Autonomic Nerves

Overview of Peripheral Nervous System

  • This lecture focuses on Fibrofatty tissue, Blood vessels, Unmyelinated fibers, Myelinated fibers, and Autonomic nerves in relation to human anatomy.

Structure of Peripheral Nerves

  • Epineurium: The outermost layer that surrounds the entire nerve.

  • Perineurium: The middle layer that surrounds groups of nerve fibers forming fascicles.

  • Endoneurium: The innermost layer that surrounds individual nerve fibers.

Types of Peripheral Nerves

Somatic Nerves

  • Voluntary Functions: Responsible for conscious control.

  • Nerve Pathway: A single continuous nerve from the Central Nervous System (CNS) to the target effector.

  • Functions: Moves skeletal muscle & transmits sensation from body walls such as the skin and mucous membranes.

Autonomic Nerves

  • Involuntary Functions: Controls automatic body functions without conscious effort.

  • Nerve Pathway: Involves two nerves linked by a synapse occurring between the CNS and the target.

  • Functions: Activates organs and transmits sensations from organs, glands, and internal structures.

Neuronal Structure

Neuron Components

  • Dendrites: Projections from the neuron that receive signals.

  • Cell Body: Contains the nucleus and organelles.

    • Nucleus: The control center of the neuron.

  • Central Axon Terminals: The end of the axon where neurotransmitters are released.

Neural Conduction Directions

  • Efferent (Motor): Carries instructions from the brain or spinal cord to peripheral axon terminals, leading to an effector organ or postsynaptic neuron.

  • Afferent (Sensory): Carries information from body receptors to the CNS.

Myelin Sheath and Synapses

Myelin Sheath

  • Functions to insulate axons and increase the speed of nerve impulse conduction.

Synapses

  • Described as electrochemical communication between nerve cells, likened to a text message.

  • Synaptic Cleft: The gap between the pre-synaptic and post-synaptic neurons.

  • Postsynaptic Neuron: The receiving neuron in a synapse.

  • Receptors on Postsynaptic Membrane: These bind neurotransmitters released from the synaptic vesicles.

Autonomic Nervous System: Sympathetic vs. Parasympathetic

Sympathetic Nervous System

  • Function: Prepares the body for "fight or flight" emergencies, stress, and activities.

  • Pathway: Neurons typically synapse in the sympathetic trunk or prevertebral ganglia before reaching their target organs.

Parasympathetic Nervous System

  • Function: Manages "rest and digest" activities and conserves energy.

  • Pathway: Neurons synapse in or near the walls of target tissues and organs.

Detailed Autonomic Pathways

Sympathetic Pathways

  • Consists of structures such as the Sympathetic Trunk and associated ganglia (e.g., paravertebral ganglion, prevertebral ganglia).

  • Peripheral Nerves: Follow somatic nerves to periphery, innervating glands and smooth muscles.

  • Key Ganglia: Includes the Celiac Ganglion, which serves abdominal organs and the Inferior Mesenteric Ganglion.

Parasympathetic Pathways

  • Originate from crania nerves and the sacrum, utilizing pelvic splanchnic nerves for outflow.

  • Major Structures: Include the Ciliary Ganglion for eye functions, the Pterygopalatine for lacrimal gland functions, and others for specific glands and organ systems.

    • Example: The Otic Ganglion innervates salivary glands.

Functional Differences Between Sympathetic and Parasympathetic Nerves

Digestive System

  • Parasympathetic: Promotes secretion of fluids (saliva, pancreatic enzymes) and smooth muscle contraction in the digestive tract.

  • Sympathetic: Suppresses secretion of fluids and inhibits muscle contraction.

Cardiovascular System

  • Parasympathetic: Slows down heart rate and dilates blood vessels.

  • Sympathetic: Accelerates heart rate and constricts blood vessels.

Autonomic Sensation and Referred Pain

  • Certain visceral organs correspond to specific areas of referred pain. For example:

    • Duodenum and pancreas pain can often refer to locations that are not immediately adjacent.

    • Important structures in referred pain include the Gallbladder, Liver, and various other digestive organs.