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Nerve and Muscle Physiology

Smooth and Cardiac Muscle Physiology Practice Questions

32 free Smooth and Cardiac Muscle Physiology practice questions for the Physiology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.

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Question 1 of 32 Medium

Which structural feature distinguishes smooth muscle from skeletal muscle?

  1. A Presence of sarcomeres
  2. B Multinucleated fibers
  3. C Absence of striations
  4. D Voluntary control

Correct answer: Absence of striations

Smooth muscle lacks organized sarcomeres, so it does not show striations. This structural difference underlies its slower and sustained contractions.

Question 2 of 32 Medium

The primary regulatory protein involved in smooth muscle contraction is:

  1. A Troponin
  2. B Tropomyosin
  3. C Calmodulin
  4. D Actinin

Correct answer: Calmodulin

Smooth muscle contraction is regulated by calmodulin, which binds calcium ions. This complex activates myosin light chain kinase to initiate contraction.

Question 3 of 32 Medium

Which ion plays the most critical role in initiating cardiac muscle contraction?

  1. A Sodium
  2. B Potassium
  3. C Calcium
  4. D Chloride

Correct answer: Calcium

Calcium influx through L-type calcium channels triggers calcium-induced calcium release in cardiac muscle. This process initiates contraction.

Question 4 of 32 Medium

Intercalated discs in cardiac muscle primarily function to:

  1. A Store intracellular calcium
  2. B Anchor myofibrils together
  3. C Allow rapid electrical conduction
  4. D Increase mitochondrial ATP output

Correct answer: Allow rapid electrical conduction

Intercalated discs contain gap junctions that enable rapid spread of electrical impulses. This ensures synchronized contraction of cardiac muscle.

Question 5 of 32 Medium

Which type of smooth muscle exhibits spontaneous rhythmic contractions?

  1. A Multiunit smooth muscle
  2. B Visceral smooth muscle
  3. C Skeletal muscle
  4. D Cardiac muscle

Correct answer: Visceral smooth muscle

Visceral smooth muscle shows spontaneous rhythmic activity due to pacemaker potentials. This is seen in organs like the intestine and uterus.

Question 6 of 32 Medium

The plateau phase of the cardiac action potential is mainly due to:

  1. A Rapid sodium influx
  2. B Delayed potassium efflux
  3. C Sustained calcium influx
  4. D Chloride channel opening

Correct answer: Sustained calcium influx

The plateau phase results from prolonged calcium entry through L-type calcium channels. This delays repolarization and prolongs contraction.

Question 7 of 32 Medium

Which mechanism allows smooth muscle to maintain tension with minimal energy expenditure?

  1. A Sliding filament mechanism
  2. B Latch mechanism
  3. C Calcium-induced calcium release
  4. D All-or-none contraction

Correct answer: Latch mechanism

The latch mechanism allows smooth muscle to maintain force with low ATP consumption. This is important for sustained contractions like vascular tone.

Question 8 of 32 Medium

Cardiac muscle differs from skeletal muscle in that cardiac muscle:

  1. A Is voluntary
  2. B Has no refractory period
  3. C Shows all-or-none contraction
  4. D Has shorter action potentials

Correct answer: Shows all-or-none contraction

Cardiac muscle contracts in an all-or-none manner due to its functional syncytium. This ensures coordinated pumping action.

Question 9 of 32 Medium

Which protein phosphorylates myosin light chains in smooth muscle?

  1. A Protein kinase A (PKA)
  2. B Myosin light chain kinase
  3. C Troponin C regulatory subunit
  4. D Actin thin-filament protein

Correct answer: Myosin light chain kinase

Myosin light chain kinase phosphorylates myosin, enabling cross-bridge formation. This step is essential for smooth muscle contraction.

Question 10 of 32 Medium

The refractory period of cardiac muscle is long primarily to:

  1. A Increase heart rate
  2. B Prevent tetany
  3. C Enhance calcium uptake
  4. D Reduce oxygen consumption

Correct answer: Prevent tetany

A long refractory period prevents tetanic contractions in cardiac muscle. This allows adequate relaxation and filling between beats.

Question 11 of 32 Medium

Which type of smooth muscle is found in the iris of the eye?

