Chapter 13: The Peripheral Nervous System and Reflex Activity

                The peripheral nervous system contains all the neural structures outside the brain and spinal cord. This includes the sensory receptors, peripheral nerves, associated ganglia, and motor endings. The peripheral nervous system provides links to and from the external environment.

                Sensory receptors are a big portion of the peripheral nervous system; they are special structures to respond to stimuli. The activation of sensory receptors results in the depolarization that triggers impulses to the CNS. The understanding of these stimuli, sensation and perception all occur in the brain. It is important to remember with sensory receptors is that is isn’t necessarily important where the information is coming from, but more so where the input goes in the brain is what is important. All the receptors can be classified by their type of stimulus.

a. Mechanoreceptors-  respond to touch, pressure, vibrations, stretch, and itch

b. Thermoreceptors- responds to change in temperature

c. Photoreceptors- responds to light energy, for example the retina

d. Chemoreceptors- responds to chemicals, for example, smells, taste, and also changes in blood chemistry

e. Nociceptors- sensitive to pain-causing stimuli

Not only can receptors be classified by stimulus type, but they can also be categorized by their location.

1.       Exteroceptors (outside the body)- these type of receptors respond to stimuli arising outside the body, these are usually found near the body’s surface. They are sensitive to touch, pressure, pain, and temperature, this classification includes the special sense organs.

2.       Interoceptors (within the body)- these receptors are found in internal viscera and blood vessels. These are sensitive to chemical changes, stretch, and temperature changes.

3.       Proprioceptors- these receptors respond to degree of stretch of the organs that they occupy. These are found in the skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles. It helps to think of these receptors as “advising” the brain of one’s movement. Because of these receptors, is why you know where your legs or arms are for example without even looking at them. But on the other hand, you make “know” where certain organs are in your body because you have studied diagrams but your brain can’t really distinguish exactly where they are.

Check back next week for a book review on "The Spirit Catches You and You Fall Down" by Anne Fadiman and also key points of chapter 14 in your anatomy book!

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Chapter 12: The Central Nervous System

                This week we’re discussing the central nervous system in more detail. The central nervous system is made up of the brain and spinal cord. A vocabulary word you may want to be familiar with is cephalization. This is the evolution of the brain and how the elaboration of the anterior portion of the central nervous system, it also increases in neurons in the head and the highest level of this is shown in the human brain.

                The brain is composed of wrinkled, pinkish gray matter. The adult brain structure is broken up into 3 surface structures, the forebrain, midbrain, and hindbrain. These structures are further broken down into smaller categories; this can get confusing to understand so I am going to try and break it down, also you can find a handy diagram on page 429 of the text book that gives you a good visual of the structures of the brain.

1.     1.  Prosencephalon (forebrain)

a.       Telencephalon- contains the cerebrum: cortex, white matter and basal nuclei (derived from the lateral ventricles)

b.      Diencephalon- contains the thalamus, hypothalamus, and epithalamus (derived from the third ventricle)

2.     2.  Mesencephalon (midbrain)

a.       Mesencephalon- contains the brain stem and the midbrain (derived from the cerebral aqueduct)

3.    3.   Rhombencephalon (hindbrain)

a.       Metencephalon- contains the brain stem and pons (derived from the fourth ventricle)

b.      Myelencephalon- contains the medulla oblongata (derived from the fourth ventricle)

The two cerebral hemispheres are the biggest structure of the brain and most likely what you think of when you think of the brain. The brain contains ridges which are referred to as the gyri. The cerebral hemispheres contain shallow grooves called sulci. Lastly, it contains contain deep grooves called fissures. The fissures divide the large regions of the brain. The sulci divide the hemispheres into five lobes; frontal, parietal, temporal, occipital, and insula.

The cerebral cortex is make of superficial gray matter and this portion of the brain accounts for 40% of the mass of the brain. The main function of the cortex is that is enables us to be aware of ourselves, sensations, to communicate, to remember, and also to initiates voluntary movements. There are three types of functional areas are: Motor areas (control voluntary movements), sensory areas (conscious awareness of sensation), and association area (integrates diverse information). You need to be able to identify these areas on the brain and on page 434 there is a diagram with these areas as well as other structures of the brain that you need to know.

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Chapter 11: The Nervous System

                The nervous system has a lot of information involved! It is the master controlling system of the body. Its major functions are monitoring stimuli, interpreting sensory input, and responding to stimuli.  It is broken down into the Central Nervous System which is the brain and spinal cord and the Peripheral Nervous System which is the nerves outside of the central nervous system.

The PNS has two functional divisions which include the sensory (afferent) division and motor (efferent) division. The afferent division is further divided sensory afferent fibers (carries impulses from the sensory receptors to CNS) and visceral afferent fibers which transmit impulses from visceral organs. The motor division transmits impulses from the CNS to effector organs and is also divided into two main parts, one, is the somatic nervous system which is the conscious control of the skeletal muscles and the automatic nervous system which regulates the activity of smooth and cardiac muscles as well as glands.

The nervous system is also broken up into two different cell divisions: neurons and neuroglia. Neurons are excitable cells that transmit electrical signals. Neuroglia, or glial cells, are the glue and support for neurons.  Other functions of the Neuroglia include: segregating and insulating neurons, guide young neurons to the proper connections, and promote health and growth. There are multiple types of glial cells that we are responsible for knowing.

1.       Astrocytes- these cells are the most abundant and versatile of all the glial cells and are highly branched.  These cells cling to neurons and their synaptic endings and covers capillaries. There major functions include: support and brace neurons, anchor neurons to their nutrient supplies, guide migration of young neurons, and control the chemical environment of the cell.

2.       Microglia- these cells are small, ovoid shapes with spiny processes. These types of cell act as phagocytes that monitor the health of neurons

3.       Ependymal- these cells range in shape from squamous to columnar. These function for lining the central cavities of the brain and spinal column

4.       Oligodendrocytes- these cells are branched cells that wrap CNS nerve fiber.

The nervous system has a ton of information and large vocabulary words. I wouldn’t waste time on making notecards for every single bolded word, I would check back at the end of the chapter to do the review quiz and go over the summary points!

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