Autonomic Nervous System

Beginning of Human AP II

Nervous System Organization

brain and spinal chord

central nervous system (CNS)

spinal nerves, ganglia, sensory receptors

peripheral nervous system (PNS)

transports sensory info to CNA from environment, external and internal

sensory (afferent) division

transports commands from CNS to body

motor (efferent) division

directs skeletal muscle movement → neuromuscular junctions

somatic motor division

subconscious; directs smooth and cardiac muscles and glands

automatic nervous system (ANS)

directs mobilization in response to stress, fight or flight response

sympathetic division

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

parasympathetic division

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

ganglion

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

I) Acetylcholine (ACh)

release acetylcholine

cholinergic fibers

2 types

cholinergic receptors

• all somatic neuromuscular junctions

• all preganglionic synapses (parasymp. and symp.)

• in parts of adrenal that produce epinephrine

• always stimulatory

1. nicotinic receptors

• all postganglionic parasympathetic targets

2. muscarinic receptors

most symp. postganglionic synapses

II) Norepinephrine (NE)

release norepinephrine

adrenergic fibers

2 types, alpha and beta

adrenergic receptors

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

• nerves originate from T1-T2

SYMPATHETIC DIVISION

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

T1-T6 nerves synapse in ganglia in:

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

T5-L2 nerves from symp. trunk merge into:

deals with short term crisis

fight or flight

systemic vasoconstriction

sympathetic stimulates general:

tightening of arteris; higher BP

vasoconstricion

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

vasodilation

sympathetic division must always keep partial vasoconstriction even at rest

• avoid shock

• in case fast response is needed

vasometer tone

chronically high BP (>140/90

• too much chronic stress

• too much chronic activation of sympathetic division

hypertension

(>120/80)=at risk

• diastole more important than systole

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

prehypertension

SYMPATHETIC DIVISION

stimulates (cold sweat, goose bumps (piloerectors))

Skin

Wide open (pupils dilated); ciliary muscles relaxed

Eyes

higher breathing rate and volume

Pulmonology

higher heart rate and force of heartbeat

CV system

General vasoconstriction of body arteries

Blood Vessels

Mobilizing glycogen stores; getting read for action

Muscles/Liver

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

Basal Metabolism

lower filtration by kidney; inhibiting urination

Urinary system

lower digestive activity, mouth goes dry

Digestion

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

Reproductive

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

Adrenals

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

PARASYMPATHETIC DIVISION

target organs

ganglia are very close to:

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

vagus nerve (CN X)

large intestine/rectum, bladder, and reproductive system

sacral nerves run to:

“rest and digest”; promotes general homeostasis

PARASYMPATHETIC DIVISION

• higher digestive activity (motility and enzyme production)

• higher saliva production; promotes defacation

Digestion

lower heart rate

CV system

lower breathing rate and volume

Pulmonology

controls ciliary body accommodation (making lens bulge)

Eyes

• relaxes bladder sphincters; promotes urination

• no effect of kidney

Urinary system

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

Genitalia

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

DRUGS

• adrenergic receptors keeps heart from getting overexcited

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

Beta-Blockers vs Cardiac Beta

chemical relative, also increases norepinephrine release

pseudoephredine

stimulates parasympathetic divisioon leads to vasodilation in penis/clitoris

sildenafil (Viagra)

Next part in the automatic nervous system

THE BRAIN

1. hair

2. scalp

3. Cranial bones

Brain Protection

C.T. sheaths covering/protecting CNS

4. Meninges

2 dense irregular sheets surrounding brain

a) Dura mater

superficial layer

Periosteal layer

deep layer

Meningeal layer

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

Meningeal layer is mostly fused, seperate in special areas:

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

Arachnoid mater

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

arachnoid villi

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

Pia mater

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

-floats brain, decreasing effective weight by over 97%

Cerebrospinal fluid (CSF)

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

optimal ionic concentrations:

some nutrients, ions, and hormones

assists with circulation of:

complete turnover=8 hours

~150 mL (5oz.):

capillary nest surrounded by PM and ependyma

choroid plexus

CSF reservoirs within brain

ventricles

brain and spinal chord regions

CSF circulates throughout:

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

CSF drains back into:

(“water on brain”) blockage in CSF drainage

hydrocephalus

structural feature of intra-brain capillaries

Blood-brain barrier (BBB)

chaotic environment full of nasty things, all in flux:

blood

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

CO2

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

ionic electrolytes

hormones

(some of which can double as neurotransmitters)

amino acids

foreign microbes

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

brain:

chiefly from carotid artery

brain needs constant blood flow:

• surrounds capillaries winding their way through brain

• capillary wall epithelium sealed with tight junctions

• surrounded glycoprotein basement membrane (basal lamina)

• anchored bty astrocytes

What is the blood brain barrier?

are allowed entry; most all else is prohibited

essential nutrients and electrolytes, glucose, and hydrophobic molecules:

actively pumped out of blood-brain barrier into blood

non-essential materials and wastes are:

(CH3CH2OH)=hydrophobic

ethanol

hydrophobic

most anesthetics

hydrophobic

most psychoactive drugs

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

Nucleus

part of central nervous system

Spinal Cord

control reflexes

• ascending sensory tracts and descending motor tracts

interneurons

Controls ANS and innervation of head

a) Medulla oblongata

b) Pons

c) Midbrain

d) reticular formation

I) BRAIN STEM

scattered throughout other 3

Reticular Formation

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

A) Medulla oblongata

crossover point for brain lateralization

Pyramids

R→L; L→R

brain lateralization

5 cranial nerves

Nuclei of:

hearing, equilibrium sensation

VIII Vestibulocochlear

taste, sense of carotid BP

IX Glossopharyngeal