BSC 2085 Exam 3 Review: Muscular and Nervous Systems (Chapters 9-12)

Muscle Tissue and Physiology

Types of Muscle Tissue

There are three main types of muscle tissue in the human body, 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.

• Smooth Muscle: Located in walls of hollow organs (e.g., intestines, blood vessels); controls movement of substances, involuntary control.

Functions of Muscles

• Movement: Muscles contract to produce movement of the body and its parts.

• Posture Maintenance: Continuous muscle contractions maintain posture.

• Joint Stabilization: Muscles help stabilize and strengthen joints.

• Heat Generation: Muscle activity produces heat, important for maintaining body temperature.

Microscopic Muscle Anatomy

• Connective Tissue Layers:

  • Epimysium: Surrounds the entire muscle.

  • Perimysium: Surrounds bundles of muscle fibers called fascicles.

  • Endomysium: Surrounds individual muscle fibers.

• Fascicles: Bundles of muscle fibers within a muscle.

Neuromuscular Junction (NMJ) Anatomy and Physiology

The NMJ is the synapse between a motor neuron and a skeletal muscle fiber. The process of muscle activation involves:

• An action potential (AP) travels down the motor neuron to the axon terminal.

• Calcium ions (Ca2+) enter the axon terminal, triggering the release of acetylcholine (ACh) into the synaptic cleft.

• ACh binds to receptors on the sarcolemma (muscle cell membrane), causing sodium (Na+) influx and depolarization.

• This initiates an AP in the muscle fiber, leading to contraction.

Sarcomere Anatomy and Physiology

• Sarcomere: The functional unit of muscle contraction, defined by Z-discs.

• Thick Filaments: Composed of myosin proteins.

• Thin Filaments: Composed of actin, troponin, and tropomyosin.

• Z-disc: Boundary of each sarcomere.

• A band: Dark area; length of thick filaments.

• I band: Light area; contains only thin filaments.

• During contraction: Sarcomere shortens, I band and H zone decrease, A band remains the same.

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, causing contraction.

Aerobic vs. Anaerobic Exercise

• Aerobic: Uses oxygen, produces more ATP, slower but sustainable (e.g., running, cycling).

• Anaerobic: Does not use oxygen, produces less ATP, faster but less sustainable (e.g., sprinting, weightlifting).

Factors Influencing Force of Contraction

• Muscle Size: Larger muscles generate more force.

• Fiber Recruitment: More fibers activated = greater force.

• Stimulation Frequency: Higher frequency increases force (summation, tetanus).

Skeletal Muscle Organization and Mechanics

Naming of Skeletal Muscles

• Based on location, shape, size, direction of fibers, number of origins, location of attachments, and action.

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).

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

Levers in the Musculoskeletal System

Levers are classified based on the relative positions of the load, fulcrum, and effort:

Class	Arrangement	Example in Body
First	Fulcrum between load and effort	Neck (nodding head)
Second	Load between fulcrum and effort	Standing on tiptoe
Third	Effort between fulcrum and load	Biceps curl

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: Gathering information from sensory receptors.

• Integration: Processing and interpreting sensory input.

• Motor Output: Activating effector organs (muscles/glands) to cause a response.

Divisions of the Nervous System

• Central Nervous System (CNS): Brain and spinal cord.

• Peripheral Nervous System (PNS): Cranial and spinal nerves.

• Afferent (Sensory) Division: Carries information to the CNS.

• Efferent (Motor) Division: Carries commands from CNS to effectors.

• Somatic Nervous System: Voluntary control of skeletal muscles.

• Autonomic Nervous System (ANS): Involuntary control; includes:

  • Sympathetic Division: "Fight or flight" responses.

  • Parasympathetic Division: "Rest and digest" responses.

Neuroglia (Glial) Cells

• Astrocytes: Support neurons, maintain blood-brain barrier.

• Microglia: Phagocytic cells, remove debris.

• 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

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

• Dendrites: Receive signals from other neurons.

• Axon: Transmits signals away from the cell body.

• Tracts: Bundles of axons in CNS.

• Nerves: Bundles of axons in PNS.

Action Potentials and Membrane Potentials

• Resting Membrane Potential: Typically about $-70\ \mathrm{mV}$.

• Threshold: Usually about $-55\ \mathrm{mV}$.

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

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

• Hyperpolarization: Membrane potential becomes more negative than resting.

• Synapse: Junction between neurons; neurotransmitters cross synaptic cleft.

The Central Nervous System: Brain Structure and Protection

Major Regions of the Brain

• Cerebrum: Largest part; responsible for higher brain functions.

• Diencephalon: Includes thalamus (sensory relay), hypothalamus (homeostasis), epithalamus (pineal gland).

• Brain Stem: Midbrain, pons, medulla oblongata; controls vital functions.

• Cerebellum: Coordinates movement and balance.

Lobes of the Brain

• Frontal Lobe: Motor control, speech (Broca's area), reasoning.

• 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).

• Major Sulci/Fissures: Central sulcus, longitudinal fissure, lateral sulcus.

Functional Areas and Hemispheric Dominance

• Motor Areas: Control voluntary movement (precentral gyrus).

• Sensory Areas: Receive sensory input (postcentral gyrus).

• Broca's Area: Speech production (usually left hemisphere).

• Wernicke's Area: Language comprehension.

• Left Hemisphere: Language, logic, math.

• Right Hemisphere: Spatial, artistic, musical abilities.

Functions of Major Brain Structures

• Cerebrum: Conscious thought, memory, voluntary movement.

• Thalamus: Sensory relay station.

• Hypothalamus: Regulates homeostasis, endocrine system, autonomic functions.

• Epithalamus: Contains pineal gland (melatonin secretion).

• Brain Stem: Controls heart rate, breathing, reflexes.

• Cerebellum: Coordinates movement, balance, posture.

Protection of the Brain

• Bone: Skull encases the brain.

• Membranes (Meninges): Three layers—dura mater (outer), arachnoid mater (middle), pia mater (inner).

• Watery Cushion: Cerebrospinal fluid (CSF) surrounds and cushions the brain.

• Blood-Brain Barrier: Selective barrier that protects brain from harmful substances.

Additional info: For diagrams and figures, refer to class handouts and textbook illustrations as specified in the review guide.