Autonomic Nervous System

Beginning of Human AP II

Nervous System Organization

central nervous system (CNS)

brain and spinal chord

peripheral nervous system (PNS)

spinal nerves, ganglia, sensory receptors

sensory (afferent) division

transports sensory info to CNA from environment, external and internal

motor (efferent) division

transports commands from CNS to body

somatic motor division

directs skeletal muscle movement → neuromuscular junctions

automatic nervous system (ANS)

subconscious; directs smooth and cardiac muscles and glands

sympathetic division

directs mobilization in response to stress, fight or flight response

parasympathetic division

directs resting activitiy, promotes homeostasis, “rest and digest”

ganglion

cluster of neurons where signals are compiled/combined in peripheral nervous system. In ANS, they act as waystations with a ganglion neuron innervating the target organ after its dendrites have been advised by many neurons

I) Acetylcholine (ACh)

all preganglionic synapses (both divisions), all parasympathetic, all somatic neuromuscular junctions, also used in parts of adrenal that produce epinephrine

cholinergic fibers

release acetylcholine

cholinergic receptors

2 types

1. nicotinic receptors

• all somatic neuromuscular junctions

• all preganglionic synapses (parasymp. and symp.)

• in parts of adrenal that produce epinephrine

• always stimulatory

2. muscarinic receptors

• all postganglionic parasympathetic targets

II) Norepinephrine (NE)

most symp. postganglionic synapses

adrenergic fibers

release norepinephrine

adrenergic receptors

2 types, alpha and beta

SYMPATHETIC DIVISION

• more extensive than parasymp. (must run to skin glands and piloerectors)

• nerves originate from T1-T2

T1-T6 nerves synapse in ganglia in:

sympathetic trunk, immediately outside spina chord, then run to head or thorax

T5-L2 nerves from symp. trunk merge into:

splanchnic nerves, running to collateral ganglia in abdominal aortic plexus, then run to abdomen or pelvis

fight or flight

deals with short term crisis

sympathetic stimulates general:

systemic vasoconstriction

vasoconstricion

tightening of arteris; higher BP

vasodilation

relaxation of smooth muscle in arteries; lower BP; associated with lower sympathetic activity

vasometer tone

sympathetic division must always keep partial vasoconstriction even at rest

• avoid shock

• in case fast response is needed

hypertension

chronically high BP (>140/90

• too much chronic stress

• too much chronic activation of sympathetic division

prehypertension

(>120/80)=at risk

• diastole more important than systole

• other possible causes (such as too much NaCl in diet)

SYMPATHETIC DIVISION

Skin

stimulates (cold sweat, goose bumps (piloerectors))

Eyes

Wide open (pupils dilated); ciliary muscles relaxed

Pulmonology

higher breathing rate and volume

CV system

higher heart rate and force of heartbeat

Blood Vessels

General vasoconstriction of body arteries

Muscles/Liver

Mobilizing glycogen stores; getting read for action

Basal Metabolism

High (can only be counter-acted by time; there is no parasympathetic control of metabolism)

Urinary system

lower filtration by kidney; inhibiting urination

Digestion

lower digestive activity, mouth goes dry

Reproductive

controls orgasm and ejaculation in both sexes ONLY if parasympathetic has already caused erection. Otherwise, erectile dysfunction/frigidity

Adrenals

Causes copious release of NE (positive feedback; self-reinforcing sympathetic stimulation) and its stronger chemical cousin, epinephrine

PARASYMPATHETIC DIVISION

• nerves originate from brain stem (cranial nerves) and S2-S4 regions only

ganglia are very close to:

target organs

vagus nerve (CN X)

innervates virtuallt entire visceral cavity (90% of body’s entire parasympathetic load)

sacral nerves run to:

large intestine/rectum, bladder, and reproductive system

PARASYMPATHETIC DIVISION

“rest and digest”; promotes general homeostasis

Digestion

• higher digestive activity (motility and enzyme production)

• higher saliva production; promotes defacation

CV system

lower heart rate

Pulmonology

lower breathing rate and volume

Eyes

controls ciliary body accommodation (making lens bulge)

