Exam 3 Notes PDF

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Exam notes for chapter 9 (the muscular system), chapter 10 (muscle system), and chapter 11 (introduction to the nervous system and nervous tissue). Words in bold are often important. ...

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Human Biology: Exam Three Chapter Summaries

Chapter 9: The Muscular System Overview of the Skeletal Muscles 

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A muscle fiber is surrounded by an extracellular matrix called endomysium. o A fascicle is a bundle of many muscle fibers enclosed by the perimysium. o The whole muscle consists of many fascicles wrapped by the epimysium. The pattern of fascicle arrangement greatly contributes to the appearance and function of a skeletal muscle. o Muscles may have a parallel, convergent, pennate, circular, or spiral orientation. Some muscles are names for their shape, appearance, size, position, or other structural considerations, such as number of heads (e.g., triceps) Skeletal muscles commonly move at joints and move the bones to which they are attached, which is known as the muscle’s action. Other functions of skeletal muscle include facial expression, breathing, and generating heat to regulate body temperature. Muscles often work in coordinated groups, with each muscle having a specific role. Points of attachment of a muscle are its more stationary origin and more mobile insertion. Bones and muscles work together as lever systems. o A first-class lever places the fulcrum between the point of force and the load to be moved. o A second-class lever places the load to be moved between the force and the fulcrum. o A third-class lever places the force between the load to be moved and the fulcrum.

Muscles of the Head, Neck, and Vertebral Column 

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The muscles of facial expression include the following: o The frontalis, occipitalis, and corrugator supercilia muscles move the forehead and eyebrows. o The circular orbicularis oculi muscle closes the eye. o The zygomaticus major, zygomaticus minor, levator labii superioris, risorius, and orbicularis oris muscles produce expressions of smiling, grimacing, grinning, and sneering. o The depressor anguli oris, depressor labii inferioris, and mentalis muscles contribute to sad and “doubtful” expressions. o The buccinator muscle pulls the cheeks interiorly, producing sucking motions. The six extrinsic eye muscles move the eyeball. They include the superior, inferior, medial, and lateral rectus muscles, and the superior and inferior oblique muscles. Muscles of mastication include the masseter, temporalis, medial pterygoid, and lateral pterygoid muscles. The muscles of swallowing work in the following manner: o The genioglossus, hyoglossus, and styloglossus muscles move the tongue to manipulate food during mastication and push the food into the pharynx. o The stylohyoid, mylohyoid, geniohyoid, and digastric muscles elevate the hyoid bone and nudge the food posteriorly. o The sternohyoid, sternothyroid, omohyoid, and thyrohyoid muscles depress the hyoid, larynx, and pharynx as the food enters the pharynx. o The pharyngeal constrictor muscles push the food into the esophagus. The muscles that move the head include the sternocleidomastoid and scalene muscles, which rotate and flex the head; the trapezius muscle, which extends the head; and the splenius capitis and splenius cervicis muscles, which extend and rotate the head. The muscles of the vertebral colum include the following:

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The erector spinae muscle group is composed of three columns of muscle, each of which is made up of three individual muscles:  Lateral iliocostalis muscle  Middle longissimus muscle  Medial spinalis muscle The erector spinae muscle group maintains posture and extends and laterally flexes the vertebral column. The transversospinal muscle group includes the semispinalis, multifidus, and rotatores muscles, which support posture and vertebral column extension. The quadratus lumborum extends the vertebral column

Muscles of the Trunk and Pelvic Floor  

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Muscles of inspiration include the diaphragm and external intercostal muscles. o The internal intercoastal muscles cause air to leave the lungs during forces expiration. The rectus abdominis, external oblique, and internal oblique muscles of the abdomen flex the trunk and compress the abdominal cavity. o The transversus abdominis muscle compresses the abdominal cavity. Muscles of the pelvic floor include the following: o The pelvic diaphragm is formed by the levator ani muscle group, which forms the floor of the pelvis and works like sphincters around the urethra, vagina, and anal canal. o The external urethral and anal sphincters allow voluntary control of urinations and defecation. o The deep transverse perineal and superficial transverse perineal muscles support the pelvic organs. o The bulbospongiosus and ischiocavernosus muscles support erection of penis and clitoris.

