Autonomic Nervous System

Homeostasis

Integration

Receptors EffectorsFeed-back

Somatic vs Autonomic NS

Somatic vs Autonomic Nervous systems

Somatic NSReceptors Integration Effectors5 senses Cortex (& assoc.) Skeletal

muscles

Autonomic NSReceptors Integration EffectorsChemo-baro hypothalamus cardiac,Osmo- medulla oblongata smoothReceptors muscles

glands

Autonomic Nervous system

• Two aspects

-1 to promote survival - the other to promote

in crisis state survival in stable state

Sympathetic Parasympathetic

Fight or flight Rest and digest

Figure 11.12

Brain areas involved in controlling the ANS

Functions:Sympathetic Parasympathetic

• Promote survival in crisis state:- Increase heart rate- Increase breathing rate- Increase blood pressure- Vasoconstriction of peripheral/non-

essential blood vessels and- Vasodilation in heart, brain, muscles - Bronchodilation- Iris dilation- Increase blood glucose

• Decrease digestion- Decrease digestive juice secretion- Decrease digestive tube motility- Promote sphincter closing

• Opposite of Sympathetic- Promotes digestion- Promotes rest

Figure 11.1

Anatomy of the motor ANS

Motor pathways of the ANS

Sympathetic NS

• 2 motor neurons• Motor neuron 1 in lateral

horn of spinal cord between T1 to L3

• Motor neuron 2 in the paravertebral ganglia (forming the sympathetic trunk)

• Acetylcholine (nicotinic receptor) in ganglionic synapse, norepinephrine at the organ synapse

• Nerve pathways mixed with somatic sensory and motor pathways

Motor Sympathetic NS

• Two exceptions:

- Adrenal gland: Motor neuron 2 has evolved into a “secretory” neuron which releases mostly epinephrine

- The collateral ganglia: ganglia located between spinal cord and effectors -- ex: celiac ganglia innervating the digestive system

Sympathetic trunk: all the linked paravertebral ganglia will react as a unit to a stimulation of the sympathetic NS heart rate increases, vasodilation of bronchi ….

Collateral ganglia: they will not automatically react as a unit with the motor neurons from the sympathetic trunk

The adrenal medulla

• The gland is formed by the second motor neuron

• Secretes epinephrine

• Sympathetic effect sustained

Figure 11.5

Parasympathetic NS

• 2 motor neurons• Motor neuron 1 in medulla

oblongata or sacral spine• Motor neuron 2 in a

ganglion near the organ• Acetylcholine (nicotinic

receptor) in ganglionic synapse

• Acetylcholine (muscarinic receptor) in effector synapse

• Nerve pathways mixed with sensory and motor pathways, except for Vagus nerve (75% ANS)

Parasympathetic NS (motor pathway)

Neurotransmitters and receptors from the Sympathetic NS

Figure 11.7b

Neurotransmitters and receptors from the parasympathetic NS

Receptors in the ANS

• Cholinergic receptors: Inhibitory or excitatory - Nicotinic: fast - Muscarinic: slow

Adrenergic receptors: slow, excitatory or inhibitory - α 1 and 2 - β 1 and 2 (and 3)

Figure 11.8a

Adrenergic receptors

- α 1 and 2: affinity NE > E generally excitatory

- β 1 and 3 affinity NE = E excitatory

- β 2 affinity E > NE inhibitory

Figure 11.7

Effects of various drugs on the ANS

• Drugs acting on the cholinergic receptors:

- agonist: simulate parasympathetic effect

- antagonist: blocks parasympathetic effect (mimics sympathetic agonist)

• Drugs acting on the sympathetic NS

- agonist: simulate sympathetic effect

- antagonist: blocks sympathetic effect (mimics parasympathetic agonist)

• Epinephrine and ephedrine are given in aerosol in people suffering from an asthma attack.

- Knowing that these drugs are adrenergic agonists, which effect do you expect on the bronchi?

- Which side effects are you likely to see?

Refer to Table 11-2 from the book to answer these question

• Propanolol is a beta-blocker.

- What is this drug effect on the heart?

- Which side effects are you likely to see?

Refer to Table 11-2 from the book to answer these question

• Atropine is a muscarinic cholinergic antagonist.

- What is this drug effect on the pupils?

- What is this drug effect on the heart?

- Which side effects are you likely to see?

- Will skeletal muscles be affected by this drug?

Refer to Table 11-2 from the book to answer these

question

Readings

• Chp. 11, p.303-315

• Will not be on the test:

- Autonomic neuroeffector junctions, p 310