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Unit 2 biol 273.docx

by OneClass289883 , Spring 2014
15 Pages
Spring 2014

Course Code
Vivian Dayeh

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UNIT 2: Homeostasis and Control
Chapter 8: Neurons: Cellular and Network Properties
- brain and spinal cord are integrating centers for homeostasis, movement, many
other body functions
- are the control center of nervous system
onervous system: network of billions or trillions of nerve cells linked
together in highly organized manner to form rapid control system of body
- nerve cells or neurons carry electrical signals rapidly and sometimes over long
- neurons release chemical signals called neurotransmitters into extracellular fluid
to communicate with neighbouring cells
- neurons are linked by gap junctions allowing electrical signals to pass directly
from cell to cell
-emergent properties: are complex processes that cannot be predicted from what
we know about properties of individual nerve cells and their specific connections
Organization of the Nervous System
- nervous system can be divided into two parts:
oCentral nervous system (CNS)  consists of brain and spinal cord
oPeripheral nervous system (PNS)  consists of sensory (afferent) neurons
and efferent neurons
oInfo flows through nervous system using this basic pattern:
Stimulus  sensor  input signal  integrating center  output signal
target  response
- sensory receptors continuously monitor conditions in internal and external
- CNS neurons integrate information that arrives from sensory division of PNS and
determine whether a response is needed
- Is a response is needed, CNS sends output signals that travel through efferent
neurons to their targets
- Efferent (motor) neurons subdivide into:
oSomatic motor division
Controls skeletal muscles
oAutonomic division
Controls smooth and cardiac muscles, exocrine glands, some
endocrine glands, some types of adipose tissue
Can be further divided into:
-enteric nervous system:
onetwork of neurons in walls of digestive tract
- autonomic division of PNS is also called visceral nervous system  because it
controls contraction and secretion in internal organs
Cells of the Nervous System
- nervous system is composed primarily of two cell types:
obasic signaling units of nervous system
osupport cells known as glial cells
- neurons carry electrical signals
oneurons are cells with long processes that extend outward from nerve cell
usually classified as dendrites receive incoming signals
or axons carry outgoing information
- neurons that lie entirely within CNS are known as interneurons
- efferent neurons have enlarged axon terminals
- autonomic neurons have enlarge regions along axon called varicosities
- axon terminals and varicosities store and release neurotransmitter
- long axons of afferent and efferent peripheral neurons are bundled together with
connective tissue into cordlike fibers called nerves that extend from CNS to
targets of component neurons
-Sensory nerves: nerves that carry afferent signals only
-Motor nerves: nerves that carry efferent signals only
-Mixed nerves: nerves that carry signals in both directions
- Cell body with nucleus is essential to well-being of cell because it contains DNA
that is template for protein synthesis
- dendrites:
othin, branches processes that receive incoming information from
neighbouring cells
oincrease surface area of neuron
osimplest neuron have only single dendrite
oprimary function in PNS: receive incoming information and transfer it to
integrating region within neuron
- axons carry outgoing signals:
omost peripheral neurons have single axon that originates from specialized
region of cell body called axon hillock
oeach collateral ends in swelling called axon terminal
oaxon terminal contains mitochondria and membrane-bound vesicles filled
with neurocrine molecules
oprimary function of axon: transmit outgoing electrical signals from
integrating center of neuron to end of axon
oat end of axon, electrical signal is usually translated into chemical message
be secretion of neurotransmitter, neuromodulator, neurohormone
oneurons that secrete neurotransmitters and neuromodulators terminate near
target cells
oaxons cytoplasm is filled with many types of fibers and filaments but
lacks ribosomes and endoplasmic reticulum ; they convey electrical and
chemical signals
oany proteins destined for axon or axon terminal must be synthesized on
rough ER
oproteins are then moved down axon by process known as axonal
oslow axonal transport: moves material by axoplasmic (cytoplasmic) flow
from cell body to axon terminal
oFast axonal transport: moves organelles at rates of up to 400 mm per
Neuron uses stationary microtubules as tracks along which
transported vesicles and mitochondira “Walk” with aid of
attached footlike motor proteins
Motor proteins bind and unbind to microtubules with help of ATP
Fast axonal transport goes in two directions:
Forward (anterograde) transport  moves synaptic and
secretory vesicles and mitochondria from cell body to axon
Backward (retrograde) transport returns old cellular
components from axon terminal to cell body for recycling
- establishing synapses depends on chemical signals

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