Download Autonomic Nervous System

Autonomic Nervous System
Functions of the ANS
• Regulates the activities of:
- smooth muscle
- cardiac muscle
- some glands
Structure of the ANS
• Composed entirely of visceral efferent
neurons (motor neurons to internal
organs)
• Has no sensory function (motor only)
• Neurons are organized into:
- nerves
- ganglia
- plexuses
1
Division of the ANS
The Autonomic Nervous System is
divided into two divisions that are often
antagonistic to one another
(1) Sympathetic Division
(2) Parasympathetic Division
Components of the ANS
• Composed of two efferent neurons:
(1) Preganglionic neurons – runs from
the CNS to an autonomic ganglion
(2) Postganglionic neurons – runs from
the autonomic ganglion to a visceral
effector (heart, smooth muscle, gland)
2
Notes on preceding slide
• A two motor path exists in the ANS with
the preganglionic neuron conveying
impulses from the CNS to the autonomic
ganglion, and the postganglionic neuron
relaying impulses to the visceral effectors
The Sympathetic Division
• The preganglionic fibers arise from spinal
cord segments T1 through T3, and L1
through L3
• For this reason they are called the
Thoracolumbar Division (or
Thoracolumbar outflow
The Parasympathetic Division
• Preganglionic fibers arise from the nuclei
of cranial nerves and spinal cord
segments S2 through S4
• For this reason this division is called the
Craniosacral Division (or Craniosacral
outflow)
3
Activities of the ANS
• Most effectors have duel innervation and
respond antagonistically to sympathetic
and parasympathetic stimulation
• The sympathetic division is said to be:
flight-or-fight
• The parasympathetic division is said to be
energy-conservation-restoration
• For individual activities of these divisions
see the preceding slide
Visceral Autonomic Reflexes
• Like a somatic reflex except for the two neurons
involve in the ANS reflex
• Adjusts the homeostatic activity of the viscera
such as:
- Heart rate and force of contraction
- Blood pressure
- Respiration
- Digestion
- Defecation
- Urinary bladder function
4
Neurotransmitters
• Neurotransmitters can be classified as:
(1) Cholinergic
(2) Adrenergic
Cholinergic Neurotransmitters
• Release acetylcholine
• Includes all sympathetic and
parasympathetic preganglionic fibers
• Includes all parasympathetic
postganglionic fibers
• Includes all somatic motor neurons
Adrenergic Neurotransmitter
• Release Norepinephrine
• Includes sympathetic postganglionic fibers
5
Control of the ANS
• The hypothalamus is the major control
center
6