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Chapter 34

Chapter 34. Neural Control- A Summary. AP Biology Spring 2011. Nervous System. Nervous System . Sensory Neurons: detect information about stimuli, such as light Interneurons: accept the senosory input, process it, and signal other neurons

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Chapter 34

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  1. Chapter 34 Neural Control- A Summary AP Biology Spring 2011

  2. Nervous System

  3. Nervous System • Sensory Neurons: detect information about stimuli, such as light • Interneurons: accept the senosory input, process it, and signal other neurons • Motor Neurons: relay new signals to effectors- muscles and glands- that carry out responses • Neuroglia: structurally and metabolically support the neurons

  4. Invertebrate Nervous System • Cnidarians: jellyfish, radial body plan • Two epithelial tissues: an epidermis and gastrodermis • Nerve net: asymmetrical mesh of neurons, controls simple movement of both • Motor neurons activate epithelial cells that have long contractile extensions, by making them contract the nerve net changes diameter of mouth or body or bends tentacles

  5. Invertebrate Nervous System • Bilateral animals • Ex. Flatworm • Bilateral nervous system: have nerves, branching nerves join two nerve cords in a ladder-like array

  6. Invertebrate Nervous System • Ganglion: cluster of nerve cell bodies that function as a local integrating center • Cephalization: formation of a head evolved with bilateral nervous systems Ganglion Ganglion

  7. Vertebrate Nervous System • Two functional divisions: • Central Nervous System (CNS): brain and spinal cord • Peripheral Nervous System (PNS): nerves extending through the rest of the body

  8. Invertebrate Nervous System • Afferent: deliver signals into the central system • PNS • Efferent: carry signals out of it • Motor fibers

  9. Outline of Peripheral Nervous System • Somatic System: controls the voluntary muscles • Autonomic System: controls involuntary muscles • Sympathetic: fight or flight response, increase heart and breathing rate, liver converts glycogen to glucose, bronchi of lungs dilate and increase gas exchange, adrenaline raises blood glucose levels • Parasympathetic: opposes sympathetic system, calms body, decreases heart/breathing rate, enhances digestion

  10. Neurons • Sensory Neuron: detects a stimulus at one or more receptor endings and relays information about it to other neurons • Motor Neuron: delivers excitatory or inhibitory commands from other neurons to muscles or glands • Interneurons: information from most sensory neurons flows through these before it gets to motor neurons • Receive, process, and store sensory information

  11. The Neuron • Basic functional unit of the nervous system • Cell body: contains nucleus and other organelles • Dendrites: sensory; receive incoming messages from other cells and carry electrical signals to the cell body • Axons: transmit an impulse from the cell body outward to another cell • Has only one axon, most wrapped in myelin sheet that protects it and speeds the impulse

  12. Membrane Gradients and Potentials • Membrane potential: difference in electrical charge between the cytoplasm (negative charge) and extracellular fluid (positive)

  13. Membrane Gradients and Potentials • Resting Membrane Potential: the steady voltage difference across the neuron’s plasma membrane • Is about -70 millivolts • Negative sign indicates that the inside of the cell is negative relative to the outside of the cell

  14. Membrane Gradients and Potentials • Action Potential: an impulse generated in the axon of a neuron • When stimulated to overcome threshold permeability of a region of the membrane changes

  15. Sodium-Potassium Pump • When neuron at rest • About 15 sodium ions in the fluid inside of plasma membrane for every 150 outside • About 150 potassium ions inside for every 5 outside • Creates ion gradients

  16. Sodium-Potassium Pump • Threshold overcome by axon stimulation • Sodium channels open and sodium floods into the cell, down concentration gradient • Potassium channels open and potassium floods out of the cell • Wave of depolarization: rapid movement of ions, reverses polarity of membrane (action potential)

  17. Sodium-Potassium Pump • Pump restores membrane to original state by pumping sodium and potassium ions back to original positions • Repolarization • Refractory period: neuron cannot respond to another stimuli (ensures impulse moves along axon in only one direction)

  18. Sodium-Potassium Pump • Action potential is like dominos • First action potential generates a second which generates a third • Impulse moves along axon, without losing strength, if axon myelinated can travel faster

  19. Sodium-Potassium Pump • Action potential is all-or-non event • Either stimulus is strong enough or isn’t • Strong stimulus sets up more action potential than a weak one does

  20. The Synapse • Thin cleft separates output zone of one neuron from a neighboring neuron, gland cell, or muscle cell • At this zone, electrochemical energy of action potential is transduced to the form of chemical signal that can diffuse across the cleft and activate or inhibit target cell • Chemical synapse: functional bridge between a neuron and some other cell • Synapse means to fasten together

  21. The Synapse • Neurotransmitter: type of signaling molecule that is synthesized in neurons only • Plasma membrane has many gated channels for calcium ions • In between action potentials, more calcium ions outside than inside (gate are shut)

  22. The Synapse • Action potential makes gates open- calcium ions flow in, synaptic vesicles move through cytoplasm in the axon ending and fuse with the membrane • Release neurotransmitter by exocytosis into the synapse, which sets up another potential on adjacent cell • Shortly after neurotransmitter released, is destroyed by an enzyme which stops the impulse at that point

  23. The Synapse • Most common neurotransmitters: • Acetylcholine: can be inhibitory or excitatory • Serotonin • Epinephrine • Norepinephrine • Dopamine • GABA

