& D.4 Cardiac Muscle Cells (p 685) 11.2 Movement & D.4 Cardiac Muscle Cells (p 685)

Movement KINESIOLOGY: The study of movement of the human body What happens when somebody moves? Your brain sends an impulse (an action potential) through a nerve to a muscle to tell it to contract. Muscles are connected to bones by tendons. When a muscle contracts, it will move the bone.

Bones Rigid structures for anchoring muscles They contain several different tissues and therefore are organs. Functions: provide a hard framework to support the body Protect vulnerable softer tissues and organs (ex: the heart and lungs are protected by the ribcage) Act as levers so that body movement can occur Form blood cells in bone marrow Storage of minerals (ex: calcium and phosphorus)

The Human Skeleton Adult humans have 206 bones (newborns have ~270 Remember why?) 26 bones in your vertebral column 12 pairs of ribs Teeth are not considered to be bones

Of the 206 bones in the body, 106 of them are found in your hands and feet

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Exoskeletons Some animals do not have bones but have exoskeletons that provide a similar function. Exoskeletons are external skeletons that surround and protect most of the body surface of crustaceans, insects, and spiders

Did you know? As an insect grows, its exoskeleton breaks open The enlarged insect will emerge leaving the old exoskeleton behind. It will take some time for a new exoskeleton to fully develop and harden. During this time, the insects soft exoskeleton will make it vulnerable to predators and environmental factors.

Levers Bones and exoskeletons facilitate movement by anchoring muscles and acting as a lever. Muscles are attached to the outside of bones and the inside of exoskeletons A lever is a rigid rod (the bone) that turns about a pivot (usually a joint). Levers change the size and direction of forces.

Lever Components Lever arm Effort force Fulcrum (pivot point) Load In our bodies, it’s the bone Effort force This is where the force is exerted, provided by muscles Fulcrum (pivot point) Load The body part that is moved (as a result of the Resultant Force) Provides Resistant Force

First Class Lever The fulcrum is in between the effort and the load Like a see-saw. When effort force is applied, the resultant force causes the load to move up. Ex: Nodding Your Head

First Class Lever- Nodding The pivot/fulcrum is where the skull meets the top of the spine The neck muscles contract to provide the effort force to move the spine down and the resultant force to move the chin up. When the neck muscles relax, the chin move down

Second-Class Lever The resultant force in between the pivot and the load Like a wheelbarrow. There is a mechanical advantage because less effort force is required Ex: Standing on your tip toes

Second Class Lever – Tippy Toes The pivot is at the toe joints The foot is the lever arm When the calf muscles contract, it provides the effort force required to lift the load (the body)

Third Class Levers The effort force is in between the pivot and the load No mechanical advantage, more effort force is required to lift the load. Ex: Bending your arm

Third Class Lever – Bending Arm The pivot is at the elbow joint The muscles in the upper arm (bicep) provide the effort force require to bend the forearm

Muscles and Tendons Skeletal Muscles are attached to bones Tendons are what attach muscles to bones Tendons are cords of dense connective tissue Muscles provide the force necessary for movement by shortening the length of their fibres. They work in antagonistic pairs to achieve movement When one muscle contracts, the other relaxes

Antagonistic Muscle Action When the biceps contract, the tendon pulls on the bone pulling the lower arm up. The triceps are relaxed When the triceps contract, it causes the bones to straighten. The biceps are relaxed. Biceps = muscles at front of upper arm Triceps = muscles at the back of the upper arm

Remember Ventilation? The process of ventilation required the movement of antagonistic muscle pairs INHALATION: The external intercostal muscles CONTRACT; the internal intercostal muscles RELAX to ex EXHALATION: The internal intercostal muscle CONTRACT; the external intercostal muscles RELAX

Antagonists Muscles in Insect Legs femur tibia tarsus

Antagonist Muscles in Insects Legs When the grasshopper prepares to jump: FLEXING: The flexor muscles will contract bringing the tibia and tarsus in a “Z” position. The extensor muscles are relaxed. EXTENDING: The extensor muscles contract to extend the tibia and produce a powerful propelling force.

