Transcript bio 342 human physiology

29 September
• Today
– Neurons
– Axonal transport
– Resting Membrane potential
• Next class
– Action potentials
– Conduction of action potentials
• Lab next week: Measuring action potential
conduction velocity in human ulnar nerve.
1QQ # 10 for 8:30 class
1. High levels of cortisol
a)
b)
c)
d)
e)
Can lead to weight loss
Can suppress inflammation
Are characteristic of Addison’s disease
Can be the result of prolonged sleep deprivation or pain
Are associated with subnormal sensitivity to EPI.
2. Which are expected of a 10 year old boy who develops
secondary hypersecretion of growth hormone?
a) He will have high levels of IGF in his plasma.
b) His GHRH level will be low
c) Bones of his face, hands and feet will grow disproportionately
large relative to the rest of his body
d) His hypothalamus is secreting excessive amounts of a tropic
hormone
1QQ # 10 for 9:30 class
1. A woman in menopause who is not receiving hormone
replacement therapy would be expected to
a)
b)
c)
d)
e)
Have high levels of estradiol
Have high levels of FSH
Have high levels of gonadotropin releasing hormone
Be at higher risk for breast cancer
Be at higher risk of osteoporosis.
2. Which are expected of a 10 year old boy who develops
primary hypersecretion of growth hormone?
a) He will have high levels of IGF in his plasma.
b) His GHRH level will be low
c) Bones of his face, hands and feet will grow disproportionately
large relative to the rest of his body
d) His hypothalamus is secreting excessive amounts of a tropic
hormone
S2
Ch 6 Nervous System Part A and B
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Ch 6 Part A: Basic terms
Cell types of Nervous Tissue
Components of a neuron
Components of a reflex arc
Axonal regeneration: PNS and CNS
Origin of resting membrane potential
Equilibrium Potentials (Nernst potentials)
S3
Important Terms (we’ll know these and many more as we
move through Chapter 6
Cell Body (soma)
Afferent Neuron
Astrocyte = Astroglia
Axon Terminal
Myelin
Dendrite
Microglia
Node of Ranvier
Neurotransmitter
Interneuron
Schwann cell
Axon with axon hillock
Oligodendrocyte
Synapse
Ependymal cell
Axonal pathfinding
Efferent Neuron
S4
Common symbols
CNS = Brain + Spinal Cord; PNS = axons & ganglia
S5
Nervous tissue = Neurons (for electrical signaling) and Glial cells (for...)
Know functions of CNS Glial cell types.
Schwann cells wrap axons in PNS
S6
Excitable membranes & special structures make
Neurons good Electrical Communicators
ligand-gated ion channels in membranes of
dendrites and soma…. Graded potentials
}
receiving
Axon hillock “integrates.”
Decremental conduction in
dendrites and somatic
membranes
Unidirectional Non-decremental
conduction in axons Synapse on
}
other neurons,
skeletal muscle,
smooth muscle,
cardiac muscle,
glands
sending
voltage-gated ion channels in membrane of axon hillock and axon…..
Action potentials = “all or nothing!”
S9
Nodes of Ranvier ~1mm apart
In PNS
Not all axons are
Fig. 06.02
myelinated, although all
axons are enveloped by
Schwann cells in CNS or
Oligodendrocytes in PNS
What are the advantages
of myelination?
In CNS
Lightly myelinated axon
S 10
Communication in The Vertebrate NS
Reflexes require
some part of the
CNS (i.e. frog lab)
Blood pressure
Blood gases and pH
Muscle stretch
Pain
Peripheral nerves are “mixed”
(have afferent & efferent axons)
Skin temperature
Hair movement
Light, Taste, Odor
Touch, Pain,
Temperature, Etc.
Signaling over short and long distances
Dimensions of neurons
S 11
If Nodes of Ranvier are 1 mm apart:
How many Schwann cells to
myelinate the 2 meters of a sensory
axon from hoof to dorsal root
ganglion near spinal cord?
How many oligodendries to
myelinate the 2 meters of the
sensory axon ascending in spinal
cord to brain?
Sensory (afferent)
neurons from hoof
to brain
Descending neurons
(interneurons) from brain to
spinal cord
S 12
Fig. 06.03
Orthograde =
anterograde
retrograde
Axonal Transport
• Orthograde = Anterograde = from soma
to terminals
– slow……1-2 mm/day
– fast …..200-400 mm/day (kinesin)
• Retrograde = from terminals to soma
– fast….200-400 mm/day (dynein)
• What gets transported and why?
• Axonal transport is too slow for rapid
signaling, so…
S 13
Who
Cares?
Alayna Davis
October 1992 Age 5 October 31, 1992
October 1998
Damaged axon of the Peripheral Nervous System regenerate about 1 mm per day
(dependent upon slow orthograde axonal transport!)
Regeneration in CNS?
So how can PNS axon
regenerate and what prevents
CNS axons from regenerating?
Bioelectricity is chemistry + physics
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Membrane potentials
Ohm’s law
Resting Membrane Potential
The Nernst Equation
The Goldman Equation
Fig. 06.07
From physics: Ohm’s Law Voltage = Current x Resistance
Fig. 06.08
Virtues of
Squid
Giant
Axon
Fig. 06.09
Fig. 06.10
Fig. 06.10a
There is a concentration gradient favoring the diffusion of
Na+ and K+ through the selectively permeable membrane
which has ion channels only for potassium.
Fig. 06.10b
With K+ channels open, K+ diffuses down its concentraiton
gradient, leaving behind CL- ions which are not permeable
through the membrane. As more and more K+ move to the
left, the compartment they leave becomes more and more
negatively charged.
Fig. 06.10c
Fig.
06.10d
Soon, the accumulation of negative charges seriously impeded the
diffusion of K+ as the electrostatic force builds up in opposition to the
concentration driving force.
Equilibrium potential = Nernst potential = diffusion potential
Fig. 06.10e
E ion+ = 61/Z log ([conc outside]/ [conc inside])
E K+
E K+
= 61/1 log (5/150)
= -90 mV
Eventually, the electrostatic force that impedes diffusion of K+ is exactly
equal to the driving force favoring diffusion based on a concentration
gradient. When these two driving forces are equal and opposite, the
membrane potential reaches an equilibrium at which the voltage is called
So which compartment corresponds to intracellular fluid?
The Nernst Equation
• Calculate the membrane potential if only
one ion species is permeable and the
concentrations are known on both sides of
the membrane.