Nervous System Divisions: CNS, PNS, SNS, ANS

Divisions of the Nervous System

• The nervous system has two main divisions: the Central Nervous System (CNS) and the Peripheral Nervous System (PNS).

Central Nervous System (CNS)

• Consists of the brain and spinal cord.
• Processes and interprets sensory information.
• Sends out commands.

Peripheral Nervous System (PNS)

• Includes nerves outside the CNS, specifically cranial and spinal nerves.
• Connects the CNS to the limbs and organs.
• Transmits signals to and from the brain and spinal cord.

Divisions of the Peripheral Nervous System

• The PNS is further divided into the Somatic Nervous System (SNS) and the Autonomic Nervous System (ANS).

Somatic Nervous System (SNS)

• Controls voluntary movements.
• Sends sensory and motor signals between the CNS and muscles.

Autonomic Nervous System (ANS)

• Regulates involuntary functions like heart rate, digestion, and breathing.
• The Autonomic Nervous System has two parts: the Sympathetic and Prasympathetic systems

Sympathetic Nervous System

• Controls the "fight-or-flight" response.

Parasympathetic Nervous System

• Controls the "rest-and-digest" response.

Structure of the Nervous System

• Composed of neurons and neuroglia.

Neurons (Nerve Cells)

• Neurons are the fundamental units of the nervous system, transmitting electrical and chemical signals.

Types of Neurons

• Sensory Neurons (Afferent Neurons): Carry signals from sensory organs to the CNS.
• Motor Neurons (Efferent Neurons): Send signals from the CNS to muscles and glands.
• Interneurons: Connect neurons within the CNS for processing information.

Parts of a Neuron

• Cell Body (Soma): Contains the nucleus and organelles.
• Dendrites: Receive signals from other neurons.
• Axon: Sends signals to other neurons or muscles.
• Myelin Sheath: Fatty covering that speeds up signal transmission.
• Synapse: Gap between neurons where chemical signals (neurotransmitters) are passed.

Neuroglia (Glial Cells)

• Support cells that provide structure, nourishment, and protection for neurons.
• Astrocytes: Support neurons and maintain the blood-brain barrier.
• Microglia: Act as immune cells in the CNS.
• Oligodendrocytes (CNS) & Schwann Cells (PNS): Produce myelin to insulate neurons.

Functions of the Nervous System

• Sensory Function: Detects stimuli from the environment (e.g., touch, sound, temperature).
• Integrative Function: Processes and interprets sensory input.
• Motor Function: Controls voluntary and involuntary movements.

Major Parts of the Brain

• The brain is divided into three main regions: the forebrain, midbrain, and hindbrain.

Forebrain (Prosencephalon)

• It is the largest and most complex part of the brain.
• Controls thinking, memory, voluntary movements, and sensory processing.

Cerebrum

• The cerebrum is the largest part of the brain, divided into two hemispheres (left and right).
• Each hemisphere controls the opposite side of the body.

Lobes of the Cerebrum & Their Functions

• Frontal Lobe: Responsible for problem-solving, reasoning, decision-making, motor control (via the primary motor cortex), speech production (Broca’s area), emotion, and personality.
• Parietal Lobe: Handles sensory processing (touch, temperature, pain), spatial awareness, body positioning, and understanding language.
• Temporal Lobe: Deals with hearing and auditory processing, memory formation (hippocampus), and language comprehension (Wernicke’s area).
• Occipital Lobe: Processes visual information.

Thalamus

• Acts as a relay station for sensory signals to the cerebral cortex.
• Regulates consciousness, sleep, and alertness.

Hypothalamus

• Controls the autonomic nervous system (heart rate, digestion, breathing).
• Regulates body temperature, hunger, thirst, and hormones.
• Controls the pituitary gland (master gland of the endocrine system).

Midbrain (Mesencephalon)

• Controls reflexes, eye movements, and auditory/visual processing.
• Tectum: Controls visual and auditory reflexes.
• Tegmentum: Coordinates movement and alertness.

Hindbrain (Rhombencephalon)

• Controls vital functions such as breathing, heart rate, and balance.

Cerebellum

• Coordinates movement, balance, and posture.
• Helps with motor learning (e.g., learning to ride a bike).

Pons

• Connects the brainstem to the cerebellum.
• Regulates breathing and facial expressions.

Medulla Oblongata

• Controls involuntary functions like heartbeat, breathing, and blood pressure.
• Helps with reflexes such as coughing, sneezing, and swallowing.

Brainstem

• Consists of the medulla, pons, and midbrain.
• Connects the brain to the spinal cord.
• Controls essential life functions (breathing, heart rate, digestion).
• Regulates sleep-wake cycles (Reticular Activating System).