AP-Ch09

Chapter

9 Muscle Tissue

PowerPoint® Lecture Slides prepared by Jason LaPres Lone Star College - North Harris

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An Introduction to Muscle Tissue  Muscle Tissue  A primary tissue type, divided into  Skeletal muscle  Cardiac muscle  Smooth muscle

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An Introduction to Muscle Tissue  Skeletal Muscles  Are attached to the skeletal system  Allow us to move  The muscular system  Includes only skeletal muscles

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Functions of Skeletal Muscles  Produce skeletal movement  Maintain body position  Support soft tissues  Guard openings  Maintain body temperature  Store nutrient reserves Copyright © 2010 Pearson Education, Inc.

Skeletal Muscle Structures  Muscle tissue (muscle cells or fibers)  Connective tissues  Nerves  Blood vessels

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Skeletal Muscle Structures  Organization of Connective Tissues  Muscles have three layers of connective tissues  Epimysium: – exterior collagen layer – connected to deep fascia – Separates muscle from surrounding tissues

 Perimysium: – surrounds muscle fiber bundles (fascicles) – contains blood vessel and nerve supply to fascicles

 Endomysium: – surrounds individual muscle cells (muscle fibers) – contains capillaries and nerve fibers contacting muscle cells – contains myosatellite cells (stem cells) that repair damage Copyright © 2010 Pearson Education, Inc.

Skeletal Muscle Structures

Figure 9–1 The Organization of Skeletal Muscles.

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Skeletal Muscle Structures  Organization of Connective Tissues  Muscle attachments  Endomysium, perimysium, and epimysium come together: – at ends of muscles – to form connective tissue attachment to bone matrix – i.e., tendon (bundle) or aponeurosis (sheet)

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Skeletal Muscle Structures  Nerves  Skeletal muscles are voluntary muscles, controlled by nerves of the central nervous system (brain and spinal cord)

 Blood Vessels  Muscles have extensive vascular systems that  Supply large amounts of oxygen  Supply nutrients  Carry away wastes Copyright © 2010 Pearson Education, Inc.

Skeletal Muscle Fibers  Are very long  Develop through fusion of mesodermal cells (myoblasts)  Become very large  Contain hundreds of nuclei

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Skeletal Muscle Fibers

Figure 9–2 The Formation of a Multinucleate Skeletal Muscle Fiber.

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Skeletal Muscle Fibers

Figure 9–2a The Formation of a Multinucleate Skeletal Muscle Fiber.

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Skeletal Muscle Fibers

Figure 9–2b The Formation of a Multinucleate Skeletal Muscle Fiber.

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Skeletal Muscle Fibers  Internal Organization of Muscle Fibers  The sarcolemma  The cell membrane of a muscle fiber (cell)  Surrounds the sarcoplasm (cytoplasm of muscle fiber)  A change in transmembrane potential begins contractions

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Skeletal Muscle Fibers  Internal Organization of Muscle Fibers  Transverse tubules (T tubules)  Transmit action potential through cell  Allow entire muscle fiber to contract simultaneously  Have same properties as sarcolemma

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Skeletal Muscle Fibers  Internal Organization of Muscle Fibers  Myofibrils  Lengthwise subdivisions within muscle fiber  Made up of bundles of protein filaments (myofilaments)  Myofilaments are responsible for muscle contraction  Types of myofilaments: – thin filaments: » made of the protein actin – thick filaments: » made of the protein myosin Copyright © 2010 Pearson Education, Inc.

Skeletal Muscle Fibers  Internal Organization of Muscle Fibers  Sarcoplasmic reticulum (SR)  A membranous structure surrounding each myofibril  Helps transmit action potential to myofibril  Similar in structure to smooth endoplasmic reticulum  Forms chambers (terminal cisternae) attached to T tubules

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Skeletal Muscle Fibers  Internal Organization of Muscle Fibers  Triad  Is formed by one T tubule and two terminal cisternae  Cisternae: – concentrate Ca2+ (via ion pumps) – release Ca2+ into sarcomeres to begin muscle contraction

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Skeletal Muscle Fibers

Figure 9–3 The Structure of a Skeletal Muscle Fiber.

