Nervous System and Nervous Tissue: Study Guide for Anatomy & Physiology I (Chapters 11 & 12)

Chapter 11: Fundamentals of the Nervous System and Nervous Tissue

Overview of the Nervous System

The nervous system is the master controlling and communicating system of the body. It is responsible for integrating sensory input, coordinating motor output, and maintaining homeostasis.

• Terminology: Key terms include neuron, neuroglia, synapse, action potential, and neurotransmitter.

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): Includes all neural tissue outside the CNS; connects the CNS to limbs and organs.

• Functional Divisions:

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

  • Motor (Efferent) Division: Transmits commands from the CNS to effectors (muscles/glands).

  • Somatic Nervous System: Controls voluntary movements.

  • Autonomic Nervous System: Controls involuntary functions (sympathetic and parasympathetic divisions).

Neuroglia (Glial Cells)

• Central Nervous System (CNS) Glial Cells:

  • Astrocytes: Support neurons, maintain blood-brain barrier, regulate ion/nutrient concentrations.

  • Microglia: Act as phagocytes, removing debris and pathogens.

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

  • Oligodendrocytes: Form myelin sheaths around CNS axons.

• Peripheral Nervous System (PNS) Glial Cells:

  • Schwann Cells: Form myelin sheaths around PNS axons.

  • Satellite Cells: Surround neuron cell bodies in ganglia, regulate environment.

Structure and Function of a Neuron

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

• Dendrites: Receive incoming signals from other neurons.

• Axon: Conducts electrical impulses away from the cell body.

• Myelination vs. Non-Myelination:

  • Myelinated Axons: Covered by myelin sheath, which increases speed of impulse conduction (saltatory conduction).

  • Non-Myelinated Axons: Lack myelin, resulting in slower impulse conduction.

Example: Motor neurons controlling skeletal muscles are typically myelinated for rapid response.

Functional Classification of Neurons

• Sensory (Afferent) Neurons: Transmit impulses from sensory receptors to the CNS.

• Motor (Efferent) Neurons: Carry impulses from the CNS to effectors.

• Interneurons (Association Neurons): Connect sensory and motor neurons within the CNS.

Membrane Potential

• Resting Membrane Potential: The voltage difference across the neuron's membrane at rest, typically about $-70\ \mathrm{mV}$.

• Graded Potentials:

  • Occur in dendrites and cell bodies.

  • Short-distance, localized changes in membrane potential.

  • Can be depolarizing or hyperpolarizing; magnitude varies with stimulus strength.

• Action Potentials:

  • Occur in axons; all-or-none electrical impulses.

  • Phases:

    1. Depolarization: Voltage-gated Na+ channels open, Na+ influx.

    2. Repolarization: Na+ channels inactivate, voltage-gated K+ channels open, K+ efflux.

    3. Hyperpolarization: K+ channels remain open briefly, membrane potential becomes more negative than resting.

    4. Restoration: Na+/K+ ATPase restores ionic balance.

Equation for Resting Membrane Potential (Nernst Equation):

$E = \frac{RT}{zF} \ln \left( \frac{[\text{ion}]_{\text{outside}}}{[\text{ion}]_{\text{inside}}} \right)$

Multiple Sclerosis (MS)

• Definition: An autoimmune disease where the immune system attacks myelin in the CNS, disrupting nerve impulse conduction.

• Symptoms: Muscle weakness, vision problems, impaired coordination.

Synapse

• Definition: A junction between two neurons or a neuron and an effector cell.

• Structure: Presynaptic terminal, synaptic cleft, postsynaptic membrane.

• Chemical Synapse Steps:

  1. Action potential arrives at axon terminal.

  2. Voltage-gated Ca2+ channels open; Ca2+ enters terminal.

  3. Ca2+ triggers synaptic vesicles to fuse with membrane.

  4. Neurotransmitter released into synaptic cleft.

  5. Neurotransmitter binds to receptors on postsynaptic membrane.

  6. Postsynaptic potential generated; neurotransmitter removed from cleft.

• Synaptic Delay: The brief time required for neurotransmitter release, diffusion, and receptor binding (about 0.3–0.5 ms).

