Jaw muscles and receptors Flashcards
What are the origins and attachments of the deep and superficial masseter muscle?
Superficial
Origin: zygomatic bone
Attachment: outer surface of angle of mandible
Deep
Origin: zygomatic process of temporal bone
Attachment: ramus of mandible
What are the origins and attachments of the deep and superficial temporalis muscle?
Superficial
Origin: temporal fossa + deep temporal fascia
Attachment: coronoid process
Deep
Origin: Infratemporal crest of sphenoid bone + infratemporal fossa
Attachment: medial side of coronoid process (tendon extends down to lower third molar)
What are the origins and attachments of the upper and lower lateral pterygoid muscle?
Upper
Origin: infratemporal crest of sphenoid bone + infratemporal fossa
Attachment: articulating disk + pterygoid fovea
Lower
Origin: lateral surface of lateral pterygoid plate
Attachment: articulating disk + pterygoid fovea
What are the origins and attachments of the deep and superficial medial pterygoid muscle?
Deep
Origin: medial surface of lateral pterygoid plate
Attachment: roughened area between Md foramen and angle of Md
Superficial
Origin: pyrimidal process + Mx tuberosity
Attachment: roughened area between Md foramen and angle of Md
What are the FOUR main muscles of mastication and their actions?
- Masseter (elevation and protrusion)
- Medial pterygoid (elevation and protrusion)
- Temporalis (elevation and retraction)
- Lateral pterygoid (opening and protrusion)
True or false: the medial pterygoid muscles help the lateral pterygoid muscles move the jaw from side to side
True
What are the FOUR types of motor units?
- S (slow-contracting, fatigue-resistant)
- FR (fast, fatigue-resist)
- FF (fast, fatigable)
extra:
- Fint (fast, intermediate fatigable)
What are FIVE ways in which the main motor unit types differ?
- Twitch speed
- Twitch strength
- Fatigue
- Motorneuron size
- Activation timing
What is one main way jaw muscle fibre type composition varies from limb/trunk muscles? (Link this to a purpose)
- Large quantity of hybrid fibres vs. limb/trunk
Purpose: - jaw requires ability to apply diversity of forces/movement
- jaw is also able to adapt
What are FIVE factors that may affect jaw fibre-type composition?
- Aging (less neonatal myosin)
- Hormones (e.g. testosterone)
- Food (hardness of food)
- Dentures/edentulousness
- Craniofacial morphology (e.g. open bite)
What are TWO ways to measure muscle activity?
- Electromyography (EMG)
- Mechanomyography (MMG)
What are FIVE steps to muscle contraction? (AP has reached synaptic terminal at motor end plate)
- ACh released, binding to receptors on muscle opening Na channels -> AP
- AP travels down T-tubules
- Sarcoplasmic reticulum releases Ca2+
- Ca2+ binds to troponin, moving tropomyosin to reveal active actin active site
- Myosin (thick chain) binds to actin -> contraction towards centre of sarcomere
How does the firing threshold at the input of a motorneuron compare with that of a sensory neuron?
Firing threshold of motorneuron much higher (requires integration of inputs to reach threshold)
How is recruitment timing of different motor unit types made possible?
The motorneuron types are of different sizes, larger ones having a larger firing threshold (ie. recruited last)
What are the corresponding functional and histochemical classifications of the motor unit types?
- S = Type I
- FR = Type IIA
- FF = Type IIB
What is the main function of S type motor units compared to FF type?
S = suited for postural tasks (less force reqd, less fatigable)
FF = Strong rapid bite tasks
(force reqd, short duration)
What does MVBF stand for and where is it greatest in the oral cavity?
Maximum Voluntary Bite Force
- Greatest in first molar area
Do periodontal mechanoreceptors (PMRs) have excitatory or inhibitory connections with the muscles of mastication?
Inhibitory
opening “fishbone” reflex a possible example
What are TWO ways in which PMRs at root apex differ from those at the mid-root region?
Mid-root PMRs
- Cell bodies in trigeminal ganglion
- Rapidly adapting
Root apex PMRs
- Cell bodies in mesencephalic nucleus
- Slowly adapting
What are the THREE types of sensory nerve fibres associated with muscles?
Are they excitatory or inhibitory?
- Type Ia (muscle spindles - fast adapting, detect changes in muscle length -> excitatory)
- Type Ib (GTO -> inhibitory)
- Type II (muscle fibres - slow adapting, detect muscle position -> N/A)
What are FIVE inputs that are integrated by the alpha motorneurons? (ie. give feedback to jaw muscles)
- Ia (muscle spindle)
- Ib (GTO)
- PMRs
- Mucosal
- TMJ
How long does it take an adult muscle to adapt to a new length? (e.g. jaw muscle adaptation after new dentures put in place)
A few weeks.
What occurs in MS?
Demyelination of motor axons
What occurs in Myathenia Gravis?
Blockage of ACh receptors
