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“Our conscious model of reality is low-dimensional projection of the inconceivably richer physical reality surrounding and sustaining us. Our sensory organs are limited.They evolved for reasons of survival, not for depicting the enormous wealth and richness of reality in all its unfathomable depth” -Thomas Metzinger Nervous System and Senses Chapters 27 The Nervous System Central nervous system (CNS): portion of nervous system consisting of _______________________ Integration of signals Peripheral nervous system (PNS): the nervous system outside of the brain and spinal cord, which includes the sensory organs Eyes Skin Ears Mouth The Nervous System Afferent division: collection of nerves that _________________ the brain or spinal cord Efferent division: collection of nerves that _________________ the brain or spinal cord to other parts of the PNS. Types of Neurons Sensory or afferent neuron: nerve cell that receives signals from __________________ inside and outside of the body then sends information to CNS Interneuron: nerve cells that interconnect other neurons Motor or efferent neuron: nerve cells that transmit signals from the CNS to ________ _________________ The Nervous System Somatic nervous system: portion of PNS’s efferent division that provides ________ control of skeletal muscles. Autonomic nervous system: part of the PNS’s efferent division that provided ______________________ of smooth muscle, cardiac muscle, and glands Autonomic Nervous System Parasympathetic division: controls internal organs during _____________ conditions “rest and digest” Sympathetic division: controls internal organs during periods of ________ “flight or fight” The Neuron Dendrites: extensions of neuron that receives signals and relays the signal towards nerve cell body Axon: extension of the neuron that _____________ to other neurons Cell body: area of the neuron containing organelles and nucleus Synaptic terminals: transmit signal to adjacent nerve cells across the synapse The Neuron ____________ insulate the axon of the neuron. Prevents action potential from weakening as it move through axon Only found in vertebrates Action potential: a temporary reversal of cell membrane potential that results in a conducted nerve impulse down the axon. Anatomy of a Nerve Nerve: bundle of nerve cell ______ of PNS nerve cells that transmit signals to and from the CNS Reflexes Reflex: automatic response independent of integration from the ________ Sensory neuron Spinal cord interneuron or motor neuron Automatic muscle movement Membrane Potential Membrane potential: ______ difference between the inside and outside of the plasma membrane of a neuron Resting potential: membrane potential when not sending a signal Controlled by ion channels and sodium-potassium pumps Different concentration gradients for Na+ and K+ inside and outside of cell Net ______________ inside neuron 8. Potassium release 1.Unbound protein 2. Sodium binding. Phosphorylation of pump by ATP Sodium Potassium Pump 7. Phosphate release. Shape change 3. Shape change 6. Potassium binding 5.Unbound protein 4. Sodium release Transmitting a Signal Gated ion channels: ion channels that open or close in response to stimuli Sodium (Na+) and Potassium (K+) channels ______________: positive-going change in membrane potential, which decreases the negative charge inside the nerve cell Opening of Na+ channels Action potential: a temporary reversal of cell membrane potential that results in a conducted nerve impulse down the axon. Propagation of the Action Potential 1. Stimulus causes some voltage-gated sodium channels to open 2. Sodium ions (Na+) rush into the axon causing depolarization in the neuron and initiating an action potential 3. Depolarization moves down the axon causing more voltage-gated sodium channels to open 4. Another action potential occurs further down the axon resulting in the transmission of the signal through the neuron 5. Voltage-gated ion channels become temporarily inactive causing the ______________________ of the signal Refractory period 1. Sodium ions (Na+) move into the axon 2. Positive charge inside the axon spreads 3. Positive charge causes more sodium channels to open Transmitting a Signal After depolarization occurs potassium channels open causing potassium ions to move out of the axon. Removal of potassium ions cause the membrane potential to return to resting potential. Sodium-potassium pumps regulate the concentration of sodium and potassium ions in the axon to maintain resting potential Transmitting a Signal Voltage-gated sodium channels are only located in the _____________ (gaps in myelin sheath) Fewer ion channels opening and closing means faster signal Passing the Signal Along _________: area where sending neuron, receiving nerve cell and space between the two all come together Synaptic cleft: the gap