Day 2: Nerves

Sensory receptors: Transduction Action potentials: To reiterate, it’s the nerve impulses; how the information is transmitted through the NC. All APs are the same…what’s different is the part of the brain that receives it. Sensations: APs that reach the brain via sensory neurons; the brain becomes aware of the impulses and interprets them, giving the perception of stimuli.

Sensory Receptors: Transduce Perceptions: “If a tree falls and no animal is present to hear it, is there a sound? The fall certainly produces pressure waves in the air, but if sound is defined as perception, then there is none unless an animal senses the waves and its brain perceives them.” It’s all in the head! :D

 Sensory Reception: the detection of a stimulus by sensory cells.  Sensory Receptors: specialized neurons or epithelial cells (:O) that exist singly (uno!) or in groups (>uno!) with other types in sensory organs (eyes, ears).  Extero-recptors: sensory receptors that detect stimuli coming from outside the body (heat, pressure, light, and chemicals).  Intero-receptors: detects stimuli coming from within the body such as blood pressure and body position.

Functions Performed by Sensory Receptors  Sensory transduction, amplification, transmission, and integration  Sensation converts the energy of the stimuli which in charge leads to a change in frequency of action potentials transmitted to the CNS

Sensory Transduction Conversion of stimulus energy in the membrane potential of sensory receptor Receptor potential: change in the membrane itself. Result from the opening or closing of ion channels in the sensory receptor’s plasma membrane, which changes the ionic permeability of the membrane Extreme sensitivity; can detect the smallest physical unit of stimulus (photon of light, single molecule, fraction of a nanometer)

Amplification Strengthening of stimulus energy by cells in sensory pathways Transmission: After transduction; transmits into a receptor potential, and then action potentials are transmitted into the CNS Integration Begins as soon as the information is received Sensory adaptation: a decrease in responsiveness during continued stimulation (e.g. heart beat, clothes) Transduction

Types of Sensory Receptors  Mechano-receptors: sense physical deformation caused by pressure, touch, stretch, motion, and sound; all forms of mechanical energy  Chemo-receptor:  Electro-receptor: detects various forms of electromagnetic energy (visible light, electricity, and magnetism).  Phtoreceptors: in the eyes.  Animals can detect earth’s magnetic lines to migrate.  Thermo-receptor: Response to heat or cold. Helps regulate both surface and body core temperature.  Pain : nocireceptors. Some people are born without these. Example story.  How aspirin and ibuprofen works

The mechanoreceptors involved with hearing and equilibrium detect settling particles or moving fluid  Smell:  olfactory receptor cells  neurons that line the upper portion of the nasal cavity and sends impulses along their axons directly to the olfactory bulb of the brain.  receptor ends of the cells contain cilia that extend into the layer of mucus coating the nasal cavity  When odor diffuses into this region it binds into specific proteins (odorant receptor Ors) on the plasma membrane of the olfactory cilia

 triggers a signal transduction pathway involving a G protein-enzyme adenylyl cyclase, and the 2 nd messenger cyclic AMP. 2 nd messenger opens channels in the plasma membrane permeable to both Na+ and Ca^2+  this depolarizes the membrane causing the ceptor cells to generate action potentials  more than 1000 OR genes. Much of what we taste we really smell. If the olfactory is blocked we will taste less.

Taste: taste buds, modified epithelial cells. On the tongue they’re called papillae 5 taste perceptions: sweet, sour, salty, and bitter, and umami (Japanese for delicious) MSG is a flavor enhancer; monosodium glutamate. Stimulated by a range oh chemicals Process involves depolarization that causes the cell to release neurotransmitter onto a sensory neuron which transmits action potentials to the brain. Transduction with chemo-receptors

Organization of nervous systems  Cnidarians (Hydra)  Nerve nets: neurons that control the contraction and expansion of gastro vascular activity (??)  Echinoderm (Sea Star)  Contains nerve nets and nerves (bundles of fiber like extensions of neurons). The Sea Star has nerve nets in each arms connected by radial nerves to a central nerve ring. Allows more complex movements  Flatworm (Pkanarian)  Clusters of neurons in a brain near the front end in animals with elongated, bilaterally symmetrical bodies. Has a CNS.  Annelid (Leech)  Behavior is regulated by more complicated brains and ventral nerve cords containing segmentally arranged clusters of neurons (ganglia). Has PNS (peripheral nervous system)  Anthropod (Insect)  Same  Mollusc (Chiton)  The nervous system organization correlates with an animal’s lifestyle. Has little or no cephalization and relatively simple sense organs.  Mollusc (Squid)  Has the most sophisticated NS of any inverts. Large brain, large image-forming eyes, rapid signaling among nerves. Supports the active predatory lifestyle  Chordate (Salamander)  In verebratets the CNS consists of the brain and the spinal cord which runs along the back side of the body; nerves and ganglia comprise the PNS