Muslces of the Pectoral Girdle and Upper Limb 

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The muscles of the pectoral gridle include the following: o The trapezius muscle elevates, retracts, depresses, and rotates the scapula superiorly. o The levator scapulae muscle elevates the scapula. o The rhomboid major and rhomboid minor muscles retract the scapula and rotate it inferiorly. o The serratus anterior muscle protects the scapula and rotates it superiorly. o The pectoralis minor muscle protracts and depresses the scapula The muscles that move the arm include the following: o The pectoralis major and coracobrachialis muscles flex, adduct, and medially rotate the arm. o The latissimus dorsi and teres major muscles adduct, medially rotate, and extend the arm. o The deltoid muscle is the agonist of arm abduction. o The four rotator cuff muscles stabilize the shoulder joint.  They include the teres minor, infraspinatus , supraspinatus, and subscapularis muscles. The muscles that flex the arm at the elbow joint include the biceps, brachii, brachialis, and brachioradialis muscles. Muscles that flex the arm at the elbow joint include the triceps, brachii and the anconeus muscles. The pronator teres and pronator quadratus muscles pronate the forearm, whereas the supinator and biceps brachii muscles supinate the forearm. Flexor muscles flex the hand, thumb, or fingers, whereas extensors extend the hand, thumb, or fingers. Numerous small muscles move the fingers and are usually named for their action and placement.

Muscles of the Hip and Lower Limb    

The iliopsoas, sartorius, and rectus femoris muscles flex the thigh. The adductor muscle group, pectineus muscle, and gracilis muscle adduct and medially rotate the thigh. The quadriceps femoris muscle group extends the leg at the knee. The gluteus maximus muscle extends, abducts, and laterally rotates the thigh during climbing. o The gluteus medius and gluteus minimus muscles abduct and medially rotate the thigh during walking.

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The muscles of the hamstring muscle group (the biceps femoris, semitendinosus, and semimembranosus muscles) extend the thigh and flex the leg. The main dorsiflexors of the foot are the tibialis anterior and extensor digitorum longus muscles. The fibularis longus and fibularis brevis muscles evert the foot. The main plantarflexors of the foot are the gastrocnemius and soleus muscles. Numerous small muscles move the toes and are usually named for their action and placement.

Chapter 10: Muscle System Overview of Muscle Tissue     

The three types of muscle tissue are skeletal, cardiac, and smooth muscle tissue. All muscle cells turn chemical energy into mechanical energy by contracting to generate muscle tension. All types of muscle tissue consist of muscle cells and surrounding extracellular matrix, call the endomysium. All types of muscle tissue share common properties, including contractility, excitability, conductivity, distensibility, and elasticity. The plasma membrane of a muscle cell is the sarcolemma, and the cytoplasm is the sarcoplasm. o The sarcoplasm contains myofibrils and the sarcoplasmic reticulum (SR).

Structure and functions of Skeletal Muscle Fibers    

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Skeletal muscle fibers are very long cells that consist of striated, multinucleated voluntary muscle cells. The sarcolemma has inward extensions call T-Tubules that surround myofibrils. o The Ca2+-storing SR swells where it meets T-tubules to form terminal cisternae. Myofibrils are composed of myofilaments. o Myofilaments are composed of contractile proteins, regulatory proteins , and/or structural proteins There are three types of myofilaments: o Thick filaments are composed of myosin, a contractile protein. o Thin filaments are composed of contractile actin proteins and the smaller regulatory proteins troponin and tropomyosin. o Elastic filaments are composed of the structural protein titin. The striations of skeletal muscle tissue are due to arrangement of myofilaments: o The I bands are the light regions of striations where only thin filaments are found.  In the middle of each I band is the Z-disc. o The A bands are the dark regions of striations where the thick and thin filaments overlap.  The central region of the A band is the H zone.  It is bisected by the M line. The sarcomere is the functional unit of contraction. It is defined as the area from one Z-disc to the next. The sliding-filament mechanism is the currently accepted model of muscle contraction. o In this process, the thick and thin filaments slide past one another.

