Exam 2 - Control of Mastication (Part One) Flashcards
What are the three recording techniques of mastication in human subjects?
- cineradiography
- take x-rays like picture frames of a movie and you will see moving objects on radiographs - tracking devices (i.e., light source marker applied to teeth and movements recorded in 3D)
- electrmyography (EMG) - records changes in electrical potential in activated muscle fibers during contraction most important
What 2 experiments in animals observe mastication?
- metal markers bonded to skeletal structures or teeth to track movements
- direct recordings from neural pathways involved or experimental ablation of these neural pathways
The pattern of movements and muscle activity of the masticatory muscles depend on
- species
- type of food
- individual variation
- jaw opening
- jaw closing
- contralateral balance
- variable lateral and A/P jaw movements
- tongue movemments
What are the three jaw closer muscles?
- masseter
- temporalis
- medial pterygoid
*pterygoid and masster form a muscle sling
What is the jaw opening muscle?
anterior and posterior digastric
Which two muscles form the masticatory sling?
medial pterygoid and masseter
What is the function of the lateral pterygoid?
- attaches to the condyle of the mandible
- stabilizing the condyle during mastication
How many heads does the lateral pterygoid have?
2
- superior and inferior
What are the 4 phases of mammalian masticatory movement during one ingestion ‘cycle’?
- fast closing
- slow closing
- slow opening
- fast opening
EXAM QUESTION How many phases are there in a masticatory cycle?
4
True or false: The relative time spent in the 4 phases of mastication varies with species and consistency of food.
True
**slow closing would be barely there when ingesting soft food
Compare and contrast the masticatory cycles in hard food and soft food
Hard food:
1. profile of jaw movement
- extended slow closing phase (power stroke) which will bite down and crush the food
Soft food:
1. profile of jaw movement
- no extended slow closing phase
- its hard to detect the slow closing phase
What does the tongue do during mastication?
- FAST OPENING AND CLOSING
- tongue retracts to allow food into mouth - SLOW CLOSING & SLOW OPENING
- tongue moves forward and elongates below food - MAINLY DURING OPENING
- styloglossi and genioglossus act together to form a longitudinal trough in the dorsal surface of the tongue that:
–> either pushes food to the posterior oral cavity (if both SG contract together)
–> pushes food towards the cheek for further processing if food not ready for swallowing (if one SG contracts) - PRE-SWALLOWING
- tongue presses food against the hard palate, squeezing it posteriorly
If you contract the right styloglossus and relax the left, where will the bolus go?
left posterior occlusal surface of the teeth
Inverted V***
Answer
Describe an EMG of the complete masticatory sequence
Mvt - Jaw tracking in three planes of space
- vertical
- lateral
- anterior/posterior
Op - Opening
RDIG = right digastric
LDIG = left digastric
Cl - Closing
RDMA = right masseter
LDMA = left masseter
RPTE = right pterygoid
Stage one transport = food from incisal surfaces to posterior occlusal surfaces
Stage two transport = oral cavity to oralpharyngeal space to initiate a swallow
**staggered action potentials between closer muscles and opener muscles
What is the hallmark muscle seen on an EMG which shows initiation of a swallow?
thyrohyoid muscle
What is the innervation of the thyrohyoid?
1st cervical nerve
What is the function of the thyrohyoid muscle?
stabilizes hyoid bone
What is the function of the anterior and posterior digastric muscles?
elevates hyoid bone and depresses mandible
What is the innervation of the anterior and posterior digastric muscles?
anterior digastric: trigemenal cranial nerve (5)
posterior digastric: facial cranial nerve (7)
True or false: The thyrohyoid muscle is innervated by a cranial nerve.
False, its innervated by the 1st cervical nerve.
EXAM QUESTION What is the motor innervation of the jaw-closers?
trigeminal (V)
EXAM QUESTION What is the motor innervation of the digastric muscles?
anterior digastric - trigeminal (V or 5)
posterior digastric - cranial (VII or 7)
EXAM QUESTION What is the motor innervation of the intrinsic tongue muscles?
hypoglossal XII
EXAM QUESTION What is the motor innervation of the extrinsic tongue muscles?
hypoglossal XII
*with one exception (palatoglossus muscle)
What is the exception to the innervation of the extrinsic tongue muscles?
palatoglossus is innervated by vagus cranial nerve X (or 10)
Memorize the path of mastication
Describe the afferent and efferent activities during one chewing cycle.
EFFERENT - from brainstem to oral cavity
opener EMG = opener (i.e., anterior digastric)
closer EMG = closer (i.e., temporalis)
AFFERENT = from oral cavity in opposite direction to brainstem for sensation
periodontal ligament:
cutaneous (mucosa): receptors on the skin that are sensing anything touching the skin (i.e., food touching the cheeks)
*RA –> rapidly adopting action potentials (initial burst which it adjusts to)
*SA –> slowly adopting action potentials (continuous sensation)
What are the periodontal mechanoreceptors?
- mylenated and unmylenated
- ruffini-like endings
*allow CNS to know that the root of tooth being displaced in the socket between the root and alveolar bone
Describe the oral and mucosal mechanoreceptors.
