chapter 8 dendrites Flashcards
Dendrites or
trees
Dendrites des
are short, often highly branching cytoplasmic extensions that are tapered from their bases at the neuron cell body to their tips.
Most dendrites are extensions of the neuron cell body, but
dendrite-like structures also project from the peripheral ends of some sensory
axons.
.
Dendrites usually receive
information from other neurons or from
sensory receptors and transmit the information toward the neuron cell body.
axon des
a single long cell process extending from the neuron cell body.
The area where the axon leaves the neuron cell body is
called the
axon hillock.
Axons of sensory neurons conduct
action potentials towards the CNS
axons of motor
neurons conduct
action potentials away from the CNS.
Axons also conduct
action potentials from one part of the brain or spinal cord to another part.
An axon may remain unbranched or
may branch to form collateral (ko-LAT-er-
uhl) axons.
Axons can be surrounded by a highly specialized insulating layer
of cells
myelin sheath
neurons can be
classified on the basis of their
function as well as their structure.
“sensory neuron”
indicates that it is carrying
information to the CNS from a specific receptor in the body.
“motor neuron”
it is sending
information to an effector of the body from the CNS.
three categories of neurons exist, based on the
arrangement of their processes/structure
Multipolar, bipolar, pseudo unipolar
Multipolar neurons
have many dendrites and a single axon. Most of
the neurons within the CNS and nearly all motor neurons are
multipolar.
Bipolar neurons have two processes:
one dendrite and one axon.
Bipolar neurons are located
in some sensory organs, such as in the
retina of the eye and in the nasal cavity.
Pseudo-unipolar neurons des 1
have a single process extending from the
cell body.
Pseudo-unipolar neurons des 2
This process divides into two extensions, a short distance
from the cell body.
This process divides into two extensions a short distance
from the cell body. One
One extends to the periphery, and the other
extends to the CNS.
This process divides into two extensions a short distance
from the cell body. One
One extends to the periphery, and the other
extends to the CNS.
The two extensions function
as a single axon with
small, dendrite-like sensory receptors at the periphery.
The axon receives sensory information at the periphery and transmits that
information in the form of action potentials to the CNS.
.
most sensory
neurons are
pseudo-unipolar.
Glial cells (GLEE-al), or
neuroglia (nyu-ROH-glee-ah; nerve glue),
Glial cells des
are the supportive cells of the CNS and PNS, meaning these cells do not conduct
action potentials.
Instead, glial cells carry out
different activities that enhance
neuron function and maintain normal conditions within nervous tissue.
Glial cells are far more numerous than neurons.
.
Most glial cells retain the ability to
divide, whereas neurons do not.
.
In the CNS, there are four types of glial cells.
astrocytes, (2) ependymal cells, (3) microglia, and (4)
oligodendrocytes.
The glial cells of the PNS include
Schwann cells and (2)
satellite cells.
Astrocytes (ASS-troh-sites)
serve as the major supporting cells in the CNS.
In this role, astrocytes can
stimulate or inhibit the signaling activity of nearby
neurons.
In addition, astrocytes participate with the
blood vessel endothelium
to form a permeability barrier, called the blood-brain barrier, between the
blood and the CNS.
Astrocytes help limit
damage to neural tissue; however,
the repair process can form a scar that blocks regeneration of damaged
axons .
Ependymal (ep-EN-dih-mal) cells
line the fluid-filled cavities
(ventricles and canals) within the CNS.
Some ependymal cells produce
cerebrospinal fluid
others, with cilia,
help move the cerebrospinal fluid
through the CNS.
Microglia (my-KROH-glee-ah)
act as immune cells of the
CNS.
They help protect the brain by
removing bacteria and cell debris.
Oligodendrocytes (OL-ih-goh-DEN-droh-sites)
provide an insulating
material that surrounds axons
in pns, Schwann cells
provide insulating
material around axons.
Satellite cells
found around the cell bodies of
certain neurons of the PNS.
Satellite cells 2 des
These cells provide support and nutrition to the
neurons and protect the neurons from heavy-metal poisons, such as lead and
mercury.
Myelin sheaths
specialized layers that wrap around the axons of some
neurons.
These myelin sheaths are formed by the cell processes of
oligodendrocytes in the CNS and Schwann cells in the PNS
Axons with these myelin sheaths
are called myelinated axons, Each
oligodendrocyte process or Schwann cell repeatedly wraps around a segment
of an axon to form a series of tightly wrapped cell membranes.
Myelin is an excellent insulator
that prevents almost all ion movement across the cell membrane.
Gaps in the myelin sheath, called
nodes of Ranvier
nodes of Ranvier
occur about every millimeter between the myelinated areas.
_____ can occur at the nodes of Ranvier.
Ion movement
Myelination of an axon
increases
the speed and efficiency of action potential generation along the
axon.
Unmyelinated axons
lack the myelin sheaths; however, these axons rest in
indentations of the oligodendrocytes in the CNS and the Schwann cells in the
PNS
A typical small nerve, which consists of axons of multiple
neurons, usually contains
more unmyelinated axons than myelinated axons.
