Content Summary:
The nervous system has two parts:
  • Central nervous system (CNS)
    • Brain
    • Spinal cord (SC)
  • Peripheral nervous system (PNS)
    • Cranial nerves
    • Spinal nerves

The PNS has two parts:
  • Somatic-controls voluntary processes
  • Autonomic-controls involuntary processes
    • Sympathetic
      • Fight, flight and stress reactions
    • Parasympathetic
      • Rest and digest reactions
      • Homeostasis



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Summary #1
The nervous system contains neurons, the basic structural and functioning units, and supporting cells, which aid the neurons. The job of a neuron is to respond to physical and chemical stimuli, conduct electrochemical impulses and release chemical regulators. There are three functional classifications of neurons: sensory (afferent) which bring impulses from sensory receptors to the CNS, motor (efferent) which take impulses away from the CNS to muscles or glands, and association (interneurons) coordinate motor responses with sensory stimuli. Neurons do not divided by mitosis but at times some may regenerate. Supporting cells (neuroglia or glial cells) are five times more abundant than neurons and are able to divide by mitosis. Brain tumors can be composed of glial cells because of their ability to divide and multiply. There are two types of supporting cells in the PNS: Schwann cells and satellite cells (ganglionic gliocytes). There are four types of supporting cells in the CNS: oligodendrocytes, microglia, astrocytes and ependymal cells.

Summary #2
Myelin is a phospholipid protein formed by Schwann cells in the PNS and oligodendrocytes in the CNS that surrounds axons. Myelin acts as insulation and increases the speed of an electrical impulse. Schwann cells in the PNS wrap myelin around an individual axon and that wrapping is called a myelin sheath. Axons smaller than 2 micrometers in diameter are usually unmyelinated and those larger are myelinated. Myelinated axons conduct impulses at a much faster rate than those that are unmyelinated. In the CNS, oligodendrocytes have extensions which can form myelin sheaths around many axons. The disease that attacks myelin sheaths is multiple sclerosis (MS). Lesions form on the sheaths and harden, making scars that keeps impulses from forming. The person with MS eventually loses muscle functions which can keep them from normal activity.

Schwann cells in the PNS:

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Schwann cells in the PNS


Oligodendrocyte in the CNS

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Effects of MS:



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Summary #3
Neurotransmitters (NT) are chemicals released from the presynaptic nerve ending that stimulates an action potential (AP) in the postsynaptic cell. There are many types of molecules that function as NT. Some polypeptides function as hormones secreted by endocrine glands and the small intestine. Other polypeptides are secreted from the brain, have different sizes and are called neuropeptides. Neuropeptide Y is very abundant and has many roles such as responding to stress, regulation of circadian rhythms, cardiovascular system control, inhibit excitatory NT glutamate, and stimulate appetite. Other neuropeptides are cholecystokinin (CCK) which may produce a feeling of satiety after eating, and substance P that may mediate pain sensations.

Application:
Many of the patients that I treat may have a disease of the nervous system or an injury that affects their nervous system. Nerve damage will affect their ability to complete ADL and I would be working with them to improve or adapt to their disease or injury. As an OTA, I will also need to retain the knowledge I have learned about cranial and spinal nerves, what muscles and organs they innervate and how any injury to them will affect all aspects of the person's daily living. Retaining is the key:) Our bodies are so complex and systems intertwined that it really is important to understand physiology.

On a personal note, my cousin has lived with MS for over 40 years. She has adapted and still has a wonderful outlook on life although she has depend daily on others to get her in and out of bed, her wheelchair, for toileting and bathing. Understanding the pathology of MS has been helped by the study of these chapters.


Essential Questions:

1. The dendrite of the postsynaptic neuron is stimulated to send an impulse from the axon hillock through the binding of NT to receptor

proteins that are within the postsynaptic membrane. This binding causes ligand regulated gates to open chemically regulated channels.

Opening of these channels can produce depolarization (EPSP) because of inward diffusion of Na+. There is localized, decreased

amplitude of EPSP to the axon hillock which opens voltage gated Na+ and K+ channels. The axon allows conduction of the AP.



2. All cells have a resting membrane potential (rmp) that is measured at -70 mV. To get an AP to occur, Na+ gates open. allowing Na+ to permeate the cell membrane and enters the axon through diffusion. This depolarizes the membrane and allow more Na+ voltage regulated gates to open. This increase of Na+ causes a rapid change in the rmp from -70 mV to +30 mV. The Na+ channels close, Na+ permeability decreases, voltage gated K+ channels open which causes K+ to diffuse out of the cell. Na+/K+ pumps continually work within the plasma membrane. Repolarization occurs, which returns rmp to -70 mV. These changes are called an action potential (AP). Hyperpolarization occurs when the inside of the cell becomes more negative than the rmp. The threshold level is at -50 mV.

AP travel to axon terminals and open voltage gated channels for Ca2+. The Ca2+ enters the cytoplasm, binds to a sensor protein, which alters the SNARE complex which has been held in the axon terminal. This alteration allows for the complete fusion of the synaptic vesicles with the plasma membrane and NT's are released via exocytosis.

When the neuron is inhibited, motor control can be affected. Glycine helps control skeletal movements. Strychnine blocks glycine's inhibitory effect and will cause diaphragm muscles to become spastic, causing death by asphyxiation. GABA is another inhibitory NT and a deficiency of this can cause uncontrolled movements as seen in Huntington's disease.

References: Human Physiology by Stuart Ira Fox, Anatomy and Physiology by Stanley E Gunstream, andTaber's Cyclopedic Medical Dictionary