Autonomic Nervous System Flashcards
Parasympathetic
– Non-stressful situations
– “housekeeping”
– Keeps energy use low
- Rest and digest
- Origin: Brain and sacral portion of the spinal cord
- Location of ganglia: Within or very close to the organ
-Long preganglionic and short postganglionic
Sympathetic
– Reaction to unusual stimulus
– Fight or flight
– Rapid heart, deep breathing
- Origini: Thoracic and lumbar
regions of the spinal cord
- Location of ganglia: Close to the spinal cord (Sympathetic trunk)
-Short preganglionic and long postganglionic
What is the difference between the autonomic and the somatic nervous systems?
The SNS innervates skeletal muscles and thus controls voluntary movements. The ANS innervates smooth muscle, cardiac muscle, and glands, and controls involuntary motor movements.
What are the two divisions of the ANS?
Parasympathetic and sympathetic
SNS System Summary
-Cell body in CNS
Thick, myelinated, group A fiber
-Extends in spinal or cranial nerve to skeletal muscle (which is the effector organ)
- NT is acetylcholine (ACh)
- Effect always stimulatory
ANS System Summary
Efferent pathway: Uses 2 neurons chain
- Preganglionic neuron
– Cell body in CNS
– Thin, lightly myelinated preganglionic axon. Not as fast as heavily myelinated somatic nerves - Postganglionic neuron
– Cell body in autonomic ganglion outside CNS
– Nonmyelinated postganglionic axon that extends to effector organ
– Preganglionic fibers always release ACh
– Postganglionic fibers release Ach or norepinephrine at effectors
– Effect is either stimulatory or inhibitory, depending on type of receptors
In the parasympathetic division, ganglia are located close to the ______
organ
In the sympathetic division, ganglia are located close to the ______
CNS
SNS vs ANS
SNS:
-Effector: skeletal muscle
-Voluntary
-Efferent pathways consist of one neuron from the CNS to the effector. The neuron is heavily myelinated, allowing rapid signal transmission.
No ganglia are involved in the pathway.
-Neurotransmitter: Acetylcholine (ACh), released at the neuromuscular junction.
-Receptor: Nicotinic cholinergic receptors on skeletal muscles.
-Effect: Always excitatory; causes muscle contraction.
ANS:
-Effector: smooth/cardiac muscle
-Involuntary
-Efferent pathways involve two neurons: A preganglionic neuron (originating in the CNS and lightly myelinated) and a postganglionic neuron (unmyelinated) that extends to the effector.
-Neurotransmitters:
Preganglionic neurons release ACh.
Postganglionic neurons release either: ACh (for parasympathetic division) or norepinephrine (NE) or epinephrine (for sympathetic division).
Receptors:
Parasympathetic: Muscarinic cholinergic receptors
Sympathetic: Adrenergic receptors
Effect: Can be either excitatory or inhibitory, depending on the receptor type and effector organ.
Describe how the SNS works
1) A somatic sensory neuron transmits an impulse from a somatic sensory receptor (such as one in the skin).
2) Somatic motor neuron transmits impulse to the effector (such as a skeletal muscle).
What 4 cranial nerves does the parasympathetic division include?
– Occulomotor
– Facial
– Glossopharyngeal
– Vagus
4 neuron chain
– Sensory neuron
– Interneuron
– Preganglionic neuron
– Postganglionic neuron
- In given situations one
division takes over - Most functions result
from new internal
stimulus
Sympathetic Division
Arise from thoracolumbar region of spinal cord from the lateral horns
- Leave via ventral root
- At sympathetic trunk it may have different fates
– Synapse immediately
– Passes through trunk without synapsing - Synapse at collateral ganglia
– Goes directly to renal medulla - Synapse within gland
- Much longer lasting per episode
– Epinephrine and norepinephrine - Secreted into blood
- Inactivated by kidneys and liver
- Slower than acetylcholine for PNS as it relies on second messenger systems
