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Unit 1:
Ch. 1
Ch. 2
Ch. 3
Interlude A
Unit 2:
Ch. 4
Ch. 5
Ch. 6
Ch. 7
Ch. 8
Ch. 9
Interlude B
Unit 3:
Ch. 10
Ch. 11
Ch. 12
Ch. 13
Ch. 14
Ch. 15
Interlude C
Unit 4:
Ch. 16
Ch. 17
Ch. 18
Ch. 19
Interlude D
Unit 5:
Ch. 20
Ch. 21
Ch. 22
Ch. 23
Ch. 24
Ch. 25
Ch. 26
Ch. 27
Ch. 28
Ch. 29
Ch. 30
Interlude E
Unit 6:
Ch. 31
Ch. 32
Interlude F
Unit 7:
Ch. 33
Ch. 34
Ch. 35
Ch. 36
Ch. 37
Ch. 38
Interlude G

» Getting Started » A Guide to the Reading » Tying it all together

Getting Started

Below are a few questions to consider prior to reading Chapter 25. These questions will help guide your exploration and assist you in identifying some of the key concepts presented in this chapter.

  1. What is the difference between a neuron and a nerve?
  2. What are the different parts that make up a neuron? 
  3. What is an action potential and how is it produced?
  4. How does myelin influence the speed of transmission of an action potential?
  5. How does a neuron pass its signal to other cells?
  6. What are the different neurotransmitters used by the body?
  7. How do the peripheral and central nervous systems function together?
  8. What are the differences between sensory neurons and motor neurons?
  9. What are the different parts of the human brain and why is it so large?
  10. Do the endocrine system and the nervous system ever interact?

A Guide to the Reading

When exploring the content in Chapter 25 for the first time, the following concepts typically give students the most difficulty. For each concept, one or more references have been identified which may help you gain a better understanding of these potentially problematic areas.

Action Potentials as Electrical Signals

The structure of neurons includes dendrites that receive inputs to the cell, a cell body, and an axon that moves signals from the cell body to adjoining cells.  The inputs and signals of these structures of the neuron move through the cell as electrical signals that are produced by the flow of ions into and out of the cell.  In the resting state, the cell is continuously pumping Na+ out of the axon and into the interstitial fluid.  This movement of Na+ out of the cell polarizes the plasma membrane by producing a charge difference across the plasma membrane.  An action potential occurs when special channels in the plasma membrane open.  These channels are Na+ channels that allow Na+ to flow into the cell, causing a localized change in the charge of the plasma membrane.  As a result the inside portion of the membrane becomes positively charged.  This process is known as depolarization of the plasma membrane.  The strength of membrane depolarization depends on the number of Na+ channels that open.   This localized depolarization event in turn causes Na+ channels in the downstream adjoining portions of the axon plasma membrane to depolarize. In this way the action potential moves down the axon.  As the action potential moves down the axon, its strength remains constant.  It continues only in the downstream direction, and it is an all-or-none response.  Some axons are insulated with a myelin sheath that allows an action potential to occur only at gaps that contain no myelin known as nodes of Ranvier.  The myelin and nodes speed up the transmission of impulses. Once an action potential reaches the end of the axon, the signal is passed to the next cell at a synapse.  The stimulated neuron releases a neurotransmitter such as acetylcholine or norepineprhine into the synaptic cleft where it diffuses to receptors on the target cell to bring about a response.  Additionally, some neurotransmitters inhibit a response in the target cell.

For more information on this concept, be sure to focus on:

  • Section 25.2, Neurons Transmit Rapid Electrical Signals
  • Figure 25.2, How Axons Transmit Signals

Interactions of Our Nervous System

The nervous system of humans is composed of the central nervous system (CNS) and the peripheral nervous system (PNS).  The CNS contains the brain and spinal cord and its major function is to exchange and integrate information among neurons, while the PNS contains the sensory organs and all nerves that are not part of the CNS.  Sensory neurons take inputs from sensory organs and pass them to interneurons of the CNS.  From the interneurons the signals can go out to the body via motor neurons or up to the brain.  Neurons that take input from sensory neurons, pass them to the interneurons of the spinal cord, and then back out to the motor neurons without processing by the brain are collectively known as a reflex arc.  The classic example of a reflex arc is the “knee-jerk response” used by your doctor.  Reflex arcs process information and bring about a response very quickly. The brain also processes pain information and causes additional responses to stimuli, but the response will be slower than that of the reflex arc.

For more information on this concept, be sure to focus on:

  • In Section 25.3, Signals travel between the peripheral and the central nervous system
  • In Section 25.3, Sensory information can be processed with or without the brain
  • Figure 25.5, Organization of the Human Nervous System
  • Figure 25.6, Reflex Arcs Do Not Require Processing in the Brain

Your Brain

The human brain has evolved into an organ that can take inputs from millions of sensory neurons and process and integrate the information to control millions of motor neurons.  The brain has three major regions, each with its own roles.  The forebrain is composed of the thalamus that determines the routing of sensory signals entering the brain and the cerebrum that deals with thinking, speech, reading, vision, sound, smell.  The cerebral cortex is a special area of the cerebrum responsible for higher-order processing of external stimuli. The hypothalamus is also considered part of the forebrain and is responsible for integrating the internal stimuli necessary for homeostasis and interacting with the endocrine system through the pituitary gland.  The other two regions of the brain are the midbrain that helps maintain muscle tone and passes information to higher brain centers and the hindbrain that is involved in controlling breathing and balance.   Over the past 2 to 1.5 million years, humans have evolved the largest brain relative to body size of any animal.  During this evolution, a portion of the human cerebral cortex known as the neocortex has had a disproportional increase in size.  The neocortex is involved in complex thoughts, language, and ability for innovation.

For more information on this concept, be sure to focus on:

  • In Section 25.4, The brain has three major regions
  • Section 25.5, Why Do Humans Have Big Brains?
  • Figure 25.7, The Human Brain Has Three Specialized Regions
  • Figure 25.8, How the Brain “Sees” the Body

Tying it all together

Several concepts presented in this chapter build upon concepts presented in previous chapters and are also revisited and discussed in greater detail in subsequent chapters, including:

Making Sense of Action Potentials in the Body as a Whole

  • Chapter 26 - Section  26.1, Sensory Structures: Making Sense of the Environment

Organization of the Human Brain

  • Chapter 26 – Section 26.5, The Brain’s Role in Integrating Sensory Information

Integration of the Nervous and Endocrine Systems

  • Chapter 24 – Section 24.2, Regulating Short-Term Processes: Glucose and Calcium Homeostasis

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