Neuroscience Lecture Review

Overview of Neurons

• Neurons serve as the control center of the nervous system, processing incoming information and transmitting impulses.

Structure of Neurons

• Dendrites:

  • Multiple branch-like structures that bring impulses to the cell body.
  • Important for receiving signals from other neurons or sensory cells.

• Axon:

  • A long, singular extension that transmits impulses away from the cell body.
  • The end of the axon is called the axon terminal, which communicates with the next cell (another neuron, muscle, or gland).

• Myelin Sheath:

  • A protective layer insulating the axon, speeding up impulse transmission.
  • Not all axons are myelinated; the gaps in the myelin are called the Nodes of Ranvier.

Types of Neurons

• Neurons can be classified structurally and functionally.
• Functional classification includes:
  • Sensory Neurons: Carry signals from sensory receptors to the CNS.
  • Motor Neurons: Transmit impulses from the CNS to effectors (muscles or glands).
  • Interneurons: Located within the CNS and connect sensory and motor neurons.

Structural Classification

1. Multipolar Neurons:
   • Have three or more processes and are the most common type (e.g., motor neurons).
2. Bipolar Neurons:
   • Have two processes, one dendrite, one axon; found in special senses.
3. Unipolar Neurons:
   • Have a single process that branches into two; involved in general sensory functions.

Membrane Potential

• Definition:
  • Membrane potential is the difference in charge across a neuron's membrane, typically resting at -70 mV.

Ion Distribution

• Sodium (Na+) is higher outside; potassium (K+) is higher inside the cell.
• Chloride (Cl-) also predominates outside the cell, while calcium (Ca2+) is higher outside than inside.

Importance of Charge

• The negative resting membrane potential is due to:
  • Unequal distribution of ions (more potassium leak channels than sodium).
  • The sodium-potassium pump, which moves three Na+ out for every two K+ into the cell.
  • The presence of large anionic proteins inside the cell, contributing to the negative interior.

Action Potential

• The action potential is a rapid change in membrane potential allowing for the conduction of signals.
• Initiation involves depolarization when sodium channels open, allowing Na+ to enter the cell, making the inside less negative.

Ion Channels

• Leak Channels: Always open; allow steady flow of ions down their concentration gradients.
• Gated Channels: Open or close in response to stimuli, categorized into:
  1. Ligand-gated channels: Open when a specific chemical binds (e.g., neurotransmitters).
  2. Voltage-gated channels: Open in response to changes in membrane voltage.
  3. Mechanically gated channels: Open due to physical deformation (e.g., touch).

Summary of Neuron Function

1. Dendrites bring information into the neuron.
2. The axon transmits signals away from the neuron.
3. Myelin sheath speeds up signal transmission.
4. Neurons function to detect, process, and transmit information across the nervous system.

Review of Special Senses

• Special senses include vision, hearing, taste, smell, and balance; located primarily in the head.
• General senses (like touch) are distributed throughout the body.