Weeks 3 & 4 Learning Outcomes

Skeletal muscle

• Recognize that a skeletal muscle is made up of many individual cells known as muscle fibers bound together by connective tissue.

  • Skeletal muscle fibers are very long, cylindrical, have multiple nuclei, and appear striated.

  • The striations represent alternated densities of repeated proteins.

  • They have multiple nuclei because they are very metabolically active.

• Recall that skeletal muscles are usually attached to bones by tendons.

• Describe the cytoplasm of each muscle fiber as containing cylindrical bundles of proteins called myofibrils that are composed of the orderly overlapping of thick filaments, composed almost entirely of the protein myosin, and thin filaments, principally composed of actin, troponin, and tropomyosin, in a repeating pattern. Recognize that skeletal muscle fibers are called striated muscle because the overlapping of filaments results in a pattern of light and dark bands or stripes.

  • Myofibrils are made up of myosin and actin.

  • It technically is an organelle. Almost all of the inside of a muscle cell are myofibrils.

  • “Spaghetti noodles shoved in a cell”

• Name/label the location of troponin, tropomyosin, actin and myosin, myosin head/crossbridge, myosin binding sites and actin binding sites in a diagram (e.g. Figures 9.2 and 9.3)

• Name/label the location of the sarcoplasmic reticulum, terminal cisternae, and transverse tubules within a muscle fiber (e.g. Figure 9.6).

• Recognize the structure and arrangement of the thick and thin filaments within a sarcomere, and how they are horizontally adjacent to each other along the length of a myofibril.

Molecular mechanisms of skeletal muscle contraction

• Define the term contraction, as the generation of tension in the muscle fiber and not necessarily shortening.

• Define a motor unit, and describe how whole muscles are composed of many motor units.

• Identify the functional anatomy of the neuromuscular junction and describe the events that occur when an action potential reaches a motor neuron axon terminal.

• Recognize acetylcholine as the neurotransmitter used at the neuromuscular junction, and that it binds to nicotinic (cholinergic) receptors located on the motor end plate.

• Explain how nicotinic receptors at the motor end plate operate as Na+ channels to create a change in membrane potential, initiating depolarization of the sarcolemma.

• Explain how Sarin, Strychnine, botulinum and tetanus toxins cause disruptions to neuromuscular signaling.

• Explain the process of excitation-contraction coupling, including the role of the transverse tubules, sarcoplasmic reticulum, DHP receptor and ryanodine receptor in the events leading to Ca2+ release and the role of the Ca2+-ATPase in contraction termination.

• State the roles of tropomyosin, troponin, and Ca2+ in regulating skeletal muscle contraction.

• List the four steps in the cross-bridge cycle, describe the two separate functions performed by ATP during the cycle, and recognize that the same ATP molecule

  performs both functions during a given cycle.

• Recognize the role of ATP binding to myosin heads leading to crossbridge

  detachment, so the next crossbridge cycle can begin.

Mechanics of a single fiber contraction

• Differentiate between isometric contractions and the two types of isotonic contractions: concentric contractions, and eccentric contractions.

• Provide a physiological explanation for the intracellular events associated with twitch contractions: the latent period, contraction phase, and relaxation phase.

• Differentiate between isotonic and isometric contractions.

• Discuss the action potential frequency-tension relationship in skeletal muscle fibers, and the definitions of tetanic stimulation and tetanic contraction.

• Indicate why tetanic contractions produce greater tension than twitch contractions.

• Describe the length-tension relation relationship in skeletal muscle, and the sarcomeric conditions that contribute to “optimal length” and to reduced tension at shorter-than and longer-than optimal length

Motor control hierarchy

• Describe the general organizational hierarchy of the central nervous system involved with motor control in terms of the higher, middle, and local centers of control and what areas are involved.

• Define the term motor program.

• Describe the sensorimotor cortex and its functions related to motor control.

• Define “proprioception” and explain how it influences body movement.

• Recognize that voluntary movement is complex, and often involves coordinated contraction/relaxation of many muscles/groups of muscles.

Local control of motor neurons

• Identify local control systems as relay points between higher centers and motor neurons (i.e. in “spinal reflexes”).

• Describe how information from descending motor pathways, afferent neurons, and interneurons can be integrated by an interneuron that synapses with a motor neuron.

