Study Guide: Muscle Tissue, Muscular System, and Fundamentals of the Nervous System (Chapters 9–11)

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Muscle Tissue

Types of Muscle Tissue

Muscle tissue is classified into three main types, each with distinct structural and functional characteristics.

Skeletal Muscle: Voluntary, striated, multinucleated, long fibers. Responsible for body movement and posture.
Cardiac Muscle: Involuntary, striated, usually one or two nuclei per cell, contains intercalated discs. Found only in the heart.
Smooth Muscle: Involuntary, non-striated, single nucleus, short spindle-shaped cells. Found in walls of hollow organs (e.g., blood vessels, GI tract).

Comparison Table:

Feature	Skeletal	Cardiac	Smooth
Control	Voluntary	Involuntary	Involuntary
Striations	Yes	Yes	No
Nuclei	Multiple	1–2	1
Special Features	Long fibers	Intercalated discs	Caveolae, calmodulin

Special Properties of Muscle Tissue

Excitability (Irritability): Ability to receive and respond to stimuli.
Contractility: Ability to shorten forcibly when stimulated.
Extensibility: Ability to stretch without being damaged.
Elasticity: Ability to recoil to resting length after stretching.

Functions of Muscle Tissue

Movement: Locomotion and manipulation (skeletal), movement of substances (smooth, cardiac).
Posture: Maintained by continuous skeletal muscle contraction.
Stabilizing Joints: Muscles reinforce and stabilize joints.
Heat Generation: Muscle contraction produces heat, aiding in body temperature regulation.

Connective Tissue Layers of Skeletal Muscle

Epimysium: Surrounds entire muscle.
Perimysium: Surrounds fascicles (bundles of muscle fibers).
Endomysium: Surrounds individual muscle fibers.

Microscopic Anatomy of Skeletal Muscle

Sarcomere: Structural and functional unit of muscle; contains H zone, A band, Z disc, I band.
Sarcolemma: Plasma membrane of muscle fiber; conducts action potentials.
Sarcoplasmic Reticulum (SR): Stores and releases Ca2+ for contraction.
Myofibril: Contractile organelle composed of repeating sarcomeres.
T-tubules: Invaginations of sarcolemma; transmit action potentials into fiber.
Triad: T-tubule flanked by two terminal cisternae of SR.
Myoglobin: Oxygen-binding protein in muscle.
Glycosomes: Organelles storing glycogen.

Sliding Filament Model of Contraction

Thin filaments (actin) slide past thick filaments (myosin), shortening the sarcomere.
Myosin filaments are thick and dark; actin filaments are thin and light.

Neuromuscular Junction and Excitation-Contraction Coupling

Neuromuscular Junction: Site where motor neuron communicates with muscle fiber.
Process: ACh released → binds to receptors on motor end plate → Na+ influx → action potential in sarcolemma → T-tubules → Ca2+ release from SR → contraction.
Excitation-Contraction Coupling: Sequence linking action potential to muscle contraction via Ca2+ release.

Motor Units

Consist of a somatic motor neuron and all muscle fibers it innervates.
Small motor units: fine control (e.g., eye muscles); large motor units: gross movements (e.g., gluteus maximus).

Cross-Bridge Cycle and Muscle Relaxation

Key Molecules: Ca2+ (binds troponin), ATP (energizes myosin, detaches cross-bridge).
Regulatory Proteins: Troponin and tropomyosin block myosin binding sites on actin.
Cycle: Myosin binds actin → power stroke → ATP binds myosin (detachment) → cycle repeats.
Relaxation: Ca2+ reabsorbed into SR, ACh broken down by acetylcholinesterase.
Rigor Mortis: No ATP post-mortem; cross-bridges cannot detach.

Muscle Twitch and Graded Responses

Muscle Twitch: Single contraction in response to a single stimulus; phases: latent, contraction, relaxation.
Graded Responses: Varying strength of contraction via motor unit recruitment and frequency of stimulation.
Treppe: Successive contractions become stronger due to increased Ca2+ and heat.
Tetanus: Incomplete (unfused) vs. complete (fused) tetanus based on frequency of stimulation.

