The Coordination of Muscular, Skeletal, and Nervous Systems for Movement

Integration of Body Systems

Describe how the muscular, skeletal, and nervous systems work together to produce movement. Include a description of the structure that physically links the muscular system with the skeletal system and how the tension produced in the muscles translates into movement between bones.

If you were to lift your leg when you were walking, your muscular, skeletal, and nervous system all need to work together to produce that specific movement. This all starts in the cerebrum, which creates an impulse that says “your right leg needs to lift up and take a step forward when you walk.

” The cerebrum controls muscle movement and motor functions. This impulse that is generated travels from one neuron to another, and another, and so on. At each neuron, the impulse travels down the presynaptic neuron’s axon to the axon terminal, and then onto the postsynaptic neuron. Then, the impulse travels through the thalamus, down the spinal cord, and to the peripheral nerves in the right leg.

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The impulse switches from the central nervous system (CNS) to the peripheral nervous system (PNS) when the impulse crosses from the spinal nerves to the peripheral nerves in the right leg.

Next, the nerves in the right leg stimulate the body’s muscular system. When the nerves surrounding the quadriceps muscles in the right leg (rectusfemoris, vastusmedialis (medial), and vastuslateralis (lateral) are stimulated, it causes the muscle to contract over the femur. The quadriceps muscles basically contract at two points, or two joints of the skeletal system for that matter.

The joint that connects the femur to the pelvis is a ball-and-socket joint, which allows it to move in a multiaxial direction. On the other hand, the joint that connects the femur to the tibia is a hinge joint, which allows it to move in a uniaxial direction. These joints of the skeletal system pull on the quadriceps muscle, allowing it to contract, and result in your right leg moving forward to take a step. In conclusion, the overall companionship of the nervous system (impulse), muscular system (contractions), and the skeletal system (joints) make the miracle of walking possible!

Form and Function: Explain:

How a muscle fiber is structurally organized to produce tension.

Muscle fibers are very intricately organized. The layers of a muscle fiber from superficial to deep are: the endomysium, sarcolemma, and the sarcoplasm. Each of these layers also contains other crucial parts of the muscle fiber. For example, the endomysium contains capillaries, myosatellite cells, and the axon of a neuron. Also, the sarcoplasm holds the nucleus, mitochondrion, and a plethora of myofibrils in place. For the sake of time, we will mainly be focusing on the myofibrils. Now, each muscle fiber contains a large number of myofibrils, as I mentioned earlier. These myofibrils contain the protein filaments actin (located in thin filaments), and myosin (located in thick filaments). If a muscle is stimulated by the nervous system to contract, it needs to first create tension. So, the proteins actin and myosin generate enough action potential to slide past one another in the “zone of overlap” to produce tension. Since there are a large number of myofibrils in a single muscle fiber, there are thousands of these reactions happening at the same time, which eventually results in so much tension that the muscle contracts.

How bone matrix can provide flexibility and compressive strength at the same time.

Bone matrix is composed of calcium phosphate, calcium hydroxide, and collagen fibers. Both calcium hydroxide and calcium phosphate interact to “form crystals of hydroxyapatite,” (ITC). Hydroxyapatite provides resistance to compression. This is due to the crystals being extremely durable and they can withstand high amounts of compressive force. Hydroxyapatite also creates the bones’ calcified characteristic, and also provides flexibility to the bone through the incorporation of other nutrients through chemical reactions. On the other hand, collagen fibers give bones their strength. The book states that “when subjected to tension, collagen fibers are harder than steel,” (ITC). However, these fibers are also flexible and can make the bones withstand vigorous amounts of twisting and turning as well. In conclusion, hydroxyapatite (product of calcium phosphate and calcium hydroxide) and collagen fibers provide flexibility and compressive strength simultaneously to the bone matrix.

How joint structure affects strength (resistance to dislocation) and flexibility (type and range of motion).

Joint structure can affect strength and flexibility of various body parts in many different situations. But first, I should explain the common types of joints found in our bodies. There are classifications of joints; synarthrotic joints (immovable), amphiarthrotic joints (slightly moveable), and diarthrotic (freely moveable). These three major classifications of joints are grouped by their range of motion, but also by their strength. For example, there are six classes of synovial joints (diarthotic); hinge, condylar, saddle, plane, pivot, and a ball-and-socket joint. Plane joints are barely moveable, and create a sliding movement when stimulated.

Saddle joints fit together like a saddle and a person (as the name suggests), and they create biaxial movement when stimulated. Condylar joints almost look like a hydraulic press machine, and move in a biaxial way when stimulated. Pivot joints are able to rotate, and cannot move any other way. Hinge joints only allow monoaxial movement, and move just like a hinge on a door. Plane joints are almost immoveable, and can only slide a small amount back and forth on the connecting bone. Lastly, ball-and-socket joints are the most mobile synovial joints, and are able to rotate, and they also produce triaxial movement. Now, the structures of these types of joints are very different, and they effect the strength and flexibility of each joint and its movement. For example, a plane joint would be stronger than a ball-and socket joint. However, a ball-and socket joint would be more flexible than a plane joint. Let me explain how I came up with this answer.

