Chapter 10 Flashcards
Smooth Muscle
Found in the walls of all hollow organs (GI tract, the urinary system and the uterus)
What does skeletal muscles use for movement?
The framework of the bones of the skeleton
How are skeletal muscles attached?
Skeletal muscles attach at each end to two different bones
How are muscles attached?
Muscles are attached to bones by tendons
Tendons
Strong connective tissue formed primarily of collagen
Point of origin
Point where the muscle attaches on the bone closer to the center of the body Stays in place when contraction occurs
Point of insertion
Brought closer to the point of origin during contraction Point more distant from the center of the body
Why are different muscles needed to move a joint?
Muscles can only contract so different muscles are necessary for flexion and extension of a joint
Antagonistic
Muscles that are responsible for movement in opposite directions
Synergistic
Muscles that move a joint in the same direction
Myofibril that generate contractions
Polymerized actin and myosin
Actin polymerizes to form
Thin filaments
Thin filaments
Attach to eachZ line and overlap with thick filaments in the middle of each sacromere
Myosin polymerizes to from
Thick filaments
Thick filaments
Are not attached to the Z lines
When does contraction occur in the Myofiber?
When thin and thick filaments slide across each other
How is filament sliding powered?
ATP hydrolysis; myosin is an enzyme which uses energy of the ATP to create movement
Filament sliding step 1
(1) Binding of the myosin head to a myosin binding site on actin (cross bridge formation) Myosin has ADP and P1 bound
Filament sliding step 2
The power stroke; myosin head moves to a low-energy conformation, and pulls the actin chain toward the center of the sacromere. ADP is released
Filament sliding step 3
Binding of a new ATP molecule necessary for release of actin by the myosin head
Filament sliding step 4
ATP hydrolysis occurs immediately and the myosin head is cocked. Another cycle beings when the myosin head binds to a new binding site on the thin filament
Troponin-tropopomyosin complex
Prevents contraction when Ca2+is not present
Tropomyosin
A long fibrous protein that winds around the actin polymer, blocking all the myosin binding sites
Troop in
Globular protein bounds to tropomyosin that can bind Ca2+
How does the troponin-tropomyosin complex work?
When troponin binds Ca2+, troponin undergoes a conformational change that moves tropomyosin out of the wat, so that the myosin heads can attach to actin and filament sliding can occur
Neuromuscular Junction (NMJ)
The synpase between an axon terminus (synaptic knob) and a myofiber
How is the NMJ arranged?
Not a single point, but rather a long trough or invagination (infolding) of the cell membrane; the axon terminus is elongated to fill a long synaptic cleft
Why is the NMJ arranged the way it is?
To allow the neuron to depolarize a large region of the postsynaptic membrane at once
What’s the neurotransmitter at the NMJ?
ACh
What is ACh’s affect?
ACh is released and attaches to sodium channels, which release sodium and depolarize the cell. ACh stimulates until it is destroyed
How does contaction occur in the myofiber?
Summation is required to initiate an AP in the postsynaptic cell. When sufficient EPP occurs, threshold is reached and sodium channels open in the postsynaptic membrane.
How is the AP propagated in the myofiber?
By a continuing wave of voltage gated sodium channel opening
Transverse tubules (T-tubulues)
Since the myofiber is too thick for potentials to occur at the cell surface, action potentials must travel through T-tubules to depolarize the inside
Sacroplasmi Reticium (SR)
SR contains voltage-gated Ca2+ channels which allow Ca2+ to rush out of the SR into the sacroplasm upon depolarization. Increase in sacroplasmic Ca2+ causes troponin- tropomyosin to change confirmation, allowing myosin to bind actin –> actin and myosin slide across each other and muscle fibers contract
What happens to calcium upon repolirization?
Calcium is actively sequestered by the SR and contraction is ended
Twitch
Smallest measurable muscle contraction
Motor unit recruitment
A motor unit is a group of myofiber innervated by the branches of a single motor neuron’s axon. Activation of one motor neuron can then recruit more motor neurons to produce a large twitch
Frequency summation
If a second contraction occurs rapidly enough there is insufficient time for the Ca2+ to be sequestered by the SR, and the second contraction builds on the first
Tetanus
Strongest possible contraction
How does frequency summation occur?