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Skeletal Muscle Fibers  Internal Organization of Muscle Fibers  Sarcomeres  The contractile units of muscle  Structural units of myofibrils  Form visible patterns within myofibrils

 Muscle striations  A striped or striated pattern within myofibrils: – alternating dark, thick filaments (A bands) and light, thin filaments (I bands)

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Skeletal Muscle Fibers  Internal Organization of Muscle Fibers  Sarcomeres  M Lines and Z Lines: – M line: » the center of the A band » at midline of sarcomere – Z lines: » the centers of the I bands » at two ends of sarcomere Copyright © 2010 Pearson Education, Inc.

Skeletal Muscle Fibers  Internal Organization of Muscle Fibers  Sarcomeres  Zone of overlap: – the densest, darkest area on a light micrograph – where thick and thin filaments overlap

 The H Band: – the area around the M line – has thick filaments but no thin filaments

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Skeletal Muscle Fibers  Internal Organization of Muscle Fibers  Sarcomeres  Titin: – are strands of protein – reach from tips of thick filaments to the Z line – stabilize the filaments

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Skeletal Muscle Fibers

Figure 9–4a Sarcomere Structure.

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Skeletal Muscle Fibers

Figure 9–4b Sarcomere Structure.

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Skeletal Muscle Fibers

Figure 9–5 Sarcomere Structure.

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Skeletal Muscle Fibers  Sarcomere Function  Transverse tubules encircle the sarcomere near zones of overlap  Ca2+ released by SR causes thin and thick filaments to interact

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Skeletal Muscle Fibers  Muscle Contraction  Is caused by interactions of thick and thin filaments  Structures of protein molecules determine interactions

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Skeletal Muscle Fibers  Four Thin Filament Proteins  F-actin (Filamentous actin)  Is two twisted rows of globular G-actin  The active sites on G-actin strands bind to myosin

 Nebulin  Holds F-actin strands together

 Tropomyosin  Is a double strand  Prevents actin–myosin interaction

 Troponin  A globular protein  Binds tropomyosin to G-actin  Controlled by Ca2+ Copyright © 2010 Pearson Education, Inc.

Skeletal Muscle Fibers

Figure 9–6a, b Thick and Thin Filaments.

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Skeletal Muscle Fibers  Initiating Contraction  Ca2+ binds to receptor on troponin molecule  Troponin–tropomyosin complex changes  Exposes active site of F-actin

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Skeletal Muscle Fibers  Thick Filaments  Contain twisted myosin subunits  Contain titin strands that recoil after stretching  The mysosin molecule  Tail: – binds to other myosin molecules

 Head: – made of two globular protein subunits – reaches the nearest thin filament Copyright © 2010 Pearson Education, Inc.

Skeletal Muscle Fibers

Figure 9–6c, d Thick and Thin Filaments.

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Skeletal Muscle Fibers  Myosin Action  During contraction, myosin heads  Interact with actin filaments, forming cross-bridges  Pivot, producing motion

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Skeletal Muscle Fibers  Skeletal Muscle Contraction  Sliding filament theory  Thin filaments of sarcomere slide toward M line, alongside thick filaments  The width of A zone stays the same  Z lines move closer together

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Skeletal Muscle Fibers

Figure 9–7a Changes in the Appearance of a Sarcomere during the Contraction of a Skeletal Muscle Fiber.

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Skeletal Muscle Fibers

Figure 9–7b Changes in the Appearance of a Sarcomere during the Contraction of a Skeletal Muscle Fiber.

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Skeletal Muscle Fibers  Skeletal Muscle Contraction  The process of contraction  Neural stimulation of sarcolemma: – causes excitation–contraction coupling

 Cisternae of SR release Ca2+: – which triggers interaction of thick and thin filaments – consuming ATP and producing tension

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Skeletal Muscle Fibers

Figure 9–8 An Overview of Skeletal Muscle Contraction.

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The Neuromuscular Junction  Is the location of neural stimulation  Action potential (electrical signal)  Travels along nerve axon  Ends at synaptic terminal  Synaptic terminal: – releases neurotransmitter (acetylcholine or ACh) – into the synaptic cleft (gap between synaptic terminal and motor end plate) Copyright © 2010 Pearson Education, Inc.

The Neuromuscular Junction

Figure 9–9a, b Skeletal Muscle Innervation.

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The Neuromuscular Junction

Figure 9–9b, c Skeletal Muscle Innervation.

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The Neuromuscular Junction

Figure 9–9c Skeletal Muscle Innervation.

