Anatomy + Physiology 2 Flashcards
(97 cards)
1
Q
Universal characteristics of Muscles
A
- Excitablity / responsiveness (chemical signals, stretch, electrical changes)
- Conductivity )Electrical excitation initiate waves of excitations
- Contractility (Shortens when stimulated)
- Extensibility (Stretched between contractions)
- Elasticity ( Returns to original rest lengths)
2
Q
Skeletal muscle
A
Attached to bone via tendons. Contraction brings movement across Joints
3
Q
Voluntary striated muscles
A
Voluntary - usually subjected to conscious control
Striated - alternating light and dark bands due to internal contractile protiens
4
Q
Structural hierachy of skeletal muscle w/ definitions
A
- Muscle↔Contractile organ - attached to bones with tendons. Separated from other muscles with fibrous epimysium
- Fasicle↔bundle of muscle fibres within a muscle. supplied by nerves and blood vessles and enclosed in bibrous perimysium that separates it from neighbouring fascicles
- Muscle fibre↔single muscle cell - slender, elongated enclosed in specialized plasma membrane (sarcolemma) . Contains densely packed bundles - myofibrils - of contractile protien filaments, multiple nuclei immediately beneath the sarcolemma and extensive network of specalized smooth endoplasmic reticulum.
- Myofibril↔Bundle of protien myofilaments within muscle fibre. Conenctively fill most of cytoplasm. Surrounde by sarcoplasmic reticulum and mitochondria. Banded (striated) appearance due to overlap of protien myofilaments
- Sarcomere↔Segment of myofibril from one Z disk to the next in striation pattern. Hundreds end to end to compose a myofibril. Functional, contractile unit of muscle fibre
- Myofilaments↔fibrous protien strands that carry out contraction process - thick filaments (Myosin) and thin filaments (Actin). Thick and thin side over one another to shorten each sacromere - shortening end to end shortens entire muscle
5
Q
Skeletal muscle cells (fibre)
A
Multiple Peripheral Nuclei
Mitochondria between myofibrils
6
Q
SKeletal muscle Glycogen
A
Carbohydrate stored to provide energy for excerise
7
Q
Skeletal Muscle Myoglobin
A
Red pigment - provides O2 needed for muscle activity
8
Q
Skeletal muscle Myoblasts
A
Stem cells fuse and form muscles fibres early in development
9
Q
Skeletal muscle Saatellite cells
A
unspecialized myoblasts between muscle fibre and endomysium. Play a role in regeneration of damaged skeletal muscle tissue
10
Q
Muscle Fibre - Myofibrils
A
Attached to inner surface of sarcolemma. Comprised of bundles of protien fillaments
Thin - Actin
THick - myosin
11
Q
Sarcoplasmic Reticulum - SR
A
Smooth ER network around myofibril
12
Q
Terminal Ciserns
A
Dilated end sacks of SR that cross muscles fibre from one side to the other - Ca+ reservoir
13
Q
T tubules
A
Tubular infoldings of sarcolemma which penetrate through cell and emerge on other side
14
Q
Triad
A
T Tubule and two terminal cisterns associated with it
15
Q
Muscle fibre - Sarcomeres
A
Myofilaments organized into repeating functional unis.
A bands - Dark
I bands - Light
16
Q
Sacromere
A
Segment from Z disk to Z disk.
H Band - contains thick filaments
I band - contains thin filaments
Subdivisions::
M line- Protiens that connect neighbouring thick filaments
H Band - Region either side of M line (THICK FILAMENTS ONLY)
A band - zone of overlap
17
Q
Actin
A
Thin filaments
Fibrous acitn - two intertwined strands
Glubular - single string w/ active site that binds to had of myosin molecule.
18
Q
Tropomyosin
A
Actin binding protien. Molecules that block acive sites on G actin subinits
Troponin - small calcium binding protien on each Tropomyosin
19
Q
Myosin
A
Comprise of thick filaments.
Molecules shaped like double headed golf club - 2 chains.
Heads directed outwards
Heads on 1/2 filament angle to left, other 1/2 to right
Bar zone = no heads
20
Q
Dystrophin
A
Linked actin to outermost myofilaments to membrane protiens that link to endomysium.
Transfers forces of muscle contraction to connetie tissue leading to tendon.
