Overview for unit 3

There are 206 bones in an adult body, these bones make up our skeleton. The skeleton serves many purposes. It supports the body, protects the soft body parts, it produces blood cells, it stores minerals and fats, and it permits flexible body movement. One of the bones is the long bone. The main portion of this bone is called diaphysis. It has a large medullary cavity that is composed of compact bone. Compact bone is composed of tubular units called osteons and is an organized unit. The compact bone is lined with a vascular membrane and is filled with yellow bone marrow that stores fat. The end of the large bone is called the epiphyses. This area is where the blood cells are made. It contains red bone marrow and is lined with articular cartilage which also is in the joints. The long bone is covered in periosteum which a type of connective tissue. Spongy bone is also in the long bone, it is unorganized, contains many thin plates, and is separated with unequal spaces. Spongy bone is designed for strength. The spaces are filled with red bone marrow. There is also cartilage in bones. Cartilage is flexible because it contains collagenous and elastic fibers. The matrix is a gel-like substance. Cartilage does not contain blood vessels. Hayline cartilage is firm and flexible. Fibrocartilage contains wide rows of thick collagen fibers. Elastic cartilage contains mostly elastin fibers. Fibrous connective tissue makes ligaments connect bone to bone.
There are three types of cells involved with bone growth, remodeling, and repair. They are osteoblasts, osteocytes, and osteoclasts. Osteoblasts are bone forming cells that promote the deposition of calcium salts into the matrix. Osteocytes are mature bone cells these maintain the structure of the bone. Lastly are osteoclasts which are bone absorbing cells. These break down the bone and they assist in depositing calcium and phosphates in the blood.
The formation of bone is called ossification. Intermembranous ossification is when bones develop between sheets of fibrous connective tissue. This is usually a flat bone like the skull bone. Endochondral ossification is when bone replaces the cartilaginous models of the bones. This is the process of bone growth and development. First there is the cartilage model which is in the shape of the future bones. The next step is the bone collar, and to the primary ossification center. The medullary cavity and the secondary ossification sites is the next step. The last step is the epiphyseal plate or the growth plate. The final size of the bones is determined when the plates are closed. There are several hormones involved with bone growth. Hormones are chemical messenger that is produced by one part of the body which acts on a different part of the body. Growth hormones stimulate the growth of the epiphyseal plate.
Each year 18 percent of our bones are recycled this is what keeps bones strong. Bone recycling regulates the amount of calcium in the blood. The parathyroid hormone accelerates one recycling which increases the blood calcium level. The calcitonin hormone acts the complete opposite. This is how bones respond to stress.
There are four steps of bone repair. The first step is hematoma which is when injury occurs. Fibrocartilaginous callus is when the tissue repair begins. Next is the bony callus and lastly the remodeling is finished.
The axial skeleton is in the midline of the body. It contains the skull, the hyoid bone, the vertebral column, and the rib cage. The skull is formed by the cranium and the facial bones. The cranium is composed of eight bones and protects the brain. In it are the sinuses, the frontal lobe forms the forehead, the parietal lobe is on the sides, the occipital lobe forms the base of the skull. The foramen magnum is where the spinal cord passes through and becomes the brain stem. The temporal lobe is where the opening leads to the middle ear. Next I will go over some of the bones in the skull. The sphenoid bone is shaped like a bat and all of the other bones articulate with it. This also helps with the forming of the eye sockets. The ethmoid bone is in front of the sphenoid which helps form the orbits and nasal septum. The eye sockets are called the orbits because we can rotate our eyes. The mandible is the lower jaw and is the only movable portion of the skull. The maxillae is the upper jaw. The zygomatic bones are the cheekbones. The hyoid bone is the only bone that doesn’t articulate with another bone. It is attached to the temporal bones and the larynx membrane or the voice box.
The vertebral column has 33 vertebrae. There are two types of vertebrae. The first one is the atlas which is what holds the head up. It also allows the head to tilt from side to side. The second one is the axis which allows the head to rotate to a certain degree. Between the vertebrae are the intervertebral disks. These disks are composed of fibrocartilage which acts as padding. These help prevent the vertebrae from grinding against each other and they also absorb shock from our movements. The disks also allow the vertebrae to move as we bend. Scoliosis is an abnormal curvature of the spinal cord.