Urinary system

• relaxes bladder sphincters; promotes urination

• no effect of kidney

Genitalia

Vasodilation of arteries going to clitoris/penis leads to erection and all other phenomena associated with sexual stimulation (both sexes)

DRUGS

knowing locations of specific cholinergic and adrenergic receptors allows us to target drugs to specific areas without screwing up whole system

Beta-Blockers vs Cardiac Beta

• adrenergic receptors keeps heart from getting overexcited

• stimulation of alpha-adrenergic receptors (ex: phenylephrine) stimulates vasoconstriction in sinuses leads to less congestion

pseudoephredine

chemical relative, also increases norepinephrine release

sildenafil (Viagra)

stimulates parasympathetic divisioon leads to vasodilation in penis/clitoris

THE BRAIN

Next part in the automatic nervous system

Brain Protection

1. hair

2. scalp

3. Cranial bones

4. Meninges

C.T. sheaths covering/protecting CNS

a) Dura mater

2 dense irregular sheets surrounding brain

Periosteal layer

superficial layer

Meningeal layer

deep layer

Meningeal layer is mostly fused, seperate in special areas:

(dural sinuses) for drainage of blood and CSF from arachnoid villi

Arachnoid mater

1 layer areolar C.T. enclosing and circulating cerebrospinal fluid (CSF)

arachnoid villi

AM projections into DM sinuses; where CSF drains back into blood

Pia mater

thin delicate areolar connective tissue that directly covers entire brain; marks brains outer edge

Cerebrospinal fluid (CSF)

clear liquid cushion for mechanical protection:
-softens impact with cranium walls

-floats brain, decreasing effective weight by over 97%

optimal ionic concentrations:

(Na+, K+, Cl-) for APs and H+ for homeostatic pH

assists with circulation of:

some nutrients, ions, and hormones

~150 mL (5oz.):

complete turnover=8 hours

choroid plexus

capillary nest surrounded by PM and ependyma

ventricles

CSF reservoirs within brain

CSF circulates throughout:

brain and spinal chord regions

CSF drains back into:

blood through arachnoid villi into DM sinuses for drainage into jugular veins

hydrocephalus

(“water on brain”) blockage in CSF drainage

Blood-brain barrier (BBB)

structural feature of intra-brain capillaries

blood

chaotic environment full of nasty things, all in flux:

CO2

combines with H20, → H2CO3, → H+, which messes up pH

ionic electrolytes

Na+, K+, Cl- (all of which mess with APs)

hormones

amino acids

(some of which can double as neurotransmitters)

foreign microbes

brain:

2% of bodt weight, but uses 20% of O2 and glucose consumed (glucose is only fuel usable by astrocytes → neurons)

brain needs constant blood flow:

chiefly from carotid artery

What is the blood brain barrier?

• surrounds capillaries winding their way through brain

• capillary wall epithelium sealed with tight junctions

• surrounded glycoprotein basement membrane (basal lamina)

• anchored bty astrocytes

essential nutrients and electrolytes, glucose, and hydrophobic molecules:

are allowed entry; most all else is prohibited

non-essential materials and wastes are:

actively pumped out of blood-brain barrier into blood

ethanol

(CH3CH2OH)=hydrophobic

most anesthetics

hydrophobic

most psychoactive drugs

hydrophobic

Nucleus

collection of neurons in brain with specific function; analogous to ganglia in PNS

Spinal Cord

part of central nervous system

interneurons

control reflexes

• ascending sensory tracts and descending motor tracts

I) BRAIN STEM

Controls ANS and innervation of head

a) Medulla oblongata

b) Pons

c) Midbrain

d) reticular formation

Reticular Formation

scattered throughout other 3

A) Medulla oblongata

upper continuation of spinal cord; ascending sensory tracts and descending motor tracts

Pyramids

crossover point for brain lateralization

brain lateralization

R→L; L→R

Nuclei of:

5 cranial nerves

VIII Vestibulocochlear

hearing, equilibrium sensation

IX Glossopharyngeal

taste, sense of carotid BP