Study Guide: Skeletal and Nervous System (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 (a part of the body, typically the spine, curves or bulges outward toward the back)

• Secondary Curvatures: Develop after birth; include the cervical and lumbar curvatures. These are convex anteriorly (a structure curves or bulges outward toward the front of the body) and help with upright posture.

Example: The cervical curvature develops as infants begin to lift their heads, while the lumbar curvature forms as they start to walk.

Irregular Curvatures of the Vertebral Column

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

• Kyphosis: Exaggerated thoracic curvature, leading to 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 control of body functions.

• Main Functions: Sensory input, integration, and motor output.

• Divisions:

  • Central Nervous System (CNS): Brain and spinal cord; processes and integrates information.

  • Peripheral Nervous System (PNS): Cranial and spinal nerves; connects CNS to the rest of the body.

• PNS Subdivisions:

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

  • Motor (Efferent) Division: Transmits impulses from CNS to effectors (muscles/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 (fight or flight) and parasympathetic (rest and digest) divisions.

Key Terms: Afferent = toward CNS; Efferent = away from CNS.

Levels of Organization in the Nervous System

• Hierarchical structure: Receptors → Sensory neurons → CNS (integration) → Motor neurons → Effectors

Neuroglia (Glial Cells): Names and Main Functions

Cell Type	Location	Main Function
Astrocytes	CNS	Support neurons, maintain blood-brain barrier
Microglia	CNS	Phagocytosis of debris and pathogens
Ependymal cells	CNS	Line ventricles, produce cerebrospinal fluid (CSF)
Oligodendrocytes	CNS	Form myelin sheaths in CNS
Satellite cells	PNS	Support neuron cell bodies in ganglia
Schwann cells	PNS	Form myelin sheaths in PNS

Structure and Function of Neurons

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

• Dendrites: Receive incoming signals.

• 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 CNS, oligodendrocytes form myelin; in the PNS, Schwann cells form myelin.

Structural and Functional Classification of Neurons

• Structural: Multipolar, bipolar, unipolar neurons.

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

Membrane Potentials

Membrane potential is the voltage difference across a cell membrane due to separated electrical charges.

• Resting Membrane Potential: Typically about -70 mV in neurons.

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

• Key Equation:

$V_m = \frac{RT}{F} \ln \left( \frac{[K^+]_{out}}{[K^+]_{in}} \right)$

• Depolarization: Membrane potential becomes less negative (e.g., -70 mV to -55 mV).

• Repolarization: Return to resting potential after depolarization.

• Hyperpolarization: Membrane potential becomes more negative than resting.

Graded Potentials vs. Action Potentials

• Graded Potentials: Local changes in membrane potential; vary in size; decay with distance.

• Action Potentials: All-or-none electrical impulses; propagate along axons without decrement.

Action Potential: Phases and Ion Channel Activity

• 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. (the outward flow or discharge of a fluid)

• Hyperpolarization: K+ channels remain open briefly; membrane potential dips below resting.

Key Equation:

$I = g(V_m - E_{ion})$

where I is ionic current, g is conductance, Vm is membrane potential, and Eion is equilibrium potential.

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 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: Stronger stimulus required for new action potential.

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 potential generation.

• Postsynaptic Potentials: Excitatory (EPSP) or inhibitory (IPSP).

• 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 (vision processing).

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

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

Ventricles: Names and Functions

• Lateral Ventricles (1st & 2nd): Located in cerebral hemispheres; contain CSF.

• Third Ventricle: In diencephalon; connects to lateral ventricles via interventricular foramina.

• Fourth Ventricle: Between brainstem and cerebellum; connects to third ventricle via cerebral aqueduct.

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

Cerebral Cortex: Structure and Function

• Location: Outer layer of cerebrum; gray matter.

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

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

• Motor Areas: Control voluntary movement (e.g., primary motor cortex).

• Association Areas: Integrate information, involved in higher functions (e.g., prefrontal cortex).

Flow Pathway of Sensory and Motor Information

• Sensory Pathway: Receptors → Sensory neurons → Thalamus → Primary sensory cortex → Association areas.

• Motor Pathway: Association areas → Primary motor cortex → Motor neurons → Effectors (muscles).

Example (Visual Pathway): Retina → Optic nerve → Thalamus (lateral geniculate nucleus) → Primary visual cortex (occipital lobe) → Visual association areas.

Cerebral White Matter: Fiber Types and Functions

Fiber Type	Function	Distribution
Association fibers	Connect different parts of the same hemisphere	Within a single hemisphere
Commissural fibers	Connect corresponding areas of two hemispheres	Corpus callosum
Projection fibers	Connect cortex with lower brain or spinal cord	Internal capsule, corona radiata

Basal Nuclei: Names, Locations, and Functions

• Names: Caudate nucleus, putamen, globus pallidus.

• Location: Deep within cerebral hemispheres.

• Function: Regulate voluntary motor activities, inhibit unnecessary movements.

Diencephalon: Components and Functions

• Components: Thalamus, hypothalamus, epithalamus.

• Thalamus: Relay station for sensory information; directs signals to appropriate cortical areas.

• Hypothalamus: Maintains homeostasis; regulates autonomic nervous system, endocrine system, body temperature, hunger, thirst, sleep-wake cycles, and emotional responses.

Additional info: The hypothalamus is also involved in hormone production and regulation of the pituitary gland.