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The Neuromuscular Junction  The Neurotransmitter  Acetylcholine or ACh  Travels across the synaptic cleft  Binds to membrane receptors on sarcolemma (motor end plate)  Causes sodium–ion rush into sarcoplasm  Is quickly broken down by enzyme (acetylcholinesterase or AChE)

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The Neuromuscular Junction

Figure 9–9c Skeletal Muscle Innervation.

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The Neuromuscular Junction  Action Potential  Generated by increase in sodium ions in sarcolemma  Travels along the T tubules  Leads to excitation–contraction coupling  Excitation–contraction coupling: – action potential reaches a triad: » releasing Ca2+ » triggering contraction – requires myosin heads to be in cocked position: » loaded by ATP energy Copyright © 2010 Pearson Education, Inc.

The Contraction Cycle  Five Steps of the Contraction Cycle  Exposure of active sites  Formation of cross-bridges  Pivoting of myosin heads  Detachment of cross-bridges  Reactivation of myosin

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The Contraction Cycle

Figure 9–10 The Contraction Cycle.

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The Contraction Cycle

[INSERT FIG. 10.12, step 1]

Figure 9–10 The Contraction Cycle.

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The Contraction Cycle

Figure 9–10 The Contraction Cycle.

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The Contraction Cycle

Figure 9–10 The Contraction Cycle.

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The Contraction Cycle

Figure 9–10 The Contraction Cycle.

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The Contraction Cycle

Figure 9–10 The Contraction Cycle.

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The Contraction Cycle  Fiber Shortening  As sarcomeres shorten, muscle pulls together, producing tension

 Contraction Duration  Depends on  Duration of neural stimulus  Number of free calcium ions in sarcoplasm  Availability of ATP Copyright © 2010 Pearson Education, Inc.

The Contraction Cycle  Relaxation  Ca2+ concentrations fall  Ca2+ detaches from troponin  Active sites are re-covered by tropomyosin  Sarcomeres remain contracted

 Rigor Mortis  A fixed muscular contraction after death  Caused when  Ion pumps cease to function; ran out of ATP  Calcium builds up in the sarcoplasm Copyright © 2010 Pearson Education, Inc.

The Contraction Cycle  Skeletal muscle fibers shorten as thin filaments slide between thick filaments  Free Ca2+ in the sarcoplasm triggers contraction  SR releases Ca2+ when a motor neuron stimulates the muscle fiber  Contraction is an active process  Relaxation and return to resting length are passive Copyright © 2010 Pearson Education, Inc.

The Contraction Cycle

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Tension Production  The all–or–none principle  As a whole, a muscle fiber is either contracted or relaxed

 Tension of a Single Muscle Fiber  Depends on  The number of pivoting cross-bridges  The fiber s resting length at the time of stimulation  The frequency of stimulation

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Tension Production  Tension of a Single Muscle Fiber  Length–tension relationship  Number of pivoting cross-bridges depends on: – amount of overlap between thick and thin fibers

 Optimum overlap produces greatest amount of tension: – too much or too little reduces efficiency

 Normal resting sarcomere length: – is 75% to 130% of optimal length

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Tension Production

Figure 9–11 The Effect of Sarcomere Length on Active Tension.

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Tension Production  Tension of a Single Muscle Fiber  Frequency of stimulation  A single neural stimulation produces: – a single contraction or twitch – which lasts about 7–100 msec.

 Sustained muscular contractions: – require many repeated stimuli

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Tension Production  Three Phases of Twitch  Latent period before contraction  The action potential moves through sarcolemma  Causing Ca2+ release

 Contraction phase  Calcium ions bind  Tension builds to peak

 Relaxation phase  Ca2+ levels fall  Active sites are covered  Tension falls to resting levels Copyright © 2010 Pearson Education, Inc.

Tension Production

Figure 9–12a The Development of Tension in a Twitch.

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Tension Production

Figure 9–12b The Development of Tension in a Twitch.

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Tension Production  Treppe  A stair-step increase in twitch tension  Repeated stimulations immediately after relaxation phase  Stimulus frequency <50/second

 Causes a series of contractions with increasing tension

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Tension Production  Tension of a Single Muscle Fiber  Wave summation  Increasing tension or summation of twitches  Repeated stimulations before the end of relaxation phase: – stimulus frequency >50/second

 Causes increasing tension or summation of twitches

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Tension Production  Tension of a Single Muscle Fiber  Incomplete tetanus  Twitches reach maximum tension  If rapid stimulation continues and muscle is not allowed to relax, twitches reach maximum level of tension

 Complete Tetanus  If stimulation frequency is high enough, muscle never begins to relax, and is in continuous contraction Copyright © 2010 Pearson Education, Inc.

