Transcript chapter 8 neuronal physiology A

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Response and feedback loops: setpoints
Speed and specificity of control systems
Patterns of control pathways
The organization of the nervous system
Neurons
Midterm test:
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Monday Oct. 7: 8:30 – 9:20
multiple choice questions
Location: A- P in the Education Gym
Q-Z in Erie Hall (lecture hall)
Nervous system
• Neurons
• Glial cells
• Electrical signals
– Membrane potential
– Ion movements
– Gated channels
– Graded potentials
Cells of the nervous system:
-neuron
Axonal transport of membranous organelles
Glial cells
Electrical signals
• Neurons are excitable cells, can propagate
electrical signals.
• As all other cells, neurons have a resting
membrane potential
As all other cells, neurons have a
resting membrane potential
Electrochemical gradients: Ca++ and Na++ concentrations are higher extracellular
than intracellular.
Intracellular K+ concentration is higher than extracellular
K+ outward current is much stronger than Na+ inward current.
Lots of K+ channels are open, few Na+ channels are open at rest.
Factors that influence the
membrane potential
• Concentration gradient of ions across the
membrane
• Membrane permeability to ions (channels)
• If these change, the membrane potential
changes
Ion movement across the cell
membrane creates electrical signals
• If Na channels open,
Na+ enters the cell
down its
electrochemical
gradient.
Depolarization when Na+ channels
open: electrical signal
Ion movement causes hyperpolarizaton.
Outward K+ movement.
Inward Cl- movement
Channel families
• Selective ion channels:
– Na channels
– K+ channels
– Ca++ channels
– Cl- channels
– monovalent cation selective channels (allow
both Na+ and K+)
How are channels opened or
closed?
• Leaky channels are open most of the time
• Mechanically gated channels
• Chemically gated channels (e.g. opened
by neurotransmitters)
• Voltage gated channels
Graded potentials
• Ions move across
membrane when
channels open
 Vm changes.
Graded potentials
• Amplitude depends on the strength of the
stimulus
Graded potentials
• Spread across the membrane
• Diminish away from origin
Graded potentials
Spread across the membrane
Diminish away from origin
Setpoints can vary
• Acclimatization – adaptation to a given set of
environmental conditions (first day of spring like
weather)
• Acclimation – adaptation to laboratory setting
Endocrine and Nervous Reflexes
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Specificity of target cells
Nature of signal
Speed
Duration of action
Stimulus intensity coding
Specificity of target cells
A neuron has a specific target cell. Many tissues may have receptor proteins for
a hormone and may respond to the hormone.
Nature of signal
In neurons,
electrical signals travel
long distances and
chemical signals (neurotransmitters)
move to the target cell.
Nature of signal
The endocrine system uses chemical signals.
Nature of signal: Neuroendocrine:
Electrical signals travel long distances and
chemical signals (neurohormones) move into blood
vessels.
Speed
• Electrical signals conducted very quickly
• Rapid signal transduction with many
neurotransmitters
• Hormones move by diffusion from
endocrine cell to target (slower)
• Some responses take quite a long time
Duration of action
• Nervous control is shorter than endocrine
control
• Nervous – usually neurotransmitter is
rapidly removed
Stimulus intensity coding
• Intensity is coded by neuronal firing
frequency amount of neurotransmitter
• The amount hormone that is released
codes the intensity.
Knee jerk reflex
Lactation, oxytocin
Autonomic stimulation
of insulin release
Growth hormone
Testosterone
Low glucose
and beta cells
Organization of the nervous system
• Sensory Receptors  afferent pathway 
central nervous system (CNS, brain and
spinal cord  efferent neurons (peripheral
nervous system PNS) target
• PNS:
– Somatic motor division
– Autonomic division:
– Sympathetic
– Parasympathetic
Cells of the nervous system:
-neuron