Muscle and Nervous System Essentials: Study Guide for BSC 2085 (Chapters 9-12)

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Muscle Tissue and Physiology

Types of Muscle Tissue

Muscle tissue is specialized for contraction and is classified into three main types, each with distinct locations and functions:

Skeletal Muscle: Attached to bones; responsible for voluntary movements, posture, and heat production.
Cardiac Muscle: Found only in the heart; responsible for pumping blood, involuntary control, striated, and contains intercalated discs.
Smooth Muscle: Located in walls of hollow organs (e.g., intestines, blood vessels); controls involuntary movements such as peristalsis and vasoconstriction.

Functions of Muscles

Movement: Muscles contract to produce movement of the body and substances within the body.
Posture Maintenance: Continuous muscle contractions maintain posture and body position.
Joint Stabilization: Muscles reinforce and stabilize joints.
Heat Generation: Muscle activity produces heat, contributing to body temperature regulation.

Microscopic Muscle Anatomy

Connective Tissue Sheaths: Organize muscle fibers into bundles:
- Epimysium: Surrounds the entire muscle.
- Perimysium: Surrounds fascicles (bundles of muscle fibers).
- Endomysium: Surrounds individual muscle fibers.
Fascicles: Bundles of muscle fibers within a muscle.

Neuromuscular Junction (NMJ)

The NMJ is the synapse between a motor neuron and a skeletal muscle fiber, crucial for muscle contraction.

Action Potential (AP): An electrical signal travels down the motor neuron to the axon terminal.
Neurotransmitter Release: Calcium influx triggers release of acetylcholine (ACh) into the synaptic cleft.
Stimulation of Sarcolemma: ACh binds to receptors on the sarcolemma, opening sodium channels and initiating a muscle AP.
Ions Involved: Na+ influx (depolarization), K+ efflux (repolarization), Ca2+ (for neurotransmitter release and contraction).

Sarcomere Anatomy and Physiology

Sarcomere: The functional contractile unit of muscle, defined by Z-discs.
Components:
- Thick Filaments: Composed of myosin.
- Thin Filaments: Composed of actin, troponin, and tropomyosin.
- Z-disc: Boundary of each sarcomere.
- A Band: Length of thick filaments; remains constant during contraction.
- I Band: Contains only thin filaments; shortens during contraction.
Contraction Changes: Sarcomere shortens, I band and H zone decrease, A band remains unchanged.

Excitation-Contraction Coupling

T-tubules: Invaginations of the sarcolemma that transmit APs into the muscle fiber.
Sarcoplasmic Reticulum (SR): Stores and releases Ca2+ in response to APs.
Sliding Filament Model: Myosin heads bind to actin, pulling thin filaments toward the center of the sarcomere.

Aerobic vs. Anaerobic Exercise

Aerobic Exercise: Uses oxygen, produces more ATP, supports endurance activities.
Anaerobic Exercise: Does not require oxygen, produces less ATP, supports short bursts of activity.

Factors Influencing Force of Contraction

Muscle Size: Larger muscles generate more force.
Fiber Recruitment: More fibers activated increases force.
Stimulation Frequency: Higher frequency increases force (summation, tetanus).

Skeletal Muscle Organization and Mechanics

Naming of Skeletal Muscles

Location: E.g., temporalis (temporal bone).
Fascicle Arrangement: E.g., circular (orbicularis oris), parallel, pennate.
Function: E.g., flexor, extensor, adductor.

Number of Muscles in the Human Body

There are approximately over 600 skeletal muscles in the human body.

Arrangement of Fascicles

Circular: Concentric rings (e.g., orbicularis oris).
Parallel: Fibers run parallel to long axis (e.g., sartorius).
Pennate: Short fibers attach obliquely to a central tendon (e.g., rectus femoris).

Levers in the Musculoskeletal System

Levers amplify force or speed of movement. There are three classes:

Class	Order of Components	Example in Body
First Class	Fulcrum between load and effort	Neck extension (atlanto-occipital joint)
Second Class	Load between fulcrum and effort	Standing on tiptoe (calf raise)
Third Class	Effort between fulcrum and load	Biceps curl (elbow joint)

Major Muscle Groups

Quadriceps: Rectus femoris, vastus lateralis, vastus medialis, vastus intermedius.
Hamstrings: Biceps femoris, semitendinosus, semimembranosus.

Muscle Roles

Prime Mover (Agonist): Main muscle responsible for movement.
Antagonist: Opposes the prime mover.
Synergist: Assists the prime mover.
Fixator: Stabilizes the origin of the prime mover.

