Cardiac Muscle Tissue The cardiac muscle cells are striated and are joined end   to   end,   resulting   in   a   complex   network   of interlocking   cells   (fig.   1-11).   Cardiac   muscles   are involuntary muscles and are located only in the heart. These   tissues   are   responsible   for   pumping   blood through  the  heart  chambers  and  into  certain  blood vessels. NERVE TISSUE Nerve  tissue  is  the  most  complex  tissue  in  the body. It is the substance of the brain, spinal cord, and nerves.   Nerve   tissue   requires   more   oxygen   and nutrients than any other body tissue. The basic cell of the nerve tissue is the  neuron  (fig. 1-12). This highly specialized  cell  receives  stimuli  from,  and  conducts impulses to, all parts of the body. ORGANS LEARNING  OBJECTIVE: Recall    how organs and body systems are composed of two or more kinds of tissue that perform specialized functions within the body. As a group of similar cells forms tissues, two or more kinds of tissues grouped together and performing specialized functions constitute an organ. Organs are grouped together to form systems (such as the urinary system, composed of the kidneys, ureters, bladder, and urethra). THE SKELETAL SYSTEM LEARNING  OBJECTIVE: Identify   the parts of bone and their functions. The skeleton, the bony framework of the body, is composed  of  206  bones  (fig.  1-13).  It  supports  and gives  shape  to  the  body;  protects  vital  organs;  and provides sites of attachment for tendons, muscles, and ligaments. The skeletal bones are joined members that make muscle movement possible. ANATOMY OF BONES Osteology  is  the  study  of  the  structure  of  bone. Bone is made up of inorganic mineral salts (calcium and   phosphorus   being   the   most   prevalent)   and   an organic substance called  ossein. If human bones were soaked in dilute acid until all inorganic mineral salts were  washed  out,  all  that  would  remain  would  be  a flexible piece of tissue that could be easily bent and twisted. Inorganic mineral salts give bone its strength and hardness. Bone consists of a hard outer shell, called compact bone,   and   an   inner   spongy,   porous   portion,   called cancellous tissue (fig. 1-14). In the center of the bone is   the   medullary  canal,   which   contains   marrow. There are two types of marrow, red and yellow. Yellow marrow  is  ordinary  bone  marrow  in  which  fat  cells predominate. It is found in the medullary canals and cancellous tissue of long bones. Red marrow is one of the  manufacturing  centers  of  red  blood  cells  and  is found   in   the   articular   ends   of   long   bones   and   in cancellous tissue. At the ends of the long bones is a smooth, glossy tissue that forms the joint surfaces. This tissue is called articular  cartilage   because  it  articulates  (or  joins) with,   fits   into,   or   moves   in   contact   with   similar surfaces   of   other   bones.   The   thin   outer   membrane surrounding  the  bone  is  called  the   periosteum.  An important   function   of   the   periosteum   is   to   supply nourishment to the bone. Capillaries and blood vessels run   through   the   periosteum   and   dip   into   the   bone surface,  supplying  it  with  blood  and  nutrients.  The 1-6 HM3F0112 AXON DENDRITES CELL BODY Figure 1-12.—Neuron. HM3F0111 Figure 1-11.—Cardiac muscle tissue.