1.  Christolouka Maria – Dimitra AEM 27065

2.  Lazaridis Panagiotis AEM 27220

BODY SYSTEM: NERVOUS SYSTEM

Student 1: Christolouka Maria - Dimitra

Question 1: How does the nervous system work?

The Nervous system is one of the seven main systems of the body. At first the major parts of the system will be presented so that its function will be clarified in a better way.

To start with, the basic functional unit of the nervous system is the neuron, which is responsible for conducting neural transmission through neural impulses, mostly to other neurons. It consists of a soma (cell body), dendrites, axons, synapse, and myelin. The Nervous system can be distinguished in the Central Nervous system (CNS) and the Peripheral Nervous System (PNS). The CNS consists of the brain and the spinal cord whereas the PNS consists of the spinal and the cranial nerves and all of the autonomic (involuntary) distribution of nerve fibers. The autonomic division of the PNS is further differentiated into the sympathetic and parasympathetic components.

The most complex and delicate system of all the body system is the nervous system. The brain is at the center of the system. The brain sends and receives messages through a network of nerves.

This specific network of nerves allows the brain to communicate with every part of the body. Nerves transmit information as electrical impulses from one area of the body to another. Some nerves carry information to the brain. This allows us to see, hear, smell, taste and touch (sensory nerves). Other nerves carry information from the brain to the muscles to control our body's movement (motor nerves). Generally, sympathetic fibers release norepinephrine as a neurotransmitter whereas parasympathetic fibers release acetylcholine as a neurotransmitter. The autonomic system supplies smooth muscles (e.g. intestine, urinary bladder, arterioles, penis, clitoris, lungs), glands (e.g. salivary, exocrine) and heart muscle. Often these parts of the body receive both sympathetic and parasympathetic fibers, one of the pair may stimulate or excite and the other inhibits or relaxes the muscle or gland. The CNS receives incoming information from the sensory organs, interprets and processes the information, and sends directions to skeletal muscles to contract and to glands, smooth muscles and heart muscle. Nerves that have their origin in the brain or the spinal cord supply the skeletal muscles. These are called motor neurons and their neurotransmitter is acetylcholine.

What is the difference in motor and sensory nerves?

1. Function

Sensory Nerves

These send messages to the brain about how things feel. Sensory nerves tell the brain that a stove feels hot when it is touched. Damage to sensory nerves may result in pain or a loss of feeling.

Motor Nerves

These nerves send information about movement. When sensory nerves tell the brain that the stove feels hot, motor nerves tell the hand to let go of the hot stove. Damage to motor nerves causes muscle weakness.

2. Morphology

In contrast to motor nerves, some sensory neurons do not have as many wrappings of the myelin sheath around them. Thus, they have less "membrane resistance" and lose current by standard electrical cable properties as compared to other sensory neurons with many wrappings.

3. Biochemical Properties

Transmitters that sensory and motor neurons use to communicate to other neurons or muscle cells are different. There are many variations considering the animals (invertebrates as well as vertebrates). For example, in the crayfish, the neurotransmitter secreted from a motor neuron to communicate with a muscle is glutamate for the excitatory motor neurons. However, crayfish also have inhibitory motor neurons that release GABA to inhibit the muscle fiber. These animals use mostly Ach (acetylcholine) as the neurotransmitter for their sensory neurons. This is just the opposite way around in most of the cases for mammals- Ach for motor neurons and glutamate for sensory neurons. So, there are differences in the biochemical properties within motor and sensory neurons.

4. Proteins There are differences in motor and sensory nerves as far as their proteins are concerned. That is because they serve a number of different biochemical processes. On the other hand, there may be some similar proteins that are called isoforms of proteins.

Question 2: Illustrate the nervous system that must include brain, spinal cord and nerves.

Picture 1.

