Divisions of the Nervous System Flashcards
Somatic nervous system (SNS) + ANS -> peripheral nervous system (PNS)
Introduction to the ANS
— Not under conscious control
— Is regulated by hypothalamus, brainstem
ANS
— Smooth muscle (stomach, blood vessels)
— Cardiac muscle (heart)
— Glands (sweat and digestive glands)
The ANS supplies nerves to viscera
— Controls skeletal muscle
— Conscious, voluntary control
— Motor pathway: one neuron from CNS to effector
— Does include sensory neurons (from skin, skeletal muscles, and special sense organs)
— All release the neurotransmitter ACh
SNS
— Controls viscera: smooth and cardiac muscle, and glands
— Unconscious, involuntary
— Motor pathway: series of two neurons from CNS to effector
— Does include sensory neurons (monitors viscera)
— Two divisions: sympathetic, parasympathetic
— Release either ACh or NE
ANS
Autonomic motor pathway includes two motor neurons
— Preganglionic neuron from CNS to neuron in autonomic ganglion
— Postganglionic neuron from cell body in ganglion to effector
Smooth muscle
(stomach, blood vessels)
Cardiac muscle
heart
Glands
sweat and digestive glands
from CNS to neuron in autonomic ganglion
Preganglionic neuron
from cell body in ganglion to effector
Postganglionic neuron
Most viscera supplied with nerves of both S and P divisions
dual innervation
Heart rate:
S stimulates, P inhibits
Digestive organs
S inhibit, P stimulate
• Have cell bodies located in lateral gray of spinal cord segments T1-T12 + L1-L2
— So S division is called “thoracolumbar”
• Axons pass through ventral roots of spinal nerves
— May branch many times
— May ascend or descend to many levels of S trunk
ganglia (from cervical to sacral)
— Can synapse with 20 or more postganglionic neuron cell bodies
— Results: widespread S effects (viscera respond “in sympathy with one another”)
Sympathetic preganglionic neurons
So S division is called
thoracolumbar
• S postganglionic neurons cell bodies located
— In S “trunk ganglia” (2 long chains lateral to vertebrae)
-> From cervical to sacral regions à widespread S effects
-> Many axons from these cell bodies pass back into spinal nerves to reach viscera in skin (sweat glands, hair muscles, blood vessels)
• In S “prevertebral ganglia” anterior to 3 large abdominal arteries
— Named celiac, superior and inferior mesenteric ganglia
— Supply abdominal viscera: stomach, intestine, kidneys,
liver, spleen
• Axons pass from ganglia to viscera in S nerves
Sympathetic postganglionic neurons
• Cell bodies located in brainstem + in spinal cord segments S2-S4
— Therefore P division is called “craniosacral”
• Axons in cranial nerves III, VII, IX and X and in pelvic nerves from S2-S4
— Vagus nerves (cranial nerves X) carry 80% of all P nerve impulses.
— Vagus nerves carry both motor and sensory neurons to/from viscera within the thorax and most of the abdominal cavity.
— P preganglionic axons do not branch or pass though S trunk ganglia but pass directly almost to viscera
P preganglionic neurons
• Cell bodies lie in terminal ganglia
— Located within or near the innervated organ
— So P nerves cause precise, localized (not widespread) effects
— Because of anatomical arrangement, S nerves supply all viscera but P nerves do not reach some viscera. These include sweat glands, arrector pili muscles of hairs in skin, kidneys, spleen, adrenal medullae, and the walls of most blood vessels.
• Axons pass from ganglia to viscera in P nerves
P postganglionic neurons
• Cell bodies lie in terminal ganglia
— Located within or near the innervated organ
— So P nerves cause precise, localized (not widespread) effects
— Because of anatomical arrangement, S nerves supply all viscera but P nerves do not reach some viscera. These include sweat glands, arrector pili muscles of hairs in skin, kidneys, spleen, adrenal medullae, and the walls of most blood vessels.
• Axons pass from ganglia to viscera in P nerves
P postganglionic neurons
• ACh more common;
released by:
— All S and P preganglionic axons
— All P postganglionic axons
— Some S postganglionic axons (to sweat glands)
• ACh destroyed by enzyme ACh-ase so short-lived response
Acetylcholine (ACh)
• NE less common;
released by:
— Almost all S postganglionic axons
• NE has longer lasting effects enhanced by epinephrine + NE from adrenal medullae
Norepinephrine (NE)
— Increase heart rate and contraction, and blood pressure (BP)
— Dilate pupils (mydriasis)
— Dilate airways (bronchodilation)
— Dilate vessels to skeletal muscles, heart, liver and adipose tissue (vasodilation)
— Constrict blood vessels to nonessential organs: skin, GI tract, kidneys
— Mobilize nutrients for energy: glucose and fats
Fight-or-flight activities
• SLUDD
— Salivation
— Lacrimation
— Urination
— Digestion
— Defecation
• Decrease heart rate, airway diameter, pupil diameter
Rest-and-digest activities
