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Summation, which includes both spatial summation and temporal summation, is the process that determines whether or not an action potential will be generated by the combined effects of excitatory and inhibitory signals, both from multiple simultaneous inputs (spatial summation), and from repeated inputs (temporal summation).
In homozygous cases, where individuals have two rare HOXD13 alleles, they experience finger fusions, as well as more severe symptoms such as significantly shortened hand and toe bones, [11] and the big toe can be noticeably long and angled inward. [9] Additionally, the metacarpal bones (hand) may take on the shape of carpal bones (wrist).
For example (Fig. 1), in a basic neural circuit with two input neurons—A and B—that have excitatory synaptic terminals converging on a single output neuron (C), if each input neuron's EPSP is sub-threshold for an action potential at C, then C cannot fire unless the two inputs from A and B are temporally close.
In radiology, the Terry-Thomas sign is a scapholunate ligament dissociation on an anteroposterior view of the wrist. [1] [2] Most commonly a result of a fall on the outstretched hand (), the scapholunate ligament ruptures resulting in separation of the lunate and scaphoid bones.
The hand of a person with Greig cephalopolysyndactyly with syndactyly of several digits. Syndactyly can be simple or complex. [2] In simple syndactyly, adjacent fingers or toes are joined by soft tissue. In complex syndactyly, the bones of adjacent digits are fused. The kangaroo exhibits complex syndactyly. Syndactyly can be complete or incomplete.
These joints are of the condyloid kind, formed by the reception of the rounded heads of the metacarpal bones into shallow cavities on the proximal ends of the proximal phalanges. [1] Being condyloid, they allow the movements of flexion , extension , abduction , adduction and circumduction (see anatomical terms of motion ) at the joint.
Hamate bone of the left hand. Hamulus shown in red. The hook of hamate (Latin: hamulus) is found at the proximal, ulnar side of the hamate bone. The hook is a curved, hook-like process that projects 1–2 mm distally and radially. [5] The ulnar nerve hooks around the hook of hamate as it crosses towards the medial side of hand.
The greater the value of the length constant, the further the potential will travel. A large length constant can contribute to spatial summation—the electrical addition of one potential with potentials from adjacent areas of the cell. The length constant can be defined as: = +