LECTURE16.AutonomicSys

8/17/2019 LECTURE16.AutonomicSys

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LECTURE 16: AUTONOMIC AND NEUROENDOCRINE SYSTEMS

REQUIRED READING: Kandel text, Chapter 49

Autonomic nervous system mediates visceral refex

responses that are involuntary and largely unconscious

Autonomic nervous system consists o:

1) Motor neurons which act on smooth muscle, cardiacmuscle, and exocrine glands

2) “reganglionic! "#$ neurons whose axons synapse onthese motor neurons

%) &isceral sensory neurons

') (ranches and susets o external*sensing neurons+including somatosensory , olactory, and retinal)

Autonomic postganglionic neurons release neurotransmitterswhich act through metaotropic receptors on targetcells

Autonomic responses are coordinated with one another andwith ehavioral responses and emotions through thehypothalamus in the "#$

always

cholinergic

cholinergic

or

adrenergic

nicotinic

receptors

muscarinic

or

adrenergic

receptors


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EXAMPLES OF AUTONOMIC FUNCTION

Regulation of heartbeat rate

Regulation of vascular constriction/dilation

Pupil and lens ocular reexes

Exocrine gland secretion

Glucose mobilization

Sweating and hair follicle erection

Bladder lling and empt!ing

Sexual responses

"limentar! and bronchial reexes

Gut peristalsis


3/15

THREE DIVISIONS OF THE AUTONOMIC NERVOUS SYSTEM

$ympathetic nervous system

arasympathetic nervous system

nteric nervous system

Sympathetic system controls visceral responses that prepare the body for rapid, intense activity,

often refered to as FIGHT-O-F!IGHT "#$TIO%&

esponses include accelerated heartbeat, central artery constriction, peripheral vascular dilation,

liver glycogen metabolism, ' rapid breathing&

Other sympathetic responses also wor( in balance with countering parasympathetic responses

to maintain body homeostasis )counteraction to body stress*&

+arasympathetic responses sometimes refered to as the "ST-#%-IG"ST ST#T"&

#lmost all visceral targets receive both sympathetic ' parasympathetic neuronal inputs&

"nteric neurons form pleuses that surround and etend along the length of the gut, including

stomach, small and large intestines&

"nteric system activate coordinated contraction of smooth muscles to cause peristaltic

constriction of the gut&

.ost of enteric nervous system functions independently of higher $%S control&


4/15

ANATOMY OF SYMPATHETIC & PARASYMPATHETIC NERVOUS SYSTEM

Most SYMPATHETIC

postganglionic neurons are

adrenergic

(release E or NE)

Most PARASYMPATHETIC

postganglionic neurons are

cholingeric

Site of spinal cord lesion in/ury can be rapidly assessed by surveying damaged and surviving autonomic refle responses


5/15

ANATOMY OF SYMPATHETIC & PARASYMPATHETIC NERVOUS SYSTEM

Generalized “FIGHT” response

mediated by sympathetic

activation of the adrenal gland,

triggering epinephrine

secretion into circulation


6/15

ANATOMY OF ENTERIC NERVOUS SYSTEM


7/15

SENSORIMOTOR CONNECTIONS IN ENTERIC NERVOUS SYSTEM

ARE PREDOMINANTLY LOCAL

A local circuitry drives peristalsisin the intestines

FOOD

DISTENSION + " I S T # ! S I S

+"SS0" S"%SI%G %"0O%

$I$0!# .0S$!" .OTO %"0O%S

ressure*sensing neuron senses gut distension

Acts through interneurons to activate entericmotor neurons with axons pro-ecting rostrally

causing s.uee/ing o circular muscle ehind the distension

$imultaneous inhiition o other motor neuronswith axons pro-ecting caudally relaxes downstream

circular muscle


8/15

POST-GANGLIONIC NEUROTRANSMISSION LACKS TYPICAL

PRE- AND POST-SYNAPTIC SPECIALIZATIONS

ost*ganglionic neuron0s axon terminal lacs clear*vesicle docing machinery

Multiple axonal swellings +varicosities) are sites o neurotransmitter vesicle accumulation

ost*synaptic target +smooth muscle, gland, etc) lacs post*synaptic density

3arget cell neurotransmitter receptors are roadly distriuted on surace

4eleased neurotransmitter acts di5usely over distances up to 1 mm

6ighly ranched axons with multiple varicosities enale post*ganglionic neuronto act upon many cells in the target structure


9/15

DIFFUSE TRANSMISSION FROM GANGLIONIC AXONS FACILITATED

DISCOVERY OF THE FIRST CHEMICAL NEUROTRANSMITTER

arasympathetic vagus nerve activity slows hearteat rate,while sympathetic accelerator nerve activity speeds hearteat rate

TWO BEATING FROG HEARTS DISSECTED AND MAINTAINED IN SMALL VOLUME SOLUTION;

HEART #1 DISSECTED WITH INNERVATING NERVES ATTACHED

HEART #2 DISSECTED WITHOUT NERVES

$timulation o vagal nerve slowed eating o heart 71Ater stimulation, transer o heart 710s athing solution to heart 72 slowed its eating

$timulation o accelerator nerve speeds eating o heart 71Ater stimulation, transer o heart 710s solution to heart 72 sped its eating

