Ch. 15 Learning Objectives

Nervous System: Autonomic Nervous System

15.1.1 Explain the similarities and differences between the SNS and the ANS.

SNS (somatic nervous system): initiation of motor output

• controls skeletal muscle, usually under conscious control

• uses 1 motor neuron to reach muscle

ANS (autonomic nervous system): controls automatic factors

• cardiac muscle, smooth muscle, glands

• responds to visceral (organ) sensory receptors

• uses 2 neuron chain

15.1.2 Compare and contrast lower motor neurons in the SNS and ANS.

SNS: 1 motor neuron extends from CNS to skeletal muscle fibers

• pathway is simple and fast

• have large diameter, myelinated, always release acetylcholine (ACh)

ANS: chain of 2 neurons extend from CNS to innervate cardiac muscle, smooth muscle, and glands in ANS

• preganglionic neuron from CNS to an autonomic ganglion

  • then to cardiac muscle, smooth, or glands

  • cell body lies within the brain stem or spinal cord of CNS

• smaller in diameter, myelinated and release ACh

15.1.3 Describe how the two-neuron chain in the ANS facilitates communication and control

Neuronal Convergence (convergo = to incline together): axons from many preganglionic neurons send signals and influence a single preganglionic neuron

Neuronal Divergence (di = apart): axons from one preganglionic cell sends signals and influence many ganglionic neurons

15.1.4 Describe the CNS hierarchy that controls the autonomic nervous system.

Hypothalamus: command center for autonomic functions

• contains nuclei that control organ functions of ANS

• communicates with other CNS regions (hypothalamus, spinal cord)

• involved in emotions & physiologic processes

Brainstem: control organ reflexes

• controls changes in heart rate, pupil size, etc.

Spinal Cord: reflexive activities without involvement of the brain

• fight or flight / urination (in children)

• centers for cardiac, digestive, & vasomotor functions

15.2.5 Compare and contrast the general functions of the parasympathetic and sympathetic divisions of the autonomic nervous system.

Parasympathetic Division (craniosacral): maintains body process when at rest

• conserves energy & replenishes nutrient stores

• most active when body is at rest ex: digesting meal

Sympathetic Division (thoracolumbar): regulates body during exercise/times of stress/emergency

• release of nutrients from stores

• 3 e’s : exercise, excitement, or emergency

• fight or flight

15.2.6 Compare and contrast the anatomic differences in the lower motor neurons and associated ganglia of the parasympathetic and sympathetic divisions.

Parasympathetic: close to the organs they control

• long preganglionic neuron

• short postganglionic neuron

• originates from brainstem & sacral regions

• no more than 4 branches

• close to or within effector (terminal ganglia & intramural ganglia)

Sympathetic: closer to the spinal cord

• short preganglionic neuron

• long postganglionic neuron

• originates thoracic & lumbar regions (T1-L2)

• have many branches (20+)

• close to spinal cord

15.2.7 Explain why parasympathetic activation is local and discrete, and sympathetic activation can result in mass activation.

Parasympathetic pathways have long preganglionic axons with few branches; signal stays targeted and affects small # of effectors

• activation is local and specific because ganglia are located close to target organs

Sympathetic pathways have shorter preganglionic axons that branch extensively; one signal can reach many effectors at once

• allows many organs to respond at the same time

• produces mass activation; stress, energy release

15.3.8 Name the four cranial nerves associated with the parasympathetic division, and describe their anatomic pathways and functions.

Oculomotor Nerve (CN III): innervates smooth muscle in eye

• adjust shape of lense to see objects & dialation of pupil

• axons of preganglionic neurons extend from cell bodies housed in a midbrain nucleus to the ciliary ganglion

Facial Nerve (VII): innervates submandibular & sublingual salivary glands in floor of mouth

• stimulates tear and saliva production

• stimulates glands of nasal cavity

Glossopharyngeal Nerve (CN IX): innervates the parotid salivary gland

• stimulates saliva production

Vagus Nerve (CN X): innervates thoracic organs & most abdominal organs

• regulates heart rate, digestion, & respiratory organs

  • decreases heart rate, constricts to decrease air flow to lungs, releases insulin of pancreas, etc.

15.3.9 Explain the anatomic pathways and actions of the pelvic splanchnic nerves.

preganglionic neuron cell bodies of these come from the lateral gray regions of the S2-S4 spinal cord segments, then they extend to form pelvic splanchnic nerves

pathway: axons leave through anterior roots, enter pelvic splanchnic nerves, travel to hypogastric plexus, then to terminal/intramural ganglia near target organs

Distal portion of large intestine & rec-tum: increases movement of GI tract, stimulates secretions of tract wall, relaxes internal anal sphincter

Urinary Bladder: contracts bladder wall, relaxes internal urethral sphincter which facilitates urination

distal part of the ureters: contracts smooth

15.4.10 Describe where the sympathetic preganglionic neuron cell bodies are located.

located in the lateral horns of the T1-L2 segments of spinal cord

• their axons leave the spinal cord through anterior roots, then enter T1-L2 spinal nerves

15.4.11 Describe the left and right sympathetic trunks and ganglia.

L & R sympathic trunks & ganglia are paired nerves that run alongside the vertebral column

• part of the sympathetic division of ANS

ganglia serve as relay points where preganglionic neurons connect with postganglionic neurons

• this allows sympathetic signals to spread efficiently to many body structures

• one sympathic trunk ganglion is typically associated with each spinal nerve

Superior cervical ganglion: contains cell bodies of sympathetic ganglionic neurons whos axons are distributed primarily to structures within head and neck

