Autonomic Nervous System

  • The autonomic nervous system (of the motor division of the PNS), everything that is not consciously controlled (breathing, digestion, urine production, urine release, hormone release, etc.)

  • Two divisions of the ANS: Sympathetic and Parasympathetic

    • Sympathetic:
    • “Fight or flight”
    • Thoracolumbar division (thoracic and lumbar region)
    • Nerves exit the CNS from the thoracolumbar region
    • Pre-ganglionic neurons are SHORT in length, post-ganglionic are LONG; this is because pre-ganglionic neuron passes through the sympathetic chain
    • Parasympathetic:
    • Come back to resting state (sitting, sleeping; in control during rest)
    • Craniosacral (Head and sacrum)
    • Nerves leave the CNS from the craniosacral region
    • Pre-ganglionic neurons are LONG, post-ganglionic neurons are SHORT; they do not have to pass through the sympathetic chain, they have the terminal ganglia that are in or near an organ/effector that is innervated
      • So, post-ganglionic neurons are actually on/very close to the organ, effector

  • ANS is very important in maintaining homeostasis, it adjusts the body’s functions to any activity (sweating, etc.)

  • Motor division: Somatic (skeletal muscle) and Autonomic (smooth muscle, glands, etc.)

  • Nerves are made up of axons with motor and sensory functions

  • Motor Neurons: somatic (movement) and autonomic (smooth muscle, glands, etc.)

  • Sensory neurons are NOT divided into somatic and autonomic

    • Sensory Neurons: not divided into divisions due to overlap

  • Somatic reflexes: patellar, Achille’s heel (calcanea), toe curling (plantar)

  • Autonomic reflexes: throwing up, gagging, etc.

  • Ganglion: a collection of neuron cell bodies, where the axons are pointed out and the bodies are together in the middle

  • Peripheral nerves (bundle of axons) have both motor and sensory neurons

  • Motor information LEAVES the from the ventral root of the spinal cord

  • Sensory information ENTERS the spinal cord form the dorsal root

  • Sympathetic axons reach organs through: spinal nerves and plexuses (head and neck, thoracic, abdominopelvic)

    • Cranial nerve X (Vagus) is the only cranial nerve that innervates in the thoracic cavity

  • Organs have auto reflexes

    • Receptor → Sensory Neuron → Integration Center (CNS) → Motor Neuron → Effector
    • Receptor: Some monitor hot, some cold, but NEVER both
    • Sensory Neuron: Carries information from receptor site to the CNS (Integration Center)
      • Brain handles more complex things
      • Spinal cord handles simpler stuff, meaning everything DOES NOT HAVE to go to the brain
    • Integration Center: Processes and analyzes what needs to be done, generates motor command
    • Motor Neuron: Carries action potential (motor/movement information AWAY from the CNS)

  • Sensory = AFFARENT, away from the stimulation site

  • Motor = EFFARENT, effect to happen

  • Sensory neurons transmit pain and pressure from organs to CNS

  • Most organs are innervated by BOTH sympathetic and parasympathetic divisions, that is called DUAL INNERVATION (so the organ is influenced by BOTH)

    • Parasympathetic and sympathetic have opposite effects on each other on a dual innervated organ
    • ANS effects can be widespread (sympathetic; exercising) or local (parasympathetic; digestion)

  • RESPONSES:

    • Sympathetic: DECREASE in digestion and urine production
    • Parasympathetic: STIMULATION of digestion and urine production

  • NEUROTRANSMITTERS:

    • CHOLINergic:
    • All pre-ganglionic neurons of the sympathetic and parasympathetic divisions
    • The post-ganglionic neurons of parasympathetic division
    • The neurotransmitter is ACh or acetylcholine
    • ADRENergic:
    • Only post-ganglionic of sympathetic division
    • The neurotransmitter is epinephrine/norepinephrine from the adrenal gland

  • RECEPTORS:

    • Cholinergic (ACh):
    • Nicotinic:
      • Post-ganglionic neurons, all skeletal muscle, and adrenal glands
      • Excitatory
    • Muscarinic:
      • All receptors in parasympathetic division, and some receptors on sweat glands
      • Can be excitatory OR inhibitory
    • Adrenergic (adrenaline):
    • Alpha
    • Beta

  • Drugs (medical) interact with the receptors to alter ANS activity

    • Agonists: Bind to receptors and add activity
    • Antagonists: Bind to receptors to prevent activity

  • Autonomic Reflexes (organs, glands, etc.):

    • Autonomic activity is influenced by the hypothalamus (OVERSEES the ANS and endocrine system and more)
    • Para/sympathetic influence the enteric (digestion) system, but the enteric system can also function alone
    • Heart rate is controlled by the medulla oblongata