Muscle, Bone, and Skin Flashcards
Three types of muscle tissue
Skeletal, cardiac, smooth.
4 possible functions of muscle contraction
- Body movement
- Stabilization of body position
- Movement of substances through the body
- Generating heat to maintain body temperature
Skeletal muscle
Voluntary muscle tissue (can be consciously controlled).
Muscle is attached to bone via a tendon.
Typically, a muscle stretches across a joint. The muscle origin is on the larger bone, which remains relatively stationary, and its insertion is on the smaller bone, which moves relative to the larger bone upon contraction of the muscle.
Skeletal muscle allows for movement and posture via the agonist, antagonist, and synergist muscles.
Contraction of skeletal muscle may squeeze blood and lymph vessels aiding contraction.
Contraction of skeletal muscle produces large amounts of heat.
Tendon
Attaches muscle to bone
Ligament
Attaches bone to bone
Agonist
The muscle responsible for the movement, contracts relative to the antagonist
Antagonist
A second muscle, stretches when the agonist contracts.
How does a muscle use leverage?
By applying a force to a bone at its insertion point and rotating the bone in some fashion around the joint.
Most lever systems of the body typically act to increase the required force of a muscle contraction. In other words, a greater force than mg is required to life a mass m. This is done in order to reduce the bulk of the body and increase the range of movement. If the muscle has a shorter lever arm, it is closer to the body and thus creates less bulk.
Synergistic muscles
Assist the antagonist by stabilizing the origin bone of by positioning the insertion bone during the movement.
Shivering
Shivering, controlled by the hypothalmus upon stimulation by receptors, is the rapid contraction of skeletal muscle to warm the body.
Components of muscle contraction
Understand that the H zone and I band get smaller, while the A band does not change size.
Sarcomere
Smallest functional unit of skeletal muscle Composed of many strands of the thick and thin filament, lay side by side to form a cylindrical segment.
Positioned end to end to form myofibrils.
Thick and thin filament
Protein filaments that make up the sarcomere. Do not move during muscle contraction.
Myofibril
Sarcomeres are positioned end to end to form myofibrils. Surrounded by the specialized ER of the muscle cell called the sarcoplasmic reticulum. The lumen of the SR is filled with Calcium. Lodged between the myofibrils are mitochondria and many nuclei.
Multinucleate
Skeletal muscle is multinucleate
Sarcolemma
A modified membrane called the sarcolemma wraps several myofibrils together to form a muscle cell or muscle fiber. Many muscle fibers are further bound into that fasciculus, and many fasciculae make up a single muscle.
Thick filament
Made of several long myosin molecules, which wrap around each other. Their globular heads protrude along both ends.
Thin filament
Composed mainly of a polymer of the globular protein actin. Attached to the actin are the proteins troponin and tropomyosin.
What creates the contractile fore of skeletal muscle
Myosin and actin sliding relative to each other in the 5-stage cycle
5-stage cycle
- Tropomyosin covers the binding site on actin
- Calcium binds to troponin, causing tropomyosin to expose the binding site, and myosin binds to actin
- Myosin kicks out a phosphate and ADP and bends into low-energy position, moving actin with it (This is called the POWER STROKE- causes the shortening of the sarcomere and the muscle contraction)
- ATP binds to myosin, and actin and myosin unbind
- ATP splits to ADP and phosphate, and myosin cocks into high energy position
This cycle is repeated many times to form a contraction
A muscular contraction begins with…
an action potential. A neuron attaches to a muscle cell forming a neuromuscular synapse. The action potential of the neuron releases acetylcholine into the synaptic cleft. The action potential moves deep into the muscle cell via T tubules, then is transferred to the SF, which suddenly becomes permeable to calcium ions– the calcium ions begin the 5-stage cycle.
At the end of each cycle, Calcium is actively pumped back into the SR
Acetylcholine
Released by the AP of the neuron. Activates ion channels in the sarcolemma of the muscle cell creating an action potential, which moves deep into the muscle cell via T tubules.
T-tubules
Small tunnels in the membrane which transfer the AP and allow for a uniform contraction of the muscle by allowing the AP to spread more rapidly.
Motor unit
Consists of a nerve and all the muscle fibers it synapses with.
Smaller motor units are the first to be activated, larger motor units are recruited as needed.
Muscles requiring intricate movements (like the finger) have smaller MUs, muscle requiring greater force (like the back), have larger MUs.
Three types of skeletal muscle fibers
- Slow oxidative- Type I
- Fast oxidative- Type II A
- Fast glycolytic- Type II B
Myoglobin
Oxygen storing protein similar to hemoglobin, but with only one protein subunit.
Type I fibers
AKA Slow twitch
Red from large amounts of myoglobin.
Large amounts of mitochondria.
Split ATP at a slow rate.
