Cells of the Nervous System
Functions of the Nervous System
Information Processing: Receives signals from the environment via sensory receptors.
Integration: Processes and integrates incoming sensory information.
Response Generation: Sends commands to muscles and glands to elicit responses.
Divisions of the Nervous System
Central Nervous System (CNS): Consists of the brain and spinal cord.
General Functions: Integrates sensory information and coordinates responses.
Peripheral Nervous System (PNS): Comprises all nerves outside the CNS.
Subdivisions:
Somatic Nervous System: Controls voluntary muscle movements.
Autonomic Nervous System: Regulates involuntary functions (e.g., heart rate, digestion).
Characteristics of the Nervous System Divisions
CNS: High-level functioning, decision-making, and integration.
PNS: Connects CNS to the rest of the body, including limbs and organs.
Somatic vs Autonomic Nervous Systems
Somatic:
Voluntary control over skeletal muscles.
Reflex arcs are part of this system.
Autonomic:
Involuntary control over internal organs.
Subdivided into:
Sympathetic System (fight or flight)
Parasympathetic System (rest and digest)
Structure of Neurons
Neurons: Basic unit of the nervous system, approximately 100 billion in the body.
Parts:
Cell Body (Soma): Contains nucleus, organelles (RER, Golgi apparatus).
Dendrites: Highly branched, receive signals, generate electrical currents.
Axon:
Varies in length; conducts impulses away from the cell body.
Surrounded by the myelin sheath for insulation.
Classification of Neurons
Structural Classification:
Unipolar: One process; sensory neurons connecting receptors to CNS.
Multipolar: Many dendrites; most common, includes motor neurons.
Bipolar: Two processes; specialized for sensory functions (e.g., retina).
Functional Classification of Neurons
Sensory Neurons (Afferent): Carry information from sensory receptors to CNS.
Motor Neurons (Efferent): Transmit impulses away from CNS to muscles/glands.
Interneurons: Connect sensory and motor neurons within the CNS.
Neuroglial Cells
Types in CNS:
Ependymal Cells: Line ventricles, produce and circulate cerebrospinal fluid (CSF).
Astrocytes: Support neurons, regulate blood-brain barrier, maintain homeostasis.
Microglial Cells: Act as immune defense; phagocytize debris.
Oligodendrocytes: Myelinate axons in CNS.
Types in PNS:
Schwann Cells: Myelinate axons in PNS, support neuronal regeneration.
Satellite Cells: Provide support and nutrition to neuron cell bodies.
Resting Membrane Potential (RMP)
Definition: The difference in voltage across the neuronal membrane at rest.
Typical Charges:
Inside: Negative charge (approx. -70 mV).
Outside: Positive charge.
Action Potential and Myelination
Stimulating a Neuron: Causes a change in resting potential, leading to action potential generation.
Myelination:
Increases conduction speed of action potentials.
Function of myelin sheath is to insulate axons, enabling saltatory conduction (jumping of impulses).
Synapses
Structure: Junction between two neurons, allowing for communication.
Function: Transmits signals via neurotransmitters.
Reflex vs Reaction
Reflex: An automatic response that occurs without conscious thought, often mediated by a reflex arc.
Reaction: A voluntary response requiring conscious thought.
Compendium Questions
What is the function of the nervous system?
Differentiate between the CNS and PNS.
What are roles of somatic, autonomic, and enteric nervous systems?
Identify parts of a neuron.
Differentiate sensory, motor, and interneurons.
List neuroglial cells in the PNS and CNS with their functions.
Explain resting membrane potential and its significance.
Describe changes in RMP during neuron stimulation.
Why do myelinated axons conduct impulses faster than unmyelinated axons?
Discuss the processes that occur at the synapse.
What are the main components of a reflex arc?