autonomic nervous system

major functions of autonomic nervous system

maintain optimal performance of visceral organs, glands, smooth muscle, and

cardiac muscle in order to maintain homeostatic state within body

what is the involuntary nervous system doing

not under conscious control: regulates heart rate, blood

pressure, respiratory rate, body temperature, smooth muscle contraction, glandular function, and

secretions

General visceral motor system

most “effectors” (organs & tissues regulated) are visceral

(as opposed to somatic - skeletal muscle & joints)

Effectors (Target of Motor Neuron) somatic

skeletal muscle

Effectors (Target of Motor Neuron) Autonomic

organs, glands, smooth & cardiac muscle

Efferent (Motor Neuron) Pathway. SOMATIC

one motor neuron from CNS to skeletal muscle

Efferent motor neuron pathway AUTONOMIC

two neurons in the motor pathway

preganglionic neuron

located in the CNS, sends its axon to an autonomic

ganglion located outside the CNS; lightly myelinated, thin axons

postganglionic neuron -

located in the autonomic ganglion, sends it axon

to the effector (tissue to be effected); unmyelinated, very thin axons

SOMATIC neurotransmitter function

acetylcholine (ACh); stimulatory

AUTONOMIC neurotransmitter function

post ganglionic neurons may release either ACh or Norepinephrine

(NE); whether response is stimulatory or inhibitory depends on the effect

How does coordination happen between Somatic and Autonomic Systems

Both systems send their motor neurons to effectors via the 31 pairs of spinal

nerves and 12 pairs of cranial nerves

What happens when skeletal muscle is active

When skeletal muscle is active, autonomic must regulate other body activities for

sufficient blood, oxygen, waste removal

Divisions of the Autonomic Nervous System

the sympathetic and parasympathetic divisions

work in contrasting fashion to stimulate and inhibit effectors

Sympathetic Division -

classic "flight-or-fight" response in scary situation

Sympathetic Division effect on heart

increased heart rate

Sympathetic effect on breathing

rapid, deep breathing pattern

Sympathetic Division

rapid, deep breathing pattern

Sympathetic divison effect on body temp and sweat?

cold, sweaty skin

Sympathetic divison effect on pupils?

dilated eye pupils

Sympathetic division effect on energy

large burst of energy available (glucose)

Sympathetic division effect on blood vessels

constriction of blood vessels

Sympathetic division effect on blood

increased blood pressure

Sympathetic division effect on air

dilation of bronchioles (more air)

Parasympathetic Division -

the "resting and digesting" system, keeps body calm,

stimulates digestion, urination, and defecation

What is the Autonomic Neurotransimitters used

ACh

Acetylcholine (ACh)

the same neurotransmitter at the neuromuscular junction is used by autonomic fibers in two places (cholinergic fibers):

first place ACh is used in autonomic fibers:

secreted by ALL preganglionic neurons of the ANS

second place ACh is used in autonomic fibers

secreted by MOST postganglionic neurons of PARASYMPATHETIC onto target

cells

Acetylcholine (cholinergic) receptors

nicotinic receptors and muscarinic receptors

nicotinic receptors

ACh receptors that can also be activated by nicotine STIMULATE and at neuromuscular junction of skeletal muscle

muscarinic receptors

ACh receptors which are activated by mushroom toxin muscarine STIMULATE or INHIBIT depending of target cell

where are nicotinic receptors located

located on ALL postganglionic nerve cell bodies of ANS, & hormone-producing cells of adrenal medulla

where are the muscarinic receptors located?

