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Medicine year 2 semester 2 > Case 21- Physiology and antomy > Flashcards

Case 21- Physiology and antomy Flashcards

1
Q

The basis of retinal colour blindness

A
  • Red and green photopsin on X chromosome
  • Blue photopsin on chromosome 7
  • …opia = absent gene
  • …anomalous = gene with altered sensitivity
  • Prot… = red
  • Deuter… = green
  • Tritan… = blue
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2
Q

How information moves from the retina to the brain (visual pathway)

A

Retina -> Optic nerve -> Optic chiasm -> Optic tract -> LGN (Lateral Geniculate Nucleus) -> Optic radiation -> Striate cortex

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3
Q

Visual field

A

The entire area that can be seen when the eye is directed forwards, it includes the peripheral vision. The fields are divided into temporal and nasal halves and superior and inferior halves.

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4
Q

Structure of the visual fields

A

The left visual field correlates to the left eye and the right visual field correlates to the right eye. They are divided into 4 quadrants, two are on the nasal side nearest the nose and two are temporal which are more lateral. Can also be divided into superior and inferior.

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5
Q

Binocular vision

A

Binocular vision allows the image from both eyes to be combined by the brain into one. It helps with depth perception and judging the speed of an objects movement. Gives us more information

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6
Q

Quadrants in Binocular vision

A

The image on the retina appears inverted to real life. Quadrant 1 which is in the Superior Temporal lobe moves to the Inferior Nasal quadrant. Quadrant 2 which is in the superior nasal location moves to the inferior nasal lobe
The optic nerve goes through the optic chiasm and along the optic tract.

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7
Q

How visual information is relayed through the Optic chiasm

A
  • Information from the nasal retina (1,2,7,8) crosses over at the chiasm i.e. going from the left eye to the right optic tract.
  • Information from the temporal retina (3,4,5,6) remains on the same side
  • All information from the right half of both visual fields is transferred to the left optic tract (3,4,7,8) i.e. the left half of the left and right eye
  • All information from the left half of both visual fields is transferred to the right optic tract (1,2,5,6)
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8
Q

How visual information travels from the Optic tract

A

Information from the Optic tract ends up in the Lateral geniculate nucleus of the Thalamus and is where the retinal ganglion cells terminate. Information is transferred to the optic radiation to continue the pathway. The optic radiation goes from the LGN to the Primary visual nucleus (Striate cortex).

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9
Q

Optic radiation- visual field

A
  • From LGN -> Lateral fibres (Mayers loop) ->Carry information about the inferior retinal field, because the image was inverted it corresponds to the superior visual field -> Primary visual cortex
  • From LGN -> Medial fibres -> goes through the parietal cortex -> Carry information about the superior retinal field because the image was inverted it corresponds to the inferior visual field -> Primary visual cortex
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10
Q

PITS

A

Parietal lobe -> inferior visual fields (medial fibers)

Temporal lobe -> superior visual field (lateral fibers)

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11
Q

Where visual information from the different quadrants ends up

A
  • Left optic tract, Lateral loop temporal- 3,7
  • Left optic tract, Medial loop parietal- 4,8
  • Right optic tract, Lateral loop temporal- 1,5
  • Right optic tract, Medial loop parietal- 2,6
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12
Q

Light reflex- to the Edinger-Westphal nuclei

A
  • Light is shone to the left eye and is picked up by the retina
  • Information is picked up by the optic nerve and goes through the optic chiasm to the optic tract.
  • Before the LGN there are some branching fibres which go to the midbrain
  • It goes to the Pretectal area and then via interneurons to the Edinger-Westphal nucleus. One pretectal area connects to both Edinger-Westphal nuclei. There is bilateral innervation of the nucleus
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13
Q

Light reflex= after the Edinger-Westphal nuclei

A
  • The Edinger-Westphal nuclei is the parasympathetic nuclei of Cranial nerve III. The Oculomotor cranial nerve continues to the Ciliary ganglion. Post ganglionic fibres continue via the short ciliary nerve to the iris and causes constriction of the pupil
  • The bilateral innervation of the Edinger-Westphal nucleus means there is constriction of both pupils so you have a direct and consensual response
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14
Q

Sphincter/Dilator pupillae muscles of the iris

A

Sphincter pupillae muscle of the iris= Circular muscles, Parasympathetic, Constriction/miosis
Dilator pupillae muscle of the iris= Radial muscle, Sympathetic, Dilation/mydriasis

