Subdivisions of the Nervous System

Overview of the Nervous System

The nervous system is responsible for receiving, processing, and responding to sensory stimuli. It is divided into two main parts:

• Central Nervous System (CNS): Consists of the brain and spinal cord.
• Peripheral Nervous System (PNS): Consists of all the nerves outside the CNS.

KEY TAKEAWAY: The nervous system’s primary function is to enable rapid communication and coordination throughout the body.

Central Nervous System (CNS)

Brain

• The brain is the control center of the nervous system.
• It receives and processes sensory information.
• Coordinates responses, including voluntary movements, emotions, and conscious thought.
• Different areas of the brain have specialized functions (covered in later key knowledge points).

Spinal Cord

• Connects the brain to the peripheral nervous system.
• Transmits sensory information from the PNS to the brain.
• Transmits motor commands from the brain to the PNS.
• Mediates spinal reflexes.

VCAA FOCUS: Questions often involve identifying the roles of specific parts of the brain and spinal cord in different scenarios.

Peripheral Nervous System (PNS)

The PNS connects the CNS to the body’s organs, muscles, and glands. It is divided into two main subdivisions:

• Somatic Nervous System: Controls voluntary movements of skeletal muscles.
• Autonomic Nervous System: Regulates involuntary functions of internal organs and glands.

Somatic Nervous System

• Responsible for conscious and voluntary control of skeletal muscles.
• Sensory neurons transmit sensory information from the body to the CNS.
• Motor neurons transmit motor commands from the CNS to skeletal muscles.

Autonomic Nervous System (ANS)

• Regulates involuntary functions, such as heart rate, digestion, and breathing.
• Divided into two branches:
  • Sympathetic Nervous System: Prepares the body for action (“fight-or-flight” response).
  • Parasympathetic Nervous System: Calms the body down and conserves energy (“rest-and-digest” response).

EXAM TIP: Be prepared to differentiate between the effects of the sympathetic and parasympathetic nervous systems.

Sympathetic Nervous System

• Activated during times of stress or danger.
• Increases heart rate, breathing rate, and blood pressure.
• Dilates pupils.
• Inhibits digestion.
• Releases adrenaline (epinephrine).

Parasympathetic Nervous System

• Activated during times of rest and relaxation.
• Decreases heart rate, breathing rate, and blood pressure.
• Constricts pupils.
• Stimulates digestion.

STUDY HINT: Create a table comparing the functions of the sympathetic and parasympathetic nervous systems to help you remember the key differences.

Conscious and Unconscious Responses

• Conscious Response: A reaction to a sensory stimulus that involves awareness.
  • Example: Deciding to move your hand away from a hot stove.
• Unconscious Response: A reaction to a sensory stimulus that does not involve awareness.
  • Example: Spinal reflex.
  • Physiological responses of the autonomic nervous system (heart rate changes, sweating).

Spinal Reflexes

• An unconscious, involuntary, and automatic response to a sensory stimulus.
• Occurs without involving the brain, allowing for a very rapid response.
• Involves the following steps:
  1. Sensory receptors detect a stimulus (e.g., touching a hot surface).
  2. Sensory neurons transmit the signal to the spinal cord.
  3. Interneurons in the spinal cord relay the signal to motor neurons.
  4. Motor neurons transmit the signal to the muscles, causing them to contract and withdraw from the stimulus.
  5. The brain receives the information about the stimulus after the reflex has occurred.

REMEMBER: The acronym “SAME DAVE” can help remember the direction of nerve signals: Sensory Afferent, Motor Efferent; Dorsal Afferent, Ventral Efferent

COMMON MISTAKE: Students often confuse spinal reflexes with conscious responses, forgetting that reflexes occur before the brain is involved.

The Roles of Neurons

• Sensory Neurons (Afferent): Transmit sensory information from receptors to the CNS.
• Motor Neurons (Efferent): Transmit motor commands from the CNS to muscles and glands.
• Interneurons: Relay signals between sensory and motor neurons within the CNS, especially in the spinal cord for spinal reflexes.

APPLICATION: Understanding the different divisions of the nervous system is crucial in diagnosing and treating neurological disorders.