Middle & Inferior cervical ganglia: contain cell bodies of ganglionic neurons whos axons extend to both neck structures & thoracic organs

15.4.12 Compare and contrast white and gray rami regarding their location and composition.

Rami Communicantes: connecting the spinal nerves to each sympathetic trunk

White rami: composed of preganglionic sympathetic axons from T1-L2 spinal nerves to sympathetic trunk

• associated with only T1-L2 spinal nerves

• are myelinated (gives a white appearance)

• ex: similar to entrance ramps on highway

Gray rami: composed of postganglionic sympathic axons that extend from sympathetic trunk to spinal nerve

• are unmyelinated (gives greyish appearance)

• connect to all spinal nerves

• ex: similar to exit ramps on highway

15.4.13 Explain the differences between the sympathetic trunk ganglia and the prevertebral ganglia.

Sympathetic trunk ganglia: Located along the sides of the vertebral column. They contain sympathetic neurons and allow sympathetic signals to travel to organs in the head, neck, thorax, and limbs.

Prevertebral ganglia: Located anterior to the vertebral column, mainly around major abdominal arteries. They send sympathetic signals to organs in the abdominopelvic cavity, such as the stomach, intestines, liver, and kidneys.

15.4.14 Describe the four pathways of sympathetic neurons.

Spinal Nerve Pathway: extends from spinal cord to effectors of the skin of neck, torse, & limbs (but not head)

• skin effectors: sweat glands, smooth muscle of arrector pili muscles (goose bumps) & smooth muscle cells of blood vessels

• preganglionic neuron synapse with ganglionic neuron in sympathetic trunk ganglion; postganglionic axon extends through gray ramus at same level as the ganglionic neuron

Postganglionic Sympathetic Nerve pathway: extends from the spinal cord to effectors: skin of head, pupils, organs in the neck, & throacic organs

• preganglionic neuron synapses with a ganglionic neuron in a sympathetic trunk ganglion, postganglionic axon extends away from sympathetic trunk ganglion & goes directly to autonomic effector

Splanchnic Nerve Pathway: extends from spinal cord to the abdominal & pelvic organs

• preganglionic neuron does not synapse with a ganglionic neuron in sympathetic trunk ganglion

• preganglionic axon synapses with a ganglionic neuron, postganglionic axon then projects to the autonomic effector

Adrenal Medulla Pathway: adrenal medulla is directly innervated by preganglionic sympathetic axons

• axons extend through but don’t synapse

• Preganglionic neuron passes through the sympathetic trunk without synapsing, goes directly to the adrenal medulla, stimulates it to release epinephrine and norepinephrine into the blood

15.4.15 Compare and contrast which general effectors are innervated by each pathway.

Spinal nerve → skin (sweat glands, arrector pili muscles, blood vessels

Postganglionic nerve → thoracic organs (heart & lungs)

Splanchnic nerve → abdominal/pelvic organs (stomach, intestines, kidneys, bladder, reprod. organs)

Adrenal medulla → whole body (heart, blood vessels, liver, skeletal muscle)

15.4.16 Describe the changes to effectors due to stimulation by the sympathetic division.

Cardiovascular: increases heart rate & force of heart contraction; coronary arteries: vasodialation (increases blood flow to heart)

Digestive: inhibits digestion

• salivary glands: vasoconstricts blood vessels to salivary glands (thick saliva = dry mouth)

• GI tract wall: relaxes smooth muscle in wall = decreases motility; slows digestion

• Pancreas: inhibits release of insulin, stimulates release of glucagon

Respiratory: increase airflow to lungs

Urinary: prevent urination

• bladder: constricts sphincter to hold urine

Reproductive: changes that occur during orgasm

• reproductive glands: stimulates relase of secretions in a male during ejaculation

• uterus & vag: contraction of smooth muscle

Integumentary: goosebumps, release of sweat, decreases blood flow to skin

Nervous: increased amount of light entering eye

15.5.17 Describe the structure and location of the autonomic plexuses.

autonomic plexus: networks of nerves & ganglia that help regulate the activity of internal organs

• collections of sympthetic postganglionic axons & parasympathetic preganglionic axons

• made up of sympathetic & parasympathetic nerve fibers

• contain nerve fibers, neurons, & ganglia

• help distribute autonomic signals to multiple organs

cardiac plexus: innervates the heart

pulmonary plexus: innervates bronchi of lungs

esophageal plexus: innervates the esophagus

15.5.18 Explain the function and location of the enteric nervous system (ENS).

ENS: controls & coordinates activites of the digestive system without needing direct input from brain or spinal cord

• controls movement of food

• secretion of enzymes & fluids

• blood flow

• coordination of digestion & absorption

Location: walls of GI tract, from esophagus to anus

• myenteric plexus: controls muscle movement/peristalsis

• submucosal plexus: controls secretions & blood flow

15.6.19 List the neurotransmitters of the ANS, the term for the type of neuron that releases each, and the names of the receptors that bind them.

15.6.20 Describe the two types of cholinergic receptors and the action of each when the neurotransmitter acetylcholine binds to them

15.6.21 Name the adrenergic receptors, list their locations, and describe their actions.

16.6.22 Define autonomic tone, and list some examples of autonomic tone.

15.6.23 Define dual innervation.

15.6.24 Describe the antagonistic and cooperative effects of dual innervation.

15.7.25 Describe the systems innervated only by the sympathetic division and how they function

15.8.26 Describe some examples of autonomic reflexes.