12.3 The Function of Nervous Tissue

Learning Objectives

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

  • Describe the pathway involved with neural sensation, integration and motor response.

Having looked at the components of nervous tissue, and the basic anatomy of the nervous system, next comes an understanding of how nervous tissue is capable of communicating within the nervous system. Before getting to the nuts and bolts of how this works, an illustration of how the components come together will be helpful. An example is summarized in Figure 12.3.1.

This diagram shows the complete pathway a nerve impulse takes when a person tests the temperature of shower water with their hand. First, a sensory nerve ending in the index finger sends a nerve impulse to the spinal cord. A cross section of one segment of the vertebrae is shown from a superior view. The sensory nerve connected to the nerve ending is located in the dorsal root ganglion. The nerve ending is a dendrite of the sensory neuron, as it also has an axon that synapses with an interneuron. The interneuron then synapses with a second interneuron in the thalamus. This second interneuron synapses with brain tissue in the cerebral cortex, allowing conscious perception of the water temperature. The brain then initiates a motor command by stimulating an upper motor neuron in the cerebral cortex. The axon of the upper motor neuron extends all the way to the spinal cord, where it synapses with a lower motor neuron in the gray matter of the spinal cord. The impulse then travels down the lower motor neuron back to the hand where it synapses with the skeletal muscles of the hand. This triggers the muscle contractions that turn the dials of the shower to adjust the water temperature.
Figure 12.3.1 Testing the Water. Use the text below with this figure to describe signal transmission in the body.

Imagine you are about to take a shower in the morning before going to school. You have turned on the faucet to start the water as you prepare to get in the shower. You put your hand out into the spray of water to test the temperature. What happens next depends on how your nervous system interacts with the stimulus of the water temperature and what you do in response to that stimulus.

Found in the skin is a type of sensory receptor that is sensitive to temperature, called a thermoreceptor. When you place your hand under the shower (1 in Figure 12.3.1, close up in Figure 12.3.2), the cell membrane of the thermoreceptors changes its electrical state (voltage). The amount of change is dependent on the strength of the stimulus (in this example, how hot the water is). This is called a graded potential. If the stimulus is strong, the voltage of the cell membrane will change enough to generate an electrical signal that will travel down the axon. The voltage at which such a signal is generated is called the threshold, and the resulting electrical signal is called an action potential. In this example, the action potential travels—a process known as propagation—along the axon from the initial segment found near the receptor to the axon terminals and into the synaptic end bulbs in the central nervous system (2 in Figure 12.3.1). When this signal reaches the end bulbs, it causes the release of a signaling molecule called a neurotransmitter.

This diagram shows the first step of the previous figure. A hand is placed under flowing water, causing a sensory receptor in the index finger to send a nerve impulse down the arm, to the spinal cord.
Figure 12.3.2 – The Sensory Input: Receptors in the skin sense the temperature of the water.

In the central nervous system (in this case, the spinal cord), the neurotransmitter diffuses across the short distance of the synapse and binds to a receptor protein of the target neuron. When the neurotransmitter binds to the receptor, the cell membrane of the target neuron changes its electrical state and a new graded potential begins. If that graded potential is strong enough to reach threshold, the second neuron generates an action potential at its initial segment f that graded potential is strong enough to reach threshold, the second neuron generates an action potential at its initial segment (3 in Figure 12.3.1). The target of this neuron is another neuron in the thalamus of the brain, the part of the CNS that acts as a relay for sensory information. At this synapse, neurotransmitter is released and binds to its receptor. The thalamus then sends the sensory information to the cerebral cortex, the outermost layer of gray matter in the brain, where conscious perception of that water temperature begins.

Within the cerebral cortex, information is processed among many neurons, integrating the stimulus of the water temperature with other sensory stimuli, as well as with your emotional state and memories. Finally, a plan is developed about what to do, whether that is to turn the temperature up, turn the whole shower off and go back to bed, or step into the shower. To do any of these things, the cerebral cortex has to send a command out to your body to move muscles.

A region of the cortex is specialized for sending signals down to the spinal cord for movement. The upper motor neuron starts in this region, called the precentral gyrus of the frontal cortex, and has an axon that extends all the way down the spinal cord. The upper motor neuron synapses in the spinal cord with a lower motor neuron, which directly stimulates muscle fibers to contract. In the manner described in the chapter on muscle tissue, an action potential travels along the motor neuron axon into the periphery. The lower motor neuron axon terminates on muscle fibers at the neuromuscular junction. Acetylcholine is the neurotransmitter released at this specialized synapse, and binding to receptors on the muscle cell membrane causes the muscle action potential to begin. When the lower motor neuron excites the muscle fiber, the muscle contracts (Figure 12.3.3). All of this occurs in a fraction of a second, but this story is the basis of how the nervous system functions.

