Ch 15: The Autonomic Nervous System

Front 1

How does the autonomic nervous system contribute to homeostasis?

Back 1

By responding to subconscious visceral sensations and exciting or inhibiting smooth muscle, cardiac muscle, and glands.

Front 2

How is the autonomic nervous system like the somatic nervous system?

Back 2

They operate via reflex arcs.

Front 3

What is the role of autonomic sensory neurons?

Back 3

- send main input to ANS.

- Located in blood vessels, visceral organs, muscles & the nervous system that monitor conditions in the internal environment.

Front 4

What is the role of autonomic motor neurons?
Examples?

Back 4

Regulate visceral activities by either increasing (exciting) or decreasing (inhibiting) ongoing activities in their effector tissues (cardiac muscle, smooth muscle, and glands).

Ex. Changes in the diameter of the pupils
- Dilation and constriction of blood vessels
- Adjustment of the rate and force of the heartbeat

Front 5

Most autonomic motor pathways consist of two motor neurons in series, that is, one following the other (Fig 15-1b).
Describe the first and second neuron.

Back 5

The first neuron has its cell body in the CNS; its myelinated axon extends from the CNS to an autonomic ganglion. (A cluster of cell bodies of sympathetic or parasympathetic neurons located outside the CNS in the PNS.

The cell body of the second neuron is also in that same autonomic ganglion; its unmyelinated axon extends directly from the ganglion to the effector (smooth muscle, cardiac muscle, or a gland)

Front 6

The output (motor) part of the ANS has two divisions: the sympathetic division and parasympathetic division. Define each of one of these subdivisions of the ANS:

Back 6

- having cell bodies of preganglionic neurons in the lateral gray columns of the thoracic segment and the first two or three lumbar segments of the spinal cord
- primarily concerned with processes involving the expenditure of energy.

- having cell bodies of preganglionic neurons in nuclei in the brain stem and in the lateral gray horn of the sacral portion of the spinal cord
- primarily concerned with activities that conserve and restore body energy.

Front 7

Most organs have dual innervation. What does this mean?

Back 7

This means they receive impulses from both sympathetic and parasympathetic neurons.

Front 8

How are the somatic & autonomic nervous systems different in terms of: (Table 15-1)
1.Sensory input
2.Control of motor output
3.Motor neuron pathway
4.Neurotransmitters & hormones
5.Effectors
6.Responses

Back 8

1.Sensory input
S: Somatic senses and special senses.
A: Mainly from interoceptors; some from somatic senses and special senses.

2.Control of motor output
S: Voluntary control from cerebral cortex, with contributions from basal ganglia, cerebellum, brain stem, and spinal cord.
A: Involuntary control from hypothalamus, limbic system, brain stem, and spinal cord; limited control from cerebral cortex.

3.Motor neuron pathway
S: One-neuron pathway: Somatic motor neurons extending from CNS synapse directly with effector.
A: Usually two-neuron pathway: Preganglionic neurons extending from CNS synapse with postganglionic neurons in an autonomic ganglion, and postganglionic neurons extending from ganglion synapse with a visceral effector. Alternatively, preganglionic neurons may extend from CNS to synapse with chromaffin cells of adrenal medullae.

4.Neurotransmitters & hormones
S: All somatic motor neurons release ACh.
A: All sympathetic and parasympathetic preganglionic neurons release acetylcholine (ACh). Mo

Front 9

What is the sympathetic division (also called the thoracolumbar division)?

What is the thoracolumbar outflow?

Back 9

-In the sympathetic division, the preganglionic neurons have their cell bodies in the lateral horns of the gray matter in the 12 thoracic segments and the first two (and sometimes three) lumbar segments of the spinal cord (Figure 15-2).

The axons of the sympathetic preganglionic neurons.

Front 10

Which division, sympathetic or parasympathetic, has longer preganglionic axons? Why?

Back 10

Most parasympathetic preganglionic axons are longer than most sympathetic preganglionic axons because most parasympathetic ganglia are in the walls of visceral organs, but most sympathetic ganglia are close to the spinal cord in the sympathetic trunk.

Front 11

The parasympathetic division is also known as the craniosacral division. Define.

What is the craniosacral outflow?