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15
Q

Afferent limb of the pupillary reflex

A

Light -> Cornea -> Pupil -> Lens -> Vitreous -> Retina -> Optic nerve -> Optic chiasm -> Optic tract -> Pre-tectal area

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16
Q

Relative afferent pupil defect (RAPD)

A
  • Swinging light test/Marcus Gunn test
  • Problems with optic nerve or retina
  • Shine the light from one eye to the other and look at the pupil response
  • Each pupil should construct quickly and equally to both direct (light to the eye) and consensual (light to the other eye) application of light
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17
Q

Normal response to swinging light test

A

Dimly lit room, distant focus i.e. get them to look at something far away. A light is shone in one eye and you get bilateral constriction from both eyes, when shone to the other eye the same happens.

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18
Q

Left relative afferent pupil defect (RAPD)- test results

A
  • Dimly lit room, distant focus
  • When the light is shone in the right eye you get bilateral constriction
  • When the light is shone in the left eye you get abnormal constriction as it appears to dilate
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19
Q

Accommodation reflex- summary

A

The process of focussing on objects as they move closer. It requires:
• Pupillary constriction
• Increased refractive power of the lens
• Convergence of the eyeballs

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20
Q

Accommodation reflex- pupil constriction and lens

A
  • Pupil constriction- Corticobulbar fibres activate the parasympathetic pathway as in the light reflex through to the pretectal area from the primary visual cortex. Bilateral innervation of the Edinger-Westphal nuclei and fibres sent down the Occulomotor nerve causing pupil constriction
  • Lens- the short ciliary nerve also supplies the ciliary muscle. Contraction of this muscle relaxes the zonular fibres. The lens becomes fatter, increased refraction for near vision
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21
Q

Accommodation reflex- ciliary muscle and convergence

A
  • Ciliary muscles= the ciliary muscle is circumferential. Contraction causes anterior movement of the ciliary process as it removes tension on the suspensory ligament. This reduces the tension on the fibres. The lens becomes fatter (globular)
  • Convergence- Oculomotor (CNIII) nucleus activation. CN III stimulates the contraction of the medial rectus bilaterally. The eyes converge and move medially.
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22
Q

The bony orbit- houses and protects the eye

A
  • Orbital rim= Frontal bone, Maxilla, Zygomatic bone
  • Roof= Frontal bone, lesser wing of the sphenoid
  • Floor= Maxilla, Zygomatic bone, Palatine bone
  • Medial wall= Ethmoid bone, Lacrimal bone, Maxilla, Body of the sphenoid
  • Lateral wall= Zygomatic bone, Greater wing of the sphenoid
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23
Q

Psychosis core symptoms

A

1) Delusion- a fixed and firm belief about something that is not true or is irrational (outside societal or culturally acceptable norms). Usually distressing
2) Thought disorders- difficulty with attention, making a decision, thinking it through or taking on information
3) Hallucinations- in any sensory modality, in the absence of any sensory stimuli

24
Q

Risk factors for psychosis

A

1) DNA
2) Maternal illness, winter borth
3) Living in an urban environment
4) Immigration
5) Drug use- amphetamines
6) Family history
7) Older parents
8) Premature birth/LBW
9) Seasonality effect

25
Q

Epidemiology of psychosis

A

1) Same amount of men as women
2) Young onset
3) Trauma and stress
4) Cannabis and substances

26
Q

Causes of psychosis

A 
Psychological severe distress
Physical illness
Drug intoxication
Mental illness
- Schizophrenia
- Affective disorder
- Dementia
27
Q

Primary and secondary hallucinations

A

Primary hallucination- the hallucination comes from nowhere

Secondary hallucinations- you get prodromal symptoms first i.e. low mood and then the hallucinations

28
Q

Categorisation psychoses

A

Can use ICD-10 and DSM-5
Categorical, Hierarchial, Descriptive/phenomenology. You must rule out other diagnosis before you make your decision:
1) Organic mental disorders
2) Mental and behavioural disorders due to psychoactive substances
3) Schizophrenia and delusional disorders
4) Affective disorders

29
Q

Psychoses services

A

1) Acute- crisis/liaison/diversion
2) Early intervention in psychosis
3) Community mental health team
4) Primary care

