chapter 15: the autonomic nervous system and visceral reflexes

the autonomic system is also known as the

visceral motor system

the sympathetic division is

“fight or flight” responses

the parasympathetic division is

“rest and digest” responses

what does the autonomic nervous system control?

glands, cardiac muscle, and smooth muscle

what organs are innervated by the ANS?

* viscera of thoracic/abdominal cavities
* cutaneous blood vessels
* sweat glands
* piloerector muscles

the autonomic system is _____, meaning without our conscious intent or awareness

involuntary

effectors of somatic motor

skeletal muscle

effectors of autonomic motor

glands, smooth muscle, cardiac muscle

somatic motor control is

voluntary

nerve endings for somatic motor is

neuromuscular junctions

nerve endings for autonomic motor is

varicosities

neurotransmitters for somatic motor

acetylcholine (ACh)

neurotransmitters for autonomic motor is

ACh and norepinephrine

ANS pathways have

two-neuron chain with a ganglion

the preganglionic fiber is

myelinated

the postganglionic fiber is

unmyelinated

the two-neuron chain with a ganglion ends in

varicosities

what does varicosities do?

release neurotransmitters into tissue and stimulate many cells at once

visceral reflexes are

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

what do visceral reflex arcs consist of?

* receptors
* afferent neurons
* integrating center
* efferent neurons
* effectors

receptors are

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

afferent neurons

lead to the CNS

the integrating center is

interneurons in the CNS

efferent neurons

carry motor signals away from the CNS

effectors

carry out the end response

the ANS is considered the

efferent pathway

example of visceral reflex: baroreflex

1. high blood pressure detected by arterial stretch receptors
2. afferent neuron carries signal to CNS
3. efferent signals on vagus nerve of ANS travel to the heart
4. heart then slows, reducing blood pressure

the two divisions of the ANS often

innervate the same effector, and may have cooperative or contrasting (antagonistic) effects

the sympathetic division prepares the body for

physical activity (exercise, trauma, arousal, competition, anger, or fear)

what division increases heart rate, BP, airflow, blood glucose levels, and dilates pupils?

sympathetic

the sympathetic division reduces blood flow to

the skin and digestive tract

the parasympathetic division calms many body functions by

reducing energy expenditure and assists in bodily maintenance

what division reduces heart rate, BP, airflow, and more?

parasympathetic

the parasympathetic division regulates

digestion, defecation, and urination

the sympathetic division is also known as the

thoracolumbar division

* it arises from the thoracic and lumbar regions of the spinal cord

the sympathetic has __ preganglionic and ___________ postganglionic fibers

short; long

sympathetic nerve fibers are distributed

to every level of the body

what predominates in the sympathetic division?

neuronal divergence

each preganglionic cell branches and synapses on 10-20

postganglionic cells

one preganglionic neuron in the sympathetic division can

excite multiple postganglionic fibers leading to different target organs

one signal can have

widespread effects

the “fight or flight” response requires

simultaneous activation of many systems

adrenal glands are composed of

the adrenal cortex and adrenal medulla

what is essentially an extension of the sympathetic NS

the adrenal medulla

the adrenal medulla secretes a mixture of what hormones?

* epinephrine (85%)
* norepinephrine (15%)

adrenaline does

increases BP, HR, respiration, enlarges pupils, alters metabolism and blood flow to maximize oxygen and sugar delivery to muscles and brain

the parasympathetic division is also known as

the craniosacral division

* arises from the brain/sacral regions of spinal cord
* fibers travel through cranial and sacral nerves

the parasympathetic division has relatively ____ preganglionic fibers and _____ postganglionic fibers

long;short

the preganglionic fiber in PD ends in

terminal ganglia in or near target organs

the PD is relatively

selective in stimulation of target organ with very little neural divergence

most viscera receive nerve fibers from

BOTH parasympathetic and sympathetic divisions

antagonistic effect

oppose each other

example of antagonistic effect when both divisions innervate the same effector cells

* heart rate decreases (parasympathetic)
* heart rate increases (sympathetic)

example of antagonistic effect when each division innervate different effector cells in the same organ

* pupillary dilator muscle dilates pupil (sympathetic)
* constrictor pupillae constricts pupil (parasympathetic)

cooperative effect

two divisions act on different effectors to produce a unified effect

example of cooperative effect

* parasympathetics increases salivary serous cell secretion
* sympathetics increase salivary mucous cell secretion

both divisions do not normally

innervate on an organ equally

parasympathetics exerts more influence on

digestive organs

sympathetics have greater effects on

ventricular muscles of the heart

control without dual innervation is when

some effectors receive only sympathetic fibers

sympathetic vasomotor tone

is a baseline firing frequency of sympathetics which keeps the blood vessels in a state of partial constriction

sympathetic division acting alone can exert opposite effects on the

target organ blood vessels

an increasing in firing frequency

vasoconstriction

a decrease in firing frequency

vasodilation

nicotine

binds to nicotinic receptors

* increase BP/HR

atropine

blocks muscarinic receptors

* used by optometrist to dilate pupils

beta blockers

block beta receptors

* used to decrease blood pressure

phenylephrine, pseudoephedrine

sympathomimetics

* constrict blood vessels in nasal mucosa- decrease mucus production