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The number of vertebrae in a region can vary but overall the number remains the same. In a human vertebral column, there are normally 33 vertebrae. [3] The upper 24 pre-sacral vertebrae are articulating and separated from each other by intervertebral discs, and the lower nine are fused in adults, five in the sacrum and four in the coccyx, or tailbone.
A section of the human vertebral column, showing multiple vertebrae in a left posterolateral view. Each vertebra (pl.: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...
Sectional organization of spinal cord. The spinal cord is the main pathway for information connecting the brain and peripheral nervous system. [3] [4] Much shorter than its protecting spinal column, the human spinal cord originates in the brainstem, passes through the foramen magnum, and continues through to the conus medullaris near the second lumbar vertebra before terminating in a fibrous ...
Skeletal muscle. Skeletal muscle (commonly referred to as muscle) is one of the three types of vertebrate muscle tissue, the other being cardiac muscle and smooth muscle. They are part of the voluntary muscular system [1] and typically are attached by tendons to bones of a skeleton. [2][3] The skeletal muscle cells are much longer than in the ...
A muscle cell, also known as a myocyte, is a mature contractile cell in the muscle of an animal. [1] In humans and other vertebrates there are three types: skeletal, smooth, and cardiac (cardiomyocytes). [2] A skeletal muscle cell is long and threadlike with many nuclei and is called a muscle fiber. [3] Muscle cells develop from embryonic ...
Cervical vertebrae. Position of human cervical vertebrae (shown in red). It consists of 7 bones, from top to bottom, C1, C2, C3, C4, C5, C6, and C7. In tetrapods, cervical vertebrae (sg.: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal ...
A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. [ 1 ][ 2 ] These are grouped into the corresponding cervical, thoracic, lumbar, sacral and coccygeal regions of the spine. [ 1 ]
A smooth-muscle cell is a spindle-shaped myocyte with a wide middle and tapering ends, and a single nucleus. Like striated muscle, smooth muscle can tense and relax. In the relaxed state, each cell is 30–200 micrometers in length, some thousands of times shorter than a skeletal muscle cell. [1]