30
Q

Fissures in the bony orbit

A
  • Optic canal- Optic nerve (CNII), Ophthalmic artery
  • Superior orbital fissure- Lacrimal nerve (CNV1), Frontal nerve (CNV1), Trochlea nerve (CNIV), Oculomotor nerve (CNIII), Nasociliary nerve (CNV1), Abducent nerve (CNVI), Sup. And inf. Opthalic veins. Labelled from superior to inferior as they go through the fissure
  • Inferior orbital fissure= Infraorbital nerve (CNV2), Zygomatic nerve (CNV2), infra-orbital artery and vein, inf.ophthalmic vein
31
Q

Tendinous ring of Zinn

A

Site of attachment for muscles in the eye. Only surrounds certain components that pass through these openings- Optic nerve, Opthalmic artery, Oculomotor nerve, Nasociliary nerve, Abducens nerve

32
Q

Fibrous framework of the orbit

A

Superior to the bony part of the orbit. Made of connective tissue
• Orbital septum
• Tendon of levator palpebrae superioris- attaches to the superior tarsus and allows us to raise our upper eyelid
• Superior tarsus- made of dense connective tissure
• Medial palpebral ligament- where the inferior and superior tarsus meet
• Orbital septum
• Inferior tarsus- made of dense connective tissue
• Lateral palpebral ligament- where the inferior and superior tarsus meet

33
Q

Muscles that move the eyelid- superficial to the fibrous framework

A
  • Medial palpebral ligament- where the Palpebral muscle meet
  • Orbicularis oculi muscle (Facial CNVII)- Orbital part, Palpebral part (around the eyelid).
  • Lateral palpebral ligament - where the palpebral muscles meet
  • Close eyelids- Orbital part (forcefully), Palpebral part (gently)
34
Q

Muscles that move the eyelid

A
  • Superior tarsal muscle (smooth)- Sympathetic. Goes from the inferior part of the Levator palpebrae superioris to the inferior part of the Tarsal plate
  • Orbicularis Oculi- Facial nerve (CNVII)
  • Levator palpebrae superioris- Oculomotor (CNIII). Connects from the posterior part of the orbit to the superior tarsal plate.
35
Q

Conjunctiva

A
  • Thin, translucent mucous membrane
  • Lines the eyelids and reflects onto the eyeball to form the Bulbar conjunctiva. The Palpebral conjunctiva covers the inner surface of the upper and lower eyelids
  • Prevents the entrance of infectious organisms
  • Contributes to the formation of tears and mucous
  • When the lids are closed a conjunctival sac is formed which is continuous
36
Q

Other structures in the eye

A
  • Meibomian/tarsal glands- modified sebaceous glands, secretes meibum which increases tear viscosity and reduces evaporation
  • Eyelash follicles- Sebaceous glands (Zeis), Sweat glands (Moll). Contributes an oily substance which keeps the hair follicles subtle and stops them drying out
37
Q

Things contained within the orbit

A

Eye ball, fascia, fat, lacrimal gland, nerves and vessels

38
Q

Layers of the eyeball

A
  • Outer or fibrous layer- Cornea, Sclera, Limbus (connects the cornea and sclera)
  • Middle, uveal or vascular layer- Choroid, Ciliary body (ciliary muscle and process), Lens, Iris
  • Inner layer- Retina
39
Q

Outer or fibrous layer of the eyeball

A
  • The cornea and sclera are continuous with each other, they provide shape to the eye and help support other structures
  • Cornea- transparent, avascular structure involved in the refraction of light. Positioned centrally at the front of the eye
  • Limbus- the area where the cornea merges with the sclera. A transitional zone where regeneration occurs
  • Sclera- 85% of the outer layer, the white of the eye. Extraocular muscle attachment site
40
Q

Pathology that can occur in the outer and middle layer

A

Uveitis can occur in the Middle layer

Keratitis and Scleritis occurs in the Outer layer

41
Q

Choroid

A

Within the middle, uveal or vascular layer. Its vascular, pigmented and lines the majority of the sclera

42
Q

Ciliary body- in the middle layer

A
  • Ciliary process-attaches to lens via zonular fibres /suspensory ligaments.
  • Ciliary muscle-affects the shape of the lens, under parasympathetic control
  • The zonular fibres encircle the entire lens.
  • Near vision: contraction of ciliary muscles pulls the ciliary process forward, relaxes the suspensory ligaments, the lens fattens and there is increased refraction of light.
  • Distant vision: relaxation of ciliary muscles, the zonular fibres are under tension, the lens is flattened and there is less refraction of light.
43
Q