• Recognize that interneurons receive sensory information from (1) the same muscle that is controlled by the motor neuron, (2) other nearby muscles, and (3) neurons in the tendons, joints, and skin.

• Recognize that muscle-spindle stretch receptors provide sensory information about the overall length of the muscle (and the rate of length change), and explain how they do so.

• Characterize the change in action potential generation along muscle afferent neurons when muscles lengthen and when they shorten.

• Describe how sensitivity of the muscle spindle is maintained by the phenomenon of alpha-gamma coactivation.

• Describe how the muscle spindle is involved in the stretch reflex.

• Draw/describe the wiring of the knee-jerk reflex (a stretch reflex)- account for the afferent neuron, inhibitory and excitatory interneurons, and the efferent motor neurons that innervate the muscle groups involved.

• Recognize that the Golgi tendon organs provide sensory information about the tension being generated by a muscle, and explain how they do so.

• Draw/describe how the Golgi tendon organs are involved in a protective reflex when a muscle is experiencing excessive tension- )- account for the afferent neuron, inhibitory and excitatory interneurons, and the efferent motor neurons that innervate the muscle groups involved.

• Contrast the triggering and effects of the length-monitoring systems and the tension monitoring systems during protective reflexes.

• Describe the withdrawal reflex, including the associated crossed-extensor reflex, recognizing the afferent neuron in this case is a nociceptor.

The brain motor centers and the descending pathways they control

• Identify the general locations of the primary motor cortex, premotor area, and somatosensory cortex.

• Recall that the sensorimotor cortex is associated with the planning and ongoing control of voluntary movements.

• Explain that the purpose of a somatotopic map is to provide a general reference for the anatomical arrangement of neurons of the motor cortex that control various parts of the body.

• Recognize the role of the basal nuclei in the control of motor function and explain how impairment of the basal nuclei and the signals leading to them can lead to motor control issues, as in Parkinson disease.

• Recognize the role of the cerebellum in the planning and coordination of movements.

• Differentiate between the corticospinal and brainstem descending motor pathways.

Structure of smooth muscle

• Identify the contractile structures of smooth muscle: thick filaments, thin filaments, and dense bodies.

• Compare and contrast the structure of smooth muscle and skeletal muscle.

• Illustrate the change in shape a smooth muscle fiber undergoes when it contracts.

• Provide examples of structures that contain smooth muscle.

Smooth muscle contraction and its control

• List the sequence of events of cross-bridge activation in smooth muscle.

• Contrast the mechanisms by which cytosolic Ca2+ concentration regulates contractile activity in smooth muscle and in skeletal muscle.

• Compare the sources for cytosolic Ca2+ between smooth and skeletal muscle.

• Identify five types of inputs that can influence cytosolic Ca2+ concentration, and therefore smooth muscle contraction.

• Identify the ion and type of ion channel responsible for smooth muscle cell depolarization; contrast it with skeletal muscle.

• Describe a pacemaker potential.

• Compare and contrast the neural control of skeletal muscle and smooth muscle.

• Recognize that smooth muscle can be excited or inhibited by neural activity, in contrast to skeletal muscle that is only excited.

• Describe how neural and other types of controls of smooth muscle contractile activity can be either stimulatory or inhibitory, depending upon the neurotransmitter receptors associated with smooth muscle and the intracellular signaling pathways activated.

• Contrast the properties of single-unit smooth muscle with those of multiunit smooth muscle

Cardiac muscle

• Compare and contrast cardiac muscle with skeletal muscle and smooth muscle.

• Describe the function of intercalated discs and gap junctions in cardiac muscle.

• Identify the sequence of events associated with excitation-contraction coupling in cardiac muscle, including the role of L-type Ca2+ channels.

• Recognize that the strength of contraction can be varied by neurotransmitters or hormones.

• Explain how the properties of L-type Ca2+ channels contribute to the duration of a cardiac twitch, and recognize why this relationship is important for normal cardiac function.

• Describe how a single pacemaker potential causes the entire heart to beat.

Components of the circulatory system

• List the three components that make up the circulatory system.

• Recognize that organic molecules (proteins, nutrients, metabolic waste and other molecules) are dissolved in the plasma, and that blood is used for transport of organic molecules.

• State the typical average total blood volume.