Tension Production

Figure 9–13a, b Effects of Repeated Stimulations.

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Tension Production

Figure 9–13c, d Effects of Repeated Stimulations.

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Tension Production  Tension Produced by Whole Skeletal Muscles  Depends on  Internal tension produced by muscle fibers  External tension exerted by muscle fibers on elastic extracellular fibers  Total number of muscle fibers stimulated

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Tension Production  Tension Produced by Whole Skeletal Muscles  Motor units in a skeletal muscle  Contain hundreds of muscle fibers  That contract at the same time  Controlled by a single motor neuron

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Tension Production  Tension Produced by Whole Skeletal Muscles  Recruitment (multiple motor unit summation)  In a whole muscle or group of muscles, smooth motion and increasing tension are produced by slowly increasing the size or number of motor units stimulated

 Maximum tension  Achieved when all motor units reach tetanus  Can be sustained only a very short time

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Tension Production

Figure 9–14a The Arrangement and Activity of Motor Units in a Skeletal Muscle.

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Tension Production

Figure 9–14b The Arrangement and Activity of Motor Units in a Skeletal Muscle.

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Tension Production  Tension Produced by Whole Skeletal Muscles  Sustained tension  Less than maximum tension  Allows motor units rest in rotation

 Muscle tone  The normal tension and firmness of a muscle at rest  Muscle units actively maintain body position, without motion  Increasing muscle tone increases metabolic energy used, even at rest

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Tension Production  Two Types of Skeletal Muscle Tension  Isotonic contraction  Isometric contraction

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Tension Production  Two Types of Skeletal Muscle Tension  Isotonic Contraction  Skeletal muscle changes length: – resulting in motion

 If muscle tension > load (resistance): – muscle shortens (concentric contraction)

 If muscle tension < load (resistance): – muscle lengthens (eccentric contraction)

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Tension Production  Two Types of Skeletal Muscle Tension  Isometric contraction  Skeletal muscle develops tension, but is prevented from changing length

Note: iso- = same, metric = measure

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Tension Production

Figure 9–15a, b Isotonic and Isometric Contractions.

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Tension Production

Figure 9–15c, d Isotonic and Isometric Contractions.

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Tension Production  Resistance and Speed of Contraction  Are inversely related  The heavier the load (resistance) on a muscle  The longer it takes for shortening to begin  And the less the muscle will shorten

 Muscle Relaxation  After contraction, a muscle fiber returns to resting length by  Elastic forces  Opposing muscle contractions  Gravity Copyright © 2010 Pearson Education, Inc.

Tension Production

Figure 9–16 Load and Speed of Contraction.

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Tension Production  Elastic Forces  The pull of elastic elements (tendons and ligaments)  Expands the sarcomeres to resting length

 Opposing Muscle Contractions  Reverse the direction of the original motion  Are the work of opposing skeletal muscle pairs

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Tension Production  Gravity  Can take the place of opposing muscle contraction to return a muscle to its resting state

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ATP and Muscle Contraction  Sustained muscle contraction uses a lot of ATP energy  Muscles store enough energy to start contraction  Muscle fibers must manufacture more ATP as needed

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ATP and Muscle Contraction  ATP and CP Reserves  Adenosine triphosphate (ATP)  The active energy molecule

 Creatine phosphate (CP)  The storage molecule for excess ATP energy in resting muscle

 Energy recharges ADP to ATP  Using the enzyme creatine phosphokinase (CPK or CK)  When CP is used up, other mechanisms generate ATP Copyright © 2010 Pearson Education, Inc.

ATP and Muscle Contraction  ATP Generation  Cells produce ATP in two ways  Aerobic metabolism of fatty acids in the mitochondria  Anaerobic glycolysis in the cytoplasm

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ATP and Muscle Contraction  ATP Generation  Aerobic metabolism  Is the primary energy source of resting muscles  Breaks down fatty acids  Produces 34 ATP molecules per glucose molecule

 Anaerobic glycolysis  Is the primary energy source for peak muscular activity  Produces two ATP molecules per molecule of glucose  Breaks down glucose from glycogen stored in skeletal muscles

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ATP and Muscle Contraction

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ATP and Muscle Contraction  Energy Use and Muscle Activity  At peak exertion  Muscles lack oxygen to support mitochondria  Muscles rely on glycolysis for ATP  Pyruvic acid builds up, is converted to lactic acid

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ATP and Muscle Contraction

Figure 9–17 Muscle Metabolism.