Skeletal Muscle Fibers as Electrically Excitable Cells  

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A separation of charges occurs across the sarcolemma, which is an electrical gradient or electrical potential.  Membrane potentials are electrical potentials across plasma membranes. An unstimulated muscle fiber shows a decrease in voltage across the membrane, called the resting membrane potential.  Muscle fibers at rest have a resting membrane potential of about −90 mV. Ions move across the sarcolemma via channels.  Two types of channels are leak and gated channels. The concentration of Na+ is higher in the extracellular fluid, and the concentration of K + is higher in the cytosol.  The Na+/K+ pump maintains this gradient. The negative resting membrane potential is due to the loss of K + through leak channels and the actions of the Na+/K+ pumps. Ion movement is driven by the forces of the concentration gradient and the electrical gradient.

4  The sum of these two forces is the electrochemical gradient. An action potential is a temporary, quick reversal in the membrane potential.  It consists of:  depolarization, in which Na+ enter the fiber, causing the membrane potential to become more positive  repolarization, in which K+ exit the fiber, returning it to its resting state. Process of Skeletal Muscle Contraction and Relaxation  All skeletal muscle fibers are innervated by motor neurons.  The neuron meets the fiber at the neuromuscular junction, or NMJ.  The NMJ consists of the axon terminal, the synaptic cleft, and the motor end plate.  Skeletal muscle contraction can be divided into three parts:  excitation  excitation-contraction coupling  contraction.  The excitation phase begins as the axon terminal releases ACh into the synaptic cleft, which binds ACh receptors on the motor end plate.  The result is an end-plate potential.  In excitation-contraction coupling, the end-plate potential triggers an action potential in the sarcolemma, which propagates down the T-tubules.  This triggers the opening of Ca2+ channels in the SR, and Ca2+ flood the cytosol.  In preparation for contraction, the Ca2+ in the cytosol bind troponin, which allows tropomyosin to move away from the active sites of actin.  The contraction phase then begins, and the crossbridge cycle occurs as ATP hydrolysis “cocks” the myosin head and it binds to actin.  When myosin undergoes a power stroke, it pulls actin toward the center of the sarcomere.  Muscle relaxation has two components:  The ACh in the synaptic cleft is broken down  The Ca2+ concentration in the cytosol returns to the resting level. 

Energy Sources for Skeletal Muscle   

Immediate energy sources for muscle fibers include stored ATP within the cytosol and creatine phosphate. Glycolytic catabolism is an anaerobic process during which glucose in the cytosol is split and ATP is produced. Oxidative catabolism is an aerobic process that takes place in the mitochondria, during which the products of glycolysis, fatty acids, and amino acids are oxidized to generate ATP.

Muscle Tension at the Fiber Level 

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A single contraction-relaxation cycle of a muscle fiber is called a twitch.  It consists of the latent period, the contraction period, and the relaxation period.  Muscle fibers may be classified as fast-twitch or slow-twitch fibers. The amount of tension generated by the contraction of a muscle fiber depends on the frequency of stimulation by the motor neuron and the resulting concentration of Ca2+.  If a muscle fiber is stimulated before the relaxation period is completed, unfused tetanus results.  If a muscle fiber is stimulated 80–100 times per second before the relaxation period begins, fused tetanus results. Per the length-tension relationship, a contraction can produce a maximal amount of tension at the optimal length of a sarcomere. Type I muscle fibers are slow-twitch fibers that use primarily oxidative catabolism.  Type II muscle fibers are fast-twitch fibers that use primarily glycolytic catabolism.

Muscle Tension at the Organ Level 

A motor unit consists of a single motor neuron and the muscle fibers that it innervates.  Recruitment occurs when more motor units are activated for more forceful contractions.  Muscle tone is produced by small, involuntary contractions of alternating motor units.

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There are three types of muscle contractions:  isotonic concentric (shortening) contraction  isotonic eccentric (lengthening) contraction  isometric (unchanging length) contraction

Skeletal Muscle Performance    

Endurance and resistance training result in changes in the structure and biochemistry of skeletal muscle fibers. Disuse leads to atrophy of the muscle fibers. Muscular fatigue is caused by depletion of key metabolites, inadequacy of oxygen delivery to muscle fibers, accumulation of certain metabolites, and environmental conditions. Excess postexercise oxygen consumption (EPOC) occurs after exercise to correct the homeostatic imbalances that were caused by exercise.

