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Neural Tissue
Parts list
Overview: Nervous system
functions
1. Sensory input (info travels “in” along
afferent pathways)
–
Sensory neurons
2. Integration (information is processed)
–
Spinal cord and brain
3. Motor output (info results in a response,
travels along efferent pathways)
–
Stimulation of skeletal muscle, smooth
muscle, cardiac muscle, & glands
Sensory-Motor Pathways
Overview
Neural tissue: specialized
cells
• Neurons
• Supporting cells (non-excitable cells)
or neuroglia; outnumber neurons 10 to
1
• Blood vessels
• Connective tissue
Neurons
• Specialized cells that communicate
with other cells via changes in the
membrane potential and synaptic
connections
• Characteristics:
– Extremely long-lived (> 100yrs)
– Amitotic
– Extremely high metabolic rate
Typical Neuron
Neurons have special names
for cell structures
• Cell body: contains the nucleus
• Perikaryon: cytoplasm around the
nucleus
• Nissl bodies are localized RER and
ribosomes
Typical motor neuron
Synapse of a motor neuron
Classified by structure
Classified by function
(sensory or motor)
Neuroglia are supporting
cells
Neuroglia are supporting cells
Wandering police
force
CNS
Regulating/recycling/maintaining
Circulate CSF
PNS
myelinate axons
Ependymal cells make and
help circulate CSF
Schwann cells in PNS
Nerve regeneration is assisted
by Schwann cells
Neurophysiology
Overview
Neurons are excitable cells
• Have we talked about a model in another
cell for propagation of an impulse?
• How does the chemical composition of the
cell membrane promote a separation of
ions?
• Which ions are in greater concentration
inside the cell? Outside the cell?
Electrochemical gradient
• A charge difference exists, like between poles of a
battery.
• Intracellular: high concentration of K+ ions &
negatively charged proteins
• Extracellular: high concentration of Na+ & Cl- ions
Two gradients =
• The sum of the chemical and electrical
forces acting across the membrane =
Electrochemical gradient (AKA
membrane potential)
• Size of the potential difference is
measured in milliVolts (mV)
• Neurons have a resting transmembrane
potential of approx. -70mV
Resting Membrane Potential
Electrochemical gradient
Ion diffusion in neurons
• Ions are always diffusing, BUT can cross
membrane quickly ONLY through channels
• Types of channels
– Passive or leak channels (ungated; always
open)
– Active or gated channels (always closed,
unless…)
Gated Channels
• Chemically regulated: Respond to presence
of particular chemicals
• Voltage regulated: respond to changes in
membrane potential
• Mechanically regulated: respond to
physical deformation
Have we seen examples of these channels
in other tissue?
Gated Channels
chemical
electrical
mechanical
If gated channels open…
• What happens to the transmembrane
potential?
Graded Potential
• A change in the transmembrane potential
that does not travel far from the area
of stimulation
• Definitions
– Depolarization: shift towards 0mV
– Repolarization: shift towards the resting
membrane potential (~-60mV)
– Hyperpolarization: membrane becomes more
negative
Graded Potential
Graded Potential
Graded Potential
Action Potential
• Propagated changes in the
transmembrane potential that affect an
entire excitable membrane and results
in release of a neurotransmitter
• ALL OR NOTHING response.
Action Potential
Action Potential
AP Propagation