses cranial nerves that control muscles for eating, drinking, and speaking.

What functions does the midbrain have?

It regulates auditory and visual reflexes and plays a role in cortical arousal.

What is the pons responsible for?

It houses the trigeminal (CN V) and facial (CN VII) nerves and regulates breathing, heart rate, and blood pressure.

What cranial nerves emerge from the medulla?

The glossopharyngeal (CN IX), vagus (CN X), and hypoglossal (CN XII) nerves, which are essential for speech and swallowing.

What happens if the brainstem is damaged?

Impairments in speech, swallowing, breathing, and motor control.

How can a brainstem stroke affect a person?

It can impair taste, smell, motor speech execution, chewing, and swallowing.

What can a lesion in the pons cause?

Facial paralysis or trigeminal palsy, affecting sensation and movement.

What does medullary damage affect?

It can impair respiration, tongue strength, and movement, severely impacting speech and swallowing.