muscles of mastication

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Muscles of facial expression, mastication; sensory to face; TMJ; CN VII, V : 

Muscles of facial expression, mastication; sensory to face; TMJ; CN VII, V Objectives: Identify and describe the function of the muscles of mastication and major muscles of facial expression Describe the innervation of the above muscles by the trigeminal (V) and facial (VII) nerves, and the UMN control of LMNs via the corticobulbar tract Describe the general sensory innervation of the face by the trigeminal nerve (CN V), including central pathways List and identify the major blood vessels and lymphatics of the face and infratemporal region, and know their main areas of supply/drainage

Announcements : 

Announcements The third hour of practical sessions is a good opportunity to ask staff questions you may have Please spray cadavers with tissue spray periodically during dissection, including the trunk region, and keep the trunk covered Lab coats and appropriate attire needed for dissection, explorations (neuro and anatomy mini-exploration sessions) Remember to sign in/out

Muscles of facial expression : 

Muscles of facial expression Generally from skull to skin Innervated by facial nerve (CN VII) Sphincters and dilators around mouth (lips), eyes, nostrils Wrinkle lines perpendicular to muscle fibres Netter 20

Muscles around mouth : 

Muscles around mouth Sphincter: orbicularis oris Numerous dilators (levators/depressors of upper/lower lip and angle of mouth) Buccinator Netter 48

Muscles around eye : 

Muscles around eye Sphincter: orbicularis oculi (palpebral and orbital parts) Blink (spread tears across cornea) and close eyes tightly Note: elevators of upper lid innervated by CN III, sympathetics Netter 20

Innervation of muscles of facial expression: facial n (VII) : 

Innervation of muscles of facial expression: facial n (VII) LMNs in facial nucleus in inferior pons Fibres course around abducens nucleus - internal genu Exits brainstem at cerebellopontine angle with CN VIII “acoustic neuroma” of CN VIII may secondarily affect CN VII Netter 108 Fix 29

Course of facial nerve (CN VII) : 

Course of facial nerve (CN VII) Through the petrous part of the temporal bone: Through internal acoustic meatus with CN VIII Into facial canal, along walls of the tympanic cavity (external genu of facial nerve, geniculate ganglion) Exits skull via stylomastoid foramen, most branches go through parotid gland Temporal Zygomatic Buccal Marginal mandibular Cervical Posterior auricular Netter 92, 5, 19

UMN control over facial nucleus LMNs: Corticobulbar tract : 

UMN control over facial nucleus LMNs: Corticobulbar tract Cell bodies in primary motor cortex (precentral gyrus of frontal lobe) and nearby areas Fibres travel through... Genu of internal capsule Cerebral peduncle of midbrain Basal pons LMNs for upper 1/3-1/2 of face: UMNs supply LMNs bilaterally LMNs for lower 1/2-2/3 of face: UMNs supply contralateral LMNs only Additional emotional cortical control Nolte 447

Damage to UMNs, LMNs, or facial nerve : 

Damage to UMNs, LMNs, or facial nerve Clinical testing: raise eyebrows, close eyes tightly, smile Unilateral UMN: contralateral lower 1/2-2/3 of face paralysed Unilateral LMN or CN VII: entire ipsilateral face paralysed (Bell’s palsy) Lack of blinking Leaky mouth Speech difficulties (other CN VII functions) http://mdchoice.com/photo/img/img0221.jpg http://medicine.tamu.edu/neuro/36.gif

Muscles of mastication (chewing) : 

Muscles of mastication (chewing) Temporalis, masseter Lateral and medial pterygoids Located in infratemporal fossa (Various other muscles involved in chewing: orbicularis oris, buccinator, digastric, geniohyoid, tongue muscles) Netter 48, 49 Weir 19c

Temporomandibular joint : 

Temporomandibular joint Condylar process (head) of mandible with mandibular fossa of temporal bone, separated by articular disc Hinge, gliding, side-to-side movements Elevation/depression (close/open), protrusion/retraction, ab/adduction Netter 11

Actions at TMJ : 

Actions at TMJ Open: gravity, digastric, geniohyoid, lateral pterygoid (open wide) Close: masseter, temporalis, medial pterygoid Protrusion: pterygoids, masseter Retraction: temporalis (posterior) Side-to-side grinding: pterygoids Clinical testing: clench teeth (close jaw) – palpate masseter Open jaw wide and try to force it closed – deviates to side of weakness Netter 48, 49

