Chapter 15 Neural Integration

•Specialized to respond to changes in environment (stimuli) •Activation results in graded potentials that trigger nerve impulses •Sensation (awareness of stimulus) and perception (interpretation of meaning of stimulus) occur in brain

Sensory recpetors represent the interferance between the nervous system and the internal and external environments. a sensory receptor detects an arriving stimulus and translates it into an action potiental that can be conducted to the CNS. This translation process is called transduction. if tansduction does not occur, the stimulus does not exist.

the area monitored by a single recpetor cell is its receptive field. whenever a srong sufficiently stimulus arrives in the receptive field, the CNS recieves the information "stimulus arrivng at receptor X". The larger the recpetive field, the poorer you ability to localize a stimulus. ex: page 496

Look on oage 496-497

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•Phasic (fast-adapting) receptors signal beginning or end of stimulus –Examples - receptors for pressure, touch, and smell
-normally inactive until a change occurs in the condition they are mintoring

•Tonic receptors adapt slowly or not at all –Examples - nociceptors and most proprioceptors
-always active, when the stimulus increases or decreases, the rate of action potential generation acts accordingly

The receptor repsonds strongly at first, but thereafter its activity gradually declines, in part because the size of the generator potential gradually decreases. this respnse is characteristic of phasic receptor, which are hence also called fast-adapting receptors. ex: temperature receptors (thermoreceptors) are phasic receptor; you seldom notice the room temperature unless it changes suddenly.

tonic recepors show little peripheral adaption and so are called slow-adpating receptors. ex: pain receptors (nociceptors) are slow-adapting receptors, which is one reason why pain sensations remind you of an injury long after the intial damage has occured.

-Pain receptors, or nociceptors, are especially common in the superficial portions of the skin, in joint capsules,and around the walls of blood vessels.
-Free nerve endings with large receptive fields
-Sensitive to extemes of temperature, mechanical damage, and dissolved chemicals, such as chemicals released from damaged cells

-Mylinated Type A fibers carry sensations of fast pain or prickling pain.
-Slower, Type C fibers carry sensations of slow pain, or burning and aching

•Thermoreceptors –Cold receptors (10–40ºC); in superficial dermis –Heat receptors (32–48ºC); in deeper dermis –Outside those temperature ranges à nociceptors activated à

- free nerve ending located in the dermis, in skeletal muscle, in liver, and hypothalmus.
-phasic recepotrs

Are senstive to stimuli that disort their plasma membrance

1. Tactile receptors provide closely related sensations of touch, pressure, and virbrations

2. Baroreceptors detect pressure changed in the walls of blood vessles and in portions of the digestive, reproductive, and urinary tracts.

3. Proprioceptors monitor postions of joints and skeletal muscles. they are the most structurally and functionally complex of the general sensory receptors.

Proprioceptors monitor the postions of joints, the tension in tendons and ligaments, and the state of muscular contraction

Muscles Spindles. Muscle spindles monitor skeletal muscle length and trigger reflexes

Golgi tendon organs. Dendrites branch repeatedly and wind around the densly packed collagen fibers of the tendon. Receptor is stimalted by tension in the tendon; they monitor the external tension developed during muscle contaction.

Receptors in Joint Capsules: joint capsules are richly innervated by free nerve ending that detect pressure, tension, and movement of the joint.

•First-order sensory neurons
-a sensory nueron that delivers sensations to the CNS.
-the cell body of the sensory nueron is located in a dorsal root ganglion or cranial nerve ganglion
•Second-order sensory neurons -in the CNS, the axon of that senory nueron synapses on an internueron known as the second-order sensory neuron
-located in the spinal cord or brain stem •Third-order sensory neurons –Conduct impulses from thalamus to the somatosensory cortex (perceptual level)

1. General sensory receptors
2.Sensory pathways
3.sensory processing centers in the brain

–Pain from one body region perceived from different region –Visceral and somatic pain fibers travel in same nerves; brain assumes stimulus from common (somatic) region •E.g., left arm pain during heart attack

The sensory and motor homunculus are mapped out diagrams of sensory or motor cortexs.

the proportions are very different from those of any individual because the are of the sensory and motor cortexs devoted to a particular body region is porportional to the number of sensory and motor receptors it contains.