MCAT Psych/Soc

• The cornea is the outer protective layer of the eye and refracts light toward the lens.
• Aqueous humor is between the cornea and the lens and is the transparent medium allowing light to pass through the eye.
• The ciliary muscles control the shape of the lens, which changes focus on objects at different distances from the eyes.
• Vitreous humor is the transparent medium that is found after the lens
• Iris is the ring shaped muscle that controls the amount of light that enters the eye through the pupil
• The dilator muscle of the iris dilates the pupil, letting more light into the eye.
• The sphincter muscle of the iris constricts the pupil, letting less light into the eye.
• Retina contains photoreceptors (rods and cones) that convert light energy into neural signals.
• Rods do not distinguish color and are located on the periphery of the retina
• Cones are responsible for color vision and are located in the center of the retina, called the macula.
• The macula has more rods than cones, but the fovea (center of the macula) has only cones.
• Rhodopsin is the protein found in rods that is responsible for phototransduction
• Photopsin is the protein found in cones that is responsible for phototransduction
• The optic disk is devoid of photoreceptors and gives rise to the optic nerve, creating a blind spot
• Bipolar cells synapse directly with rods and cones and are responsible for the perception of light intensity. They synapse with ganglion cells, whose axons form the optic nerve. Horizontal and amacrine cells recognize changes in color and are important in edge detection and contrast perception.
• Spatial resolution is the ability to distinguish differences in small details of an image. Temporal resolution is the ability to distinguish the speed at which visual data is changing.
• Parallel processing is the ability to process information through multiple independent pathways simultaneously. For visual stimuli, this occurs through connections between the optic tract, lateral geniculate nucleus of the thalamus, and the visual cortex in the occipital lobe.
• Parvocellular cells have high spatial resolution for stationary objects, but have low temporal resolution. Magnocellular cells primarily receive input from peripheral vision. They have temporal resolution and are suited for detecting moving objects. Binocular neurons in the visual cortex integrate information from both eyes to perceive depth.
• Pheremones are chemicals secreted by an animal that elicit a response in another animal of the same species.
• Photoreceptors detect light and are needed for sight. Mechanoreceptors detect pressure and movement and are important in hearing and kinesthetic sense. Nociceptors detect pain and are important in somatosensation. Thermoreceptors detect changes in temperature and are involved in thermosensation. Osmoreceptors detect blood osmolarity and are important in water homeostasis. Chemoreceptors detect chemical stimuli, such as volatile compounds in smelling and dissolved compounds in tasting.
• The pathway below describes the olfactory system.

  Volatile compounds -> Chemoreceptors -> Olfactory bulb -> Olfactory nerve -> Higher brain regions (ex. Limbic system)
• The pathway below describes the gustatory system.

  Dissolved compound -> Chemoreceptor -> Taste bud cells -> Thalamus -> Gustatory cortex in frontal lobe
• The somatosensory system includes the skin, mucous membranes, limbs, and joints. Mechanoreceptors detect touch, vibration, pressure, and sound. Thermoreceptors detect temperature. Proprioceptors detect movement and body position. Nociceptors detect pain. Chemoreceptors detect chemical stimuli. These receptors send signals through the CNS to the somatosensory cortex in the parietal lobe.
• Sensation is the process of obtaining sensory information. Perception is the process of interpreting and integrating sensory information.
• Bottom-up processing is object recognition using parallel processing and feature detection, perceiving parts to make a whole. It is commonly used when information is unfamiliar or complex. Top-down processing is object recognition based on prior knowledge, experience, and context, using the whole to fill in the gaps.
• Perceptual organization is how we structure sensory information into a coherent whole. This process involves depth perception, spatial reasoning, and visual attention.
• Depth perception uses visual cues to determine an object's distance from the viewer. Relative size suggests that closer objects appear larger than distant objects. Interposition is the apparent overlap of objects in the visual field, where we perceive that the object in front is closer than the object behind. Linear perspective suggests that the greater the convergence of two parallel lines, the farther the distance. Motion parallax is the idea that objects close to us move faster when we change our field of vision to look at something else.
• Form is detected by parvocellular cells that have high spatial resolution and pick up on shape of a stimulus. Motion is detected by magnocellular cells that have high temporal resolution and pick up peripheral movement.
• Constancy is our ability to perceive that certain traits of objects stay the same despite changes in the environment. This ability can be used for color, brightness, size, and shape, depending on the object of interest.
• Gestalt Principles

  Law of Proximity: elements close to each other are perceived as a group

  Law of Similarity: similar objects are grouped together

  Law of Good Continuation: elements that follow continuous patterns/pathways are grouped together

  Subjective Contours: perceiving contours and shapes that are not present

  Law of Closure: a space enclosed by a contour is perceived as a complete figure, or incomplete figures are perceived as one complete whole
• The law of pragnanz states that perceptual organization will always be as simple, regular, and symmetric as possible.
• Neurotransmitters are small molecules made in neurons that are released in response to a stimulus. Most are made from amino acids.
• Epinephrine is released in stress situations to increase heart rate, dilate pupils, and increase blood flow to the muscles.
• Norepinephrine is released in stress situations and keeps the body functioning normally. It stabilizes body temp, heart rate, and blood pressure, as well as stimulates energy production.
• Both Epi and NE act on the sympathetic nervous system.
• GABA is the inhibitory neurotransmitter in the brain and spinal cord, and influences behavior regulation.
• Acetylcholine is a neurotransmitter that binds to cholinergic receptors and involved in memory, learning, and muscle contraction. Alzheimer's is caused in part by the atrophy of neurons that produce this neurotransmitter.
• Serotonin is a neurotransmitter that is involved in mood, sleep, and appetite. Decreased levels of this neurotransmitter can cause major depressive disorder.
• Endorphins are neurotransmitters that inhibit pain and create the feeling of euphoria. They bind to opioid receptors.
• Dopamine is the neurotransmitter associated with reward, motivation, movement, and posture. Parkinson's is associated with a decrease in dopaminergic neurons and schizophrenia is associated with increased secretion or sensitivity to this neurotransmitter.