Chapter 8 Summary & Outline

Sensory Processing

Sensory Receptor Organs Detect Energy or Substances

• A sensory system furnishes selected information to the brain about internal and external events and conditions. It captures and processes only information that is significant for the particular organism. Review Table 8.1

Study questions: 1 | 2 | 3 | 4 | 5 | 6 | 7

What Type of Stimulus Was That?

• Some stimuli are detected readily by some species but have no effect on species that lack the necessary sensory receptor organs.

Study questions: 8 | 9 | 10

Sensory Processing Begins in Receptor Cells

• Some receptors are simple free nerve endings, but most include cells that are specialized to transduce particular kinds of energy. Review Figures 8.4 and 8.13, Web Activity 8.1
• Energy is transduced at sensory receptors by the production of a generator potential that stimulates the sensory neurons. Review Figure 8.5

Study questions: 11 | 12 | 13

Sensory Information Processing Is Selective and Analytical

• Coding translates receptor information into patterns of neural activity. The frequency and pattern of action potentials signal the intensity and type of stimulus encountered. Review Figure 8.6
• In adaptation, the rate of action potentials progressively decreases as the same stimulation is maintained. This decline is slow in the case of tonic receptors but rapid for phasic receptors. Adaptation protects the nervous system from redundant stimulation. Review Figure 8.7
• Other mechanisms of information suppression include accessory structures that reduce the level of sensory input, and descending pathways that modulate sensory information centrally.
• The succession of levels in a sensory pathway allows for increasingly elaborate kinds of processing. Review Figure 8.8
• The receptive field of a neuron is the region in space where a stimulus will change the firing of that cell. The receptive fields of neurons may be very different at successive levels of the sensory pathway. Review Figure 8.9, Web Activity 8.2
• Attention is the temporary enhancement of certain sensory messages during particular states. Attention is modulated at higher levels of the sensory pathway. Review Figure 8.12

Study questions: 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39

Touch: Many Sensations Blended Together

Skin Is a Complex Organ That Contains a Variety of Sensory Receptors

• The skin contains several distinct types of receptors that have specific sensitivities and use large, myelinated axons to transmit information rapidly. Inputs from the skin course through a distinct spinal pathway, the dorsal column system. Review Figure 8.15, Web Activity 8.3
• Merkel’s discs and Meissner’s corpuscles detect fine touch, while Pacinian corpuscles and Ruffini’s endings respond to vibration and stretch, providing information about textures. Review Table 8.2

Study questions: 40 | 41 | 42

The Dorsal Column System Carries Somatosensory Information from the Skin to the Brain

• The surface of the body is represented at each level of the somatosensory system, and at the level of the cerebral cortex there are multiple maps of the body surface. Review Figure 8.16
• Touch information enters the spinal cord and ascends the dorsal column system to the medulla, synapsing on neurons in the dorsal column nuclei. These neurons in turn send their axons across the midline and to the thalamus.

Study questions: 43 | 44 | 45 | 46 | 47

Pain: An Unpleasant but Adaptive Experience

Human Pain Can Be Measured

• Pain guides adaptive behavior by providing indications of harmful stimuli. Pain is a complex state that is strongly influenced by cultural factors and emotional state.

Study questions: 48 | 49

A Specific Pathway Transmits Pain Information

• Free nerve endings detect mechanical damage or temperature changes because they have specialized receptor proteins that detect these conditions (such as transient receptor potential vanilloid 1 [TRPV1], which detects heat and is activated by chili peppers), opening up ion channels to trigger action potentials. Some peripheral pain fibers have fairly large, myelinated axons to transmit sharp pain rapidly; others use small, unmyelinated axons to transmit dull, aching pain after injury. Review Figure 8.22
• Pain, temperature, and itch information enters the spinal cord, crosses the midline, and ascends through the anterolateral (spinothalamic) system to the brain. Review Figure 8.23, Web Activity 8.4

Study questions: 50 | 51 | 52 | 53 | 54 | 55 | 56 | 57 | 58 | 59

Pain Control Can Be Difficult

• Pain sensation is subject to many controlling or modulating conditions, including circuitry within the brain and spinal cord that employs opioid synapses. One component in the modulation of pain is made up of the descending pathways arising in the brain that inhibit incoming neural activity at synapses within the spinal cord. Review Figure 8.25, Web Activity 8.5
• Pain control has been achieved by the administration of drugs (including placebos), electrical and mechanical stimulation of the skin, acupuncture, and surgery, among other methods. Review Table 8.3

Study questions: 60 | 61 | 62 | 63 | 64 | 65 | 66 | 67 | 68