Nervous System Overview Quiz

Nervous System Overview

• The nervous system is the master controlling and communication system of the body, responsible for collecting information, integrating, and generating a motor output.
• Three general functions of the nervous system:
  • Collect information (sensory input)
  • Integration (interpret sensory input and determine proper response)
  • Motor output (activate effectors including muscle and glands)

Nervous Tissue

• Nervous tissue is composed of neurons and glia.
• Two main cell types:
  • Neurons (basic unit of the nervous system, excitable cells that transmit electrical signals, do not divide after developmental period)
  • Glia (non-excitable, support and protect neurons, outnumber neurons 10:1, undergo mitosis throughout life)

Distinguishing Features of Neurons

• Excitable (neuronal membrane generates electrical activity in response to stimulation)
• Conductive (electrical signals are propagated across the plasma membrane)
• Extreme longevity (most neurons are formed before birth and are still present in advanced age)
• Amitotic (neurons lose their ability to divide)

Microscopic Anatomy of Neurons

• The neuron cell body is the biosynthetic center of the cell, containing cytoplasm, nucleus, and other organelles.
• Dendrites (branch off the cell body, receive information from other neurons, and transfer to the cell body)
• Axon (singular process that transmits signals to other neurons, muscle cells, or glands)
• Axon hillock (where axon leaves the cell body)
• Axon terminals (form synapses with target cells, contain synaptic vesicles, and release neurotransmitters)

Synapse

• A synapse is made of a presynaptic neuron, the synaptic cleft, and a postsynaptic neuron.
• The cytoskeleton provides support and structure for neurons (microfilaments, intermediate filaments, and microtubules)

Anatomical Classes of Neurons

• Three different anatomical classes of neurons:

Glial Cells

• Glial cells are "non-excitable" and support, protect, and provide a scaffold for neurons.
• CNS glial cells:
  • Astrocytes (most abundant glial cell in the CNS, regulate nutrients to neurons, control chemical environment)
  • Oligodendrocytes (highly branched from a single soma, wrap processes tightly around axons, produce an insulted covering - myelin sheath)
  • Microglia (monitor neurons and extracellular space for health and signs of disrupted homeostasis, transform into a type of macrophage)
  • Ependymal cells (line CNS cavities, produce cerebrospinal fluid, cilia help circulate CSF)
• PNS glial cells:
  • Satellite cells (surround ganglion neuron cell body, regulate cellular environment, similar to astrocytes in the CNS)
  • Schwann cells (myelinate PNS axons, similar to oligodendrocytes)

Myelination

• Large axons in the CNS and PNS are myelinated.
• Myelination insulates and protects the axon, speeds conduction of electrical impulses down the axon.
• Schwann cells myelinate axons in the PNS, while oligodendrocytes myelinate axons in the CNS.

PNS Structures

• Nerve (cable-like bundle of parallel axons in the peripheral nervous system)
• Ganglion (cluster of neuron cell bodies in the peripheral nervous system)

Connecting CNS and PNS

• Pseudounipolar neurons connect the CNS and PNS, transmitting sensory information from skin receptors to the spinal cord.