  24. Synaptic Integration • Excitatory Postsynaptic Potential (EPSP): is the electrical charge caused by the binding of the neurotransmitter to its receptor on the postsynaptic membrane • Has depolarization effect, drive membrane closer to threshold • Inhibitory Postsynaptic Potential (IPSP): is the voltage charge associated with chemical signaling at an inhibitory synapse • Hyperpolarizing effect, can help drive membrane farther from threshold or help maintain it at resting level

  25. Synaptic Integration • Synaptic Integration: postsynaptic neuron sums all signals that are arriving at its input zone on more than one communication line • Two or more incoming signals may be dampened, suppressed, reinforced, or sent on to other cells

  26. Types of Neurotransmitters

  27. Neuropeptides • Neuropeptides: larger than neurotransmitters • Act as neuromodulators: magnify or reduce the effects of neurotransmitter on neurons that are either close to the secreting cell or some distance away • Examples: • Substance P: enhances pain perception • Enkephalins and endorphins: natural painkillers and resemble morphine in their structure, inhibit substance P, secreted in response to strenuous activity or injuries, can elevate mood and enhance function of immune cells • Endorphins released when people laugh, acupuncture, massage

  28. The Reflex Arc • Simplest nerve response • Inborn, automatic, and protective • Ex. Knee jerk reflex • Consists of only a sensory and a motor neuron • Impulse moves from sensory neuron in your knee to the motor neuron that directs the thigh muscle to contract • Spinal cord not involved

  29. The Reflex Arc • More complex reflex arc: 3 neurons- a sensory, a motor, and an interneuron or association neuron • Sensory neuron transmits an impulse to the interneuron in the spinal cord which sends one impulse to the brain for processing and also one to the motor neuron to effect change immediately (at the muscle) • This is the response that quickly jerks your hand away from a hot iron before your brain has figured out what has occurred

  30. The Vertebrate Brain • Brain is divided into specialized regions: forebrain, midbrain, hindbrain • Brain stem: most ancient nervous tissue, persists in all three regions and is continuous with spinal cord Forebrain Midbrain Hindbrain

  31. The Vertebrate Brain • Hindbrain: • Medulla oblongata: houses reflex centers for respiration, circulation, and other essential tasks , governs some reflexes (coughing), affects sleep • Cerebellum: uses inputs from eyes, ears, muscle spindles, and forebrain regions to help control motor skills and posture • Axons from its two halves reach the pons (bridge), control signal flow between the cerebellum and integrating centers in forebrain

  32. The Vertebrate Brain • Midbrain: • Has centers for visual input • Forebrain has took over task integrating most visual stimuli

  33. The Vertebrate Brain • Forebrain: • Cerebrum: two cerebral hemispheres • Thalamus: sorting out sensory input and relaying it to the cerebrum • Hypothalamus: main center for homeostatic control of the internal environment; assesses and regulates all behaviors related to internal organ activities, such as thirst, sex, and hunger; governs related emotions, such as sweating with passion and vomiting with fear

  34. The Vertebrate Brain • Cerebrospinal fluid: forms inside brain ventricles, seeps out and bathes tissues of brain and spinal cord; cushions them against potentially jarring movements • Blood-brain barrier: protects spinal cord and brain from harmful substances • Exerts some control over which solutes enter cerebrospinal fluid

  35. The Human Cerebrum • Each half of cerebrum (cerebral hemisphere) is divided into 4 lobes • Frontal, temporal, occipital, parietal

  36. The Human Cerebrum Grey Matter: areas of neuron cell bodies, dendrites, and unmyelinated axons, plus neoroglia, in brain and spinal cord White Matter: consists mostly of myelinated axons • Cerebral Cortex: grey matter at surface of each lobe, distinct areas receive and process different signals, still interact • Two hemispheres overlap in function • Left more concerned with analytical skills, math, speech • Right interprets music, judges spatial relations, assesses visual inputs

  37. The Human Cerebrum • Motor Areas: • Body is spatially mapped out in primary motor cortex of each frontal lobe- controls and coordinates the movements of skeletal muscles on opposite side of the body • Premotor cortex of each frontal lobe governs leaned patterns of motor skills • Ex. Dribble a basketball • Broca’s area helps translate thoughts into speech

  38. The Human Cerebrum • Sensory Areas: • Primary somatosensory cortex is located at front of parietal lobe • Organized as a map corresponding to body’s parts • Receiving center for sensory input from skin and joints • Taste perception • At back of occipital lobe, primary visual cortex receives signals from eyes • Temporal lobe: perceptions of sound and odor

  39. The Human Cerebrum • Association Areas: • Scattered through cortex, not in primary motor and sensory areas • Ex. Visual association area around primary visual cortex compares what we see with visual memories • Prefrontal cortex: foundation of our personality and intellect, of abstract thought, judgment, planning, and concern for others

  40. Limbic System • Limbic System: encircles upper brain stem • Governs emotions, assists in memory, correlates organ activities with self-gratifying behavior • Includes hypothalamus, part of thalamus, and cingulate gyrus, hippocampus, and amygdala

  41. Reticular Formation • Reticular Formation: low level path to motor centers in medulla oblongata and spinal cord • Network of interneurons, extends from upper spinal cord, through brain stem, and into cerebral cortex • Promotes chemical changes that affect states of consciousness, such as sleeping or waking

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