Essay Questions

Muscle Tissue: Structure and Function

Differences Between Skeletal and Smooth Muscle

Muscle tissue is classified based on structure and function. Skeletal muscle and smooth muscle differ in several key aspects:

• Cell Shape: Skeletal muscle cells are long, cylindrical, and multinucleated; smooth muscle cells are spindle-shaped and have a single nucleus.

• Striations: Skeletal muscle fibers are striated due to organized sarcomeres; smooth muscle fibers lack striations.

• Control: Skeletal muscle is under voluntary control; smooth muscle is involuntary.

• Location: Skeletal muscle attaches to bones; smooth muscle is found in walls of hollow organs (e.g., intestines, blood vessels).

• Contraction Speed: Skeletal muscle contracts rapidly; smooth muscle contracts slowly and can sustain contractions longer.

Example: Skeletal muscle enables movement of limbs, while smooth muscle regulates blood vessel diameter.

Isometric vs. Isotonic Contractions

Muscle contractions are classified by changes in muscle length and tension:

• Isometric Contraction: Muscle tension increases, but length remains constant. No movement occurs. Example: Holding a weight steady.

• Isotonic Contraction: Muscle changes length while tension remains constant. Includes:

  • Concentric: Muscle shortens as it contracts (e.g., lifting a dumbbell).

  • Eccentric: Muscle lengthens while contracting (e.g., lowering a dumbbell).

ATP Generation in Muscle

Anaerobic Pathways

Muscles generate ATP without oxygen via glycolysis:

• Glycolysis: Glucose is converted to pyruvate, yielding 2 ATP per glucose molecule.

• Lactic Acid Formation: In absence of oxygen, pyruvate is converted to lactic acid.

Aerobic Pathways

ATP is generated in the presence of oxygen via cellular respiration:

• Krebs Cycle and Electron Transport Chain: Occur in mitochondria, producing up to 32 ATP per glucose.

• Byproducts: Carbon dioxide and water.

Force of Muscle Contraction

The force generated by muscle contraction depends on several factors:

• Number of Muscle Fibers Recruited: More fibers = greater force.

• Size of Muscle Fibers: Larger fibers produce more force.

• Frequency of Stimulation: Rapid stimulation increases force (temporal summation).

• Degree of Muscle Stretch: Optimal overlap of actin and myosin maximizes force.

Nervous System: Structure and Function

Neuron Structure and Function

Neurons are specialized cells for communication. Key structures include:

• Cell Body (Soma): Contains nucleus and organelles; integrates signals.

• Dendrites: Receive incoming signals from other neurons.

• Axon: Transmits electrical impulses away from cell body.

• Axon Terminals: Release neurotransmitters to communicate with other cells.

Classification of Neurons

• Structural:

  • Multipolar: Many dendrites, one axon (most common).

  • Bipolar: One dendrite, one axon (retina, olfactory).

  • Unipolar: Single process (sensory neurons).

• Functional:

  • Sensory (Afferent): Transmit impulses toward CNS.

  • Motor (Efferent): Transmit impulses away from CNS.

  • Interneurons: Connect sensory and motor neurons within CNS.

Resting Membrane Potential

The resting membrane potential is the voltage difference across the neuron's membrane at rest, typically -70 mV. It is generated by:

• Na+/K+ Pump: Actively transports 3 Na+ out and 2 K+ in.

• Ion Channels: Differential permeability to K+ and Na+.

• Large Anions: Negatively charged proteins inside the cell.

Action Potential Propagation

Action potentials travel along the axolemma (axon membrane) by:

• Depolarization: Na+ influx causes local membrane depolarization.

• Repolarization: K+ efflux restores resting potential.

• Propagation: Sequential opening of voltage-gated channels moves the impulse.

Conduction Velocity of Action Potentials

Several factors affect how fast action potentials travel:

• Axon Diameter: Larger diameter = faster conduction.

• Myelination: Myelinated axons conduct faster via saltatory conduction.

• Temperature: Higher temperature increases speed.

Synapse Structure

A synapse is the junction between two neurons. Key components:

• Presynaptic Neuron: Releases neurotransmitter.

• Synaptic Cleft: Gap between neurons.

• Postsynaptic Neuron: Receives signal.

• Neurotransmitter Vesicles: Store and release chemical messengers.

Inhibitory vs. Excitatory Postsynaptic Potentials

• Excitatory Postsynaptic Potential (EPSP): Depolarizes postsynaptic membrane, increasing likelihood of action potential.

• Inhibitory Postsynaptic Potential (IPSP): Hyperpolarizes membrane, decreasing likelihood of action potential.

Functions of Neurotransmitters

• Acetylcholine: Stimulates muscle contraction, involved in learning and memory.

• Dopamine: Regulates mood, reward, and motor control.

• Serotonin: Modulates mood, appetite, and sleep.

• GABA: Main inhibitory neurotransmitter in CNS.

• Glutamate: Main excitatory neurotransmitter in CNS.

Brain Structure and Function

Motor Areas of the Brain

• Primary Motor Cortex: Controls voluntary movements.

• Premotor Cortex: Plans and coordinates complex movements.

• Broca's Area: Controls speech production.

Sensory Areas of the Brain

• Primary Somatosensory Cortex: Processes touch and proprioception.

• Visual Cortex: Processes visual information.

• Auditory Cortex: Processes sound information.

Cortex Communication

The cortex communicates via association fibers (within same hemisphere), commissural fibers (between hemispheres), and projection fibers (to/from lower brain or spinal cord).

Functions of the Hypothalamus

• Regulates body temperature.

• Controls hunger and thirst.

• Manages circadian rhythms.

• Controls endocrine system via pituitary gland.

• Regulates emotional responses.

Nuclei of the Midbrain and Medulla

• Midbrain: Contains nuclei for visual and auditory reflexes (e.g., superior and inferior colliculi).

• Medulla: Contains nuclei for autonomic functions (e.g., cardiovascular, respiratory centers).

Cerebellum Communication

The cerebellum communicates with the cerebrum via cerebellar peduncles, integrating motor commands and coordinating movement.

Limbic System Structures and Functions

• Amygdala: Processes emotions, especially fear.

• Hippocampus: Involved in memory formation.

• Cingulate Gyrus: Regulates emotional responses and behavior.

Reticular Activating System (RAS) Tracts

• Ascending Tracts: Carry sensory information to the cortex, maintaining alertness.

• Descending Tracts: Influence motor activity and autonomic functions.

Cerebrospinal Fluid (CSF) Production and Circulation

CSF is produced by choroid plexuses in ventricles, circulates through ventricles, subarachnoid space, and is absorbed into venous blood via arachnoid villi.

Spinal Cord Structure and White Matter Tracts

Cross Section of the Spinal Cord

• Dorsal Horn: Contains sensory neurons.

• Ventral Horn: Contains motor neurons.

• Central Canal: Contains CSF.

• White Matter: Contains ascending and descending tracts.

Ascending White Matter Tracts

• Dorsal Column: Carries fine touch and proprioception.

• Spinothalamic Tract: Carries pain and temperature.

• Spinocerebellar Tract: Carries proprioceptive information to cerebellum.

Descending White Matter Tracts

• Corticospinal Tract: Controls voluntary motor activity.

• Rubrospinal Tract: Modulates motor activity.

• Vestibulospinal Tract: Maintains balance and posture.

Additional info: Some content was expanded for clarity and completeness, including examples and definitions for key terms.