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0V015 Biology & Pathology > L39 Ocular Pain & The Trigeminal Nerve > Flashcards

L39 Ocular Pain & The Trigeminal Nerve Flashcards

1
Q

What are the two main classes of sensory receptors in somatic tissue?

A

1) Free nerve endings

2) Specialized Mechanoreceptors

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2
Q

What information do free nerve endings pass on?

A

Pain or temperature sensitivity.

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3
Q

Name two types of Specialised Mechanoreceptor.

A 
Tactile Receptors (touch, pressure).
Proprioceptors (e.g., joint position)
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4
Q

Trigeminal (V) nerve mediates touch, thermal, and pain sensation of what parts of the eye?

A

Anterior corneal surface/epithelium.
Inside the eye: Uvea=choroid ,ciliary body & iris
Orbital Contents & Eyelids + Conjunctiva.

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5
Q

Why is the Trigeminal (V) Nerve so important for ocular defence?

A

It triggers the Corneal-Eyeblink reflex which is incredibly important for dealing with foreign bodies, grit, blunt trauma.

Furthermore, Px is alerted about damage and disease via pain (which is transmitted across this nerve from receptors).

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6
Q

The trigeminal nerve can divides into three major nerve branches (Opthalmic ‘V1’, Maxillary ‘V2’, Mandibular ‘V3’) - are these crossed or uncrossed?

A

Uncrossed.

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7
Q

True or false - the trigeminal nerve which can be split into 3 major nerve branches can again be split into smaller sub nerve branches!

A

You guessed it - It’s true - enjoy how complicated its gonna get!

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8
Q

What are the three subdivisions of the Opthalmic (V1) nerve [which is already a subdivison of the trigeminal nerve]?

A

1- Nasociliary nerve

2-Lacrimal Nerve

3-Frontal Nerve

(NB: All join together & exit the orbit vias Superior Orbital Fissure as V1).

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9
Q

Nasociliary Nerve Flashcard :

What is it a subdivison of?

What path does it take?

Describe its structure.

A

Opthalmic (V1) nerve [which is a branch of the trigeminal nerve].

Medial orbital path.

Has long and short Ciliary branches: taking sensory information from the eye.
Nasal branches: which take sensory information from inside the nasal cavity.
Infra-trochlear: which comes from Medial upper eyelid.

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10
Q

Lacrimal Nerve Flashcard :

What is it a subdivison of?

What path does it take?

What does it do?

A

Opthalmic (V1) nerve [which is a branch of the trigeminal nerve].

Lateral orbital path.

Takes sensory information from lateral side of upper eyelid, conunctiva and from sensory supply of lacrimal gland.

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11
Q

Frontal Nerve Flashcard :

What is it a subdivison of?

What path does it take?

What does it do?

A

Opthalmic (V1) nerve [which is a branch of the trigeminal nerve].

Upper orbital path

Takes sensory information from the forehead skin and scalp.

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12
Q

All small & 3 major nerve branches of the Trigeminal (V) nerve contain peripheral axons of…..

A

Trigeminal ganglion cells. ( How the structure works is that basically all the small nerves and 3 major nerves meet at the trigeminal ganglion at which point it all meets to form the 5th nerve root which enters the brainstem and terminates in different trigeminal nuclei.

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13
Q

True or False- The surface of your cornea contains a high density of receptors - as much as the skin of your fingertips!

A

ITS TRUE!!

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14
Q

How do sensations arise from the cornea (& uvea)?

A

Receptors are present in the anterior epithelium. Their axons pass via bowman’s membrane to run radially through the stroma (basically like spokes on a bike wheel) to leave in all directions at the limbus and enter the ‘supra-choroid’ just below the sclera & join axons coming from receptors in the uveal tract.

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15
Q

Define phasic in respect to receptors

A

It means to provide fast responses to stimulation

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16
Q

What are nocireceptors?

A

Pain receptors

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17
Q

What does it mean for a receptor to be poly-modal?

A

To be polymodal means responding to several different forms of sensory stimulation (as heat, touch, and chemicals.

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18
Q

What does it mean for a response to be tonic?

A

Long lasting response may also be called slow adapting.