JOINT Also called an articulation or arthrosis The point where 2 or more bones contact one another Joints cause mobility and hold the body together Most joints include: Bones Ligaments Muscles Tendons nerves

Annotate Human Elbow Joint p478 Tendon Spongy Bone Ligament

Elbow Joint Spongy Bone Cartilage the end of each bone is made of spongy bone It is light but strong (provides strength without too much mass) Cartilage The covering at the end of a bone It has a smooth surface which provides easy movement, preventing friction Absorbs shocks

Elbow Joint Joint Capsule Synovial Fluid Synovial Membrane Seals the space between the bones at a joint Helps prevent dislocation Synovial Fluid Fluid at joint capsule Acts as a lubricant for the joint to prevent friction. Contains the required food and oxygen to maintain cartilage Synovial Membrane Secretes synovial fluid and keeps it within the joint

Elbow Joint Ligaments Biceps Triceps Tough tissues that attach bones to bones Keeps the bones together in correct relative position Biceps Muscles in upper arm that will bend the arm Triceps Muscles in upper arm that will straighten the arm

Elbow Joint Humerus Radius Ulna Upper arm bone attached to the biceps and triceps Radius Lower arm bone attached to the biceps (via a tendon) Ulna Lower arm bone attached to the triceps (via a ligament)

Elbow Joint The elbow joint is called a synovial joint because of the presence of the synovial cavity. There is a rich supply of blood to joints. If blood vessels supplying the joint gets damaged and there is local bleeding, it may result in swelling of the area

Other Joints Synovial Joints have a lubricating synovial cavity Most common Provides lots of movement Cartilaginous Joints Joins bones with cartilage Ex: spinal column Fibrous Joints Joins bones with connective tissue (collagen) Immobile Ex: Skull Bones

“Joint Terms” Flex and Extend = ex: movement that moves your leg back and forth (like a pendulum) Flexion = decrease the angle between the connecting bones Extension = increase the angle between the connection bones Abduction and adduction = moving your leg sideways (away from the center of the body) Abduction = bones moves away from body’s midline Adduction = bones move toward body’s midline Rotation = bone moves along its own longitudinal axis

Hinge Joints Provides an opening-and-closing type of movement like the action of a door This movement is in one direction – flex and extend Ex: the elbow joint, the knee joint

Ball-and-Socket Joints Allows for movement in several directions Flex and extend Abduction and adduction Rotational movement Ex: hip joint the head of the femur is ball shape and fits into a cup like depression of the hip bone

Joints and Movement The structure of the joint (including the joint capsule and ligaments) determine the movements that are possible. KNEE JOINT HIP JOINT Synovial Joint Involved in movement of the leg and required for walking Involved in the movement of the leg and required for walking Hinge Joint Ball and Socket Possible Motions: Flex and Extend Small amount of rotation Abduction and Adduction Rotation Movement in one direction Movement in many directions (multiaxial)

Muscles Human body has 3 types of muscles Cardiac muscle (muscle exclusive to the heart) Smooth muscle (also known as non-striated muscle) Muscle that makes up organs such as the stomach Skeletal Muscle (also known as striated muscle) Muscle associated with bones and therefore involved in movement

Striated Muscle Fibres Like all other body tissues, muscles are made up of cells. Muscle cells are called muscle fibres They are elongated in shape The arrangement of proteins within them create a banded appearance or stripes under a microscope which is why is it called striated muscle

Parts of a Muscle Fibre Each muscle cell was originally many cells fused together, which is why a muscle cell has many nuclei. Sarcolemma: membrane surrounding the muscle cell Sarcoplasm: the cytoplasm of the muscle cell Within the sarcoplasm there are multiple mitochondria for ATP production (because muscle contractions require a lot of energy)

Parts of a Muscle Fibre Sarcoplasmic Reticulum: membrane found within the sarcoplasm (similar to the ER) Stores and releases calcium ions into the sarcoplasm which will trigger a muscle contraction

