Skeletal muscle architecture is the structural property of whole muscles that dominates their function. This review describes the basic architectural properties of human upper and lower extremity muscles. The designs of various muscle groups in humans and other species are analyzed from the point of view of optimizing function. Muscle fiber arrangement and motor unit arrangement is discussed in terms of the control of movement. Finally, the ability of muscles to change their architecture in response to immobilization, eccentric exercise, and surgical tendon transfer is reviewed. Future integrative physiological studies will provide insights into the mechanisms by which such adaptations occur. It is likely that muscle fibers transduce both stress and strain and respond by modifying sarcomere number in a way more suited to the new biomechanical environment.

http://billnordt.com/COREANATOMYFUNCTION/FUNCTIONALANDCLINICALSIGNIFICANCE.pdf

Functional and clinical significance of skeletal muscle architecture.

This book is about the processing of information in face-to-face communication when a speaker makes both audible and visible information available to a perceiver. Both auditory and visual sources of information are evaluated and integrated to achieve speech perception. The evaluation of the information source provides information about the strength of alternative interpretations, rather than just all-or-none categorical information, as claimed by “categorical perception” theory. Information sources are evaluated independently; the integration process insures that the least ambiguous sources have the most influences on the judgment. Similar processes occur in a variety of other behaviors, ranging from personality judgments and categorization to sentence interpretation and decision making. The experimental results are consistent with a fuzzy logical model of perception, positing three operations in perceptual (primary) recognition: feature evaluation, feature integration, and pattern classification. Continuously valued features are first evaluated, then integrated and matched against prototype descriptions in memory; finally, an identification decision is made on the basis of the relative goodness-of-match of the stimulus information with the relevant prototype descriptions.

Speech Perception By Ear and Eye: A Paradigm for Psychological Inquiry

The terminal distribution of thalamic afferents in primate prefrontal cortex has never been examined in any detail. In the present study, WGA-HRP was injected into major subdivisions of the mediodorsal nucleus (MD) in the rhesus monkey in order to determine (1) The areal distribution of MD projections, (2) the layer (s) in which MD afferents terminate, (3) the tangential pattern of the MD axonal terminals, (4) the cells of origin of the reciprocal corticothalamic pathway, and (5) the degree of reciprocity between the corticothalamic and thalamocortical pathways in the different regions of the prefrontal cortex.



As expected on the basis of retrograde degeneration and transport studies, injections centered in the magnocellular (MDmc) subnucleus of MD labeled cells and terminals in the ventral and medial prefrontal cortex. Injections involving ventral MDmc labeled the more lateral of these areas (Walker's areas 11 and 12); injections of the dorsal MDmc labeled the ventromedial regions (areas 13 and 14). In contrast, injections involving mainly the lateral, parvicellular (MDpc) moiety labeled cells and terminals in dorsolateral and dorsomedial areas (Walker's 46, 9, and 8B). Area 8A was labeled most prominently when injections included the multiform portion of MD (MDmf) and area 10 had connections with anterior portions of MD. A dorsal-ventral topography for MDpc exists with dorsal MDpc labeling dorsal and dorsomedial prefrontal areas and ventral MDpc labeling dorsolateral prefrontal cortex. Our findings with respect to MD are consistent with a nucleus-to-field organization of its thalamocortical projection system.



Outside of the traditional boundaries of prefrontal cortex, lateral MD projections extended to the supplementary motor area (SMA) and the dorsal part of the anterior cingulate (AC) whereas the medial MD projection targeted the ventromedial cingulate cortex and spared SMA. In addition, a few labeled cells and sparse terminals were found in the inferior parietal lobule, the superior temporal sulcus, and the anterior part of the insula after injections that involved the medial part of MD.



Labeled terminals were invariably confined to layer IV and adjacent deep layer III. No terminal label was ever observed in layers I, II, superficial III, V, or VI in any part of the cerebral cortex following injections confined to any part of MD. The projection from MD to the PFC formed a disjunctive pattern of bands ranging from 0.3 to 1.3 mm, which were especially evident when injections were relatively small; when the injection involved a larger thalamic volume, the pattern of terminal labeling was somewhat more diffuse and tangentially extensive throughout layers III and IV. These data may indicate an interdigitation of the terminal fields originating from adjacent clusters of thalamic cells (Goldman-Rakic and Porrino: J. Comp. Neurol. 242:535–560, '85).



Analysis of retrograde transport in the PFC, SMA and AC revealed unexpected regional differences in the laminar origin of corticothalamic cells. In all prefrontal areas, labeled corticothalamic neurons were found mainly in the superficial part of layer VI with a few labeled cells situated also in the superficial part of layer V. In the supplementary motor area the distribution of cells was essentially bilaminar with the number of labeled cells in superficial V much more substantial than in PFC. Finally, in the anterior cingulate cortex, the labeled cells were confined to and stratified in layer VI with about equal density in its superficial and deep strata.



