Comprehensive Study Guide: Muscle and Nervous System Structure & Function

Muscle Tissue

Differences Between Skeletal and Smooth Muscle

Muscle tissue is classified based on structure and function. Skeletal and smooth muscles 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 is striated due to organized sarcomeres; smooth muscle lacks 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.

Isometric vs. Isotonic Contractions (Concentric & Eccentric)

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

• Isometric Contraction: Muscle tension increases, but length does not change (e.g., holding a weight steady).

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

  • 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 ATP Generation

When oxygen is limited, muscles generate ATP via anaerobic glycolysis:

• Process: Glucose is converted to pyruvate, which is then converted to lactic acid.

• Equation: $\text{Glucose} \rightarrow 2 \text{Pyruvate} \rightarrow 2 \text{Lactic Acid} + 2 \text{ATP}$

• Features: Rapid ATP production, but less efficient and leads to lactic acid buildup.

Aerobic ATP Generation

With sufficient oxygen, muscles use aerobic respiration:

• Process: Glucose is fully oxidized in mitochondria.

• Equation: $\text{Glucose} + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + 36\text{ATP}$

• Features: Efficient ATP production, supports prolonged activity.

Determinants of Muscle Contraction Force

• Number of Muscle Fibers Recruited: More fibers activated increases force.

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

• Frequency of Stimulation: Rapid stimuli can lead to summation and tetanus.

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

Nervous Tissue and Nervous System

Neuron Structure and Function

Neurons are specialized cells for transmitting electrical signals. Key structures:

• Cell Body (Soma): Contains nucleus and organelles; metabolic center.

• Dendrites: Receive signals from other neurons.

• Axon: Transmits impulses away from cell body.

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

Structural and Functional Classification of Neurons

• Structural:

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

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

  • Unipolar: Single process splits into two branches (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 Generation

The resting membrane potential is the voltage difference across the neuron membrane at rest:

• Key Factors:

  • Na+/K+ ATPase pump maintains ion gradients.

  • Membrane is more permeable to K+ than Na+.

  • Inside is negative relative to outside (~ -70 mV).

• Equation: $V_m = \frac{RT}{F} \ln \left( \frac{[K^+]_{out}}{[K^+]_{in}} \right)$ (Nernst equation for K+)

Action Potential Propagation Along Axolemma

• Depolarization: Na+ channels open, Na+ enters cell.

• Repolarization: K+ channels open, K+ exits cell.

• Propagation: Local currents depolarize adjacent membrane, moving the action potential along the axon.

Factors Affecting Conduction Velocity of Action Potentials

• 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:

• Presynaptic Neuron: Releases neurotransmitter.

• Synaptic Cleft: Gap between neurons.

• Postsynaptic Neuron: Receives signal.

• Neurotransmitter Vesicles: Contain chemical messengers.

Inhibitory vs. Excitatory Postsynaptic Potentials

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

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

Functions of Neurotransmitters

• Acetylcholine: Stimulates muscle contraction.

• Dopamine: Regulates mood and movement.

• Serotonin: Modulates mood, sleep, appetite.

• GABA: Main inhibitory neurotransmitter.

• Glutamate: Main excitatory neurotransmitter.

The Central Nervous System

Motor Areas of the Brain

• Primary Motor Cortex: Controls voluntary movements.

• Premotor Cortex: Plans 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.

Cortex Communication

• Association Fibers: Connect regions within the same hemisphere.

• Commissural Fibers: Connect corresponding regions between hemispheres (e.g., corpus callosum).

• Projection Fibers: Connect cortex with lower brain regions and 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 substantia nigra (movement), red nucleus (motor coordination).

• Medulla: Contains cardiovascular and respiratory centers.

Cerebellum Communication with Cerebrum

• Cerebellum receives input from cerebrum via pontine nuclei.

• Sends feedback to motor cortex to coordinate movement.

Limbic System Structures and Functions

• Amygdala: Processes emotions.

• Hippocampus: Involved in memory formation.

• Cingulate Gyrus: Regulates emotional responses.

Reticular Activating System Tracts

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

• Descending Tracts: Modulate motor activity and autonomic functions.

Cerebrospinal Fluid (CSF) Production and Circulation

• Production: CSF is produced by choroid plexus in ventricles.

• Circulation: Flows 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: Receives sensory input.

• Ventral Horn: Contains motor neurons.

• Central Canal: Contains CSF.

• White Matter: Contains ascending and descending tracts.

Ascending White Matter Tracts

• Dorsal Columns: Carry touch and proprioception.

• Spinothalamic Tract: Transmits pain and temperature.

• Spinocerebellar Tract: Conveys proprioceptive information to cerebellum.

Descending White Matter Tracts

• Corticospinal Tract: Controls voluntary movement.

• Rubrospinal Tract: Modulates motor activity.

• Vestibulospinal Tract: Maintains balance and posture.

Additional info: Some content was expanded for clarity and completeness based on standard Anatomy & Physiology curriculum.