ANP Study Guide: Muscle and Nervous System, Homeostasis, Chemistry, and Cell Biology

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Muscle Tissue and Contraction

Muscle Anatomy: Connective Tissue Layers

The skeletal muscle is organized into layers of connective tissue that provide structure and support.

Epimysium: The outermost layer, surrounds the entire muscle.
Perimysium: Surrounds bundles of muscle fibers called fascicles.
Endomysium: Surrounds individual muscle fibers (cells).

Bundling Anatomy: Myofibrils are bundled into muscle fibers, which are grouped into fascicles, and fascicles form the whole muscle.

Sarcomere Structure and Function

The sarcomere is the basic contractile unit of muscle, composed of actin (thin) and myosin (thick) filaments.

Actin: Thin filament, involved in contraction.
Myosin: Thick filament, forms cross-bridges with actin.
H zone: Central region of the sarcomere containing only myosin; shortens during contraction.
I band: Region containing only actin; shortens during contraction.
A band: Length of the myosin filaments; remains constant during contraction.

Which change length during contraction? The H zone and I band decrease in length, while the A band remains unchanged. This occurs because actin filaments slide over myosin, shortening the sarcomere.

Cross Bridge Cycle and ATP Role

The cross bridge cycle describes the interaction between actin and myosin during muscle contraction.

Attachment: Myosin head binds to actin (requires calcium).
Power Stroke: Myosin head pivots, pulling actin; ADP and Pi are released.
Detachment: ATP binds to myosin, causing it to release actin.
Reactivation: ATP is hydrolyzed, re-cocking the myosin head.

Role of ATP: ATP is required for detachment and reactivation of the myosin head.

What keeps the cycle from running when muscle is relaxed? Low calcium levels prevent myosin from binding to actin.

Role of Action Potential in Muscle Contraction

An action potential triggers calcium release from the sarcoplasmic reticulum, enabling the cross bridge cycle and muscle contraction.

Tension vs Load; Types of Contractions

Tension: Force produced by muscle.
Load: Resistance the muscle works against.
Isometric Contraction: Muscle generates tension without changing length.
Isotonic Contraction: Muscle changes length while moving a load.

Summation and Tetanus

Summation: Increased force from repeated stimulation before relaxation.
Tetanus: Sustained contraction; can be fused (no relaxation) or unfused (partial relaxation).

Factors Affecting Muscle Force

Number of muscle fibers recruited
Frequency of stimulation
Degree of muscle stretch
Type of muscle fiber

Skeletal Muscle Fiber Types

Muscle fibers differ in speed, metabolism, and appearance.

Type	Characteristics	Example	Color
Slow-oxidative	Fatigue-resistant, aerobic	Postural muscles	Red (high myoglobin)
Fast-glycolytic	Quick, powerful, anaerobic	Jumping, sprinting	White (low myoglobin)
Fast-oxidative	Intermediate	Walking	Pink

Color differences: Due to myoglobin content and capillary density.

Nervous System

Glial Cells

Glial cells support neurons in the nervous system.

Astrocytes: Support, regulate environment.
Oligodendrocytes: Myelinate CNS axons.
Schwann cells: Myelinate PNS axons.
Microglia: Immune defense.
Ependymal cells: Line ventricles, produce cerebrospinal fluid.

Membrane Potential and Resting State

Membrane potential is the voltage difference across a cell membrane.

Resting membrane potential: Typically -70 mV in neurons.
Ion distribution: More sodium (Na+) outside, more potassium (K+) inside.
Channels: K+ channels mostly open, Na+ channels mostly closed.
Sodium-potassium pump: Maintains gradient by pumping 3 Na+ out and 2 K+ in per ATP used.

Classification of Neurons

Sensory (afferent): Carry information to CNS.
Motor (efferent): Carry commands from CNS.
Interneurons: Connect within CNS.

Graded Potential vs Action Potential

Graded potential: Local, variable strength, fades with distance.
Action potential: All-or-none, propagated along axon.

