neurons = nerve cells the major function of nerve cells is to transmit messages (nerve impulses)...
TRANSCRIPT
Neurons = nerve cells The major function of nerve cells is to
transmit messages (nerve impulses) from one part of the body to another.
◦ Major regions of neurons Cell body —nucleus and
metabolic center of the cell
Processes —fibers that extend from the cell body
◦ Major regions of neurons Cell body —nucleus and
metabolic center of the cell
Processes —fibers that extend from the cell body
Dendrites and Axons
Some Functions: 1.supporting cells act as phaogcytes2.protect and myelinate 3.act as a selective barrier between the
capillary blood supply and neurons
See the next 5 slides for details of support cells
Astrocytes◦ Abundant, star-shaped cells◦ Brace neurons◦ Form barrier between capillaries and neurons◦ Control the chemical environment of
the brain
Microglia◦ Spiderlike phagocytes◦ Dispose of debris
Ependymal cells◦ Line cavities of the brain and spinal cord◦ Circulate cerebrospinal fluid
Oligodendrocytes◦ Wrap around nerve fibers in the central nervous
system◦ Produce myelin sheaths
Satellite cells◦ Protect neuron cell bodies
Schwann cells◦ Form myelin sheath in the peripheral nervous
system
Central nervous system (CNS)◦ Brain◦ Spinal cord
Peripheral nervous system (PNS)◦ Nerves outside the brain and spinal cord
Spinal nerves Cranial nerves
Figure 7.6
Nuclei- collections of cell bodies inside the central nervous system
Ganglion—collection of cell bodies outside the central nervous system
Tract – cranial and spinal nerves ( nerve process in CNS)
Nerves – nerve processes outside the CNS (in the PNS)
Terms for collections of nerve cell bodies and collections of nerve fibers
Sensory (afferent) neurons◦ Carry impulses from the sensory receptors to the
CNS Cutaneous sense organs Proprioceptors—detect stretch or tension
Motor (efferent) neurons◦ Carry impulses from the central nervous system
to viscera, muscles, or glands Interneurons (association neurons)
◦ Found in neural pathways in the central nervous system
◦ Connect sensory and motor neurons
Axonal terminals contain vesicles with neurotransmitters-chemical released by axon terminals
Axonal terminals are separated from the next neuron by a gap◦ Synaptic cleft—gap between adjacent neurons◦ Synapse—junction or point of close contact
between neurons
Myelin sheath—whitish, fatty material covering axons
Schwann cells—produce myelin sheaths in jelly roll–like fashion
Nodes of Ranvier—gaps in myelin sheath along the axon
Multipolar neuron have several processes extending from its cell body
All motor neurons and interneurons!
Neurons have only ONE axon that carries impulses away from the nerve cell body toward the synapse
Bipolar neurons—one axon and one dendrite
Found in eyes and nose as receptor cells
Figure 7.8b
Unipolar neurons—have a short single process leaving the cell body
Sensory neurons found in PNS ganglia
Figure 7.8c
Figure 7.5
Axons in the PNS are myelinated by special supporting cells called Schwann cells, which may wrap themselves tightly around the axon in jelly roll fashion so that when the process is completed, a tight core of plasma membrane material called myelin sheath encompasses the axon. The Schwann cell nucleus and the bulk of its cytoplasm end up just beneath the outermost portion of the plamsa membrane. The part of the schwann cell which is external to the myelin sheath, is referred to as the neurilemma.