Fundamentals of the Nervous System

Functions of the Nervous System

Sensory Input: Detects changes inside and outside the body.
Integration: Processes and interprets sensory input.
Motor Output: Activates effector organs (muscles/glands) to cause a response.

Divisions of the Nervous System

Central Nervous System (CNS): Brain and spinal cord; integration and command center.
Peripheral Nervous System (PNS): Cranial and spinal nerves; communication lines.
Afferent (Sensory) Division: Transmits impulses to CNS.
Efferent (Motor) Division: Transmits impulses from CNS to effectors.
Somatic Nervous System: Voluntary control of skeletal muscles.
Autonomic Nervous System (ANS): Involuntary control of smooth/cardiac muscle and glands.
- Sympathetic: "Fight or flight" responses.
- Parasympathetic: "Rest and digest" responses.

Neuroglia (Glial Cells)

Astrocytes: Support neurons, maintain blood-brain barrier.
Microglia: Immune defense in CNS.
Ependymal Cells: Line ventricles, produce cerebrospinal fluid.
Oligodendrocytes: Form myelin sheaths in CNS.
Satellite Cells: Support neurons in PNS.
Schwann Cells: Form myelin sheaths in PNS.

Neuron Structure

Special Characteristics: Longevity, amitotic, high metabolic rate.
Cell Body (Soma): Contains nucleus and organelles.
Processes:
- Dendrites: Receive signals.
- Axons: Transmit signals away from cell body.
Bundles of Processes:
- Tracts: CNS bundles.
- Nerves: PNS bundles.

Action Potentials and Synaptic Transmission

Resting Membrane Potential: Typically -70 mV; maintained by Na+/K+ pumps.
Depolarization: Na+ channels open, Na+ enters cell, membrane potential becomes less negative.
Repolarization: K+ channels open, K+ exits cell, membrane potential returns to negative.
Hyperpolarization: Membrane potential becomes more negative than resting.
Threshold: Typically around -55 mV; if reached, AP is generated.
Synapse: Junction between neurons; neurotransmitters cross synaptic cleft to propagate signal.

Key Equation:

Where is the membrane potential, is the potential inside the cell, and is the potential outside the cell.

The Central Nervous System: Brain Structure and Protection

Major Regions of the Brain

Cerebrum: Largest part; responsible for higher brain functions (thought, memory, voluntary movement).
Diencephalon: Includes thalamus (sensory relay), hypothalamus (homeostasis, endocrine), epithalamus (pineal gland).
Brain Stem: Midbrain, pons, medulla oblongata; controls basic life functions (breathing, heart rate).
Cerebellum: Coordinates movement and balance.

Lobes of the Brain and Their Functions

Frontal Lobe: Motor control, speech (Broca's area), decision making.
Parietal Lobe: Sensory processing.
Temporal Lobe: Hearing, memory, language (Wernicke's area).
Occipital Lobe: Vision.
Insula: Taste, visceral sensation.

Surface Markings of the Brain

Gyri: Elevated ridges.
Sulci: Shallow grooves.
Fissures: Deep grooves (e.g., longitudinal fissure separates hemispheres).
Major Sulci/Fissures: Central sulcus, longitudinal fissure, lateral sulcus.

Hemispheric Dominance

Left Hemisphere: Language, logic, analytical tasks.
Right Hemisphere: Spatial abilities, creativity, intuition.

Broca's and Wernicke's Areas

Broca's Area: Motor speech area (frontal lobe).
Wernicke's Area: Language comprehension (temporal/parietal lobe).

Functions of Brain Regions

Cerebrum: Conscious thought, voluntary movement.
Thalamus: Sensory relay station.
Hypothalamus: Homeostasis, endocrine regulation.
Brain Stem: Autonomic functions (breathing, heart rate).
Cerebellum: Coordination, balance.
Epithalamus: Pineal gland, circadian rhythms.

Protection of the Brain

Bone: Skull protects brain tissue.
Membranes (Meninges): Three layers—dura mater (outer), arachnoid mater (middle), pia mater (inner).
Watery Cushion: Cerebrospinal fluid (CSF) absorbs shock.
Blood-Brain Barrier: Regulates passage of substances from blood to brain.

Order of Meninges (outermost to innermost): Dura mater → Arachnoid mater → Pia mater

Example: Damage to Broca's area results in expressive aphasia (difficulty producing speech), while damage to Wernicke's area causes receptive aphasia (difficulty understanding language).

Additional info: For diagrams and figures, refer to textbook illustrations or class handouts as specified in the course materials.