What are the three major types of neurons, and what is the primary function of each?

What are the three major types of neurons?

Sensory neurons, interneurons, and motor neurons.

What is the function of sensory neurons?

Receive information from the internal and external environment and send it to the CNS.

What is the function of interneurons?

Integrate and process information within the CNS.

What is the function of motor neurons?

Carry signals from the CNS to muscles or glands.

What part of a neuron receives signals?

Dendrites.

What part of a neuron contains the nucleus and organelles?

Cell body (soma).

Where are action potentials generated?

Axon hillock.

What is the function of the axon?

Conduct action potentials away from the cell body.

What is the function of synaptic terminals?

Release neurotransmitters into the synapse.

What is the resting membrane potential of a neuron?

Approximately -70 mV.

What does it mean for a neuron to be polarized?

The inside is negatively charged relative to the outside.

What is hyperpolarization?

A shift to a more negative membrane potential.

What ion commonly causes hyperpolarization when it leaves the cell?

Potassium (K⁺).

What is depolarization?

A shift to a more positive membrane potential.

What ion commonly causes depolarization when it enters the cell?

Sodium (Na⁺).

What are graded potentials?

Small membrane potential changes whose magnitude depends on stimulus strength.

Do graded potentials weaken as they travel?

Yes, they dissipate over distance.

What is the threshold potential for firing an action potential?

Approximately -55 mV.

What causes voltage-gated sodium channels to open?

Reaching threshold.

What happens during the rising phase of an action potential?

Massive sodium influx causes rapid depolarization.

What is the peak membrane potential during an action potential?

Approximately +62 mV.

What happens during repolarization?

Sodium channels close and potassium channels open.

What causes hyperpolarization (undershoot)?

Potassium channels remain open too long, allowing excess K⁺ to leave.

What is the refractory period?

A period when a neuron cannot easily fire another action potential.

What are the two purposes of the refractory period?

Prevent overstimulation and ensure one-way signal conduction.

What is the all-or-none principle?

Action potentials occur at full strength or not at all.

What ion enters the synaptic terminal to trigger neurotransmitter release?

Calcium (Ca²⁺).

What process releases neurotransmitters into the synapse?

Exocytosis.

What is an EPSP?

Excitatory postsynaptic potential; moves membrane potential closer to threshold.

What is an IPSP?

Inhibitory postsynaptic potential; moves membrane potential farther from threshold.

Which ion commonly produces EPSPs?

Sodium (Na⁺).

Which ion commonly produces IPSPs?

Chloride (Cl⁻)

What is summation?

The combined effect of multiple EPSPs and IPSPs.

What determines whether a postsynaptic neuron fires?

The net effect of EPSPs and IPSPs.

What neurotransmitter is important in both skeletal and cardiac muscle?

Acetylcholine (ACh).

What enzyme breaks down acetylcholine?

Acetylcholinesterase.

What are the three types of muscle tissue?

Skeletal, smooth, and cardiac muscle.

Which muscle type is voluntary?

Skeletal muscle.

Which muscle type is attached to bones?

Skeletal muscle.

Which muscle types are involuntary?

Smooth and cardiac muscle.

What is a muscle fiber?

A single muscle cell.

What are myofibrils?

Contractile structures within muscle fibers.

What is the smallest contractile unit of skeletal muscle?

Sarcomere.

What protein forms the thin filament?

Actin.

What protein forms the thick filament?

Myosin.

What are the boundaries of a sarcomere?

Z-lines.

What structure anchors actin filaments?

Z-lines.

What structure anchors myosin filaments?

M-line.

What is the sliding filament theory?

Actin slides past myosin to shorten the sarcomere.

Do actin and myosin change length during contraction?

No

What happens to Z-lines during contraction?

They move closer together.

Which filament actually moves during contraction?

Actin

What is a cross-bridge?

A connection formed between myosin and actin.

What molecule binds to myosin before contraction can occur?

ATP

What does ATP hydrolysis produce?

ADP and Pi.

What is the power stroke?

The pulling of actin toward the M-line by myosin.

What causes the power stroke?

Release of ADP and Pi.

What breaks the cross-bridge

Binding of a new ATP molecule.

What are the four major energy sources for muscle contraction?

Stored ATP, creatine phosphate, aerobic respiration, and anaerobic respiration.

What is rigor mortis?

Postmortem muscle stiffness caused by persistent cross-bridges.

Why does rigor mortis occur?

ATP is unavailable to break cross-bridges.

What protein blocks myosin-binding sites on actin?

Tropomyosin.

What protein binds calcium?

Troponin.

What happens when calcium binds troponin?

Tropomyosin moves and exposes myosin-binding sites.

What ion is required for muscle contraction?

Calcium (Ca²⁺).

What is a motor unit?

One motor neuron and all the muscle fibers it controls.

What are T-tubules?

Plasma membrane extensions that carry action potentials deep into muscle fibers.

What is the function of the sarcoplasmic reticulum (SR)?

Stores calcium.

What neurotransmitter stimulates skeletal muscle contraction?

Acetylcholine.

What sequence leads to skeletal muscle contraction?

ACh release → muscle depolarization → T-tubules activate → SR releases Ca²⁺ → cross-bridge cycling.

How many chambers does the heart have?

Four

What are the upper chambers of the heart called?

Atria

What are the lower chambers of the heart called?

Ventricles

What characteristic does cardiac muscle share with skeletal muscle?

Striations

What structures connect cardiac muscle cells?

Intercalated discs.

What is the function of intercalated discs?

Coordinate electrical activity between heart cells.

What does it mean that cardiac muscle is autorhythmic?

It can generate its own action potentials.

What is the natural pacemaker of the heart?

Sinoatrial (SA) node.

Where is the SA node located?

Right atrium.

What is the function of the AV node?

Delays the electrical signal before ventricular contraction.

How long is the AV node delay?

Approximately 0.1 seconds.

What structures conduct signals to the ventricles after the AV node?

Bundle branches and Purkinje fibers.

What is an ECG (EKG)?

A recording of the heart's electrical activity.

What is systole?

Contraction phase of the cardiac cycle.

What is diastole?

Relaxation phase of the cardiac cycle.

What is cardiac output?

Amount of blood pumped by the heart per minute.

What is the formula for cardiac output?

Cardiac Output = Heart Rate × Stroke Volume.

What is the normal resting heart rate?

60–100 bpm.

What is average stroke volume?

Approximately 70 mL/beat.

What is average cardiac output?

Approximately 5 L/min.

What are AV valves?

Valves between atria and ventricles.

What is the function of AV valves?

Prevent backflow into the atria.

What are semilunar valves?

Valves at the exits of the ventricles.

What is the function of semilunar valves?

Prevent backflow into ventricles.

What causes the "lub" heart sound?

Closing of AV valves.

What causes the "dub" heart sound?

Closing of semilunar valves.

What effect does ACh have on cardiac muscle?

Slows heart rate.

How does ACh slow heart rate?

Opens potassium channels and inhibits adenylyl cyclase.

What is the pathway of blood flow through vessels?

Artery → Arteriole → Capillary Bed → Venule → Vein.

What type of vessel carries blood away from the heart?

Artery.