Muscle and Nervous System Structure and Function: Study Notes

Chapter 9: Muscles and Muscle Tissue

9.1 There are three types of muscle tissue

Muscle tissue is classified into three main types, each with distinct structure and function.

• Skeletal muscle: Attached to bones, voluntary, striated, responsible for movement.

• Cardiac muscle: Found in the heart, involuntary, striated, responsible for pumping blood.

• Smooth muscle: Found in walls of hollow organs, involuntary, non-striated, controls movement of substances.

Key locations: Skeletal (attached to bones), Cardiac (heart), Smooth (walls of hollow organs).

9.2 A skeletal muscle is made up of muscle fibers, nerves, blood vessels, and connective tissue

Skeletal muscles are complex organs composed of muscle fibers bundled together, supplied by nerves and blood vessels, and surrounded by connective tissue.

• Epimysium: Surrounds entire muscle.

• Perimysium: Surrounds fascicles (bundles of muscle fibers).

• Endomysium: Surrounds individual muscle fibers.

9.3 Skeletal muscle fibers contain sarcomeres: organized molecular motors

The sarcomere is the functional unit of muscle contraction, composed of actin and myosin filaments.

• Myofibril: Rod-like unit containing sarcomeres.

• Myofilaments: Actin (thin) and myosin (thick) filaments.

• Sarcomere: Segment between two Z discs; site of contraction.

9.4 Motor neurons stimulate skeletal muscle fibers to contract

Muscle contraction is initiated by signals from motor neurons at the neuromuscular junction.

• Acetylcholine (ACh): Neurotransmitter released at the neuromuscular junction.

• Action potential: Electrical signal that triggers muscle contraction.

• Calcium ions: Released from sarcoplasmic reticulum, enabling actin-myosin interaction.

9.5 The sliding filament model of muscle contraction

Muscle contraction occurs as actin and myosin filaments slide past each other, shortening the sarcomere.

• Cross bridge formation: Myosin head binds to actin.

• Power stroke: Myosin head pivots, pulling actin filament.

• Detachment: Myosin head releases actin after ATP binds.

• Cocking: Myosin head returns to its original position.

Step of cross bridge cycle	Brief description
1. Cross bridge formation	Myosin head binds to actin
2. The power (working) stroke	Myosin head pivots, pulling actin filament
3. Cross bridge detachment	ATP binds, myosin releases actin
4. Cocking of the myosin head	Myosin hydrolyzes ATP, returns to original position

9.6 Temporal summation and motor unit recruitment allow smooth, graded skeletal muscle contractions

Muscle force is regulated by the frequency of stimulation and the number of motor units activated.

• Temporal summation: Increased frequency of stimulation increases force.

• Motor unit recruitment: More motor units activated increases force.

9.7a: Differentiate between isometric and isotonic contractions

• Isometric contraction: Muscle tension increases, but length does not change.

• Isotonic contraction: Muscle changes length (shortens or lengthens) while tension remains constant.

9.8 ATP for muscle contraction is produced aerobically or anaerobically

ATP is required for muscle contraction and can be generated by three main pathways.

Energy source	Creatine phosphate	Anaerobic pathway	Aerobic pathway
Oxygen use	None	None	Required
Products	1 ATP per creatine phosphate	2 ATP per glucose, lactic acid	32 ATP per glucose, CO2, H2O
Duration of energy provided	15 seconds	30-40 seconds	Hours

9.9 Define EPOC and muscle fatigue. List possible causes of muscle fatigue.

• Muscle fatigue: Inability of a muscle to maintain tension despite continued stimulation.

• EPOC (Excess Postexercise Oxygen Consumption): Extra oxygen required after exercise to restore metabolic conditions.

• Causes of fatigue: Ionic imbalances, decreased ATP, accumulation of lactic acid.

9.10 Three types of skeletal muscle fibers and their relative value

• Fast glycolytic fibers: Contract quickly, fatigue rapidly, used for short bursts of power.

• Slow oxidative fibers: Contract slowly, resist fatigue, used for endurance activities.

• Fast oxidative fibers: Intermediate properties.