Genetic defect = myscular dystrophy
21
Q
Titin (hehe titty)
A
Elastic filaments
Runs through core of thin filament and anchors it to Z disk and M line
- stabalize and position thick filament
22
Q
Skeleal muscle contraction in order
A
- Sarcomere shorten
- H bands and I bands get smaller
- Zones of overlap get larger
- Z lines move closer together as thick and thin filaments slide past eachother
- Width of A band remains constant
- During shortening↔Dystrophin and linking protiens pull on extracellular protiens
- Transfers pull to extracellular tissue
- Sliding in all sarcomeres in Myofibril
- Myofibril gets shorter
- muscle fibre gets shorter
- muscle gets shorter
- produces tension
- ONLY CONTRACT WHEN STIMULATED BY A NERVE
23
Q
Motor neurons and motor units
A
Somatic motor neurons - nerve cells who bodies lie in brainstem and spinal cord
Somatic motor fibres - axons that lead to skeletal msucle
Motor Unity - one nerve fibre and all muscle fibres innovated by it.
24
Q
Muscles fibres in one motor unit
A
- dispersed throughout muscle
- Contract in unison
- produce weak contraction over wide area
- Able to sustain long term contraction as motor units take turn contracting
- Contraction usually requires contraction of several motor units at once .
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Small motor unit
- Fine degree of control
- 3-6 muscles per neuron
- eye and hand muscles
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Large motor units
- More strength than control
- Powerful contractions supplied by alrge motor units with hudreds of fibres
- Gastrocnemius has +- 1000 muscle fibres per neuron
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Neuromuscular Junction
nerve fibre meets target cell - target cell is muscle cell
- Terminal branches of nerve fibres within NMJ forms synapses with muscle fibres
- one nerve fibre stimulates the muscle fibre at several points within MNJ
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Nerve parts
Axon terminal - swolen end of nerve fibre
Synaptic cleft - gap beween axon terminal and sarcolemma
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Electrivally excitable cells
- Muscle fibers and neurons are electrically excitable
- Cell membranes exhibit voltage changes in responce to stimulation
- Voltage - difference in eectrical charge from one point to another
- resting membrane potential +- 90mV in skeletal muscle cells
- Maintained by sodium/potassiun point
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Unstimulated resting cell
- More anions (-ve) on inside of cell membrane than outside
- anions make inside of pl asma membrane negatively cahrged by comparison to outer surface
- plasma membrane is electrcially polarized with negative resting membrane potential
- there are excess Na+ In extracellular fluid (ECF)
- Excess potassium Ions (K+) in intracellular fluid.
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Stimulated
- Na+ Ion gates open in the plasma memrbrane
- Na+ flows into cell down its electrochemical gradient
- these cations overide the negative charges in ICF
- depolarization↔inside of plasma membrane becomes positive
- Na+ gates close and K+ gates open
- K moves otu of cell partly repelled by na+ cahrge and aprtly because of concentration gradient
- Loss of positive K+ ions turns membrane negative again - repolarization
- this voltage shift - depolarization and repolarization - is an action potential
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Resting membrane potential - cell not stimulated
- Action potential is quick event in stimulated excitable cell
- perpetuates itself down length of cell membrane
- AP causes another ot happen immediatly infront of it
- triggers another
- wave of excitation is called a impulse
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Neruomuscular toxins and paralysis
- toxins can interfere with synaptic function - paralyzem uscles
- some pesticisdes contain cholisterase inhibitors
- bind to acetylcholinestrae and prevent it from degrading ACh
- Spastic paralysis - state of continual contraction of muscles - suffocation
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Teatnus / lockjaw
Form of spastic paralysis cauased by toxin Clostridium Tetani
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Flaccid paralysis
Muscles are limp and cannot contract
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Butolism
Food poisoning caused by neruomsuclar toxin secreted by the bacterium colstridum botulinum
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Exccitation
- Excitation↔process in which nerve action potential lead to muscle action porentials
- Action potential arrives at synaptic terminal
- scetylcholine is relaseased
- permeability of membrane changes and triggers ACh
- ACh molecules cross synaptic cleft and bind to ACh receptors on Sarcolemma
- Na+ ions rush into sarcolemma generate action potential
- K+ moves out of cell - concentration gradient
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Excitation - contracting coupling
events that link action potentials on sarcolemma to activation of myofilaments - preparing them to contract
- Action potential spreads along each T tubule (lie between two ends of sarcoplasmic reticulum
- In resting state tropmyosin srands cover active sites on thin filaments
- Prevents cross-bridge formation
- Ca+ binds to and cahnges shape of troponin molecule
- Troponin molecule roles tropomyosin from active sites
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Contraction
- Contraction↔muscle fibre develops tension and may shorten
- Energised (ADP) myosin heads bind to active sites of F actin
- Formation of cross bridges
- contraction cycle begins
- Myosin head pivots towards M line - requires energy. REFERED AS A POWER STROKE
- Breaking of new ATP - breaking of cross bridge.