Lens- in the middle layer

A
  • Biconvex, 1 cm in diameter.
  • Avascular, covered by a capsule and is bathed in fluid.
  • Consists of cellular lens fibres (proteins called crystallins).
  • Focuses light, producing clear, sharp images.
  • Cataracts occurs here
44
Q

Iris- in the middle layer

A
  • Controls the size of the pupil.
  • Circular fibres-sphincter pupillae (parasympathetic CNIII), contraction makes the pupil smaller.
  • Radial fibres-dilator pupillae (sympathetic), contraction makes the pupil bigger.
  • Miosis-a constricted pupil.
  • Mydriasis-a dilated pupil.
45
Q

Chambers of the eye

A
  • Anterior chamber- bounded by the cornea and the iris, filled with aqueous humour
  • Posterior chamber- bounded by the iris, ciliary processes, zonular fibres and lens, filled with aqueous humour
  • Vitreous chamber- bounded by the lens and the retina, contains vitreous humous. Keeps the round shape of the eye and acts as a shock absorber, clear so allows light to pass through to the retina
46
Q

Blow out fractures- the eye

A
  • Direct trauma to the orbit, increases the inter-orbital pressure causing a fracture
  • The orbital rim remains intact
  • A fracture to the orbit floor may open up the maxillary sinus causing an air leak
47
Q

Cellulitis

A
  • Cellulitis (bacterial infection) in this region is divided into pre-septal (anterior to the orbital septum) and orbital (posterior to the orbital septum
  • Orbital cellulitis- its an emergency with risk of intracranial infection, sepsis and visual loss. You get double vision, pain on eye movements and reduced acuity
  • Treatment- emergency referral to opthalamology, IV antibiotics
48
Q

Ptosis- CN III/Oculomotor lesion

A
  • Supplies levator palpebrae superioris
  • Strong elevator of the eyelid
  • Causes a full eyelid ptosis
  • Also in a CN III lesion- eye looks down and out, pupil dilation (mydriasis
49
Q

Ptosis- sympathetic supply lesion

A
  • Supplies the superior tarsal muscle
  • Weak elevator of the eyelid
  • Causes a partial eyelid ptosis
  • Part of Horners syndrome presentation- pupil constriction (miosis), absence of sweating (anhidrosis)
50
Q

Conjunctivitis

A
  • Inflammation of the conjunctiva
  • Causes= infective (bacterial, viral), allergic, mechanical/contact lens related, chemical (eye drops) or immunological
  • Signs and symptoms= red eye, discharge or sticky eyes, watery eyes, itching (allergic), gritty sensation
51
Q

Style/Hordeolum

A
  • External- acute infection of the glands of Zeis or Moll. Asceses on the eyelid edge
  • Internal- acute infection of a meibomian gland within the tarsal plate
52
Q

Chalazion

A
  • Blockage of ameibomian gland forming a cyst
  • Presents as a small, painless lump on the eyelid
  • Uncommon to become infected
  • Can occur secondary to an internal hordeolum
53
Q

Keratitis- inflammation of the cornea

A
  • Causes- infective (bacterial, viral, fungal or protozoal), Non-infective (hypersensitivity to bacterial toxins, trauma, autoimmune
  • Signs and symptoms- ulceration, red eye, Hypopyon (pus in the anterior chamber)
54
Q

Scleritis- inflammation of the sclera

A
  • Causes- idiopathic, autoimmune condition (RA, SLE, IBD), trauma, infection
  • Signs and symptoms- severe, deep pain to the globe (tender), visual loss, photophobia, red eye
55
Q

Cataracts

A
  • Opacity/clouding of the crystalline lens
  • Risk factors= aging, trauma, diabetes
  • Signs and symptoms= blurred vision, gradual visual loss/acuity, Glare (particularly at night), loss of red reflex
  • Treatment involves surgery to replace the lens with an artificial one
56
Q

Uveitis

A
  • Inflammation of the iris and ciliary body
  • Causes- infection, trauma, HLA-B27 association
  • Signs and symptoms- pain, redness, photophobia, watering and blurred vision
  • Intermediate uveitis- inflammation of the vitreous gel
  • Posterior uveitis- inflammation of the retina and choroid

Medicine year 2 semester 2 (47 decks)

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