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Chapter 44 Neurons and Nervous Systems
Fear and survival in the brain
-amygdala is the brain’s center for emotion and memory of fear
-when cells in amygdale are activated, heart beats faster, breathing becomes rapid and shallow,
hands get cold and clammy
-a person with amygdale does not have reflex to pull away from a threat
has trouble engaging in normal social relationship
cannot read nature, mood, or intentions of other by reading their facial expression
What Cells are Unique to the nervous System?
-nervous systems are composed of neurons and glia
-neurons are excitable and can generate and send action potential
-extensions of neuron are axons, which conduct action potential over long distance
-glia do not conduct action potentials
-support neurons physically and metabolically
-nerve is a bundle of axons that come from many neurons
-neurons are organized into 3 categories of cells
1) input, 2) integration, 3) output
-afferent neurons carry sensory information into nervous system
-sensory information comes from sensory neurons that convert input into action potential
-efferent neurons carry commands to effectors, like muscles and glands
-interneurons integrate information and facilitate communication between sensors and effectors
Neuronal networks range in complexity
-cnidarian’s nerve net is developed around tentacles and oral opening
facilitate detection of food or danger that causes tentacles to extend or retract
-ganglia are clusters of a number of neurons
-animals that are bilaterally symmetrical, ganglia come in pair, one on each side of the body
-in complex animals, one pair of ganglia is larger than the others
-in vertebrates, most cells of the nervous system are found in brain and spinal cord
-brain and spinal cord are called central nervous system (CNS)
-information is transmitted from sensory cells to central nervous system and from central
nervous system to effectors
-neurons that extend outside of brain and spinal cord are called peripheral nervous system (PNS)
-synapses are the gap between two neurons
-presynaptic neuron is the cell that sends the message
-postsynaptic neuron is the cell that receives message
Neurons are the functional units of nervous systems
-neurons have 4 regions: cell body, dendrites, axon, and axon terminals
-cell body contains nucleus and most of the cell’s organelles, projection sprout from cell body
-dendrites are the projection that brings information from other neurons to the cell body
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-axon is a projection as well and is the longest
carry information away from cell body
action potential is conducted along axon to target cell
-axon terminal is the tip of the branching nerve ending of axon
form synapse with the target cell
-synapse separates presynaptic and postsynaptic membranes
-action potential at axon terminal causes release of neurotransmitter, a chemical messenger
molecule
-neurotransmitter binds to the receptor of the target cell
Glial cells are also important components of nervous system
-amount of glial cells is greater than that of neurons
are not excitable and do not transmit electrical singles
physically support and orient neurons to help them make the right contacts in embryonic
development
supply neurons with nutrients, maintain extracellular environment, consume foreign particles
and cellular debris, or insulate axons
-oligodendrocytes are glia in CNS
wrap around axon of neuron, covering them with concentric layers of insulating plasma
membrane
-Schwann cells are glia in the PNS that perform this function
-myelin is the covering produced by oligodendrocytes and Schwann cells
-axons are myelinated to conduct action potentials more rapidly
-astrocytes contribute to blood-brain barrier, protects brain from toxic chemicals in the blood
surround small and permeable blood vessels in the brain
-the barrier is permeable to fat-soluble substance, like anesthetics and alcohol
How do Neurons Generate and Conduct Signals?
-action potential are generated when ion channels in plasma membrane of neurons open and
permit ion to move across the membrane
-movement of ions is driven by difference in concentration gradient and electrical charge
difference on two sides of membrane
-at rest, inside neuron is electrically negative compared to outside
-membrane potential is difference in electric potential across plasma membrane, measured in
millivolt
-resting potential is when neuron is resting and not firing action potential
Simple electrical concepts underlie neuronal function
-voltage is electric potential difference
a force that causes electrically charged particles to move between two points
-major ions across plasma membranes of neurons are sodium (Na+), potassium (K+), calcium
(Ca2+) and chloride (Cl-)
Membrane potentials can be measured with electrodes
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Document Summary

Amygdala is the brain"s center for emotion and memory of fear. When cells in amygdale are activated, heart beats faster, breathing becomes rapid and shallow, hands get cold and clammy. A person with amygdale does not have reflex to pull away from a threat. cannot read nature, mood, or intentions of other by reading their facial expression. Nervous systems are composed of neurons and glia. Neurons are excitable and can generate and send action potential. Extensions of neuron are axons, which conduct action potential over long distance. Nerve is a bundle of axons that come from many neurons. Neurons are organized into 3 categories of cells: input, 2) integration, 3) output. Afferent neurons carry sensory information into nervous system. Sensory information comes from sensory neurons that convert input into action potential. Efferent neurons carry commands to effectors, like muscles and glands. Interneurons integrate information and facilitate communication between sensors and effectors.

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