Download Cells of the Nervous System

Cells of the
Nervous System
Layout of the Nervous System
Central Nervous System (CNS)
Brain (in the skull)
Spinal Cord (in the spine)
Interprets sensory input, initiates
movement, and mediates complex
cognitive processes
Peripheral Nervous System (PNS)
Located outside of the skull and
spine
Serves to bring sensory
information into the CNS and
carry motor signals out of the CNS
Functional Unit of the Nervous System
The functional unit of the
nervous system is the neuron.
Neurons are specialized cells
for the reception, conduction,
and transmission of electrochemical signals
Many sizes and shapes
~100 billion neurons
~100 trillion connections
Major External Features of a Neuron
A typical neuron has a cell
body, dendrites and an
axon.
Flow of information:
• dendrites receive inputs
from other neurons
• the cell body (or soma)
integrates (processes)
information
• the axon transmits the
output of processing to
other neurons
Major Internal Features of a Neuron
Similarities with other cells:
• Contains a nucleus that
holds genetic information
• Contains organelles that
support the life of the cell,
including mitochondria and
ribosomes
• Surrounded by a membrane
that protects the cell
Differences with other cells:
• Stop dividing (reproducing)
after birth
• Have dendrites and axons,
specialized structures
designed to receive and
transmit information
The Cell Membrane
Lipid bilayer with
embedded proteins
• separates inside and
outside of cell
• selective permeability
controls flow of
substances into and
out of the cell
The particular composition of embedded
proteins in the cell membrane is critical for
proper neuron function
Visualizing Neurons 1
The major problem in
visualizing neurons is not their
minuteness. Rather, the major
problem is neurons are so
tightly packed and their
dendrites and axons intricately
intertwined.
Golgi stain: for as-yet unknown
reasons, silver stains some
neurons black in their entirety
but stains others not at all.
Allows for visualization of
individual neurons
Visualizing Neurons 2
Nissl stain: selectively stains
cell bodies. Used to indicate
the number of neurons in an
area
Visualizing Neurons 3
Electron microscopy: provides
information about the details of
neuronal structure
Visualizing Neurons 4
Tract tracing techniques: used
to trace the paths of axons
Anterograde: to trace axons
projecting away from cell
bodies
www.seriousmadscience.com
Retrograde: to trace axons
projecting into an area of cell
bodies
cmbn-approd01.uio.no
Neuroanatomical Structures
Two kinds of gross neural structures; those composed
primarily of cell bodies and those composed primarily of
axons.
CNS
PNS
Clusters of cell Nuclei
bodies
(singular nucleus)
Grey matter
Ganglia
(singular ganglion)
Bundles of
axons
Nerves
Tracts
White matter
Anatomical Classes of Neurons
Neurons do not all look alike. One way to classify them is
based on the number of processes emanating from their cell
bodies.
Functional Classes of Neurons
information from
tissue/organs
integrate
intermediate
information to
effector cells
www.studyblue.com
CNS Neurons Are Usually Multipolar
PNS Neurons are Unipolar or Multipolar
Connections Between Neurons
Direction:
afferent (approaching)
efferent (exiting)
Type:
axon-dendrite
but also axon-soma,
axon-axon, dendrite-dendrite
Neuroscience: Exploring the Brain, 3rd ed
Glia: The Forgotten Cells of the NS
• Helper cells (glia = “glue”)
• Outnumber neurons 5:1
• Provide structural/metabolic
support to neurons
• Recent evidence for glial
communication and
modulatory effects of glia on
neuronal communication
www.jaynejubb.com
Classes of Glial Cells
• Oligodendrocytes: extensions
rich in myelin; create myelin
sheaths in CNS
• Schwann cells: similar to
function of oligodendrocytes,
but in PNS; can guide axonal
regeneration
• Microglia: involved in response
to injury or disease
• Astrocytes: largest glia; starshaped; many functions
blogs.scientificamerican.com
Myelination of neurons
Microglia respond to injury or disease
ramified
motile
ucsf.edu
Astrocytes perform a variety of duties
Control and communicate widely with
many neurons:
• form a barrier to unwanted
substances entering the brain
• control blood flow to neurons
(activity allows functional imaging)
• maintain the proper chemical state
outside of neurons/remove waste
• surround synapses and can modify
neuronal signals
• send nutrients (glucose) to neurons
• digest old neuronal parts
• secrete neurotransmitters and glialtransmitters
www.nature.com