Neuroscience lecture 12

How many times do we swallow in one day?

Around 500 times a day

When do we start swallowing?

The fetus starts swallowing starts at week 17 of pregnancy

Stages of swallowing

a. oral stage

1. preparatory

2. propulsive/ oral

b. Pharyngeal

c. Esophageal

What cranial nerves are involved in swallowing? 

trigeminal (V), facial (VII), glossopharyngeal (IX), vagus (X), Spinous accessory (XI), and hypoglossal (XII) nerves

1. Oral Preparatory Stage 

• Voluntary

• Varies in time 

• involves preparation of bolus 

• nasal breathing continues 

• requires labial seal 

What is a Bolus

a semi cohesive ball of food or liquid that’s ready to swallow

The oral preparatory stage: mastication 

what is involved? 

Mostly trigeminal nerve, but also facial nerve, hypoglossal 

Mandibular elevators: masseter, temporalis, medial pterygoid 

Mandibular depressors: Mylohyoid, anterior belly of digastric muscle, lateral pterygoid

The oral preparatory stage: Gland Secretion

Saliva: has some antibacterial components to it

• consists of water & enzymes to break down food

• 1 to 1.5 liters of saliva a day

Three major salivary glands:

• parotid gland (IX)

• Submandibular gland (VII)

• Sublingual glands (VII)

Activated by taste receptors (CN VII & IX)

how much saliva production does the parotid gland make

25% if saliva production

how much saliva production does the submandibular gland make

70% of saliva production

how much saliva production does the Sublingual gland make

5% of saliva production

2. The Oral Propulsive stage 

Voluntary stage of swallow 

It lasts approximately 1 second 

the formation of bolus completed 

tongue forms a ramp and moves bolus from the oral cavity to pharyngeal cavity 

labial seal and nasal breathing maintained 

The Oral stage: Labial seal 

Facial muscles: 

• orbicularis oris 

• mentalis 

• buccinator 

• risorius 

The Oral stage: Tongue Movement

The tongue holds and pushes the bolus by 3 movements

1. lowering of the posterior tongue (genioglossus)

2. Elevation of the tongue tip superior longitudinal 

3. anterior to posterior movement of tongue 

There are 4 muscles of the “tongue”

Intrinsic Muscle:

Superior longitudinal muscle

Inferior longitudinal muscle

transverse muscle

vertical muscle

Extrinsic muscle:

Genioglossus

3. The Pharyngeal stage: Overview 

Involuntary stage 

Pharyngeal swallow response (not reflex)

Lasts approximately 1 second 

The triggering of the pharyngeal swallow: when bolus head passes a reference point (faucial pillars/ ROM/ Vallecuale) 

The Pharyngeal stage: Soft palate closure 

velopharyngeal closure 

• keeps food/liquid out of the nasal cavity 

5 muscles are involved in soft palate movement 

1. levator veli palatini (CN X, XI)

2. palatoglossal (CN X, XI)

3. tensor veli palantini (CN V)

4. musculus uvulae (CN X, XI)

5. palatopharyngeus (CN X, XI)

During regular nasal breathing soft palate is _____

Down

The Pharyngeal stage: Elevation of the hyoid and Larynx

Hyolaryngeal excursion

raising of the hyoid and larynx (in .5 sec)

anterior displacement of the hyoid and larynx

assist with epiglottal-laryngeal closure

The Pharyngeal stage: Laryngeal closure 

1. level of epiglottis 

2. level of false vocal folds 

3. level of true vocal folds 

these close to protect the airway from the bolus entering it 

Some people may have 1 or 2 of these levels effected or all 3 effected (just a open airway)

The Pharyngeal stage: pharyngeal constriction

superior pharyngeal constrictor

middle pharyngeal constrictor

inferior pharyngeal constrictor

CNs: X & XI

The Pharyngeal stage: upper esophageal sphincter (UES)

cricopharyngeal muscle contracts, and respiration begins again

CNs: X & XI

typically it’s closed but it opens and relaxes when a bolus moves through the pharynx

