muscles of mandible
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Muscles of mandible
By: Abdul Muhaimin (D11 A007)Reference: Veterinary anatomy of domestic animal
(Book)
Mandibular muscles
• Comprise muscle of mastication and superficial muscles of mandibular space.
• Innervated by mandibular nerve (trigeminal nerve)
• Responsible for movement jaw (mastication)
• Covers mandibular space and hyoid apparatus ventrally.
• Different species have their own structure of muscle for mastication.
Mandibular muscle
• Muscle of mastication– Masseter muscle– Medial and lateral pterygoid muscles– Temporal muscle
• Superficial muscles of mandibular space– Digastric muscle– Mylohyoid muscle
• Masseter muscle– Broad multipennate muscle– Multiple tendinous intersections
• Origin– From ventral border of zygomatic arch and facial crest
• Insertion– On the lateral aspect of mandible
• Extend– From facial notch to temporomandibular joint.
Muscle of mastication
• In carnivores, it is separated into 3 layers – Superficial, middle, deep (by tendinous sheets)
• Superficial portion is the strongest• Middle layer is the weakest• In pig, these three layers are firmly fused• Tendinous intersections are pronounced, forming 5
distinct parts in the ox.• Change in fibre direction between each portion
increases masticatory force of this muscle
Masseter muscle
• In horse, it shows up to 15 tendinous intermuscular strands which are orientated sagitally and divide muscle into multiple layers.
• Both sides masseter muscles act together will force upper and lower jaw together
• Mandible can be move to the side of contracting muscle (grinding in herbivores)
Masseter muscle
• Pass from palatine, pterygoid and sphenoid bones to the medial aspect of mandible.
• Lateral pterygoid muscle is smaller than medial one.
• In carnivores, both are fused at their origin• Horse: medial pterygoid muscle is covered by
lateral one. Mandibular nerve passes across lateral surface of medial pterygoid muscle (separating 2 pterygoid muscles).
Pterygoid muscle
• Pterygoid and masseter muscles contract bilaterally will raise mandible, but if working unilaterally, will draw mandible to side of contracting muscle.
• Lateral portion also able to move mandible rostrally (mouth open)
Pterygoid muscle
• Size varying in different species depending size fossa
• The strongest muscle of head in carnivores.• Dolichocephalic dogs: temporal muscle meets
corresponding muscle of opposite side in midline (form mid-line sulcus)
• Brachycephalic dogs: two muscles don’t meet, no sulcus visible
Temporal muscle
• Ruminant: temporal muscle is indistinct but visible in horse
• Horse: temporal muscle however do not well developed compared to other masticatory muscles.
• It raises mandible acting together with other masticatory muscles.
Temporal muscle
• Assist muscles of mastication. Cover ventral side of lingual muscles in mandibular space.
• Digastric muscle– Single bellied muscle in domestic animal (except
horse)– Horse: has caudal and rostral bellies– Other domestic mammals: evolutionary bipartite
structure is indicated by a fibrous intersection.
Superficial muscle of mandibular space
• Rostral part is innervated by mylohyoid nerve (branch of mandibular nerve)
• Caudal part by digastric branch of facial nerve• In carnivores: it is strong single-bellied muscle
with delicate tendinous strands (mark division between rostral and caudal portion)
• Ruminants: tendinous intersection between two bellies is indistinct.
• Horse: rostral belly depresses mandible and opens mouth
Digastric muscle
• Form sling between inner surface of body of mandible
• Innervated by mylohyoid nerve (branch of mandibular nerve), assigned to mandibular group
• Can also be seen as lingual muscle (its function)
• Supports tongue and raises it towards palate
Mylohyoid muscle
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