NEU 5 Flashcards
Define exophthalmos
A normal sized globe that has been pushed forwards
- Leads to increased opening of the eyelids, third eyelid protrusion, visible sclera
Define enophthalmos
Normal sized globe that has sunken into the orbit
- Leads to third eyelid protrusion
Define microphthalmos
Abnormally small globe
- Leads to smaller gap between eyelids, third eyelid protrusion
Define hydrophthalmos/buphthalmos
Enlarged globe
Describe the role of cranial nerve II in relation to the eye
Vision
What is the role of cranial nerve III in the eye?
- Extraocular muscles (dorsal, ventral and medial rectus and ventral oblique)
- Upper eyelid
What is the role of cranial nerve IV in the eye?
Innervates dorsal oblique
What is the role of cranial nerve V in the eye?
Sensory for globe and adnexa
What is the role of cranial nerve VI in the eye?
Innervated intraocular muscles (lateral rectus and retractor bulbi)
What is the role fo the parasympathetic fibres in cranial nerve III in the eye?
Innervates pupillary constrictor muscle
What is the role of the parasympathetic fibres of cranial nerve VII in the eye?
Controls lacrimal gland secretion
What are the roles of the sympathetic fibres from T1-3 in the eye?
- Pupillary dilator
- Orbital smooth muscle
- Eyelid smooth muscle
Describe the menace response (giving afferent, efferent path, stimulus, the normal response)
- Afferent: II
- Efferent: VII
- Involves cerebellum
- Stimulus: quick threatening gesture to each eye in turn
- Normal response: stimulated eye should blink
- Learned response - is not a reflex
Describe the tracking reflex test (afferent, efferent, stimulus, normal response)
- Afferent: II
- Efferent: III, IV, VI, VIII
- Stimulus: move or drop cotton ball in field of view
- Normal response: should follow the movement of the cotton ball
Describe the visual placing reflex
- Useful for small dogs/cats
- Support thorax and bring forelimbs towards edge of table top
- Normal response: place both forepaws on tbale before carpi touch surface
Describe the pupillary light reflex (afferent, efferent, stimulus, normal)
- Afferent: II
- Efferent: PSNS fibres of III
- Stimulus: light shone in eye
- Normal: pupil should constrict (contralateral eye should also constrict)
What is strabismus?
- Static alteration of the direction of gaze
- Can be neurological or due to a mass
- Squint
What nerve could be affected if a down and out strabismus is present?
Cranial nerve III
What is nystagmus?
- Involuntary rapid rhythmic movement of the eyes
- Associated with visual and vestibular stimuli
Describe the 3 neurone pathway of sympathetic innervation to the brain
- First order neurones: travel down spinal cord in tectotegmental spinal tract. Synapse in lateral horn of SC grey matter
- Second order neurones: exit via T1 to T3 nerve roots as ramus communicans, form thoracic sympathetic trunk, passes beside X, forming vagosympathetic trunk within carotid sheat
- Third order neurones: pass rostrally, synapse in cranial cervical ganglion, beside tympanic bulla, pass into cranial cavity with CN V, then exit to orbit to supply eye
Describe the anatomy of the eyelids
- Skin is thinner, and has cilia
- Palpebral conjunctiva lines inner side of eyelid
- Meibomian glands produce lipids
- Also have musculature of the eyelids
- All but one muscles of eyelid innervated by facial nerve (middle levator of upper eyelid innervated by oculomotor)
Describe the nictitating membrane
- Third eyelid
- Not present on higher primates
- In berivores is a large structure, moves passiely due to retraction of the globe
- Pouch of conjunctival membrane
- T-shaped white band of hyaline cartilage
Give the functions of the eyelids
- Protects eyeball
- Wipes the cornea to distribute tear film
- Remove debris
- Produces certain componens of the tear film
What is the fornix?
Part of the conjunctiva (only attached to sclera and ends at limbus. Is the fold that covers the anterior part of the globe
Describe the anatomy and function of the conjunctiva
- Outer non-keratinised epithelium with goblet cells
- Underlying stoma with lymphocytes and hystiocytes
- Tigh junctions between cells so pathogens cannot enter
- CALT is important components (cunjunctiva associated lymphoid tissue)
- Deep fibrous layer of connective tissue, nerves and blood vessels
- Rich vascular supply with lymphatic drainage
What is ectropian?
- Outturned eyelids
- Eyelids hang loose and there is a mismatch in size of eyelid and eye ball
What is diamond eye?
