Motor System Chapter 10 - PDF

Motor System Ch 10 (9.4) Key Questions What are the functions of muscles? What are the three types of muscles and their characteristics? How do muscles attach to bone? What is the sliding filament theory? What is an antagonistic pair? Explain how nerves stimulate muscle cells. Explain muscle contrac...

Motor System Ch 10 (9.4) Key Questions What are the functions of muscles? What are the three types of muscles and their characteristics? How do muscles attach to bone? What is the sliding filament theory? What is an antagonistic pair? Explain how nerves stimulate muscle cells. Explain muscle contraction. What are the different graded responses? What causes fast and slow twitch? Key Questions How do muscles get energy for contractions? What is creatine phosphate? Explain muscle fatigue and oxygen debt. Function of Muscles 1. Produce movement 2. Maintain posture 3. Stabilize joints 4. Generate heat Muscles and Body Movements Movement is attained due to a muscle moving an attached bone  Muscles and Body Movements Muscles are attached to at least two points Origin – attachment to a immovable bone Insertion – attachment to an movable bone Muscle Cells Muscle cells are elongated ○ (muscle cell = muscle fiber) Contraction of muscles is due to the movement of microfilaments ○ When muscles contract, they shorten ○ When muscles relax, they lengthen Muscles Muscles working pairs are called antagonistic muscles This means that when one contracts the other relaxes ○ EX) bicep contracts, tricep relaxes The muscle that contracts to bend a joint is a flexor The muscle that relaxes to bend a joint is a extensor Muscles Three types: Cardiac muscle – involuntary muscle found in heart control by autonomic nervous system Smooth muscle – involuntary muscle found in lining of various organs Ex) digestive system, uterus, blood vessels Skeletal muscle – voluntary muscle found covering body, attached to bones using tendons Cardiac Muscle Cardiac Muscle Characteristics Has striations Involuntary contractions Usually has a single nucleus Joined to another muscle cell at an intercalated disc Found only in the heart Smooth Muscle Smooth Muscle Characteristics Has no striations Spindle-shaped cells Single nucleus Involuntary – no conscious control Found in walls of hollow organs Skeletal Muscle  Skeletal Muscle Characteristics Most are attached by tendons to bones Cells are multinucleate Striated – have visible banding Voluntary – subject to conscious control Cells are surrounded and bundled by connective tissue Skeletal Muscles Skeletal muscles are composed of several bundles of cells called fibre, The muscle cells that make up the fibre contain more than one nucleus each The fibres are enclosed in a membrane called the sarcolemma Within the muscles fibre are tiny myofilaments, a thread of contractile protein Skeletal Muscles The myofilaments types are: 1) actin – thin myofilament 2) myosin – thick myofilament The length of the muscle fibre is defined by the Z lines that anchor the actin fibres The length between Z lines is a sarcomere The myosin length forms the A band (darker) The actin that does not overlap the myosin forms the I band (lighter) Sliding Filament Theory This is a working model of what scientists believe happens during muscle contraction The end of the fiber contains a Z line which is attached to the actin fibers Ca binds the actin fibers to reveal binding sites that myosin will power stroke to attach to reducing the I band When ATP interacts with the myosin, the club like head releases, resetting the I band ATP is reduced to ADP until the next power stroke  How do the muscle filaments know when to move? Muscle is Stimulated by Nerve Skeletal muscles must be stimulated by a nerve to contract Motor unit ○ One neuron ○ Muscle cells stimulated by that neuron Nerve Stimulus to Muscles Neuromuscular junctions – the site of nerve and muscle association Nerve Stimulus to Muscles Synaptic cleft – gap between nerve and muscle Nerve and muscle do not make direct contact Area between nerve and muscle is filled with interstitial fluid Figure 6.5b Transmission of Nerve Impulse Neurotransmitter – a chemical released by the nerve upon arrival of nerve impulse The neurotransmitter - acetylcholine Neurotransmitter attaches to receptors on the sarcolemma Sarcolemma becomes permeable to sodium (Na+) Sodium enters the cell and generates an action potential Once started, muscle contraction cannot be stopped https://www.youtube.com/watch?v=nTZn BdeIb5c Muscle Contraction Starts with a nerve impulse stimulating muscles cells Muscle fiber contraction is “all or none” The pause between impulse and contraction is called latent period Contraction phase - The actin and myosin filaments contract causing the shortening of the muscle Relaxation phase – the filaments relax and disengage returning the muscle to resting length  What happens when multiple nerve impulses get sent to a muscle? Muscle Contraction Stimulation of the muscle can occur before the relaxation phase is complete This leads to increases overlap and greater muscle shortening causing greater force of contraction Since the stimuli are being added together this process is called summation If you have muscles that continually work without relaxation that’s called tetanus Muscle Contraction Within a skeletal muscle, not all fibers may be stimulated during the same interval Different combinations of muscle fiber contractions may give differing responses Graded responses – different degrees of skeletal muscle shortening Types of Graded Responses Twitch ○ Single, brief contraction ○ Not a normal muscle function Tetanus (summing of contractions) ○ One contraction is immediately followed by another ○ The muscle does not completely return to a resting state ○ The effects are added Types of Graded Responses Unfused (incomplete) tetanus ○ Some relaxation occurs between contractions ○ The results are summed Fused tetanus ○ No evidence of relaxation before the following contractions ○ The result is a sustained muscle contraction Fast and Slow Twitch 3 Different forms of myosin ○ Type I – slow twitch, for distance and endurance, also slow ATP break down (aerobic) ○ Type IIa – fast twitch, for speed, also fast ATP break down (anaerobic) ○ Type IIx – same as Type IIa Muscle Response to Strong Stimuli Muscle force depends upon the number of fibers that are stimulated More fibers contracting results in greater muscle tension Muscles can continue to contract unless they run out of energy Energy for Muscle Contraction Muscles use stored ATP for energy ○ Bonds of ATP are broken to release energy After this initial use, other pathways must be utilized to produce ATP Direct phosphorylation ○ Muscle cells contain creatine phosphate (CP) ○ After ATP is depleted, ADP is left ○ CP transfers energy to ADP, to regenerate ATP Energy for Muscle Contraction Aerobic Respiration (cellular respiration) Series of metabolic pathways that occur in the mitochondria Glucose is broken down to carbon dioxide and water, releasing energy This is a slower reaction that requires continuous oxygen Energy for Muscle Contraction Anaerobic glycolysis Reaction that breaks down glucose without oxygen Glucose is broken down to pyruvic acid to produce some ATP Pyruvic acid is converted to lactic acid What happens when your muscles get tired? Muscle Fatigue Creatine phosphate, is naturally found in the muscle cells to ensure that ATP supplies remain high It supplies phosphate to ADP to become ATP Under heavy exercise, the environment around muscles becomes acidic This leads to a burning feeling and eventually muscle failure The rapid breathing that follows is designed to repay the oxygen debt Muscle Fatigue and Oxygen Debt When a muscle is fatigued, it is unable to contract The common reason for muscle fatigue is oxygen debt Oxygen must be replaced Oxygen is required to rid of accumulated lactic acid Increase acidity (from lactic acid) and lack of ATP causes the muscle to contract less What happens to your muscles when you don’t exercise regularly? Effects of NO Exercise on Muscle Atrophy ○ a decrease in total mass of a muscle ○ happens when muscles aren’t contracting frequently enough Effects of Exercise on Muscle Hypertrophy ○ Increase in muscle size ○ Increase in muscle strength ○ Increase in muscle efficiency ○ Muscle becomes more fatigue resistant The end…