Anatomy and physiology

Structural Classification of Neurons

• Types of Neurons: Based on size, shape, and structure.

  • Multipolar Neurons:

    • Multiple dendrites and one axon from cell body.

    • Found in CNS, primarily interneurons and motor neurons.

  • Bipolar Neurons:

    • Two processes: one dendrite and one axon.

    • Located in special senses (e.g., eyes, nose, ears).

  • Unipolar Neurons:

    • One axon that splits into two branches.

    • Dendrites are near peripheral parts; cell bodies located in ganglia outside CNS.

    • Primarily sensory neurons.

Functional Classification of Neurons

• Sensory (Afferent) Neurons:

  • Carry impulses from receptors to CNS.

  • Typically unipolar, though some are bipolar.

• Interneurons:

  • Multipolar neurons located within CNS.

  • Connect other neurons; cell bodies may form nuclei in CNS.

• Motor (Efferent) Neurons:

  • Multipolar neurons that carry signals from CNS to muscles or glands (effectors).

Neuroglia

• Definition: Support cells for neurons (glial cells).

• Functions:

  • Fill spaces, support and insulate neurons, protect neurons.

  • Do not generate or conduct nerve impulses.

• Types of Neuroglia:

  • Central Nervous System (CNS):

    • Microglia: Phagocytes for debris and bacteria; form scar tissue.

    • Oligodendrocytes: Form myelin sheaths around CNS axons.

    • Ependymal Cells: Produce cerebrospinal fluid.

    • Astrocytes:

      • Structural support, nutrient/ion regulation, form blood-brain barrier.

  • Peripheral Nervous System (PNS):

    • Schwann Cells: Produce myelin around PNS axons.

    • Satellite Cells: Protect neuron cell bodies in PNS.

Membrane Potential and Ions

• Membrane Potential:

  • Charge inside a cell; Resting Membrane Potential is about -70 mV in neurons.

  • Greater concentration of sodium outside and potassium inside cells.

Stimulation and Action Potential

• Neurons remain at rest until stimulated; excitatory stimuli can cause changes in resting potential.

• Key Concepts:

  • Threshold Stimulus: Strong enough to change potential from -70 to -55 mV.

  • Depolarization: Reaching +30 mV due to Na+ influx, causing action potential to occur.

  • Repolarization: Return to -70 mV via K+ outflow, may lead to hyperpolarization.

Impulse Conduction

• Continuous Conduction: In unmyelinated axons, occurs consistently down the fiber.

• Saltatory Conduction: In myelinated axons; impulses jump between Nodes of Ranvier.

  • Speeds of conduction vary based on axon diameter.

Synapse and Neurotransmitters

• Synapse: Junction between two communicating neurons, consisting of a synaptic cleft.

• Neurotransmitters: Chemicals released by presynaptic neurons, bind to postsynaptic neuron receptors, causing excitatory or inhibitory effects.

• Types of Actions:

  • Excitatory: Increase the likelihood of action potentials.

  • Inhibitory: Decrease the likelihood of action potentials.

Major Neurotransmitters and Their Actions

• Common Neurotransmitters:

  • Acetylcholine: Controls skeletal muscle actions.

  • Norepinephrine and Dopamine: Influence mood and emotional response.

  • Serotonin: Affects mood and sleep, often linked to depression.

Central Nervous System Structure and Functions

• Brain:

  • Comprises cerebrum, diencephalon, cerebellum, and brainstem.

  • Functions in regulation of sensory, motor, higher mental processes.

Spinal Cord Structure**

• Segments: 31 pairs of spinal nerves, organized into anterior, lateral, and posterior funiculi (columns).

• White Matter and Gray Matter: White matter consists of myelinated fibers, while the gray matter comprises neuron cell bodies and interneurons.

Blood Components

• Red Blood Cells (RBC):

  • Transport oxygen; produced by erythropoiesis in red bone marrow.

• White Blood Cells (WBC):

  • Defend the body against disease; produced from hemocytoblasts in red bone marrow.

• Platelets:

  • Vital for blood clotting; developed from megakaryocytes.