Study Guide: Skeletal and Nervous System (Chapters 7, 11, 12)

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Chapter 7: The Skeleton

Irregular Curvatures of the Vertebral Column

The vertebral column, or spine, is a flexible structure composed of 26 bones. It has normal curvatures that help absorb shock and maintain balance. However, irregular curvatures can occur, leading to clinical conditions.

Scoliosis: Lateral (side-to-side) curvature, often in the thoracic region.
Kyphosis: Exaggerated thoracic curvature, resulting in a hunchback appearance.
Lordosis: Exaggerated lumbar curvature, often seen in pregnant women or individuals with obesity.

Clinical Relevance: These abnormal curvatures can cause pain, reduced mobility, and in severe cases, impact organ function.

Differences Between Male and Female Pelves

The pelvis differs between males and females to accommodate childbirth in females. The following table summarizes the main differences:

Feature	Male Pelvis	Female Pelvis
General Structure	Heavier, thicker, more prominent markings	Lighter, thinner, smoother
Pelvic Inlet	Narrow, heart-shaped	Wide, oval
Pubic Arch Angle	Less than 90°	Greater than 90°
Sacrum	Narrow, longer, more curved	Wider, shorter, less curved
Acetabula	Larger, closer together	Smaller, farther apart

Example: The wider pelvic inlet and broader pubic arch in females facilitate childbirth.

Chapter 11: Fundamentals of the Nervous System and Nervous Tissue

Functions of the Nervous System

The nervous system is responsible for controlling and communicating information throughout the body. Its main functions include:

Sensory Input: Gathering information from sensory receptors about internal and external changes.
Integration: Processing and interpreting sensory input to determine an appropriate response.
Motor Output: Activating effector organs (muscles and glands) to produce a response.

Divisions of the Nervous System

Central Nervous System (CNS): Consists of the brain and spinal cord; responsible for integration and command.
Peripheral Nervous System (PNS): Consists of cranial and spinal nerves; connects the CNS to the rest of the body.
- Sensory (Afferent) Division: Transmits sensory information to the CNS.
- Motor (Efferent) Division: Transmits commands from the CNS to effector organs.
  - Somatic Nervous System: Controls voluntary movements of skeletal muscles.
  - Autonomic Nervous System (ANS): Controls involuntary functions (e.g., heart rate, digestion).
    - Sympathetic Division: Prepares the body for "fight or flight" responses.
    - Parasympathetic Division: Promotes "rest and digest" activities.

Key Distinctions

Sensory vs. Motor: Sensory (afferent) brings information to the CNS; motor (efferent) carries commands away from the CNS.
Somatic vs. Visceral: Somatic relates to the body wall and limbs; visceral relates to internal organs.
Voluntary vs. Involuntary: Voluntary actions are under conscious control; involuntary actions are automatic.
Afferent vs. Efferent: Afferent = toward CNS; efferent = away from CNS.

Levels of Organization in the Nervous System

Receptor Level: Sensory receptors detect stimuli.
Circuit Level: Processing in ascending pathways.
Perceptual Level: Processing in cortical sensory centers.

Neuroglia (Glial Cells): Names and Main Functions

Astrocytes (CNS): Support neurons, maintain blood-brain barrier, regulate ion balance.
Microglia (CNS): Act as phagocytes, removing debris and pathogens.
Ependymal Cells (CNS): Line ventricles, produce and circulate cerebrospinal fluid (CSF).
Oligodendrocytes (CNS): Form myelin sheaths around CNS axons.
Satellite Cells (PNS): Surround neuron cell bodies in ganglia, regulate environment.
Schwann Cells (PNS): Form myelin sheaths around PNS axons.

Structure and Function of Neurons

Cell Body (Soma): Contains nucleus and organelles; metabolic center.
Dendrites: Receive incoming signals.
Axon: Conducts electrical impulses away from the cell body.

Function of Myelin: Insulates axons, increases speed of impulse conduction.

Cells Forming Myelin: Oligodendrocytes (CNS), Schwann cells (PNS).
Nodes of Ranvier: Gaps in myelin sheath; facilitate saltatory conduction.

Myelination in the PNS vs. CNS

PNS: Schwann cells wrap around axons, forming a single segment of myelin.
CNS: Oligodendrocytes extend processes to multiple axons, myelinating segments of each.

Classification of Neurons

Structural: Multipolar, bipolar, unipolar.
Functional: Sensory (afferent), motor (efferent), interneurons (association).

Membrane Potentials

Neurons use electrical signals to communicate. The separation of electrical charges across the membrane creates a potential energy called the membrane potential.

Voltage: The measure of potential energy generated by separated charges.
Gated Ion Channels: Proteins that open or close in response to stimuli (chemical, voltage, mechanical).
Resting Membrane Potential: The voltage across the membrane at rest, typically about .
Forces Responsible: Differences in ionic composition (Na+, K+), selective permeability, and the sodium-potassium pump.

Measuring Membrane Potential: Use of microelectrodes to record voltage difference across the membrane.