located on the target cells of the body receiving ACh from the

parasympathetic division

example of inhibitory and exhibitory reactions

cardiac muscle -> INHIBITORY

smooth muscle of GI tract -> STIMULATORY

Norepinephrine (noradrenaline)

released by most postganglionic neurons of the

SYMPATHETIC system (adrenergic fibers)

exceptions of Noreinephrine

postganglionic sympathetic fibers to some sweat glands of skin, some blood vessels to skeletal

muscle and external genitalia

norepinephrine (noradrenergic) receptors

alpha adrenergic receptors and beta adrenergic receptors

alpha adrenergic receptors

generally STIMULATE the effector organ/tissue

beta adrenergic receptors

generally INHIBIT the effector organ/tissue

Drug Effects on the Autonomic NS

synaptic cleft enzyme inhibitors

neostigmine

blocks acetylcholinesterase for accumulation of ACh (myasthenia

gravis)

tricyclic antidepressants -

prolong the binding of norepinephrine to postsynaptic receptors

beta-blockers -

block binding of norepinephrine to beta-I receptors; reduce heart rate

Parasympathetic effect on eyes

eye pupil constricts

Parasympathetic effect on heart

decreases heart rate

Parasympathetic effect on lung

constricts bronchioles

Parasympathetic effect on GI tract

increases digestion

sympathetic effect on GI tract

decrease digestion

Parasympathetic effect on urinary

promotes urination

sympathetic effect on urinary

inhibits urination

Parasympathetic effect on most glands

stimulate secretion

sympathetic effect on most glands

inhibits secretion

Sympathetic Tone -

constriction of blood vessels almost exclusively controlled by sympathetic

blood pressure sympathetic tone

sympathetic stimulation causes vasoconstriction of blood vessels and increase in blood pressure; when stimulation decreases, blood pressure likewise decreases

phentolamine sympathetic tone

blocks NE, used to treat with high blood pressure

Parasympathetic Tone

primary control of heart rate (decrease), GI tract (stimulate), and urinary

function (stimulate)

anticholinergic drugs Parasympathetic Tone

block ACh causing increased heart rate, decreased defecation and

urination

anticholinergic side effects

drugs that partially block ACh causing problems of

symptoms of anticholingeric drugs (many pschotropic drugs like anti-depressants)

Cooperative Effects

parasympathetic causes vasodilation of penis and clitoris; sympathetic

causes ejaculation and peristalsis of vagina

Sympathetic ONLY on hormones

stimulation of adrenal medulla to secrete hormones norepinephrine and epinephrine

Sympathetic ONLY (sweat glands)-

stimulates sweat glands to secrete

Sympathetic only- hair cells

arrector pili hair to stand up on arm/neck

sympathetic only- blood vessels

blood vessels - causes to constrict

sympathetic only thermoregulation -

vasodilation of capillaries in skin and sweat gland stimulation

sympathetic only release of renin from kidney

release of hormone causes increased blood pressure

metabolic effects (sympathetic only)

increases general alertness, increased metabolic rate, increased glucose release to blood, mobilization of fat for fuel use, and activate reticular formation of brain

medulla effect on ANS by CNS

can regulate heart rate (cardiac center), blood vessel constriction (vasomotor

center), respiration, and some gastrointestinal activity

pons effect on ANS by CNS

can regulate respiration (respiratory center), and the pupils (ocularmotor nuclei)

spinal cord effect on ANS by CNS

- can regulate defecation/urination

Hypothalamus - Overall Integration of Autonomics

can coordinate the regulation of heart rate, blood pressure, body temperature,

water/electrolyte balance, hormonal activity, pleasure, rage, thirst, hunger, and sex drive

sympathetic location of hypothalamus

lateral & posterior hypothalamus

parasympathetic location of hypothalamus

medial & anterior hypothalamus

pathway of hypothalamus signals

hypothalamus ----> reticular formation ----> preganglionic autonomics

Cerebral Cortex and Biofeedback

- making patient aware of autonomically controlled functions

(heart rate, blood pressure) can allow them to learn how to better control them

hypertension

increased blood pressure due to overstimulation of sympathetics that results from

stress; NE blockers to treat

Raynaud’s disease

abnormal vasoconstriction of vessels in the extremities; surgery to sever

sympathetic fibers used to treat this problem

autonomic hyperflexia

massive reflex activation of all autonomics that occurs in response to spinal injury; can cause death due to loss of control of visceral function