The amount of time between successive stimulations must be greater than the duration of the refractory period, but brief enough so that the sacroplasmic Ca2+ has not been returned to its low resting level
Length-tension relationship
A muscle contracts most forcefully at an optimum length (2.2 microns). This is where there is maximum degree of overlap between thick and thin filaments.
Intermediate term energy storage molecule
Creating phosphate; during contraction its hydrolysis drives the regeneration of ATP from ADP+P
What is the role of Myoglobin?
Muscle is highly aerobic tissue. The role of myoglobin is to provide an oxygen reserve by taking O2 from hemoglobin and then releasing it as needed.
What happens during prolonged contractions?
The supply of oxygen runs low, and metabolism becomes anaerobic. Lactic acid is produced and moves into the blood stream, causing a drop in pH.
Rigor Morris
Rigidity of skeletal muscles which occurs soon after death. Occurs after ATP exhaustion. Without ATP, myosin heads cannot release actin and the muscle can neither contract nor relax.
How are cardiac muscles the same as skeletal muscles
(1) thick and thin filaments are organized into sarcomeres (2) T-tubules are present (3) Tropononin-tropomyosin regulates contraction (4) Length-tension relationship works the same way and is more significant in cardiac muscle
How are cardiac different from skeletal muscles?
(1) They each have only one nucleus (2) Cardiac muscle cells are each connected to several neighbors by intercalated disks (3) Cardiac muscle contractions do not depend on stimulation by motor neurons (4)AP in cardiac muscle depends not only on voltage-gated sodium channels but also on voltage-gated calcium channels
What is the most important nerve in a cardiac muscle?
Vagus nerve (a parasympathetic nerve) synapses with the sinoatrial node, where it releases ACh to inhibit spontaneous depolarization resulting in a slower heart rate
What is the significance of a plateau phase?
(1) Longer duration of contraction facilitates ventricular emptying (better ejection fraction) (2) a longer refractory period helps prevent disorganized transmission of impulses through the heart and makes summation and tetanus impossible
What kind of AP do skeletal muscles cells exhibit?
A steeply-spiking AP
What type of AP do smooth and cardiac muscle cells exhibit?
A spike and a plateau
Smooth muscles compared to skeletal muscles 1-4
(1) Smooth muscle cells are much narrower and shorter than skeletal muscle cells (2) T-tubules are not present in smooth muscle cells (3) each cell has only one nucleus and is connected to its neighbors by gap junctions (4) Thick and thin filaments are not organized into sacromere in smooth muscle
Smooth muscles compared to skeletal muscles 5-8
(5) Troponin-tropomyosin complex is not present (6) SR in smooth muscles are poorly developed. SR stores very little Ca2+, most rely on extra cellular Ca (7) AP is determined by slow channels only, it takes ten to twenty times as long as skeletal muscle action potential (8) Smooth muscles that must sustain prolonged contractions have action potentials similar to those of cardiac muscles
Smooth muscles compared to skeletal muscles 9-10
(9) Smooth muscles have a constantly fluctuating resting potential (10) Smooth muscle cells are innervated by motor neurons. Smooth muscle cells are autonomic motor neurons instead of somatic motor neurons
What roles does the vertebrae skeletal system serve?
(1) Support the body (2) Provide the framework for movement (3) Protect vital organs (brain, heart, etc.) (4) Store calcium (5) Synthesize the formed elements of the blood.
Hematopoisis
When synthesis of the formed elements occurs in the marrow of flat bones
Axial skeleton
Consists of the skull, the vertebral column, and the rib cage
The appendicular skeleton
All other bones in the body that are not the axial skeleton
Connective tissue
Bone; consists of cells and the materials they secrete
Where does all connective tissue cells derived from?
Fibroblast
Elastin
Gives tissue the ability to stretch and regain its shape
What cells are derived from fibroblast
Adipocytes, chondrocytes and osteocytes
Loose connective tissue
Includes adipose tissue and material located between cells throughout the body, known as the extra cellular matrix
Basement membrane
Sheet of collagen that supports cell layers
Dense connective tissue
Refers to tissues that contain large amounts of collagen, such as bones, cartilage, tendons and ligaments
Compact bone
Hard and dense while spongy bone is porous.
