chapter 15: the autonomic nervous system and visceral reflexes

autonomic

"self governed"; the autonomic nervous system is independent of our will

autonomic nervous system

regulates fundamental states and life processes such as heart rate, bp, and body temperature

who coined the terms 'homeostasis' and 'flight-or-fight'

Walter Cannon

what did Walter Cannon dedicate his career to studying

the autonomic nervous system (ANS)

what happens to animals without an autonomic nervous system

they cannot survive on their own and must be kept warm and stress-free

autonomic nervous system (ANS)

a motor nervous system that controls glands, cardiac muscle, and smooth muscle

what is another name for autonomic nervous system

visceral motor system

primary organs of the ANS

viscera of thoracic and abdominal cavities

structures of the body wall

cutaneous blood vessels, sweat glands, arrector muscles

carries out actions involuntary; without our conscious intent or awareness

autonomic nervous system (ANS)

visceral effectors

do not depend on the ANS to function; only to adjust their activity to the body's changing needs

denervation hypersensitivity

exaggerated response of cardiac and smooth muscles if autonomic nerves are severed

visceral reflexes

unconscious, automatic, stereotyped responses to stimulation involving visceral receptors and effectors

visceral reflex arc

receptors, afferent neurons, integrating center, efferent neurons, effectors

receptors in visceral reflex arc

nerve endings that detect stretch, tissue damage, blood chemicals, body temperature, and other internal stimuli

afferent neurons in visceral reflex arc

lead to CNS

integrating center of visceral reflex arc

interneurons in the CNS

efferent neurons in visceral reflex arc

carry motor signals away from the CNS

effectors in visceral reflex arc

carry out and response

ANS is considered

the efferent pathway

divisions of autonomic nervous system

two division often innervate same target organ; may have cooperative or contrasting effects

sympathetic division

prepares body for physical activity; exercise, trauma, arousal, competition, anger, or fear; "fight or flight"

increases heart rate, blood pressure, airflow, blood glucose levels etc.; reduces blood flow to the skin and digestive tract

sympathetic division

parasympathetic division

calms many body functions reducing energy expenditure and assists in bodily maintenance; "resting and digesting" state

digestion and waste elimination

parasympathetic division

autonomic tone

normal background rate of activity that represents the balance of two systems according to the body's needs

parasympathetic tone

maintains smooth muscle tone in intestines

holds resting heart rate down to about 70 to 80 beats per minute

parasympathetic tone

sympathetic tone

keeps blood vessels partially constricted and maintains blood pressure

sympathetic division excites

the heart but inhibits digestive and urinary function, while parasympathetic has the opposite effect

ANS has components

in both the central and peripheral nervous system

where are the control nuclei in the autonomic output pathway

in the hypothalamus and other brainstem regions

where are the motor neurons located in the autonomic output pathway

in the spinal cord and peripheral ganglia

what do the nerve fibers in the autonomic output pathway travel through

cranial and spinal nerves

somatic pathway

a motor neuron from brainstem or spinal cord issues a myelinated axon that reaches all the way to skeletal muscle

autonomic pathway

a signal must travel across two neurons to get to the target organ

must cross a synapse where these two neurons meet in an autonomic ganglion

autonomic pathway

presynaptic neuron

the first neuron has a neurosome in the brainstem or spinal cord

synapses with a postganglionic neuron

whose axon extends the rest of the way to the target cell

the sympathetic division

also called the thoracolumbar division because it arises from the thoracic and lumbar regions of the spinal cord

baroreflex

automatic, negative feedback response to change in blood pressure

preganglionic fibers

small myelinated fibers that travel from spinal nerve to the ganglion by way of the white communicating ramus (myelinated)

postganglionic fibers

long fibers extending to target organs; leave the ganglion by the way of the gray communicating ramus (unmyelinated)

postganglionic fibers forms

a bridge back to the spinal nerve

preganglionic neurosomas

in lateral horns and nearby regions of spinal cord gray matter

fibers exit spinal cord by way of

spinal nerves T1-L2

sympathetic chain of ganglia

lead to nearby sympathetic chain of ganglia (paravertebral ganglia)

ganglia distribution

Usually 3 cervical, 11 thoracic, 4 lumbar, 4 sacral, and 1 coccygeal ganglion

sympathetic nerve fibers

are distributed to every level of the body

series of longitudinal ganglia adjacent to both sides of the vertebral column from cervical to coccygeal levels

