The last class we started to discuss the special senses. The special sense that was focused on was the eyeball. The external structures covering the eyeball include the eyelids (Palpebrae), eyelashes, and eyebrow. Along with the external structures of the eye itself, is the sclera which is the white of the eye and it is made up of collagen and is covered by the conjunctiva, which is the clear layer above the sclera. Other structures include the pupil, which allows light to enter into the eye and the iris which is the color of the eye. These two structures are covered by the cornea which has no blood supply.
The internal structures of the eye consist of the lens which is composed of layers and these layers continue to accumulate throughout the years of life. The lens is held in place behind the pupil by connective ligaments called the Ciliary Body which are located beneath the iris. The gel like substance called Fibrous Humor holds the retina in place without destructive pressure and is the place where the veins and arteries are located and held in place within the eye.
In addition there are three layers also known as tunics of the eye.
Layers
Sclera – Outermost layer
Retina – Innermost Layer
Choroid – Middle Layer
Tunics
Fibrous Tunic- Outermost Layer
Visual Tunic – Innermost layer
Pigmented Tunic – Middle Layer

Somatic and Autonomic Nervous Systems

The Peripheral Nervous System consists of two divisions
1. Somatic Nervous System - which consists of afferent, sensory cranial and spinal nerves that connect somatic receptors to the central nervous system. They are the nerves that inform the brain and body about an internal or external stimulus. The somatic nervous system also consists of efferent, motor cranial and spinal nerves that connect the central nervous system to skeletal muscles. These nerves inform the body, (skeletal muscles) of the decision of how to correct the problem. The somatic nervous system is considered to be involved with voluntary(consious) activities of the body.
2. Autonomic Nervous System - which consists of autonomic sensory neurons, these are the intergrating centers within the Central Nervous System. The autonomic nervous system also consists of autonomic motor neurons, these would send the response to the rest of the body. The autonomic nervous system usually operates without conscious knowledge so it is considered to be involuntary. The autonomic nervous system has control and regulates the activity of smooth muscle, cardiac muscle, and the glands.

We need both of these nervous systems to function properly in order to respond properly internal and external stimulus's so that way the body remains in homeostasis. These nerves help to regulate body temperature and the the body temperature is to high or to low the receptors send the impulses to the appropriate nerves to help the body to regulate and control the unwanted conditions.

Neuroglia Cells Central Nervous System

There are four neuroglia cells in the central nervous system, these are the supporting cells of the central nervous system and the neurons within the central nervous system.
1. Astrocyte
Are star shaped and are the formers of the blood brain barrier, this barrier regulates what passes through and gets to the neurons in the central nervous system. They also control the release of calcium that releases the neurotransmitters from the synapse of the axon.
2. Microglial Cell
These are the smallest of the Central nervous system glial cells, they are macrophages which are phagocytes. Phagocytes are emzymes that engulf non-self foreign material.
3. Ependymal Cells
These cells are located within the body of the spine, (vertabraes). They make cerbral spinal fluid and transport. Cerbral spinal fluid is derived from blood.
4.Oligodendrocytes
They make the myelin in the central nervous system. Myelin is the fatty covering that surrounds the axons. The myelin sleath acts as an insulator and a protector of the axon. These cells can also wrap multiple axons at a time.
One can tell that it is important for these cells to exists just from reading the above. Together, they protect the central nervous system from pathogens and foreign material along with providing structural protection. Without these cells we would be very suseptible to many diseases and just normal wear and tear that happens on a daily basis. All four of theses cells are found within the Central Nervous System.

Neurons (Week One)

The neuron is the fundamental cell of the nervous system, it is a communicating cell, which means that the neuron receives and sends messages from one neuron to another neuron. Neurons function (send and retreive messages) in the following way, 1. when the body is introduced to an internal or external stimulus the sensory function of the nervous system is working, sensory(afferent) neurons are sending the messages to the spinal cord and brain which make up the Central Nervous System. Once the brain and spinal cord receive the message it is process and a decision about what needs to take place is put in motion, this is the integrative funcution of the Nervous system, this is where all decisions are made. Once the decision is made interneurons relay the message to the Motor function that is responsible for performing the decided course of action, the neurons that that perform the course of action are efferent neruons. Neurons help the body to produce needed reponses to stimulus's in the internal and external environment.

We see this every day, such as in the way our body response to when we touch something extremely hot. In most cases the message is relayed to the brain and spinal cord before we realize that we have touched something hot. Or when we apply pressure to a part of our body the neurons are constantly moving and informing the brain and spinal cord of changes in or around our body. When we apply pressure to our body the afferent (sensory) neurons are moving toward the brain and spinal cord letting the brain and spinal cord know that that is unusual pressure, the brain and spinal cord receive the message and send it through interneurons to motor (efferent) neurons which produce the movement or action needed to reduce of remove the pressure.