NEU 6 Flashcards
What are the different types of epileptic seizures?
- Focal (partial) epileptic seizure
- Generalised epileptic seizures (previously called primary generalised seizure)
- Focal seizure with secondary generalisation
Describe the sibdivisions of focal seizures
- Simple: animal usually alert and aware of its surroundings
- Complex: consciousness is altered, fly catching, aggression, running, resonant vocal sounds, crouching or hiding
What is meant by a focal seizure?
A seizure that presents with focal motor, autonomic or behavioural signs alone or in combination
Describe the stages of epileptic seizures in the dog.
- Prodome: subtle changes in behaviour (often overlooked, hours or days)
- Aura or preictus: anxiety, excitability, barking (seconds to minutes)
- Icuts or seizure stage: convulsions (clonic/tonic), loss of consciousness, urination, defecation, salivation (seconds to minutes)
- Postictus: exhaustion, also aggression or increasing appetite (minutes - days)
Describe the mechanisms by which anticonvulsants work
- Decrease excitation or increase inhibition
- Alter intinsic membrane properties (mostly Na+ channels)
- Increase inhibitory transmitter function (mostly GABA system)
- Decrease excitatoy transmitter function (glutamate system)
What drugs are primarily used in veterinary medicine to treat seizures?
- Benzodiazepines
- Barbiturates
- Imepitoin (pexion)
- Bromide
Describe how inhibitory function can be increased to treat seizures
- GABA receptor-Cl- channel complex binding sites, potentiates endogenous GABA (benzodiazepines, barbiturates)
- GABA transaminase inhibition, GABA build up
- Triggered GABA release from presynaptic terminal
- Ion competition with chloride for passage through Cl- channel, increased hyperpolarisation
- Partial agonists at GABA-A receptors (imepitoin)
Describe the mechanism of action of barbiturates
- Bind to GABA receptor Cl- channel complex
- Potentiate GABA
- Metabolised by liver, enzyme induction
- Long half life
- Phenobarbital is drug of choice in cats and dogs, less toxic than benzodiazepine
- Bind to sam receptor but different site as BZD do not need GABA, open channel, influx of Cl-
Describe the mechanism of action of benzodiazepines
- Bind to GABA-A receptors, facilitate endogenous GABA effects
- Also used for sedative-hypnotic, anxiolytic, muscle relaxant and appetite stimulant effects
- Metabolised by liver
- Can be quitte toxic in cats
- Diazepam
- Bind to binding site, agonist effect, facilitate effect and increase frequency of Cl- travel through channel = hyperpolarisation and inhibitory postsynaptic potential
Describe the mechanism of action of bromide as an anticonvulsant
- Competes with Cl- in Cl- channel
- Has more of a hyperpolarising effect than Cl-
- Distributed through body like Cl-
- Very long half life (2-3 months to steady state)
Describe the mechanism of action of imepitoin (pexion)
- Partial agonist
- Potentiates amplitude of GABA - evoked currents by acting at the benzodiazepines recognition site of the GABA-A receptor
- Low affinity partial agonist with low intrinsic activity
- Binds to same site and receptor as a BZD but is not one
List the drugs that can be used to treat anxiety behaviours
- Benzodiazepines
- Tricyclic antidepressants
- Selective Serotonin Uptake Inhibitors (SSRIs)
- Monoamine oxidase inhibitors (MAOIs, not first choice as anxiolytic drug)
- Azapirones
Describe the mechanism of action of benzodiazepines as an anxiolytic drug
- Activate specific benzodiazepine receptor that facilitates inhibitory GABAergic
transmission - Amygdala has BZD receptors
- Reduce anxiety and agression
- Some memory impairment
- Dependence is a problem (need to reduce dose slowly)
Describe the mechanism of tricyclic antidepressants as anxiolytic drugs
- Enhance functioanl acitivity of norepinephrine and serotonin
- Block reuptake of both NTs
- Treat separation anxiety
- Increase availability of serotonin and NE
- Serotonin associated with mood, NE associated with activity
Describe the mechanism of action of selective serotonin reuptake inhibitors (SSRIs) as anxiolytic drugs
- Block reuptake of serotonin
- So increases its functional activity
- Adaptive changes in pre- and postsynaptic receptors (1-4 weeks for benefit), postsynaptic side more receptors and higher affinity for serotonin
Describe the mechanism of action of monoamine oxidase inhibitors as anxiolytic drugs
- Not first choice as anxiolytic drugs
- Enhance functional activity of norepinephrine, serotonin, dopamine
- Inhibit degredation of NTs by monoamine oxidase
Describe the mechanism of action of azapirones as anxiolytic drugs
- Activate a specific serotonin receptor
What is canine cognitive disorder?