  1. A Visceral smooth muscle
  2. B Single-unit smooth muscle
  3. C Multiunit smooth muscle
  4. D Cardiac muscle

Correct answer: Multiunit smooth muscle

Multiunit smooth muscle consists of individual fibers acting independently. It allows fine control, such as pupil diameter regulation.

Question 12 of 32 Medium

In cardiac muscle, calcium that triggers contraction is primarily released from the:

  1. A Membrane-bound mitochondria
  2. B Sarcoplasmic reticulum
  3. C Cytoplasmic Golgi apparatus
  4. D Rough endoplasmic reticulum

Correct answer: Sarcoplasmic reticulum

Calcium-induced calcium release occurs from the sarcoplasmic reticulum. This amplifies the initial calcium influx from the extracellular space.

Question 13 of 32 Medium

Which feature is common to both smooth and cardiac muscle?

  1. A Presence of troponin
  2. B Voluntary control
  3. C Involuntary activity
  4. D Multinucleated fibers

Correct answer: Involuntary activity

Both smooth and cardiac muscles function involuntarily. Their activity is regulated by autonomic and intrinsic mechanisms.

Question 14 of 32 Medium

Which ion channel is responsible for spontaneous depolarization in cardiac pacemaker cells?

  1. A Fast sodium channels
  2. B L-type calcium channels
  3. C Funny sodium channels
  4. D Potassium leak channels

Correct answer: Funny sodium channels

Funny sodium channels slowly depolarize pacemaker cells during diastole. This leads to automatic rhythmic firing.

Question 15 of 32 Medium

Smooth muscle contraction can be initiated by all EXCEPT:

  1. A Circulating hormones
  2. B Passive mechanical stretch
  3. C Autonomic nerve stimulation
  4. D Somatic motor neurons

Correct answer: Somatic motor neurons

Smooth muscle is not innervated by somatic motor neurons. Its contraction is controlled by autonomic input, hormones, and local factors.

Question 16 of 32 Medium

Which factor primarily determines the strength of cardiac muscle contraction?

  1. A Fiber length and calcium level
  2. B Number of recruited motor units
  3. C Frequency of incoming nerve impulses
  4. D Degree of temporal summation

Correct answer: Fiber length and calcium level

Cardiac contractile force depends on fiber length and intracellular calcium levels. This relationship is described by the Frank-Starling mechanism.

Question 17 of 32 Medium

Compared to skeletal muscle, smooth muscle contracts:

  1. A More rapidly
  2. B With higher ATP consumption
  3. C More slowly and for longer duration
  4. D Only in response to nerve stimulation

Correct answer: More slowly and for longer duration

Smooth muscle contractions are slow and sustained. This suits functions like maintaining vascular tone and peristalsis.

Question 18 of 32 Medium

Gap junctions in smooth muscle primarily function to:

  1. A Increase cellular ATP synthesis rate
  2. B Electrically couple adjacent cells
  3. C Store and buffer calcium ions
  4. D Anchor and align actin filaments

Correct answer: Electrically couple adjacent cells

Gap junctions permit ion flow between adjacent smooth muscle cells. This allows coordinated contraction of the muscle layer.

Question 19 of 32 Medium

Which component is absent in smooth muscle but present in cardiac muscle?

  1. A Actin
  2. B Myosin
  3. C Troponin
  4. D Calmodulin

Correct answer: Troponin

Smooth muscle lacks troponin and instead uses calmodulin for regulation. Cardiac muscle uses troponin for calcium-mediated control.

Question 20 of 32 Medium

The primary role of the autonomic nervous system in cardiac muscle is to:

  1. A Initiate every single heartbeat
  2. B Directly trigger fiber contraction
  3. C Modulate heart rate and force
  4. D Abolish the cardiac refractory period

Correct answer: Modulate heart rate and force

The autonomic nervous system adjusts heart rate and contractility. The heartbeat itself originates from intrinsic pacemaker activity.

Question 21 of 32 Medium

Which ion channel is primarily responsible for spontaneous depolarization in cardiac pacemaker cells?

  1. A Funny (If) channels
  2. B Fast sodium channels
  3. C Potassium channels
  4. D Chloride channels

Correct answer: Funny (If) channels

Funny (If) channels allow slow sodium influx during diastole, causing gradual depolarization in pacemaker cells. This generates automatic rhythmic activity.

