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Peripheral Nervous System

Peripheral Nervous System. Chapter 7. Function of the PNS. The Peripheral Nervous System (PNS) is responsible for communicating between the CNS and the rest of the body by collecting information from sensory neurons (from sense organs) and to motor neurons (muscles and glands)

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Peripheral Nervous System

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  1. Peripheral Nervous System Chapter 7

  2. Function of the PNS • The Peripheral Nervous System (PNS) is responsible for communicating between the CNS and the rest of the body by collecting information from sensory neurons (from sense organs) and to motor neurons (muscles and glands) • The sensory nerves collects information about the body and its surroundings • The system of motor nerves triggers voluntary and involuntary responses within the body

  3. Structures of the PNS • The PNS included 12 pairs of nerves in the head and 31 pairs of spinal nerves • Most nerves contain axons from both sensory and motor neurons that carry information to and from the CNS

  4. Two divisions of the motor PNS • The somatic nervous system regulates all of the movements over which you have voluntary control • It connects the CNS to target organs

  5. Two divisions of the motor PNS cont. • The autonomic nervous system controls automatic functions that you do not have to think about (involuntary) • Important in maintaining homeostasis • It takes messages from the hypothalamus to organs in the circulatory, digestive, and endocrine systems

  6. Two subdivisions ofAutonomic Nervous System • Sympathetic Nervous System • Prepares the body for action and stress called the “fight or flight” response • Reduces blood flow to skin and internal organs, blood flow increases to heart, brain, lungs, and skeletal muscles, heart rate increases, airways enlarge and breathing becomes more efficient for quick thinking and action

  7. Two subdivisions ofAutonomic Nervous System • Parasympathetic Nervous System • Calms the body and helps the body to conserve energy • Lowers blood pressure and heart rate; active during relaxation • The sympathetic and parasympathetic nervous systems have opposite effects on the same organ system • Like gas pedal vs. brake pedal on a car

  8. Sympathetic vs. Parasympathetic Systems • An easy way to remember the most important roles of the two ANS divisions is to think of the parasympathetic division as the D • Digestion, Defecation, Diuresis (urination) • Sympathetic division as E • Exercise, Excitement, Emergency, Embarassment

  9. Spinal Cord • Consists of vertebrae, fluid, meninges, and the spinal cord • The spinal cord is a ropelike bundle of neurons that is about as wide as your thumb • Connects the brain to the nerves that are found throughout the body • Brain depends on your spinal cord to deliver messages to the proper muscles • Paralysis results when the spinal cord is damaged

  10. Spinal Cord Impulse Pathway • Cerebrum sends an impulse down the spinal cord • Then the impulse is directed by an interneuron to the motor neuron that connects to the arm muscles • The motor neuron then carries the impulse to receptors in the arm muscle • When the receptors are stimulated by the impulse, the arm moves

  11. Functions of the Spinal Cord • Involuntary movements can be controlled by the spinal cord called reflexes • Reflex arcs are nerve pathways that need to cross only two synapses before producing a response • Because the signal never has to travel up the spinal cord to the brain, you react quickly • Ex. Sneezing, blinking, removing hand from stove, doctor checking knee reflex

  12. Reflex Arc Pathway • Sensory receptor -> sensory neuron -> motor neuron -> effector

  13. Protection of the Nervous System • Nervous tissue is very soft and delicate and the irreplaceable neurons are injured by even the slightest pressure. • Nature has tried to protect the brain and spinal cord by enclosing them within bone (skull and vertebral column), membranes (meninges), and a watery cushion • Protection from harmful substances in the blood is provided by the blood-brain barrier

  14. Meninges • Three connective tissue membranes are collectively known as the meninges • Underly the skull • Dura mater (outermost), arachnoid mater (middle), pia mater (innermost)

  15. Cerebrospinal Fluid • Also known as the CSF is a watery “broth” similar to blood plasma • Continuously formed from blood by clusters of capillaries • The CSF in and around the brain and cord forms a watery cushion that protects the fragile nervous tissue from blows and other trauma • CSF continually moves and circulates • CSF testing is called lumbar (spinal) tap

  16. Blood-Brain Barrier • Metabolic wastes, such as urea, toxins, proteins, and most drugs are prevented from entering the brain tissue • It is useless against fats, respiratory gases and other fat-soluble molecules that diffuse easily through the plasma membranes • This explains why blood-borne alcohol, nicotine, and anesthetics can affect the brain

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