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

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


Synapse


Receivingneuron

Figure 7.10, step 2

Axonterminal

Vesicles

Synapticcleft


Synapse


Receivingneuron


Synaptic cleft


Transmitting neuron

Figure 7.10, step 3

Axonterminal

Vesicles

Synapticcleft


Synapse


Receivingneuron





Transmitting neuron

Figure 7.10, step 4

Axonterminal

Vesicles

Synapticcleft


Synapse


Receivingneuron






Transmitting neuron

Figure 7.10, step 5

Axonterminal

Vesicles

Synapticcleft


Synapse


Receivingneuron






Transmitting neuron

Receptor

Neurotransmitter

Na+

Ion channel opens

Figure 7.10, step 6

Axonterminal

Vesicles

Synapticcleft


Synapse


Receivingneuron






Transmitting neuron

Receptor

Neurotransmitter

Na+Na+



Figure 7.10, step 7

Axonterminal

Vesicles

Synapticcleft


Synapse


Receivingneuron






Transmitting neuron

Receptor

Neurotransmitter

Na+Na+



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

Documents

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