paravertebral ganglia

each paravertebral ganglion is connected to a spinal nerve by two branches

communicating ramus

after entering the sympathetic chain, the preganglionic fibers may follow

any of three courses

course 1 of sympathetic division

some end in the ganglia which they enter the synapse immediately with the postganglionic neuron

course 2 of sympathetic division

some travel up and down the chain and synapse in ganglia at other levels; only route by which ganglia at the cervical, sacral, and coccygeal levels receive input

course 3 of sympathetic division

some pass through the chain without synapsing and continue as splanchnic nerves

these fibers link the paravertebral ganglion into a chain

preganglionic fibers

nerve fibers leave the sympathetic chain by three routes

spinal, sympathetic, and splanchnic nerves

spinal nerve route

some postganglionic fibers exit a ganglion by way of the gray ramus

return to the spinal nerve and travel the rest of the way to the target organ

most sweat glands, piloerector muscles, and blood vessels of the skin and skeletal muscles choose this sympathetic route

spinal nerve route

what do sympathetic nerves extend to in the sympathetic nerve route

the heart, lungs, esophagus, and thoracic blood vessels

what structure do sympathetic nerves form around each carotid artery (sympathetic nerve route)

carotid plexus

what do the sympathetic nerves issue fibers to in the head (sympathetic nerve route)

sweat, salivary, nasal glands; piloerector muscles; blood vessels; dilators of iris

what type of nerves do some fibers of the superior and middle cervical ganglia form (sympathetic nerve route)

cardiac nerves to the heart

what spinal nerves give rise to the splanchnic nerves

T5 to T12

do some fibers that arise from T5 to T12 synapse in the sympathetic ganglia

no, they pass through without synapsing

what do the fibers that pass through the sympathetic ganglia continue as

splanchnic nerves

where do the splanchnic nerves lead to for synapsing

collateral (prevertebral) ganglia

collateral ganglia

contribute to a network called the abdominal aortic plexus; wraps around abdominal aorta

three major collateral ganglia in the abdominal aortic plexus

celiac, superior mesenteric, and inferior mesenteric

postganglionic fibers accompany

arteries of the same names and their branches to their target organs

solar plexus

collective name for the celiac and superior mesenteric ganglia

nerves radiate from

ganglia like rays of the sun

adrenal glands

rests like hats on the superior poles of kidneys

adrenal cortex

outer layer of adrenal glands; secrets steroid hormones

adrenal medulla

inner core of the adrenal gland; essentially a sympathetic ganglion consisting of modified postganglionic neurons (without fibers)

stimulated by preganglionic sympathetic neurons

adrenal medulla

sympathoadrenal system

the name for the adrenal medulla and sympathetic nervous system

secrets a mixture of hormones in the bloodstream

catecholamines - 85%, epinephrine (adrenaline) and 15% norepinephrine (nonadrenaline)

parasympathetic division is also called

craniosacral division

parasympathetic division

arises from the brain and sacral regions of the spinal cord; fibers travel in certain cranial and sacral nerves

origins of long preganglionic neurons

midbrain, pons, medulla

relatively selective in stimulation of target organ

parasympathetic division

oculomotor nerve (III)

narrows pupil and focuses lens

facial nerve (VII)

tear, nasal, and salivary glands

glossopharyngeal nerve (IX)

parotid salivary gland

vagus nerve (X)

viscera as far as proximal half of colon; cardiac, pulmonary, and esophageal plexus

enteric nervous system

the nervous system of the digestive tract

enteric nervous system does not

arise from the brainstem or spinal cord (no CNS components)

enteric nervous system is composed of

100 million neurons found in the walls of the digestive tract

enteric nervous system has

its own reflex arcs

enteric nervous system functions

regulates motility of esophagus, stomach, and intestines and secretion of digestive enzymes and acid

normal digestive function

also requires regulation by sympathetic and parasympathetic systems

how do autonomic neurons have contrasting effects on organs

two fundamental reason

reason one of autonomic neurons contrasting

sympathetic and parasympathetic fibers secret different neurotransmitters (norepinephrine and acetylcholine)

how do target cells respond to neurotransmitters in autonomic neurons contrasting

target cells respond to the same neurotransmitter differently depending on the type of receptor they have for it

how many classes of receptors are there for acetylcholine in autonomic neurons contrasting

there are two different classes of receptors for acetylcholine

how many classes of receptors are there for norepinephrine in autonomic neurons contrasting

there are two classes of receptors for norepinephrine

acetylcholine (ACh)

secreted by all preganglionic neurons in both divisions and by postganglionic parasympathetic neurons

axons that secrete ACh are called

cholinergic fibers

any receptor that binds to ACh is called a

cholinergic receptor