BIOB30_Chapt8:Nash

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Published on 28 Sep 2011
School
UTSC
Department
Biological Sciences
Course
BIOD27H3
Sept. 15th 2011
BIOB30 - Chapter 8: Neurons - Cellular and Network Properties
Definitions:
nervous system - a network of trillions of nerve cell linked together in a
highly organized manner to form the rapid control system of the body
neurons - uniquely shaped cells that have long, thin extensions that carry
electrical signals rapidly and sometimes over long distances and release
chemical signals called neurotransmitters into the extracellular fluid.
interneurons - neurons that lie entirely within the CNS
varicosities - enlarged regions along the axon of some neurons in the
autonomic division
sensory nerves - carry only afferent signals
motor nerves - carry only efferent signals
mixed nerves - carry signals in both directions
ganglion - cluster of nerve cell bodies found outside the CNS
microglia - specialized immune cells in the CNA that remove damaged cells
and foreign invaders
astrocytes - highly branched cells that contact neurons and blood vessels
and may transfer nutrients between the two, and maintain homeostasis in
the ECF around CNS neurons by taking up K+ and neurotransmitters from
the ECF. [communicate with one another through gap junctions]
ependymal cells - specialized cells that create a selectively permeable
epithelial layer (ependyma) that separates the fluid compartments of the
CNS. It is also the source of neural stem cells
channel conductance - the ease with which ions pass through a channel
current - the electrical charge carried by an ion
channelpathies - inherited diseases caused by mutations in ion channel
proteins
_____________________________________________________________________________
Organization of the Nervous System:
The nervous system is divided into two parts:
1. CNS - consists of the brain and the spinal cord: used for integration of
neuronal reflexes.
2. PNS - consists of afferent (sensory) neurons and efferent neurons
sensory receptors throughout the body continuously monitor the internal and
external environments and send information along the afferent neurons
(through the PNS) to the CNS, which creates output signals directing an
appropriate response to travel through the efferent neurons to the effector
cells of the body (muscles).
There are two types of efferent neurons:
1. somatic motor division - control skeletal muscles
2. autonomic division (visceral nervous system) - controls smooth and cardiac
muscles, exocrine glands, some endocrine glands, and some types of
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Sept. 15th 2011
BIOB30 - Chapter 8: Neurons - Cellular and Network Properties
adipose tissue, as well as the contraction and secretion in various internal
organs
There are two types of autonomic neurons:
1. sympathetic branch
2. parasympathetic branch
enteric neurons system - new branch of nervous system that consists of a
network of neurons in the walls of the digestive tract.
For some processes, the CNS does not need input from the PNS. It is more
than capable of initiating activity without sensory input.
Cells of the Nervous System
The nervous system is comprised of two cell types:
1. neurons - the basic functional and signaling units of the nervous system
2. glial cells - support cells
-axons carry outgoing information
-dendrites are the thing, branched processes that receive incoming signals
from neighboring cells
the long axons of both afferent and efferent peripheral neurons are bundled
together with connective tissue into cord-like fibers called nerves that
extend from the CNS to the targets of the component neurons.
cell body is the control centre of the neuron (contains the nucleus)
dendrites increase the surface area of a neuron, allowing it to communicate
with multiple neurons. It’s main function within the PNS is to receive
information and transfer it to an integrating region within the neuron. In the
CNS, a dendrite can act independently in that it can send signals back and
forth with other neurons in the brain.
neurons that secrete neurotransmitters and neuromodulators terminate near
their target cells, which are usually neurons, muscles or glands
axonal transport - the process by which proteins that have been synthesized
on the RER in the cell body are moved down the axon towards the axon
terminal where it will leave and look to the target cell
slow axonal transport - moves material by axoplasmic flow from the cell
body to the axon terminal; used for components that are not consumed
rapidly by the cell (enzymes)
fast axonal transport - neurons use stationary microtubules as tracks along
which transported vesicles and mitochondria walk with the aid of attached
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BIOB30 - Chapter 8: Neurons - Cellular and Network Properties
motor-like proteins. The proteins alternately bin and unbind to the
microtubules with the help of ATP
Fast axonal transport goes in two directions:
1. forward (anterograde) = from cell body to axon terminal
2. Backward (retrograde) = from axon to cell body for recycling of old cellular
components
-glial cells provide structural stability to neurons by wrapping around them.
They may also maintain homeostasis of the brain’s extracellular fluid and
provide metabolic support to neurons.
-glial cells communicate through chemical signals
-there are two types of glial cells in the PNS
-schwann cells - support and insulate one axon by forming myelin (lots
of layers of phospholipid membrane)
-satellite cells - form supportive capsules around nerve cell bodies
located in ganglia (non-myelinated)
-there are also 4 types glial cells in the CNS
-oligodendrocytes - support and insulate portions of many axons at a
time by forming myelin (lots of layers of phospholipid membrane)
-astrocytes
-ependymal cells
-microgalia
nodes of ranvier play a very important role in the transmission of electrical
signals along the axon. They are the gaps in between the myelinated axons.
Electrical Signals in Neurons
Two factors influence the resting membrane potential”
1. concentration gradients of ions across the membrane
i. Na+, Cl-, Ca2+ are more concentrated in the ECF
ii. K+ is more concentrated in the ICF
2. membrane permeability to those ions.
i. resting cell membrane is more permeable to K+ than Na+ or Ca2+.
-The Nernst equation describes the membrane potential that a single ion
would produce if the membrane were permeable to only that one ion
-The GHK equation is used to calculate the RMP that results from the
contribution of all ions that cross the membrane
**A significant change in membrane potential occurs with the movement of
very few ions**
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Document Summary

[communicate with one another through gap junctions] ependymal cells - specialized cells that create a selectively permeable epithelial layer (ependyma) that separates the fluid compartments of the. There are two types of efferent neurons: somatic motor division - control skeletal muscles. 1: autonomic division (visceral nervous system) - controls smooth and cardiac muscles, exocrine glands, some endocrine glands, and some types of. Biob30 - chapter 8: neurons - cellular and network properties adipose tissue, as well as the contraction and secretion in various internal organs. There are two types of autonomic neurons: sympathetic branch. 1: parasympathetic branch enteric neurons system - new branch of nervous system that consists of a network of neurons in the walls of the digestive tract. For some processes, the cns does not need input from the pns. It is more than capable of initiating activity without sensory input.