The rib cage is composed of the thoracic vertebrae, the ribs, cartilages, and the sternum. It is also part to of the axial skeleton. It protects the heart and the lungs. The ribs are flattened bones. There are 12 pairs of ribs that all connect to the thoracic vertebrae. The upper seven pairs connect to the sternum by the costal cartilage. These are considered the true ribs. The next three pairs are considered false ribs. They connect to the sternum by the common cartilage. The last two pairs of ribs are floating ribs because they do not attach to the sternum. The sternum is located in the midline of the body. It is the flat breast bone that is shaped like a knife. The sternum is composed of three bones. The first bone is the manubrium is the handle, the second one is the body or the blade, and the last one is the xiphoid process or the point of the blade. The manubrium joins the body of the sternum at an angle. The sternum occurs at the second rib and allows the ribs to be counted. The xiphoid process is where the diaphragm is attached.
The appendicular skeleton is composed of the pectoral bones and the pelvic bones. The pectoral bones include the scapula or shoulder blade and the clavicle or the collar bone. The glenoid cavity is part of the scapula it allows the arm to move in many directions. The humerus is the long bone in the arm. The pelvic bone has two large coxal bones. The pelvis bears the weight of the body, it also protects the organs within the pelvic cavity, and is where the legs are attached. The femur is the longest and the strongest bone in the body.
Bones are joined at the joints and are called the synovial. Many of the joints are immovable. The synovial joint is a joint that has a cavity filled with the synovial fluid. This fluid is a lubricant for the joints.
The next section is overview the muscular system.
All the muscles in the body contract which makes the body parts move. There are three types of muscles smooth, cardiac, and skeletal muscles. The cells with in the muscles are called muscle fibers. Smooth muscle is located in the walls of the hollow internal organs. The contractions are involuntary and they don’t get tired easily. They also sustain longer contractions. Cardiac muscles form the walls of the heart. The muscle fibers interlock at intercalated disks. These contractions are involuntary and are rhythmical. The muscles relax completely in between contractions. The last kind is skeletal muscles. These muscle fibers are tubular. Their contractions are voluntary and can last a very long time.
The skeletal muscles have many functions some of them are: they support the body, they make bones move, they help maintain a constant body temperature, they help protect internal organs, they stabilize joints, and the contractions assist with the movement in the cardiovascular and lymphatic vessels. The skeletal muscles work in pairs and they only pull, they never push. Skeletal muscles can categorized into size, shape, location, direction of the muscle fibers, attachment, number of attachment, and action. The following are the components of muscle fiber contraction. The muscle fiber is a cell that contains the normal cellular components. It has a plasma membrane which is called the sarcolemma. The cytoplasm part is called the sarcoplasm. The endoplasmic reticulum area is the sarcoplasmic reticulum. Myofibrilis are also part of a muscle fiber. Sarcomers contain two types of proteins myosin and actin. The thick filaments are composed of several hundred molecules of myosin. Each filament is shaped like a golf club that ends with a cross bridge. Actin are made up of thin filaments. The thin filaments are composed of two interwinding strands of actin. A sliding filament is when an actin filament moves in relation to the myosin filaments.
Muscle fibers are stimulated to contract by the motor neurons. The neuromuscular junction is the area where the axon motor neurons are stimulated. The axon terminals contain synaptic vesicles are filled with neurotransmitters called acetylocholine or Ach. The nerve impulse travels down the motor neuron to an axon terminal and then to the synaptic vesicles releases Ach into the cleft. On example of this is botox. The tropomyosin wind around an actin filament. The troponin is in intervals along the threads. When the calcium is released from the sarcoplasmic reticulum, which also combine with the troponin, it causes the tropomyosin threads to shift position.
Whole muscle contraction depends on the muscle fiber contraction. Muscles have motor units and the motor units is a nerve fiber that have all the muscle fiber it innervates. Motor units obeys the all-or-none law. This is when all of the muscle fibers in a motor unit are stimulated at once and they either contract or not contract. A muscle twitch happens when a motor unit is stimulated by infrequent electrical impulses last only a fraction of a second. The muscle twitch is divided into three stages the latent stage, the contraction stage, and the relaxation stage. Tetanus is when the summation is increased by muscle contraction until the maximal sustained contraction. This continues until fatigue kicks in do to the lack of energy reserves. Fatigue is appearent when the muscle relaxes even though the contractions are continuing. One muscle contains many motor units. Not all of the muscles contract at the same time because if that happened all the muscles would get tired at the same time. Some of the muscles rest while the others contract. Muscle tone is dependent on muscle contraction.
