L35+electric+sens+motor+preview+26+apr+2010.ppt

* Anatomic diagrams of major components of mammalian CNS and PNS Schwann cell, myenates axons Axons Nerve * * The autonomic nervous system consists of two division that act on body organs with opposing effects. Activation of the sympathetic division correlates with arousal and energy generation; the heart beats faster, the liver converts glycogen to glucose, bronchi of the lungs dilate and support increased gas exchange, digestion is inhibited, and secretion of adrenaline from the adrenal medulla is stimulated. Activity of the parasympathetic division causes approximate the mirror image of this; a calming and a return to emphasis on self-maintenance functions. The Autonomic Nervous System Controls Internal Processes PARASYMPATHETIC NERVES ?Rest and digest? SYMPATHETIC NERVES ?Fight or flight? Constrict pupils Stimulate saliva Slow heartbeat Constrict airways Stimulate activity of stomach Inhibit release of glucose; stimulate gallbladder Stimulate activity of intestines Contract bladder Promote erection of genitals Sacral nerves Lumbar nerves Thoracic nerves Cervical nerves Cranial nerves Dilate pupils Inhibit salivation Increase heartbeat Relax airways Inhibit activity of stomach Stimulate release of glucose; inhibit gallbladder Inhibit activity of intestines Relax bladder Promote ejaculation and vaginal contraction Secrete epinephrine and norepinephrine (hormones that stimulate activity; see Chapter 47) Sympathetic chain: bundles of nerves that synapse with nerves from spinal cord, then send projections to organs The vertebrate CNS develops from the hollow, dorsal, embryonic neural tube. The brain forms from three swellings at its anterior end, which become the hindbrain, midbrain, and forebrain * Pituitary Cerebral peduncles Cerebrum Telencephalon Diencephalon The brain is made up of four distinct structures. Inside view Diencephalon Information relay and control of homeostasis Brain stem Information relay and center of autonomic control for heart, lungs, digestive system Cerebrum Conscious thought, memory Cerebellum Coordination of complex motor patterns Except for the cerebrum, these functions generally apply to mammals in general. The cerebrum in mammals in general, functions in movement, sensory processing, olfaction, communication, learning and memory Human Cerebral Function Coritical function Sensory perception Voluntary control of muscle Language & communication Personality traits Sophisticated mental events; thinking, memory, decision-making, creativity, self-conciousness Many aspects of behavior & intellect in general Basal Nuclei function Organize motor output Cortical structure and function Functional areas in each lobe Primary sensory areas Association areas Lecture Topic: Sensory Mechanisms Receptor systems; Structure & Function Mechanisms of action in a complex vertebrate receptor organ; vision and the mammalian eye Receptor systems; Structure & Function Sensory receptors process stimuli external and internal to the body Basic model of animal behavior Sensory Receptor Function SENSORY TRANSDUCTION Conversion of sensory input to electrical signal AMPLIFICATION Some receptor mechanisms amplify (enhance) stimulus; strengthen stimulus energy TRANSMISSION Conduction of impulses to CNS following transduction of stimulus energy into receptor potential. INTEGRATION Processing of sensory information -- occurs at all levels within the nervous system Mechanoreceptors Thermoreceptors Chemoreceptors Photoreceptors Electroreceptors Pain receptors Sensory receptors are categorized by the type of stimulus they detect and transduce Most sensory receptors are specialized neurons or epithelial cells that occur singly or occur in groups with other cell types within sensory organ Sensory receptors in human integument Sensory receptors in human taste bud http://webvision.med.utah.edu/imageswv/pupil.jpeg Eye structures facilitate light transmission and control of the amount of light entering the eye Sensory Transduction Receptor cells transduce sensory input to a change in membrane potential. This change in potential allows different types of stimuli to be transduced to a common type of signal. Transduction occurs when, in response to sensory stimuli, ion channels open or close and ions flow or stop flowing across the membranes of receptor cells. Sensory Transduction If ion flows cause the cell interior to become more positively charged (less negatively charged), the membrane is depolarized. If changes in ion channels cause the cell interior to become more negative than the resting potential, the membrane is hyperpolarized. The amount of de- or hyperpolarization of the sensory receptor is proportional to the intensity of the stimulus If a sensory stimulus induces a large change in a sensory receptor?s membrane potential, there is a change in the firing rate of action potentials sent to the brain. Sensory Input Changes the Membrane Potential of Receptor Cells Sound stimulus Depolarized Louder sound Softer sound Highest response occurs at a characteristic frequency Sound-receptor cells in the human ear depolarize in response to sound. Sound-receptor cells in the human ear respond more strongly to louder sounds. Taste pore Sugar molecule Sensory receptor cells Sensory neuron Taste bud Tongue G protein Adenylyl cyclase ?Ca2+ ATP cAMP Protein kinase A Sugar Sugar receptor SENSORY RECEPTOR CELL Synaptic vesicle K+ Neurotransmitter Sensory neuron 2. Binding initiates a signal transduction pathway involving cyclic AMP and protein kinase A. 3. Activated protein kinase A closes K+ channels in the membrane. 