ANS

Overview of Objectives:
- Describe the parts of a spinal nerve.
- Explain what a nerve plexus is and its purpose.
- Distinguish between sensory and motor, voluntary and involuntary functions.
- Differentiate between autonomic and somatic motor circuits.
- Describe the outflows of both Parasympathetic Nervous System (PsNS) and Sympathetic Nervous System (SNS) and their innervation targets.
- Outline how autonomic systems control heart functions and involvement of nerves.

CNS (Central Nervous System):
- Composed of the brain and spinal cord.
PNS (Peripheral Nervous System):
- Encompasses all nerves outside of the CNS.
- Starting Branches:
  - Cranial nerves and spinal nerves.
- Functionality:
  - Sensory (Afferent) nerves send impulses to the CNS.
  - Motor (Efferent) nerves transmit signals from the CNS.
  - Somatic:
    - Efferent, voluntary control of striated/skeletal muscles.
    - One neuron from cell body in CNS.
  - Visceral Efferent (ANS):
    - Involuntary control over smooth and cardiac muscles, and glands.
    - Involves two neurons: one in the CNS and one in a ganglion.
    - Divided into Parasympathetic and Sympathetic divisions.

Definition: PNS includes all nerves, ganglia, and nerve plexi outside of the CNS.
Spinal Nerves:
- Total: 33 spinal nerves comprising:
  - 8 cervical nerves
  - 13 thoracic nerves
  - 7 lumbar nerves
  - 3 sacral nerves
  - 5 caudal (coccygeal) nerves.
Cranial Nerves: Nerves in the head referred to as I-XII.

Neurons:
- Nerve cells categorized into:
  - Sensory (Afferent): Transmits signals to the CNS.
  - Motor (Efferent): Sends impulses to organs, muscles, and glands.

Anatomical Features:
- Sensory Ganglion: Area where sensory neuron cell bodies reside.
- Dorsal Root and Ventral Root of the spinal nerve
- Gray Matter: Contains cell bodies.
- White Matter: Contains myelinated axons.

Definition of Rami: Branches of the spinal nerve.
Branching:
- Dorsal ramus, ventral ramus, and ramus communicans.
- Each branch carries both sensory and motor information.
- Dorsal Ramus: Carries information to/from epaxial structures.
- Ventral Ramus: Serves the rest of the body.

Definition: Nerve plexus is a network of intersecting nerves, e.g., brachial plexus.
Purpose: Ensures complete innervation throughout the body.
Phrenic Nerve: Root values include C5, C6, and C7.

CNS: Brain and spinal cord
PNS: All nerves outside the CNS, including cranial and spinal nerves.
Efferent and Afferent Nerves:
- Afferent brings sensory info to CNS.
- Efferent sends motor commands from CNS.

Efferent Pathways:
- Somatic Efferent: Involves one neuron for voluntary muscle innervation.
- Visceral Efferent: Involves two neurons for involuntary tissue innervation.

Key point: Nerve impulses pass through synapses to connect neurons (passing the baton).

Buffering Key Information: Efferent and afferent nerves and their respective functionalities continue to be a focal point in understanding the CNS and PNS.

Visceral Efferent: Handles automatic body functions (e.g., digestion, respiration).
- Characteristics:
  - Not under conscious control.
  - Affects smooth muscle, cardiac muscle, and glands.
  - Comprises at least two neurons.
  - Has sympathetic and parasympathetic divisions.

Preganglionic neuron:
- Cell body located in the CNS.
- Axon exits CNS and synapses onto a second neuron in a ganglion.
Postganglionic neuron:
- Cell body in ganglion.
- Targets organs (smooth muscle, cardiac muscle, glands).

Sympathetic Nerves:
- Dilate pupils, inhibit salivation, raise heartbeat, dilate airways, stress responses.
Parasympathetic Nerves:
- Constrict pupils, stimulate salivation, slow heartbeat, stimulate digestive processes.

Similar reiteration of key functions and roles of each nervous system division
PsNS changes for homeostasis and SNS activity in stress responses remain critical concepts.

Functionality:
- Centers on the "fight or flight" response.
Neuroanatomy:
- Preganglionic neurons originate in the thoracolumbar region.
- Postganglionic neurons located in cervical, thoracic, or abdominal ganglia.
- Referred to as the thoracolumbar system.

A sympathetic preganglionic axon can synapse on a postganglionic cell body in a ganglion that is not nearby, providing flexibility in the SNS structure.

Ganglia Locations: Found on either side of the vertebral column, encompassing cervicothoracic ganglion and the sympathetic trunk.

Important to reinforce the distinctions and functionalities between CNS and PNS.

Focus: Responsible for rest and digest functions.
Neuroanatomy:
- Preganglionic neurons found in the brainstem and sacral region.
- Postganglionic neurons' cell bodies are located in terminal ganglia at the site of innervation.
- Also known as the craniosacral system.

Diagrams showing preganglionic and postganglionic nerve fibers, emphasizing ganglia at the organ of innervation.

Key Structures:
- Contributions from the vagus nerve to the autonomic functions, including innervation of organs in the thoracic cavity.