Types of Muscle Contractions

Isometric: Tension increases, but muscle length does not change.
Isotonic: Muscle changes length (concentric: shortens; eccentric: lengthens).
Muscle Tone: Slight, constant contraction for posture and readiness.

Muscle Metabolism

Direct Phosphorylation: Creatine phosphate + ADP → ATP (lasts ~15 sec).
Anaerobic Respiration: Glycolysis (no O2), produces lactic acid, 2 ATP/glucose (lasts ~60 sec).
Aerobic Respiration: Glycolysis + Krebs cycle + ETC (with O2), 36 ATP/glucose (lasts hours).
Oxygen Debt: Extra O2 needed to restore muscle to resting state.

Equation for Aerobic Respiration:

Types of Skeletal Muscle Fibers

Fiber Type	Oxygen Use	Fatigue	Speed	Metabolism
Slow Oxidative	High	Resistant	Slow	Aerobic
Fast Glycolytic	Low	Quick to fatigue	Fast	Anaerobic
Fast Oxidative	Intermediate	Intermediate	Fast	Aerobic & Anaerobic

Muscle Growth and Adaptation

Hypertrophy: Increase in muscle size.
Atrophy: Decrease in muscle size due to disuse.
Hyperplasia: Increase in number of muscle cells (rare in humans).

Smooth Muscle

Functions: Maintains blood pressure, propels food, regulates blood flow.
Layers: Circular (inner, around lumen) and longitudinal (outer).
Key Differences: Uses calmodulin (not troponin), has varicosities, contracts slowly, adapts to stretch, uses caveolae instead of T-tubules.
Contraction: Peristalsis (alternating contraction/relaxation for propulsion).
Neurotransmitters: ACh (contracts), norepinephrine (relaxes bronchioles, contracts blood vessels).

Muscular System

Organization and Naming of Muscles

Muscles are grouped by function: Prime mover (agonist), antagonist, synergist, fixator.
Named by location, shape, size, direction of fibers, number of origins, attachments, and action.
Fascicle arrangements: parallel, fusiform, circular, convergent, unipennate, bipennate, multipennate.

Muscle Attachments and Levers

Tendon: Cordlike connective tissue attaching muscle to bone.
Aponeurosis: Sheetlike connective tissue attachment.
Origin: Attachment to stationary bone.
Insertion: Attachment to movable bone.
Levers: Bones act as levers with effort (muscle force), load (resistance), and fulcrum (joint).

Major Muscles and Their Functions

Head: Buccinator (cheek compression), frontalis (raises eyebrows), masseter (elevates mandible), orbicularis oculi (closes eye), orbicularis oris (purses lips), temporalis (closes jaw), zygomaticus (smiling).
Neck: Sternocleidomastoid (flexes/rotates head), trapezius (stabilizes scapula).
Shoulder: Deltoid (abducts arm), latissimus dorsi (extends/adducts arm), levator scapula (elevates scapula).
Rotator Cuff: Supraspinatus (abducts arm), infraspinatus/teres minor (lateral rotation), subscapularis (medial rotation).
Arm: Biceps brachii (flexes elbow), brachialis (forearm flexor), triceps brachii (extends elbow).
Forearm: Brachioradialis (flexes forearm), flexor/extensor carpi muscles (flex/extend wrist), extensor digitorum (extends fingers), pronator teres (pronates forearm), palmaris longus (wrist flexor).
Thorax: Diaphragm (breathing), intercostals (inspiration/expiration), pectoralis major (flexes/adducts arm), serratus anterior (rotates scapula).
Abdomen: External/internal obliques (flex/compress abdomen), rectus abdominis (flexes lumbar spine), transversus abdominis (compresses abdomen).
Hip: Gluteus maximus (extends thigh), gluteus medius (abducts/medially rotates thigh).
Thigh: Adductors (adduct/flex/rotate thigh), gracilis (adducts thigh), hamstrings (extend thigh/flex knee), quadriceps (extend knee), sartorius (flexes/abducts/laterally rotates thigh), tensor fascia lata (steadies knee/trunk).
Leg: Gastrocnemius/soleus/fibularis longus (plantar flexion), tibialis anterior (dorsiflexion), extensor digitorum longus (extends toes).

