Biology 12-4.1E Divisions of the Nervous System

The Vagus Nerve

The vagus nerve partly controls feelings of nervousness, such as those experienced in a difficult social situation. Symptoms such as loss of speech control, butterflies in the stomach, and excessive perspiration. Some people may even faint or suddenly urinate when they experience a sudden shock.

Which ANS subdivision has long pre-ganglionic fibres and short post-ganglionic fibres?

Parasympathetic

What physiological advantage results from having synapses in the ganglia?

Release of neurotransmitter adrenalin causes overall sympathetic response during emergency situations. This heightened response is long lasting and therefore more appropriate to such situations.

Can you think of a situation you have experienced that initiated a sympathetic nervous system release of adrenalin and caused you to feel a characteristic adrenalin rush?

Sudden emergency, such as trying to brake a bike to miss an obstacle, running away from perceived danger, being spoken to harshly, suddenly being in danger, etc.

Why are you taught as a beginning swimmer that it is not a good idea to swim right after eating?

Swimming inhibits digestion, which causes bacteria in the bowel to increase activity (undigested food represents more food for them). Bacterial activity causes production of intestinal gas which may cause cramps.

Which division controls emergency situations?

Sympathetic

Where do the neurons that control each division originate?

Sympathetic--thoracic and lumbar regions of the spinal cord; parasympathetic--cranial and sacral regions of the spinal cord.

Name the neurotransmitters used in the synapses of each division.

Sympathetic: Norepinephrine (NE), Parasympathetic: Acetylcholine (ACh)

sympathetic division of the PNS

The Autonomic nervous system is an involuntary control of smooth muscle. The connection between CNS and organs allows the system to be in two different functional states: sympathetic and parasympathetic.

Peripheral Nervous System (PNS)

The PNS can be further subdivided into two divisions--the somatic and autonomic nervous systems. Both control motor functions, and they determine how our muscles and organs respond to output from the CNS. The somatic nervous system includes all neurons involved in controlling voluntary muscle movement. Voluntary means that something is under conscious control. Involuntary means the opposite. Think about each of the following activities. Blinking, coughing, and digesting a sandwich are involuntary. Planning strategy in a game, reading, and holding your breath while hiding are voluntary actions. Voluntary muscle is made up of striated muscle, which appears to have a banded or striated appearance when studied under a microscope. The control of various organs is done entirely by the autonomic nervous system. These organs are involved with secreting hormones, pumping blood, breathing, and digesting food, to name a few, and all of them are under involuntary control. This frees up the brain make conscious decisions about when do homework or watch TV, deciding whether to eat a donut or granola bar, and so on. Notice that some autonomically controlled functions are muscular. These include contractions of the smooth muscle found in the walls of the bladder and the blood vessels, and the cardiac muscle found in the walls of the heart. The autonomic nervous system is divided into sympathetic and parasympathetic motor systems. These control the way your body responds to different control commands from the ANS. Generally, if things aren't going well, the sympathetic motor fibres work overtime to make sure your body manages the difficulty. If things are running smoothly, then the parasympathetic fibres send messages that allow your body to relax, digest your meal, and feel relaxed.

What kinds of tissue are controlled by the autonomic nervous system?

cardiac muscle, smooth muscle, glands

Summary. Completing this lesson has helped you to:

contrast the locations and functions of the central and peripheral nervous systems differentiate between the functions of the sympathetic and parasympathetic divisions of the autonomic nervous system

vagus nerve

each of the tenth pair of cranial nerves, supplying the heart, lungs, upper digestive tract, and other organs of the chest and abdomen.

What important physiological balance is controlled reflexively by the ANS?

Homeostasis

central nervous system (CNS)

the complex of nerve tissues that controls the activities of the body. In vertebrates it comprises the brain and spinal cord.

peripheral nervous system (PNS)

the nervous system outside the brain and spinal cord.

autonomic nervous system

the part of the nervous system responsible for control of the bodily functions not consciously directed, such as breathing, the heartbeat, and digestive processes.

How would each of the following respond in the given situation? bronchioles if you are worried about writing an exam? liver while you are watching the TV? intestine while you are swimming?

A: Dilate B: gall bladder releases bile C: Intestine slows contractions and reduces secretions from intestinal wall, slowing digestion.

Central Nervous System (CNS)

The CNS processes information received from various sensory neurons. The spinal cord was once thought to be simply a highway for information to and from the brain, but we now know it has memory functions. Spinal cord learning is easily understood if you consider how you learned to walk, to ride a bike, or play the piano. Initially the brain was fully engaged in those activities as you learned them. Once mastered, the brain releases control and the spine takes over. This makes it possible to eat a sandwich while riding a bike, talk while playing a game, or walk and chew gum at the same time.

parasympathetic division of PNS

The PNS is divided into two sections: an Autonomic Division, which controls smooth muscles (involuntary), such as the stomach and heart, and a Somatic Division, which controls striated muscles (voluntary), which are the skeletal muscles. In summary, the PNS consists of: Sensory (afferent nerves) Motor (efferent nerves)

Divisions of the Nervous System

The following chart summarizes the divisions of the nervous system. Refer to it as you read the material in this section. Chart used with permission. To help us understand the nervous system, scientists have artificially divided it into two main divisions--the central nervous system (CNS) and the peripheral nervous system (PNS). Keep in mind that the two are closely connected and continually communicate with each other.

Consider the action of both sympathetic and parasympathetic neurons on the genitals. It would appear that both are required for their correct functions during copulation. What type of situations would prevent their correct functioning?

Excessive nervousness or uneasiness would prevent activity of the parasympathetic neurons, which could prevent orgasm; intoxication or excessive fatigue would prevent stimulation of the sympathetic neurons, preventing the necessary arousal response it controls.

What three similarities do the two subdivisions of the ANS have in common?

They function automatically and in an involuntary manner. They control all internal organs. For each signal, two neurons synapse at a ganglion.

Overview

To this point you have focused on the cellular design of the nervous system. In this lesson you will consider its macroscopic design. Your nervous system does most of its work without you being aware of what it is doing. If you consciously had to monitor and adjust each of the various systems in your body and the events that take place, your brain would be too distracted to perform necessary functions. Automatic functions of the nervous system are carefully choreographed by the autonomic nervous system (ANS). Let's look at the division of labour of the nervous system.

Which large cranial nerve in the parasympathetic nervous system has branches to most of the internal organs?

Vagus nerve