There are four fuel sources for energy. Muscle triglycerides, plasma fatty acids, blood glucose, and muscle glycogen are the four sources. Muscle cells store some ATP, which is used for energy, and there are three ways to make more. The first is the CP pathway which is the simplest and fastest way. It creates creatine phosphate. This is an anaerobic or resting process. The next way is fermentation, this process uses glycogen an lactate. It is an anaerobic process which is also very fast. The last way is cellular respiration. This uses glucose and fatty acids. It is an aerobic process and is the process that burns fat while we exercise.
Next I will talk about fast twitch and slow twitch muscle fibers. Fast twitch muscle fibers are anaerobic and are designed for strength. They give explosions of energy but they fatigue very fast. Slow twitch muscle fibers are steadier and have more endurance. They are used more in long distance sports and are aerobic.
There are many common muscular conditions. Spasms are a sudden and an involuntary contraction. Multiple spasms of the skeletal muscles are called convulsions. Cramps are painful spasms. There are also facial tissues. A strain is the stretching or tearing of a muscle. A sprain is the twisting of a joint that leads to swelling and further injury. Tendonitis is when the tendon is inflamed and the movement of joint is very painful. The most common cause of tendonitis is overuse. Bursa is like a plastic bag filled with a small amount of oil that provides a smooth slippery surface for when the muscles and tendons glide over the bones. Bursitis is an inflammation of a bursa. This is caused from repetitive movement or excessive pressure.
There are also many muscle diseases that are serious and require medical attention. Myalgia is achy muscles and is caused from overuse or overstretching. Fibromyalgia is achy pain, tenderness, and stiffness in the muscles. Muscular dystrophy is progressive degeneration and weakening of the muscles. In this disease the muscle fiber dies and fat and connective tissue replaces it. Duchenne muscular dystrophy is the most common type. Myasthenia gravis is an autoimmune disease. This is when weakness affects the muscles of the eyelids, face, neck, and extremities. Muscle contraction is impaired because the immune system mistakenly produces antibodies that destroy Ach. Amyotrophic lateral sclerosis or ALS also called Lou Gehrig disease. With this disease you lose the ability to walk, talk, chew, and swallow. This disease cannot be cured.
Movement is essential to maintaining homeostasis. The skeletal and muscular systems work together to make the body move. Both systems protect the body parts. Both the skeletal and muscular systems store and release calcium. The blood cells are produced in the bones. And finally the muscles help maintain a constant body temperature.
There are two parts to the Nervous System, the central nervous system or CNS and the peripheral nervous system or PNS. The CNS control the brain and spinal cord and the PNS control the nerves. The nerves are outside the CNS. The CNS has three major functions: the first is the nervous system receives sensory input, the second is it performs integration, the last is it generates motor output.
Nervous tissue has two types of cells neurons and neuroglia. Neurons transmit nerve impulses between parts of the nervous system. Neuroglia support and nourish the neurons. There are three types of neurons. Sensory neurons take nerve Impulese from the sensory receptors to the CNS. Sensory receptors are special structures that detect changes in the environment. The next is interneuron which is in the CNS. These receive input from sensory neurons and from other interneurons. The last is motor neurons which takes nerve impulses away from the CNS to the effector. The effectors carry out responses to environmental changes. All the neurons have three parts. The cell body which contains the nucleus, the dendrites short extensions that receive signals from the sensory receptors and other neurons, and lastly the axon conducts nerve impulses.
The myelin sheath is a protective covering. The axons are covered and protected with it. The covering is a typed of neuroglia schwann cell that have a lipid substance in the plasma membrane. The are nodes of ranvier which are gaps where there is no sheath. Only axons have a myelin sheath.
Nerve impulses convey information within the nervous system. The resting potential is when an axon is not conducting an impulse. Action potential is a rapid change in polarity across the plasma membrane as a nerve impulse occurs. Action potential is all or nothing. It requires two gated channels. The first is the sodium gate it depolarization happens because the charge inside the axon changes from a negative to a positive. The second gate is the potassium gate. Repolarization happens because inside of the axon resumes a negative charge as K+ exits the axon.
Saltatory conduction is when a nerve impulse jumps from one node to another node. It happens very fast. Action potential are self propagating, each one generates another along the length of an axon. Once it has passed by each axon it goes through a refractory period. This is when the sodium gates are unable to open. It makes sure the action potential can’t move backward only down.
