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.