6. NEURONS VS. OTHER CELLS IN THE BODY
NEURONS ARE SIMILAR TO OTHER CELLS IN THE BODY BECAUSE:
• Neurons are surrounded by a cell membrane.
• Neurons have a nucleus that contains genes.
• Neurons contain cytoplasm, mitochondria and other
organelles.
• Neurons carry out basic cellular processes such as
protein synthesis and energy production.
NEURONS DIFFER FROM OTHER CELLS IN THE BODY BECAUSE:
• Neurons have specialized extensions called dendrites
and axons. Dendrites bring information to the cell body
and axons take information away from the cell body.
• Neurons communicate with each other through an
electrochemical process.
• Neurons contain some specialized structures (for
example, synapses) and chemicals (for
example, neurotransmitters).
10. THREE GENERAL CATEGORIES OF NEURONS
SENSORY NEURON INTERNEURON MOTOR NEURON
Long dendrites and Short dendrites and Short dendrites and
LENGTH OF FIBERS
short axon short or long axon long axon
Cell body and
Dendrites and the
dendrite are
cell body are
outside of the
Entirely within the located in the
LOCATION spinal cord; the cell
spinal cord or CNS spinal cord; the
body is located in
axon is outside of
a dorsal root
the spinal cord
ganglion
Interconnect the
Conduct impulse to
Conduct impulse to sensory neuron with
FUNCTION an effector (muscle
the spinal cord appropriate motor
or gland)
neuron
21. DENDRITES VS. AXON
Take information away Bring information to the
from the cell body cell body
Rough Surface (dendritic
Smooth Surface
spines)
Generally only 1 axon per Usually many dendrites
cell per cell
No ribosomes Have ribosomes
Can have myelin No myelin insulation
Branch further from the Branch near the cell
cell body body
When a neuron is not sending a signal, it is "at rest." When a neuron is at rest, the inside of the neuron is negative relative to the outside. Although the concentrations of the different ions attempt to balance out on both sides of the membrane, they cannot because the cell membrane allows only some ions to pass through channels (ion channels).
The resting membrane potential of a neuron is about -70 mV (mV=millivolt) - this means that the inside of the neuron is 70 mV less than the outside.
The resting potential tells about what happens when a neuron is at rest. An action potential occurs when a neuron sends information down an axon, away from the cell body. Neuroscientists use other words, such as a "spike" or an "impulse" for the action potential.
The resting potential tells about what happens when a neuron is at rest. An action potential occurs when a neuron sends information down an axon, away from the cell body. Neuroscientists use other words, such as a "spike" or an "impulse" for the action potential. If the neuron does not reach this critical threshold level, then no action potential will fire. Also, when the threshold level is reached, an action potential of a fixed sized will always fire...for any given neuron, the size of the action potential is always the same. There are no big or small action potentials in one nerve cell - all action potentials are the same size. Therefore, the neuron either does not reach the threshold or a full action potential is fired - this is the "ALL OR NONE" principle.
Because there are many more sodium ions on the outside, and the inside of the neuron is negative relative to the outside, sodium ions rush into the neuron. Remember, sodium has a positive charge, so the neuron becomes more positive and becomes depolarized.The action potential actually goes past -70 mV (a hyperpolarization) because the potassium channels stay open a bit too long.
The vesicle membrane will fuse with the presynaptic membrane releasing the neurotransmitters into the synaptic cleft. Until recently, it was thought that a neuron produced and released only one type of neurotransmitter. This was called "Dale's Law." However, there is now evidence that neurons can contain and release more than one kind of neurotransmitter.
Diffusion of Neurotransmitters Across the Synaptic CleftThe neurotransmitter molecules then diffuse across the synaptic cleft where they can bind with receptor sites on the postsynaptic ending to influence the electrical response in the postsynaptic neuron. In the figure on the right, the postsynaptic ending is a dendrite (axodendritic synapse), but synapses can occur on axons (axoaxonic synapse) and cell bodies (axosomatic synapse).When a neurotransmitter binds to a receptor on the postsynaptic side of the synapse, it changes the postsynaptic cell's excitability: it makes the postsynaptic cell either more or less likely to fire an action potential. If the number of excitatory postsynaptic events is large enough, they will add to cause an action potential in the postsynaptic cell and a continuation of the "message."
Diffusion of Neurotransmitters Across the Synaptic CleftThe neurotransmitter molecules then diffuse across the synaptic cleft where they can bind with receptor sites on the postsynaptic ending to influence the electrical response in the postsynaptic neuron. In the figure on the right, the postsynaptic ending is a dendrite (axodendritic synapse), but synapses can occur on axons (axoaxonic synapse) and cell bodies (axosomatic synapse).When a neurotransmitter binds to a receptor on the postsynaptic side of the synapse, it changes the postsynaptic cell's excitability: it makes the postsynaptic cell either more or less likely to fire an action potential. If the number of excitatory postsynaptic events is large enough, they will add to cause an action potential in the postsynaptic cell and a continuation of the "message."
Diffusion of Neurotransmitters Across the Synaptic CleftThe neurotransmitter molecules then diffuse across the synaptic cleft where they can bind with receptor sites on the postsynaptic ending to influence the electrical response in the postsynaptic neuron. In the figure on the right, the postsynaptic ending is a dendrite (axodendritic synapse), but synapses can occur on axons (axoaxonic synapse) and cell bodies (axosomatic synapse).When a neurotransmitter binds to a receptor on the postsynaptic side of the synapse, it changes the postsynaptic cell's excitability: it makes the postsynaptic cell either more or less likely to fire an action potential. If the number of excitatory postsynaptic events is large enough, they will add to cause an action potential in the postsynaptic cell and a continuation of the "message."
