Chapter 10 - LO

Explain how information passes from a presynaptic neuron to a postsynaptic cell.

-Action potential arrives at the end of the axon of the presynaptic neuron -Ca channels open allowing Ca into the neuron -Ca causes cytoskeleton to move the synaptic vesicles to the cell membrane and causes them to fuse with it. -Neurotransmitters are released from the synaptic vesicles into the synaptic cleft. -Neurotransmitters bind to chemically gated channels in the post synaptic cleft. -Chemically gated channels open allowing either Na ions to flow in (excitatory) or Cl ions in or K ions out (inhibitory) -If the membrane depolarizes to its threshold value, voltage gated ion channels open allowing Na to flow in and an action potential is generated. -The neurotransmitters are either enzymatically broken down or are reabsorbed by the presynaptic neuron to reduce the neurotransmitters level in the cleft and stop the signaling to the post synaptic neuron.

Describe the general functions of the nervous system.

- Detecting a change in the environment (outside or inside of the body) - Processing the information and deciding what to do. - Sending out signals to different body parts to take action

Distinguish between the sources of white matter and gray matter.

- Gray matter is nervous tissue that is rich in cell bodies - White matter is nervous tissue that is rich in myelinated axons

Identify the types of neuroglia in the central nervous system and their functions.

-Astorcyte- star shaped cells, between neurons and blood vessels, support and use concentration gradient into the nervous tissue. -Oligodendrocytes- Myelination increases speed of nerve signaling, Damage to Oligodendrocytes implicated in multiple sclerosis, and cerebral palsy microglial- 20% of glial cells, Macrophage of Brain (immune system cells do not get into brain) -Ependymal-Epithelial cells lining ventricles, Ciliated simple cuboidal, Regulate composition of cerebral spinal fluid

Describe the events leading to the generation of an action potential.

Sodium Potassium Pump: -Cell needs to export a solute it does not need like Na+. -Every time the pump cycles 1 ion is transported out of the cell. -K+ diffuse out very fast -Na+ diffuse in slowly Resting Membrane Potential: -Gated channels closed -K+ pore open, K+ leaking out -Inside of cell net negative to outside Depolarization: -Na+ gated channel opens, Na+ flows in. -Inside of cell becomes net positive to outside Repolarization: -Na+ gated channel closes -K+ gated channel opens, K+ flows out of cell. -Na+ also pumped out as part of Na/K pump. -Inside of cell becomes net negative again. Local Potential Changes

Explain how a cell membrane becomes polarized.

The Na/K ATP pump moves three Na ions out for every two K ions moved in for a net movement of one positive charge out of the cell. Also K ion channels allow K ions to leak out of the cell increasing the polarization of the membrane.

Identify the two major groups of nervous system organs.

The central nervous system contains the brain and spinal cord. The peripheral nervous system contains cranial nerves and spinal nerves and also connects the central nervous system to other body parts.

Explain what prevents a postsynaptic cell from being continuously stimulated.

The neurotransmitters are either broken down by enzymes or they are pumped back into the presynaptic neuron.

Identify the two types of cells that comprise nervous tissue.

The two types of cells that comprise nervous tissue are neurons and neuroglia. Neurons are nerve cells. Neuroglia produce myelin, maintain the ionic environment, provide growth factors and support neurons, provide structural support, and play a role in cell-to-cell communication.

Explain how action potentials move down an axon.

Axons are capable of action potentials, but the cell body and dendrites are not. An action potential at the trigger zone causes an electrical current to flow a short distance down the axon, which stimulates the adjacent membrane to reach its threshold level, triggering another action potential. The second action potential causes another electric current to flow farther down the axon. This sequence of events results in a series of action potentials occurring sequentially all the way to the end of the axon without decreasing in amplitude, even if the axon branches. The propagation of action potentials continues along the axon.

Describe the parts of a neuron.

Cell body: •Neurofilaments •Chromatophilic substance Dendrites Axon: •Axon hillock •Collaterals •Axon terminal •Synaptic knob

Identify the changes in membrane potential associated with excitatory and inhibitory neurotransmitters.

Neurons are excitable, meaning they can respond to changes in their environment. Some neurons detect temperature, light, or pressure outside of the body, while others respond to signals inside the body usually from other neurons. Such changes usually affect the membrane potential in the region of the membrane exposed to the stimulus, causing a local potential change. Usually, the environmental change affects the membrane potential by opening a gated ion channel. The effect depends on the ion that can pass through the channel. If the membrane potential becomes more negative than the resting potential, the membrane is hyperpolarized. If the membrane becomes less negative than the resting potential, the membrane is depolarized. The degree of change in the resting potential is directly proportional to the intensity of the stimulation. If neurons are sufficiently depolarized, the membrane potential reaches a level called the threshold potential. If threshold is reached, an action potential results.

Describe the basic ways in which the nervous system processes information

Neurons can "add" several different stimuli together since excitatory stimuli depolarize the membranes while inhibitory stimuli hyperpolarize the membrane. A decision is reached when the threshold value is either achieved (in which case an action potential is generated) or not achieved (in which case no action potential is generated). Neurons can also amplify the signal by having one neuron stimulate more than one neuron.

Describe the role of Schwann cells in the peripheral nervous system.

Schwann cells myelinate the peripheral nerves thus increasing the speed of impulse conduction. They also help support the neurons by removing excess ions. They also are involved in axon regeneration by guiding the regenerating axons to the correct location.

List the functions of sensory receptors.

Sensory receptors gather information by detecting changes and then bring those signals to the central nervous system.

Identify structural and functional differences among neurons.

Structural differences -Multipolar - found in CNS and motor neurons - bipolar - found in retina, auditory nerves and nasal cavity - Pseudo-unipolar - found in other sensory nerves Functional differences - Sensory neurons (afferent) bring impulses to the CNS from the sensory organs - Motor neurons (efferent) conduct impulses away from the CNS to effectors in the body - Interneurons (association or internuncial) In the CNS and relay impulses from one neuron to another

Describe the relationships among myelin, the neurilemma and nodes of Ranvier.

Surrounding larger axons and dendrites of peripheral nerves are sheaths of neuroglial cells called Schwann cells. These cells are wound tightly around the fibers and, as a result, the cell membranes are layered closely together with little or no cytoplasm between them. The layers are composed of a lipoprotein called myelin, which forms a myelin sheath on the outside of the fibers. The outermost Schwann cells contain most of the cytoplasm and their nuclei remain outside the myelin sheath. This layer is known as neurolemma or neurolemmal sheath.

Describe how the nervous system responds to stimuli.

The nervous system responds to stimuli through the homeostatic mechanism. The nervous system receives information, decides what to do, and then acts on the decisions; better known as sensory, integrated, and motor. Sensory receptors at the ends of neurons in the peripheral nervous system provide the sensory function of of the nervous system. These receptors gather information by detecting changes inside and outside of the body. They monitor external environmental factors such as light and sound intensities as well as temperature, oxygen concentration, and other conditions of the body's internal environment. Sensory receptors convert their information into impulses which are conducted along the peripheral nerves to the central nervous system. In the central nervous system, the signals are integrated. After integration occurs, conscious or subconscious decisions are made and then acted upon by means of motor functions.

Compare impulse conduction in myelinated and unmyelinated neurons.

non-myelinated axon each section of the membrane must depolarize and repolarize. In a myelinated axon only those sections of the membranes at the nodes actually depolarize and repolarize. Underneath the Schwann cells the impulse is carried by the flow of Na ions towards the next node. The action potential appears to jump from node to node.