senses

• Sensory systems are hierarchical, with sensory receptors as transducers, neural relays, sensation (sensory coding and representation), and perception.
• Sensory receptors are transducers and there are four main types based on the stimulus they transduce.
• Transduction involves physical or chemical stimuli opening/closing ion channels in the receptor membrane directly or indirectly (second messenger).
• Depolarization/Hyperpolarization of the membrane results in a Graded Potential or Receptor Potential.
• If the receptor potential is strong enough, it can trigger action potentials travelling to the CNS or release of neurotransmitter in non-neural receptors.
• A sensory neuron has a receptive field.
• Sensitivity of an area depends on how large is the secondary receptor field.
• Neural relays allow sensory system to interact, for example, perception of speech sounds is influenced by the speaker's facial gestures (McGurk Effect) and pain gateing.
• Neural relays include spinal reflexes.
• Sensation is the process of registering and representing physical effects (of objects) upon our sense organs.
• The brain uses four properties of a stimulus that are preserved: Modality (nature), Location, Intensity, and Duration.
• The VNO and pheromones are important for most mammals, but less so for humans.
• The vestibular organ comprises two otolith organs (the saccule and utricle) and three semicircular canals.
• An example of a response to pheromones is the synchronization of menstrual cycles in women.
• Action potentials travel to the brain stem and cerebellum from the vestibular organ.
• The VNO is tiny in human adults and has no receptors and is considered vestigial.
• Semicircular canals are filled with a jellylike substance and hair cells that are activated when the head moves.
• Audition is a complex mechanical sense.
• The mechanical senses respond to pressure, bending, or other distortions of a receptor, including touch, pain, and other body sensations, as well as vestibular sensation, which detects the position and movement of the head.
• Humans unconsciously respond to some pheromones through receptors in the olfactory mucosa.
• The vestibular organ is in the ear and is adjacent to the cochlea.
• The vestibular sense is a system that detects the position and movement of the head, directs compensatory movements of the eye, and helps to maintain balance.
• Otoliths are calcium carbonate particles that push against different hair cells and excite them when the head tilts.
• We are sensitive to a wide range of harmful substances, but not highly sensitive to any single one.
• Fatigue of receptors can lead to a decrease in the response to a stimuli.
• Different receptors respond with different patterns of action potentials.
• Cross-adaptation refers to the reduced response to one stimuli after exposure to another.
• Sour receptors detect the presence of acids.
• Sweetness, bitterness, and umami receptors activate a G protein that releases a second messenger in the cell when a molecule binds to a receptor.
• The saltiness receptor permits sodium ions to cross the membrane, resulting in an action potential.
• Most taste cells contain only a small number of these receptors.
• Animal species vary in taste sensitivities, with carnivores like cats, hyenas, seals, and sea lions having no sweetness receptors, and dolphins having few taste receptors of any type because they eat only fish which they swallow whole.
• It is important for modality, for example in rats.
• Bitter taste is associated with a wide range of dissimilar substances that are toxic, and about 25 types of bitter receptors are sensitive to a wide range of chemicals with varying degrees of toxicity.
• Modality refers to the type/nature of stimulus (heat, pressure, etc.) and depends on which sensory receptor/neuron is activated by the stimulus.
• Each sensory neuron responds to a stimulus of a specific nature.
• Labeled Line Coding: a signal arising from a specific sensory neuron/group of neurons is always associated to a specific modality from the brain.
• Location of the stimulus depends on which receptor field is activated.
• Itch: comes only from nociceptors located in the skin and often activated by histamine.
• Emotional Pain: Pain may be accompanied by emotional distress and autonomic reactions due to ascending nociceptive pathways sending branches to the Limbic System and Hypothalamus.