Divisions of the Nervous System

Question 1

Somatic nervous system (SNS) + ANS -> peripheral nervous system (PNS)

Answer 1

Introduction to the ANS

Question 2

— Not under conscious control
— Is regulated by hypothalamus, brainstem

Answer 2

ANS

Question 3

— Smooth muscle (stomach, blood vessels)
— Cardiac muscle (heart)
— Glands (sweat and digestive glands)

Answer 3

The ANS supplies nerves to viscera

Question 4

— 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

Answer 4

SNS

Question 5

— 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

Answer 5

ANS

Question 6

Autonomic motor pathway includes two motor neurons

Answer 6

— Preganglionic neuron from CNS to neuron in autonomic ganglion
— Postganglionic neuron from cell body in ganglion to effector

Question 7

Smooth muscle

Answer 7

(stomach, blood vessels)

Question 8

Cardiac muscle

Answer 8

heart

Question 9

Glands

Answer 9

sweat and digestive glands

Question 10

from CNS to neuron in autonomic ganglion

Answer 10

Preganglionic neuron

Question 11

from cell body in ganglion to effector

Answer 11

Postganglionic neuron

Question 12

Most viscera supplied with nerves of both S and P divisions

Answer 12

dual innervation

Question 13

Heart rate:

Answer 13

S stimulates, P inhibits

Question 14

Digestive organs

Answer 14

S inhibit, P stimulate

Question 15

• 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”)

Answer 15

Sympathetic preganglionic neurons

Question 16

So S division is called

Answer 16

thoracolumbar

Question 17

• 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

Answer 17

Sympathetic postganglionic neurons

Question 18

• 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

Answer 18

P preganglionic neurons

Question 19

• 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

Answer 19

P postganglionic neurons

Question 20

• 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

Answer 20

P postganglionic neurons

Question 21

• 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

Answer 21

Acetylcholine (ACh)

Question 22

• NE less common;
released by:
— Almost all S postganglionic axons
• NE has longer lasting effects enhanced by epinephrine + NE from adrenal medullae

Answer 22

Norepinephrine (NE)

Question 23

— 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

Answer 23

Fight-or-flight activities

Question 24

• SLUDD
— Salivation
— Lacrimation
— Urination
— Digestion
— Defecation
• Decrease heart rate, airway diameter, pupil diameter

Answer 24

Rest-and-digest activities

Question 25

SLUDD

Answer 25

• Salivation
• Lacrimation
• Urination
• Digestion
• Defecation