- Similar to Alzheimer’s
- Can be summarised by DISH: disorientation, interaction changes, sleep changes, house soiling
Which drug can be used to treat canine cognitive disorder and give its mechanism of action?
- Segeline
- MAOI
- Irreversibe
- Greater affinity for MAO-B (dopamine is the substrate) than MAO-A
- Selectivity not absolute
- Species variations in dopamine metabolism
- Allows more dopamine to be available for release
List some common side effects of anxiolytic drugs
- Sedation
- Appetite changes
- Diarrhoea
- Vomiting
- Anorexia
List the common side effects of selegiline
- Restlessness
- Agitation
- Vomiting
- Disorientation
- Diarrhoea
- Nausea
- Diminished hearing
List the common side effects of anticonvulsants
- Sedation
- Nystagmus
- Ataxia
- Polydipsia
- Polyphagia
- CV and respiratory depression
- Gastric irritation
What does ARAS stand for?
Ascending activating reticular system
Describe the reticular formation
- Consists of network of grey and white matter
- Deep thoruhgout brainstem thoruhg pons, midbrain and diencephalon
- Continuous with similar system in spinal cord located deeply around grey matter
- Phylogenetically older region of the brain
- Can be divided into 2 functional divisions: ascending and descending
Describe the descending reticular formation
Linked to sensory and motor nerves and the cerebellum
Describe the ascending reticular formation
Relays impulses to higher centres for arousal (ARAS)
What are the inputs into the reticular formation?
- Spinoreticular tracts from spinal cord
- Collateral neurons from sensory/afferent neurons travelling to diencephalon
What are the outputs of the reticular formation
- Reticulospinal tracts to spinal level
- Intralaminar nuclei of thalamus and on to cerebral cortex
Describe the role of the reticular formation in the transmission of pain
- Pain information transmitted via spinoreticular tract and ascending reticular formation to thalamus and ultimately cerebral cortex
- Projects to cortex via diffuse thalamic projections
Describe the role of the reticular system in arousal
- ARAS sensitises cerebral cortex to particular sensory modalities
- Keeps cortex active during wakefulness
- Reduced activity results in sleep
- Severe lesion usually leasd to coma
Describe the mechanism of sleep
- Main sleep centre believed to be in hypothalamus
- Balance occur between activities of ARAS and sleep centre
- ARAS is main brain structure that maintains wakefulness and arousal
- Is a flip flop system - hypothalamus and ARAS inhibit each other
- Oxinergic neurons in lateral hypothalamus triggers switching between the 2
- Orexin produced - stimulates activity and food intake
- Peptides have receptors on reticular formation and activate it
What is the role of the vlPOA in sleep regulation?
vlPOA = ventrolateral preoptic area
- is the main sleep centre
- Accumulation of adenosine (result of metabolic activity) turns sleep centre on
- Caffeine is an antagonist of adenosine so keeps you awake
What are the inputs into the orexinergic neurons?
- Biological clock (suprachiasmatic nucleus)
- Hunger signlas activate system
- Satiety signals inhibit system
What are the 2 types of sleep?
- Slow wave (deep) sleep
- Rapid eye movement sleep (dreaming, atonia, fluctuating blood pressure, heart rate, respiration)
- They follow each other cyclically during sleep periods
What is orexins mechanism of action?
Inhibits the inhibition of lower motor neurons causing wakefulness
Describe the external ear
- 2 to echolocate
- Cartilages lining the ear help direct the sound
- Pinna (auricle) is vertical canal
- Moved by 5 sets of muscles innervated by VII (rostral, dorsal, caudal, ventral, intrinsic)
- Horizontal part of external acoustic meatus
Describe the pinna
- Receives sound waves
- Reflected and amplified down the canal
- Very directional, heance ear movement helos locate source
- Consducts sound waves to tympanic membrane
- Fine hairs - tragi
- Themoregulatory and behavioural roles
Describe the external acoustic meatus
- Long and curved
- Cartilaginous part (long)
- Osseus part next to bulla (short, longer with age)
- Lined with stratified squamous epithelium
- Contains sebaceous glands producing earwax (cerumen)
- Epithelial cells migrate outwards
- Sliding conveyor for debris etc trapped in cerumen
- Hence vertical canal may be dirty while horizontal canal is clean
Describe the development of the middle and inner ear
- Develops as otic placode of ectoderm lateral to developing rhombencephalon
- Otic placode invaginates to form otic vesicle
- Otic vesicle produces inner ear
- Utricle - semicircular canals
- Saccule - cochlea
- Ossicles form from mesoderm of 1st and 2nd pharyngeal arches
What is the middle ear made up of?
