Overview
This lecture introduces the structure and function of the nervous system, its key cell types, and the processes of sensory input, integration, and motor output.
Functions of the Nervous System
- The nervous system controls all organs, physiological, and psychological reactions in the body.
- Its main functions are sensory input (detecting stimuli), integration (processing and interpreting), and motor output (responding to stimuli).
Organization of the Nervous System
- The central nervous system (CNS) comprises the brain and spinal cord, functioning as the main control center.
- The peripheral nervous system (PNS) consists of nerves connecting the CNS to the rest of the body.
- The PNS splits into sensory (afferent) division (transmits sensory signals to CNS) and motor (efferent) division (sends commands to muscles/glands).
- The motor division includes the somatic (voluntary muscle movement) and autonomic (involuntary functions) nervous systems.
- The autonomic system divides into sympathetic (activates fight/flight response) and parasympathetic (calms the body) branches.
Nervous Tissue and Cell Types
- Nervous tissue is densely packed with cells, mainly neurons and neuroglia (glial cells).
- Neurons are specialized for transmitting signals but are outnumbered about 10:1 by glial cells.
Types of Glial Cells
- Astrocytes (CNS): anchor neurons to blood supply, regulate exchange with capillaries.
- Microglial cells (CNS): provide immune defense in the brain and spinal cord.
- Ependymal cells (CNS): produce and circulate cerebrospinal fluid.
- Oligodendrocytes (CNS): form myelin sheath around neurons.
- Satellite cells (PNS): support neuron cell bodies, similar to astrocytes.
- Schwann cells (PNS): create myelin sheath, similar to oligodendrocytes.
Neuron Structure and Classification
- Neurons have three parts: soma (cell body, life support), dendrites (receive signals), and axon (sends signals).
- Neurons are long-lived, mostly amitotic (do not divide), and have high metabolic needs for glucose and oxygen.
- Neurons are classified by structure: multipolar (many processes, most common), bipolar (two processes, rare), unipolar (one process, mainly in sensory receptors).
- By function: sensory (afferent, mostly unipolar), motor (efferent, mostly multipolar), interneurons (connect sensory and motor neurons, mostly multipolar).
Example: Spider on the Knee Reflex
- Sensory neurons detect the spider and send signals to the CNS.
- Interneurons in the spinal cord process the signal and trigger a motor neuron response.
- Motor neurons cause a physical reaction (e.g., kicking the leg, moving away).
Key Terms & Definitions
- Central Nervous System (CNS) — brain and spinal cord; main control center.
- Peripheral Nervous System (PNS) — all nerves outside CNS; connects CNS to body.
- Afferent Division — carries sensory information to CNS.
- Efferent Division — carries motor commands from CNS.
- Somatic Nervous System — controls voluntary muscle movements.
- Autonomic Nervous System — controls involuntary body functions.
- Neuroglia/Glial Cells — support and protect neurons.
- Neuron — nerve cell that transmits electrical and chemical signals.
- Myelin Sheath — insulating layer around axons, speeds up signal transmission.
- Interneuron — neuron that connects sensory and motor neurons.
Action Items / Next Steps
- Review the three main nervous system functions: sensory input, integration, motor output.
- Study the structure and roles of neurons and glial cells.
- Prepare for next lesson on nerve cell communication via electricity and chemistry.