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Physiology Exam 2 Key Concepts

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  • Receptors blocked to treat persistent tachycardia and dilated pupils
    Adrenergic receptors are blocked to inhibit sympathetic effects causing tachycardia and pupil dilation.
  • Contractile units responsible for muscle shortening
    Sarcomeres are the contractile units responsible for muscle fiber shortening during contraction.
  • Ion channels implicated in arrhythmias with abnormal pacemaker activation
    Unstable Na+ channels cause abnormal activation of pacemaker cells leading to arrhythmias.
  • Compensatory response to acute blood loss maintaining blood pressure
    Sympathetic vasoconstriction increases vascular resistance to maintain blood pressure.
  • Somatic nervous system controls which muscle type?
    The somatic nervous system controls skeletal muscle under conscious control.
  • Neurotransmitter deficit causing weak skeletal muscle contraction
    A deficit of acetylcholine (ACh) results in weak or absent skeletal muscle contraction.
  • Receptors affected in myasthenia gravis
    Nicotinic receptors at the neuromuscular junction are affected, reducing ACh binding and weakening contraction.
  • Number and type of motor neurons from CNS to somatic effectors
    One myelinated motor neuron extends from the CNS to the skeletal muscle effector.
  • Definition of reciprocal inhibition
    One muscle contracts while the antagonist muscle on the same side relaxes to allow smooth movement.
  • Crossed extensor reflex characteristics
    It is polysynaptic, involves divergent processing, flexes one limb while extending the opposite, and balances the body.
  • Neurotransmitter release mechanism at neuromuscular junction
    Voltage-gated Ca++ channels open in the bouton, allowing Ca++ influx that triggers ACh vesicle fusion and release.
  • Functional unit of muscle composed of which filaments?
    The sarcomere contains thin filaments (actin) and thick filaments (myosin).
  • Bands within a sarcomere: H-band, I-band, A-band
    H-band contains only myosin, I-band contains only actin, and A-band includes the entire length of myosin including overlap.
  • Causes of muscle fatigue
    Accumulation of lactic acid, increased inorganic phosphate, increased H+ ions, and glycogen depletion contribute to fatigue.
  • Sequence of events in muscle contraction initiation
    ACh release → ACh binds nicotinic receptors → action potential in sarcolemma → Ca++ release from SR → crossbridge formation.
  • Role of troponin and tropomyosin in contraction
    Ca++ binds troponin causing tropomyosin to move, exposing actin binding sites for myosin to attach and contract.
  • Mechanisms to stop muscle contraction
    ACh is broken down by acetylcholinesterase, Ca++ is pumped back into the SR, and ATP binds myosin to detach it from actin.
  • Characteristic of myoglobin in muscle fibers
    Myoglobin carries O2, is a red pigment, abundant in slow fibers, and supports aerobic respiration.
  • Mechanism of asynchronous recruitment
    Different motor units activate at different times to prevent muscle fatigue during sustained contractions.
  • Primary muscle responsible for forearm flexion
    The biceps brachii is the primary flexor moving the hand and forearm toward the shoulder.
  • Difference between arteries and veins
    Arteries carry blood away from the heart; veins carry blood toward the heart.
  • Function of the fibroskeleton in the heart
    It prevents the apex and base from being pulled together and supports valve openings.
  • Percentage of autorhythmic myocardiocytes in the heart
    Approximately 1% of cardiac cells are autorhythmic pacemaker cells.
  • Source of Ca++ for cardiac muscle contraction
    About 25% of Ca++ comes from the sarcoplasmic reticulum; the rest enters from extracellular fluid.
  • Ion responsible for depolarization in myocardial contractile cells
    Na+ influx causes the depolarization phase in myocardial contractile cells.
  • Sequence of cardiac conduction system
    SA node → AV node → Bundle of His → Right and left bundle branches → Purkinje fibers.
  • Valves open when atria and ventricles relax
    Atrioventricular (AV) valves are open during relaxation to allow ventricular filling.
  • Heart sound caused by valve closure
    The first heart sound is caused by AV valves closing.
  • Definition of stroke volume
    Stroke volume is the amount of blood pumped by one ventricle in a single contraction.
  • Effect of parasympathetic stimulation on heart rate
    Parasympathetic stimulation decreases heart rate by releasing ACh on muscarinic receptors.
  • Effect of sympathetic stimulation on heart rate during exercise
    Sympathetic stimulation increases heart rate by releasing norepinephrine on beta1 receptors.
  • Factors affecting oxygen binding to hemoglobin
    Blood pH, gas concentration gradients, and cooperativity influence oxygen binding to hemoglobin.
  • Definition of cardiac output
    Cardiac output is the volume of blood pumped by one ventricle per minute.
  • Relationship between blood flow and pressure gradient
    Liquids and gases flow from areas of higher pressure to areas of lower pressure.
  • Effect of vessel radius on blood flow resistance
    Doubling the radius of a blood vessel significantly decreases resistance to blood flow.
  • Definition of total peripheral resistance
    Total peripheral resistance is the friction blood encounters during flow through blood vessels.