- Tympanic cavity within tympanic bulla
- Auditory ossicles
- Auditory tube (Eustachian tube)
Describe the temporal bone
- Made up of 3 bones
- Squamous - extends into zygomatic arch
- Petrosal - very dense bone, no air chambers, contains inner ear, does not resonate
- Tympanic - resonant cavity, dorsal part contains auditory ossicles
Describe the tympanic cavity
- Normally air filled
- Has epithelial mucosal lining
- Is within tympanic part of petrosal bone
- Contains dorsally the auricular ossicles in the epitympanic recess
- Middle part includes tympanic membrane in lateral wall of cavity and opens into auditory tube
- ventral part is tympanic bulla (enhances hearing at low and high frequencies)
- 2 windows into medial wall: oval vestibular window covered by the stapes and the cochear window closed by the secondary tympanic membrane
Describe the tympanic membrane
- Separates external from middle ear
- 3 layers
- External epithelial lining (ectoderm)
- Connective tissue with collagen and elastic fibres, fibrocartilaginous ring (mesoderm) and inner mucous membrane towards tympanic cavity (endoderm)
- Insertion of malleus (hammer)
- Transmission of sound waves from air onto auditory ossicles
Describe the development of the auditory ossicles
- Incus and malleus develop from 1st pharyngeal arch mesoderm (mammals) from ancient parts of jaw bonw
- Stapes develops from 2nd pharyngeal arch mesoderm
- Mandible derived from 1st arch as well as incus and malleus to make commplex jaw bone in reptiles
- Definind feature of mammals is the presence of 3 ear ossicles
- During evolition, bones of jaw becomes ossicles of ear
Describe the structure of the middle ear
- 2 striated muscles
- Stapedius muscle attached to stapes
- Tensor tympani muscle attached to malleus
- Reflective contraction in response to loud sounds => protects inner ear from damage
Describe the function of the auditory ossicles
- Transmit vibrations for the tympanic membrane across the tympanic cavity to the inner ear
- Air-bone coupling
- Bone - liquid coupling
- Reduction of sound reflection
- Initiation of wave in perilymph of inner ear
- 2 muscles involved in attenutation of vibrations
- Tensor tympani (V3 since from 1st pharyngeal arch)
- Stapedius (facial nerve, from 2nd pharyngeal arch)
What is the importance of the Eustachian tube in the ear?
- Connection between nasophayrnx and middle ear for air pressure equalisation
- Important in perissodactyls (guttural pouch)
What nerves are present in the middle ear?
- Facial nerve
- Tympanic nerve (from cr. n. IX - glossopharyngeal)
Describe the roleof cr. n. VII in the middle ear
- Runs thoruhg facial canal, open to tympanic cavity
- Innervates stapedius via stapedial nerve
- Gives off chorda tympani (tast to rostral 2/3 of tonge, heat and mechanoreceptors), joins lingual branch of V3 nerve
Describe the tympanic nerve function
- Branch of cr. n. IX
- PSNS supply for parotid and zygomatic salivary glands
- Postganglionic sympathetic fibres from cranial cervical ganglion join ophthalmic nerve nerve for sympathetic supply of the eye
- Damage leads to facial nerve paralysis (Horner’s syndrome)
Describe the vestibulocochlear organ
- Located inside petrosal part of temporal bone
- Fluid is present within the cochlea
- Ducts sit inside the canals
- Ducts contain endolymph
- Perilymph is almost like CSF
- Vibrations through the ossicles, through fluid then out through cochlear window
- Set sup vibrations in coiled tube
- The osseus larbyrinth contains the membranous labyrinth
What are the 3 parts of the cochlea
- Scala vestibularis
- Scala media
- Scala tympani
Describe the scala media
- Can also be called cochlear duct
- Only part that can bend is Reissner’s membrane which does not resist mechanical changes
- Basilar membrane changes in stiffness
- Reissner’s membrane is an electrolyt pump and does not resist transmission of energy into endolymph
Desribe the hair cells of the scala vestibuli
- Inner and outer hair cells
- Stereocilia: very stiff, bend at the bottom and together
- Lenfht of cell changes going through cochlea
- Fibres of VIII are efferent to outer hair cells
- Inner hair cells have afferent connections
- IHCs are not embedded in tectorial membrane
- Afferents give infomation to brain then information comes back down to the OHCs
Describe the innervation of the inner hair cells by the cochlear root of VIII
- Afferent
- 1 IHC: 10 axons
- Myelinated
- Form radial afferents
- To cochlear nuclei in medulla
- Efferent innervation from ipsilateral olivary nuclei
Describe the innervation of the outer hair cells by the cochlear root of VIII
- Efferent innervation
- 10 OHC: 1 axon
- From both sides of olivary nucleus
- Form spiral nonmyelinated axons
Describe the role of OHCs
- Amplify local vibrations