Back 11

Cell bodies of preganglionic neurons of the parasympathetic division are located in the nuclei of four cranial nerves in the brain stem (III, VII, IX, and X) and in the lateral gray matter of the second through fourth sacral segments of the spinal cord (Figure 15-3)

= the axons of the parasympathetic preganglionic neurons

Front 12

Identify and describe the 2 major groups of autonomic ganglia:

Back 12

1.Sympathetic ganglia
= Components of the sympathetic division of the ANS
= the sites of synapses between sympathetic preganglionic and postganglionic neurons
- 2 major types:
a.Sympathetic trunk ganglia lie in a vertical row on either side of the vertebral column. These ganglia extend from the base of the skull to the coccyx (Fig 15-2).
b. Prevertebral ganglia lie anterior to the vertebral column, close to the large abdominal arteries.

2.Parasympathetic ganglia
= Components of the parasympathetic division of the ANS.
= Synapse with postganglionic neurons in terminal ganglia. Most of these ganglia are located close to or actually within the wall of a visceral organ.

*Terminal ganglia = cluster of cell bodies of parasympathetic postganglionic neurons either lying very close to the visceral effectors or located within the walls of the visceral effectors supplied by the postganglionic neurons.

Front 13

Which ganglia are associated with the parasympathetic division? Sympathetic division?

Back 13

Terminal ganglia are associated with the parasympathetic division.
Sympathetic trunk and prevertebral ganglia are associated with the sympathetic division.

Front 14

What is a postganglionic neuron?

Back 14

The second autonomic motor neuron in an autonomic pathway, having its cell body and dendrites located in an autonomic ganglion and its unmyelinated axon ending at cardiac muscle, smooth muscle, or a gland.

Front 15

What are autonomic plexuses?

Back 15

Tangled networks of axons of sympathetic and parasympathetic neurons in the thorax, abdomen, and pelvis.
- Many lie along major arteries.
- May contain sympathetic ganglia and axons of autonomic sensory neurons.

Front 16

What are the structural differences in anatomical components of the sympathetic and parasympathetic divisions of the autonomic nervous system?

Back 16

Cell bodies of sympathetic preganglionic neurons are part of the lateral gray horns of all thoracic segments and of the first two lumbar segments of the spinal cord (see Figure 15-2). The preganglionic axons leave the spinal cord along with the somatic motor neurons at the same segmental level.

Cell bodies of parasympathetic preganglionic neurons are found in nuclei in the brain stem and in the lateral gray matter of the second through fourth sacral segments of the spinal cord (see Figure 15-3). Their axons emerge as part of a cranial nerve or as part of the anterior root of a spinal nerve.

Front 17

Autonomic neurons are classified into 2 categories based on the neurotransmitter they produce and release.

Identify and describe the 2 categories.

a.What hormone is produced?

b.What types of receptors?

Back 17

1.Cholinergic neuron
a. ACh
b. Nicotinic & Muscarinic receptors

2.Adrenergic neuron
a.NE (aka. Noradrenalin)
b. alpha & beta receptors

Front 18

ACh is stored in synaptic vesicles and released by exocytosis. It then diffuses across the synaptic cleft and binds with specific cholinergic receptors, integral membrane proteins in the postsynaptic plasma membrane. Both of the cholinergic receptors bind ACh. Identify and describe the 2 cholinergic receptors.

a.Identify the receptor

b.Where is it located?

c.Why are they so named?

Back 18

1a.Nicotinic receptors

b.Plasma membrane of dendrites and cell bodies of both sympathetic and parasympathetic postganglionic neurons (Figure 15-7a, b), plasma membranes of chromaffin cells of the adrenal medullae, and in the motor end plate at the neuromuscular junction.

c.They are so named because nicotine mimics the action of ACh by binding to these receptors. (Nicotine, a natural substance in tobacco leaves, is not a naturally occurring substance in humans and is not normally present in nonsmokers.)

2a.Muscarinic receptors

b. plasma membranes of all effectors (smooth muscle, cardiac muscle, and glands) innervated by parasympathetic postganglionic axons, sweat glands receive (Fig 15-7b).

c.They are so named because a mushroom poison called muscarine mimics the actions of ACh by binding to them.
*Nicotine does not activate muscarinic receptors, and muscarine does not activate nicotinic receptors, but ACh does activate both types of cholinergic receptors.

