CHP 15 Autonomic Nervous System

What is the Autonomic Nervous System

(ANS) or Visceral Motor System

motor nervous system that controls glands, cardiac muscle, smooth muscle

primary organs

• viscera of thoracic and abdominal cavities

• structures of body wall (cutaneous blood vessels, sweat glands, piloerector muscles

General properties of the ANS

-INVOLUNTARY actions without conscious intent or awareness

-note: visceral effectors do not depends on the ANS to function, ANS just adjusts them

Denervation Hypersensitivity

exaggerated responses of cardiac and smooth muscles if autonomic nerves are severed

Visceral Reflexes

-unconscious, automatic, responses to stimulation

-reflex arc

• receptors = sense and detect

• Afferent neurons = send to the CNS

• Integrating Center = within the CNS that process

• Efferent neurons = carry away from CNS

• Effectors = carry out end response

Divisions of ANS

1) Sympathetic division = fight or flight or freeze, STRESS

2) Parasympathetic division = rest and digest, repair, calm

Autonomic Tone

normal background rate of activity that represents the balance of the two divisions according to the body’s needs

Parasympathetic Tone + Sympathetic Tone

Autonomic Output Pathways compared to a Somatic Pathway

Somatic = motor neuron from brainstem/spinal chord has a myelinated axon that goes all the way to the skeletal muscle

Autonomic = travel across TWO neurons to get to target organ + cross a synapse where those neurons meet (called an autonomic ganglion), goes from a presynaptic neuron to a postganglionic neuron to along an axon to a target cell

Sympathetic Division Pathways using communicating Rami

-short preganglionic fibers (in the lateral horns + regions of spinal chord gray matter) send signal through white communicating ramus (myelinated)

-leads to sympathetic chain of ganglia called paravertebral ganglia

-leave the chain by postganglionic fibers using gray communicating ramus (unmyelinated) of three ways:

• synapse immediately with a postganglionic neuron

• travel up and down the chain and synapse with other ganglia at other levels

• pass through chain w/o synapsing and continue as splanchnic nerves

-goes all the way to the target organ

difference between parasympathetic division and sympathetic division output pathways

sympathetic: shorter preganglionic fibers and longer postganglionic fibers

parasympathetic; very long preganglionic fibers and super short postganglionic fiber

Adrenal Glands

-located on superior poles of kidneys with two parts

1) Adrenal Cortex: outer layer, secretes steroid hormones

2) Adrenal Medulla: inner core, modified postganglionic neuron w/o fibers, secretes a mixer of hormones into bloodstream

Parasympathetic Division pathways

-super long preganglionic neurons from midbrain, pons, medulla or sacral spinal chord segments

-goes to terminal ganglia either in or near target organ

-then super short postganglionic fibers

*VERY SELECTIVE in the stimulation of target organ

Nerves to the Parasympathetic division

-Oculomotor Nerve (III) = narrows pupil and focuses lens

-Facial Nerve (VII) = tear, nasal, and salivary glands

-Glossopharyngeal nerve (IX) = parotid salivary gland

-Vagus Nerve (X) = viscera as far proximal half of colon

Enteric Nervous System

-nervous system of the digestive tract

-technically subdivision of parasympathetic division

-NO CNS components

-innervates smooth muscle and glands

-regulated by the sympathetic and parasympathetic systems