Overview
This lesson covers neural control pathways, focusing on the organization of the nervous system, structure of neurons, the process of nerve signaling, and reflex arcs.
Organization of the Nervous System
- The nervous system is divided into the central nervous system (CNS) and peripheral nervous system (PNS).
- The CNS consists of the brain and spinal cord.
- The PNS includes all other nerves outside the brain and spinal cord.
- PNS is divided into sensory (detects changes like sight, sound, pressure, pain) and motor pathways (controls movement and internal functions).
- Motor pathways are further split into somatic (voluntary actions) and autonomic (involuntary actions) systems.
- The autonomic system is divided into sympathetic ("fight or flight") and parasympathetic ("rest and digest") divisions.
Structure of a Neuron
- A neuron (nerve cell) has a soma (cell body) containing the nucleus and organelles.
- The axon is a long extension that sends impulses away from the soma, usually one direction.
- The myelin sheath, made of Schwann cells, insulates the axon to ensure accurate signal transmission.
- Axon terminals are the endpoints where signals are sent to other neurons or effectors.
- Dendrites are projections from the soma that receive impulses from other neurons.
Types of Neurons
- Sensory neurons carry impulses from tissues and organs to the CNS.
- Interneurons (relay neurons) interpret impulses and connect other neuron types.
- Motor neurons carry impulses from the CNS to muscles or effectors.
Nerve Signal Transduction
- Signal transmission involves a stimulus detected by a receptor, sent through a sensory neuron to the CNS.
- Interneurons relay the signal, and a motor neuron carries the response to an effector (like a muscle).
- Example: Optic nerve signals lead to pupil constriction or dilation depending on light intensity.
Reflex Arcs
- Reflex arcs allow for rapid, involuntary responses by sending sensory input directly to the spinal cord, bypassing the brain.
- This process enables quick reactions, like pulling your hand away from pain, before the brain is involved.
- Reflexes save critical time in dangerous situations.
Key Terms & Definitions
- Central Nervous System (CNS) — The brain and spinal cord.
- Peripheral Nervous System (PNS) — All nerves outside the CNS.
- Somatic Nervous System — Controls voluntary movements.
- Autonomic Nervous System — Controls involuntary functions.
- Sympathetic Nervous System — Triggers "fight or flight" responses.
- Parasympathetic Nervous System — Promotes "rest and digest" activities.
- Neuron — A nerve cell transmitting electrical impulses.
- Soma — Cell body of a neuron.
- Axon — Long projection sending impulses away from the soma.
- Myelin Sheath — Insulating layer around the axon.
- Dendrite — Branches receiving impulses from other neurons.
- Reflex Arc — Direct pathway for rapid, involuntary responses.
Action Items / Next Steps
- Review diagrams of the nervous system and neuron structure.
- Practice labeling parts of neuron and tracing signal pathways.
- Read assigned textbook chapter on neural control and reflexes.