Front 19

What does Acetylcholine esterase (AChE) do?

Back 19

Inactivates the effects of acetylcholine

Front 20

Adrenergic receptors bind both norepinephrine and epinephrine. The norepinephrine can be either released as a neurotransmitter by sympathetic postganglionic neurons or released as a hormone into the blood by chromaffin cells of the adrenal medullae; epinephrine is released as a hormone.

a.What are the two main types of adrenergic receptors?

b.Where are they found?

Back 20

a.alpha (α) receptors and beta (β) receptors

b. found on visceral effectors innervated by most sympathetic postganglionic axons.

Front 21

Define:
a. Receptor Agonist

b. Receptor Antagonists

Back 21

a. substance that binds to and activates a receptor, in the process mimicking the effect of a natural neurotransmitter or hormone.

b. a substance that binds to and blocks a receptor, thereby preventing a natural neurotransmitter or hormone from exerting its effect

Front 22

What is the autonomic tone?
What is it regulated by?

Back 22

The balance between sympathetic and parasympathetic activity in an organ.

Hypothalamus

Front 23

What are sympathetic responses?

Back 23

Sympathetic division dominates the parasympathetic division during physical or emotional stress.
- Reduces body functions that favor the storage of energy.
- Besides physical exertion, various emotions—such as fear, embarrassment, or rage—stimulate the sympathetic division.
*E situations: exercise, emergency, excitement, and embarrassment

Front 24

What is the fight-or-flight response?

What are the different effects it can cause?

From where are the hormones for this response released from?

Back 24

Activation of the sympathetic division and release of hormones by the adrenal medullae set in motion a series of physiological responses collectively


- The pupils of the eyes dilate.
- Heart rate, force of heart contraction, and blood pressure increase.
- The airways dilate, allowing faster movement of air into and out of the lungs.
- The blood vessels that supply the kidneys and gastrointestinal tract constrict, which decreases blood flow through these tissues. The result is a slowing of urine formation and digestive activities, which are not essential during exercise.
- Blood vessels that supply organs involved in exercise or fighting off danger—skeletal muscles, cardiac muscle, liver, and adipose tissue—dilate, allowing greater blood flow through these tissues.
- Liver cells perform glycogenolysis (breakdown of glycogen to glucose), and adipose tissue cells perform lipolysis (breakdown of triglycerides to fatty acids and glycerol).
- Release of glucose by the liver increases blood glucose level.

Front 25

What are parasympathetic responses?

Back 25

Rest and digest activities are enhanced.
Support body functions that conserve and restore body energy during times of rest and recovery.

In the quiet intervals between periods of exercise, parasympathetic impulses to the digestive glands and the smooth muscle of the gastrointestinal tract predominate over sympathetic impulses. This allows energy-supplying food to be digested and absorbed. At the same time, parasympathetic responses reduce body functions that support physical activity.

"SLUDD"
Salivation
Lacrimation
Urination
Digestion
Defecation

Other important parasympathetic responses are “three decreases”:
1.decreased heart rate
2.decreased diameter of airways (bronchoconstriction)
3.decreased diameter (constriction) of the pupils.

Front 26

Identify and describe the 5 components of an autonomic reflex:

Back 26

1. Receptor
= Like the receptor in a somatic reflex arc (see Figure 13.13 on page 481), the receptor in an autonomic reflex arc is the distal end of a sensory neuron, which responds to a stimulus and produces a change that will ultimately trigger nerve impulses. Autonomic sensory receptors are mostly associated with interoceptors.

2. Sensory receptor
= Conducts nerve impulses from receptors to the CNS.

3. Integrating centre
= Interneurons within the CNS relay signals from sensory neurons to motor neurons. The main integrating centers for most autonomic reflexes are located in the hypothalamus and brain stem. Some autonomic reflexes, such as those for urination and defecation, have integrating centers in the spinal cord.

4. Motor neuron
= Nerve impulses triggered by the integrating center propagate out of the CNS along motor neurons to an effector. In an autonomic reflex arc, two motor neurons connect the CNS to an effector: The preganglionic neuron conducts motor impulses from the CNS to an autonomi