Special senses Flashcards
Primary sensory cell
Sensory cell contained within nerve ending, with own axon (skin & olfactory)
Secondary sensory cell
Lack an axon
Synapse with sensory nerve fibres (ear, eye, taste)
Lacrimal
Tear producing apparatus in the eye
Lens function
Focusing light onto retina
Where are sensory cells located in the eye?
Retina
Optic nerve function
Transmits visual information to the brain
Are the cornea and sclera attached?
Yes
When the ciliary muscle contracts the lens is…
The lens is wide
Zonular fibres have more room
When ciliary muscle relaxes the lens is
The lens is flat (contracted)
Less space for zonular fibres - puts pressure on lens
How is the ciliary muscle attached to the lens?
Via zonular fibres (connective tissue)
Eye ball
Fluid filled sphere
Covered by three layers (tunic)
- Fibrous (outer)
- Vascular (mid)
- Nervous (internal)
Vitreous body
Gel-like material
Why is cornea transparent and sclera white? (made out of same fibres)
Fibre arrangement
- neatly layered in cornea
- Scattered and tightly packed in sclera
Fibrous tunic of the eye
Outer layer
Contains:
Sclera
Cornea
Only complete tunic
Protects the eye
Vascular tunic of the eye
Mid layer Contains: Choroid (lines sclera) Ciliary body Iris
Blood vessels and smooth muscle
Nourishes retina
Regulates shape of lens and size of pupil
Produces aqueous humour
Cornea
Like a window it allows light to enter to eye
Iris
Regulates the amount of light that enters your eye by adjusting the size of the pupil opening.
Contains muscles that allow the pupil to become larger (open up or dilate) and smaller (close up or constrict).
Tapetum lucidum
Located within choroid directly behind retina
it reflects visible light back through the retina, increasing the light available to the photoreceptors
- cause animal eyes to glow in the dark
What produces aqueous humour
Ciliary processes
Nervous tunic
Inner layer
Contains:
Retina
The retina contains photoreceptor cells:
- Rods (night)
- Cones (colour)
Ora serrata
- Junction between optic & non-sensory parts of retina
Optic disc
- Axons of nerve cells contracted - blind spot (no receptor cells)
Blind spot also known as
optic disc
What is the junction between optic and non-sensory parts of the retina
Ora serrata
Colour vision
Cones
Black and white vision
Rods
Lens
Consists of fibres arranged in concentric rings
Transparent
Secured by zonular fibres (extend from ciliary body) around equator
Focuses light
How many voluntary muscles control the rotation, retraction and sideways movement of the eye?
7
Muscle control is complex
Eyelids
2 folds of muscular & fibrous tissue
Skin outside, conjunctiva (mucous membrane) inside
Glands associated with eyelid
Lacrimal glands: nourish and keep eye moist
Tarsal glands: secrete fatty , lipid barrier substance (open along eyelid
Lacrimal glands
nourish and keep eye moist
Tarsal glands
secrete fatty , lipid barrier substance (open along eyelid
Third eyelid
Conjunctival fold supported by cartilage
What is a vestibulocochlear organ?
Ear
Main functions of the ear
Hearing & balance
Where is the middle and internal ear housed?
Within temporal bone of the skull
External ear
Two parts:
1. Pinna (auricle)
- External acoustic meatus (external ear canal)
What separates external and middle ear?
Tympanic membrane
ear drum
Middle ear
Consists of:
Tympanic cavity
Auditory ossicles mediate transmission of sound waves
Auditory tube balances pressure on either side of tympanic membrane
Inner ear
Mechanical stimuli transmitted into nerve impulses
Cochlea: hearing
- Sensory cells = hair cells
- Do not have their own axons (synapse with sensory nerve fibres)
Vestibular apparatus: equilibrium & posture
Cochlea location
Inner ear
Cochlea function
Hearing
- Sensory cells = hair cells
- Do not have their own axons (synapse with sensory nerve fibres)
What does the curvature of the cornea do?
Converges light rays together
Is a flat lens better for short or long distance vision?
Long distance vision
Ciliary muscle relaxed - zonular fibres taut - Lens flat
When an animal focuses on something close the ciliary muscle….
Contracts - zonular fibres slacken - lens is round
What controls the ciliary muscle in the eye?
ANS
Sympathetic fibres induce relaxation of the
muscle (for distant vision) while parasympathetic fibres cause contraction for near focus.
Binocular vision
Where the eyes have overlapping visual fields
Necessary for depth perception
Monocular vision
The vision covered by only one eye
Are rods or cones more sensitive to light?
Rods are more sensitive to light
What is the point of greatest visual accuracy in the eye?
Fovea or visual streak
Otoliths
tiny crystals of calcium carbonate suspended within the gelatinous layer in the ear, making it heavier and giving it more inertia
How does the ear help with balance
When the head tilts, the hairs bend in the direction of the tilt, due to gravity pulling the
heavy gelatinous layer. The hair cell bundles send different patterns of neural activity to the brain,
depending on the position of the head with respect to gravity.