A plane joint, such as the clavicle connecting to the sternum, is almost immoveable. This means that since it only generates a sliding motion, and it is it would be extremely difficult (or resistant) to dislocation, and that there would be almost no flexibility and a minute ROM (range of motion). On the other hand, a ball-and- socket joint, such as the shoulder joint, is triaxial. This means that it can move in almost every direction, and it is able to perform circumduction. However, having this large capability of movement comes with a large risk of dislocation, which is very common with this specific joint. This joint also has a larger ROM because it is so freely moveable, and it is much more flexible than almost any other synovial joint.

Cells are the foundations of structure and function: Explain how bone cells work together to produce, repair, and remodel bone matrix.

Bone cells such as osteogenic cells, osteocytes, osteoblasts, and osteoclasts, work together to produce, repair and remodel bone matrix. Osteogenic cells are produced at the start of bone formation. They are “stem cells whose divisions produce osteoblasts,” (Fundamentals of Anatomy&Physiology, 11e. 184). Osteoblasts are “immature bone cells that secrete organic components of matrix,” (Fundamentals of Anatomy&Physiology, 11e. 184). Osteocytes are “mature bone cells that maintain bone matrix, (Fundamentals of Anatomy&Physiology, 11e. 184). And lastly, osteoclasts are “multinucleate cells that secrete acids and enzymes to dissolve bone matrix,” (Fundamentals of Anatomy&Physiology, 11e. 184). All of these definitions of cells are pretty self-explanatory as far as the process of producing, repairing, and remodeling bone matrix.

However, I feel that it would be better to explain these processes through an example. So, let’s say you are a nurse in the NICU unit and a child is born with a broken leg. While the child was in the womb, the osteogenic cells of the bone matrix set the foundation for their constantly developing bones. Once the child was born, their left leg was broken due to the stress and pressure of childbirth. Then, once they are out of the womb, their osteogenic cells divide and produce osteoblasts. These osteoblasts secrete nutrients and chemicals to the cite of the injured bone to keep it from deteriorating, and to produce the bone matrix. Then, the osteocytes step in and repair the bone matrix at the injured cite, and also maintain it after the break has healed. Lastly, once the break has completely healed, the osteoclasts dissolve the old bone matrix to create (remodel) new bone matrix in order to keep the bones healthy and strong as the child grows.

Information flow between cells coordinates bodily functions:

Explain how the nervous system communicates with skeletal muscles to produce movement. Include how the electrical signal is transformed into the mechanical events of muscle contraction.

When you touch a hot stove with your hand, your nervous system communicates with your skeletal muscles to move your hand away. When your hand touches a hot stove, your nerves in your hand send a message from through the spinal cord, to the thalamus, and then to the cerebral cortex, where it registers that there is pain in your right hand. Then, the message translates and changes so that you pull your hand away from the pain.

This NEW message travels from the cerebral cortex, through the thalamus, then down the spinal cord, and to the peripheral nerves in the affected hand. I should also mention that the signal crosses over from the central nervous system to the peripheral nervous system once the impulse travels from the spinal cord to the peripheral nerves in the affected hand. This electrical signal in the peripheral nerves stimulate the hand muscles to pull the hand away from the painful stimuli. The electrical signal also stimulates the skeletal muscles of the biceps femoris to lift the hand away from the hot stove.

Explain how the nervous system instructs a skeletal muscle to produce more or less tension as needed to perform different types of work.

The nervous system instructs a skeletal muscle to produce more tension when you are lifting a fifty-pound dumbbell, and less tension when you are lifting a dish from the dishwasher to put it in the kitchen cabinet. First, let me explain how your brain registers each of these events. Your brain’s motor cortex, located in the frontal lobe, controls voluntary muscle movement. Each time you need to move, your motor cortex sends an impulse to your thalamus, which works together with the motor cortex to process this impulse. Then, the impulse travels from the thalamus, through the cerebral cortex, down the spinal cord, and to the intended skeletal muscle to produce more or less tension.

Depending on how much weight you are lifting in this situation, the nervous system will tell the intended skeletal muscle to produce more or less tension. So, when you are lifting a fifty-pound dumbbell, your motor cortex sends an impulse to the thalamus, then it travels down the spinal cord to the peripheral nerves in the biceps femoris muscle. Your cerebral cortex registers that you are lifting an extremely heavy object, so it sends an impulse through the same pathway, which stimulates the skeletal muscle (biceps femoris) to produce more tension than usually needed to lift a normal object. The impulse also travels to the nerves in the hand, which stimulates the skeletal muscles in that area to grasp the dumbbell and lift it. On the other hand, when you are lifting a dish from the dishwasher to put it in the kitchen cabinet, the impulse goes through the same pathway, and the cerebral cortex registers that you do not need to generate a large amount of muscle tension. So, the skeletal muscle in the arm (biceps femoris) is stimulated by the peripheral nerves in that area, but it produces rarely any tension since it is such a light object. It also stimulates the skeletal muscles in the hand to grasp the plate in order to place it in the kitchen cabinet.