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

Chapter 7: The Skeleton

Primary and Secondary Curvatures of the Vertebral Column

The vertebral column exhibits distinct curvatures that are essential for balance, flexibility, and shock absorption.

• Primary Curvatures: Present at birth; include the thoracic and sacral curvatures. These are convex posteriorly.

• Secondary Curvatures: Develop after birth; include the cervical (develops as infants lift their heads) and lumbar (develops as children begin to walk) curvatures. These are convex anteriorly.

Example: The lumbar curvature allows for upright posture and efficient weight distribution during walking.

Irregular Curvatures of the Vertebral Column

• Scoliosis: Abnormal lateral curvature, often in the thoracic region.

• Kyphosis: Exaggerated thoracic curvature, resulting in a hunchback appearance.

• Lordosis: Exaggerated lumbar curvature, often seen in pregnancy or obesity.

Additional info: These conditions can affect posture, movement, and may require medical intervention.

Chapter 11: Fundamentals of the Nervous System and Nervous Tissue

Functions and Divisions of the Nervous System

The nervous system is responsible for rapid communication, integration, and coordination of body functions.

• Functions: Sensory input, integration, and motor output (see Fig 11.1).

• Divisions:

  • Central Nervous System (CNS): Brain and spinal cord; integration and command center.

  • Peripheral Nervous System (PNS): Cranial and spinal nerves; communication lines between CNS and the rest of the body.

  • PNS Subdivisions:

    • Sensory (Afferent) Division: Transmits impulses from sensory receptors to the CNS.

    • Motor (Efferent) Division: Transmits impulses from CNS to effector organs (muscles and glands).

    • Somatic Nervous System: Voluntary control of skeletal muscles.

    • Autonomic Nervous System (ANS): Involuntary control of smooth muscle, cardiac muscle, and glands. Subdivided into sympathetic and parasympathetic divisions.

Key Terms: Sensory vs. motor, somatic vs. visceral, voluntary vs. involuntary, afferent vs. efferent.

Levels of Organization in the Nervous System

• Hierarchical structure from neurons to complex neural networks (see Fig 11.3).

Neuroglia (Glial Cells): Names and Main Functions

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

• Microglia: Immune defense in CNS.

• Ependymal Cells: Line ventricles, produce and circulate cerebrospinal fluid (CSF).

• Oligodendrocytes: Form myelin sheaths in CNS.

• Schwann Cells: Form myelin sheaths in PNS.

• Satellite Cells: Support neuron cell bodies in PNS.

Structure and Function of Neurons

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

• Dendrites: Receive signals from other neurons.

• Axon: Conducts impulses away from the cell body.

• Myelin Sheath: Insulates axons, increases conduction speed.

• Nodes of Ranvier: Gaps in myelin sheath; facilitate saltatory conduction.

Myelination: In the PNS, Schwann cells form myelin; in the CNS, oligodendrocytes form myelin.

Classification of Neurons

• Structural: Multipolar, bipolar, unipolar.

• Functional: Sensory (afferent), motor (efferent), interneurons.

Membrane Potentials

Membrane potentials are differences in electrical charge across the neuron's plasma membrane, serving as a form of stored energy.

• Voltage: Measure of potential energy generated by separated charges.

• Gated Ion Channels: Include chemically gated, voltage-gated, and mechanically gated channels (see Fig 11.7).

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

• Forces Responsible: Differences in ionic composition (Na+, K+, Cl-), selective membrane permeability, and the sodium-potassium pump.

• Measuring Membrane Potential: Using microelectrodes to compare inside and outside voltages.

Changes in Membrane Potential

• Depolarization: Membrane potential becomes less negative (e.g., from $-70\ \mathrm{mV}$ to $-55\ \mathrm{mV}$).

• 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 electrical signals; do not decrease with distance.

Action Potential Phases

• Resting State: All voltage-gated Na+ and K+ channels closed.

• Depolarization: Voltage-gated Na+ channels open; Na+ influx.

• Repolarization: Na+ channels inactivate, K+ channels open; K+ efflux.

• Hyperpolarization: K+ channels remain open, Na+ channels reset.