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Relaxation
stimulation ends - muscle fibres relaxes and returns to resting length
- Cessation of nervous stimulation and ACh release.
- ACh breakdown by Acetylcholinesterase (AChE)
- Reabsorption of Ca ions by sarcoplasmic reticulum
- Free myosin head splits ATP int ADP and phosphate group
- Energy released cocks Myosin head
- cycle can now be repeated
- ATP binds to myosin head and breaks link to action
- Active site now free.
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Length tension relationship
amount of tension generateed by a muscle depending on how stretched or shortened it was before it was stimulated
- If overally shortened before stimulation - weak contraction results as thick filaments approached Z discks
- if to stretched before stimulated - weak contraction results as minimal overlap between thich and thin filaments in minimal corss bridge formation
- Optimum resting length produces greatest force of muscle contracts↔Nervous system maintains muscle tone (partial contraction) to ensure that resting muscles are near this length
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Rigor Mortis
- Hardening of muscles and stiffening of body
- Starts 3-4 hours after death
- teriorating sarcoplasmic reticulum releases Ca+2
- Allows Ca+2 to enter cytosol
- Ca+2 activates Myosin actin cross bridging
- muscle contracts, but cannot relax
- Muscle relaxation requires ATOP - No longer produced after death
- Fibres remain contracted until Myofilaments begin to decay
- Rigor mortis peaks +- 12 hours after death
- Diminishes over next 8-60 hours.
43
Threshold
Minimul voltage neccessary to generate an action potential in muscle fibre and produce contraction
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Twitch
cycle of contraction and relaxation when stimulus is at threshold or higher
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Latent Period
very bried delay betweein stimulus and contraction
- Time required for excitation, excited Contraction coupling, and tensing of elastic Components of muscle
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Contraction phase
time when muscle generates external tension
- Force generated can overcome load and cause movement
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- Relaxation phase↔time when tension declines to baseline
- SR reabosrbs Ca+2 myosin released actin adn tension decreases
- Takes Longer than contraction.
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Integumentary system
Skin and accessory organs (hair nails + glands).
Largest and heaviest organ - thick and thin
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Thick skin (location, accessories and epidermis thickness)
Plams of hands/soles of feet
sweat glands
Sweat glands, NO hair follicles or Sebacenous glands
Epidermis - 0.5mm thick
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Thin skin (location, accessories and epidermis thickness)
Rest of body (Not soles/palms)
Hair follicles, sebaceous glands and sweat glands
Epidermis +/- 0.1mm thick
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Functions of the skin
Resistance to trauma/infection
H2 barrier (prevents h2 getting in) - tight junctions between cells (prevents dehydration)
Uv radiation + harmful chemicals
Vitamin D synthesis (First step - liver and kidneys complete)
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Epidermis - outer stratified squamous epithelium
Keritinized (tough protein)
layered + flat cells.
MAIN CELL = Keratinocytes
No blood vessels - nutrients fro diffusion from underlying connective tissue.
Nerve endings and receptors for touch/pain
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Layers of epidermis (Deepest to top)
1. Stratum basale - single layer stem cells + keratinocytes. Migrate to surface to replace lost cells - also contains melanocytes nad tactile cells
2. Stratum spinosum - several layers of keratinocytes + desmosmes and tight junctions
3. Stratum granulosum - 3-5 layers of flat keratinocytes (dark staining keratohyalin granules)
4. Stratum lucidum - thin + pale layer only in thick skin - keratinocytes packed with clear protein eleidin.
5. Stratum corneum - surface layer - several layers (up to 30) of dead scaly keratinized cells.
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Keratinocytes
synthesis keratin - produced by mitosis of stem cells. needs abundant Oxygen and nutrients - once away from Blood vessels, itosis cannot occur
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Melanocytes
Synthesise pigment melanin - sheilds DNA from UV radiation (only in stratum basale)
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Dendric cells
Macrophages, originate in bone marrow - guard against pathogens (Stratum spinosum + stratum granulosum)
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Tactile cells
Touch receptor cells associated w/ dermal nerve fibres - base layer of epidermis
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Dermis
Connective tissue layer under epidermis - 0.2mm to 4mm.
