Functional Organization of the Nervous System

The nervous system has three main functions:

Sensory Input: Detecting the environment, both external (light, temperature) and internal (hunger, balance, sleepiness).
Integration: The brain interprets nerve impulses and determines the appropriate bodily response. This involves both conscious and unconscious processes.
- Examples:
  - Unconscious: Increased breathing rate during exercise due to low oxygen levels.
  - Conscious: Eating when hungry.
  - Unconscious: Feeling sleepy and digesting food after a full meal.
Output (Response): Actions taken by the body, such as eating, breathing faster, or running.

The nervous system can be divided into two main parts:

Central Nervous System (CNS):
- Function: Integration.
- Components:
  - Brain: Thinking and interpreting signals.
  - Spinal Cord: Primarily responsible for reflexes.
Peripheral Nervous System (PNS):
- Function: Sensory input and motor output.
- Components:
  - Sensory Neurons: Transmit information to the CNS.
  - Motor Neurons: Carry signals from the CNS to the body.

Motor neurons are divided into:

Somatic Nervous System: Voluntary movement.
- Examples:
  - Reaching for something.
  - Running faster.
  - Holding in urine.
Autonomic Nervous System: Involuntary control.
- Examples:
  - Balance adjustments when pushed.
  - Enteric Nervous System: Controls the digestive system.
    - Function: Unconscious control of digestion.
    - Example: Peristalsis (pushing food down the esophagus and through the intestines).

The autonomic nervous system is further divided into:

Sympathetic Nervous System: "Fight or flight" response.
- Functions: Prepares the body to run or fight.
- Characteristics:
  - Increased alertness.
  - Increased heart rate.
Parasympathetic Nervous System: "Rest and digest" response.
- Functions: Promotes relaxation and digestion.
- Characteristics:
  - Slower heart rate.
  - Increased blood flow to the digestive system.
  - Sleepiness.
  - Less acute vision.

Brain: Protected by the skull.
Spinal Cord: Protected by vertebrae.
Both are cushioned by cerebral spinal fluid.
Brain: Interprets signals and activates responses.
Spinal Cord: Responsible for reflexes.
- Example: Pulling away from a hot stove.

Cerebellum: Balance and coordination of muscles and ligaments.
Brainstem: Controls involuntary responses like breathing and heart rate (related to chemoreceptors in the cardiovascular and respiratory systems).
- The chemoreceptors are connected to the cardiovascular and respiratory systems.

Sympathetic (Fight or Flight):
- Pupil dilation (increased visual acuity).
- Reduced salivation.
- Bronchi relaxation (increased airflow).
- Increased heart rate.
- Inhibited peristalsis (slowed digestion).
- Glucose release (energy for muscles).
- Adrenaline/Noradrenaline (Epinephrine) secretion.
- Inhibited bladder contraction.
- Potentially stimulates orgasm during sex.
Parasympathetic (Rest and Digest):
- Opposite effects of sympathetic nervous system.
- Stimulated digestion.
- Fat digestion.
- Sugar is converted back to glycogen by the liver.
- Slower heartbeat.
- Constricted bronchi.
- Increased saliva flow.
- Constricted pupils.

Sensory nerves (neurons) detect stimuli (thermal, touch, pain, light) on the skin or organs.
Signals are sent to the spinal cord and then to the brain.
The brain interprets the signals and sends instructions back down to motor neurons.

Function: Immediate response to dangerous stimuli.
Process:
1. A sensory nerve detects a dangerous stimulus (e.g., touching a hot stove).
2. The signal travels to the spinal cord.
3. The spinal cord sends a signal to motor neurons.
4. Motor neurons cause muscles to react and remove the body part from danger.
Integration: The spinal cord integrates the signal.
The spinal cord sends a pain signal to the brain simultaneously.

Dangerous Reflex: Pulling hand away from a hot stove.
Non-Dangerous Reflex: Knee-jerk reaction
- Tapping the kneecap causes the knee to flick upwards.