Smooth and Cardiac Muscle      

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The functions of smooth muscle tissue include peristalsis, forming sphincters, and regulating the flow of material through hollow organs. Smooth muscle cells are uninucleate; lack T-tubules, striations, and sarcomeres; and have a less extensive SR than do skeletal muscle fibers. Smooth muscle contraction is stimulated by the autonomic nervous system, stretch, hormones, and the activity of pacemaker cells. Smooth muscle cell contraction is activated by Ca 2+ binding to calmodulin.  This activates myosin light-chain kinase (MLCK), which initiates crossbridge cycles. Smooth muscle cell relaxation involves removal of Ca 2+ from the cytosol. There are two types of smooth muscle tissue:  Single-unit smooth muscle cells contract together as a single unit.  Multi-unit smooth muscle cells that can contract independently of one another. Cells of cardiac muscle are joined physically and electrically by intercalated discs.  Their electrical activity is coordinated by pacemaker cells.

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Chapter 11: Introduction to the nervous system and Nervous Tissue Overview of the Nervous System 

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The nervous system is divided structurally into the central nervous system (CNS) and the peripheral nervous system (PNS).  The brain and spinal cord make up the CNS.  The PNS includes the cranial and spinal nerves. The nervous system can be functionally classified into three divisions:  The PNS sensory, or afferent, division has two branches:  somatic sensory division  visceral sensory division  The CNS receives the sensory input and processes it; this is called integration.  The PNS motor, or efferent, division has two branches:  the somatic motor division  autonomic nervous system (ANS)

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Nervous tissue consists of neurons and neuroglial cells. Neurons are excitable cells that send, propagate, and receive action potentials.  They consist of three parts:  the cell body  one or more receptive dendrites  a single axon Neurons are classified both structurally and functionally.  Structural classes include multipolar neurons, bipolar neurons, and Pseudounipolar neurons.  Functional classes include sensory, or afferent, neurons; interneurons; and motor, or efferent, neurons. The neuroglia in the CNS include astrocytes, which anchor neurons and blood vessels in place; oligodendrocytes, which form the myelin sheath; microglia, which are phagocytes; and ependymal cells, which produce and circulate cerebrospinal fluid. The neuroglia of the PNS include Schwann cells, which form the myelin sheath, and satellite cells, which surround cell bodies of neurons in the PNS. Oligodendrocytes in the CNS and Schwann cells in the PNS wrap around the axon up to 100 times to form the myelin sheath.  This covering significantly speeds up conduction of an action potential through the axon. Unmyelinated axons in the PNS are embedded in Schwann cells. Axons of the PNS may be regenerated if the cell body remains intact.  When regeneration occurs, an axonal growth process is guided toward its target cell by a regeneration tube made of Schwann cells and the basal lamina.

Electrophysiology of Neurons 

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A separation of charges occurs across the membrane of neurons.  An unstimulated neuron shows a decrease in voltage across the membrane, called the resting membrane potential.  Neurons at rest are polarized with a resting membrane potential of about −70 mV. Ions move across the axolemma via channels.  Two types of channels  leak (always open)  gated channels Two important ion gradients are those of Na+ and K+: The concentration of Na+ is higher in the extracellular fluid, and the concentration of K+ is higher in the cytosol. A local potential is a small, local change in the membrane potential of a neuron.

7 A local potential may either depolarize the neuron, making it less negative, or hyperpolarize the neuron, making it more negative.  Local potentials are graded, reversible, decremental with distance, and useful for short-distance signaling only. Voltage-gated K+ channels have two states, resting and activated, whereas voltage-gated Na+ channels have three:  Resting  Activated  inactivated An action potential is a rapid depolarization and repolarization of the membrane potential of the cell.  During the depolarization phase Na+ flood the axon, and the membrane potential rises toward a positive value.  During the repolarization phase K+ flow out of the axon, returning the axon to its negative resting membrane potential.  Many neurons hyperpolarize after repolarization completes. Action potentials are nondecremental, they obey the all-or-none principle, they are irreversible, and they are long-distance signals. The refractory period is the span of time during which it is difficult or impossible to elicit another action potential. Action potentials are propagated along an axon via the flow of current. The speed of action potential propagation depends on the diameter of the axon (larger axons conduct more rapidly) and on the presence or absence of a myelin sheath.  Conduction may occur in two ways:  Saltatory conduction occurs rapidly because the current is insulated as it flows through each internode and action potentials are generated only at nodes of Ranvier.  Continuous conduction occurs much more slowly, as each consecutive region of the membrane must be depolarized to threshold and generate an action pot...