Action Potential Phases

Phase	Description
Threshold	Minimum voltage to trigger AP
Depolarization	Na+ influx, membrane becomes positive
Repolarization	K+ efflux, membrane returns negative
Hyperpolarization	Excess K+ leaves, membrane more negative than resting

Intensity Perception and Refractory Period

Intensity: Encoded by frequency of action potentials, not amplitude.
Refractory period: Time when neuron cannot fire another AP; ensures one-way propagation and limits firing rate.

Synapse and Synaptic Transmission

The synapse is the junction between two neurons.

Process: AP arrives, Ca2+ enters, neurotransmitter released, binds to postsynaptic receptors.
Other ions: Ca2+ is crucial for neurotransmitter release.

EPSP vs IPSP

EPSP (Excitatory Post-Synaptic Potential): Depolarizes membrane, often via Na+ influx.
IPSP (Inhibitory Post-Synaptic Potential): Hyperpolarizes membrane, often via K+ efflux or Cl- influx.

Somatic vs Autonomic Nervous System

Somatic: Voluntary control of skeletal muscles.
Autonomic: Involuntary control of smooth muscle, cardiac muscle, glands.

Sympathetic vs Parasympathetic

Division	Neurotransmitter	Response
Sympathetic	Norepinephrine	Fight or flight
Parasympathetic	Acetylcholine	Rest and digest

Dual innervation: Most organs receive input from both divisions, allowing fine control.

Sensory Receptors and Adaptation

Modality: Type of stimulus detected (e.g., touch, light).
Adequate stimulus: The specific stimulus a receptor is most sensitive to.
Sensory adaptation: Decreased response to constant stimulus.

Grey vs White Matter

Grey matter: Neuron cell bodies, dendrites.
White matter: Myelinated axons.

Major Regions of the Brain

Cerebrum: Higher functions, sensory, motor.
Ventricles: CSF-filled spaces.
Cerebellum: Coordination, balance.
Thalamus: Relay station.
Brainstem: Includes pons, medulla oblongata.

Major landmarks: Fissures, cortex, hypothalamus, diencephalon, pituitary gland.

Roles of Brain Regions

Pons: Relay, breathing regulation.
Cortex: Conscious thought, perception.
Hypothalamus: Homeostasis, hormone control.
Diencephalon: Contains thalamus, hypothalamus.
Pituitary gland: Hormone secretion.
Medulla oblongata: Vital functions (heart rate, breathing).
Blood brain barrier: Protects brain from toxins.

Spinal Cord Roots and White Matter

Ventral root: Motor output.
Dorsal root: Sensory input.
White matter: Contains ascending (sensory), descending (motor), and commissural (crossing) tracts.

Homeostasis and Feedback

Homeostasis

Homeostasis is the maintenance of a stable internal environment.

Negative feedback: Counteracts changes (e.g., temperature regulation).
Positive feedback: Amplifies changes (e.g., blood clotting).

Chemistry: Atoms, Isotopes, Ions

Atoms and Subatomic Particles

Proton: Positive charge, in nucleus.
Neutron: No charge, in nucleus.
Electron: Negative charge, orbits nucleus.

Isotopes and Ions

Isotope: Same element, different number of neutrons.
Ion: Atom with net charge due to loss/gain of electrons.

Major Elements in Human Body

Oxygen
Carbon
Hydrogen
Nitrogen

Cell Biology

Major Parts of the Cell

Plasma membrane: Controls entry/exit, maintains cell integrity.
Nucleus: Contains genetic material.
Cytoplasm: Site of metabolic activity.

Proteins and ATP

Proteins: Made of amino acids, perform structural and functional roles.
ATP (Adenosine Triphosphate): Main energy currency of the cell.

Catabolic vs Anabolic Reactions

Catabolic: Breakdown of molecules, releases energy.
Anabolic: Building molecules, requires energy.

Transport Mechanisms

Diffusion: Passive movement from high to low concentration.
Facilitated diffusion: Passive, uses carrier proteins.
Active transport: Requires energy, moves against gradient.
Osmosis: Diffusion of water across membrane.

Mitosis vs Meiosis

Mitosis: Cell division for growth/repair; produces identical cells.
Meiosis: Cell division for gametes; produces cells with half the chromosome number.

Difference: Mitosis maintains chromosome number; meiosis reduces it for sexual reproduction.

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