Chapter 10: Functions of Skeletal Muscle

Functions

• Movement of the Skeleton
• Posture and Body Position
• Support of Soft Tissues
• Guard Entrances and Exits
• Maintain Body Temperature
• Storing Nutrients

3 Layers of Connective Tissue

1. Epimysium – surrounds entire muscle
2. Perimysium – surrounds fascicles (muscle bundles)
3. Endomysium – surrounds individual muscle fibers

Tendon Formation

• Collagen fibers from epimysium, perimysium, and endomysium converge to form a tendon or aponeurosis.

Characteristics of Skeletal Muscle

• Multinucleated
• Striated appearance
• Voluntary control
• Long cylindrical fibers

Myosatellite Cells

• Stem cells involved in muscle repair and regeneration

Sarcolemma

• Plasma membrane of a muscle fiber

Sarcoplasm

• Cytoplasm of muscle cell containing organelles, glycogen, and myoglobin

Sarcoplasmic Reticulum

• Modified ER that stores calcium ions (Ca²⁺)
• Releases Ca²⁺ to trigger contraction

Myofibrils

• Long protein bundles inside muscle fibers
• Responsible for contraction
• Composed of repeating units called sarcomeres

Myofilaments

• Thin filaments: Actin, tropomyosin, troponin
• Thick filaments: Myosin

Sarcomeres

• Functional unit of a myofibril
• From Z-line to Z-line
• Includes A band, I band, H zone, M line

Sliding Filament Theory

• Myosin heads bind to actin and pull, causing the sarcomere to shorten
• Requires Ca²⁺ and ATP

Acetylcholine (ACh)

• Neurotransmitter released at neuromuscular junction
• Triggers action potential in sarcolemma

Acetylcholinesterase (AChE)

• Enzyme that breaks down ACh in synaptic cleft to end stimulation

Steps That Initiate Contraction

1. ACh released at the neuromuscular junction
2. ACh binds to the ACh receptors on the sarcolemma
3. Gated channels open
4. Sodium ions rush into the cell generating an action potential inside the muscle cell
5. The action potential travels down the sarcolemma to the T tubules then to the triads
6. The action potential reaches the sarcoplasmic reticulum
7. Ca²⁺ binds to troponin → tropomyosin moves
8. The active sites on actin are exposed
9. Energized myosin heads (ATP-ADP+P) Bind to active sites on actin forming cross-bridges
10. Myosin heads pivot towards the M line (power stroke) - the bound ADP+P are released
11. ATP binds to myosin heads, breaking the bond between myosin and actin.
12. Myosin reactivation can occur when a free myosin head splits another ATP to ADP

Contraction Cycle

• Myosin binds → Power stroke → Detach (ATP required) → Reset

Rigor Mortis

• After death, ATP is depleted → myosin heads can’t detach → muscles stay contracted

Skeletal vs. Cardiac vs. Smooth Muscle

• Skeletal Muscle
  • Voluntary control
  • Striated
  • Long, cylindrical fibers
  • Multinucleated
  • Attached to bones
  • Rapid, forceful contractions
• Cardiac Muscle
  • Involuntary control
  • Striated
  • Branched cells with a single nucleus
  • Connected by intercalated discs
  • Found only in the heart
  • Rhythmic, coordinated contractions
• Smooth Muscle
  • Involuntary control
  • Non-striated
  • Spindle-shaped cells with a single nucleus
  • Found in walls of hollow organs
  • Slow, sustained contractions

Key Diagrams

• Neuromuscular junction: where a motor neuron communicates with a skeletal muscle fiber
• Sarcomere structure: overlapping thin (actin) and thick (myosin) filaments arranged in a repeating pattern

Chapter 12: Nervous Tissue Review

Types of Cells in Nervous Tissue

• Neurons – transmit impulses
• Neuroglia (glial cells) – support and protect neurons

Anatomical Divisions

• Central Nervous System (CNS) – brain + spinal cord
• Peripheral Nervous System (PNS) – all neural tissue outside CNS

Functional Divisions

• CNS – integration and processing
• PNS – communication to/from CNS
  • Afferent division – sensory input (to CNS)
  • Efferent division– motor output (from CNS)

Efferent Subdivisions

• Somatic Nervous System (SNS) – controls skeletal muscle (voluntary)
• Autonomic Nervous System (ANS) – regulates smooth/cardiac muscle, glands (involuntary)
  • Enteric Nervous System– digestive tract-specific, semi-autonomous

Key Structures

• Receptors – detect stimuli
• Effectors – muscles/glands responding to stimuli
• Neurons – functional units
• Dendrites – receive input

Neuron Classifications

• Structural
  • Multipolar – most common in CNS
  • Unipolar – sensory neurons
  • Bipolar – special senses (retina, olfactory)
• Functional
  • Sensory (afferent)
  • Motor (efferent)
  • Interneurons – integration

Neuroglia

• CNS: Astrocytes, oligodendrocytes, microglia, ependymal cells
• PNS: Schwann cells, satellite cells

Membrane Potential Terms

• Depolarization – membrane potential becomes more positive (Na⁺ in)
• Repolarization – returns to resting potential (K⁺ out)
• Hyperpolarization– membrane becomes more negative than resting

Signal Propagation

• Continuous– unmyelinated axons (slow)
• Saltatory – myelinated axons (fast, jumps node-to-node)

Fiber Types

• Type A fibers: largest diameter, heavily myelinated, fastest
• Type B fibers: smaller, myelinated, slower than A
• Type C fibers: smallest, unmyelinated, slowest

Chapter 14: Major Brain Structures – Locations & Functions

Brain Structures

• Cerebrum: Largest part, responsible for higher brain functions
• Cerebellum: Coordinates movement, balance, posture
• Gyri (gyrus): Raised ridges, increase surface area
• Sulci (sulcus): Grooves between gyri
• Thalamus: Relay station for sensory and motor signals
• Hypothalamus: Regulates body functions and hormones
• Midbrain: Processes visual/auditory info
• Pons: Connects brain to cerebellum
• Medulla Oblongata: Controls autonomic functions

Brain Protections

• Physical Protections: Skull, meninges, cerebrospinal fluid
• Chemical Protection: Blood-brain barrier

Disorders

• Stroke: Blood flow cut off, cell death
• Ataxia: Lack of control, cerebellum damage
• Seizure: Abnormal electrical activity

Other Key Brain Parts

• Superior/Inferior colliculi: Visual/auditory reflexes
• Cerebral/Cerebellar hemispheres: Divided by fissures

Lobes and Cortices – Functions

• Frontal lobe: Decision-making, movement
• Parietal lobe: Sensory perception
• Temporal lobe: Hearing, language
• Occipital lobe: Vision
• Motor/Somatosensory cortex: Movement/touch processing
• Prefrontal cortex: Reasoning, planning

Special Sensory Areas

• Visual cortex: Processes vision
• Auditory cortex: Processes sound
• Olfactory/Gustatory cortex: Smell and taste

Language Areas

• Wernicke’s area: Language understanding
• Broca’s area: Produces speech

Other Structures

• Arbor vitae: Branching in cerebellum
• Pineal gland: Secretes melatonin
• Optic chiasm: Visual info processing

Cranial Nerves – Key Ones

• I (Olfactory): Smell
• II (Optic): Vision
• III (Oculomotor): Eye movement
• VII (Facial): Facial expressions
• VIII (Vestibulocochlear): Hearing, balance
• X (Vagus): Heart rate, digestion control