19
Q

How does the corneal eyeblink reflex work?

A

It has two limbs - Sensory Limb and Motor Limb.

Sensory Limb=> this is sensitive to cornea being touched or dry. Receptors are activated on corneal surface. These receptors have axons that travel down the long ciliary, nasociliary and opthalmic nerves and then the 5th nerve root to trigeminal brainstem nuclei.

Motor limb=> Somatic motor neurones in main facial nucleus. Their axons run in facial (VII) nerve,then via temporal and zygomatic branches to forcefully contract the orbicularis oculi.

20
Q

What are the two parts to the orbicularis occuli and which is used when?

A

The palpebral part and orbital part of the muscle.

When you gently blink you contract the palpebral part of the orbicularis oculi.

When you forcefully blink you contract both the palpebral and orbital parts of the Orbicularis Oculi. This part of the orbicularis oculi is associated with ocular defence as its usually done to move something around out of your eye.

21
Q

Which of these nerve carries sensory information from the cornea?

a) Frontal nerve
b) Lacrimal
c) Naso-ciliary
d) Optic

A

c) Naso-ciliary nerve

22
Q

What do pain stimuli & Nocireceptors respond to?

A 
Damage caused by combinations of:
Mechanical deformation (pinch, cut)
Temperature extremes (heat,cold)
Chemical irritants (e.g., acid, histamines)
23
Q

What are the two major nocireceptor classes?

A

C-fibres & A-delta fibres

24
Q

What is the difference between A-fibres and C-fibres? -(Both of which are a type of nocireceptor)

A

C-fibres :

  • small diameter
  • unmyelinated axons
  • cause pains that you may percieve as dull,aching,throbbing (cold) & stinging pains.
  • Usually polymodal - i.e. respond to any/all of the three types of tissue damage.

A-delta fibres:

  • small diameter axons
  • have some myelinated.
  • Mechano-thermal sensitive NOT chemical sensitive (or to cold temp).
  • cuase what is percieved to be sharp,stabing or sticking (hot) pain.
25
Q

Where do C-fibres get their name from?

A

Capsaicin - its an irritant present in chillies and only C-fibres respond to it. (c-fibres respond to histamine only do).

26
Q

What is the composition of nocireceptor classes across the cornea and uvea?

A

Around 66% C-fibres and 33% A-delta fibres.

27
Q

Why is it easier to specifically locate pain in cutaneous (skin) tissue rather than in visceral (deep) tissues (like the eye)?

A

In Cutaneous tissue there is 1 free nerve ending per axon and free nerve endings are very compact - in the sense that there are lots of them present and so they all have a very small ‘receptive field’ i.e. each nerve ending has a very small area they are responsible for detecting a change in . Futhermore, there’s also no overalp in these receptive fields thus locating pain on ur skin can be very precise.

Whereas, in visceral tissue there are many widespread endings per axon. This results in large ‘receptive fields’ & overalpping. Thus it can be harder to identify where exactly pain is located in deep tissue.

28
Q

What are some common examples of naturally-occuring ocular pain ON or IN the eye?

A

Dry-eye & corneal scratches (irritation)
Uveitis (infection), Glaucoma (raised IOP)
Tumours (e.g., melanoma)

29
Q

What are some examples of naturally-occuring ocular pain on the OUTSIDE of the eye?

A

Orbital blow-out fracture
Conjunctivitis & Orbital Cellulitis
Optic Neuritis (inflammation of the Optic Nerve)
Herpes Zoster Opthalmicus (inflammation of V1)

30
Q

What are some examples of Iatrogenic pain (pain caused by health professionals)?

A 
Eye drops (acidic vehicle for atropine causes irritation to eye)
Laser Eye surgery (e.g.,to repair retinal tears)
31
Q

What is Uveitis?

How can it be caused?

What symptoms are experienced?

How is it mediated?

Major concerns associated?

How can it be treated?

A

Inflammation of the Uveal tract.

Autoimmune or Microbial

Deep Dull pain (which is caused by the release of histamine)

T cell mediated

It doesnt just stay in the uvea it spreads via anterior iridal circle. (Causing the appearance of a ‘circum-limbal’ flush- basically thick red blood vessels around the limbus)

Steroids- for the sake of immune supression and & anti-inflammatory purposes.