Parts of a Muscle Fibre Myofibrils: Thin fibres inside the muscle cell There are many myofibrils in a muscle fibre Create the striated (striped) pattern of light and dark skeletal muscles Contain 2 types of myofilaments: myosin and actin which are made of proteins Each myofibril is made up of contractile sarcomeres Sarcomere: a functional unit of the muscle (a segment of a myofibril)

Sarcomere

Sarcomere Intermediate Section Light section Dark Section Dark Section Light Section

Sarcomere Z line Z line

Sarcomere A sarcomere is found between two Z-lines

Sarcomere Thin actin filaments form the I band They are attached to the Z line Thick myosin filaments are found in the A band In the dark regions, myosin and actin overlap In the gray H zone, only myosin is present

Myofilaments - MYOSIN Myosin filaments contain several myosin strands bundled together (that’s why they’re the thick filament!) Each myosin strand has a “hook” or a “head” that binds to actin. The ends without “heads” are the “tails” and they are found within the H zone

Myofilaments -ACTIN Actin filaments contain strands of actin and 2 proteins: TROPOMYOSIN and TROPONIN 2 strands of tropomyosin wind around the actin filament covering the binding site for the myosin hooks This prevents the muscle from contracting

Actin Filament

Sliding Filament Theory Actin and myosin slide over each other to make the muscle shorter (actin and myosin stay the same size!) Little “hooks” on the myosin filaments attach to the actin and pull them closer to the center of the sarcomere This shortens the sarcomere and the overall length of the muscle fibre  muscle contraction Myosin then releases the actin and repeats the hooking and pulling action further down the actin. This is done with ATP energy (from the mitochondria!) As the filaments slide over each other, the H bands disappears and the I band shortens

Which one is relaxed? Which one is contracted?

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Muscle Contraction When you want to start a muscle contraction, a nerve impulse arrives at the muscle The action potential causes the sarcoplasmic reticulum to release calcium ions into the sarcoplasm The Ca2+ attach to troponin (which is attached to tropomyosin) causing tropomyosin to uncover the binding sites for the myosin hooks.

Actin Filament

Muscle Contraction The myosin hooks will have an ATP molecule bonded to it already. The ATP will hydrolyse into ADP and Pi (but will still be attached to the myosin hook) The myosin hooks can now bind to the binding sites on the actin filament, forming cross-bridges.

Muscle Contraction The ADP and Pi dissociate from the cross-bridge and the myosin hooks bend, pulling the actin filaments toward the M line. This is called the power stroke. It causes the myofilaments to slide over each thus the muscle fibre contracts A new ATP molecule will attach to the myosin hook and the myosin will detach from the binding site. The process may repeat with the hooks attaching to binding sites further down the actin filament.

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Muscle Relaxation Contraction cycles will continue as long as ATP is available and Ca2+ is present in the sarcoplasm When the nerve impulse stops, Ca2+ move back into the vesicle of the sarcoplasmic reticulum by active transport This causes the binding sites on the actin to be covered again (so myosin cannot bind) The muscle will relax.

Cardiac Muscle Cells p685 The structure of cardiac muscle cells allows for propagation of stimuli through the heart wall. Remember, cardiac muscle tissue is unique. It is also striated in appearance, and the arrangement of myofilaments is similar to skeletal muscle.

Cardiac Muscle Cells How do they differ from skeletal muscle fibres? Cardiac muscle cells are shorter and wider. They have only 1 nucleus per cell. Cardiac muscle contraction is not under voluntary control (myogenic!) Many cardiac muscle cells contract even in the absence of stimulation by nerves for the entire life of the organism!

Cardiac Muscle Cells The cells are Y-shaped. There is a specialized junction called an intercalated disc where the end of one cell meets the end of another cell The intercalated disc consists of a double membrane containing gap junctions which are channels that provide a connection between the cytoplasm of adjacent cells. This allows for the rapid movement of ions from one cardiac cell to the next, with low electrical resistance.

Cardiac Muscle Cells So, their Y-shape and gap junctions allows them to be electrically connected This means a wave of depolarization can easily pass form one cell to a network of other cells leading to synchronization of muscle contraction allowing for both atria or both ventricles to contract simultaneously as if it was one large cell.