Question 22 of 32 Medium

Which factor most strongly determines the force of cardiac muscle contraction?

  1. A Intracellular calcium concentration
  2. B Frequency of action potentials
  3. C ATP and energy availability
  4. D Extracellular potassium levels

Correct answer: Intracellular calcium concentration

The strength of cardiac contraction depends mainly on intracellular calcium levels. More calcium leads to stronger actin-myosin interactions.

Question 23 of 32 Medium

Which structural feature distinguishes smooth muscle from cardiac muscle?

  1. A Lack of striations
  2. B Presence of actin and myosin
  3. C Presence of mitochondria
  4. D Calcium dependence

Correct answer: Lack of striations

Smooth muscle lacks the striations seen in cardiac muscle due to its non-sarcomeric organization.

Question 24 of 32 Medium

Which ion is most critical for initiating cardiac muscle contraction?

  1. A Sodium
  2. B Potassium
  3. C Calcium
  4. D Chloride

Correct answer: Calcium

Calcium influx triggers calcium-induced calcium release from the sarcoplasmic reticulum, initiating contraction in cardiac muscle.

Question 25 of 32 Medium

Compared to skeletal muscle, smooth muscle contraction is:

  1. A Faster and more forceful
  2. B Slower and sustained
  3. C Independent of calcium
  4. D Always voluntary

Correct answer: Slower and sustained

Smooth muscle contracts more slowly and can maintain tension for longer periods with less energy consumption.

Question 26 of 32 Medium

Which enzyme phosphorylates myosin light chains in smooth muscle?

  1. A Myosin light chain phosphatase
  2. B Rho-associated kinase
  3. C Myosin light chain kinase
  4. D Protein kinase A

Correct answer: Myosin light chain kinase

Myosin light chain kinase (MLCK) phosphorylates myosin, enabling cross-bridge formation and contraction.

Question 27 of 32 Medium

The primary regulatory protein in smooth muscle contraction is:

  1. A Troponin
  2. B Tropomyosin
  3. C Calmodulin
  4. D Actin

Correct answer: Calmodulin

Calmodulin binds calcium and activates MLCK, initiating smooth muscle contraction.

Question 28 of 32 Medium

The autonomic nervous system primarily affects cardiac muscle by:

  1. A Directly initiating the contraction
  2. B Altering heart rate and contractility
  3. C Controlling voluntary body movement
  4. D Regulating intracellular calcium storage

Correct answer: Altering heart rate and contractility

Autonomic input modulates heart rate and force of contraction through sympathetic and parasympathetic pathways.

Question 29 of 32 Medium

In cardiac muscle, calcium that triggers contraction is mainly released from the:

  1. A Endoplasmic reticulum
  2. B Sarcoplasmic reticulum
  3. C Mitochondrial matrix
  4. D Extracellular fluid compartment

Correct answer: Sarcoplasmic reticulum

Calcium-induced calcium release from the sarcoplasmic reticulum is essential for cardiac contraction.

Question 30 of 32 Medium

The long refractory period in cardiac muscle helps to:

  1. A Increase contraction speed
  2. B Prevent tetanic contraction
  3. C Enhance oxygen delivery
  4. D Reduce calcium levels

Correct answer: Prevent tetanic contraction

The long refractory period prevents continuous contraction, allowing the heart to relax and refill between beats.

Question 31 of 32 Medium

Cardiac muscle differs from skeletal muscle in that it:

  1. A Is under voluntary control
  2. B Contains no mitochondria
  3. C Is electrically coupled
  4. D Has no actin filaments

Correct answer: Is electrically coupled

Cardiac muscle cells are connected by gap junctions, allowing electrical signals to spread rapidly for coordinated contraction.

Question 32 of 32 Medium

Which mechanism allows smooth muscle to maintain tension with minimal energy use?

  1. A Fast ATP hydrolysis
  2. B Latch mechanism
  3. C Calcium depletion
  4. D High oxygen use

Correct answer: Latch mechanism

The latch mechanism allows smooth muscle to maintain contraction with low ATP usage by slowing cross-bridge cycling.

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