PSYB65H3- Final Exam Guide - Comprehensive Notes for the exam ( 49 pages long!)

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Published on 29 Mar 2018
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PSYB65H3
Final EXAM
STUDY GUIDE
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Chapter 9 – Sensory Systems: Visual System
Sensory Receptors
- Sensory receptor neurons are specialized to convert sensory energy into neural activity
-Vision: photoreceptors in the retina convert light energy chemical energy action potentials
-Auditory: air pressure waves mechanical energy which activates auditory receptors action potentials
-Somatosensory: mechanical energy activates receptors sensitive to touch, pressure, or pain. Somatosensory
receptors then generate APs in somatosensory receptor neurons
-Taste & Olfactory: various chemical molecules in the air/food fit themselves into receptors of various shapes to
activate APs in respective receptor neurons
Receptive Field: sensory region that stimulates a receptor cell on neuron (Ex: what you see with your eyes is your
receptive field)
-Optic flow: streaming of visual stimuli that accompanies an observer’s movement through space
-Auditory flow: change heard as a person and a source of sound move relative to one another
Receptor Density & Sensitivity
-Receptor density is important for determining a sensory system’s sensitivity
-Ex: colour photoreceptors are small and densely packed to make sensitive colour discriminations in bright light.
Receptors for black-white vision are larger and more scattered, but their sensitivity to light is remarkable
Neural Relays
- All receptors connect to the cortex through a sequence of 3-4 intervening neurons. The visual & somatosensory
systems have 3 relays, and the auditory system has 4.
- Information can be modified at various stages in the relay.
- Neural relays allow sensory systems to interact.
- Some of the 3 or 4 relays in each system are in the spinal cord, brainstem, or in the neocortex.
Sensory Coding & Representation
- After info is transduced and encoded by APs, the APs travel along peripheral nerves in the somatic NS until they
enter the spinal cord or brain. APs then travel on nerve tracts within the CNS.
- Each sensation (touch, sound, and small) are processed in their own distinct cortical region. Each sensory system
has a preferential link with certain reflexive movements
-Synthesia: mixing of the senses (ex: hearing in colour or identifying smells by how the smell sounds)
-Topographic map: spatially organized neural representation of the external world. Every animal has at least one
primary cortical area per sensory system. Additional areas are referred to as secondary since most info that
reaches here is relayed through the primary area. Additional areas probably are dedicated to encoding a specific
aspect of the sensory modality (ex: for vision, additional areas may take part in perceiving colour, movement, etc)
Perception: subjective interpretation of sensations by the brain
-Sensation: registration by the sensory organs of physical stimuli from the environment
- Proof that perception is more than sensation is that different people transform the same sensory stimulation into
totally different perceptions
Structure of the Retina
- Light energy travels through the pupil, into the eyes, where it strikes a light-sensitive surface (retina) at the back
of the eye. This stimulation of photoreceptor cells on the retina constructs a visual world.
-Muller cells: special glial cells in the retina that span from the retina’s inner membrane at the front to the
photoreceptors at the back of the retina. They act as optical fibers, channeling light to buried photoreceptors
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- Our vision is better at the center of the visual field than at the margins (periphery).
-Blind spot: small area of the retina AKA the optic disc. It’s a retinal region where axons forming the optic nerve
leave the eye and blood vessels enter and leave. It has no photoreceptors, thus is said to be blind. Your optic disc
is in a different location in each eye (lateral to fovea), the right eye can see the left eye’s blind spot.
-Optic neuritis: inflammation of the optic nerve itself
Photoreceptors: convert light energy into chemical energy, then into neural activity
- Light striking one triggers a series of chemical reactions that lead to a change in membrane potential, thus leading
to the release of neurotransmitters onto nearby neurons
-Rods: longer than cones, they’re sensitive to low levels of brightness (luminance), especially in dim light. They
function primarily for night vision. All rods have the same light-absorbing pigments.
-Cones: don’t respond to dim light but are highly responsive to bright light. They mediate both colour vision and
our ability to see fine detail (visual acuity). Each cone has one of 3 light-absorbing pigments. The number of red
& green cones are equal but there are less blue cones.
- Rods & cones are unevenly distributed over the retina. The fovea only has cones.
- The gene for the red cone is carried on the X chromosome so men only see one type of red. Some women are
more sensitive since they have two X-chromosomes.
Types of Retinal Neurons
- 3 cell types: bipolar, horizontal, and amacrine
- Horizontal cells link photoreceptors with bipolar cells
- Amacrine cells link bipolar cells with cells in the second neural layer, the retinal ganglion cells (RGCs). RGC
axons collect in a bundle at the optic disc and leave the eye to form the optic nerve (back of eye to brain)
- RGCs split into 2 major categories: Magnocellular cells (M) & Parvocellular cells (P)
- M cells are larger so they receive their input primarily from rods (longer than cones). They’re sensitive to light
and not colour. They’re found throughout the retina.
- P cells receive input primarily from cones and are sensitive to colour. P cells are found primarily in the fovea
region where we are sensitive to colour and fine details.
Optic Chiasm: as optic nerves exit from each eye, before entering the brain, they partly cross, forming the optic chiasm
- Half the fibers in each eye cross in such a way that the left half of each nerve goes to the left side of the brain and
the right half goes to the brain’s right side
-Nasal retina: medial path, crosses to the opposite side
-Temporal retina: travels straight back on the same side of the brain
- Light falling on the right half of each retina comes from the left side of the visual field, information from the left
visual field goes to the brain’s right hemisphere and info from the right visual field goes to the left hemisphere
Three Routes to the Visual Brain
- There are 2 main pathways that lead to the visual cortex in the occipital lobe: geniculostriate pathway (processes
an object’s image) and the tectopulvinar pathway (directing rapid eye movements). They’re formed from RGC
axons separating.
- Another pathway tracks into the hypothalamus
Geniculostriate System
- All P ganglion axons and some M ganglion axons form this pathway
- This pathway goes from the retina to the lateral geniculate nucleus (LGN) of the thalamus and then to layer IV of
the primary visual cortex in the occipital lobe
- When strained, the primary visual cortex shoes a broad stripe across it in layer IV, thus it’s known as striate
(striped) cortex
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