The eyeball

Recently we started talking about the eyeball and all of its parts and its functions. There are three layers to the eyeball. The outermost layer is called the sclera. The sclera is what forms the white part of your eye. On top of the sclera is the conjunctiva. This is a thin clear covering that helps to protect your eye. It also is a lining on the inside of your eyelids. Also on the outermost layer is the cornea. The cornea is another transparent layer that allows light to enter into the eye. The cornea, together with the lens helps focus and direct light onto the retina.

The next, or middle layer is called the Choroid. It is a membrane found between the sclera and the retina, it lines the back of the eye. It contains many blood vessels that supply oxygen and nutrients to the retina, and is highly pigmented to help absorb light and prevent scattering.

The innermost layer is the retina. The retina lines the inside of the back part of the eye, and is the light-sensitive part. The retina contains millions of cells known as photoreceptors, and each photoreceptor is linked to a nerve fiber. You have a blind spot, also known as the optic disc, at the back of each eye where all of these nerve fibers come together to form the optic nerve. Once an image is detected by the photoreceptors, this information is converted into nerve impulses that are sent to the brain through the optic nerve.

The iris of the eyeball sits right on top of the ciliary body. The iris is the colored part of our eye. The black circle in the center of the iris is called the pupil and it is actually a hole.

There are six small muscles of the eye. The superior oblique is the muscle the moves the eye inward and downward. The lateral rectus moves the eye outward (away from the nose). The medial rectus is the muscle that allows you to cross your eyes (move eyes toward your nose). The superior rectus is what makes the eye moves the eye upward and slightly out. The inferior rectus moves the eye down and slightly inward. The sixth and final muscle of the eye is inferior oblique moves the eye outward and upward.

Blog #4 ::::: Cranial Nerves

In my last blog I talked about spinal nerves, now I am going to talk about cranial nerves. The difference between cranial and spinal nerves is that cranial nerves emerge directly from the brain stem while spinal nerves are nerves that emerge from segments of the spinal cord. There are twelve different cranial nerves. The twelve cranial nerves can be divided into different groups. These groups being motor, sensory or mixed nerves. Sensory nerves tend to be located in the lateral brain stem. While motor nerves are located medially.

The function of the cranial nerves is for the most part similar to the spinal nerves, the nerves that are associated with the spinal cord. The motor components of the cranial nerves are derived from cells that are located in the brain. These cells send their axons out of the cranium where they will control muscles. , glandular tissue or specialized muscle. The sensory components of cranial nerves originate from groups of cells that are located outside of the brain. These collections of nerve cell bodies are called sensory ganglia. They have the same role as the dorsal root ganglia which are associated with the spinal cord.

In general, sensory ganglia of the cranial nerves send out a branch that divides into two branches. The motor components of cranial nerves transmit nerve impulses from the brain to target tissue outside of the brain while sensory components send nerve impulses from sensory organs to the brain. Without cranial nerves, we would be unable to chew, smell or see. These twelve nerves help to control many muscles of the body. All of them have their own purpose. Who knew one little nerve could control your mouth and how you chew.

Nerves are what control the body’s functions including the vital organs, sensation and movement. Spinal nerves are the paths of communication between the spinal cord and nerves innervating specific regions of the body. There are thirty-one pairs of spinal nerves along the vertebral column. The spinal nerve is the bit that passes out of the vertebrae through the foramen. There are eight pairs of cervical nerves, twelve pairs of thoracic nerves, five pair of lumbar and five pairs of sacral nerves and then there is one pair of coccyx nerves.
Each nerve has two roots connecting to the spinal cord. The dorsal one is the sensory root and the ventral is the motor root. Sensory receptors send information to the spinal cord and the brain through the spinal nerve. The dorsal roots contain afferent sensory axons and the dorsal roots from both sides continue outward and form the dorsal root ganglion. The ventral roots contain efferent motor neurons. In sort of the same way as the dorsal roots, the ventral roots continue to move away from the spinal cord. They then meet up with their corresponding dorsal root at a point after the ganglion and mix.
I decided to write on this topic because of an accident that just recently happened. My cousin was in a snowmobile accident just the other day. When they took the x-ray, it showed that one of the side foramen was no longer there. They thought maybe he had a fracture. I am not sure which one they said it was, but no major damage was done due to it because of the fracture. He was however told to wear a neck brace to prevent further injury.

Week 2

This week we continued to talk about the nervous system. There are four different neuroglia of the central nervous system. There are astrocytes, these are star shaped cells with many processes. These cells provide nutrients to neurons, take up excess neurontransmitters and they also act as components of the blood-brain barrier. This helps to maintain the right chemical environment for generation of nerve impulses. Then there are oligodendrocytes. These are smaller than astrocytes and they also have fewer processes. The oligodendrocytes form a supporting network around the central nervous system neurons. They also produce myelin sheath around several adjacent axons of central nervous system neurons. Another neuroglia of the centarl nervous system is microglia. These are small cells with few processes that have many small branches. The function of the microglia is to protect the cells of the central nervous system from disease by engulfing invading microbes. Microglia also migrates to areas of injured nerve tissue (this is where they clear away debris of dead cells) The fourth and final neruoglia of the central nervous system is the ependymal cells. These are epithelial cells arranged in a single layer. Theyrange in shape from cuboidal to columnar. Many of these cells are ciliated.
There are also two neuroglia that are part of the peripheral nervous system. One of those neuroglia are called schwann cells. Schwann cells are flattened cells that encircle peripheral nervouse sytem axons. Each of these cless surround multiple unmyelinated axons with a single layer of its plasma membrane or produces part of the myelin sheath around a single axon pf a peripheral nervous system neuron. They also participate in regeneration of the peripheral nervous system axons. The final neruoglia that are in the peripheral nervouse sytem are satellite cells. These are cells that are flattened and arranged around the cell bodies of neruons in ganglia. The function of the satellite cells is to support the neurons within the peripheral nervous system ganglia.
As you can see, these cells are viatal in our being. They are there to protect the nervous systems from pathogens and other foreign materials. They also provide structural protection. Without these cells we would be much more likely to get diseases. This can also be from just everyday things that can start to break the system down.

Week 1

This week we talked about the nervous system. One of the responsibilities of the nervous system is to maintain the internal homeostasis of the human body. There are a few different structures that help to make up the nervous system. These structures include the brain, the spinal cord, nerves, ganglia, enteric plexuses and sensory receptors. The activities formed by the nervous system can be divided into three groups. These groups are... sensory function, integrative function and motor function. We talked a lot about different vocabulary that has to do with the nervous system. A neuron is the findamental cell type of the nervous sytem. A neuron has three parts. There is the cell body, and axon and dendrites. The cell body is where the nucleus is surrounded by cytoplasm. Dendrites look somewhat like little trees coming out from the cell body. Dendrites are the recieving part of the neuron. For the most part the are short, tapering, and have a lot of branches. An axon conducts inpulses from the cell body. The axon is long, thin and cylindrical projection that joins the the cell body at a cone shaped elevation . This elevation is called the axon hillock. The cytoplasm of an axon is called axoplasm. The axoplasm is surrounded by a plasma membrane called axolemma. Along the axon there are branches called axon collaterals that extend out. The axon and its collaterals are divided into many processes called axon terminals. We also talked a bit about neurontrasmitters. These are molecules within the axon terminals that are released in the synaptic cleft. This is in response to a neve impulse. They also change the the membran potential of the post synaptic neuron.