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Summary Biology of Domestic Animals - Case 7 Dog/Sense
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Summary of case 7 (dog/sense) of course Biology of Domestic Animals
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Biology of domestic animals case 7Case 7 Dogs:
1.0 Introduction: sense organs in general
1.1 Pavlov’s experiment
o Classical conditioning, a response that was originally elicited by one stimulus can now be
elicited by another stimulus that originally had no effect.
o Unconditioned stimulus: something that does not need to be learned to elicit the response.
o Conditioned stimulus: something that is neutral in the learning environment that over time
paired with unconditioned stimulus elicit the same response even in absence of the
unconditioned stimulus.
1.2 Sense organs
o Gain info by using sense organs.
o Stimulus is a form of energy- electrical, mechanical chemical or radiant.
o Senses:
Vision: electrical energy, photoreceptors, eye (sensory structure)
Hearing: Air pressure waves (mechanical energy), mechanoreceptors, ear (sens.)
Touch: Tissue distortion (mechanical energy/radiant), mechanoreceptors &
thermoreceptors, skin/muscle etc (sens.)
Taste/smell: chemical, chemoreceptors, nose/mouth (sens.)
o Sensory receptors: energy from stimulus into action potentials. Sensitive for one specific kind
of stimulus. Action potentials can be transmitted to central nervous system, eliciting a
response via reflex arc.
o When sensory receptors repeatedly exposed to stimulus, then sensory receptors stop
sending nerve stimuli to central nervous system, e.g. pressure of clothes.
1.3 Reflex arc
o Reflex arc are neurons which work in groups. Contain at least 2 neurons, but usually more
involved. Parts of typical reflex arc are:
Receptor: sense organ in skin, muscle or another organ
Afferent neuron (sensory neuron): carries stimuli to central nervous system (brain
and nerve cord)
Central nervous system: synaptic connections are made between sensory neurons
and interneurons
Efferent neuron (motor neuron): makes synaptic connection with interneuron and
carries stimuli from central nervous system
Effector: examples are muscles and glands. With effector animal responds to
environmental changes.
o Simplest form of reflex arc contains only 2 neurons: afferent and efferent neuron. In most
cases there are interneurons interposed. Interneuron can connect afferent and efferent
neurons on same side of spinal cord but also on opposite sides.
o Reflex act is involuntary, not under control of will.
o Almost any reflex act, a number of reflex arcs are involved. An efferent neuron may receive
signals from many afferent neurons.
, 2.0 Vision
2.1 Human eye
o Focuses light on light-sensitive surface (retina) using a lens and an opening (pupil).
o Process vision divided into three steps:
1. Light enters eye. Lens focuses light on retina
2. Photoreceptors of retina transduce light energy into electrical signal
3. Neural pathways from retina to brain process electrical signals into visual images.
2.1.1 Anatomy
o Eyes protected by bony ridge, the orbit. Formed by facial bones of skull.
o Lacrimal apparatus ensures exposed system of eye remains moist and free of debris. Keeps
continuous flow of tears to reach this goal.
o Pupil, can change size with help of ring of pupillary muscle.
o Eye colour determined by pigment and other components of iris.
o Eye has two compartments separated by lens. Lens suspended by ligaments called zonules.
Focuses light.
o In retina, small arteries and veins are crisscrossed and all come together in the optic disk.
o Left visual field goes to right side of brain and vice versa.
2.1.2 Processing of light
o Before it strikes the retina, the light is modified in two ways:
1. The light that reaches photoreceptors is regulated by changes in size of pupil.
2. The light is focused by changes in the shape of the lens.
o Bright pupil narrows. Dark pupil expands.
o Dilation of pupil occurs when muscles contract. Light hitting retina in one eye activates a
reflex: Efferent neurons constrict the pupils in both eyes.
Phototransduction occurs at the retina:
o Our brains only perceive small portion of broad energy spectrum. For humans visible light is
limited to electromagnetic energy with waves of 400-750 nm.
o Electromagnetic energy is measured in units called photons.
o Human eyes do not respond to ultraviolet and infrared light. Some other animals are able to
see these wavelengths.
o Phototransduction = process by which animals convert light energy into electrical signals. In
humans this takes place when light hits retina.
o 5 types of neurons in retinal layers: photoreceptors, bipolar cells, ganglion cells, amacrine
cells and horizontal cells.
o When looking at object, lens focuses image on fovea. Everything that falls on fovea is in sharp
focus. Image is upside down and reversed again by the brain.
o Images cannot be seen when projected on blind spot. Blind spot is on the retina where the
optic disk is, because optic disk has no photoreceptors.
Photoreceptors transduce light into electrical signals
o Rods and cones:
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