Sensory adaptations in exotics - NMSK

Why is it important to be aware of the different sensory organs in exotics?

The relative importance and anatomy varies depending on:

• species

• habitat

• diet

• lifestyle

Need to consider how each organ is relevant to each species and what may affect it.

Which snake species use infrared detection

• pythons, boas and pit vipers

why do snakes use infrared detection?

• enables them to ‘see’ infrared

• gives them night vision

• can see small and very still prey

• can detect prey

• pinpoint where to strike

Why is infrared detection in snakes clinically relevant?

• anorexia is common in captivity

• should we be able to get a special license to feed live prey?

What is the vomeronasal organ?

• paired, accessory olfactory organ

• used for chemosensory stimuli

what are chemosensory stimuli detected in some species?

• social or reproductive behaviour

in what species do we find the vomeronasal organ?

• amphibians

• lizards

• snakes

• many domestic species

in which species is the vomeronasal organ NOT present?

• fish

• birds

• chelonians

what varies with the vomeronasal organ and what may if be connected to

• anatomy and exact location varies

• may be connected to the mouth via nasopalatine duct

Outline the vomeronasal organ in squamates

• present in lizards

• very well developed in snakes

• roof oral cavity

• vomeronasal nerve = branch of olfactory nerve CNI

Why do snakes flick their tongue?

• how snakes monitor their environment

• take chemicals from the air presenting them phemoronasal organ in the dorsal part of the nasal cavity

Outline reptile ears

• external ear is absent or diminished (in most species except crocodiles)

• tympanum absent in some species

• if it is present, it’s superficial.

Outline the structure of the ear organ in birds and reptiles

• much simpler

• 1 auditory ossicle = columella (equivalent to the stapes)

• connects tympanic membrane to the inner ear

• cochlea duct is not coiled (poor hearing)

Outline snake hearing

• no tympanic membrane

• Quadrate bone connects to stapes (columella) to oval window of cochlea

• low frequencies

Outline hearing in birds

• hearing is their 2nd most important sense

• particularly important in nocturnal birds

• some species use magnetic force, some use echolocation

what special adaption do birds have?

• regenerate hair cells if they get damaged

Outline ear anatomy in birds

• outer, middle and inner ear

• no pinna, they have specialised feathers

• can have ear lobes

• some have an operculum

• 2 tympanic membranes in songbirds

• short external auditory meatus

• single auditory ossicle

what is the operculum

• found in owls

• accessory structure

• aids sound location

What type of feathers are on owl heads

• auricular feather

• contour feathers

• reflector feather

Outline owl ear structure

• tightly packed rim of facial feathers

• sound → external auditory meatus

• left and right external auditory meatuses are different sizes and shapes

• helps to localise sounds

Why do owls have asymmetrical external auditory canals

• enables precise pinpointing of prey

• intensity and timing of sounds

• horizontal and vertical planes

How are fish able to hear/detect acoustic information

• auditory system - otolithic inner ear

• mechanosensory system = lateral line

Where do we find the lateral line

• runs just below the surface of the skin

• along the side of the body

• covered by pored scales

What is the lateral line used for?

• detects movement

• vibration

• pressure gradients

used for:

• detecting obstacles

• swimming in schools

• avoiding predators

How does vision in the air compare to vision in water

• air: light is strongly refracted through the cornea - cornea focuses

• water: cornea/water have a similar refractive index = lens focuses instead

Outline fish eye anatomy

• generally, large variation in species structure/shape/colour

• most can see colour (some see UV light)

• rod: cone ration varies

What are the main differences in fish eye anatomy to mammalian anatomy

• no lacrimal gland

• rigid, immoveable iris

• pupil is fixed

• lens: spherical, protrudes through the iris

• light is focussed by the lens changing position in relation to the retina

What keeps the lens in place in fish

• suspensory ligament dorsally

• retractor lentis muscle ventrally

outline the nictitating membrane in reptile and birds

• very present in reptiles

• very developed in birds

• it’s a striated muscle

• rapidly sweeps and cleans the cornea

outline the lower eyelid in birds and reptiels

• more mobile

• larger in birds

what are scleral ossicles and what are their function?

• bones within the sclera

• provide protection and support

• aid ciliary muscle function (visual accommodation) - especially relevant in night vision

What is the fovea

• lots of rods and cones

• enables sharp vision and visual acuity

In which species is the fovea present

• fish, reptiles, birds and primates

In which species do we find 2 fovea and what do they enable?

• diurnal species, especially raptors

enables:

• wide, binocular field of view

• very sharp vision

Outline avian eye structure

• relatively large: socket size = exophthalmic

• no tapetum lucidum

• avascular retina

• pecten

Why is having an avascular retina beneficial for birds?

• less light is scattered from the blood vessels

• provides higher visual acuity

What is the pecten?

• highly vascularised

• thin

• highly folded

• think it has a nutritive role for the retina

What species are these?

Left = goat fundus

Right = avian fundus - see the pecten

What do we look at for clinical relevance of the avian eye?

• note the normal appearance of the pecten

head trauma;

• common in birds of prey

• remember - must triage and provide first aid to all species

• if the pecten is destroyed, must euthanise

What can birds see

• some birds can see colour

• many nocturnal birds can see UV light

• Diurnal birds have a higher proportion of cones

• nocturnal birds have a higher proportion of rods

what should we do in practice with diurnal birds to ease handling/catching and why

• dim the lights

• higher proportion of cones

Outline squamate eyes

• retina is avascular

• ± papillary cone (in lizards and some snakes)

Outline the spectacles in snakes and some lizards

• fused eyelids, transparent

• subspectacular space

• shed during ecdysis (colour change)

What is the clinical relevance of dyseccdysis

• retained spectacles

• correct husbandry

• rehydration = important (bathe in warm water daily)

• apply eye lubricant

• gently lift the spectacle off the eye using a wet cotton bud, from the very edge of the eye

• never just pull skin off

Outline the pineal gland in reptiles

• endocrine gland in brain

• it’s in msot vertebrate species

• produces melatonin

• involved in sleep/wake cycles: responds to light/dark

outlien the parietal eye in lizards

• ‘third eye’ - a photoreceptive structure

• usually ontop of the head

• in many lizard species (and amphibian)

• lens, cornea, retina

• produces and secretes melatonin

• involved in: light/dark, sleep cycle, hormone production, thermoregulation

what is the clinical relevance of the PLR in reptiles and birds

• can’t be use to assess

• both eyes are under independent control

what is meant by a consensual PLR

• the PLR affecting the contralateral eye

Can we use mydraitics in birds and reptiles?

• no

• iris and ciliary muscle are skeletal muscle not smooth

• under voluntary control