Mainly collagen + blood vessels, sweat glands, sebaceous glands and nerve endings
Hair follicles + nail roots.
FOrms wavy boundary with epidermis
DERMAL PAPILLAE - Upward finger like extension of dermis.
- Prominant wave on fingers - finger prints
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Dermis layers
Papillary layer - superficial zone - thin areolar tissue in and near dermal papilla (allows mobility of leukocytes and other defence cells)
Reticular layer - deeper, thicker layer. Dense irregular connective tissue. (stretch marks - tears in collagen fibres)
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Hypodermis
Deep connective tissue layer below dermis - not considered apart of the skin, but associated with it)
Subcutaneous tissue - more areolar and adipose tissue than in dermis. Pads the body and binds skin to underlying tissues
Abundant blood vessels - common injection sites
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Skin disorders
Ichthyosis - inherited, shedding process inhibited (can result in overheating)
Eczema - chronic inherited inflammatory skin condition w/ dry itchy and reddening of skin
Exfoliative dermatitis - excessive shedding of skin
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Skin colour
Melanin produced by melanocytes - accumulates in keratinocytes
Eumelanin - brownish black
Pheomelanin - reddish yellow
Haemoglobin - pink/red hue to skin
Carotene - yellow pigment aquired from egg yolks / orange/ yellow vegetables
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Hair
Slender filament of keratinized cells gorwing from follicle in skin
- not on palms/ soles.
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Structure of Hair
Bulb↔A swelling at the base of a hair follicle where hair originates in Dermis - only living hair cells are in or near bulb
Root↔the remainder of the hair in the follicle
Shaft↔the portion above the skin surface
Hair matrix↔region of mitotically active cells immediately above papilla - hair growths centre
Dermal papilla↔Bud of vascular connective tissue encase by bulb - only source of nutrition for hair
Hair receptors↔Sensory nerve fibres entwining follicles
Piloerector muscle (arrector pili)↔smoothe muscle attaching follicle to the dermis - contracts to make hair stand on end - goosebumps
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Skin apendages - Nails
Clear derivates of stratum corneum - thin dead cells packed with hard keratin
Nail plate - hardp art of the nail, free bit hangs over fingertip (nail body attached to finger, nail root, under skin)
Nail fold surrounding rising skin around nail
Nail groove - separates nail fold from nail plate
Nail bed - skin under naiN
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Sweat glands
Apocrine sweat glands - groin/anal region, areola, beard area in men - near hair follicles. milky sweat + pheromones.
Merocrine sweat glands- most numerous, dese on palms, soles + forehead. Simple tubular glands + watery perspiration
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Sweat
Protein free filtrate of blood plasma - 99% water with a ph of 4-6
500ml/day
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Mammary glands
Produce milk - develop during pregnancy and lactation
MODIFIED APOCRINE SWEAT GLANSD - Rich secretion
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Skin cancer
§ Basal cell carcinoma
□ Most common type and least dangerous - seldom metatasizes
□ Forms from cells in stratum basale
□ lesion is small shiny bump with central depression and beaded edges
§ squamous cell carcinoma
□ Arises from keratinocytes of stratum spinosum. Lesions usally on scalp, ears, lower lip or back of hand.
□ raised reddened scaly appearance later formed a concave ulcer
□ cahnce of recovery good with early detection and surgical removal
□ tends to metastasize to lymph nodes - may become lethal
§ malignant melanoma
□ Cancer arises from melanocytes <5% of skin cancers - most deadly form.
□ Can be successfully removed if caught early, but if metastasizes it is usually fatal
□ Greatest risk factor - familial history
Highest incidence in men, redheads and people who had severe sunburn as a child
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Burns
Leading cause of accidental death
First degree burns
□ Only involve epidermis
□ Redness, slight edema and pain
□ heal in days
Second degree burns
□ Partial thickness burn - involves part of dermis
□ May appear red, tan or white - blistered and painful
□ two weeks to several months to heal and may leave scars
Third degree burn
□ Full thickness burn - involves epidermis, all of dermis and often some deeper tissue.
□ Often requires skin grafts
needs fluid replacement, infection control, supplemental nutrition
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stages of healign a skin wound
§ Several vessels bleed into cut
§ mast cells and damaged cells release histamine
§ histamine dialates blood vessels and makes capillaries more permeable
§ blood plasma seeps into wound carrying antibodies and clotting proteins
§ Blood clot forms↔Knits edges of cut together. Inhibits spread of pathogens
§ Forms scab that temporarily seals wound and blocks infection
§ Macrophages phagocytise and digest tissue debris
§ New capillaries sprout from nearby vessels.