- Lower lid hangs - ectropian of lower lateral lid
- Entropian of upper medial lid
List somme conditions of cilia and explain what they are
- Ectopic cilia - cilia are in the wrong place
- Distichiasis - extra row of eyelashes
- Trichiasis - cilia touching the eye but lashes themselves are normal (drooping of upper eyelid)
Describe the anatomy and function of the nasolacrimal system
- Lacrimal puncta - upper and lower
- Tube connected to it has 2 arms: upper and ower, meet where orbit finishess and ends with nasal punctum, drains eye
- Openings of nasal punctum more caudal in dog
- Lacrimal galnds produce aqueous portion, out via lacrimal ducts
- Meibomian glands produce lipid fraction of tears
What are the 3 layers of the precorneal tear film
- Lipid (produced by Meibomian glands)
- Aqueous
- Mucin (produced by coonjunctival goblet cells)
Describe the function of the precorneal tear film
- Extremely smooth optical surface
- Nutrition and protection of the cornea
- Lipid stabilises tear film between ligs
- Aqueous components include defence mechanisms
- Mucin binds tear film to epithelium
Describe the gross anatomy of the cornea
- Circular shape, domed
- Herbivores horizontal shape
- Corneal curvature responsible for refractive power
- Joined to sclera by limbus
Describe the structure of the sclera
- Opaque sclera is largest portio of the outer coat of the eye
- Composed of collagen and fibroblasts
- Limbus joins cornea to sclera
Describe the microscopic anatomy of the cornea
- Epithelium: hydrophobic barrier, is on the outside, at least 6 cells thick, stratified squamous epithelium, stuck to stroma by basement membrane tissue (hemi-desmosomes)
- Stroma is middle layer, major structural tissue, transparent and avascular and is made of collagen
- Endothelium is hydrophobic, is on inside, monolayer
What are the functions of the cornea?
- Boundary of the globe to the environment
- Main refractive surface of the eye
- Optical transparency
- Mechanical resistance
- Highly sensitive innervation
- Special defence mechanisms
Outline some causes of corneal ulcers
- Lid lesions
- Eyelash lesions
- Trauma - lacerations, abrasions, foreign body
- Dystrophies/degenerations
- Infections
- Keratoconjunctivitis sicca
Outline corneal wound healing
- Epithelial healing (epithelialisation, mitosis, sliding, gluing)
- Cornea can undergo “melting” where the body digests it
- Stromal healing (fibroplasia, vascularisation)
Describe the fundus and how the tapetum relates to the appearance of the fundus
- Fundus is the part of the posterior segment of the eye that is viewed with an ophthalmoscope
- Consists of optic disc, tapetal fundus, non-tapetal fundus, retinal vasculature
- The tapetal fundus is the colourful bit
Describe the anatomy of the retina
- 10 layers
- Can be simplified into 2: the retinal pigment epithelium and the neurosensory layer (made up of 9 of the 10 sublayers)
Describe the function of the retina
Absorb light rays and convert into nerve impulse which travels to the brain
Describe the important histological layers of the retina
- The retinal pigment epithelium
- The neurosensory retina (photoreceptor layer, outer nuclear layer, retinal ganglion cells, nerve fibre layer)
- Other layers are interconnecting neural cells
Decribe the gross anatomy and function of the optic nerve
- Afferent pathway to visual cortex
- consits of axons of ganglion cells
- 3 regions: intraocular, retrobulbar and intracranial
Explain the relationship between the retina and uveal tract with respect to systemic disease
Hypertension can lead capillaries to burst, obscuring the retina
Describe the embryology, anatomy and function of the vitreous
- Gel between lens and retina
- Transparent
- Avascular and nerve free
- Functions: shock absorber, removes waste products, maintains intraocular anatomy, some nutrition for the lens
- Embryology: vascular in develoment, regresses and avascular adult vitreous forms
Describe the general physical relationship between the lens vitreous and retina and role in lens luxation
- Sits between lens and retina
- Is attached to retina and lens
- When lens luxation occurs, retinal detachment may also occur due to movement of the vitreous
Describe the tapetum
- Part of choroid
- Lies behind retina
- Retina is translucent so tapetum can be seen underneath
- Shiny reflective layer, like a mirror
- Responsible for eye-shine at night
- Reflects light rays for retina to receive light twice
Describe the retinal pigment epithelium
- Lies in front of tapetum
- Single layer of cells
- Can be pigmented or non-pigmented
- Pigmented in ventral fundus where tapetum is absent, non-pigmented in dorsal fundus where tapetum is present, allowing tapetum to be seen
- Essential for retinal integrity and function
- Photoreceptors are therefore embedded within RPE
Describe the photoreceptor layer of the retina