What does the pinna (external ear) do
collects sound waves and channels them down the external ear canal
The olfactory organ consists of:
Sensory cells lining mucosa in caudal nasal cavity
Vomeronsal organ
Important in detection of pheromones
Sensory taste cells are organised in clusters called
Taste buds
Taste buds are located
In side walls of tongue papillae
Do taste cells have their own axon?
No, but form synapsed with sensory nerve fibres form cranial nerves
What determines the stimuli an animal can detect?
Sensory receptors
How does the cortex process the signal?
3 factors contribute to sorting:
- Type of stimulus - determined by type of receptor activated
- Intensity of stimulus - determined by frequency and area of APs
- Location of stimulus - message sent via specific pathways - activate specific area in brain
Two classifications of receptors?
- Adequate stimulus - Sensory receptors are specialised to respond more to one type of stimulus than another e.g. mechanoreceptors or photoreceptors
- Stimulus location is also used to categorise sensory receptors
Generator potentials
No refractory period can be summed Local Last for as long as stimulus Stimulus intensity related to size of generator potential
Sensory pathways are generally 3 neuron chains:
1st order afferent carries info to CNS, where it synapses with 2nd order afferent
2nd order afferent synapses with 3rd order afferent, usually in thalamus
3rd order afferent conveys message to higher brain for full perception
what type of receptors are involved in somatosensory?
mechanoreceptors, nocireceptors and thermoreceptors
What are the 2 somatosensory pathways?
The spinothalamic and dorsal column (medulla of brain stem)
Once signal reaches the thalamus the animal
becomes aware
Dorsal column pathway (touch) detects
Precise touch, texture, joint position & movement
Spinothalamic pathway detects?
Crude, coarse touch, pressure, temperature, pain
What type of receptors are involved in Dorsal column pathway?
Mechano-receptors
What type of receptors are involved in spinothalamic pathway?
Noci, thermo, mechano
Which pathway involved in somatosensory is the primitive pathway?
Spinothalamic pathway
What type of receptors are used in olfaction & gustation (taste)?
Chemo
Are the pathways uncrossed in taste sensation?
Yes
Where are Olfactory cells located?
On ethmoidal turbinate bones
- longer noses = better smelling - more folding - larger SA
Function of cornea and lens?
Ned light to focus on single point on retina
Lens changes its strength to do this –> accomodation
Accomodation
Ability of lens to adjust strength (thickness)
regulated by ciliary muscle
Relaxation = Symp.
Contraction = parasymp.
Do rods and cones face the front or the back of the eye?
Back
How many types of cone cells are there?
4
Most mammals have 2
Vision pathway
Light hits retina - triggers photopigment - transduced into generator potential in receptors - bipolar cells - triggers AP in ganglion cells
Do rods and cones converge onto the same pathway?
No, separate pathways, brain gets info about colour and light from different parts of the eye
The image detected on the retina before processing is…
Upside down and backwards - because light rays bend
How does depth vision occur?
Fibres from interior of each retina cross over (lateral fibres dont)
Brings together fibres carrying information on same visual field, from two aspects = depth vision
How aural sensory cells work
Hair cells send continuous impulses at rest
If a force bend the cilia - signal pattern to brain changes
How does the auditory cortex determine location of sound source?
Sound reaches close ear slightly before farther ear - differences in timing between ears
How is pitch discriminated?
Sound waves of different frequencies move different parts of basilar membrane -CNS interprets pattern of hair cell movement as sound of particular frequency
What is pain?
Nociception + sensation of unpleasantness
What areas of CNS are highly involved in pain response?
Hypothalamus & limbic system
Nociceptors
Naked nerve endings of afferent neurons 3 categories 1. Mechanical 2. thermal 3. Polymodal (chemical)
Nociceptive pain
due to damaging stimuli
Visceral or somatic
Two type of fibres involved in pain response
- Type A-delta fibres - Large, myelinated - FAST
2. Type C fibres - small- unmyelinated fibres - SLOW
What type of pain fibres only occur in viscera?
Type C fibres
What pathway is important for pain transmission
Spinothalamic
What is the most important neurotransmitter in pain response
Substance P
Sensitisation (pain)
Prolonged stimuli may increase pain intensity
Hyperalgesia
An increased sensitivity of receptors due to repeated stimulation
Opiates
Pain relief NTRs - suppress the release of substance P - block transmission of pain signal
Natural analgesia in animals
Opiates (provide pain relief via NTRs)
Detrimental effect of pain
Delays healing & prolongs recovery
Catabolism, drop in feed intake
Can lead to self mutilation
Only beneficial as diagnostic sign
Why is analgesia good for animals?
reduces suffering
improves healing and reduces healing time
Improves food intake - prevents catabolism
Stops self mutilation
Makes animals easier to handle
- Treatment best started before pain begins
Different ways to treat pain?
Inhibit the activation of nociceptors
Block the conduction of impulses by nociceptors
Block the transmission of pain pathways in CNS
Activate body’s own pain modulating system
Opoids examples
Morphine
Opoids function
Stimulate bodys natural pain modulating system
