Anatomy Ch. 11-12

Overall Functions of the Nervous System

Two Key Functions:
  1. Communication – The nervous system transmits signals between different body parts.

  2. Control & Coordination – It regulates body activities by responding to internal and external stimuli.

Three Overlapping Tasks (with Examples):
  1. Sensory Input – Detects changes in the environment (e.g., touching a hot stove).

  2. Integration – Processes and interprets sensory input (e.g., recognizing the heat as dangerous).

  3. Motor Output – Responds by activating muscles or glands (e.g., pulling the hand away).


Divisions of the Nervous System

Functions & Key Structures:
  1. Central Nervous System (CNS)

    • Function: Processes information and coordinates responses.

    • Structures: Brain and spinal cord.

  2. Peripheral Nervous System (PNS)

    • Function: Connects the CNS to limbs and organs.

    • Structures: Cranial nerves, spinal nerves, and ganglia.

    • Subdivisions:

      • Sensory (Afferent) Division – Transmits signals to the CNS.

      • Motor (Efferent) Division – Sends responses from CNS to muscles/glands.

        • Somatic Nervous System (Voluntary) – Controls skeletal muscles.

        • Autonomic Nervous System (Involuntary) – Regulates internal organs.

          • Sympathetic (Fight or Flight) – Increases heart rate, dilates pupils.

          • Parasympathetic (Rest and Digest) – Slows heart rate, stimulates digestion.


Cells of the Nervous System

Neuroglia (Glial Cells) – Six Types:
  1. CNS Glial Cells:

    • Astrocytes – Provide structural support, regulate the blood-brain barrier.

    • Microglia – Act as immune cells, removing debris and pathogens.

    • Ependymal Cells – Line brain ventricles, produce cerebrospinal fluid (CSF).

    • Oligodendrocytes – Form myelin sheaths in the CNS.

  2. PNS Glial Cells:

    • Schwann Cells – Produce myelin sheath in the PNS.

    • Satellite Cells – Support neuron cell bodies in ganglia.

Neurons
  • Diagram Labels & Functions of Each Part:

    • Dendrites – Receive signals from other neurons.

    • Cell Body (Soma) – Contains the nucleus and organelles.

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

    • Axon Terminals – Release neurotransmitters to signal other neurons or muscles.

Myelin Sheath
  • Overall Function: Insulates axons and speeds up electrical impulses.

  • Difference in CNS vs. PNS:

    • CNS: Myelin is produced by oligodendrocytes.

    • PNS: Myelin is produced by Schwann cells.


Action Potential

Key Steps & Ion Flow:
  1. Resting Potential (-70mV):

    • Na⁺/K⁺ pump maintains resting state (Na⁺ out, K⁺ in).

  2. Depolarization:

    • Voltage-gated Na⁺ channels open → Na⁺ rushes into the neuron.

    • Membrane potential becomes positive (+30mV).

  3. Repolarization:

    • Na⁺ channels close, K⁺ channels open → K⁺ rushes out of the neuron.

    • Membrane potential returns to negative.

  4. Hyperpolarization:

    • Too much K⁺ exits, making the membrane briefly more negative than resting potential.

  5. Return to Resting Potential:

    • Na⁺/K⁺ pump restores ion balance.

End of the Axon:
  • Neurotransmitter Release:

    • Action potential reaches the axon terminal → triggers Ca²⁺ influx.

    • Vesicles release neurotransmitters into the synaptic cleft.

    • Neurotransmitters bind to receptors on the next neuron or muscle.

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