FUNCTIONAL ASPECTS OF THE AUTONOMIC NERVOUS SYSTEM

3

AUTONOMIC NERVOUS SYSTEM

The autonomic nervous system is the subdivision of the peripheral nervous system that regulates body activities that are generally not under conscious control

Autonomic nervous system innervate smooth muscle (eg, blood vessels, gut

wall, urinary bladder) cardiac muscle glands (eg, sweat glands, salivary glands)

DIVISION OF ANS

Parasysmpathetic: routine maintenance

“rest &digest”

Sympathetic: mobilization & increased metabolism

“fight, flight or fright”

4

5

WHERE THEY COME FROM

Parasympathetic:craniosacral

Sympathetic:thoracolumbar

PARASYMPATHETIC SYSTEM

6

7

PARASYMPATHETIC OUTFLOW

Cranial outflow III - pupils constrict VII - tears, nasal mucus, saliva IX – parotid salivary gland X (Vagus n) – visceral organs of thorax & abdomen:

Stimulates digestive glands Increases motility of smooth muscle of digestive tract Decreases heart rate Causes bronchial constriction

Sacral outflow (S2-4): form pelvic splanchnic nerves Supply 2nd half of large intestine Supply all the pelvic (genitourinary) organs

SYMPATHETIC SYSTEM

8

9

SYMPATHETIC OUTFLOW“fight, flight or fright”

Also called thoracolumbar system: all its neurons are in lateral horn of gray matter from T1-L2

Lead to every part of the body (unlike parasymp.) Easy to remember that when nervous, you sweat; when

afraid, hair stands on end; when excited blood pressure rises (vasoconstriction): these sympathetic only

Also causes: dry mouth, pupils to dilate, increased heart & respiratory rates to increase O2 to skeletal muscles, and liver to release glucose

10

PRE AND POST GANGLION NEURON

Somatic division: Cell bodies of motor neurons reside in CNS (brain or

spinal cord) Their axons (sheathed in spinal nerves) extend all the

way to their skeletal muscles Autonomic system: chains of two motor neurons

1st = preganglionic neuron (in brain or cord) 2nd = gangionic neuron (cell body in ganglion outside

CNS)

(see next diagram)

11

PRE AND POSTGANGLION FIBER

Axon of 1st (preganglionic) neuron leaves CNS to synapse with the 2nd (ganglionic) neuron

Axon of 2nd (postganglionic) neuron extends to the organ it serves

Note: the autonomic ganglion is motor

12

13

Figure 8-2

SYMPATHETIC AND PARA SYMPATHETIC GANGLIA

Sympathetic ganglia Many lie close to spinal cord(paravertebral) Others lie approximately midway between

spinal cord and effector organ(prevrtebral or collateral)

Parasympathetic ganglia Lie close to or within the walls of effector organ

Figure 8-2

IMPORTANT NEUROTRANSMITTERS

Acetylcholine =Cholinergic Fibers that release acetylcholine are

known as cholinergic fibers All preganglionic neurons of the autonomic

division and all postganglionic neurons of the parasympathetic division are cholinergic

17

Norepinephrine = Adrenergic Neurotransmitter between the sympathetic

postganglionic fiber and the effector cell Fibers that release norepinephrine are

adrenergic fibers

Most postganglionic neurons of the sympathetic division are adrenergic Few are cholinergic(sweat gland,some blood

vessels in skeletal muscle)

CHOLINERGIC RECEPTOR

Nicotinic receptor Nicotinic receptors are found on the

postganglionic cell bodies in all autonomic ganglia.

Response to acetylcholine released from both sympathetic and parasympathetic

18

Muscuranic receptor found on cell membranes of effectors

organ (smooth muscle, cardiac muscle, and glands)

they bind with acetylcholine released from parasympathetic postganglionic nerve fiber

19

ADRENERGIC RECEPTOR

Alpha receptors are located at sympathetic neuroeffector junctions of many organs.

In general, alpha receptors mediate excitation or increased activity of the effector cells.

alpha receptor have greater affinity for norepinephrine

20

TYPES OF -ADRENERGIC RECEPTOR

-adrenergic receptors are adrenergic receptors that respond to norepinephrine

They are subdivided into two types:

1, found in smooth muscle, heart, and liver, with effects including vasoconstriction, intestinal relaxation, uterine contraction and pupillary dilation,

2, found in platelets, vascular smooth muscle, nerve termini, and pancreatic islets, with effects including platelet aggregation, vasoconstriction, and inhibition of norepinephrine release and of insulin secretion.

Beta receptors are also located postsynaptically at sympathetic neuroeffector junctions of many organs.

beta receptors mediate relaxation or decreased activity of the effector cells.

Heart muscle is an important exception to this rule. Activation of beta adrenoceptors in heart increases the automaticity and contractility of all parts of the heart.

-RECEPTOR TYPES -adrenergic receptors respond particularly to epinephrine

and nor epinephrine

There are three known types of beta receptor, designated β1, β2 and β3.

β1-Adrenergic receptors are located mainly in the heart. Sensitive to both EN and NOR EN

β2-Adrenergic receptors are located mainly in the lungs, gastrointestinal tract, liver, uterus, vascular smooth muscle, and skeletal muscle

sensitive to EN only.

β3-receptors are located in fat cells.

24

25

ADRENAL GLAND IS EXCEPTION

On top of kidneys

Adrenal medulla (inside part) is a major organ of the sympathetic nervous system

26

Adrenal gland is exception

Synapse in gland

Can cause body-wide release of epinephrine and norepinephrine

27

28

29

30

31

32

SYMPATHETIC PARASYMPATHETIC TONE

DUAL INNERVATION MASS DISCHARGE(ALARM OR STRESS

RESPONSE) LOCAL RESPONSE SOME EXCEPTIONS: BLOOD VESSELS

SWEAT GLAND, SALIVARY GLAND33

VISCERAL REFLEXES

These are the simplest functions of the ANS. Each visceral reflex arc consists of a receptor, a sensory

neuron, an interneuron, and two visceral motor neurons. All visceral reflexes are polysynaptic. PS reflexes include : gastric and intestinal reflexes,

defecation, urination, direct light reflexes, swallowing reflex, coughing reflex, baroreceptor reflex and sexual arousal.

S reflexes: cardioaccelaratory reflex, vasomotor reflex, pupillary reflex and ejaculation (in males).

35

VISCERAL REFLEX ARCS

*e.g. “enteric” nervous system: 3 neuron reflex arcs entirely within the wall of the gut

36

Central control of the Autonomic NS

Amygdala: main limbic region for emotions

Hypothalamus: main integration center

Reticular formation: most direct influence over autonomic function