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ATP and Muscle Contraction

Figure 9–17a Muscle Metabolism.

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ATP and Muscle Contraction

Figure 9–17b Muscle Metabolism.

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ATP and Muscle Contraction

Figure 9–17c Muscle Metabolism.

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ATP and Muscle Contraction  Muscle Fatigue  When muscles can no longer perform a required activity, they are fatigued

 Results of Muscle Fatigue  Depletion of metabolic reserves  Damage to sarcolemma and sarcoplasmic reticulum  Low pH (lactic acid)  Muscle exhaustion and pain Copyright © 2010 Pearson Education, Inc.

ATP and Muscle Contraction  The Recovery Period  The time required after exertion for muscles to return to normal  Oxygen becomes available  Mitochondrial activity resumes

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ATP and Muscle Contraction  The Cori Cycle  The removal and recycling of lactic acid by the liver  Liver converts lactic acid to pyruvic acid  Glucose is released to recharge muscle glycogen reserves

 Oxygen Debt  After exercise or other exertion  The body needs more oxygen than usual to normalize metabolic activities  Resulting in heavy breathing Copyright © 2010 Pearson Education, Inc.

ATP and Muscle Contraction  Skeletal muscles at rest metabolize fatty acids and store glycogen  During light activity, muscles generate ATP through anaerobic breakdown of carbohydrates, lipids, or amino acids  At peak activity, energy is provided by anaerobic reactions that generate lactic acid as a byproduct Copyright © 2010 Pearson Education, Inc.

ATP and Muscle Contraction  Heat Production and Loss  Active muscles produce heat  Up to 70% of muscle energy can be lost as heat, raising body temperature

 Hormones and Muscle Metabolism  Growth hormone  Testosterone  Thyroid hormones  Epinephrine Copyright © 2010 Pearson Education, Inc.

ATP and Muscle Contraction  Muscle Performance  Power  The maximum amount of tension produced

 Endurance  The amount of time an activity can be sustained

 Power and endurance depend on  The types of muscle fibers  Physical conditioning Copyright © 2010 Pearson Education, Inc.

Muscle Fiber Types  Three Types of Skeletal Muscle Fibers  Fast fibers  Slow fibers  Intermediate fibers

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Muscle Fiber Types  Three Types of Skeletal Muscle Fibers  Fast fibers  Contract very quickly  Have large diameter, large glycogen reserves, few mitochondria  Have strong contractions, fatigue quickly

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Muscle Fiber Types  Three Types of Skeletal Muscle Fibers  Slow fibers  Are slow to contract, slow to fatigue  Have small diameter, more mitochondria  Have high oxygen supply  Contain myoglobin (red pigment, binds oxygen)

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Muscle Fiber Types  Three Types of Skeletal Muscle Fibers  Intermediate fibers  Are mid-sized  Have low myoglobin  Have more capillaries than fast fibers, slower to fatigue

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Muscle Fiber Types

Figure 9–18 Fast versus Slow Fibers.

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Muscle Fiber Types

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Muscle Fiber Types  Muscles and Fiber Types  White muscle  Mostly fast fibers  Pale (e.g., chicken breast)

 Red muscle  Mostly slow fibers  Dark (e.g., chicken legs)

 Most human muscles  Mixed fibers  Pink Copyright © 2010 Pearson Education, Inc.

Muscle Fiber Types  Muscle Hypertrophy  Muscle growth from heavy training  Increases diameter of muscle fibers  Increases number of myofibrils  Increases mitochondria, glycogen reserves

 Muscle Atrophy  Lack of muscle activity  Reduces muscle size, tone, and power

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Muscle Fiber Types  Physical Conditioning  Improves both power and endurance  Anaerobic activities (e.g., 50-meter dash, weightlifting): – use fast fibers – fatigue quickly with strenuous activity  Improved by: – frequent, brief, intensive workouts – hypertrophy

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Muscle Fiber Types  Physical Conditioning  Improves both power and endurance  Aerobic activities (prolonged activity): – supported by mitochondria – require oxygen and nutrients

 Improved by: – repetitive training (neural responses) – cardiovascular training

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Muscle Fiber Types  What you don t use, you lose  Muscle tone indicates base activity in motor units of skeletal muscles  Muscles become flaccid when inactive for days or weeks  Muscle fibers break down proteins, become smaller and weaker  With prolonged inactivity, fibrous tissue may replace muscle fibers Copyright © 2010 Pearson Education, Inc.