9.11 Effects of aerobic and resistance exercise on skeletal muscle

Effect	Aerobic	Resistance
Increase in muscle capillaries	X
Increase in mitochondria	X
Increase in myofibrils		X
Increase in muscle size		X

9.9 Smooth muscle is nonstriated involuntary muscle

Characteristic	Smooth muscle	Skeletal muscle
Small spindle-shaped cells	X
Long, cylindrical cells		X
Multinucleate		X
Uninucleate	X
Striations		X
Has sarcomeres		X
Has gap junctions	X

9.9c: Distinguish between unitary and multi unit smooth muscle

Characteristic	Unitary smooth muscle	Multi unit smooth muscle
Contractions rarely synchronous		X
Found in walls of large arteries		X
Cells joined by gap junctions	X
Contracts as a unit	X
Involves recruitment		X
Found in the stomach wall	X

Chapter 10: The Muscular System

10.1 For any movement, muscles can act in one of three ways

• Prime mover (agonist): Main muscle responsible for movement.

• Antagonist: Muscle that opposes the action of the agonist.

• Synergist: Assists the prime mover.

• Fixator: Stabilizes the origin of the prime mover.

10.2 How are skeletal muscles named?

• Location: e.g., Temporalis (temple).

• Shape: e.g., Deltoid (triangle).

• Size: e.g., Gluteus maximus (largest).

• Direction of fibers: e.g., Rectus abdominis (straight).

• Number of origins: e.g., Biceps brachii (two origins).

• Location of attachments: e.g., Sternocleidomastoid (sternum, clavicle, mastoid).

• Action: e.g., Flexor carpi radialis (flexes wrist).

10.3 Fascicle arrangements help determine muscle shape and force

• Parallel: Fascicles run parallel to long axis (e.g., sartorius).

• Pennate: Fascicles attach obliquely to tendon (e.g., rectus femoris).

• Circular: Fascicles arranged in rings (e.g., orbicularis oris).

• Convergent: Fascicles converge toward a single tendon (e.g., pectoralis major).

10.4 Muscles acting with bones form lever systems

Muscles and bones interact as levers to produce movement, classified as first, second, or third class levers.

Characteristic	Mechanical advantage	Mechanical disadvantage
Moves a heavier load over a smaller distance	X
Allows rapid movement over a large distance		X
Effort is applied farther from fulcrum than load	X
Effort is applied closer to fulcrum than load		X

Chapter 11: Fundamentals of the Nervous System and Nervous Tissue

11.1 The nervous system receives, integrates, and responds to information

• Central nervous system (CNS): Brain and spinal cord; integration and control center.

• Peripheral nervous system (PNS): Communication lines linking CNS to body.

11.2 Neuroglia support and maintain neurons

• Astrocytes: Support neurons, maintain environment.

• Microglia: Immune defense in CNS.

• Ependymal cells: Line brain ventricles, circulate cerebrospinal fluid.

• Oligodendrocytes: Form myelin in CNS.

• Schwann cells: Form myelin in PNS.

11.3 Neurons are the structural units of the nervous system

• Cell body: Contains nucleus and organelles.

• Dendrites: Receive signals.

• Axon: Transmits signals away from cell body.

11.4 The resting membrane potential depends on differences in ion concentration and permeability

• Resting membrane potential: Voltage across membrane at rest, typically -70 mV.

• Key ions: Na+ (outside), K+ (inside).

• Electrochemical gradient: Combination of concentration and electrical gradients.

Equation for membrane potential:

$V_m = E_{K^+}$

11.5 Graded potentials are brief, short-distance signals within a neuron

• Graded potential: Local change in membrane potential, decreases with distance.

11.6 Action potentials are brief, long-distance signals within a neuron

• Action potential: All-or-none electrical signal, travels along axon.

• Threshold: Minimum stimulus required to trigger action potential.

Phase	Na+ channels	K+ channels	Direction of K+
Resting state	Closed	Closed	None
Depolarization	Open	Closed	None
Repolarization	Closed	Open	Out
Hyperpolarization	Closed	Open	Out

11.7 Synapses transmit signals between neurons

• Synapse: Junction between neurons for signal transmission.

• Neurotransmitter: Chemical messenger released at synapse.

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