The Nervous System: CNS and PNS

• The nervous system is a complex network that enables organisms to receive, process, and respond to stimuli from both internal and external environments.
• It is responsible for coordinating and regulating bodily functions and activities.
• It is divided into two major divisions: the central nervous system (CNS) and the peripheral nervous system (PNS).

Central Nervous System (CNS)

• Composed of the brain and spinal cord.
• The brain serves as the control center, responsible for processing information, decision-making, and initiating responses.
• The spinal cord serves as a pathway for transmitting information between the brain and the peripheral nervous system.
• It also mediates reflexes.

Peripheral Nervous System (PNS)

• Consists of all the nerves and ganglia outside of the brain and spinal cord.
• It is responsible for transmitting information between the CNS and the rest of the body.
• Divided into two main subdivisions: the somatic nervous system and the autonomic nervous system.

Somatic Nervous System

• Controls voluntary movements of skeletal muscles.
• It transmits sensory information from the sensory organs to the CNS and conveys motor commands from the CNS to the muscles.

Autonomic Nervous System

• Regulates involuntary functions such as heart rate, digestion, respiration, and glandular secretions.
• It operates without conscious control.
• Further divided into the sympathetic and parasympathetic nervous systems.

Sympathetic Nervous System

• Prepares the body for action in stressful or emergency situations, often referred to as the "fight-or-flight" response.
• Increases heart rate, dilates the pupils, inhibits digestion, and stimulates the release of glucose for energy.

Parasympathetic Nervous System

• Promotes relaxation, conserves energy, and restores normal bodily functions, often referred to as the "rest-and-digest" response.
• Slows down heart rate, constricts the pupils, stimulates digestion, and promotes relaxation.

Neurons

• The basic building blocks of the nervous system.
• Specialized cells responsible for transmitting information throughout the body.
• Composed of three main parts: the cell body, dendrites, and axon.

Cell Body

• Contains the nucleus and other cellular organelles.
• It is responsible for the metabolic functions of the neuron.

Dendrites

• Branch-like extensions that receive signals from other neurons.
• Transmit them towards the cell body.

Axon

• A long, slender projection that transmits signals away from the cell body to other neurons, muscles, or glands.
• Axons are often covered by a myelin sheath, which insulates the axon and increases the speed of signal transmission.

Synapses

• The junctions between neurons where communication occurs.
• When an action potential reaches the axon terminal, it triggers the release of neurotransmitters into the synaptic cleft.
• These neurotransmitters bind to receptors on the postsynaptic neuron, leading to either excitation or inhibition of the postsynaptic neuron.