Changes in Membrane Potential

Depolarization: Membrane potential becomes less negative (e.g., from to ).
Repolarization: Return to resting membrane potential after depolarization.
Hyperpolarization: Membrane potential becomes more negative than resting.

Graded Potentials vs. Action Potentials

Graded Potentials: Short-distance, variable-strength signals; decrease with distance.
Action Potentials: Long-distance, all-or-none signals; do not decrease with distance.

Action Potential Phases

Resting State: All voltage-gated Na+ and K+ channels closed.
Depolarization: Na+ channels open, Na+ enters cell.
Repolarization: Na+ channels inactivate, K+ channels open, K+ exits cell.
Hyperpolarization: K+ channels remain open, membrane potential becomes more negative.

Voltage-Gated Na+ Channels: Have closed, open, and inactivated states.

Ca2+ Voltage-Gated Channels: Important in neurotransmitter release at synapses.

Propagation of Action Potentials

Continuous Conduction: In unmyelinated axons; slower.
Saltatory Conduction: In myelinated axons; action potential jumps between nodes of Ranvier; faster.

Coding for Stimulus Intensity: Stronger stimuli generate higher frequency of action potentials.

Conduction Velocity: Depends on axon diameter and myelination.

Refractory Periods

Absolute Refractory Period: No new action potential can be generated.
Relative Refractory Period: A stronger-than-usual stimulus can initiate another action potential.

Homeostatic Imbalances

Multiple Sclerosis (MS): Demyelination in CNS, leading to impaired nerve conduction.
Other Disorders: May involve ion channel dysfunction or neurotransmitter imbalances.

Synapses: Structure, Function, and Mechanism

Structure: Presynaptic terminal, synaptic cleft, postsynaptic membrane.
Function: Transmit signals between neurons or from neurons to effectors.
Mechanism: Neurotransmitter release, binding to receptors, postsynaptic response.

Postsynaptic Potentials

Excitatory Postsynaptic Potentials (EPSPs): Depolarize membrane, increase likelihood of action potential.
Inhibitory Postsynaptic Potentials (IPSPs): Hyperpolarize membrane, decrease likelihood of action potential.

Summation: EPSPs and IPSPs can summate temporally or spatially to influence action potential generation.

Synaptic Potentiation: Repeated use increases synaptic strength.

Presynaptic Inhibition: Reduces neurotransmitter release from presynaptic neuron.

Neurotransmitter: Acetylcholine

Function: Excitatory at neuromuscular junctions; can be inhibitory in other locations.
Mechanism: Binds to receptors, opens ion channels, alters membrane potential.

Chapter 12: The Central Nervous System

Lobes of the Brain and Their Functional Areas

Frontal Lobe: Motor cortex (voluntary movement), prefrontal cortex (decision making, personality), Broca's area (speech production).
Parietal Lobe: Somatosensory cortex (touch, pressure, pain), spatial awareness.
Occipital Lobe: Visual cortex (processing visual information).
Temporal Lobe: Auditory cortex (hearing), olfactory cortex (smell), Wernicke's area (language comprehension).
Insula: Gustatory cortex (taste), visceral sensory area.

Ventricles: Names and Functions

Lateral Ventricles (2): Located in each cerebral hemisphere; contain CSF.
Third Ventricle: Located in diencephalon; connects to lateral ventricles via interventricular foramen.
Fourth Ventricle: Located between brainstem and cerebellum; connects to third ventricle via cerebral aqueduct.

Function: Circulate cerebrospinal fluid (CSF), cushion brain, remove waste.

Cerebral Cortex

Definition: Outer layer of gray matter covering the cerebral hemispheres.
Location: Surface of the cerebrum.
Function: Site of conscious thought, perception, voluntary movement, and complex mental processes.

Sensory, Motor, and Association Areas

Primary Motor Cortex: Controls voluntary movements.
Premotor Cortex: Plans movements.
Primary Somatosensory Cortex: Receives sensory input from skin, muscles.
Somatosensory Association Cortex: Integrates sensory input.
Visual Cortex: Processes visual information.
Auditory Cortex: Processes sound.
Olfactory Cortex: Processes smell.
Gustatory Cortex: Processes taste.
Vestibular Cortex: Processes balance.
Association Areas: Integrate information from multiple modalities (e.g., prefrontal cortex, posterior association area).

Flow Pathway of Sensory and Motor Information

Sensory Pathway: Sensory receptor → primary sensory cortex → sensory association area → multimodal association area.
Motor Pathway: Multimodal association area → premotor cortex → primary motor cortex → motor neuron.

Example (Visual Information): Retina → thalamus → primary visual cortex (occipital lobe) → visual association area → multimodal association area.

Cerebral White Matter

Function: Communication between different brain regions.
Association Fibers: Connect areas within the same hemisphere.
Commissural Fibers: Connect corresponding areas of the two hemispheres (e.g., corpus callosum).
Projection Fibers: Connect the cerebrum with lower brain regions and spinal cord.

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