Relevant Equations:

• $I = g(V_m - E_{ion})$ (Current through an ion channel)

• $E_{ion} = \frac{RT}{zF} \ln \left( \frac{[ion]_{out}}{[ion]_{in}} \right)$ (Nernst equation for equilibrium potential)

Propagation of Action Potentials

• Continuous Conduction: In unmyelinated axons; slower.

• Saltatory Conduction: In myelinated axons; action potentials jump between nodes of Ranvier; faster.

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

• Conduction Velocity: Depends on axon diameter and myelination.

• Refractory Periods:

  • Absolute Refractory Period: No new action potential possible.

  • Relative Refractory Period: New action potential possible with stronger stimulus.

Homeostatic Imbalances

• Examples include multiple sclerosis (demyelination) and channelopathies (ion channel dysfunction).

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: Temporal and spatial summation integrate multiple inputs.

• Synaptic Potentiation: Enhanced response with repeated use.

• Presynaptic Inhibition: Decreased 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 postsynaptic membrane potential.

Chapter 12: The Central Nervous System

Lobes of the Brain and Their Functional Areas

• Frontal Lobe: Motor cortex, prefrontal cortex (planning, decision-making), Broca's area (speech production).

• Parietal Lobe: Somatosensory cortex (touch, pressure, pain), spatial processing.

• Occipital Lobe: Visual cortex (processing visual information).

• Temporal Lobe: Auditory cortex (hearing), Wernicke's area (language comprehension), memory.

• Insula: Gustatory cortex (taste), visceral sensory functions.

Ventricles of the Brain

• Lateral Ventricles: Paired, located in each cerebral hemisphere.

• Third Ventricle: Midline, within diencephalon.

• Fourth Ventricle: Between brainstem and cerebellum.

• Function: Contain and circulate cerebrospinal fluid (CSF).

Cerebral Cortex

• Definition: Outer layer of gray matter covering the cerebral hemispheres.

• Location: Surface of the cerebrum.

• Function: Conscious thought, perception, voluntary movement, language, reasoning.

Sensory, Motor, and Association Areas

• Sensory Areas: Receive and interpret sensory input (e.g., primary visual cortex, primary auditory cortex, primary somatosensory cortex).

• Motor Areas: Control voluntary movement (e.g., primary motor cortex, premotor cortex, Broca's area).

• Association Areas: Integrate information (e.g., prefrontal cortex, somatosensory association cortex, visual 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 neurons.

Example (Visual Pathway): Retina → thalamus (lateral geniculate nucleus) → primary visual cortex (occipital lobe) → visual association area.

Cerebral White Matter

• Function: Communication between different brain regions.

• Types of Fibers:

  • Association Fibers: Connect areas within the same hemisphere.

  • Commissural Fibers: Connect corresponding areas of the two hemispheres (e.g., corpus callosum).

  • Projection Fibers: Connect cerebral cortex with lower brain or spinal cord (see Fig 12.9).

Basal Nuclei

• Names: Caudate nucleus, putamen, globus pallidus.

• Location: Deep within cerebral hemispheres.

• Function: Regulate movement, influence cognition and emotion.

Diencephalon

• Components: Thalamus, hypothalamus, epithalamus.

• Thalamus: Located superior to brainstem; major relay station for sensory information to the cerebral cortex.

Hypothalamus: Functions

• Regulates autonomic nervous system (heart rate, blood pressure, digestion).

• Controls endocrine system via pituitary gland.

• Regulates body temperature, hunger, thirst, sleep-wake cycles.

• Involved in emotional responses and behavior.

Neuroglia Cell	Location	Main Function
Astrocyte	CNS	Support, blood-brain barrier, ion regulation
Microglia	CNS	Immune defense
Ependymal cell	CNS	Line ventricles, produce CSF
Oligodendrocyte	CNS	Form myelin sheath
Schwann cell	PNS	Form myelin sheath
Satellite cell	PNS	Support neuron cell bodies

Additional info: For more detailed pathways and mechanisms, refer to the relevant textbook figures and diagrams as indicated in the study guide.