As a result, are slow to fatigue, but also have a slow contraction velocity.
Large amounts found in the postural muscles
Type II A fibers
AKA Fast-twitch A
Contract rapidly. Resistant to fatigue, but not as resistant as Type I fibers.
Large amounts found in the upper legs
Type II B fibers
AKA Fast-twitch B
Low myoglobin content, thus appear white under the light microscope.
Contract very rapidly.
Contain large amounts of glycogen.
Large amounts found in the upper arms.
Growth in skeletal muscle
Adult human skeletal muscle tissue generally does not undergo mitosis to create new muscle cells (hyperplasia). Instead, a number of changes occur over time when the muscles are exposed to forceful, repetitive contractions.
The diameter of the muscle fibers increase, the number of sarcomeres and mitochondria increases, and sarcomeres lengthen.
This increase in muscle cell diameter and change in muscle conformation is called hypertrophy.
Cardiac muscle
Composes the human heart.
Striated (composed of sarcomeres).
Has a single nucleus and large/numerous mitochondria. Each cell is separated from its neighbor by an intercalated disc.
Cardiac muscle is not connected to bine, but forms a net which contracts (involuntarily) upon itself like a squeezing disc.
Grows by hypertropy.
Striated
Composed of sarcomeres
Intercalated disc
Separates cardiac muscle cells from each other. Contain gap junctions which allow an action potential to spread from one cardiac cell to the next via electrical synapses.
The action potential of cardiac muscle
Experiences a plateau after depolarization, created by slow voltage-gated calcium channels, which allow Calcium to enter and hold the inside of a membrane at a positive potential difference. The plateau lengthens the time of contraction.
The importance of calcium in the cardiac action potential
Without it, the heart would beat far too quickly to serve as a functional pump, and we would die.
Smooth muscle
Mainly involuntary, innervated by the autonomic nervous system. Smooth muscle: responds to neural stimulus, contracts or relaxes in the presence of hormones, and responds to changes in pH, oxygen and carbon dioxide levels, temperature, and ion concentrations.
Only contains one nucleus.
Has thick and thin filaments that are not organized into sarcomeres. Also contain intermediate filaments, which are attached to dense bodies spread throughout the cell. The thick and thin filaments are attached to the intermediate filaments, and when they contract, they cause the intermediate filaments to pull the dense bodies together.
Upon contraction, the smooth muscle cell shrinks. lengthwise.
Intermediate filaments
Smooth muscle cells contain intermediate filaments, which are attached to dense bodies spread throughout the cell. The thick and thin filaments are attached to the intermediate filaments, and when they contract, they cause the intermediate filaments to pull the dense bodies together.
Two types of smooth muscle
- Single-unit, aka visceral: most common, connected by gap junctions which spread the AP from a single neuron through a large group of cells, and allow the cells to contract as a single unit. Found in small arteries and veins, intestines, uterus, and urinary bladder.
- Multi-unit: attached directly to a neuron. A group of multi-unit muscle fibers can contract independently of other muscle fibers in the same location. Found in the large arteries, bronchioles, pili muscles attached to hair folllicles, and the iris.
Bone
Living tissue. Supports soft tissue, protects internal organs, assists in movement of the body, stores minerals, produces blood cells, and stores energy as adipose cells in bone marrow.
Four types of cells contained in bone tissue
Note that all are surrounded by an extensive matrix.
- Osteoprogenitor: differentiate into osteoblasts (don’t need to know).
- Osteoblasts: secrete collagen and organic compounds upon which bone is formed. Incapable of mitosis. As they release matrix materials around themselves, become enveloped by the matrix and differentiate into osteocytes.
- Osteocytes: also incapable of mitosis. Exchange nutrients and waste materials with the blood.
- Osteoclasts: Reabsorb bone matrix, releasing minerals back into the blood. Believed to develop from white blood cells called monocytes.
Spongy bone
Contains red bone marrow, the site of red blood cell development.
Red bone marrow
The site of hemopoiesis or red blood cell development
Compact bone
Surrounds the medullary cavity, which holds yellow bone marrow. Highly organized.
Yellow bone marrow
Contains adipose cells for fat storage.
Haversian system
AKA osteon. In a continuous remodeling process, osteoclasts burrow tunnels called Haversian (central) canals, through compact bone. The osteoclasts are followed by osteoblasts, which lay down a new matrix onto the tunnel walls, forming concentric rings called lamellae.
Osteocytes trapped between lamellae exchange nutrients via canaliculi. Haversian canals contain blood and lymph vessels, and are connected by crossing canals called Volkmann’s clnals.
Haversian canals
AKA central canals; tunnels which are burrowed by osteoclasts through compact bone.
Lamellae
Concentric rings laid down by osteoblasts
Canaliculi
Osteocytes trapped between lamellae exchange nutrients via canaliculi.