- Rods and cones (contain visual pigments)
- Is where light energy is converted to a nerve impulse
- Cones are for colour vision and visual acuite
- Rods are for night vision
Describe the outer nuclear layer of the retina
- Nuclei of rods and cones
Describe the ganglion cell layer and nerve fibre layer of the retina
- Ganglion cells form the last layer of neural cells (lie adjacent to vitreous)
- Axons of ganglion cells form nerve fibre layer
- Nerve fibres converge on optic disc forming optic nerve
Describe the components of the brain stem
Made up of midbain, pons and medulla oblongata
Describe the functions of the brain stem
- CV system control
- Respiratory control
- Pain sensitivity control
- Alertness
- Awareness
- Consciousness
Describe the structure of the mesencephalon
- Part of midbrain
- Tectum is dorsal part of midbrain
- Caliculi make up whole of tectum (auditory and visual responses)
- Tegmentum: in ventral part cranial nerve nuclei are located (vision, hearing, motor control, sleep/wake, arousal)
- Red nuclei appear red - input from cerebellum and motor cortex, involved in motor control
- Medial leminiscus - goes up through brainstem and decussates, touch and pressure from skin, moves around within sections of brain
- Ocular motor nuclei - eye movement (cranial nerve III), at level of superior caliculus
Describe the structure of the pons
- In metencephalon
- No tectum
- Under tegmentum is basilar area
- Arousal, controlling autonomic function, relaying sensory informtion between cerebrum and cerebellum, sleep centre
Describe the structure of the medulla
- Myencephalon
- Associated with 5 pairs of cranial nerves VIII, IX, X, XI, XII
- Point at which spinal cord becomes brainstem
- Have ventral and lateral spinal tracts that enter and merge to form pyramids
- Tectospinal tract goes through centre of medulla
- Inferior olive is where decussation happens before it enters the cerebellum
Describe the difference between the spinal cord vs the brainstem
- In brainstem, central canal is expanded
- Pyramids decussate
- Formation of medial lemniscus through the decussation of ascending fibres arising from cuneate and gracile tracts
- Dorsolateral displacement of dorsal horn grey matter
- Appearance of cranial nerve nuclei and various relay nuclei projecting to cerebellum
Describe the functional anatomy of the vestibular system
- Located in semicircular canals
- 3 semicircular canals that sit in different planes
- Swellings at end of each called ampulla, feed into vestibular ganglion
- Ampulla conain cupula
- Semicircular canals are bony
- In vestibular region have otolith organs
- Endolymph contained in a membrane sac
Name the 2 functional units of the vestibular system and give their functions
- Semicircular canals = dynamic information
- Otolith organs = satic information
Describe the otolith organs and how they work
- In vestibular canal
- Have utricle and saccule
- Hair cells embedded in membrane with projections out to ganglion
- Hair like processes with some long haris and some short - no particular order
- Macula = cellular region
- Calcium carbonate crystal (otoconia crystals) make gelatinous mass heavy, when fluid moves around, shearing force produced between macula and gelatinous mass
- Causes displacement of hair cells, signal sent to ganglion
- Direction endolymph pushes hair cells determines what direction moving
Describe how orientation occurs (vestibular organs)
- Utricle and saccule
- Work in 2 different planes
- Utricle only horizontal information
- Saccule only vertical information
- Together make 3D image
Describe the semicircular canals
- Endolymph filled tubes
- Dynamic reaction
- Fluid moves in opposite direction of movement
- Detect initiation of movement
- Cupula have hair cells embedded within them
- Hairs are arranged with all long hairs on one side and all short on the other
- Cupula sits on top of hair cells and reaches other side of canal
- Blocks flow of endolymph
- When move, endolymph pushes onto cupula, whole force ecertedon hair cells
- Only detects movement in one direction (but have 3 different planes so can detect all directions)
Describe the central pathway of the vestibular organ
Towards cranial nerve VIII in rostral medulla
Describe the central projections of the vestibular system
- From vestibular nuclei in medulla
- Medial geniculate nucleus is bilateral, goes to cerebral cortex
- Branches of nuclei of III, IV and VI all involved in movement of eye in terms of balance information etc
- Reticular formation
- Vestibulospinal tract is part of extrapyramidal system
- Runs ipselaterally into cerebellum via caudal cerebellar peduncle
- Pyramid system decussates and controls contralateral side
- Extrapyramidal system (where vestibulospinal tract runs) no decussation
What fibres go via the rostral peduncle?
