Nervous+System

= Nervous System = [|Nervous System]

In chapter 7 we learned about neurons and synapses. The nervous system is divided in to the central nervous system and peripheral nervous system. The CNS includes the brain and spinal cord. The PNS includes the cranial nervous arising from the brain and spinal nerves arising from the spinal cord.

The nervous system is composed of only two principal types of cells- neurons and supporting cells. Neurons are the basic structural and functional units of the nervous system. Supporting cells help in the functions of neurons and are about five times more abundant than neurons. They can be called neuroglia or glial cells.

Neurons have three parts. 1. Cell body- enlarged portion of the neuron that contains the nucleus 2. Dendrites- tree branch- thin branchlike processes off the cell body 3. Axons- a longer process the conducts impulses away from the cell body

Neurons are classified by their function or structure. 1. Sensory- afferent neurons- conduct impulses from the sensory receptors into the CNS 2. Motor- efferent neurons- conduct impulses out of the CNS 3. Association neurons- interneurons- located entirely withing the CNS and serve the associative, or integrative, functions the nervous system. 4. Somatic motor neurons- are responsible for both refled and voluntary control of skeletal muscles 5. Autonomic motor neurons- innervate the involuntary effectors- smooth muscle, cardiac muscle, and glands.

=Supporting Cells=

2 types in PNS 1. schwann cells- form myelin sheaths around peripheral axons 2. satellite cells- support neuron cell bodies within the ganglia of the PNS

4 types in the CNS 1. oligodendrocytes- form myelin sheaths around axons of the CNS 2. microglia- migrate through the CNS and phagocytose foreign and degenerated material 3. astrocytes- help to regulate the external environment of neurons in the CNS 4. ependymal cells- line the ventricles of the brain and the central canal of the spinal cord.

Myelin is the fatty material the covers the cell membrane. The nodes of ravier is the gap between the exposed axons.

Next we learned about the function of astrocytes. Astrocytes are large stellate cells with numerous cytoplasmic processes that radiate outward. They are the most abundant of the glial cells in the CNS. 1. Astrocytes take up K positive from the extracellular fluid 2. Astrocytes take up some neurotransmitters released from the axon terminals of neurons 3. The astrocytes end-feet surrounding blood capillaries take up glucose from the blood 4. Astrocytes appear to be needed for the formation of synapses in the CNS 5. Astrocytes regulate neurogenesis in the adult brain 6. Astrocytes induce the formation of the blood-brain barrier 7. Astrocytes release transmitter chemicals that can stimulate or inhibit neurons

The blood brain barrier is composed of tight junctions between endothelial cells of brain capillaries and resticts the paracellular movement of molecules between epithelial cells requiring the molecules to instead pass through the epithelial cells.

Next we learned about depolarization and hyperpolarization and action potentials.

We learned about Acetylcholine in the PNS and CNS and neurotransmitters



http://people.eku.edu/ritchisong/301notes2.htm

Questions? A neuron is an electrically excitable cell that processes and transmits information by electrical and chemical signaling, via a synapse. The axon hillock is the part of the neuron that connects the cell body to the axon. It is the location where the summation of inhibitory post synaptic potentials and excitatory post synaptic potentials from numerous synaptic inputs on the dendrites or cell body occurs.

In chapter 9 we learned about the Autonomic Nervous System. The autonomic nervous system helps regulate the activities of cardiac muscle, smooth muscles, and glands. In this regulation, impulses are conducted from the CNS by an axon that synapses with a second autonomic neuron. It is the axon of this second neuron in the pathway that innervates the involuntary effectors.

There are two types of motor or efferent neuronsk 1. Somatic motor neurons- send messages to skeletal muscles 2. Autonomic- the axon of this neuron soes not direcly innervate the effector organ but instead synapses with a second neuron within an autonomic ganglion. A gangion is a collection of cell bodies outside the CNS. This first neuron is a preganglionic neuron and the second is a postganglionic neuron. The postganglionic neuron has an axon that extends from the automomic ganglion to an effector organ, where it synapses with its target tissue.

The ANS is divided into 2 divisions 1. Sympathetic Division- Thoracolumbar division 2. Parasympathetic Division- craniosacral division

The functions of the ANS include the fight or flight response. This is the bodies natural reaction to danger. The body releases norepinephrine to give a shot of adrenaline to flee the scene or give a body strength that is might otherwise not have.

Personal Application: I will use the information in these two chapters to understand how the CNS works and the PNS works. In classes this semester we have learned about nerve roots and how the spinal cord if injured different parts of the body will loose function. This is very important when understanding a diagnoses and the functions that will not be able to operate and thus strengthen the other ones to still be able to have as much function as possible.

Question: Wow this is a big question. Here it goes:) The dendrite or cell body is stimulated by a action potential. Excited of depolarization happens when the Na+ goes above the resting potential -70mv, and this opens the Na+ gates and allows more sodium to come in causing a negative charge in the axon. The inside of the axon should be negative and the outside positive. When the Na+ grows it causes a reversal of negative charge in the inside to a positive. This causes the K+ gates to open and depolarization occurs. If the K+ falls below -70 mv this is called hyperpolarization. The sodium/potassium pump causes the Na+ and K+ to move in and out, which is located in the wall of the cell body. After the gated channels open causing depolarization the axon is excited from the terminal bud over the synapse causing a excitatory post synaptic potential which causes an excited axon and action potential or a inhibitory post synaptic potential which causes no action.

References: All information was obtained by sites provided or by our text. Human Physiology, by Stuart Ira Fox.