The Nervous System and Its Role in Coordinating Physiological Responses

1. The nervous system is a specialised network of cells (neurons) that communicate electrical signals throughout the body.
2. It enables the body to sense and respond to internal and external stimuli, maintaining homeostasis through coordinated regulation of physiological processes.

Basic structure of the nervous system

Key Functions of the Nervous System

1. Sensory Input: Detects changes in the internal and external environments.
2. Integration: Processes and interprets sensory input.
3. Motor Output: Initiates responses to changes, such as muscle contraction or gland secretion.

Main divisions of the nervous system

The nervous system is divided into two main parts:

1. Central Nervous System (CNS)
   1. Components: Brain and spinal cord.
   2. Function: Serves as the control centre of the body, processes information, and sends instructions to the body.
2. Peripheral Nervous System (PNS)
   1. Components: Nerves extending from the spinal cord to the rest of the body (limbs, organs, etc.).
   2. 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.

Central Nervous System

The CNS consists of the brain and spinal cord and is responsible for processing information, making decisions, and directing responses.

Brain

1. The brain integrates sensory input and generates responses.
2. It is involved in everything from conscious thought to unconscious functions like breathing.

Major brain areas and their functions

1. Cerebrum: The largest part of the brain, responsible for higher brain functions such as thought, memory, and voluntary movement.
2. Cerebellum: Coordinates voluntary movements and balance.
3. Brainstem: Controls vital functions like heart rate and breathing.

Spinal Cord

1. The spinal cord relays messages between the brain and the rest of the body.
2. It is essential for both sensory input and motor output.

Efferent Division of the Nervous System

1. The efferent division is responsible for carrying motor commands from the CNS to various body parts, resulting in movement or other physiological responses.
2. 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.

Somatic Nervous System

1. The somatic nervous system controls voluntary movements, such as muscle contractions during physical activity.
2. It is involved in conscious control of skeletal muscles and mediates sensory input from the skin, muscles, and joints to the CNS.

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).

2. Breathing and Ventilation

1. The regulation of breathing is primarily controlled by the brainstem (medulla oblongata).
2. It responds to the levels of carbon dioxide (CO₂) in the blood.
3. If CO₂ rises, the brainstem sends signals to the respiratory muscles to increase breathing rate and depth.

3. Temperature Control

1. The body maintains a stable internal temperature (homeostasis) through processes like sweating, shivering, and vasodilation (blood vessel expansion).
2. Core temperature: ~37°C (±1).
   1. When the body becomes too hot, the sympathetic nervous system triggers sweating and vasodilation (widening of blood vessels) to release heat.
   2. When the body becomes too cold, the sympathetic nervous system triggers vasoconstriction (narrowing of blood vessels), and somatic motor pathways trigger shivering to conserve and generate heat.

Specialised receptors and the stimuli they detect

Specialised receptors detect specific internal changes and trigger responses through the nervous system.

Proprioceptors

1. Function: Detect changes in body position and movement, helping the brain to adjust posture and balance.
2. Location: muscles, tendons, joints, and inner ear (balance).

Baroreceptors

1. Function: Monitor blood pressure and help regulate heart rate and blood vessel dilation.
2. Location: Found in the carotid arteries and aortic arch.

Chemoreceptors

1. Function: Detect changes in the chemical composition of blood, particularly levels of oxygen, carbon dioxide, and pH.
2. Location: Found in the carotid arteries, aortic arch, and medulla oblongata.