§ Deeper portion of cloinfiltrated by capilaries and friblasts
§ Transforms into soft mass called granulation tissue
§ macrophages remove blood cot
§ fibroblasts deposit new collagen
§ begins 3-4 days after injury and lasts up to two weeks
§ Epithelial cells multiply and migrate beneath scab - tissue regenerates
§ underlying connective tissue undergoes fibrosis
§ Scar tissue may or may not show through epithelium
Remodeling phase begins several weeks after injury and may last up to 2 years
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Blood
Connective tissue.
Plasma - liquid in blood
cells - forms elements of the blood
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Function of the blood.
§ Transportation↔Dissolved gases, nutrients, hormones and metabolic wastes
§ Regulation of pH and ion composition of interstial fluids
§ Restriction of fluid loss at injury sites - clotting
§ defence against toxins and pathogens
stabilisation of body temperature
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Haeme - recycling of red blood cells
○ Macrophages of liver, spleen and bone marrow monitor quality and engulf old RBC's
○ Each component of haemoglobin molecule is recycled
○ Globular proteins dissembled into amino acids and released for other cells to use
○ Heme units are stripped of ion and turned into biliverdin (green in bruises)
○ Biliverdin is turned into bilirubin (orange/yellow in jaundice) and transported to liver- excreted as bile
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blood antigens
○ Type A↔Surface antigen A only
○ Type B↔Surface antigen B only
○ Typpe AB↔Surface antigen A and B
Type O↔Neither surface antigen or AB
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Blood antibodies
○ Type A↔Anti-B antibodies in plasma
○ Type B↔Anti-A antibodies in plasma
○ Type AB↔Neither Anti-A/B antibodies in plasma
Type O↔Both Anti-A/B antibodies in plasma
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Haemolytic disease of the newborn
arise when Rh-neg. woman is carrying Rh-pos. fetus. When fetal and maternal blood mix at delivery - antepartum haemorrhage, amniocentesis - the mother recognises fetus Rh antigens as being foreign
○ Mixing of blood can stimulate mothers immune system to produce anti Rh antibodies - sensitisation
○ if mother has another rh pos. fetus her anti Rh antibodies cross placenta and attack fetus RBCS
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The THorax
○ RIB CAGE
○ Wall comprises↔12 Thoracic vertebrae (posteriorly), sternum (anteriorly) and rubs (Anterolaterally)
○ Inlet - root of neck‒ and outlet - diaphram.
○ Encloses heart and lungs - some protection for spleen , liver and kidney.
Provides atachement for pectoral girdle and upper limbs. Able to contract and expand during respiration
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Sternum
○ Bony plate anteriro to the heart - palpable (subcutaneous) in parts.
○ Three parts
§ manubrim
§ body - gladiolus
§ xiphoid process
Other features↔jugular notch and manubriosternal junction/joint - sternal angle
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The Ribs
○ 12 pairs
○ articulate posteriorly with bodies and transverse processes of vertebrae
○ articulate anteriorly with their costal cartilages
○ costal cartialges - hyaline cartilage - to attach rib to sternum.
○ Costochondral joints classified as priamry cartilaginous joints
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Ribs anatomy
○ Head↔portion of rib that articulates w/ bodies of thoracic vertebrae. - superior and inferior articular facets
○ Neck↔narrow portion distal to the head
○ tubercle↔wider, rough area distal to the neck. - articulates with transverse costal facet of vertebra
○ Angle↔lateral curve of rib
○ Shaft↔long sloping blade like portion of rib. - costal groove on inferior margin of shaft
True ribs↔Ribs 1-7. Each articulate with sternum via costal cartilage
False ribs↔ribs 8-12. Connects to costal cartilage of above ribs. forms costal margin.
