The Nervous System and Its Role in Coordinating Physiological Responses
- The nervous system is a specialized network of cells (neurons) that communicate electrical signals throughout the body.
- It enables the body to sense and respond to internal and external stimuli, maintaining homeostasis through coordinated regulation of physiological processes.
Homeostasis
Homeostasis is the maintenance of a stable internal environment within an organism, ensuring optimal conditions for cellular processes.
Basics of Nervous System
Key Functions of the Nervous System
- Sensory Input: Detects changes in the internal and external environments.
- Integration: Processes and interprets sensory input.
- Motor Output: Initiates responses to changes, such as muscle contraction or gland secretion.
Divisions of the Nervous System
The nervous system is divided into two main parts:
- Central Nervous System (CNS)
- Components: Brain and spinal cord.
- Function: Serves as the control center of the body, processes information, and sends instructions to the body.
- Peripheral Nervous System (PNS)
- Components: Nerves extending from the spinal cord to the rest of the body (limbs, organs, etc.).
- Function: Connects the CNS to the limbs and organs, transmitting sensory information to the CNS and motor commands from the CNS to muscles and glands.
Think of the CNS as the brain of a computer and the PNS as the wires connecting it to the rest of the system (like keyboard, screen, etc.).
Central Nervous System
The CNS consists of the brain and spinal cord and is responsible for processing information, making decisions, and directing responses.
Brain
- The brain is the body's "central computer," integrating sensory input and generating responses.
- It is involved in everything from conscious thought to unconscious functions like breathing.
Key Areas of the Brain
- Cerebrum: The largest part of the brain, responsible for higher brain functions such as thought, memory, and voluntary movement.
- Cerebellum: Coordinates voluntary movements and balance.
- Brainstem: Controls vital functions like heart rate and breathing.
Spinal Cord
- The spinal cord relays messages between the brain and the rest of the body.
- It is essential for both sensory input and motor output.
Efferent Division of the Nervous System
- The efferent division is responsible for carrying motor commands from the CNS to various body parts, resulting in movement or other physiological responses.
- This division is further subdivided into the autonomic nervous system and the somatic nervous system.
The Autonomic Nervous System (ANS)
The ANS regulates involuntary body functions and is divided into two branches: the sympathetic and parasympathetic nervous systems.
Sympathetic nervous system
The part of the autonomic nervous system that triggers the body's "fight or flight" responses.
Parasympathetic nervous system
The part of the autonomic nervous system that triggers the "rest and digest" functions.
| Branch | Function | Example of Action |
|---|---|---|
| Sympathetic | Activates "fight or flight" response. Increases heart rate, dilates pupils, increases respiration. | Heart Rate Increase during stress or physical activity. |
| Parasympathetic | Promotes "rest and digest." Slows heart rate, stimulates digestion. | Heart Rate Decrease after exercise or during relaxation. |
The sympathetic system is activated during stressful situations, such as exercise or emotional stress, while the parasympathetic system is activated when the body is at rest and relaxed.
Tip- Sympathetic Nervous System: Think of S for Stress or Speed. It speeds up the body’s functions, preparing it for action.
- Parasympathetic Nervous System: Think of P for Peace or Pause. It slows down bodily functions and promotes rest and recovery.
Somatic Nervous System
- The somatic nervous system controls voluntary movements, such as muscle contractions during physical activity.
- It is involved in conscious control of skeletal muscles and mediates sensory input from the skin, muscles, and joints to the CNS.
When you decide to pick up a cup, your brain sends a signal through the somatic nervous system to the muscles in your hand and arm to execute the movement.
Functions Coordinated by the Nervous System
The nervous system coordinates several vital functions, including cardiac function, breathing and ventilation, and temperature control.
1. Cardiac Function
The heart rate is controlled by a combination of intrinsic mechanisms (built-in mechanisms) and extrinsic factors (influences from outside the heart, like nervous input).
| Mechanism | Description | Example |
|---|---|---|
| Intrinsic Mechanism | The Sinoatrial (SA) node is the heart's natural pacemaker that sets the baseline heart rate. | At rest, the SA node sets the heart rate at around 60-100 beats per minute. |
| Extrinsic Mechanism | Autonomic nervous system controls the heart rate. Sympathetic increases heart rate, and parasympathetic decreases it. | During exercise, the sympathetic system increases heart rate. |
For cardiac function, always relate the sympathetic nervous system to fight or flight (increases heart rate) and the parasympathetic nervous system to rest and digest (decreases heart rate).
2. Breathing and Ventilation
Ventilation
Ventilation is the process of moving air or water across the gas-exchange surface to refresh the supply of gases and maintain the concentration gradient.
- The regulation of breathing is primarily controlled by the brainstem (medulla oblongata).
- It responds to the levels of carbon dioxide (CO₂) in the blood.
- If CO₂ rises, the brainstem sends signals to the respiratory muscles to increase breathing rate and depth.
| Effect on Breathing | Sympathetic Response | Parasympathetic Response |
|---|---|---|
| Increased CO₂ levels | Increases respiratory rate to expel CO₂. | Reduces respiratory rate. |
| Decreased CO₂ levels | Decreases respiratory rate to retain CO₂. | Increases respiratory rate. |
During exercise, CO₂ levels increase, prompting the medulla to send signals that increase the breathing rate.
3. Temperature Control
- The body maintains a stable internal temperature (homeostasis) through processes like sweating, shivering, and vasodilation (blood vessel expansion).
- This process is regulated by thermoreceptors located in the skin and hypothalamus, which detect temperature changes.
- When the body becomes too hot, the SNS triggers sweating and vasodilation (widening of blood vessels) to release heat.
- When the body becomes too cold, the PNS triggers shivering and vasoconstriction (narrowing of blood vessels) to conserve heat.
Vasodilation
The widening of blood vessels, allowing more blood flow to active tissues, like muscles during exercise.
Vasoconstriction
The narrowing of blood vessels, directing blood to vital organs during stress or physical exertion.
After running on a hot day, the body cools down through sweating (sympathetic response) and increases blood flow to the skin (vasodilation) to release excess heat.
Temperature Regulation
Types of Specialized Receptors
These specialized cells are responsible for detecting specific stimuli in the environment and initiating appropriate responses.
Proprioceptors
Proprioreceptors
Specialized receptors that detect changes in body position and movement.
- Function: Detect changes in body position and movement, helping the brain to adjust posture and balance.
- Location: Found in muscles, tendons, and joints.
Muscle spindles and Golgi tendon organs monitor muscle stretch and tension, respectively.
Baroreceptors
Baroreceptors
Receptors that monitor changes in blood pressure.
- Function: Monitor blood pressure and help regulate heart rate and blood vessel dilation.
- Location: Found in the carotid arteries and aortic arch.
When blood pressure rises, baroreceptors send signals to the brain to decrease heart rate and dilate blood vessels.
Chemoreceptors
Chemoreceptors
Receptors that detect changes in the chemical composition of the blood, including oxygen and carbon dioxide levels.
- Function: Detect changes in the chemical composition of blood, particularly levels of oxygen, carbon dioxide, and pH.
- Location: Found in the carotid arteries, aortic arch, and medulla oblongata.
When CO₂ levels rise, chemoreceptors stimulate an increase in the respiratory rate to expel excess CO₂.
Self review- How does the sympathetic nervous system affect heart rate during physical activity?
- What role do proprioceptors play in maintaining balance during physical activity?
- How do chemoreceptors help regulate breathing rate?
- Explain the difference between sympathetic and parasympathetic control of heart rate.