The axon branches into fine endings with a small swelling called axon terminal. Each axon terminal lies very close to each other. The close proximity is called the synapse. The synaptic cleft is a small gap that separates the sending neuron from the receiving neuron. The nerve impulses are not able to jump the cleft. The transmission across the synapse is carried out by the molecules called neurotransmitters which are stored in the synaptic vesicles. The process is as follows: nerve impulses travel along the axon and reach the terminal, the calcium enters the terminal and stimulate synaptic vesicles to merge with the sending membrane, and finally neurotransmitters are released into the synaptic cleft where they diffuse across the receiving membrane and bind with specific receptor proteins. Once a response is initiated it is removed. The integration is the summing up of the excitatory and inhibitory signals. Excitatory signals produce potential charge and inhibitory signals drive neurons farther from the action potential.
The CNS is where sensory information is received and the motor control is initiated. The spinal cord is protected by the vertebrae and the brain is protected by the skull. Both are in meninges which are protective membranes. The spaces between the meninges are filled with cerebrospinal fluid. This fluid cushions and protects the CNS. The fluid is also in the ventricles of the brain and in the central canal of the spinal cord. The brain is composed of four chambers which are interconnecting chambers that produce and serve as the reservoir for the fluid. Excess fluid normally drains away and any blockages can result in injury. With in the CNS there are two types of tissue gray matter which has cell bodies and short nonmyelinated fibers and white matter which has myelinated axons that run together in tracts.
The spinal cord extends from the base of the brain into the vertebral canal. The spinal nerves project from the spinal cord. The spinal cord provides communication between the brain and the peripheral nerves. This is the center for thousands of reflex arcs. Stimulus causes the sensory receptors to generate nerve impulses to travel to sensory axons to the spinal cord. This is the same with the internal organs except it is sensory fibers and not sensory receptors.
The brain is the last great frontier of biology. The cerebrum is the largest portion of the brain. It is the last center to receive sensory input and carry out integration before the motor responses. It communicates with and coordinates activities with other parts of the brain. The two halves are called the right and left cerebral hemispheres. Longitudinal tissue divides the two halves. Sulci divide the hemispheres into lobes which are the frontal lobe, the parietal lobe, the occipital lobe, and the temporal lobe. The cerebral cortex covers the hemispheres and consists of one billion cell bodies. The it is responsible for sensation, voluntary movement, and consciousness. The primary motor area is in the frontal lobe. The primary somatosensory is in the parietal lobe. The processing centers receive information from other areas and perform a higher level of analytical functions. There is the prefrontal, the wernicke’s area is in the temporal lobe and is responsible for speech. The broca’s area in the left frontal lobe is also for speech. There is also white matter in the cerebrum. The diencephalons encircles the third ventricle and is made of the hypothalamus which forms the floor and regulates hunger, sleep, thrist, body temperature, and water balance. The thalamus has two masses of gray matter in the sides and the roof. This is the receiving end and also sends things to the other areas of the cerebrum.
The cerebellum is under the occipital lobe and is separated by the fourth ventricle. It has two portions that are composed of white matter. It receives input from the eyes, the ears, the joints, and the muscles. The cerebellum sends motor impulses and maintains posture and balance. It ensures that all muscles work together. It also lets us learn new motor skills. The brain stem contains the midbrain, the pons, and the medulla oblongata. The midbrain is the relay station between the cerebrum and the spinal cord. It is the reflex for visual, auditory, and the tactile responses. The pons which means bridge regulates breathing rate, is the reflex for head movements, and responds to visual and auditory stimuli. The axons travel between the cerebellum and the rest of the CNS. The medulla oblongata is the reflex center for the heart beat, breathing, blood pressure, vomiting, coughing, sneezing, hiccupping, and swallowing. The reticular formation is a complex network of nuclei or masses of gray matter. The fibers extend the length of the brain. It receives sensory and motor signals and sends them on to the appropriate area of the brain.
The limbic system is linked to structures deep in the cerebrum. It has functional grouping not anatomical. It blends emotion and higher mental function which is why activities seem pleasurable. There are two structures the amygdale which cause experiences to have emotional overtones such as fear. The other is the hippocampus which helps with learning and memory, it is the information gateway.
Memory is the ability to hold a thought in mind or recall events from the past. Learning is when you retain and utilize memory. There are two types of memory short-term and long-term memory. There are two types of long-term memory semantic memory such as numbers and words. Episodic memory are things like persons or events. Skill memory is performing motor skills. The left hemisphere is for verbal, logical, analytical, and rational. The right hemisphere is nonverbal, visual, intuitive, and creative. The left side is more global and the right side is more specific.