Regional differences were also apparent in relationships of retrogradely labeled cells and anterogradely labeled terminal fields. In prefrontal areas, fluctuations in the density of labeled cells paralleled changes in terminal field density. The anterior cingulate and supplementary motor cortex, however, contained high concentrations of labeled neurons but only sparse terminal label, indicating that the mediodorsal nucleus may have a different anatomical relationship with its “essential” target than with its “accessory” or “secondary” targets.

Mediodorsal nucleus: Areal, laminar, and tangential distribution of afferents and efferents in the frontal lobe of rhesus monkeys

Social dilemmas occur when the pursuit of self-interest by individuals in a group leads to less than optimal collective outcomes for everyone in the group. A critical assumption in the human sciences is that people's choices in such dilemmas are individualistic, selfish, and rational. Hence, cooperation in the support of group welfare will only occur if there are selfish incentives that convert the social dilemma into a nondilemma. In recent years, inclusive fitness theories have lent weight to such traditional views of rational selfishness on Darwinian grounds. To show that cooperation is based on selfish incentives, however, one must provide evidence that people do not cooperate without such incentives. In a series of experimental social dilemmas, subjects were instructed to make single, anonymous choices about whether or not to contribute money for a shared “bonus” that would be provided only if enough other people in the group also contributed their money. Noncontributors cited selfish reasons for their choices; contributors did not. If people are allowed to engage in discussion, they will contribute resources at high rates, frequently on irrational grounds, to promote group welfare. These findings are consistent with previous research on ingroup biasing effects that cannot be explained by “economic man” or “selfish gene” theories. An alternative explanation is that sociality was a primary factor shaping the evolution of Homo sapiens. The cognitive and affective mechanisms underlying such choices evolved under selection pressures on small groups for developing and maintaining group membership and for predicting and controlling the behavior of other group members. This sociality hypothesis organizes previously inexplicable and disparate phenomena in a Darwinian framework and makes novel predictions about human choice.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0140525X00025292

Selfishness examined: Cooperation in the absence of egoistic incentives.

The sections in this article are:


1
Kinematics and Muscle Activity
1.1
Hindlimb Locomotor Movements

1.2
Forelimb Locomotor Movements

1.3
Walking at Different Speeds, Slopes, and Directions

1.4
Interlimb Coordination

1.5
Other Stereotypic Movements




2
Stereotypic Movements in Spinal Animals
2.1
Stereotypic Movements after Complete Spinal Lesions

2.2
Stereotypic Movements after Partial Spinal Lesions

2.3
Pharmacology of Stereotypic Patterns




3
Central Generation of Stereotypic Patterns
3.1
Locomotion

3.2
Interneurons

3.3
Scratching and Paw Shake

3.4
Ontogeny of Stereotypic Movements

3.5
Central Pattern Generator(s)




4
Afferent Controls
4.1
Proprioceptive Control

4.2
Cutaneous Control

4.3
Mechanisms of Reflex Modulation




5
Supraspinal Control
5.1
Initiation of Locomotion

5.2
Posture and Corrections




6
Concluding Remarks

Neural Control of Stereotypic Limb Movements

The anatomy, architecture, and innervation patterns of the hamstring muscles, biceps femoris, and semitendinosus were examined in adult cats using microdissection and glycogen-depletion techniques. The biceps femoris muscle consists of two heads. The anterior head, which attaches mainly to the femur, is divided into two parts by the extramuscular branches of its nerve. The posterior head is innervated by a single nerve. Semitendinosus is composed of two heads, one proximal and one distal to a tendinosus inscription, each of which is separately innervated. The extramuscular branches of the nerves to these hamstring muscles thus partition them into innervation subvolumes termed parts. The available evidence suggests that each of the parts of these muscles so innervated is not equivalent to the collections of single motor units that have been described for ankle extensors as neuromuscular compartments. It is quite likely that each of the parts of the hamstring muscles may contain more than one neuromuscular compartment. Using chronically implanted EMG electrodes, the activation patterns of different parts of the hamstring muscles were analyzed during locomotion. The anterior and middle parts of biceps femoris are active during the early stance phase, probably producing hip extensor torque. The posterior part of biceps femoris and semi-tendinosus act most consistently as flexors, during the early swing phase, but also may function in synergy with hip, knee, and ankle joint extensors near the time of foot placement. Greater variability is found in the activity patterns of posterior biceps femoris and semitendinosus with respect to the kinematics of the step cycle than is observed for anterior and middle biceps femoris. It is suggested that this variation may reflect a larger role of sensory feedback in shaping the timing of activity in posterior biceps femoris and semitendinosus than in "nonarticular" muscles.

