Chapter 12. The Nervous System and Nervous Tissue

12.1 Structure and Function of the Nervous System

Learning Objectives

By the end of this section, you will be able to:

Describe the anatomical structure and basic functions of the nervous system

  • Identify the anatomical and functional divisions of the nervous system
  • List the basic functions of the nervous system

The Central and Peripheral Nervous Systems

The picture you have in your mind of the nervous system probably includes the brain, the nervous tissue contained within the cranium, and the spinal cord, the extension of nervous tissue within the vertebral column. Additionally, the nervous tissue that reach out from the brain and spinal cord to the rest of the body (nerves) are also part of the nervous system. We can anatomically divide the nervous system into two major regions: the central nervous system (CNS) is the brain and spinal cord, the peripheral nervous system (PNS) is the nerves (Figure 1). The brain is contained within the cranial cavity of the skull, and the spinal cord is contained within the vertebral canal of the vertebral column. The peripheral nervous system is so named because it is in the periphery—meaning beyond the brain and spinal cord.

 

Figure 12.11 – Central and Peripheral Nervous System: The CNS contains the brain and spinal cord, the PNS includes nerves.

Functional Divisions of the Nervous System

In addition to the anatomical divisions listed above, the nervous system can also be divided on the basis of its functions. The nervous system is involved in receiving information about the environment around us (sensory functions, sensation) and generating responses to that information (motor functions, responses) and coordinating the two (integration).

Sensation. Sensation refers to receiving information about the environment, either what is happening outside (ie: heat from the sun) or inside the body (ie: heat from muscle activity). These sensations are known as stimuli (singular = stimulus) and different sensory receptors are responsible for detecting different stimuli. Sensory information travels towards the CNS through the PNS nerves in the specific division known as the afferent (sensory) branch of the PNSWhen information arises from sensory receptors in the skin, skeletal muscles, or joints this is known as somatic sensory information; when information arises from sensory receptors in the blood vessels or internal organs, this is known as visceral sensory information.

Response. The nervous system produces a response in effector organs (such as muscles or glands) due to the sensory stimuli. The motor (efferent) branch of the PNS carries signals away from the CNS to the effector organs. When the effector organ is a skeletal muscle, the information is called somatic motor; when the effector organ is cardiac or smooth muscle or glandular tissue, the information is called visceral (autonomicmotor. Voluntary responses are governed by the somatic nervous system and involuntary responses are governed by the autonomic nervous system, which are discussed in the next section.

Integration. Stimuli that are received by sensory structures are communicated to the nervous system where that information is processed. This is called integration (see figure 12.12 below). In the CNS, stimuli are compared with, or integrated with, other stimuli, memories of previous stimuli, or the state of a person at a particular time. This leads to the specific response that will be generated.

 

Figure 12.12: Integration occurs in the CNS where sensory information from the periphery is processed and interpreted. The CNS then creates a motor plan that is executed by the efferent branch working with effector organs.

 

Chapter Review

The nervous system can be separated into divisions on the basis of anatomy and physiology. The anatomical divisions are the central and peripheral nervous systems. The CNS is the brain and spinal cord. The PNS is everything else and includes afferent and efferent branches with further subdivisions for somatic, visceral and autonomic function. Functionally, the nervous system can be divided into those regions that are responsible for sensation, those that are responsible for integration, and those that are responsible for generating responses.

Review Questions

Critical Thinking Questions

1. What responses are generated by the nervous system when you run on a treadmill? Include an example of each type of tissue that is under nervous system control.

2. When eating food, what anatomical and functional divisions of the nervous system are involved in the perceptual experience?

Glossary

autonomic nervous system
functional division of the efferent branch of the PNS that is responsible for control of cardiac and smooth muscle, as well as glandular tissue
brain
the large organ of the central nervous system contained within the cranium and continuous with the spinal cord
central nervous system (CNS)
anatomical division of the nervous system that includes the brain and spinal cord
integration
nervous system function that processes sensory perceptions and produce a response
peripheral nervous system (PNS)
anatomical division of the nervous system that extends from the brain and spinal cord to the rest of the body
response
nervous system function that causes a target tissue (muscle or gland) to produce an event as a consequence to stimuli
sensation
nervous system function that receives information from the environment and translates it into the electrical signals of nervous tissue
somatic nervous system (SNS)
functional division of the nervous system that is concerned with conscious perception, voluntary movement, and skeletal muscle reflexes
spinal cord
organ of the central nervous system found within the vertebral cavity and connected with the periphery through spinal nerves; mediates reflex behaviors
stimulus
an event in the external or internal environment that registers as activity in a sensory neuron

Solutions

Answers for Critical Thinking Questions

  1. Running on a treadmill involves contraction of the skeletal muscles in the legs (efferent somatic motor), increase in contraction of the cardiac muscle of the heart (efferent autonomic motor), and the production and secretion of sweat in the skin to stay cool (sensation of temp = afferent visceral sensory, sweat gland activation = efferent autonomic motor).
  2. The sensation of taste associated with eating is sensed by nerves in the periphery that are involved in sensory and somatic functions.