- contractile cells
Describe mechanotransduction in the hair cells
- Scala vestibuli and cochlear duct (scala media) behave as single hydraulic tube
- Sound pressure cause resonance at certain distances from oval window
- Basilar membrane vibrates, bends stereocilia on OHCs
- K+ enters the OHC and they depolarise
- OHCs contract which amplifies the initial vibration (reverse transduction)
- IHC are excited (vibrate, K+ enters) and afferent axons are stimulated, send signal centrally
Give the most basic explanation of reverse transduction in the hair cells of the cochlear duct
- OHCs vibrated
- K+ enters
- Vibrate more
- Amplify initial vibration in endolymph
- Moves IHCs more
- Afferent signal sent to brain
- Efferent fibres send signal to OHCs and ACh hyperpolarises them, preventing further contraction
Explain how frequency recognition occurs
- Basilar membrane is narrow and stiff near round window
- Vibrates at high frequencies
- Close to helicotrema membrane is wide and flexible
- Vibrates at low frequencies
- Tonotopic arrangement of frequency
- Response: each small part of membrane vibrates at a particular frequency
Explain why the coiled cochlea is useful compared to an uncoiled cochlea
- Increases sensitivity to hearing
- Energy cannot leak out as easily into areas that are not cochlea
- Only coiled in mammals
- Non-mammal is straight
Explain what BAER stands for and how it works and what it is used for
- Brainstem Auditory Evoked Response
- Each ear stimulated by separate click stimuli
- Accumulated action potential from cochlea via cochlear nerve can be measured as auditory evoked potential
- Responses recorded for each ear separately
- 5 possible peaks
- Sedation or anaesthesia needed to avoid artefacts
- Can be used to determine brain health in coma
What is peak one of BAER
- Stimulation of cochlea and cochlear nerve to the brain stem
Explain how directional hearing works
- Arrival time difference between both ears
- Sound shadow of head
- Sound modulation by auricles
- Works best with mid to high frequencies
What are the central glial cells
- Astrocytes, oligodendrocytes, microglia
What is the difference between oligodendrocytes and Schwann cells
- Oligodendrocytes can myelinate multiple axons, Schwann cells can only myeline one
- Oligodendrocytes are found in the CNS and Schwann cells are found in the PNS
Briefly describe the structure of the neocortex
- 6 layers - no segregation between layers
- Neurones have very prominent nuclei
- Many capillaries to supply nutrition to the brain
Describe the white matter in the cerebrum
- Tightly packed axons
- Wrapped in myelin sheaths and oligodendrocytes
- Fibres run parallel mostly
- Very little space so oligodendrocytes sit in rows
- See rows of blue dots = oligodendrocytes
- Only present in white matter
Briefly describe the grey matter in the cerebellum
- Some neurones in molecular ayer
- Mostly dendrites from Purkinje cells
- Grey matter in cerebellum reduces excitatory actions (Purkinje cells are inhibitory)
Describe the histological appearance of the dorsal nerve root in the spinal cord
- Looser
- Peripheral nerves
Describe the histological appearance of autonomic nerves
- Neurones sit in clusters (look like squid - oblong, nucleus, some fibres leaving)
- Blue dots are satellite cells
Explain how several cranial nerves can be affected by pathology
- Many leave from same place (medulla oblongata) so pathology here would affect many nerves
- Some have same exit sites from the skull (jugular foramen for example) so pathology over foramina can affect multiple cells
- Multiple tumours coud be present
- Infection (encephalopathy) affecting multiple cranial nerves
- Parasite
- Oedema due to hypertension
Compare the olfactory and optic lobes of birds and reptiles
- Reptiles have prominent olfactory bulbs
- Birds have large optic lobes and forebrains
Explain why fish forebrain enlargement is necessary
- Olfaction
- Complex behaviour (schooling)
- Muscle control
Describe the spinal cord and peripheral nerves of reptiles
- Functional autotomy locomotor centres
- No cauda equine (spinal cord goes all the way down the vertebrae)
- Relfexes not established for neuro exm
Describe the spinal cord and peripheral nerves of birds
- No cauda equina
- Enlarge brachial or lumbosacral plexus
- Brachial plexus in flying birds, lumbosacral plexus in running birds. Near kidney
- Glycogen body
- Mass of glycogen containing astrocytes
- On dorsal surface of LS plexus
- Function unknown
Describe the meninges of fish, reptiles and birds
Fish: meninx, single layer
- Reptiles: 2 layers, dura mater and meninx (fused pia-arachnoid), no subarachnoid space
- Birds: all 3 layers, epidural space with gelatinous tissue
How many cranial nerves in fish, amphibians, reptiles and birds?
