AP Biology Nervous System Notes

Nervous System Overview

Aim and Importance of the Nervous System

• Purpose: To understand how impulse travels through nerve cells.

• Question: Why do animals need a nervous system?

  • Allows rapid communication and response to stimuli.

Structure of Neurons

• Neuron Components:

  • Dendrites: Receive signals from sensory receptors or other neurons.

  • Cell Body (Soma): Contains the nucleus and metabolic machinery of the neuron.

  • Axon: Long fiber that transmits signals away from the cell body.

  • Axon Terminals: Release neurotransmitters to communicate with other neurons.

  • Myelin Sheath: Insulates axon, enhancing speed of transmission through saltatory conduction.

  • Nodes of Ranvier: Gaps in myelin sheath where action potentials are generated.

Signal Transmission in Neurons

• Direction of Signal: Dendrite → Cell Body → Axon.

• Speed Comparison:

  • Myelinated neurons (150 m/sec) vs. unmyelinated (5 m/sec).

• Multiple Sclerosis: Condition where the immune system attacks the myelin sheath, leading to slower signals.

Synapse Structure and Function

• Synapse/Synaptic Cleft: Gap between neurons where communication occurs.

  • Pre-synaptic Neuron: Releases neurotransmitters.

  • Post-synaptic Neuron: Contains receptors to receive neurotransmitters.

Types of Neurons

• Sensory Neurons: Carry signals from sensory organs to the CNS.

• Motor Neurons: Carry messages from the CNS to muscles and glands.

• Interneurons: Connect sensory and motor neurons; primarily found in the brain and spinal cord.

Neurotransmitters

• Types and Functions:

  • Acetylcholine: Involved in movement, memory, and learning.

  • Adrenaline/Norepinephrine: Involved in fight-or-flight response; increases heart rate.

  • Dopamine: Associated with reward mechanisms.

  • Serotonin: Regulates sleep.

  • GABA: Inhibitory neurotransmitter affected by alcohol; influences movement and sleep.

Impulse Activation and Response

• Stimulus: Activating factor for neurons (light, sound, etc.).

• Effector: Body part that responds to the stimulus.

Neuron Polarization and Action Potential

• Resting Potential: -70mV, with a negative charge inside (Cl⁻, amino acids) and positive outside (Na⁺).

• Depolarization: Occurs when the stimulus reaches -50mV, opening Na⁺ channels which allow Na⁺ ions to flow into the cell, changing the neuron’s charge to more positive.

• Action Potential Wave: A rapid sequence of depolarization and repolarization travels down the neuron like a wave.

  • Repolarization: After depolarization, K⁺ channels open and K⁺ ions flow out, restoring the negative internal charge.

  • Resetting: Na⁺ and K⁺ ions are returned to their original sides by sodium-potassium pumps, preparing the neuron for the next impulse.

Synaptic Transmission

• Process:

  1. Action potential reaches axon terminal.

  2. Voltage-gated Ca²⁺ channels open, Ca²⁺ enters.

  3. Synaptic vesicles fuse with membrane, releasing neurotransmitters into synapse.

  5. Neurotransmitters bind to receptors on post-synaptic neuron initiating a new signal.

Nervous System Overview

• Central Nervous System (CNS): Composed of the brain and spinal cord.

• Peripheral Nervous System (PNS): Connects CNS to the rest of the body.

• Autonomic Nervous System: Handles involuntary actions (e.g., heart rate, digestion); divided into sympathetic (fight-or-flight) and parasympathetic (rest and digest).

• Somatic Nervous System: Manages voluntary movements.

Reflex Arcs vs. Complex Responses

• Reflex Arc: Fast, automatic response that only involves the spinal cord (e.g., blinking).

• Higher Processing Responses: Involve the brain and are slower but allow for more complex decision making.

Fun Facts about Neurons

• Longest neuron in marine mammals (blue whale: 10-30 meters).

• Human neurons can reach up to 1-2 meters.