Neurotransmitters

• Definition: Chemical messengers that transmit signals across synapses.

• Examples: Acetylcholine, dopamine, serotonin, norepinephrine, GABA.

• Functions: Can be excitatory (promote action potentials) or inhibitory (suppress action potentials).

Chapter 12: The Central Nervous System

Overview of the Central Nervous System (CNS)

The CNS consists of the brain and spinal cord, serving as the main control center for processing and integrating information.

• Terminology: Key terms include cerebrum, cortex, nuclei, tracts, ventricles.

Regions of the Brain

• Four Major Regions:

  1. Cerebrum

  2. Diencephalon

  3. Brainstem

  4. Cerebellum

Cerebrum

• Structures: Includes cerebral hemispheres, cortex, white matter, basal nuclei.

• Function: Responsible for higher brain functions such as thought, memory, voluntary movement, and sensory perception.

• Lobes of the Cerebrum:

  • Frontal Lobe: Voluntary movement, planning, reasoning, problem-solving.

  • Parietal Lobe: Sensory perception, spatial awareness.

  • Temporal Lobe: Auditory processing, memory, language.

  • Occipital Lobe: Visual processing.

  • Insula: Taste, visceral sensation, emotion.

  Overlap and Unique Functions: Some functions (e.g., language) involve multiple lobes, while others (e.g., vision) are primarily localized.

• Gray vs. White Matter:

  • Gray Matter: Contains neuron cell bodies, dendrites, and unmyelinated axons; forms the cortex and nuclei.

  • White Matter: Composed of myelinated axons; forms tracts connecting different brain regions.

• Parkinson’s Disease: Degeneration of dopamine-producing neurons in the basal nuclei, leading to motor deficits.

• Huntington’s Disease: Genetic disorder causing degeneration of basal nuclei and cerebral cortex, resulting in uncontrolled movements and cognitive decline.

Cerebral Cortex

• Four Generalizations:

  1. Three types of functional areas: motor, sensory, association.

  2. Each hemisphere controls the opposite side of the body (contralateral control).

  3. Hemispheres are functionally specialized (lateralization).

  4. Conscious behavior involves the entire cortex.

Functional Areas of the Cerebral Cortex

• Motor Areas:

  • Primary Motor Cortex: Controls voluntary movements; located in precentral gyrus.

  • Motor Mapping (Homunculus): Body parts are represented proportionally to the degree of motor control.

  • Premotor Cortex: Plans and coordinates complex movements.

  • Broca’s Area: Controls speech production; usually in the left hemisphere.

• Sensory Areas:

  • Primary Sensory Cortex (Somatosensory Cortex): Receives sensory input from skin, muscles, joints; located in postcentral gyrus.

  • Somatosensory Association Cortex: Integrates sensory input for understanding objects.

  • Primary Visual Cortex: Receives visual information from the retina.

  • Visual Association Area: Interprets visual stimuli (e.g., recognizing faces).

  • Primary Auditory Cortex: Receives auditory information from the inner ear.

  • Auditory Association Area: Interprets sounds (e.g., speech, music).

Region	Main Function	Associated Disorders
Frontal Lobe	Voluntary movement, planning, speech	Broca's aphasia, motor deficits
Parietal Lobe	Sensory perception, spatial awareness	Neglect syndrome
Temporal Lobe	Auditory processing, memory	Wernicke's aphasia
Occipital Lobe	Visual processing	Cortical blindness
Insula	Taste, visceral sensation	Gustatory deficits

Additional info: The above table summarizes the main functions and associated disorders of each cerebral lobe, which is useful for clinical correlations and understanding the impact of brain injuries.