Nervous System Functions and Membrane Potentials

Functions of the Nervous System

• The nervous system has three fundamental functions:
  1. Sensory Input: Collecting data from sensory receptors regarding internal and external stimuli.
  2. Integration: Processing and interpreting sensory input and deciding on actions.
  3. Motor Output: Sending signals that result in responses or actions.

Types of Neurons

• Three neuron types responsible for the above functions:
  1. Sensory Neurons (Afferent): Transmit sensory information to the central nervous system (CNS).
  2. Interneurons: Connect sensory and motor neurons; responsible for integration and processing.
  3. Motor Neurons (Efferent): Carry signals from the CNS to effectors (muscles and glands).

Central Nervous System

• Central Nervous System (CNS): Composed of the brain and spinal cord, it serves as the main control center.

Motor Division of the Nervous System

• The motor (efferent) division has two subdivisions:
  1. Somatic Nervous System: Controls voluntary movements of skeletal muscles.
  2. Autonomic Nervous System: Regulates involuntary functions (e.g., heart rate, digestion).

Autonomic Nervous System

• Responsible for sending signals to:
  • Cardiac muscle
  • Smooth muscle
  • Glands

Sympathetic Responses

• Four common sympathetic responses include:
  1. Increased Heart Rate: Enhances blood flow.
  2. Dilated Pupils: Improves vision under low light.
  3. Bronchodilation: Expands air passages to increase airflow.
  4. Decreased Digestive Activity: Prioritizes blood supply for emergencies.

Parasympathetic Responses

• Parasympathetic: Refers to responses that oppose sympathetic effects, promoting rest and digestion.

Membrane Potentials

• There are three types of membrane potentials:
  1. Resting Membrane Potential: The electrical potential across the membrane at rest.
  2. Graded Potential: Small changes in membrane potential that can lead to action potentials.
  3. Action Potential: A rapid change in membrane potential that results in nerve impulse transmission.

Membrane Channel Associations

• Different types of channels correlate with specific membrane potentials:
  • Chemically Gated Channels: Associated with graded potentials; open upon chemical binding.
  • Leakage Channels: Linked to resting membrane potential; are always open and allow ions to move passively.
  • Voltage Gated Channels: Associated with action potentials; open in response to changes in membrane potential.

Ion Channel Functionality

• The causes for channel openings:
  • Leakage Channels: Constantly open, allowing ongoing ion flow.
  • Chemically Gated Channels: Open when a specific chemical (e.g., neurotransmitter) binds.
  • Voltage Gated Channels: Open in response to changes in membrane voltage.

Ion Characteristics and Resting Membrane Potential

• Resting Membrane Potential Formation:
  • At rest, K⁺ is more concentrated inside the cell (ICF).
  • Na⁺ and Cl⁻ are more concentrated outside the cell (ECF).
  • The membrane is highly permeable to K⁺, which diffuses out, making the inside negative.
  • There is low permeability to Na⁺, leading to minimal Na⁺ inflow.
  • Negatively charged proteins (A⁻) remain inside, contributing to a negative charge.
  • Sodium/Potassium ATPase pumps 3 Na⁺ out and 2 K⁺ in, maintaining a negative internal environment.