exam deck 7 Flashcards
What is the difference between neurogenic and myogenic muscle contraction?
Neurogenic contraction requires nerve stimulation (e.g., skeletal muscle).
Myogenic contraction occurs spontaneously (e.g., cardiac and most smooth muscles).
What is the difference between isotonic and isometric contractions?
Isotonic contraction: Muscle shortens as it moves a load.
Isometric contraction: Muscle develops tension without changing length.
What happens during the latent period of muscle contraction?
The muscle is stretching the series elastic component, and tension develops after the action potential ends.
What factors determine the force a muscle generates?
Initial muscle length (length-tension relationship).
Number of active muscle fibers (motor unit recruitment).
Rate of contraction (fiber type).
Frequency of stimulation.
Muscle cross-sectional area (more myofibrils = more force
At what muscle length is maximum tension developed?
When the muscle begins shortening from its optimal resting length, maximizing actin-myosin overlap.
How can a muscle increase tension?
By activating more motor units. Minimum contraction uses one motor unit.
What are the two basic types of muscle fibers?
Slow-twitch fibers: Fatigue-resistant, for sustained activities.
Fast-twitch fibers: Fatigue quickly, for rapid, powerful contractions.
How does the frequency of stimulation affect muscle tension?
Single stimulus: Twitch.
Rapid stimuli: Summation.
High frequency: Unfused tetanus.
Very high frequency: Fused tetanus (useful physiologically).
How does load affect muscle shortening velocity?
No load: Maximum shortening velocity (isotonic).
Increased load: Slower shortening.
Maximum load: No shortening (isometric contraction).
What is the relationship between work, power, and muscle efficiency?
Work: Force × distance.
Power: Work ÷ time (or Force × velocity).
Muscles are most efficient at ~1/3 of their maximum shortening velocity.
How does cross-sectional area affect muscle strength?
Strength is proportional to the number of myofibrils in a muscle fiber. Resistance training increases cross-sectional area but not the number of fibers.
What causes fused tetanus?
A high-frequency stimulus causes Ca²⁺ to build up in the sarcoplasm, preventing relaxation between stimuli.
How are striated and non-striated muscles differentiated histologically?
Striated muscle: Highly ordered arrangement of contractile proteins (e.g., skeletal and cardiac muscles).
Non-striated muscle: Less ordered arrangement of contractile proteins (e.g., smooth muscle).
What are caveolae, and what is their function in smooth muscle?
Caveolae are small membrane invaginations that concentrate calcium (Ca²⁺) and are essential for excitation-contraction coupling in smooth muscle.
What is the difference between single-unit and multi-unit smooth muscle?
Single-unit smooth muscle: Cells are connected by gap junctions, allowing them to contract as a single unit (e.g., gut, uterus, bladder).
Multi-unit smooth muscle: Cells are not connected by gap junctions and are stimulated individually by nerves (e.g., iris, piloerector muscles).
What types of contractions are found in smooth muscle?
Myogenic contraction: Spontaneous contractions driven by pacemaker activity.
Neurogenic contraction: Contractions triggered by nerve activity.
How does calcium activate contraction in smooth muscle?
Ca²⁺ binds to calmodulin (CaM).
This complex activates myosin light chain kinase (MLCK), which phosphorylates myosin, enabling cross-bridge formation and contraction.
What mechanisms regulate smooth muscle relaxation?
Removal of Ca²⁺ from the cytoplasm.
Deactivation of MLCK and activation of myosin phosphatase, which dephosphorylates myosin.
What structures enable cardiac muscle cells to function as a syncytium?
Gap junctions: Allow electrical coupling.
Desmosomes: Provide strong mechanical attachment between cells.
Why is cardiac muscle unable to achieve tetanus?
Due to its long refractory period, which prevents summation of action potentials.
What initiates contraction in cardiac muscle?
Depolarization opens voltage-gated Ca²⁺ channels, allowing Ca²⁺ influx. This triggers further Ca²⁺ release from the sarcoplasmic reticulum (Ca²⁺-induced Ca²⁺ release), leading to contraction.
How does sympathetic stimulation affect heart contraction?
Sympathetic stimulation increases heart rate (chronotropic effect) and contraction strength (inotropic effect) by activating β₁-adrenoceptors, which increase cAMP and protein kinase A (PKA) activity.
This leads to enhanced Ca²⁺ entry and stronger contractions.
What is the role of parasympathetic stimulation in cardiac muscle?
Parasympathetic activity slows heart rate by activating muscarinic ACh receptors, which increase K⁺ efflux and decrease Ca²⁺ influx in pacemaker cells.
How does the length-tension relationship benefit cardiac function?
Stretching cardiac muscle (due to increased venous return) increases contraction force, ensuring the heart pumps out all blood it receives (Starling’s Law of the Heart).
What is the role of the sinoatrial (SA) node in the heart?
The SA node acts as the pacemaker by generating spontaneous action potentials that initiate the heartbeat.
What is the “funny” current (I_f), and where is it found?
The funny current is a mixed Na⁺/K⁺ inward current in pacemaker cells, contributing to their rhythmic depolarization.
What are the key features of skeletal muscles?
Skeletal muscle: Voluntary, striated, rapid contractions, requires neural input.
What are the key features of smooth muscles?
Smooth muscle: Involuntary, non-striated, slower contractions, modulated by hormones and autonomic nerves.
What are the key features of cardiac muscles?
Cardiac muscle: Involuntary, striated, rhythmic contractions, myogenic initiation with autonomic modulation.
What are the primary roles of sensory systems?
Awareness of the environment, prevention of harm, and conscious control and integration.
What is an exteroreceptor, and can you give examples?
Receptors for external stimuli such as photoreceptors (light), hair cells in the inner ear (sound), olfactory receptors (smell), taste receptors, and mechanoreceptors (touch).
What do interoreceptors detect?
Internal stimuli such as pressure, pH, and volume within the gastrointestinal, respiratory, and cardiovascular systems.
Define proprioceptors and their role.
Receptors that provide information on muscle reflexes and body position, often operating at the spinal level for reflexes.
What is the process of sensory transduction?
Conversion of environmental energy into action potentials in sensory neurons, starting with a graded receptor potential that may reach threshold to fire an action potential.
What is the concept of a receptive field?
The area where a stimulus activates a sensory neuron. Overlapping fields can create a larger secondary receptive field due to convergence of primary neurons.
How does lateral inhibition enhance stimulus location coding?
By inhibiting neighboring neurons, it sharpens the perception of the primary stimulus.
What distinguishes tonic from phasic receptors?
Tonic receptors adapt slowly and continuously respond to stimulus intensity and duration.
Phasic receptors adapt rapidly, signaling only the onset and offset of a stimulus.
What is the adequate stimulus?
The specific type and strength of stimulus that most effectively activates a sensory receptor.
How is sensory intensity coded in the nervous system?
By the frequency of action potentials and the number of sensory receptors activated.
Which sensory pathway projects directly to the cortex without passing through the thalamus?
The olfactory pathway.