• Define the term hematocrit.

• Identify the three types of blood cells found in plasma.

• Recognize the function of erythrocytes in gas transport- that erythrocytes contain iron-rich hemoglobin that binds/releases oxygen (and carbon dioxide) and is the primary mechanism for oxygen delivery throughout the body.

• State the functions of leukocytes and platelets.

• Explain the importance of the bulk flow of blood from the heart to the tissues.

• Describe the two circuits (two circulations) through which blood is pumped, and name the structures carrying blood away from the heart and back to the heart in both cases.

Pressure, flow, and resistance

• Discuss the relationship of the flow of fluid in a tube to the pressure driving the flow and the resistance hindering the flow, and write the basic equation relating these variables.

• Describe the determinants of resistance to flow and recognize the profound effect that altering the radius of a blood vessel has on resistance.

• Recognize that changing blood vessel radius is the principal way in which resistance is controlled

Heart anatomy

• Name the sac that surrounds the heart and the layers of the heart wall including the pericardium, epicardium, myocardium, endothelium, and interventricular septum.

• Draw/label the four chambers of the heart, the valves that separate them, and the blood vessels that connect to each chamber; recognize the importance of valves to the flow of blood through the heart and draw/flowchart/describe the sequence of structures that blood flows through in the heart (e.g. starting in the right atrium).

• Differentiate between conducting system cells and myocardial cells.

• Recognize that the heart has its own circulation, which includes coronary arteries, coronary capillaries, and coronary veins.

• Describe the autonomic innervation of the heart, differentiating between nodal cells (“atria”) and myocardial cells (“ventricles") in Figure 12.12 (noting that “atria” and “ventricles” are not how we will refer to this in this class- we will refer to autonomic innervation to nodal cells and myocardial cells).

Heartbeat coordination

• Describe the sequence of the spread of excitation from the SA node through the atria and then into the ventricles.

• Recognize the importance of the delay in signal conduction between the AV node and the bundle of His.

• Describe the characteristics of action potentials in ventricular muscle cells, and the sequence of changes in ion permeabilities that are responsible for these characteristics (and the ion channels involved).

• Describe the characteristics of action potentials in SA node cells, and the sequence of changes in ion permeabilities that are responsible for these characteristics (and the ion channels involved). Explain the “pacemaker potential” in nodal cells.

• Explain how the SA node acts as the “pacemaker” for the whole heart.

• Identify the components of a normal ECG recording.

• Recognize the usefulness of the ECG as a tool to monitor the electrical activity of the heart, and how that ECG information can be used to infer mechanical activity of the heart.

• Recognize that the amount of Ca2+ released from the sarcoplasmic reticulum, and thus the strength of contraction, is variable in a cardiac muscle cell.

• Discuss the mechanism that is responsible for the inability of myocardial cells to undergo summation and tetanic contractions and recognize the importance of this lack of summating to the heart’s proper functioning.

Mechanical events of the cardiac cycle

• Define the two major phases of the cardiac cycle, systole and diastole.

• Describe/flowchart the events in the cardiac cycle taking into account the changes in pressure, structures (i.e. chordae tendineae and valves) and contractions that mediate the movement of blood from one chamber/vessel to the next (e.g start at the right atrium).

• Recognize that most of the ventricular filling occurs before atrial contraction.

• Define stroke volume.

• Recognize that the pulmonary circulation is a low-pressure system.

The cardiac output

• Define cardiac output and write the equation relating it to heart rate and stroke volume.

• Discuss how the autonomic nervous system influences heart rate, and describe the effects of norepinephrine and acetylcholine on the ion channels that produce the pacemaker potential.

• Discuss the effect of end-diastolic volume (or preload) on stroke volume.

• State the Frank-Starling mechanism.

• Describe why the Frank-Starling mechanism represents a myocardial length- tension relationship, and discuss the functional importance of the Frank-Starling mechanism.

• Define contractility and recognize that the increase in strength of contraction is independent of changes in muscle length (the Frank-Starling mechanism). g. Describe the effects of the sympathetic nervous system on the strength of ventricular contraction, the speed of ventricular contraction and relaxation, and recognize the importance of shortening the duration of systole during sympathetic stimulation.

• Define afterload, and describe the relationship between stroke volume and

  afterload.