Cardiac Muscle Tissue  Structure of Cardiac Tissue  Cardiac muscle is striated, found only in the heart

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Cardiac Muscle Tissue  Seven Characteristics of Cardiocytes  Unlike skeletal muscle, cardiac muscle cells (cardiocytes)  Are small  Have a single nucleus  Have short, wide T tubules  Have no triads  Have SR with no terminal cisternae  Are aerobic (high in myoglobin, mitochondria)  Have intercalated discs Copyright © 2010 Pearson Education, Inc.

Cardiac Muscle Tissue  Intercalated Discs  Are specialized contact points between cardiocytes  Join cell membranes of adjacent cardiocytes (gap junctions, desmosomes)  Functions of intercalated discs  Maintain structure  Enhance molecular and electrical connections  Conduct action potentials Copyright © 2010 Pearson Education, Inc.

Cardiac Muscle Tissue

Figure 9–19 Cardiac Muscle Tissue.

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Cardiac Muscle Tissue

Figure 9–19a-b Cardiac Muscle Tissue.

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Cardiac Muscle Tissue

Figure 9–19c Cardiac Muscle Tissue.

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Cardiac Muscle Tissue  Intercalated Discs  Coordination of cardiocytes  Because intercalated discs link heart cells mechanically, chemically, and electrically, the heart functions like a single, fused mass of cells

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Cardiac Muscle Tissue  Four Functions of Cardiac Tissue  Automaticity  Contraction without neural stimulation  Controlled by pacemaker cells

 Variable contraction tension  Controlled by nervous system

 Extended contraction time  Ten times as long as skeletal muscle

 Prevention of wave summation and tetanic contractions by cell membranes  Long refractory period Copyright © 2010 Pearson Education, Inc.

Smooth Muscle Tissue  Smooth Muscle in Body Systems  Forms around other tissues  In blood vessels  Regulates blood pressure and flow

 In reproductive and glandular systems  Produces movements

 In digestive and urinary systems  Forms sphincters  Produces contractions

 In integumentary system  Arrector pili muscles cause goose bumps Copyright © 2010 Pearson Education, Inc.

Smooth Muscle Tissue  Structure of Smooth Muscle  Nonstriated tissue  Different internal organization of actin and myosin  Different functional characteristics

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Smooth Muscle Tissue

Figure 9–20a Smooth Muscle Tissue.

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Smooth Muscle Tissue

Figure 9–20b Smooth Muscle Tissue.

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Smooth Muscle Tissue  Eight Characteristics of Smooth Muscle Cells  Long, slender, and spindle shaped  Have a single, central nucleus  Have no T tubules, myofibrils, or sarcomeres  Have no tendons or aponeuroses  Have scattered myosin fibers  Myosin fibers have more heads per thick filament  Have thin filaments attached to dense bodies  Dense bodies transmit contractions from cell to cell Copyright © 2010 Pearson Education, Inc.

Smooth Muscle Tissue  Functional Characteristics of Smooth Muscle  Excitation–contraction coupling  Length–tension relationships  Control of contractions  Smooth muscle tone

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Smooth Muscle Tissue  Functional Characteristics of Smooth Muscle  Excitation–contraction coupling  Free Ca2+ in cytoplasm triggers contraction  Ca2+ binds with calmodulin: – in the sarcoplasm – activates myosin light–chain kinase

 Enzyme breaks down ATP, initiates contraction

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Smooth Muscle Tissue  Functional Characteristics of Smooth Muscle  Length–Tension Relationships  Thick and thin filaments are scattered  Resting length not related to tension development  Functions over a wide range of lengths (plasticity)

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Smooth Muscle Tissue  Functional Characteristics of Smooth Muscle  Control of contractions  Multiunit smooth muscle cells: – connected to motor neurons

 Visceral smooth muscle cells: – not connected to motor neurons – rhythmic cycles of activity controlled by pacesetter cells

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Smooth Muscle Tissue  Functional Characteristics of Smooth Muscle  Smooth muscle tone  Maintains normal levels of activity  Modified by neural, hormonal, or chemical factors

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Comparing Muscle Tissues

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Comparing Muscle Tissues

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