- Mainly efferents
- Afferents: ventral spinocerebellar tract, tectocerebellar tract
What fibres go via the middle peduncle?
- Only afferents
- Form nuclei in the pons
- Corticopontocerebral pathway
- Originate in the upper motor neurones of the cortex
What fibres go through the caudal peduncle?
- Afferents: dorsal spinocerebellar, reticulocerebellar, olivocerebellar, cuneocerebellar, vestibulocerebellar
- Efferents: cerebellovestibular, cerebelloreticular
Describe the cerebellar afferents
- Proprioceptive input from the limbs, body and head (spinocerebellar, vestibulocerebellar, tectocerebellar pathways)
- Input about planned motor activity:
a) coordination of function from motor cortex. Originates from cerebrum, thalamus, midbrain and nuclei in pons to middle cerebellar peduncle
b) coordination of extrapyramidal function, originates from cerebrum, thalamus, midbrain and projecting to olivary nucleus in medulla oblongata
Describe the intracerebellar communication using Mossy fibres
- Incoming fibre
- Excite granule cells which project to molecular layer and excite Purkinje cells
- A single mossy fibre can excite several granule cells
- Also excites stellate cells which inhibit Purkinje cells
- Excite cerebellar nuclei
Describe intracerebellar communication using Climbing fibres
- Incoming fibres
- Excite Purkinje cells one to one
- Excite cerebellar nuclei
Describe intracerebellar communication in terms of Purkinje fibres
- Are the only fibres to project information outside of the cerebellum
- Do not project outside the cerebellum themselves but project to nuclei
- Information leaves the cerebellum via the nuclei
- Are inhibitory
- Hemispheres to lateral nucleus, vermis to fastigial nucleus and paravermis to interposital nucleus
What are the signs of a vestibocerebellar lesion?
- Swaying posture
- Wide based stance
What are the signs of spinocerebellar disease?
- Hypermetria and hypertonus (spasticity)
- Exaggeration of spinal reflexes (hopping, wheelbarrowing, hemiwalking)
What are the signs of pontocerebellar disease?
- Loss of harmonary and synchrony in movements
- Dysmetria, overshooting, tremor
What are the signs of a vestibular lesion?
- Head tilt
- Nystagmus
Explain simple learning
- Habituation and sensitisation.
- A relatively permanent change instrength of response to a single stimulus due to repeated exposure
- This does not include changes due to sensory adaptation, fatigue or injury
Explain associative learning
- Learning to automatically make a particular response in the presence of a particular stimulus
- Classical and operant conditioning
Explain classical conditioning
- When a stimulus that initially produces no particular response is followed several times by an unconditioned stimulus that produces a defensive or appetitive response
- Involves an unconditioned stimulus, conditioned stimulus, conditioned response
Explain operant conditioning
- All behaviour has a consequence and the nature of that consequence modifies its tendency to repeat the behaviour in future
- Can select a response using reinforcement or punishment
Differentiate between positive reinforcement and negatice reinforcement
- Positive: behaviour is followed by a favourable stimulus
- Negative: behaviour is followed by the removal of an aversive stimulus
- Both increase the behaviour
Differentiate between positive punishment and negative punishment
- Positive: behaviour is followed by an aversive stimulus
- Negative: behaviour is followed by the removal of a favourable stimulus
- Both decrease the behaviour
Describe imprinting
- Any kind of phase sensitive learning
- Long lasting learning effect
- Innate
- Occurs in a sensitive period during development
- Imprinting is a narrowing of the range of stimuli that elicit a particular (social reponse)
Describe social learning
- Learning from another member of a social group
- Reduces risk: not carrying out behaviour but watching others
- Improving and training of skills (foraging, hunting)
Describe the conditioning of anxiety
- Link between emotions and memory
- Can condition an emotional response
- Requires a conditioned stimulus
- Amygdala projects to other regions of the body
- Unconditioned stimulus can be one or several
Describe briefly how long term potentiation occurs in associative learning
- Strong synapse (conditioned stimulus synapse) induces and action potential which passes down axon
- In pyramidal cells may have backwash of depolarisation to the dendrite, depolarising the post synaptic site
- At same time AP arrives from weak synapse (unconditioned stimulus)
- After repetition will become a strong synpase
- Whenever these pairings occur together, weak becomes strong
What is meant by a strong synapse?