This diagram shows the later steps of Figure 12.13. A hand is placed under flowing water. The axon of a motor neuron travels down the forearm and then branches as it reaches the hand. Each branch synapses with a different skeletal muscle in the hand. The synapse between the axon branches and the muscle is a neuromuscular junction. An impulse travelling down the motor neuron will cause the skeletal muscles to contract, resulting in muscle movement. In this case, the movement results in the person adjusting the faucet dials to change the temperature of the water.
Figure 12.3.3 – The Motor Response: On the basis of the sensory input and the integration in the CNS, a motor response is formulated and executed.

Career Connections – Neurophysiologist

There are many pathways to becoming a neurophysiologist. One path is to become a research scientist at an academic institution. A Bachelor’s degree will get you started, and for neurophysiology that might be in biology, psychology, computer science, engineering, or neuroscience. But the real specialization comes in graduate school. There are many different programs out there to study the nervous system, not just neuroscience itself. Most graduate programs are doctoral, and are usually considered five-year programs, with the first two years dedicated to course work and finding a research mentor, and the last three years dedicated to finding a research topic and pursuing that with a near single-mindedness. The research will usually result in a few publications in scientific journals, which will make up the bulk of a doctoral dissertation. After graduating with a Ph.D., researchers will go on to find specialized work called a postdoctoral fellowship within established labs. In this position, a researcher starts to establish their own research career with the hopes of finding an academic position at a research university.

Other options are available if you are interested in how the nervous system works. Especially for neurophysiology, a medical degree might be more suitable so you can learn about the clinical applications of neurophysiology. Biotechnology firms are eager to find motivated scientists ready to tackle the tough questions about how the nervous system works so that therapeutic chemicals can be tested on some of the most challenging disorders such as Alzheimer’s disease or Parkinson’s disease, or spinal cord injury.

Others with a medical degree and a specialization in neuroscience go on to work directly with patients, diagnosing and treating mental disorders. You can do this as a psychiatrist, a neuropsychologist, a neuroscience nurse, or a neurodiagnostic technician, among other possible career paths.

Chapter Review

Sensation starts with the activation of a sensory receptor, such as the thermoreceptor in the skin sensing the temperature of the water. The sensory receptor in the skin initiates an electrical signal that travels along a sensory axon within a nerve into the spinal cord, where it synapses with a neuron in the gray matter of the spinal cord. At the synapse the temperature information represented in that electrical signal is passed to the next neuron by a chemical signal (the neurotransmitter) that diffuses across the small gap of the synapse and initiates a new electrical signal. That signal travels through the sensory pathway to the brain, synapsing in the thalamus, and finally the cerebral cortex where conscious perception of the water temperature occurs. Following integration of that information with other cognitive processes and sensory information, the brain sends a command back down to the spinal cord to initiate a motor response by controlling a skeletal muscle. The motor pathway is composed of two cells, the upper motor neuron and the lower motor neuron. The upper motor neuron has its cell body in the cerebral cortex and synapses with the lower motor neuron in the gray matter of the spinal cord. The axon of the lower motor neuron extends into the periphery where it synapses with a skeletal muscle fiber at a neuromuscular junction.

Review Questions

Critical Thinking Questions

1. Suppose the thalamus were damaged at the area where the second sensory neuron synapsed with the third sensory neuron. Would you be able to consciously feel the water temperature? Why or why not?

2. Suppose the upper motor neuron were damaged. What symptoms would you expect?


action potential
change in voltage of a cell membrane in response to a stimulus that results in transmission of an electrical signal; unique to neurons and muscle fibers
cerebral cortex
outermost layer of gray matter in the brain, where conscious perception takes place
graded potential
change in the membrane potential that varies in size, depending on the size of the stimulus that elicits it
lower motor neuron
second neuron in the motor command pathway that is directly connected to the skeletal muscle
chemical signal that is released from the synaptic end bulb of a neuron to cause a change in the target cell
precentral gyrus of the frontal cortex
region of the cerebral cortex responsible for generating motor commands, where the upper motor neuron cell body is located
movement of an action potential along the length of an axon
region of the central nervous system that acts as a relay for sensory pathways
type of sensory receptor capable of transducing temperature stimuli into neural action potentials
membrane voltage at which an action potential is initiated
upper motor neuron
first neuron in the motor command pathway with its cell body in the cerebral cortex that synapses on the lower motor neuron in the spinal cord


Answers for Critical Thinking Questions

  1. If the thalamus were damaged at the site of synapsing between the second sensory neuron and the third sensory neuron, signals would not reach the cerebral cortex. This would result in a person not being able to detect the temperature information consciously.
  2. If the upper motor neuron were damaged, you would expect that someone would not be able to activate the lower motor neuron and then the muscle innervated by that lower motor neuron would not be able to move when brain signals asked for it to move. However, the lower motor neuron would be able to participate in.

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Anatomy & Physiology Copyright © 2019 by Lindsay M. Biga, Staci Bronson, Sierra Dawson, Amy Harwell, Robin Hopkins, Joel Kaufmann, Mike LeMaster, Philip Matern, Katie Morrison-Graham, Kristen Oja, Devon Quick, Jon Runyeon, OSU OERU, and OpenStax is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License, except where otherwise noted.