Floating ribs↔ribs 11-12. No cartilaginous connection to sternum. No connections to costal cartilages above. No tubercles. No attachments to transverse processes of vertebra
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Chest cavity + contents
○ Contains
§ Right and left lungs and pleural cavities
§ heart and great vessels - centrally, in mediastinum
§ trachea, oesophagus, nerves
Mediastinal boundaries
○ Anteriorly↔sternum
○ posteriorly↔vertebral column
○ inferiorly↔diaphragm
superiorly↔thoracic inlet
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Mediastinal subdivisions
○ T4 plane
§ Arching aorta
§ tracheal bifurcation
§ azygos vein enters SVC
§ thoracic duct crosses vertebral column
○ Inferior mediastinum
§ Further subdivided by fibrous pericardium into
□ Anterior mediastinum
□ Middle mediastinum
□ Posterior mediastinum
□ Pericardium
□ heart
roots of great vessels
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Pulmonary circuits
○ Major divisions of circulatory system
○ Pulmonary circuit↔right side of heart - carries blood to lungs for gas exchange and back to heart
§ Oxygen poor blood arrives at inferior and superior venae cavae
§ Blood sent to longs via pulmonary trunk
○ Systemic circuit↔Left side of heart - supplies oxygenated blood to all tissues of body and returns it to heart
§ Fully oxygenated blood arrives from lungs via pulmonary veins
§ Blood sent to all organs of the body via aorta
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Histology (anatomy) of blood vessles
§ Tunica intima - innermost
§ tunica media - middle
tunica adventitia - outer
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Anatomy of the heart
○ Hollow four chambered fibromuscular pump
○ Right and left atria and right and left ventricles
Base, apex, surfaces and borders
□ Outer fibrous pericardium↔Outer collagenous, inelastic sac. Fused to central tendon of diaphragm and adventitia of great vessels. Attached by 'ligaments' to sternum - variable. Securely anchored heart within thorax
□ Parietal serous Pericardium↔Lines the fibrous pericardium and reflects on to surface of the heart
□ Visceral serous pericardium
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Chambers of the heart
○ Right and left atria↔superior in position. receive blood returning to heart. Auricles (seen on surface) - extensions of chamber
Right and left ventricles↔inferior in position. Pump blood into aorta and pulmonary trunk
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Atriums
○ Openings for veins - venae cavae, pulmonary veins
○ Reveive venous blood from systemic and pulmonary circulations
○ Blood reservoir - weak pump
Right atrium
§ Musculi pectinati.
§ Crista terminalis - suculus terminalis
§ Limbus fossa ovalis + Fossa ovalis
§ cusps of tricuspid valve
§ Openings for↔Superior/inferior vena cavae and Coronary sinus
○ Left atrium
§ Openins of 4 pulmonary veins.
§ Cusps of bicuspid valve.
Roughened auricle
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Ventricles
○ Thick muscular chambers - cardiac muscle
○ receive blodo from atria via AV openings.
○ Pump blood into systemic and pulmonary circulation
○ Features
§ Trabeculae carneae
§ valve cusps
§ chordae tendinae
§ papillary muscles
aortic/pulmonary opening
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Atrioventricular valves
○ Collagenous tissue lined with endothelium. Control blood flow from atria to ventricles
○ Right AV has three cusps - tricuspid valve
○ Left AV has two cusps - mitral or bicuspid valve
Chordae tendinae - attach to valves. Prevents AV valves from flipping back into atria when ventricles contract. Each papilalry muscle has 2-3 attachments to heart wall - distribute physical stress, coordinate timing of electrical conduction and provide redundancy
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Semilunar valves
○ Conenctive tissue lined with endothelium. Control flow into aorta and pulmonary trunk
○ Pulmonary semilunar valve↔between right ventricle and pulmonary trunk
aortic semilunar valve↔between left ventricle and aorta
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Blood flow through the chambers
○ In a typical cycle↔followign ventricular contraction, ventricles relax. Pressure inside ventricles drop. Semilunar valves close as blood flows back into ventricles from great vessels. AV valves open - blood flows from atria into ventricles
○ Ventricles contract↔AV valves close as blood attempts to back up into atria. Pressure rises inside of ventricles. Semilunar valves open and blood flows into great vessels
○ Opening and closing of all heart valves - passive.
○ Close when backward pressure gradient pushes blood back
○ open when forward pressure gradient pushes blood forwards
○ I.E. Opening and closing due to pressure differences between chambers.
○ Flimsy AV valves dont require to much pressure to close. Semilunar valves have fibrous nodles in centre - stronger back pressure for short duration
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Structure of cardiac muscle
○ Cardiomyocytes↔short, thick branched cells
○ striations of actin and myosin - as in skeletal muscle
○ Central nucleus surrounded by light staining mass of glycogen
○ intercalated discs - join cardiomyocytes end to end
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The conduction system of the heart
○ Specialised muscle cells that control and coordinate heart beat
○ cardiac muscle contracts on its own - auto-rhythmicity (without stimulation)
○ Maximum heart rate is 230bpm - maximum rate that AV node can conduct impulses.
§ Comprises an internal pacemaker and nerve like conduction pathways through myocardium
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