- One that has more vesicles on the presynaptic side
- Shorter cleft or more synapsing at same neuron
- Higher receptor sensitivity
- More receptors
Explain the role of NMDA receptors for LTP
- One of 2 main types of glutamate receptors, controls calcium influx
- Normally blocked by magnesium
- Postsynaptic depolarising ejects magnesium and channel is free
- In presence of presynaptic glutamate, Ca ions can enter the cell
Describe the role of glutamate receptors in LTP
- Kinase enzyme produced (activated by Ca), moves materal from intracellular space to membrane to build another receptor type called AMPa (glutamate receptor)
- Increased production of receptors
- Post synaptic side more excitable
- NO released by post synaptic side
- Triggers release of more neurotransmitter
Describe photoreceptor function
- Phototransduction
- Have an outer and an inner section
- Photopigment discs sit in segments like a stack of CDs
- Rods contrain rhodopsin, cones contain many different types
- Pigments track light
- Free flow of sodium in the dark (pumped out of inner segment)
- When light hits, flow of sodium stops and outer segment becomes more negative
- Stimulation causes hyperpolarisation
Describe the retinal ganglion cells
- Form the optic nerve
- Cover the entire retina
- Inner most layer is closest to vitreous humour
- When cells move out of retina, blind sport where ganglion cells become axons
Explain the functions of amacrine and horizontal cells in the retina
- Take information from different ganglion cells an put them together to form a picture
- Sent to visual areas of brain
- Allows for integration at retinal level
Explain lateral inhibition in the retina
- If light hits centre of ganglion cell, increases or decreases signal frequency
- When light hits periphery then is inhibited
- If centre and periphery are lit then lateral inhibition takes place
- Improves edge detection
- Detection of contrast between light and dark gives better visualisation
- Can get on and off centre cells
- an ON centre cell fires rapidly when stimulated and periphery is dark. No firing if periphery is lit and centre is dark. After suppression have rebound and will fire
- an OFF centre cell fires when periphery is light. Will decrease firing when centre is lit
What is the function of the optic nerve coming from the retina
- Purely to relay information
- Integration occurs before the signal enters the cell
- Signal moves through optic chiasm and into lateral geniculate nucleus
What is Brodmans area and what is its function
- A collecting of pyramidal cells which integrate information from the geniculate radiation
- Project to surrounding areas
- Different cells receive input
- 3 different types
- Simple cells: can be mapped with spots of light, on or off
- Complex: respond to bars of light or an edge of specific orientation
- Hypercomplex: do not respond to inhibitory or excitatory response, respond to faces or hands
- Integrated response laterally
- Cells organised in columns of similar receptive fields
- Rest is made up of previous experiences
Explain colour encoding in the brain
- Is an additional tier of information
- 3 colour cones: red, green, blue
- Little representation in area 17
- Split into 6 areas
- Most prominent in teh recognition areas than the form areas
Describe what epilepsy is
- A group of neurological disorders, all of which develop periodic seizures
- Characterised by recurrent episodes of paroxysmal brain dysfunction due to a sudden, dirsorderly and excessive neuronal discharge
Describe what occurs in epilepsy
- Increased excitation in an epileptic brain
- Glutamate is the excitatory NT
- GABA is inhibitory NT
- Glutamate is agonist at NDMA, causes influx of Na+ and Ca2+, eventual excitation
- GABA agonists facilitate influx of Cl- into cell, leads to inhibitory post-synaptic potential, hyperpolarisation, more difficult to achieve action potential
What is a paroxysmal depolarising shift?
- Bursting activity resulting from the relatively prolonged depolarisation of the neuronal membrane
- Due to influx of extracellular Ca2+, leads to influx of Na+ voltage gated channels, repetitive APs
- Subsequently hyperpolarising after potential mediated by GABA receptors and Cl- influx, or K+ efflux depending on cell type
What are the 2 types of epilepsy?
Idiopathic and structural
Describe idiopathic epilepsy
- Previously known as primary epilepsy
- Proven or suspected genetic background
- Unknown cause and no indication of structural epilepsy
- Chemical imbalance between excitatory and inhibitory messengers of the brain
Describe structural epilepsy
- Can also be called symptomatic
- Caused by identified cerebral pathology - trauma, change in brain structure, tumour
- Unknown cause
