Week 4: Globe, EOM and Sclera Flashcards
What are the peripheral nervous systems?
- Somatic nervous system
2. Autonomic nervous system
Explain what is somatic nervous system, its neurotransmitter and what it contains
- Voluntary movement of the body
- Covers skeletal muscles and sensory stimuli
- Neurotransmitter: acetylcholine
1. Afferent (signal travelling inwards): sensory - pressure, heat, pain
2. Efferent (signal travelling outwards): motor: skeletal muscle
Explain what is autonomic nervous system, its neurotransmitters and what it contains
- Involuntary movement of the body (e.g. heart rate, digestion)
- Neurotransmitters: acetylcholine & norepinephrine
1. Sympathetic nervous system
2. Parasympathetic nervous system
What is sympathetic nervous system and what ocular innervations does it include?
- Fight or flight response
- Ocular innervation includes: iris dilator (pupil larger), ciliary muscle, superior tarsal muscle, lacrimal gland, choroidal & conjunctival blood vessels
- Sympathetic ganglion is the Superior Cervical Ganglion
What is parasympathetic nervous system and what ocular innervations does it include?
- Rest and digest response
- Ocular innervations include: iris sphincter (pupils smaller), ciliary muscle, lacrimal gland
- Parasympathetic Ganglion is the Ciliary Ganglion
What type of pathway is the optic nerve (CNII) and describe the pathway process
- Sympathetic afferent pathway (going in)
- Pathway:
1. Retinal ganglion cells
2. Cortical & sub-cortical visual centres in the brain
3. RGC axons become myelinated in the optic nerve & sends message - Surrounded by cranial meninges
What type of pathway is the oculomotor nerve (CNIII) and explain its function and what it innervates
- Efferent pathway (going out)
- Function: eye movement
- Innervation of:
inferior rectus
inferior oblique
medial rectus
superior rectus
levator palpaebrae superioris
iris sphincter (parasympathetic innervation)
ciliary muscle (parasympathetic innervation)
What type of pathway is the trochlear nerve (CNIV) and explain its function, what it innervates and action of the EOM
- Efferent pathway (going out)
- Function: eye movement (intorsion, depression & abduction)
- Innervation of: superior oblique
- Action of SO is depression and adduction (eye will point down and in)
What type of pathway is the trigeminal nerve (CNV) and explain its function and its three divisions
- Afferent pathway (going in)
- Function: facial motor and sensory
- Divisions: ophthalmic division (V1), Maxillary division (V2), mandibular division (V3)
What is the ophthalmic nerve function and its three main branches?
- Most superior and smallest division
- Function: sensory
- Prior to entering the orbit, through the superior orbital fissure, it divides into 3 main branches: lacrimal nerve, frontal nerve & nasociliary nerve
Describe the lacrimal nerve
- Sensory innervation of the lacrimal gland, upper eyelid and conjunctiva
- Contains parasympathetic and sympathetic efferent to lacrimal gland
Describe the frontal nerve and what they divide into & what branches supply
- Largest branch of ophthalmic nerve
- Half way in the orbit, it divides into 2: large supraorbital branch & small supratrochlear branch
- Supraorbital branch (supplies skin & conjunctiva of upper eyelid, skin of forehead & scalp, mucus membrane of frontal sinus)
- small supratrochlear branch (supplies skin & conjunctiva of upper eyelid, skin of medial forhead)
Describe the nasociliary nerve, what they divide into & what they innervate
- Short ciliary nerves
- Two long ciliary nerves
- Divides into: infratrochlear nerve & posterior ethmoid nerve
- Infratrochlear nerve innervates conjunctiva of medial upper eyelid, medial canthus, lacrimal sac, caruncle & skin on bridge of nose
- Posterior ethmoid nerve innervates mucosa of sphenoid & posterior ethmoidal sinuses
What is the maxillary nerve three main branches (elaborate)?
- Infraorbital nerve: sensory fibers from cheek, upper lip, lower eyelid, lateral aspect of nose
- Zygomatic nerve: sensory fibers from temporal region, cheek and lower eyelid
- Posterior superior alveolar: sensory to teeth, maxillary sinus
What is the mandibular nerve functions and their sensory and motor?
- Function: has sensory and a motor root
- Sensory: teeth and gums of mandible, lower lip, lower part of face
- Motor: chewing
What does the abducens nerve (CNVI) innervate and explain its function
- Innervates: lateral rectus muscle
- Function: eye movement (lateral rectus)
- Has a long intracranial course exposing it to a high risk of dysfunction
What does the facial nerve (CNVII) contain? (2 roots)
- Large motor root: innervates facial muscles
- Smaller sensory root: from superior salivatory nucleus
Explain the eye movement of abduction
- Eye moves temporally
- LR contracts & MR relaxes
Explain the eye movement of adduction
- Eye moves nasally
- MR contracts & LR relaxes
Explain the eye movement of elevation
- Eye moves upwards
- SR contrats, IO contracts
Explain the eye movement of depression
- Eye moves downwards
- IR contracts & SO contracts
Define version (binocularly)
- Simultaneous movement of both eyes in same direction
Define vergence (binocularly)
- Simultaneous movement of both eyes in opposite directions
1. Convergence (contract both MR)
2. Divergence (contract both LR)
Define position of gaze (binocularly)
- Primary: both eyes fixate a distant object directly ahead
- Secondary: up, down, left, right
- Tertiary: up-right, up-left, down-right, down-left
Define agonist muscle (binocularly)
- Main muscle that moves eye in a given direction
1. Synergistic muscle: EOM in the same eye that achieve same eye movement as agonist
2. Antagonist muscle: EOM in the same eye that achieve opposite eye movement as the agonist
3. Yoked muscles: muscles in the two eyes that accomplish a given movement
List the ductions and define them
- Supraduction = elevation in one eye
- Infraduction = depression in one eye
- Incycloduction (intorsion) = nasal rotation in one eye
- Excycloduction (extorsion) = temporal rotation in one eye
List the conjugate (versions) and define them
- Dextroversion = movement of both eyes to the right
- Levoversion = movement of both eyes to the left
- Supraversion = elevation of both eyes
- Infraversion = depression of both eyes
List the disconjugate (vergences)
- Convergence (contract both MR)
- Divergence (contract both LR)
List the measurement of the sclera and describe the colour of it
- Posterior 5/6th if fibrous layer of the eyeball
Colour:
- Opaque white in adults
- Slightly bluish in children
- Yellowish from fat deposition in elderly
What is the connections for the sclera?
- Connected by delicate connective tissue to the fascial sheath of the eye ball
- Connected with EOMs at insertions
List the structure/layers of the sclera and explain them in detail
- Episclera
- Outermost layer
- Loose connective tissue - Sclera stroma (main body)
- Dense fibrous tissue - Lamina fusca
- Inner most layer
- Brown due to melanocytes
List the types of EOM fibers and explain in detail
- Type A
- Large diameter
- Fast twitch (contracts quickly)
- Used for saccadic movement - Type B
- Intermediate diameter
- Slow twitch (contracts slowly)
- Used for smooth pursuit movements - Type C
- Small diameter
- Tonic contractions (sustained, slow, graded contractions)
- Used to align right & left visual axes - fine tuning local contractions
