Peripheral Nervous System
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The Peripheral Nervous System
Introduction to the Peripheral Nervous System (PNS).
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Overview of the Peripheral Nervous System
Connected to brain and spinal cord.
Contains:
12 pairs of cranial nerves (connected to brain).
31 pairs of spinal nerves (connected to spinal cord).
Both cranial and spinal nerves directly supply skeletal muscles.
Divisions of the Peripheral Nervous System:
Sensory (Afferent) Division
Motor (Efferent) Division
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Sensory Division
Function: Transmits information from the periphery (body) to the brain.
Includes major families of sensory receptors:
Mechanoreceptors: detect physical forces.
Thermoreceptors: detect temperature changes.
Nociceptors: detect pain signals.
Photoreceptors: respond to light.
Chemoreceptors: respond to chemical stimuli.
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Special Families of Sensory Receptors
Joint Kinesthetic Receptors:
Sensitive to joint angles and rate of angle change, sensing joint position and movement.
Muscle Spindles:
Sensitive to muscle length and rate of change, sensing muscle stretch.
Golgi Tendon Organs:
Sensitive to tension in tendons, sensing strength of muscle contractions.
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Motor Division
Function: Transmits information from the brain to the periphery.
Divided into two subdivisions:
Autonomic: regulates involuntary visceral activity.
Somatic: stimulates skeletal muscle activity.
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Autonomic Nervous System
Involves control of involuntary internal functions such as:
Heart rate, blood pressure, lung function during exercise.
Contains two complementary divisions:
Sympathetic Nervous System
Parasympathetic Nervous System
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Sympathetic Nervous System
Known for 'Fight or Flight' response: preps body for exercise.
Effects of sympathetic stimulation include an increase in:
Heart rate
Blood pressure
Blood flow to muscles
Airway diameter (bronchodilation)
Metabolic rate and glucose levels
Mental activity enhancement
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Parasympathetic Nervous System
Responsible for 'Rest and Digest' functions, active during rest.
Opposes effects of the sympathetic nervous system:
Increases digestion and urination.
Conserves energy by decreasing heart rate and reducing diameter of vessels and airways.
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Effects of the Sympathetic and Parasympathetic Nervous Systems on Various Organs
Target Organs/System | Sympathetic Effects | Parasympathetic Effects |
|---|---|---|
Heart Muscle | Increases rate and force of contraction | Decreases rate of contraction |
Coronary Blood Vessels | Causes vasodilation | Causes vasoconstriction |
Lungs | Causes bronchodilation; mildly constricts blood vessels | Causes bronchoconstriction |
Blood Vessels | Increases blood pressure; causes vasoconstriction where necessary | Has little or no effect |
Liver | Stimulates glucose release | Has no effect |
Cellular Metabolism | Increases metabolic rate | Has no effect |
Adipose Tissue | Stimulates lipolysis | Has no effect |
Sweat Glands | Increases sweating | Has no effect |
Adrenal Glands | Stimulates secretion of epinephrine and norepinephrine | Has no effect |
Digestive System | Decreases activity of glands and muscles; constricts sphincters | Increases peristalsis and glandular secretion; relaxes sphincters |
Kidney | Causes vasoconstriction; decreases urine formation | Has no effect |
Note: Lipolysis is the process of breaking down triglyceride into its basic units to be used for energy.