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Nervous Systems

Nervous Systems. Chapter 48. General Functions. Recognizes and coordinates the body’s response to changes in its internal and external environments. Sensory input – vision, hearing, balance, smell, taste, and touch Motor output – muscle contraction and movement

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Nervous Systems

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  1. Nervous Systems Chapter 48

  2. General Functions • Recognizes and coordinates the body’s response to changes in its internal and external environments. • Sensory input – vision, hearing, balance, smell, taste, and touch • Motor output – muscle contraction and movement • Memory and integration of information

  3. A Circuit of Neurons • All animals except sponges have a nervous system • What distinguishes nervous systems of different animal groups is how neurons are organized into circuits

  4. The Neuron • Specialized cells that carry electrical signals called impulses • 3 Types of Neurons: • Sensory – carry impulses from the sense organs to the spinal cord and brain • Motor – carry impulses from brain and spinal cord to muscles and glands • Interneurons – Connect sensory and motor neurons and carry impulses between them

  5. Reflexes: Different Types of Neurons Working Together • Automatic responses to stimuli • Controlled by 5-part reflex arc: • 1. Sensory receptor reacts to stimulus (heat on finger) • 2. Impulse is carried to the spinal cord by a sensory neuron • 3. In the spinal cord, the impulse is transferred to a motor neuron • 4. Motor neuron conducts a nerve impulse to an effector (arm muscles) • 5. Effector responds to the impulses by contracting (hand gets pulled away from the heat)

  6. Reflex Arc

  7. Organization of Nervous Systems • Cnidarians, sea stars • Nerve nets • Flatworms, leeches • Relatively simple cephalization, have a central nervous system (CNS) • Annelids, arthropods • Ganglia (arranged clusters of neurons) connect to CNS, making a peripheral nervous system (PNS)

  8. The Resting Neuron • At rest, the outside of the cell has a net positive charge, and the inside has a net negative charge. • This charge difference is called the resting potential (-70mVolts). • This charge difference is due to active transport by the sodium-potassium pump. • The sodium-potassium pump moves sodium (Na+) outside the cell, and potassium (K+) inside the cell.

  9. The Nerve Impulse Begins • 1. An impulse begins when a neuron is stimulated by another neuron or by the environment. • 2. Sodium pores open on the membrane and sodium ions diffuse into the neuron. • 3. The internal charge goes from -70 mVolts to +30 mVolts. • 4. This is called the action potential.

  10. 5. The influx of sodium stimulates the opening of potassium pores and (K+) flows out. • 6. This restores the resting potential to normal. • 7. But now all of the sodium is inside and the potassium is outside. • How does the cell go back to its original condition? • The sodium/potassium pump kicks in. • 8. The depolarization on one segment starts a domino effect down the neuron.

  11. The Synapse • The gap between the axon of one neuron and the dendrites or cell body of the next neuron. • When the impulse reaches the end of the axon, chemicals called neurotransmitters are released and carry the impulse to the next neuron.

  12. Organization of the Vertebrate Nervous System

  13. Central Nervous System • Receive and process information, relay response to body system(s)for action(s) • Brain and spinal cord

  14. CNS: The Brain • Cerebrum • Largest region; folds and grooves increase surface area • Controls voluntary activities and all higher brain functions (intelligence, learning and judgment) • Right and left hemispheres are connected by corpus callosum

  15. Cerebellum • Center for balance and coordination of voluntary muscle movements. • Brain Stem • Relays information between brain and spinal cord • Comprised of the pons and medulla oblongata • Work together to control involuntary processes like breathing, heart rate, blood pressure, digestion, and swallowing

  16. Thalamus • Relay station for all sensory input to the cerebrum. • Hypothalamus • Homeostatic center that controls endocrine system (hormones), body temperature, thirst, hunger, fatigue, etc.

  17. CNS: The Spinal Cord • Two main functions: • Reflex center • Carries info to and from brain to body

  18. Peripheral Nervous System • Receives information from the environment and relays to and from CNS and sensory, motor and gland cells • Two divisions: Sensory and Motor • Motor is divided into: • Somatic NS (voluntary) responds to external stimuli. • Regulates activities that are under conscious control (e.g. picking your nose) • Some reflex control • Autonomic (involuntary) NS respond to internal stimuli; two divisions: • Sympathetic ↑energy consumption (increase HR) • Parasympathetic ↓energy consumption (decrease HR) • Both help maintain homeostasis by having opposing effects

  19. Autonomic Nervous System

  20. Nervous System Disorders • Bell’s Palsy – unexplained episode of facial weakness or paralysis • Dementia - damaged brain cells caused by injury or disease (Alzheimer’s); memory loss, confusion and personality change • Migraine Headaches – caused by a drop in serotonin levels? (triggered by stress, hormones, certain foods) • Multiple sclerosis (MS) – myelin sheaths deteriorate resulting in progressive loss of coordination • Parkinson’s – uncontrollable shaking caused by damage to dopamine transmitters; no cure • Tay-Sachs – fatal genetic lipid storage disorder where fat builds up on brain tissues and neurons during the first few months of life causing mental and physical deterioration

  21. Drugs and the Nervous System • Stimulants • Accelerate HR, BP, and breathing rate • Increases the release of neurotransmitters; leads to release of energy and feeling of well-being • When effect wears off, brain’s supply is depleted leaving the user depressed and fatigued • Caffeine – prevents binding of adenosine • Cocaine – sudden release of dopamine • Methamphetamines – same effect as cocaine

  22. Drugs and the Nervous System • Depressants • Slow down HR, lower BP and breathing rate, relax muscles and relieves anxiety • Alcohol – physical and mental impairment, depression, liver damage • Marijuana – more lung damage than cigarettes; memory loss, reduced levels of testosterone in males • Sleeping Pills

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