Stimulus at distalend of neuron
Skin Spinal cord(in cross section)
Interneuron
Receptor
Effector
Sensory neuron
Motor neuron
Integrationcenter
(a)
Resting neuron◦ The plasma membrane at rest is polarized◦ Fewer positive ions are inside the cell than
outside the cell Depolarization
◦ A stimulus depolarizes the neuron’s membrane◦ A depolarized membrane allows sodium (Na+) to
flow inside the membrane◦ Reversal of the resting potential owing to an
influx of sodium ions Depolarization initiates an action potential
in the neuron----BUT only if the stimulus is greater than the threshold intensity
Figure 7.9a–b
Action potential◦ If the action potential (nerve impulse) starts, it is
propagated over the entire axon◦ Impulses travel faster when fibers have a myelin
sheath◦ Transmission of the depolarized wave along the
neural membrane
Figure 7.9c–d
Repolarization◦ Potassium ions rush out of the neuron after
sodium ions rush in, which repolarizes the membrane
◦ Period during which potassium ions are diffusing out of the neuron
sodium-potassium pump, mechanism that restores the resting membrane voltage and intracellular ionic concentrations using ATP
Figure 7.9e–f
Impulses are able to cross the synapse to another nerve◦ Neurotransmitter is released from a nerve’s axon
terminal◦ The dendrite of the next neuron has receptors
that are stimulated by the neurotransmitter◦ An action potential is started in the dendrite
Figure 7.10
Axonterminal
Vesicles
Synapticcleft
Actionpotentialarrives
Synapse
Axon oftransmittingneuron
Receivingneuron
Neurotrans-mitter is re-leased intosynaptic cleft
Neurotrans-mitter bindsto receptoron receivingneuron’smembrane
Vesiclefuses withplasmamembrane
Synaptic cleftNeurotransmittermolecules
Ion channels Receiving neuron
Transmitting neuron
Receptor
Neurotransmitter
Na+
Na+
Neurotransmitterbroken downand released
Ion channel opens Ion channel closes
Figure 7.10, step 1
Axonterminal
Vesicles
Synapticcleft
Actionpotentialarrives
Synapse
Axon oftransmittingneuron
Receivingneuron
Figure 7.10, step 2
Axonterminal
Vesicles
Synapticcleft
Actionpotentialarrives
Synapse
Axon oftransmittingneuron
Receivingneuron
Vesiclefuses withplasmamembrane
Synaptic cleft
Ion channels Receiving neuron
Transmitting neuron
Figure 7.10, step 3
Axonterminal
Vesicles
Synapticcleft
Actionpotentialarrives
Synapse
Axon oftransmittingneuron
Receivingneuron
Neurotrans-mitter is re-leased intosynaptic cleft
Vesiclefuses withplasmamembrane
Synaptic cleftNeurotransmittermolecules
Ion channels Receiving neuron
Transmitting neuron
Figure 7.10, step 4
Axonterminal
Vesicles
Synapticcleft
Actionpotentialarrives
Synapse
Axon oftransmittingneuron
Receivingneuron
Neurotrans-mitter is re-leased intosynaptic cleft
Neurotrans-mitter bindsto receptoron receivingneuron’smembrane
Vesiclefuses withplasmamembrane
Synaptic cleftNeurotransmittermolecules
Ion channels Receiving neuron
Transmitting neuron
Figure 7.10, step 5
Axonterminal
Vesicles
Synapticcleft
Actionpotentialarrives
Synapse
Axon oftransmittingneuron
Receivingneuron
Neurotrans-mitter is re-leased intosynaptic cleft
Neurotrans-mitter bindsto receptoron receivingneuron’smembrane
Vesiclefuses withplasmamembrane
Synaptic cleftNeurotransmittermolecules
Ion channels Receiving neuron
Transmitting neuron
Receptor
Neurotransmitter
Na+
Ion channel opens
Figure 7.10, step 6
Axonterminal
Vesicles
Synapticcleft
Actionpotentialarrives
Synapse
Axon oftransmittingneuron
Receivingneuron
Neurotrans-mitter is re-leased intosynaptic cleft
Neurotrans-mitter bindsto receptoron receivingneuron’smembrane
Vesiclefuses withplasmamembrane
Synaptic cleftNeurotransmittermolecules
Ion channels Receiving neuron
Transmitting neuron
Receptor
Neurotransmitter
Na+Na+
Neurotransmitterbroken downand released
Ion channel opens Ion channel closes
Figure 7.10, step 7
Axonterminal
Vesicles
Synapticcleft
Actionpotentialarrives
Synapse
Axon oftransmittingneuron
Receivingneuron
Neurotrans-mitter is re-leased intosynaptic cleft
Neurotrans-mitter bindsto receptoron receivingneuron’smembrane
Vesiclefuses withplasmamembrane
Synaptic cleftNeurotransmittermolecules
Ion channels Receiving neuron
Transmitting neuron
Receptor
Neurotransmitter
Na+Na+
Neurotransmitterbroken downand released
Ion channel opens Ion channel closes
Figure 7.23
Endoneurium surrounds each fiber
Groups of fibers are bound into fascicles by perineurium
Fascicles are bound together by epineurium
The connective tissue wrappings help insulate the nerve.
A bundle of neuron fibers or processes that extends to and/or from the CNS and visceral organs or structures of the body periphery such as skeletal muscle, glands, and skin
Mixed nerves◦ Carry both sensory and motor fibers
Sensory (afferent) nerves◦ Carry impulses toward the CNS
Motor (efferent) nerves◦ Carry impulses away from the CNS