Sensory Systems

• The cerebral cortex serves as an integrating center for somatosensory information
• The amount of space on the somatosensory cortex devoted to each body part is proportional to the sensitivity of that part via receptive field distribution
• The receptive field is the physical space in which these receptors are located
• Mechanoreceptors respond to pressure, cell stretch, vibration, acceleration, and sound stimuli
• Photoreceptors respond to photons of light
• The two types of receptor cells are nerve cells and specialized epithelial cells
• Receptor potentials are graded responses that are generally depolarizing but might not elicit an AP. Stimulus intensity and duration as transduced via RPs, ultimately impact action potentials fired and neurotransmitter release
• Graded potentials in free and encapsulated nerve endings are called generator potentials. When they are strong enough to reach the threshold they can directly trigger an action potential along the axon of the sensory neuron.
• the amount of space on the somatosensory cortex devoted to each body part is proportional to the sensitivity of that part via receptive field distribution
• Convergence is characterized by many primary sensory neurons converging onto a single secondary neuron that creates a very large receptive field
• Most special or sensory pathways pass through the thalamus which acts as a relay and processing station on their way to the cerebral cortex
• Perilymph is the fluid found the the vestibular and tympanic ducts in the cochlea of the inner ear
• endolymph is the fluid found in the cochlear duct of the cochlea in the inner ear. It is also where the Organ of Corti is located and where all the hair cells are
• When the cilia bend against the tectorial membrane, tip links between them open and close ion channels, allowing K+ to come inside and depolarize the cell, signaling the voltage-gated channels to turn on and cause an influx of K+ and an AP.
• The vestibular system is the equilibrium system that allows us to maintain our balance and posture during linear and rotational movement
• The hammer, anvil, and stirrup are the three bones that connect the tympanic membrane to the oval window
• The semicircular canal is for posture and equilibrium during rotational and angular acceleration. The Utricle is for posture and equilibrium during linear acceleration in the horizontal direction. The Saccule is for posture and equilibrium during linear acceleration in the vertical direction
• The macula is the otolith organ that contains the cupula, hair cells, and the otoliths
• The otoliths are crystals that move in response to gravitational forces. As gravity and acceleration change, the crystals put pressure on the hair cells and send signals to the brain
• Movement of the endolymph pushes on the gelatinous cupula and activates the hair cells
• Conductive hearing loss is when there is a lack of transmission through either the external or the middle ear
• central hearing loss is damage to neural pathways between the ear and the cerebral cortex or damage to the cortex itself
• sensorineural hearing loss is damage to structures of the inner ear
• Depolarizing action potentials occur when stereocilia are bent toward the tallest kinocilium
• phasic receptors are rapidly adapting receptors that fire when they first receive a stimulus but cease firing if the strength of the stimulus remains constant. Tonic receptors are slow-adapting receptors. They will respond to the stimulus as long as it persists, and produce a continuous frequency of action potentials.