- slowly or rapidly adapting to stimuli
- have specific structural & physiological adaptations depending on area/function
Afferent feedback from oral function comes from other mechanoreceptors such as
- muscle spindles
- golgi tendon organs
- periodontal ligament receptors
True or false: Different textures and properties of food are detected by mucosal mechanoreceptors, to enable modulation of the masticatory pattern according to food consistency.
True
What type of receptive field and adaptive response is good for detecting hard lumpy foods?
- small receptive field
- rapidly-adapting response
What type of receptive field and adaptive response is good for detecting soft, spreading foods?
- large receptive field
- slowly-adapting response
Proprioceptors that lie in the muscle in parallel with muscle fibers
muscle spindles
What happens when the spindle (intrafusal) fibers are stretched?
deforms sensory afferent endings, causing them to fire APs
How is the sensitivity of the spindles to stretch adjusted?
gamma (fusimotor) efferents supplying the intrafusal fibers
In afferent innervation, what do the group Ia afferents singal?
change in length
In afferent innervation, what do group II afferents singal?
absolute length
What are the two functions of gamma motor (fusimotor) supply?
- used to adjust sensitivity of afferents to length changes
- in load compensation, i.e., detection of and compensation for, unexpected alterations to a movement predicted or planned by the CNS (ex. when food is harder than expected)
What are the 2 brainstem structures involved in mastication?
- motor - various cranial motor nuclei
- sensory - trigeminal sensory nucleus - a column or neurons which extend along the lateral borders of the brain stem from the pons to the first two segments of the spinal cord
Primary afferents that detect the peripheral signal will have their cell bodies in 2 places, what are they?
- trigeminal ganlia
- trigeminal mesencephalic sensory nucleus
Secondary afferents are the next step in the afferent pathway, where are their cell bodies located and where do they project?
location: trigeminal main sensory nuclus
projection to: CPG and sensory cortex
Describe the trigeminal neurophysiology diagram
- Mucosal mechanoreceptors found in the mesencephalic sensory nucleus (in CNS)
**monosynaptic: can be direct - PDL mechanoreceptors found in both the mesencephalic sensory nucleus and in the trigeminal ganglion*
*trigeminal ganglion is external to CNS
**need an interneuron b/c external
Where does the trigeminal mesencephalic sensory nucleus lie?
rostral (near the front) to main sensory nucleus
The trigeminal mesencephalic sensory nucleus contains primary afferent cell bodies from what three things?
- spindles of jaw-closing muscles
- periodontal ligament mechanoreceptors
- gingival and palatal mechanoreceptors
The primary afferent neurons send collaterals to which nerve to form the basis fr masticatory reflexes?
motor nucleus of trigeminal (Vth or 5th) nerve
The only part of the CNS with primary afferent cell bodies is
gingival and palatal mechanoreceptors
The ____ contains cell bodies of alpha and gamma motorneurons which innervate the jaw muscles.
trigeminal motor nucleus
How are jaw-opening alpha motorneurons excited?
inputs from the central pattern generator that drives chewing
How are jaw-closing alpha motorneurons excited?
- inputs from the central pattern generator that drives chewing
- by inputs from muscle spindles
How are jaw-closing alpha motorneurons inhibited?
by strong stimuli to mucosal & periodontal ligament afferents
The temporalis muscle is located mostly ___ on the trigeminal motor nucelus?
dorsal
*jaw closing
The diagstric muscle is located mostly ___ on the trigeminal motor nucleus?
ventral
*jaw opening
What are two other motor nuclei that have to be coordinated with the trigeminal motor nuclei during mastication?
- hypoglossal motor nucleus
- crossover to contralateral side
- inputs from CPG (tongue movements during opening/closing) - facial motor nucleus
- facial muscles: buccinator and obicularis oris need to contain food during mastication
- posterior digastric (needs to contract with anterior digastric)
What is patterning the trigeminal motor nuclei to produce movements of opening/closing?
- MOST IMPORTANT: CPG (central pattern generator) responsible for most chewing
- by a reflex (opening or closing)
Where is the CPG located?
brainstem
It’s activity is influence by drive from motor cortex and peripheral receptors
CPG
Describe how the CPG “patterns” movement
electrical recording of
- dorsal masseter skeletal muscle fibers
- ventral on anterior digastric muscles
CLOSING
- inhibitory patterns sent for digastric (ventral motor neuron)
- activation patterns sent for masseter (dorsal motor neuron)
OPENING
- inhibitory patterns sent for masseter (dorsal motor neuron)
- activation patterns sent for digastric (ventral motor neuron)
sterotyped nervous system response to a stimulus
reflex
A reflex can be altered in ____ but not ____
strength (quantitatively)
kind of response (quality)
True or false: Reflexes are ALWAYS unconscious/automatic/innate.
False, they are often but not ALWAYS.
For example, they can be consciously suppressed or learned
What is the jaw-opening reflex?
- main sensory Vth and spinal sensry Vth nuclei
- protective functions for tongue, face, and jaw (i.e., overlad on one tooth with inflamed PDL will inhibit jaw closing)
- usually di-synaptic within CNS and fast
What is the jaw-closing reflex?
- mesencephalic nucleus
- jaw-jerk reflex: monosynaptic reflex elicited by stretching closer muscles, causing the jaw to close
True or false: The jaw closing (jaw jerk) reflex is a di-synaptic reflex.
False, it is monosynpatic.