Spongy Bone
Always surrounded by a layer of compact bone
Bone marrow
Non bony material found in the shafts of long bones and in the pores of spongy bones
Red marrow
Found in spongy bone within flat bones. Activity increases in response to erythropoietin (hormone made by the kidneys)
Yellow marrow
Found in the shafts of long bones, filled with fat and is inactive
Tow principal ingredients of bone
Collagen and hydroxyapatite
Osteoblasts
Basic unit of compact bone structure. Sometimes referred to as the Haversian system
In the center of the osteon is a hole called
The central (or Haversian) canal which contains blood, lymph vessels and nerves
Osteocytes
Mature bone cell. Allows cells to exchange nutrients and waste through an otherwise impermeable membrane
Cartilage
Strong but very flexible extracellular tissue secreted by cells called chondrocytes
Hyaline Cartilage
Strong and somewhat flexible (larynx & trachea)
Elastic Cartilage
Found in structures that require support and more flexibility than hyaline cartilage can provide (outer ear & epiglottis)
Fibrous Cartilage
Very rigid and is found in places where very strong support is needed (pelvis & spinal chord)
Cartilage is avascular
Cartilage is not innervated and does not contain blood vessels. Cartilage receives nutrition and immune protection from the surrounding fluid
Ligaments
Connect bones to other bones
Tendons
Connect bones to muscles
Synarthroses
Immovable joints. Points where two bones are fused together.
Amphiarthoses
Slightly movable joints. Provides both movability and a great deal of support
Diarthroses
Freely movable joints (most of the joints of in the body)
What lubricates movable joints?
Synovial fluid; kept within the joint by the synovial capsule
How are bones connected?
The surface of two bones that contact each other are perfectly smooth because they are lined by articulate cartilage
How does most bone growth occur?
By endochondral ossification
endochondral ossification
Hyaline cartilage is produced and then replace by bone
Intramembranous ossification
Refers to the synthesis of bone from an embryonic tissue called mesenchyme
Epiphyseal plate
Seen between the diaphysis and the epiphysis
What happens when the chondrocytes divide?
The epiphysis and diaphysis are forced apart. Cartilage is then replaced by bone (ossified)
Epiphyseal line
The fusion point in adults
Osteoclasts
Continually destroy bone by dissolving the hydroxyapatite crystals
PTH’s effects on bones
Stimulates osteoclasts activity
PTH effects on kidneys
Increases reabsorption of calcium, stimulates conversation of vitamin D into calcitriol
PTH effect on intestines
Indirectly (via calcitriol) increases intestinal calcium absorption
Calcitriol effect on bones
may stimulate osteoclasts activity, but has a minor effect
Calcitriol effect on kidneys
Increases reabsoprtion of phosphorous
Calcitriol on intestines
Increases intestinal absorption of calcium
Calcitonin effects on bones
Inhibits osteoclasts activity
Calcitonin effect on kidneys
Decreases reabsoprtion of calcium
Calcitonin on intestines
N/A
What is the epidermis composed of?
Stratified (many layers of) squamous epithelial cells
Squamous cells of the epidermis are keratinized
As they die, they become filled with a thick coating of the though, hydrophobic protein keratin
Melanin
Brown pigment, produced by specialized cells in the epidermis termed melanocytes which help absorb the ultraviolet light of the sun to prevent damage to underlying tissues
Dermis
Consists of various cell-types embedded in a connective tissue matrix. Also contains sensory receptors and sudoriferous (sweat) glands, sebaceous (oil) glands and hair follicles
How do we cope with cold weather?
(1) Contraction of skeletal muscles produce heat (2) the skin insulates us so that we conserve heat generated by the metabolism (3) Heat loss is minimized by constriction of blood vessels in the dermis (cutaneous vasoconstriction) (4) Clothing & blankets
Mechanisms for dissipation of excessive heat
(1) Sweating, which allows heat loss by evaporation (2) Dilation of blood vessels in the dermis results in heat loss by conduction