The peripheral nervous system is outside the CNS and contains the nerves. There are twelve pairs of cranial nerves some of them contain sensory fibers, some contain motor fibers, some have both. The cranial nerves are linked with the head, neck, and other facial areas. There are 31 pairs of spinal nerves which take impulses to and from the spinal cord. The somantic system serves the skin muscles and the tendons. They take information from the external sensory receptors to the CNS and sends motor commands away from the CNS to the skeletal muscles. It also has reflexes which are automatic responses to stimuli.
The autonomic system regulates the acivity of the cardiac and the smooth muscles and glands. It divides into the sympathetic and the parasympathetic. The sympathetic is in the middle portions of the spinal cord. It is important in emergency situations and it increases the heartbeat and dilates the active muscles. Parasympathetic is involved with the cranial nerves and fibers. It also promotes internal responses to relaxing.
Drug abuse is when a person takes a dose of a drug that has a harmful effect. A person can overdose on alcohol, nicotine, cocaine, methamphetamines, herion, marijuana, and neurological drugs are just some of the drugs. Dependency occurs when the body compensates for the presence of drugs.
Sensory receptors are specialized to detect certain types of stimuli. Exteroceptors detect stimuli from the outside body like taste, smell, vision, hearing, and equilibrium. Interoceptors receive stimuli from the inside body like blood pressure. There are four categories of sensory receptors they are: chemoreceptors respond to chemical substances. Pain receptors respond to chemicals released by the damaged tissue. Photoreceptors respond to light energy. Mechanoreceptors are stimulated by mechanical force. Lastly thermoreceptors are stimulated by change in temperature. An example is the skin or the hypothalamus.
Sensation is a conscious perception of stimuli. Sensory receptors initiate nerve impulses, the sensation depends on part of the brain receiving the nerve impulses. Before sensory receptors initiate nerve impulses they carry out integration. First they sum up the signals and then the sensory adaptation is decreased due to response to stimuli. Without sensory receptors we wouldn’t receive information about the internal and external environments which leads to the appropriate reflex and voluntary actions.
Sensory receptors in muscles, joints, tendons, skin, and internal organs send nerve impulses to the spinal cord. There are three types of general sensory receptors. Proprioceptors are mechanoreceptors which are involved in the reflex actions and they maintain muscle tone, equilibrium, and posture. The next type is cutaneous which is the skin specifically the dermis. It makes skin sensitive to touch, pressure, pain, and temperature. The last type is pain or nociceptors. This is sensitive to chemicals released by damaged tissue. Referred pain is when internal pain is felt as pain from the skin.
The sense of taste and smell are chemical senses because the receptors are sensitive to molecules in the food we eat and the air we breathe. The chemoreceptors are plasma membrane receptors which bind to particular molecules. A person has around 3000 taste buds which are located on the tongue. They taste sweet, salty, sour, and bitter. Eighty to ninety percent of our taste is due to smell. The sense of smell depends on the 10-20 million olfactory cells that are located on the roof of the nasal cavity. This number declines as a person ages.
The sense of vision occurs in the eyes before nerve impulses are sent to the brain. One third of the cerebral cortex is for processing visual information. They eye is made up of many different parts. The sclera is the white part of the eye and is made up of fibers. The cornea is made of transparent collagen fibers and is considered the window of the eye. The choroid is the where light rays are absorbed. It is in the middle of the eye, is a thin layer, and is the dark pigmented layer. The iris regulates light entrance. The pupil admits light. The ciliary body is what holds the lens in place. It also controls the shape of the lens for near and far sighted vision. The lens refracts and focuses light rays. The retina is filled with clear gelatinous material. It contains sensory receptors for sight, it has rod cells that make black and white vision, the cone cells make color vision, and the fovea centrails make acute vision. The optic nerve transmits impulses to the brain. The humos transmits light rays and supports the eyeball. A person can be nearsighted, farsighted, or have astigmatism which is when the light rays can’t be evenly focused on the retina.
The sense of hearing has two functions hearing and balance. There are sensory receptors in the inner that are in the form of hair cells. The outer ear has a pinna otherwise called the external flap. This is where the auditory canal is also located. These areas are lined with fine hairs and sweat glands. The middle ear is where the tympanic membrane or ear drum is located that ends with oval and round windows. The inner ear has a semicircular canal and vestibule or equilibrium.
The equilibrium is the vestibular nerve that takes impulses to the brain stem and the cerebellum. This communication helps maintain the equilibrium. The rational equilibrium is composed of mechanoreceptors in the semicircular canals. It detects rotational and angular movement of the head. The gravitational equilibrium detect head movements in the vertical and horizontal planes.