364894, #4&*#; #


10/15

MECHANISMS OF AUTONOMIC MODULATION OF CARDIAC FUNCTION

+arasympathetic release of acetylcholine reduces cardiac output in two ways

Sympathetic release of norepinephrine increases cardiac output in two ways

1) Muscarinic generation o =βγ

directly activates a potassium channel +=4?) in pacemaer

cardiocytes, which slows their depolari/ation and rate o hearteat

2) Muscarinic generation o =αi in heart muscle lowers cAM and ?A levels, causing

reduced opening o >*type calcium channels, therey reducing orce o heart contraction

β

1*adrenergic generation o =αs in pacemaer cardiocytes elevates cAM and ?A levels,

which reduces the threshold voltage or action potential initiation, therey increasing rate o hearteat

2 β

1*adrenergic elevation o cAM and ?A in heart muscle increases opening o >*type

calcium channels, therey increasing orce o heart contraction


11/15

SENSORY INPUTS TO AUTONOMIC FUNCTION

9ur odies sense deleterious changes and undertae automatic responsesto maintain homeostasis

$ensory inputs eliciting autonomic responses include:

1) xternal sensations which trigger corrective refexes

xamples: a) 9cular refexes ** pupil dilation or constriction in response to light,lens stretching to ad-ust ocus

http#//librar!$med$utah$edu/%w/h!perbrain/anim/reex$html

) ainul laceration ** vasoconstriction to limit lood losssympathetic activation o coordinated @ghtfight responses

2) &isceral sensations induce homeostatic responses

xamples:a) 9pposing sympatheticparasympathetic control o hearteat and lood pressure **

sympathetic activity drives hearteat and artery constriction too much,

pressure*sensitive sensory a5erents in the aorta trigger the baroreceptor refex ,which includes parasympathetic vagal input to heart and induction o

arterial dilationhttp#//highered$mcgraw&hill$com/sites/''()*'(+('/student,view'/chapter)-/animation,,baroreceptor,reex,control,of,blood,pressure$htm l

4eciprocally, pressure*sensitive sensory a5erents in the cardiac right atriam sense distentiontriggering the right atrial refex , y which sympathetic accerelerator nerve @ring speeds rate

) rritants to oronasal cavities act through parasympathetic ganglia

to trigger nasal and lacrimal glandular secretions

http://library.med.utah.edu/kw/hyperbrain/anim/reflex.htmlhttp://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter21/animation__baroreceptor_reflex_control_of_blood_pressure.htmlhttp://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter21/animation__baroreceptor_reflex_control_of_blood_pressure.htmlhttp://library.med.utah.edu/kw/hyperbrain/anim/reflex.htmlhttp://library.med.utah.edu/kw/hyperbrain/anim/reflex.htmlhttp://library.med.utah.edu/kw/hyperbrain/anim/reflex.htmlhttp://library.med.utah.edu/kw/hyperbrain/anim/reflex.htmlhttp://library.med.utah.edu/kw/hyperbrain/anim/reflex.htmlhttp://library.med.utah.edu/kw/hyperbrain/anim/reflex.htmlhttp://library.med.utah.edu/kw/hyperbrain/anim/reflex.htmlhttp://library.med.utah.edu/kw/hyperbrain/anim/reflex.htmlhttp://library.med.utah.edu/kw/hyperbrain/anim/reflex.htmlhttp://library.med.utah.edu/kw/hyperbrain/anim/reflex.htmlhttp://library.med.utah.edu/kw/hyperbrain/anim/reflex.html


12/15

PREGANGLIONIC FIBERS RELEASE SMALL MOLECULE AND PEPTIDE

NEUROTRANSMITTERS TO ELICIT COMPLEX GANGLIONIC NEURON RESPONSES

$ingle or low*re.uency preganglionic @ring releases Ach which activates nicotinicreceptors triggering ast $ in postganglionic neuron

6igh*re.uency stimulation releases more Ach and >646 peptide 3he complexpostganglionic response consists o ast $, slow $ mediated ymuscarinic receptor activation o =4?s, and delayed $ resulting

rom >646 inding to peptidergic receptors


13/15

SENSORY PATHWAYS OF SYMPATHETIC AND PARASYMPATHETIC SYSTEMS

PASS LOOP THROUGH BRAIN STEM, BUT ALSO PROJECT TO CONSCIOUS CORTICAL AREAS

A$"#;#= &$"4A>$#$94B A36CAB$

;$"#;#= A


14/15

HYPOTHALAMUS COORDINATES PHYSIOLOGY AND BEHAVIOR

IN RESPONSE TO VISCERAL SENSORY INPUTS

DAM>: (>99; 9$M9>A43B 69M9$3A$$

1IS$"#! S"%SO2 I%+0TS

(lood pressure(lood osmolarity

H2+OTH#!#.0S $OOI%#T" O0T+0TS

Autonomic ** action on smooth muscles in central and peripheral vasculature

(ehavioral ** conscious thirst which drives search or fuid intae

ndocrine ** secretion o vasopressin into lood, which promotes water resorption y idneys


15/15

HYPOTHALAMUS CONTROLS HORMONE RELEASE FROM PITUITARY GLAND

BOTH DIRECTLY AND INDIRECTLY

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LECTURE16.AutonomicSys