Week 6: The Nervous System

What are the 3 Basic Functions of the Nervous System?

1. Sensory - Sensory receptors detect changes in the environment.

2. Integration - Input is processed so that the system (brain) can decide on what to do.

3. Motor Output - Response initiated which then activates the body’s muscles and glands.

Name and describe the Divisions of the Nervous System:

Name and describe what the Nervous System is made of?

1. Neurons

   • Communication

   • Processes information

   • Control functions

2. Neuroglia (Glial Cells)

   • Supporting cells

Name and describe the 6-Types of Neuroglia:

CNS

1. Astrocytes

   • Maintain blood-brain barrier.

   • Regulate nutrient and ion balance.

   • Provide structural support.

   • Repair damaged tissue (scar formation).

2. Ependymal Cells

   • Line brain ventricles and spinal cord central canal.

   • Produce and circulate cerebrospinal fluid (CSF).

3. Oligodendrocytes

   • Form myelin sheath around CNS axons.

   • Provide structural framework.

4. Microglia

   • Immune cells of the CNS.

   • Remove waste and pathogens (phagocytosis).

   • Activated during injury or disease.

PNS

5. Satellite Cells

   • Surround neuron cell bodies in PNS ganglia.

   • Regulate O2 and CO2, nutrient, and neurotransmitter levels around in ganglia.

6. Schwann Cells

   • Form myelin sheath around PNS axons.

   • Aid in axon regeneration.

Name and describe the Structures of a Neuron:

1. Dendrites - Receives electrical signal from other neurons.

2. Soma (Cell Body) - Holds the Nucleus and supports cell function.

3. Nucleus - Holds DNA and controls function and repair.

4. Axon - Long fibre that transmits electrical signal.

5. Myelin Sheath - Insulates axon and speeds process. Made from Oligodendrocytes (CNS) and Schwann Cells (PNS).

6. Axon Terminal - Releases neurotransmitter to synapse.

7. Synapse - The gap between 2 neurons.

8. Post-Synaptic Cell - The neuron (muscle or gland) receives neurotransmitter. Has receptors to detect/respond to chemical message.

What is an Electrical Synapse?

• Cytoplasmic continuity between two neurons (like a bridge). It’s called a Gap Junction (connexons).

• Fast messaging

  • e.g., reflexes

What is a Chemical Synapse?

• Instead of a Gap Junction it releases a chemical, ‘neurotransmitters’ into the Synaptic Cleft.

• Neurotransmitters float across the Synaptic Cleft and enter a post-synaptic cell.

• Slow/controlled

  • e.g., Neuromuscular Junction

Name the structures of the Chemical Synapse:

1. Pre-Synaptic Vesicle

2. Mitochondria

3. Post-Synaptic Neuron

4. Pre-Synaptic Vesicle (Pre-Synaptic Membrane)

5. Synaptic Cleft

Describe the Process of a Chemical Synapse:

1. In the pre-synaptic cell, the electrical signal travels via the axon to the axon terminals.

2. Action potential

3. The voltage charged Ca2+ (calcium) channels open.

4. Ca2+ enters the channels and enter the axon terminal.

5. The Ca2+ enter pre-synaptic vesicles.

6. The vesicles hold neurotransmitters.

7. The vesicles fuse with the pre-synaptic membrane for exocytosis (exit).

8. The neurotransmitters travel through the synaptic cleft.

9. The neurotransmitters enter post-synaptic receptors and bind.

10. Ion channels open (graded potential).