Exam 2 - Control of Mastication (Part 2) Flashcards
What is the masticatory central pattern generator?
- interconnected neural circuits producing a neural oscillatory network capable of generating simple patterns of masticatory movements
- probably located in the reticular formation and parts of the pons that contain the trigeminal nuclei
- it has both rhythm generator and pattern generator functions
- its output to masticatory motorneurons may be modified by input from afferent and central areas
How des a CPG work?
top neuron = temporalis muscle (jaw closing)
- first neuron fires –> second neuron fires –> third neuron sends action potential to alphamotor nucleus in temporalis muscle which causes jaw closing
- interneuron is activated by the second neuron which causes positive feedback and keeps the temporalis muscle activated
- in neuron 2 there is another interneuron which causes inhibition, when this occurs it will cause circuit 2 to activate (see below)
low neuron = anteiror digastric (jaw opening)
- first neuron fires –> second neuron fires –> third neuron sends action potential to the alphamotor nucleus in anterior digastric muscle which causes jaw opening
- also has a positive feedback loop similar to above from neuron 2, and an inhibitory loop which will cause activation of circuit 1
If the brain stem is cut off from higher centers and afferent input… is the CPG alone sufficient?
basic rhythmical movement will still occur
BUT
it cannot be modulated to meet the variety of challenges involved in normal mastication
What is the influence of higher centers?
- in dysfunction of masticatory area of motor cortex (i.e, stroke) there is generally failure to fully recover normal mastication
- cortex initiates feeding and tongue posture (helps with stage I transport of food)
- motor cortex is essential for co-ordination and modulation of all the motor systems in response to afferent input
What does experimental evidence from animal studies show when the sensorimotor cortex is electrically stimulated?
sensorimotor cortex produces short latency changes in excitability of masticatory motor neurons (i..e, there is a neuronal pathway linking them)
Describe the afferent and efferent information pathways used in chewing and swallowing
jaw = 5, trigeminal
hyoid =
tongue = hypoglossal
cheeks (buccinator)/ obicularis oris = 7, facial
*efferent are arrows going down
*afferent are arrows going back up to CPG
- you know when its time to stop masticating because the mucosa mechanoreceptors will tell the CPG to stop because a soft bolus has been achieved
- muscle spindle for load compensation
- PDL mechanoreceptors is for tooth dispalcement in socket
- joint is golgi tendon organs will prevent jaw from disclocating
Describe the transport pathway
What happens when you initiate stage II transport of food?
slow opening phase lengthens to allow time for pharyngeal swallow
a sequence of muscle contractions and relaxations which move material from the oral cavity to the stomach
swallowing
Describe the 4 characteristics of swallowing in an average adult human
- up to 1000 swallows/day
- relatively few while asleep
- most during waking hours (mainly to clear saliva)
- additional swallows (i.e., 150) when eating
What are the 3 stages of swallowing?
stage 1 - oral
stage 2 - pharyngeal
stage 3 - oseophageal
This stage of swallowing is traditionally considered “conscious” or when a food bolus is moved back to a glossopharyngeal nerve area
Stage 1
This stage of swallowing is traditionally considered a “striated muscle” reflex movement elicited by bolus stimulation of glossopharyngeal receptors
Stage 2
This stage of swallowing is considered a
“smooth muscle” reflex/autonomic
Stage 3
What is the traditional view of swallowing? What is the problem with this view
- human studies have looked at swallowing on “command” or consciously
- when you eat lunch and are talking with your friends are you conscious??? probably not
THUS –> swallowing can be conscious but it does not have to be conscious
How many stages of transport are there?
2
How many stages of swallow are there?
3
In the oral stage, what is the trigger for bolus transport?
diffuse stimulation of palatal and lingual mechanoreceptor afferents
In the pharyngeal stage, what is the trigger for reflex?
spatial summation of similar sensory inputs from
- mucosa innervated by glossopharyngeal
- superior laryngeal (branch of Xth) nerves
What happens when you swallow a large pill?
