Chapter 2 Notes

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26 Nov 2010
Chapter 2
Main Teaching Points:
Module 2.1: Cells of the Nervous System
1. Neurons and Glia: Structure and Function
2. Communication within the Neuron: The Action Potential
3. Communication between Neurons: The Synapse
4. Neurotransmitters
Module 2.2: The Nervous System
1. Positional Terms
2. Divisions of the Nervous System
3. The Spinal Cord
4. Divisions of the Brain
5. Connections between the Two Halves of the Brain
6. Cranial Nerves
7. Blood Supply
8. Protections
Module 2.1 Cells of the Nervous System
x Communicators
x Reacts and responds to stimuli; basis of behavior
x Learns and stores information about their external environments
Glia t support functions
Neurons and Glia: Structure and Function
Gross Anatomy of the Neuron
x Eµ}v[Z]o}oÇo}]v]}vWd}]ÀU}vµvvu]]Pvot to
collect information and send it on (or not)
Parts of the Neuron
x Dendrites t receives incoming information from other neurons
x Soma (Cell Body) t contains genetic machinery and most of the metabolic machinery needed for
common cellular functions
x Axon t sends neural information to other neurons
x Information is passed from the axon to the dendrite through the synapse
¾ Presynaptic t events that occur in the axon
¾ Postsynaptic t events that occur in the dendrite
1. Dendrites
¾ Increases the surface area available for the reception of signals from the axons of other
¾ Extent of branching of the dendrites gives an indication of the number of connections or
synapses it makes with incoming axons
¾ Information is sent to the rest of the neuron in the form of an electrical charge t action
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Chapter 2
¾ Are often covered with tiny spines which grow and retract in response to experience t
spines can form synapses with other neurons
2. Axon
¾ Information sender
¾ Only one axon / neuron
¾ A long thin fiber or wire that can pass its message along to many different cells
¾ Covered with myelin t helps to speed rate of information transferred and ensures that
the message gets to the end of the axon
Internal Anatomy of the Neuron
x Plasma membrane t bilayer of continuous sheets of phospholipids the separate the internal
environment from the outside; proteins and channels allow passage of materials
x Nucleus t genetic processes; packages and controls the genetic information contained in DNA
x Ribosomes & Endoplasmic Reticulum t Synthetic processes
x Mitochondria t metabolic processes
Structure and Function of Neurons
Classification of Neurons:
1. Patterns of Branching
¾ Unipolar neurons t one process emanating from cell body
¾ Bipolar neurons t two process
¾ Multipolar t numerous processes extending from cell body
¾ Interneurons t neurons with no axons or very short axons; integrates information
within a structure rather than sending information between structures
2. Types of signals they process
¾ Sensory Neurons t processes information elicited from sensory-type stimuli
¾ Interneurons t makes connection between cells; enables convergence and combination
of behavioral resposnes
¾ Motor Neurons t conveys muscle contractions
3. Afferent neuron t brings information to CNS
4. Efferent neuron t sends information from the brain or away from a structure
x Neurons vary in size, shape, and function and can shape as a result of experience
x Support functions
x Satellite Cells t support cells outside of the brain and spinal cord
1. Astrocytes
x Largest glia t star-shaped
x Fills the space between neurons t results in close contact between neurons and
astrocytes and can affect the growth of neurons
x Blood-brain barrier t protective system that keeps the brain separate from the rest of
the body
x Nutritive and metabolic functions for neurons
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Chapter 2
x Regulates chemical content of extracellular space t because they envelop the synapse,
they can regulate how far neurotransmitters and other substances released by the
terminal button can spread
x Important in the storage of neurotransmitter
2. Oligodendrocytes
x Makes myelin for CNS t wraps their processes around most axons in brain and spinal
¾ Fatty substances that act to insulate axon
x Schwann Cells t makes myelin for PNS
x Note:
¾ Oligodendrocytes t can contribute myelin to many axons in CNS
¾ Schwann cells t can contribute only one segment of myelin to an axon
3. Microglia
x Smallest of glia
x Phagocytes that remove debris from nervous system t debris from injury, disease,
infection, aging
x Made outside of brain and spinal cord by macrophages
x Excessive activation results in neurodegenerative diseases t multiple sclerosis,
Communication within the Neuron: The Action Potential
x The electrical events that underlie the transmission (or inhibition) of information rely on the
balance of ions between the inside of the neuron (intracellular) and the outside of the neuron
¾ Resting Membrane Potential: -70mV
x At rest, the extracellular fluid contains high concentrations of Na+ and the intracellular fluid
contains a high concentration of K+
Properties that promote uneven distribution of ions at rest
1. Permeability of the cell membrane that covers the neuron
¾ Not permeable to all types of ions
¾ Ion channels t at rest K+ can readily cross membrane, whereas Na+ cannot easily enter
the neuron; however, given enough time, enough Na+ would sneak into the cell and
enough K+ would leak out of the neuron that would be homogeneous distribution of the
2. Neuron active transport of ions by the neuron
¾ Sodium-Potassium Pump t uses energy to actively import K+ and actively export Na+
o Exchanges three Na+ ions for two K+ ions that are outside the cell
x When a neurotransmitter diffuses across the synapse, it can open ion channels that allow the
rapid influx (inflow) of Na+ into the neuron and rapid efflux (outflow) of K+ from the neuron t
makes intracellular membrane more positive
x Depolarization: membrane potential moves from its resting state of about -70mV to -50mV
x Action Potential t results in the release of neurotransmitter that allows communication
between neurons
x Repolarization: neuron returns to resting state of -70mV; triggered by the opening of K+
channels and closing of Na+ channels
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