4. The decrease in the membrane?s permeability to K+ depolarizes the membrane. 6. The increased Ca2+ concentration causes synaptic vesicles to release neurotransmitter. 1. A sugar molecule binds to a receptor protein on the sensory receptor cell. 5. Depolarization opens voltage-gated calcium ion (Ca2+) channels, and Ca2+ diffuses into the receptor cell. Example of sensory receptor function, in human taste buds Mechanisms of action in a complex vertebrate receptor organ; vision and the mammalian eye The structure of the vertebrate eye. In the retina, cells are arranged in layers. Ganglion cells Connecting neurons Photoreceptor cells Pigmented epithelium Retina Direction of light Fovea Optic nerve (to brain) Sclera Iris Pupil Cornea Lens Axons to optic nerve Lens focuses incoming light on receptor cells; light energy is transduced at the photoreceptors; ensuing altered membrane potential can result in altered rates of firing of action potentials, transmitted to the visual cortex by the optic nerve Vertebrates have camera eyes with a single lens Photoreceptors in the vertebrate eye consist of rods and cones. Rods are sensitive to dim light but not respond differentially to different wavelengths (colors). Cones are much less sensitive to faint light, but different types of cone cells are stimulated by different wavelengths of light (colors). Rods and cones have segments packed with membrane-rich disks that contain large quantities of a transmembrane protein called opsin. Each opsin molecule is associated with a molecule of the pigment retinal to form rhodopsin. Retinal changes shape when it absorbs a photon of light, leading to a change in opsin?s conformation. This change, in turn, leads to a series of events that culminates in a different stream of action potentials being sent to the brain. Absorption Spectra of Cone Cells. The three kinds of cone cells contain slightly different opsin molecules, which absorb different wavelengths of light. Signal transduction pathway in a rod cell, from light reception to receptor potential. In this case, the receptor potential is a hyperpolarization of the membrane, rather than the more common depolarization. The action potential conducted from the eye to the brain has about 100 times as much energy as the few photons that triggered it. Motor output; Vertebrate Skeleto-muscular System Vertebrate skeletal muscle Is characterized by a hierarchy of smaller and smaller units The sarcomere, the functional unit of skeletal muscle, appears as light and dark bands on the myofibril These bands are made up of two types of filaments, thick filaments composed of myosin and thin filaments composed of actin, which slide past each other during muscle contraction. Sliding filament model of sarcomere action Action of the Myosin Heads Catalyze the hydrolysis of ATP ? the source of the energy responsible for generation of force, ie, contraction Bind to and release from actin, pulling against the actin in the process Changes in the conformation of the myosin head produce movement HOW DO ACTION POTENTIALS TRIGGER MUSCLE CONTRACTION? Motor neuron Muscle cell Thick filaments (myosin) Thin filaments (actin) Ca2+ ions 3. Action potentials propagate across muscle cell?s plasma membrane and into interior of cell via T tubules. 4. Proteins in T tubules open Ca2+ channels in sarcoplasmic reticulum. 5. Ca2+ is released from sarcoplasmic reticulum. Sarcomeres contract when troponin and tropomyosin move in response to Ca2+ and expose actin binding sites in the thin filaments (see Figure 46.23). The Effects of Action Potentials at the Neuromuscular Junction       Tropomyosin and troponin work together to block the myosin binding sites on actin. Myosin head Troponin Tropomyosin Actin Myosin binding sites blocked Calcium ions Myosin binding sites       When a calcium ion binds to troponin, the troponin-tropomyosin complex moves, exposing myosin binding sites. Myosin binding site exposed to myosin head Calcium ion Troponin-tropomyosin complex, moved Troponin and Tropomyosin Regulate Muscle Activity Spinal cord Nerve Motor neuron cell body Motor unit 1 Motor unit 2 Motor neuron axon Muscle Tendon Synaptic terminals Muscle fibers Each muscle supplied by many neurons, but each neuron innervates a few, to several thousand, muscle fibers Motor unit = single motor neuron and the fibers it innervates Neurons may overlap in the muscle fibers they innervate; motor units are not composed of mutually exclusive groups of muscle fibers Graded Force; CNS can selectively increase total output force until it matches load appropriately *