- localized pressure by pill has inhibitory effects
- mechanoreceptors in the pharyngeal stage
- dogs do this
Regarding tongue position, the hyoid bone is dependent on the muscles which pull on the hyoid, what are the 3 muscles?
- anterior digastric
- posterior digastric
- sternohyoid
What is the action of the submandibular muscles on the tongue?
genioglossus = push everything from hard palate, from soft palate and touch uvula and push food into throat
hyoglossus = pull hyoid bone toward the hard palate to make space in throat
styloglossus = going to contract and make everything tense to make a hole back at the throat for swallowing
What is the order of pharyngeal muscle contraction?
SC –> MC –> IC
superior constrictor
middle constrictor
inferior constrictor
What is the importance of the valleculae?
mucosal afferents very sensitive - slightest accumulation of food or saliva helps to elicit a swallow and suppress respiration
**when you think food goes down the wrong pipe it actually goes here
Describe the stages of swallow diagram
A) pre-swallowing = oral phase of swallowing
B) start of pharyngeal (stage 2) swallowing
C) transition from end stage 2 pharyngeal swallow to stage 3 oesophageal
D) oesophageal (i.e., stage 3) initial under control by vagal somatic neurons
Describe the transition to esophageal muscle and it’s innervation
** TRANSITION OF INNERVATION IN THIRD PHASE OF SWALLOWING FROM SOMATIC –> AUTONOMIC
- muscles transition from skeletal (striated) to smooth
- neurons of enteric nervous system
True or false: The vagus nerve participates in both the somatic and automatic nervous systems.
True
How is swallowing controlled?
Preparatory & Oral phases
- voluntary control from higher CNS centers
Pharyngeal and esophageal phases
- involuntary control from brain stem
The whole control system of swallowing involves what four things?
- large areas of brain stem
- several cranial nerves
- numerous muscles
- many afferent receptors
Describe the brainstem swallowing center
motor output = will cause skeletal muscle to contract
- hypoglossal: tongue
- trigeminal: mastication
- facial nucleus
skeletal muscle to contract in throat that is basis for reflex activity
- nucleus ambiguous: motor nuclei to vagus nerve (X)
- glossopharyngeal (IX)
sensory input
nucleus tractus solitarious has afferent information from mucosa mechanoreceptors in cranial nerves VII, IX, X
trigeminal sensory nucleus has mucosa mechanoreceptors in cranial nerve V
What do the brainstem neurons form during swallowing?
text version of previous diagram
a CPG for the pharyngeal and oesophageal phases of swallowing
- motor cortex information coming down for phase I of swallowing, most of phase 2 swallowing is controlled by reflexes
In the brainstorm swallowing center, what are the three main components?
- sensory afferents
- from oral cavity, pharynx, larynx and oesophagus - dorsal and ventral interneurons
- these form an integrating center (CPG) which generates a precisely-timed sequence of activation of motorneurons supplying the muscles involved in swallowing - motor nuclei
- these contain the cell bodies of the motorneurons that are activated by the swallowing center and directly innervate the muscles
Stimulation to the pharynx or upper airway can cause what four things?
- sneezing
- coughing
- gagging
- choking
What are the four mechanisms to protect the lower airway?
- closure of the glottis
- flexion of the epiglottis over the laryngeal inlet
- interruption of respiration
- the swallow is timed to occur near to end inspiration
What does timing ensure if there were any accidental entry of food/liquid into the lower airway?
- at the first opening of the glottis there would be an escape of air helping to clear the laryngeal opening of material
- there would be an adequate volume of air in the lungs to permit a forceful cough to dislodge a greater quantity of material
What are 7 conditions which interfere with swallowing and reflexes that protect the airway?
- stroke (affecting internal capsule)
- parkinson’s disease
- myasthenia gravis
- motor neuron disease
- recurrent larygngeal, superior laryngeal nerve and main vagus nerve palsies
- severe COPD
- over-enthusiastic spraying of local anaesthetic on back of mouth (in attempt to prevent gagging while taking dental impressions)