Fundamentals of the Nervous System

Nervous vs. Endocrine System

Both maintain homeostasis.
Nervous: Fast (milliseconds), uses electrical impulses and neurotransmitters.
Endocrine: Slower (seconds to months), uses hormones in blood/ECF.

Functions and Organization of the Nervous System

Sensory Input: Monitors changes inside/outside body.
Integration: Processes and interprets sensory input.
Motor Output: Activates effectors (muscles/glands).
CNS: Brain and spinal cord.
PNS: Cranial/spinal nerves, ganglia.
PNS Divisions: Sensory (afferent) and motor (efferent).
Motor Division: Somatic (voluntary, skeletal muscle) and autonomic (involuntary, cardiac/smooth muscle, glands).
Autonomic Subdivisions: Sympathetic and parasympathetic.

Neuroglia (Glial Cells)

CNS: Astrocytes (support, regulate environment), microglia (phagocytosis), ependymal cells (circulate CSF), oligodendrocytes (myelinate axons).
PNS: Schwann cells (myelinate axons), satellite cells (regulate environment).

Neurons

Parts: Dendrites (receive input), cell body (soma, integration), axon hillock (trigger zone), axon (conducts impulses).
Types: Multipolar (most common, motor/interneurons), bipolar (special senses), unipolar (sensory).

Membrane Potentials and Action Potentials

Resting Membrane Potential: -70 mV (ICF more negative).
Depolarization: Na+ influx, membrane becomes less negative.
Threshold: -55 mV; Peak: +30 mV.
Repolarization: K+ efflux, membrane returns to negative.
Hyperpolarization: Excess K+ outflow, membrane more negative.
Refractory Periods: Absolute (no new AP), relative (stronger stimulus needed).
Na+/K+ Pump: Restores ion gradients ( out, in).

Organization of Nervous Tissue

Nuclei: Cell bodies in CNS.
Ganglia: Cell bodies in PNS.
Tracts: Axon bundles in CNS.
Nerves: Axon bundles in PNS.
White Matter: Myelinated axons (fast conduction, saltatory).
Gray Matter: Cell bodies, dendrites, unmyelinated fibers.

Graded Potentials vs. Action Potentials

Feature	Graded Potentials	Action Potentials
Location	Dendrites/cell body	Axon
Distance	Short	Long
Amplitude	Variable, decreases	All-or-none, constant
Channels	Chemically gated	Voltage-gated

EPSP: Excitatory, depolarizes membrane (Na+ in, K+ out).
IPSP: Inhibitory, hyperpolarizes membrane (K+ out or Cl- in).

Synaptic Transmission

Chemical Synapse: AP arrives at axon terminal → Ca2+ influx → neurotransmitter release → binds postsynaptic receptor → opens ion channels → graded potential (EPSP/IPSP).
Neurotransmitter removal: Enzymatic breakdown (e.g., acetylcholinesterase), reuptake, diffusion.
Types of Synapses: Axodendritic, axosomatic, axoaxonic.
Channel Types: Ligand-gated (postsynaptic), voltage-gated (axon).

Selected Neurotransmitters

Neurotransmitter	EPSP/IPSP	Main Function
Acetylcholine (ACh)	EPSP (skeletal), IPSP (cardiac)	Muscle contraction, autonomic functions
Norepinephrine (NE)	EPSP/IPSP	Alertness, mood, autonomic functions
Dopamine	EPSP/IPSP	Pleasure, reward, motor control
Serotonin	IPSP	Mood regulation
GABA	IPSP	Main inhibitory neurotransmitter in brain
Glutamate	EPSP	Main excitatory neurotransmitter, learning/memory
Endorphins	IPSP	Pain inhibition
Substance P	EPSP	Pain transmission

Summary: Chapters 9–11 cover the structure and function of muscle tissue, organization and actions of the muscular system, and the fundamentals of the nervous system, including cell types, membrane potentials, synaptic transmission, and neurotransmitters. Mastery of these concepts is essential for understanding human physiology and preparing for exams in anatomy and physiology courses.