5.2

Module Overview

• Focus on the nervous system and its organization

• Review of neuronal behavior from the previous lecture

• Aim to understand how the brain and nervous system interact to control behaviors and responses

Neurons and Signal Processing

• When inhibitory signals outweigh excitatory signals in a neuron:

  • Answer: Neuron does not fire (B).

• Threshold voltage for action potential to occur:

  • Answer: Negative 55 millivolts (C).

  • Explanation: Action potential is an all-or-nothing response that initiates at the axon hillock once the threshold is surpassed.

Nervous System Structure

• Central Nervous System (CNS): Comprises the brain and spinal cord; serves as the command center.

  • Responsible for processing information and making decisions based on environmental stimuli.

• Peripheral Nervous System (PNS): Connects the CNS to the rest of the body; includes all nerves outside of the brain and spinal cord.

  • Somatic Nervous System: Governs voluntary movements and actions made consciously, e.g., walking or climbing.

  • Autonomic Nervous System: Manages involuntary functions, e.g., heart rate and digestion.

    • Subdivided into Sympathetic and Parasympathetic Systems:

      • Sympathetic Nervous System (SNS): Prepares body for stress or emergencies (fight or flight).

      • Parasympathetic Nervous System (PNS): Promotes relaxation and recovery (rest and digest).

Brain Organization

• Divided into three major regions:

  • Hindbrain: Regulates basic life functions (breathing, heart rate, balance).

    • Structures include:

      • Medulla: Controls heartbeat and breathing

      • Pons: Connects different parts of the brain and coordinates movement

      • Cerebellum: Maintains balance and coordination

  • Midbrain: Acts as a communication bridge, processes sensory information and coordinates movements.

    • Involved in auditory and visual responses.

  • Forebrain: Handles advanced processes like cognition, emotions, and memories.

    • Includes the limbic system (emotions and memories) and cerebral cortex (higher-level thinking).

Neural Communication

• Afferent Signals: Carry sensory information to the brain

  • Examples: Touching a hot surface (pain response).

• Efferent Signals: Send instructions from the brain to muscles and glands

  • Examples: Moving hand away from danger or other actions requiring motor control.

Reflexes

• Automatic responses controlled by the spinal cord, bypassing the brain initially, leading to faster reactions in emergency situations.

  • Example: Pulling hand back from a hot stove immediately through a reflex arc without brain processing.

• Key Reflex Types:

  • Patellar Reflex: Knee-jerk reaction in response to a tap.

  • Withdrawal Reflex: Pulling away from a hot surface.

  • Crossed Extensor Reflex: Posture adjustment to maintain balance when one limb withdraws due to pain.

Sympathetic vs. Parasympathetic Functions

• SNS acts as a gas pedal in emergencies, increasing heart rate and energy levels.

• PNS acts as a brake, restoring the body to a state of calm after stress.

• Importance of balance between the two systems to maintain proper bodily functions and overall health.

Key Takeaways

• Understanding the nervous system reveals how deeply interconnected the brain and body are.

• All sensations, reflexes, emotions, and thoughts originate from neuron firing and neural signals traveling through the body.