Campbells Ap Biology Chapter 48 Notes Essay Example

of information processing are illustrated in the knee-jerk reflex

Oligodendrocytes (in the CNS) and Schwann cells (in the PNS) are glia that form the myelin sheaths around the axons of many vertebrate neurons 48. 2:

1. Ion pumps and ion channels maintain the resting potential of a neuron
2. Across its plasma membrane, every cell has a voltage called a membrane potential
3. The inside of a cell is negative relative to the outside
4. The membrane potential of a cell can be measured The resting potential is the membrane potential of a neuron that is not transmitting signals
5. In all neurons, the resting potential depends on the ionic gradients that exist across the plasma membrane
6. The concentration of Na+ is higher in the extracellular fluid than in the cytosol while the opposite is true for K+
7. By modeling a mammalian neuron with an artificial membrane we can gain a better understanding of the resting potential of a neuron
8. A neuron that is not transmitting signals contains many open K+ channels and fewer open Na+ channels in its
   

plasma membrane

Gated ion channels open or close, in response to membrane stretch or the binding of a specific ligand and in response to a change in the membrane potential 48. 3:

1. Action potentials are the signals conducted by axons If a cell has gated ion channels its membrane potential may change in response to stimuli that open or close those channels
2. Some stimuli trigger a hyperpolarization an increase in the magnitude of the membrane potential
3. Other stimuli trigger a depolarization a reduction in the magnitude of the membrane potential
4. Hyperpolarization and depolarization are both called graded potentials because the magnitude of the change in membrane potential varies with the strength of the stimulus
5. In most neurons, depolarizations are graded only up to a certain membrane voltage, called the threshold
6. A stimulus strong enough to produce a epolarization that reaches the threshold triggers a different type of response, called an action potential
7. An action potential is a brief all-or-none depolarization of a neuron’s plasma membrane and is the type of signal that carries information along axons
8. Both voltage-gated Na+ channels and voltage-gated K+ channels are involved in the production of an action potential
9. When a stimulus depolarizes the membrane Na+ channels open, allowing Na+ to diffuse into the cell
10. As the action potential subsides K+ channels open, and K+ flows out of the cell
11. A refractory period follows the action potential during which a second action potential cannot be initiated
12. An action potential can travel long distances by regenerating itself along the axon
13. At
    

the site where the action potential is generated, usually the axon hillock an electrical current depolarizes the neighboring region of the axon membrane

Action potentials in myelinated axons jump between the nodes of Ranvier in a process called saltatory conduction 48. 4:

1. Neurons communicate with other cells at synapses
2. In an electrical synapse electrical current flows directly from one cell to another via a gap junction
3. The vast majority of synapses are chemical synapses In a chemical synapse, a presynaptic neuron releases chemical neurotransmitters, which are stored in the synaptic terminal
4. When an action potential reaches a terminal the final result is the release of neurotransmitters into the synaptic cleft
5. The process of direct synaptic transmission involves the binding of neurotransmitters to ligand-gated ion channels
6. Neurotransmitter binding causes the ion channels to open, generating a postsynaptic potential
7. Postsynaptic potentials fall into two categories: excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs)
8. After its release, the neurotransmitter diffuses out of the synaptic cleft and may be taken up by surrounding cells and degraded by enzymes
9. Unlike action potentials postsynaptic potentials are graded and do not regenerate themselves
10. Since most neurons have many synapses on their dendrites and ell body a single EPSP is usually too small to trigger an action potential in a postsynaptic neuron
11. If two EPSPs are produced in rapid succession an effect called temporal summation occurs
12. In spatial summation EPSPs produced nearly simultaneously by different synapses on the same postsynaptic neuron add together
13. Through summation
    

an IPSP can counter the effect of an EPSP

Gases such as nitric oxide and carbon monoxide are local regulators in the PNS 48. 5:

1. The vertebrate nervous system is regionally specialized
2. In all vertebrates, the nervous system shows a high degree of cephalization and distinct CNS and PNS components
3. The brain provides the integrative power that underlies the complex behavior of vertebrates
4. The spinal cord integrates simple responses to certain kinds of stimuli and conveys information to and from the brain
5. The central canal of the spinal cord and the four ventricles of the brain are hollow, since they are derived from the dorsal embryonic nerve cord
6. The PNS transmits information to and from the CNS and plays a large role in regulating a vertebrate’s movement and internal environment
7. The cranial nerves originate in the brain and terminate mostly in organs of the head and upper body
8. The spinal nerves originate in the spinal cord and extend to parts of the body below the head
9. The PNS can be divided into two functional components the somatic nervous system and
   

the autonomic nervous system

main output center for motor information leaving the cerebrum

left hemisphere becomes more adept at language, math, logical operations, and the processing of serial sequences

Modern brain-imaging techniques suggest that consciousness may be an emergent property of the brain that is based on activity in many areas of the cortex 48. 6:

1. CNS injuries and diseases are the focus of much research
2. Unlike the PNS, the mammalian CNS cannot repair itself when damaged or assaulted by disease
3. Current research on nerve cell development and stem cells may one day make it possible for physicians to repair or
   

replace damaged neurons

caused by the death of dopamine-secreting neurons in the substantia nigra and is characterized by difficulty in initiating movements, slowness of movement, and rigidity