Human Anatomy & Physiology FIFTH EDITION Elaine N. Marieb PowerPoint ® Lecture Slide Presentation by Vince Austin Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Chapter 15 Neural Integration Part A

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Sensory Integration Survival depends upon sensation and perception Sensation is the awareness of changes in the internal and external environment Perception is the conscious interpretation of those stimuli

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Organization of the Somatosensory System Input comes from exteroceptors, proprioceptors, and interoceptors The three main levels of neural integration in the somatosensory system are: Receptor level – the sensor receptors Circuit level – ascending pathways Perceptual level – neuronal circuits in the cerebral cortex Figure 15.1

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Processing at the Receptor Level Receptor potential – a graded potential from a stimulated sensory receptor Generator potential – depolarization of the afferent fiber caused by a receptor that is a separate cell (e.g., hair cell of the ear’s hearing receptor) If the receptor potential is above threshold, an action potential is sent to the CNS Strength of stimulus is determined by the frequency of action potentials

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Adaptation of Sensory Receptors Adaptation occurs when sensory receptors are subjected to an unchanging stimulus Receptor membranes become less responsive Receptor potentials decline in frequency or stop Receptors responding to pressure, touch, and smell adapt quickly Receptors responding slowly include Merkel’s discs, Ruffini’s corpuscles, and interoceptors that respond to chemical levels in the blood

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Processing at the Circuit Level Chains of three neurons (1 st, 2 nd, and 3 rd order) conduct sensory impulses upward to the brain First-order neurons – soma reside in dorsal root or cranial ganglia, and conduct impulses from the skin to the spinal cord or brain stem Second-order neurons – soma reside in the dorsal horn of the spinal cord or medullary nuclei and transmit impulses to the thalamus or cerebellum Third-order neurons – located in the thalamus and conduct impulses to the somatosensory cortex of the cerebrum

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Main Ascending Pathways The central processes of fist-order neurons branch diffusely as they enter the spinal cord and medulla Some branches take part in spinal cord reflexes Others synapse with second-order neurons in the cord and medullary nuclei Pain fibers synapse with substantia gelatinosa neurons in the dorsal horn Fibers from touch and pressure receptors form collateral synapses with interneurons in the dorsal horns

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Three Ascending Pathways The nonspecific and specific ascending pathways send impulses to the sensory cortex These pathways are responsible for discriminative touch and conscious proprioception The spinocerebellar tracts send impulses to the cerebellum and do not contribute to sensory perception

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Specific and Posterior Spinocerebellar Tracts Specific ascending pathways within the fasciculus gracilis and fasciculus cuneatus tracts, and their continuation in the medial lemniscal tracts The posterior spinocerebellar tract Figure 15.2a

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Nonspecific Ascending Pathway Nonspecific pathway for pain, temperature, and crude touch within the lateral spinothalamic tract Figure 15.2b

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Processing at the Perceptual Level The thalamus projects fibers to: The somatosensory cortex Sensory association areas First one modality is sent, then those considering more than one The result is an internal, conscious image of the stimulus

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Main Aspects of Sensory Perception Perceptual detection – detecting that a stimulus has occurred and requires summation Magnitude – how much of a stimulus is acting Spatial discrimination – identifying the site or pattern of the stimulus Feature abstraction – used to identify a substance that has specific texture or shape Quality discrimination – the ability to identify submodalities of a sensation (e.g., sweet or sour tastes) Pattern recognition – ability to recognize patterns in stimuli (e.g., melody, familiar face)

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Motor Integration In the motor system: There are effectors (muscles) instead of sensory receptors The pathways are descending efferent circuits, instead of afferent ascending ones There is motor behavior instead of perception

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Levels of Motor Control The three levels of motor control are: Segmental level Projection level Programs/instructions level

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Levels of Motor Control Figure 15.3

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Segmental Level The segmental level is the lowest level of motor hierarchy It consists of segmental circuits of the spinal cord Its circuits control locomotion and specific, oft- repeated motor activity These circuits are called central pattern generators (CPGs)

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Projection Level The projection level consists of: Cortical motor areas that produce the direct (pyramidal) system Brain stem motor areas that oversee the indirect (mulitneuronal) system Helps control reflex and fixed-pattern activity and houses command neurons that modify the segmental apparatus

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Descending (Motor) Pathways Descending tracts deliver efferent impulses from the brain to the spinal cord, and are divided into two groups Direct pathways equivalent to the pyramidal tracts Indirect pathways, essentially all others Motor pathways involve two neurons (upper and lower)

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The Direct (Pyramidal) System Direct pathways originate with the pyramidal neurons in the precentral gyri Impulses are sent through the corticospinal tracts and synapse in the anterior horn Stimulation of anterior horn neurons activates skeletal muscles Figure 15.4a

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The Direct (Pyramidal) System Parts of the direct pathway, called corticobulbar tracts, innervate cranial nerve nuclei The direct pathway regulates fast and fine (skilled) movements Figure 15.4a

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Indirect (Extrapyramidal) System Includes the brain stem, motor nuclei, and all motor pathways not part of the pyramidal system This system includes the rubrospinal, vestibulospinal, reticulospinal, and tectospinal tracts These motor pathways are complex and multisynaptic, and regulate: Axial muscles that maintain balance and posture Muscles controlling coarse movements of the proximal portions of limbs Head, neck, and eye movement

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Extrapyramidal (Multineuronal) Pathways Reticular nuclei – maintain balance Vestibular nuclei – receive input from the equilibrium apparatus of the ear and from the cerebellum Vestibulospinal tracts – control the segmental apparatus during standing Figure 15.4b

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Extrapyramidal (Multineuronal) Pathways Red nuclei – control flexor muscles Superior colliculi and tectospinal tracts mediate head movements Figure 15.4b

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Programs and Instructions Level The program/instructional level integrates the sensory and motor systems This level is called the precommand area They are located in the cerebellum and basal nuclei Regulate precise start/stop movements and coordinate movements with posture Block unwanted movements and monitor muscle tone