Volkmann’s canals
Crossing canals which cross Haversian canals.
Hydroxyapatite
Most of the calcium in the body is stored in the bone matrix in this form. Crystals lie alongside collagen fibers, and give bone greater compressive strength than reinforced concrete!
Four types of bones
- Long: have a shaft that is curved for strength. Composed of compact and spongy bone. (Leg, arm, finger, toe.)
- Short: Cuboidal. (Ankle, wrist.)
- Flat: Made from spongy bone surrounded by compact bone, provide large areas for muscle attachment and organ protection. (Skull, sternum, ribs, and shoulder blades.)
- Irregular: Irregular shape, variable amounts of compact and spongy bone. (Ossicles of the ear.)
Calcium and phosphate
Is stored in bone, helping to maintain a homeostatic concentration of these ions in the blood.
Cartilage
Flexible, resilient connective tissue. Composed primarily of collagen, has great tensile strength. Contains no blood vessels or nerves interiorly.
3 types: Hyaline, Fibro, and Elastic.
Hyaline cartilage is the most common, it reduces friction and absorbs shock in joints.
3 types of joints
Classified by structure:
- Fibrous joints: occur between 2 bones held closely and tightly together by fibrous tissue, permitting little or no movement. (Skull, teeth + mandible)
- Cartilaginous: Also allow little/no movement. Occur between 2 bones held closely together by cartilage. (Ribs, sternum, pubic symphysis.)
- Synovial joints: not bound directly by the intervening cartilage, but separated by a capsule filled with synovial fluid, which provides lubrication and nourishment. Fluid also contains phagocytotic cells that remove particles that result from wear and tear. Allow for a wide range of motion.
Skin and 7 functions
An organ- group of tissues working together to perform a specific function.
- Thermoregulation
- Protection
- Environmental sensory input
- Excretion
- Immunity
- Blood reservoir
- Vitamin D synthesis
Thermoregulation
The skin helps regulate body temperature. Blood conducts heat form the body’s core to the skin. Some can be dissipated by evaporation of sweat/most is dissipated by radiation.
Blood can also be shunted away from the capillaries of the skin to reduce heat loss, keeping the body warm.
Hairs can be erected, trapping insulating air next to the skin.
Protection
The skin is a physical barrier to abrasion, bacteria, dehydration, many chemicals, and UV radiation.
Environmental sensory input
The skin gathers information from the environment by sensing temperature, pressure, pain, and touch.
Excretion
Water and salts are excreted through the skin. This water loss occurs by diffusion (is independent of sweating).
Adults lose 1/4-1/2 liter of water per day via this type of insensible fluid loss. Burning of the skin can reduce water loss dramatically.
Immunity
Besides being a physical barrier to bacteria, specialized cells of the epidermis are components of the immune system.
Blood reservoir
Vessels in the dermis hold up to 10% of the blood of a resting adult
Vitamin D synthesis
UV radiation activates a molecule in the skin that is a precursor to vitamin D. The activated molecule is modified by enzymes in the liver and kidneys to produce vitamin D.
Two principal parts of skin
Epidermis and dermis.
Beneath the skin is a subcutaneous tissue. The fat of this layer is an important heat insulator for the body. The fat helps maintain normal core body temperatures on cold days while the skin approaches the temperature of the environment.
Epidermis
Avascular epithelial tissue.
4 major cell types of the epidermis:
- 90% keratinocytes, which produce the protein keratin that helps waterproof the skin
- Melanocytes, which transfer melanin to keratinocytes
- Langerhans cells, which interact with helper T cells of the immune system
- Merkel cells, which attach to sensory neurons and function in the sensation of touch
5 strata (layers) of the epidermis
The deepest layer contains Merkel cells and stem cells, which continually divide to produce keratinocytes and other cells. Keratinocytes are pushed to the top later. As they rise, they accumulate keratin and die. When the cells reach the outermost layer of skin, they slough off the body.
The process of keratinization from birth of a cell to sloughing takes 2-4 weeks. The outermost later of epidermis consists of 25-30 layers of flat, dead skin cells.
Callus
Exposure to friction or pressure stimulates the epidermis to thicken, forming a callus
Dermis
Connective tissue derived from mesodermal cells. Embedded by blood vessels, nerves, glands, and hair follicles. Collagen and elastic fibers in the dermis provide skin with strength, extensibility and elasticity. The dermis is thick in the palms and soles.
Hair
A column of keratinized cells held tightly together. As new cells are added to its base, the hair grows. Most hairs are associated with a gland that empties oil directly into the follicle and onto the skin. When contracted, smooth muscle stands hair up pointing it perpendicular to the skin.
Nails
Keratinized cells.
Integumentary system
Skin, hair, nails, glands, and some nerve endings.
