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Neural Control and the Senses Chapter 25 In Pursuit of Ecstasy • MDMA is amphetamine-like drug • Interferes with removal of chemical messenger (serotonin) used by nervous system • Memory loss and depression are common side effects • Can causes seizures, hypothermia, and even death Impacts, Issues Video In Pursuit of Ecstasy Neurons • Communication units of nervous systems • Detect information about internal and external conditions • Issue commands for responsive actions Types of Neurons • Sensory neurons – Detect and relay information • Interneurons – Receive and process information stimulus (output) receptors sensory neurons integrators interneurons of brain, spinal cord • Motor neurons – Transmit signals from interneurons to effectors motor neurons effectors muscles, glands response (output) Structure of a Neuron dendrites INPUT ZONE cell body axon TRIGGER ZONE CONDUCTING ZONE OUPUT ZONE axon endings Neurons Neuron structure and function Action Potential • Brief reversal in membrane potential • Voltage change causes voltage-gated channels in membrane to open • Inside of neuron briefly becomes more positive than outside Action Potential Action potential propagation Propagation of Action Potentials • Action potential in one part of an axon brings neighboring region to threshold • Action potential moves from one patch of membrane to another • Can only move one direction Chemical Synapses • Action potentials cannot jump from cell to cell • Signal is transmitted from axon end, across a synaptic cleft, by chemical signals called neurotransmitters Chemical Synapse • Gap between the terminal ending of an axon and the input zone of another cell plasma membrane of axon ending of presynaptic cell synaptic vesicle plasma membrane of postsynaptic cell synaptic cleft membrane receptor Synaptic Transmission • Action potential in axon ending triggers release of neurotransmitter from presynaptic cell into synaptic cleft vesicle inside presynaptic cell synaptic cleft postsynaptic cell Synaptic Transmission • Neurotransmitter diffuses across cleft and binds to receptors on membrane of postsynaptic cell • Binding of neurotransmitter to receptors opens ion gates in membrane of postsynaptic cell Chemical Synapse Chemical synapse Neurotransmitters • Acetylcholine (ACh) • Norepinephrine • Epinephrine • Dopamine • Serotonin • GABA Cleaning Up • After neurotransmitter has acted, it is quickly removed from synaptic cleft • Molecules diffuse away, are pumped out, or broken down Information Flow sensory neuron interneuron motor neuron Organization • Neurons are bundled in nerves • Nerves are organized in circuits and reflex pathways • Information from sensory neurons is relayed to interneurons in spinal cord and brain • Motor neurons carry signals to body Reflexes • Automatic movements in response to stimuli • In simplest reflex arcs, sensory neurons synapse directly on motor neurons • Most reflexes involve an interneuron Stretch Reflex STIMULUS Biceps stretches. sensory neuron motor neuron RESPONSE Biceps contracts. Stretch Reflex Stretch reflex Central and Peripheral Nervous Systems • Central nervous system (CNS) – Brain – Spinal cord • Peripheral nervous system – Nerves that thread through the body Table 25-1, p.434 Function of Spinal Cord • Expressway for signals between brain and peripheral nerves • Sensory and motor neurons make direct reflex connections in spinal cord • Spinal reflexes do not involve brain The Brain corpus callosum hypothalamus thalamus pineal gland location part of optic nerve midbrain cerebellum pons medulla oblongata Fig. 25-15, p.434 Vertebrate Brains Sagittal view of a human brain Anatomy of the Cerebrum • Largest and most complex part of human brain • Outer layer (cerebral cortex) is highly folded • A longitudinal fissure divides cerebrum into left and right hemispheres Lobes of the Cerebrum primary somatosensory cortex primary motor cortex frontal parietal occipital temporal Drugs and Addiction • Psychoactive drug: A substance that affects the action of neurotransmitters • Drug addiction: chemical dependence – drug assumes “essential” biochemical role in the body Types of Drugs • Stimulants • Depressants, hypnotics • Analgesics • Hallucinogens Signs of Addiction • Tolerance • Habituation • Inability to stop use • Concealment • Extreme actions • Deteriorating relationships • Anger and defensive behavior • Preferred activity Table 25-2, p.436 Effects of Cocaine Sensory Receptors Convert stimulus into action potentials Mechanoreceptors Chemoreceptors Thermoreceptors Osmoreceptors Pain receptors Photoreceptors Snake Thermoreceptors Somatic Sensations Touch Pressure Temperature Pain Motion Position Smell • A special sense • Olfactory receptors • Receptor axons lead to olfactory lobe receptor cell olfactory bulb Smell Olfactory pathway Taste • A special sense • Chemoreceptors • Five primary sensations: – sweet, sour, salty, bitter, and umami taste bud hairlike ending of taste receptor section through circular papilla sensory nerve Fig. 25-24, p.440 Taste Taste receptors Vision • Sensitivity to light is not vision • Vision requires – Eyes – Capacity for image formation in the brain The Eye • Perceives visual field • Lens collects light • Image formed on retina • Contains visual pigments • Stimulate photoreceptors Human Eye sclera retina choroid iris lens pupil cornea aqueous humor ciliary muscle vitreous body fovea optic disk part of optic nerve Human Eye Eye structure Pattern of Stimulation • Image on retina is upside down and reversed right to left compared with the stimulus • Brain corrects during processing Visual Accommodation • Adjustments of the lens • Ciliary muscle encircles lens • When this muscle relaxes, lens flattens, moves focal point farther back • When it contracts, lens bulges, moves focal point toward front of eye Visual Accommodation Visual accommodation Focusing Problems (focal point) distant object (focal point) close object Fig. 25-27, p.442 Focusing Focusing problems The Photoreceptors • Rods – Contain the pigment rhodopsin – Detect very dim light, changes in light intensity • Cones – Three kinds; detect red, blue, or green – Provide color sense and daytime vision Eye Diseases • Macular degeneration • Cataract • Glaucoma fovea start of an optic nerve in back of the eyeball Hearing • Outer ear • Middle ear • Inner ear INNER EAR vestibular apparatus, cochlea OUTER EAR pinna, auditory canal MIDDLE EAR eardrum, ear bones Fig. 25-32a, p.444 Properties of Sound • Ear detects pressure waves • Amplitude of waves corresponds to perceived loudness • Frequency of waves (number per second) corresponds to perceived pitch Properties of Sound Amplitude one cycle Frequency per unit time Soft Low note Loud High note Same frequency, different amplitude Same loudness, different pitch Properties of Sound Properties of sound Anatomy of Human Ear stirrup anvil auditory nerve hammer auditory canal eardrum cochlea Anatomy of Human Ear Ear structure and function Sound Reception • Sound waves make the eardrum vibrate • Vibrations are transmitted to the bones of the middle ear • The stirrup transmits force to the oval window of the fluid-filled cochlea Sound Reception • Movement of oval window causes waves in the fluid inside cochlear ducts oval window (behind stirrup) eardrum round window scala vestibuli scala tympani Sound Reception hair cells in organ of Corti lumen of cochlear duct tectorial membrane basilar membrane to auditory nerve lumen of scala tympani Sound Reception Sound detection Balance and Equilibrium • Mechanoreceptors located in the inner ear semicircular canals • Maintains body position vestibular apparatus