- Fish and amphibians = 10 + lateral line nerves
- Reptiles and birds: 12
Describe the lateral line system
- Present in fish and truly aquatic amphibians
- Sensitive to tiny local displacement of water
- Receptors for touch at a distance
- Prevent contact between organisms
- Primary organ is neuromast organ
- 3 neuromast organs
- Sense hairs project into cupula
- Cupula bends when water moves across it, bends hairs and gives signal to sensory cells
- Most fish also have lateral line canals - secondary specialisation
- Series of neuromasts
- Allows sensing of different pressures along the body
- Recognition of strength of water movement
Describe and explain the infrared sensors in some snakes
- Heat pits detect temp of prey
- Bilaterally symmetrical
- Nostril, pit hole and eye closely related
- Heat sensitive membrane inside pit organ
- Locate prey via triangulation
- Can turn head to identify exact location
What is a pineal complex?
- Epithalamus can invaginate and forms up to 4 structures
- Does not usually do all 4
- Paraphysis, dorsal sac, parietal organ, epiphysis
- Pineal complex is when 2 or more are present
Describe the parietal organ
- Parapineal organ, parietal eye
- Photoreceptive organ
- +/- cornea, lens, photoreceptive does
- Does not form an image, just detects presence of light
Describe the epiphysis
- Pineal organ/pineal gland
- Dorsal evagination of midbrain
- Under skin or within cranium
- Secretes melatonin
- Cyclic activities (daily and seasonal)
- Photic stimuli -> neuroendocrine messages
- variable within classes of vertebrates
Describe the epiphysis and parietal organ of bonyy fish, amphibians, reptiles, birds and mammals
- Fish: prominent epiphysis, rudimentary parietal organ
- Amphibians: epiphysis, parietal organ
- Reptiles: epipysis and parietal organ (third eye in lizards)
- Birds and mammals: no parietal organ, epiphysis has endocrine function only aka pineal gland
Compare the location of photoreceptors and endogenous pacemakers of non-mammals, birds and mammals
- Non-mammals: photoreceptors and endogenous pacemaker within pineal organ
- Birds: pacemakers in other parts of CNS
- Mammals: photoreceptors in retina, endogenous oscillators in SCN of hypothalamus
Describe prgans of olfaction in fish, amphibians, reptiles and birds
- Fish: ends in nasal sacs, water carries chemicals in, choana
- Amphibians: nasal sac, vomeronasal organ, nasolabial grooves move chemicals into vomeronasal organ
- Reptiles: vestibule (receives air, anterior), nasal chamber is posterior, may or may not have conchae or turbinals, nasophayngeal duct
- Birds: olfactory bulb size relative to lifestyle, smallest in seed eaters, larger in aquatic birds
Describe the vomeronasal (Jacobson’s) organ
- Present in amphibians, lizards, snakes and many domestic species and non-domestic mammals
- Responds to chemosensroy stimuli including social or reproductive behaviour
- Not present in fish, birds or chelonians
- Accessory olfactory organ (paired)
- Sits on roof of oral cavity
- Linked to vomeronasal nerve
Describe the location of the vomeronasal organ in amphibians, snakes, lizards and mammals
- Amphibians: recessed area of main nasal cavity
- Snakes and lizards: separate pit in oral cavity, tongue and oral membrane deliver chemicals
- Mammals: nasal cavity, isolated area of olfactory membrane and connects to mouth via nasopalatine duct
Describe the external ear of fish, amphibians, birds and mammals
- Fish and amphibias have no external ear
- Reptiles sometimes have an external acoustic meatus
- Birds and mammals have elongated external auditory meatuses
Describe hearing in reptiles
- Tympanic membrane level with skin (not snakes or chameleons)
- 1 middle ear bone - stapes (connects tympanic membrane to inner ear)
- Vibrations from air or ground go tympanic membrane -> stapes -> perilymphatic fluid (inner ear)
Describe hearing in snakes
- No tympanic membrane
- Stapes connect quadrate bone with cochlea
Quadrate -> stapes -> oval window - Hear low frequencies
Describe hearing in birds
- Short external acoustic meatus = tympanum
- Songbirds have 2 tympanic membranes
- No pinna, special feathers instead