Levels of swallowing summarized

1. soft palate closes

2. Hyolaryngeal excursion

3. laryngeal closure

4. upper esophageal opening

What hemisphere does swallowing occur

swallowing occurs on both hemispheres

Cortical and subcortical controls:

Insula: May mediate motor and sensory information involved in swallowing 

anterior cingulate cortex 

premotor cortex 

Subcortical and cortical controls

thalamus: sensory relay station, especially with afferent information

basal ganglia: and “editor” that filters out unnecessary movement

cerebellum: connections with thalamus and BG

Brainstem involvement - Nucleus tractus solitarius (NTS):

• located in the medulla

• receives afferent information from CN V, VII, IX, and X (taste and touch info)

• sends information to second nucleus and supramedullary centers

• one of the most important areas for swallowing

• medulla strokes are very severe

Brain stem involvement - Nucleus ambiguous (NA):

• located in the medulla 

• innervates the swallowing muscles via CN V, VII, IX, X, and XII

Cranial nerve involvement in swallowing

CN:

V: motor and sensory

VII: both

IX: both

X: both

XII: motor

Reflexive circuits associated with swallowing function

In infants rooting and suckling reflexes

** infants turning head toward the light touch on the cheek to feed will disappears around 4-6 months old

gag reflex

retch and vomit reflex (caused by smells, vertigo, distress, and bad taste)

Neurology of silent aspiration

aspiration

• normally would couch but with dysphagia they don’t cough

about 1/3 of dysphagic patients aspirate without and signs of distress: “silent aspiration”

neurological damage can suppress the cough response system

how do we know if they are aspirating? we will have to do imaging to see

Dysphagia can cause 

aspiration pneumonia 

malnutrition (since some of the food isn’t getting to the stomach)

Dehydration (since some of the liquids aren’t getting to the stomach) 

causes of dysphagia

• acute inflammations

• cancer

• cervical spinal disease

• stroke (most common)

• TBI

• spinal cord injury

• degenerative diseases

• brain tumors

Swallowing problems associated with neurological damage - oral preparatory stage & Oral stage:

oral preparatory stage:

• difficulty chewing

• food falling out of mouth

Oral stage:

• food remaining in mouth (pocketing)

• difficulty forming bolus

• difficulty moving bolus backwards in mouth (anterior to posterior movement)

could be problems in motor cortex or basal ganglion

Swallowing problems associated with neurological damage - Pharyngeal stage & esophageal stage

Pharyngeal stage: 

• delays pharyngeal swallow response 

• absence of pharyngeal swallow/ response 

• pooling of bolus 

• aspiration 

** Parkinson or ALS and even global stroke could cause these 

Esophageal stage: 

• bolus staying in esophagus (dysmotility due to lack of peristaltic waves)

Clinical presentation of neurogenic dysphagia - Cerebral hemisphere and brainstem

a. CVA

b. Swallowing Apraxia

c. TBI

Clinical presentation of neurogenic dysphagia - Demyelinating diseases 

MS 

could get demyelination in the brain stem and muscles which effect swallowing

Clinical presentation of neurogenic dysphagia - Disorders of movement

a. Huntington’s disease

b. Parkinson’s disease

c. Spinocerebellar Ataxia 

Clinical presentation of neurogenic dysphagia - Motor unit abnormalities 

a. ALS (LMN effected: change posture diet modification) 

b. Guillain Barre Syndrome (during those months that they are having their episodes that’s when they need help.)

Brain death

When a brain is declared brain dead it’s has no brain activity but the spinal cord may still work so they could have spinal reflexes

Dementia: Alzheimer’s

Is 60% or more causes for dementia

Extended consciousness and loss of autobiographical self. Later loss of core consciousness

Epilepsy

Both core consciousness and extended consciousness are usually impaired during epileptic episode

How SLPS can help with coma stimulation

Slps can recommend stimulation to a persons five senses

Like smells, touch etc.

but it’s not scientifically backed so recommend to tell people that it may not work but it could work to not give false hope