between adjacent nerve cells within the synapse __________________: A chemical, secreted into the synaptic cleft, that affects another neuron or effector by binding with receptors on it. Passing the Signal Along 1. Action potential depolarizes presynaptic membrane 2. Depolarization triggers voltage-gated Ca2+ channels to open 3. Ca2+ channels cause synaptic vesicles to fuse with presynaptic membrane, releasing neurotransmitter into synaptic cleft 4. Neurotransmitters bind to ligand-gated ion channels on postsynaptic membrane which sets off new action potential Neurotransmitter Major Neurotransmitters Neurotransmitter Function Problems Caused by Imbalance Affects mood, hunger, sleep, arousal Oversupply linked to depression Influences movement, learning, attention, and emotion Oversupply linked to schizophrenia Undersupply linked to tremors and decreased mobility (Parkinson’s and ADHD) Acetylcholine (Ach) Enables muscle action, learning, and memory Degeneration of Ach-producing neurons cause progression of Alzheimer’s disease Norepinephrine Helps control alertness and arousal Undersupply can depress mood and cause attention problems Inhibitor neurotransmitter Undersupply linked to seizures, tremors, and insomnia Excitatory neurotransmitter, memory Oversupply can overstimulate the brain producing migraines or seizures Serotonin ______________ GABA (gammaaminobutyric acid) Glutamate Check Your Understanding True or False: The autonomic nervous system regulates involuntary functions such as digestion and breathing. True or False: The parasympathetic division is involved in the flight or fight response True or False: The myelin sheath slows down the action potential Check Your Understanding Which of the following parts of the neuron receives signals from neighboring neurons? a. Axon b. Dendrites c. Synapse d. Cell body Check Your Understanding The chemicals released into the synaptic cleft that initiate the transmission of a signal between neurons are known as ________________. a. Sodium ions b. Potassium ions c. Neurotransmitters d. Calcium ions e. Reflexes Sensory Receptors _______________________: receptors that responds to pressure or distortion Touch, hearing Thermoreceptors: receptors that respond to changes in temperature Touch, pit vipers, spicy food (capsaicin receptor), menthol Chemoreceptors: receptors that respond to different chemical stimuli in the environment Taste, smell, solute concentration (osmoreceptors), glucose, oxygen, carbon dioxide Photoreceptors: receptors that respond to different wavelengths of light _________________ Electromagnetic Receptors: receptors that respond to electric or magnetic signals Ampullae of Lorenzini, platypus bill, elephant fish, magnetite Sending a Signal Tonic receptors: receptors that actively send the signal as long as the stimulus is present Ex. Photoreceptors, ear mechanoreceptors _________ receptors: receptors that begin to ignore stimulus after a period of continued activation. Sensory adaptation. Ex. Olfactory sense, touch Touch Touch receptors in the skin Ex: Pacinian corpuscle receptor Chemoreceptors: Olfaction (Smell) Chemoreceptors: Taste Mechanoreceptors: Hearing Sound wave Hearing High frequency waves are detected at beginning of cochlea Low frequency waves towards the end of cochlea Human range = 20 – 20,000 Hz Dog range = 40 – 60,000 Hz Whales sensitive to lower and bats to higher frequencies Mechanoreceptors: Balance Anatomy of the Human Eye _________: allows light to enter eye, changes diameter based on light conditions Lens: biconvex structure that refracts light passing into the eye Iris: pigmented smooth muscle controls pupil diameter Ciliary body: controls lens shape With near objects lens bulges, far objects it is thin Retina: inner layer of eye tissue containing _________________ Photoreceptors: Vision Rods: photoreceptors that function in __________________ (night vision) Provide only black-and-white vision Cones: photoreceptors responsible for _______________ Three types of cones with different color sensitivities Focusing Normal vision: light rays converge on retina Farsighted vision: light rays converge ________ retina Nearsighted vision: light rays converge __________ of the retina Check Your Understanding True or False: Phasic receptors will actively send a signal as long as the stimulus is present. True or False: Light rays converge in front of the retina in nearsighted people True or False: Rods are responsible for color vision Check Your Understanding Which of the following controls the amount of light that enters the eye? a. Lens b. Ciliary body c. Retina d. Iris e. Pupil Check Your Understanding What type of receptors are used in human touch? a. Mechanoreceptors b. Chemoreceptors c. Photoreceptors d. Thermoreceptors e. More than one of the above Check Your Understanding Describe how an action potential is transmitted through the axon.