- Single auditory ossicle = stapes
- Regenerate damaged hair cells (mammals do not)
Describe the Eustachian tubes in reptiles and birds
- Connects middle ear to oropharynx
- Not closed
- Adjustment to high altitudes facilitated
- Pathogens can easily ascend into tympanic cavity and inflammatory debris can enter pharynx
Describe the facial feathers of the owl
- Auricular feathers are acoustically transparent
- Reflector feathers are densly ramified and able to direct sound to ear
- Tightly packed rim of facial feathers
- Sound -> external auditory meatus
Describe and explainn owl ear asymmetry
- Left and right external acoustic meatuses are different size and shape
- Helps localise sound by the intensity and timing of sounds
- Can hear in horizontal and vertical planes
Describe fish eye anatomy
- Bulbous eye - dome shaped cornea, rigid iris, lens protrudes
- Difficult to adjust to light changes - pupil fixed, position of photoreceptors
- Focus: change lens position instead of lens shape
- Rods:cones ratio varies
- Can see in colour and UV
Describe amphibian eye anatomy
- Move lens to accomodate
- Iris - striated muscle (voluntary) so cannot evaluate PLR
- Vision is by pattern recognition
- Retina processes most visual info
Describe avian eye anatomy
- Large compared to head and brain
- Larger, sharper images
- Nictitating membrane (striated msucles, rapid sweeps to clean cornea)
- Lacrimal and Harderian glands - in many lacrimal reduced, Harderian gland is on posterior aspect of orbit and associated with base of nictitating membrane
- Composition of secretions from HG unknown
Describe the scleral ossicles in birds
- Forms ring around eye
- Reinforces scleral junction
- Extra support for eye
Explain how visual acuity is improved in birds
- Avascular retina - less light scatter from blood vessels, higher visual acuity
- Pecten - highly vascularised, thin, highly folded, nutritional role
Describe the role of the fovea in improving visual acuity
- High concentration of rods and cones
- Sharpen vision
- Present in fish, reptiles, birds and primates
- Usually 2 fovea in diurnal species especially raptors
Describe rods and cones in birds
- Double cone
- Principle and accessory cone
- Diurnal birds have more cones, nocturnal more rods
- Colour vision varies in birds
- Some diurnal can see UV
Describe the structure of bird cones
- Have oil droplets on cones
- Light through droplet first
- Lipids and carotenoid pigments in oil
- UV light shield
- Focuses light
- Allows perception of UV light
- UV is used for signalling in birds (feather reflecting UV, food reflecting UV differently)
Describe accomodation in avian vision
- Lens shape - softer so more rapid changes
- Corneal curvature
- Each eye is independent
- Iris sphincter is made up of striateed muscle and so is under voluntary control
Describe reptile eye anatomy
- Eyelids - lower lid is mobile
- Scleral ossicles
- Nictitating membranes
- Lacrimal and Harderian glands
- Harderian gland provides enzymes facilitating vomerolfaction in reptiles
Describe the spectacles in snakes and some lizards
- Fused eyelids, transparent
- Dry horny scale
- Insensitive
- Subspectacular space
- Shed during ecdysis (colour change)
Describe accomodation in reptile vision
- Muscles of ciliary body to change curvature of lens (lizards, chelonians)
- Iris sphincter - striated muscles (chelonians, snakes), under voluntary control
Describe the retina of reptiles
- Avascular
- Conus papillaris may or may not be present (lizards, some snakes)
- Choroidal blood vessels
- Rods and cones
- Fovea centralis - lizards (diurnal)
Describe the relationship between memory and emotions
- Learning can be based on repetition
- Can also occur wihout it, particularly following events that cause a strong emotional response
- Anxiety for example can be a conditioned emotional response that occurs when a neutral stimulus is followed by an aversive stimulus
Describe counterconditioning
- Can learn new responses to something that previously elicited a different response
- ## Can use respondent or operant counter conditioning
Describe desensitisation
Reducing the response to a stimulus through repetitive neutral exposure