32
Q

What is an Orbital blow-out fracture caused by and what occurs as a result?

A

Trauma from object larger than orbit fractures orbital floor (maxilla bone).

Causes pressure waves inside the orbital cavity - these pressure waves cause the bone that forms the main floor to fracture.

Herniation (movement) of orbital contents(fat) into maxillary sinus.

33
Q

What is Orbital Cellulitis?

How can it be caused?

What symptoms are experienced?

Major concerns associated?

How can it be treated?

A

Begins with common cold- this is associated with inflamation of sinuses , maxillary sinus is one of these sinuses. Ethmoid bone seperates two orbits. This also has an air sinus inside it. Bacteria causing sinusitis stays there and doesnt go away. This vauses chronic inflamation of sinuses. Over a period of time bacteria eats it’s way through bone and get into orbital cavity behind eyeball.

Red & Swollen eyelids, ocular pain especially when moving the eyes.

It is officially a medical emergency! Get them to a hospital because spread of infection causes cranial infection which can lead to death!

IV steroids.

34
Q

What is ZOSTER associated with?

A

Chicken Pox

35
Q

What is Herpes Zoster Opthalmicus?

Why is it common in older people?

Symptoms?

A

SHINGLES associated with V1 nerve. (It’s basically chicken pox that has hidden in that particular nerve).

As you get older to a degree you become immuno supressed.

Painful Rash (vesticular erruptions ) affceting V1 nerve territroy.

36
Q

Refrerred Pain

A

Pain you get in one location because you have damage in another location. (Think left arm pain when you have a heart attack).

37
Q

When may you have refered ocular pain (usually accompanied with a headache)?

A

Membranes that surround your brain (meninges) become inflammed (meningitis) or by compression (tumours)- both cuase referred eye pain.

Large arteries around base of brain - if these have any pathology to them (i.e. an aneurysm or arthero-scelerosis) sometimes you get eye pain.

38
Q

WHY may you have referred ocular pain due to inflamed or compressed membranes around the brain or because of pathology of large arteries around brain?

A

Pain receptors located in these membranes & walls of arge arteries have axon branches that also run in the opthalmic & ciliary nerves into the eye.
Px experiences ocular pain ‘as if’ the pain receptors in the cornea & uvea are also being stimulated.

39
Q

What are some mechanisms we have for dampening pain?

A

Analgesics- Opiates:
Distributed around our brains and spinal chords there are chemical receptors for endorphins. Neurones release opiods (analgesics- drugs that relieve pain) to dampen pain.

Local control via inhibitory interneurones:
-activated by fast-conducting mechano-receptors via opiodergic interneurones in substansia gelatinosa in the second layer of the spinal cord and equivalent trigeminal nucleus. These inhibit/block layer V neurones receiving pain signals and sending them ton the brain. –> This is the gate theory.

40
Q

How is the gate therory on pain applied to caring for individuals?

A

It is exploited in Trans-Cutaneous Electrical Nerve Stimulation (TENS) as a means of palliative care. Basically you relief the pain but don’t actually sort out the problem. (Normally used in palliative care).

41
Q

What is a projection neurone?

A

One that fires action potentials.

42
Q

How does Rubbing a cut/graze make it ‘better’?

A

‘Rubbing it better’ stimuates Type I,II mechanoreceptors . These activate inhibitory neuornes. which inhibit projection neuron. This blocks off transmission of Nociceptive signals to the brain.

That is what TENS does.

43
Q

How can TENS be used for pain relief in herpes Zoster?

A

By stimulating superficial , cutaneous (intra-trochlear) branches of the opthalmic nerve.

44
Q

Which of these is true about pain sensation?

a) C-fibres mediate sharp pinch and cutting pains.
b) the retina contains no pain receptors
c) Pain from inside the eye is conveyed to the brain via the optic nerve
d) Diagnosis of the painful condition of anterior Uveitis requires a CT scan of the eye.

A

b- the retina has no pain receptors

0V015 Biology & Pathology (57 decks)

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