Innervation of muscles of mastication: mandibular division of trigeminal nerve (V3) : 

Innervation of muscles of mastication: mandibular division of trigeminal nerve (V3) LMNs in trigeminal motor nucleus in middle pons CN V exits brainstem laterally from middle pons Netter 108 Fix 31

Course of trigeminal nerve, mandibular division (V3) : 

Course of trigeminal nerve, mandibular division (V3) Exits skull via foramen ovale Travels through infratemporal fossa Various branches to mm of mastication, etc Netter 41, 5, 98

UMN control of trigeminal nucleus LMNs: Corticobulbar tract : 

UMN control of trigeminal nucleus LMNs: Corticobulbar tract Cell bodies in primary motor cortex (precentral gyrus of frontal lobe) and nearby areas Fibres travel through... Internal capsule (genu) Cerebral peduncle of midbrain basal pons UMNs supply LMNs bilaterally Unilateral UMN damage: Little/no effect Unilateral LMN or V damage: Ipsilateral paralysis Difficulty chewing, speaking Nolte 447

Cutaneous innervation of face and scalp : 

Cutaneous innervation of face and scalp Branches of trigeminal nerve (CN V): Ophthalmic (V1) Maxillary (V2) Mandibular (V3) Each has 3-5 named cutaneous nn Cervical plexus branches (C2) Lesser occipital Great auricular Greater occipital nerve (dorsal ramus of C2) Netter 18

Primary sensory neurons in trigeminal ganglion : 

Primary sensory neurons in trigeminal ganglion Central processes enter lateral mid-pons Exception: proprioceptive primary sensory neurons in mesencephalic nucleus of V in midbrain - only known primary sensory cell bodies in CNS Netter 98, 108

Secondary sensory neurons: main and descending nuclei of V : 

Secondary sensory neurons: main and descending nuclei of V Pain and temperature in descending nucleus of V Touch, vibration in main sensory nucleus of V Axons cross the midline Ascend as trigeminothalamic tract Fix 20,23,30 Netter 111

Tertiary sensory neurons: VPM of thalamus Fourth order neurons: primary somatosensory cortex : 

Tertiary sensory neurons: VPM of thalamus Fourth order neurons: primary somatosensory cortex Tertiary: Ventroposteromedial (VPM) nucleus of thalamus Fourth order: post-central gyrus of parietal lobe Homunculus – face area is lateral Fix 56, Nolte 72, Netter 99

Clinical testing of sensory component of V : 

Clinical testing of sensory component of V Gentle pinprick (should feel sharp) and light touch (wisp of cotton) with eyes closed – test V1, V2, V3 areas Corneal blink reflex – touch cornea with wisp of cotton – both eyes should blink (afferent V, efferent VII) Netter 99, Nolte 312

Structure of the scalp : 

Structure of the scalp Skin Connective tissue (dense) Aponeurosis, epicranial Occipitofrontalis muscle Loose connective tissue Pericranium (outer periosteum) Scalp wounds bleed heavily Netter 20 Rosse 31.14

Arteries of face and scalp : 

Arteries of face and scalp Branches of external carotid a Facial artery (pulse pt) Superficial temporal (pulse pt) Occipital Posterior auricular Branches of ophthalmic a (from internal carotid) Netter 17

Maxillary artery : 

Maxillary artery A terminal branch of external carotid artery Supplies maxilla and mandible (upper and lower jaws), muscles of mastication, nasal cavity, palate Middle meningeal a (involved in epidural haematoma) Netter 3, 35

Veins of face and scalp : 

Veins of face and scalp Generally parallel arteries Superficial temporal joins maxillary, forming retromandibular (posterior part and posterior auricular form EJV) Facial vein joins retromandibular (anterior part), to IJV Connections to ophthalmic veins, pterygoid plexus, which are connected to cavernous sinus in cranial cavity (potential route of infection spread) Netter 64

Lymphatics of face and scalp : 

Lymphatics of face and scalp Located along veins Superficial and deep groups Facial to submandibular to deep cervical nodes (along IJV) Submental to deep cervical nodes Parotid to superficial (along EJV) and deep cervical nodes Netter 66, Rosse 31.22