NS + ES

The Nervous System and the Endocrine System

Overview of Physiological Systems

• Humans have two major physiological systems regulating behavior in response to environmental changes:
  • Nervous System
  • Endocrine System

Divisions of the Nervous System

• Central Nervous System (CNS)
  • Comprises the brain and spinal cord.
  • Origin of all complex commands and decisions.
• Peripheral Nervous System (PNS)
  • Transmits information to the CNS from the outside world.
  • Transmits messages from the CNS to muscles and glands in the body.

Further Subdivisions of the PNS

• Somatic Nervous System (SNS)
  • Transmits information from receptor cells in the sense organs to the CNS.
  • Receives information from the CNS directing muscles to act.
• Autonomic Nervous System (ANS)
  • Transmits information to and from internal bodily organs; operates autonomically (involuntarily).
  • Divided into:
  • Sympathetic Nervous System
  • Parasympathetic Nervous System

Function and Speed of the Nervous System

• Speed of Responses
  • The nervous system acts faster than the endocrine system.
  • Average response time for the nervous system: $0.25$ seconds, as quick as $100$ milliseconds.
  • Endocrine responses take $2$ to $3$ seconds but last longer.

The Nervous System Defined

• Specialized network of cells regulating internal communication via electrical and chemical signals.
• Two main functions:
  1. Collect, process, and respond to environmental information.
  2. Coordinate the functioning of organs and cells throughout the body.

Central Nervous System (CNS)

• Structure
  • Composed of the brain and spinal cord.
  • The brain is the center of all conscious awareness.
  • The cerebral cortex, covering the brain, is only $3$ mm thick and unique to mammals.
• Brain Development
  • Highly developed in humans, distinguishing higher mental functions from other animals; only few animals like sponges and jellyfish lack a brain.
• Hemispheres
  • Brain divided into two hemispheres.
• Spinal Cord
  • Extension of the brain connecting nerves to the PNS and facilitates reflex actions, e.g., pulling away from a hot surface.

Peripheral Nervous System (PNS)

• Functionality
  • Transmits messages to and from CNS via millions of neurons.
• Subdivisions
  • Autonomic Nervous System (ANS): Controls vital bodily functions including:
  • Breathing
  • Heart rate
  • Digestion
  • Sexual arousal
  • Stress responses
  • Somatic Nervous System (SNS): Governs muscle movement and sensory receptor information.

The Endocrine System

• The endocrine system operates alongside the nervous system to regulate vital bodily functions.
• Functions slower than the nervous system but leads to widespread and powerful effects due to hormones released into the bloodstream.

Glands and Hormones

• Glands produce hormones and secrete them into the bloodstream affecting target organs.
• Example:
  • Thyroid Gland: Produces thyroxine, affecting heart rate and increasing metabolic rates influencing growth rates.

Key Endocrine Gland: Pituitary Gland

• Known as the master gland, it controls the hormone release from other glands in the body.

Fight or Flight Response

• The endocrine system and ANS often work in parallel, especially during stress.
• When a stressor is perceived, the hypothalamus activates the pituitary gland, triggering the sympathetic ANS which induces arousal.
• Adrenaline (the stress hormone) is released from the adrenal medulla into the bloodstream, leading to physiological changes such as increased heart rate necessary for the fight-or-flight response.

Physiological Changes Detected Upon Stress

• Body reacts almost instantly post-threat detection, exemplifying an acute response:
  • Increased heart rate
  • Increased breathing rate
  • Dilated pupils
  • Inhibited digestion
  • Inhibited saliva production
  • Contracted rectum

Parasympathetic State

• Post threat, the parasympathetic nervous system returns the body to a resting state, known as the rest-and-digest response.
• This system acts as a brake, reducing activities heightened by the sympathetic system, yielding:
  • Decreased heart rate
  • Decreased breathing rate
  • Constricted pupils
  • Stimulated digestion
  • Stimulated saliva production
  • Relaxed rectum

Ethical, Philosophical, and Practical Implications

• Stress from major life events (e.g. marriage, divorce, death) can lead to increased illness.
• Research indicating a positive correlation between stressful life events and subsequent illness days off work:
  • Participants indicated major life events experienced over the last three years and reported illness days.
  • Correlation signifies both co-variables move in the same direction.

Application Concepts

• Understanding the roles of CNS and ANS in behavior can be illustrated through real-life experiences, such as feeling physiological changes during fear or stress.