An anatomical and functional analysis of cat biceps femoris and semitendinosus muscles

The distribution of muscle fibers in single muscle units in cat lateral gastrocnemius (LG) muscle was analyzed using the method of glycogen depletion. Single, type FF motor units in LG were identified by stimulation of dissected ventral rootlets and then activated to produce depletion of glycogen in their innervated muscle fibers. Serial histological sections were made of the entire triceps surae muscles and then reacted for the demonstration of glycogen. Projected tracings of the sections were used to compare the distribution of glycogen depleted muscle fibers to the heads of the LG muscle. Results of analysis of single muscle units indicate that the muscle fibers innervated by single cat LG type FF motor units are distributed to the same regions of muscle which are innervated by primary branches of the nerve to the LG muscle. The single units are thus compartmentalized. These results support the hypothesis that each of the neuromuscular compartments of LG contains a unique population of motor units. It is suggested that compartmentalization of muscles about primary branches of their muscle nerves may from a major organizational principle in the design of skeletal muscles.

Compartmentalization of single muscle units in cat lateral gastrocnemius

The spatial and size distributions of motoneurons which supply the cat lateral gastrocnemius (LG) neuromuscular compartments were examined to determine their anatomical organization. Individual primary muscle nerve branches (PMNB) to LG were isolated by microdissection, cut, and soaked in horseradish peroxidase (HRP). As a control in each case, the entire contralateral lateral gastrocnemius-soleus (LG-S) nerve was similarly cut and soaked. Retrogradely labeled motoneurons were identified, their positions plotted, and their sizes measured on both sides of the cord. Results show that extensive overlap exists in the spatial distribution of motoneurons innervating different PMNBs. Labeled cells supplying each PMNB also vary considerably in their sizes. However, both a highly significant topography-like organization and a preferential size distribution are found between different groups of motoneurons. Neurons which supply proximal compartments occupy more rostral portions of the LG motor nucleus and are among the largest in the pool. Very few small motoneurons innervate proximal compartments. Neurons supplying more distal compartments are distributed in more caudal parts of the pool and contain both large and small cells in relatively equal numbers. If the large cells are alpha and the small cells gamma motoneurons, then proximal compartments are relatively poor in gamma innervation and presumably muscle spindles, and distal compartments are rich in fusimotor innervation.

Compartmentalization of the cat lateral gastrocnemius motor nucleus

Cat triceps surae motor nuclei are organized topologically.

The cytoarchitecture and thalamic afferents of cortical area 6 located on the anterior sigmoid gyrus were mapped and analyzed in the dog by means of cytoarchitectonic, horseradish peroxidase (HRP), and autoradiographic methods.



Cytoarchitectonically, area 6 consists of medial and lateral subdivisions that correspond, respectively, to areas 6aα and 6aβ in the cat. In the dog, area 6aα is characterized by a wide layer III, the merging of borders between layers III and V, the presence of small-to-medium-size pyramidal cells in layer V, and a pallisade arrangement of cells in layer VI. Area 6aβ appears more stratified, with a relatively acellular layer present between layers V and VI and the presence of large pyramidal cells in layer V. Neither area 6aα nor 6aβ contains a layer IV.



Data obtained from injections of HRP into areas 6aα or 6aβ revealed that labeled thalamic neurons were distributed in a longitudinal band extending from the rostral part of the ventral anterior nucelus (VA) through the caudal part of the mediodorsal nucleus (MD). Labeled cells were observed in the ventral and ventral medial thalamic nuclei as well as in several of the intralaminar nuclei including the central lateral, central medial, parafascicular, and centrum medianum nuclei. A few labeled cells were also located in the suprageniculate nucleus. The densest thalamic labeling was present in VA and MD following injections into area 6aα. Equivalent or even larger injections into area 6aβ resulted in much less thalamic labeling. The band of labeled cells also extended into the hypothalamus, zona incerta, amygdala, claustrum, periaqueductal gray of the midbrain, and the nucleus of Darkschewitsch.



Results from autoradiographic experiments showed that area 6 subdivisions receive a loosely organized topographic input from VA. Injections of tritiated amino acids were made into selected regions of VA and into the caudal part of MD, areas in which the largest numbers of HRP-labeled cells were located. Area 6aα receives afferents primarily from the rostromedial part of VA and the caudal part of MD while area 6aβ receives its principal input from the caudal and lateral parts of VA with minimal input from MD. Axons originating from VA terminate in both layers I and III of area 6 while those originating from the caudal part of MD terminate only in layer III.



The results of this study show that area 6 in the dog may be divided cytoarchitectonically into two distinct regions, each of which receives a characteristic pattern of thalamic inputs. The organization of these inputs, as well as those from other, nonthalamic subcortical areas, lends anatomical support for the functional division of area 6 into an electrophysiologically defined medial eye movement field and a lateral supplementary motor area.

Ophelia I. Weeks

Papers

An anatomical and functional analysis of cat biceps femoris and semitendinosus muscles

Compartmentalization of single muscle units in cat lateral gastrocnemius

Compartmentalization of the cat lateral gastrocnemius motor nucleus

Cat triceps surae motor nuclei are organized topologically.

Thalamic afferents to cytoarchitectonic subdivisions of area 6 on the anterior sigmoid gyrus of the dog: a retrograde and anterograde tracing study.