The above picture (picture 1) shows the human nervous system. We can clearly see the location of the brain, the spinal cord and the spinal nerves on the body. Brain and spinal cord compose the CNS. In contrast, spinal nerves consist of one of the two divisions of the PNS. Cranial nerves, the other division, are undistinguishable extending from the cerebrum and the brain stem. All together consist a network. This network can be explained as similar to a road network as it is illustrated from the picture above.

Freeway: The spinal cord is a thick bundle of nerves, which runs down the centre of the spine.

Highways: Along the spinal cord smaller bunches of nerves branch out.

Main roads: From these bundles, smaller bundles of nerves branch out again.

Normal roads: Finally, individual nerves branch out to every part of the body.

Picture 2.

Nerves are long structures consisted of nerve fibres. Neurons accumulate and shape nerve fibres. That means that the basic unit of them is the neuron (picture 2). Neurons come in many shapes and sizes. There are billions of them in a human brain. Basically they have a cell body that contains the nucleus surrounded by cytoplasmic elements for protein synthesis and energy production. There are two kinds of cell processes, the axon that conducts electrical impulses away from the cell body and dendrites that are short extensions of the cytoplasm that conduct electrical impulses toward the cell body. Because axons can be quite long, neurons have well-developed transport systems between the nerve cell body and axon terminals. Axons, depending on their function, may terminate at neurons, muscles, and glands.

Question 3: Describe the function of the major parts of the brain.

1.  Basic knowledge

Brain, portion of the central nervous system contained within the skull. The brain is the control center for movement, sleep, hunger, thirst, and virtually every other vital activity necessary to survival. The brain controls all human emotions—including love, hate, fear, anger, elation, and sadness. It also receives and interprets the countless signals that are sent to it from other parts of the body and from the external environment. The brain makes us conscious, emotional, and intelligent. The adult human brain is a 1.3-kg (3-lb) mass of pinkish-gray jellylike tissue made up of approximately 100 billion nerve cells, or neurons; neuroglia (means nerve glue) are smaller and 10 times more numerous than neurons. Neuroglia function to support and protect neurons as well as containing enzymes that can degrade neurotransmitters. This mass also contains vascular (blood-carrying) cells and other tissues.

2. The three major parts of the brain

From the outside, the brain appears as three distinct but connected parts: the cerebrum —two large, almost symmetrical hemispheres; the cerebellum (“little brain”)—two smaller hemispheres located at the back of the cerebrum; and the brain stem—a central core that gradually becomes the spinal cord, exiting the skull through an opening at its base called the foramen magnum. Two other major parts of the brain, the thalamus and the hypothalamus, lie in the midline above the brain stem underneath the cerebellum.

1. / Cerebrum

Here, the most high-level brain functions take place. Its two large hemispheres make up approximately 85 percent of the brain's weight. The exterior surface of the cerebrum, the cerebral cortex, is a convoluted, or folded, grayish layer of cell bodies known as the gray matter. The gray matter covers an underlying mass of fibers called the white matter. The convolutions are made up of ridgelike bulges, known as gyri, separated by small grooves called sulci and larger grooves called fissures. The two cerebral hemispheres are partially separated from each other by a deep fold known as the longitudinal fissure. Communication between the two hemispheres is through several concentrated bundles of axons, called commissures, the largest of which is the corpus callosum. Sulci and gyri divide the cerebrum into five lobes: the frontal, parietal, temporal, and occipital lobes and the insula. The frontal lobe is the largest of the five and consists of all the cortex in front of the central sulcus. Broca's area, a part of the cortex related to speech, is located in the frontal lobe.

Information from all the sense organs is received from the cerebrum, which sends motor commands to other parts of the brain and the rest of the body. Motor commands are transmitted by the motor cortex, a strip of cerebral cortex extending from side to side across the top of the cerebrum just in front of the central sulcus. The sensory cortex, a parallel strip of cerebral cortex just in back of the central sulcus, receives input from the sense organs. A lot of other areas of the cerebral cortex have also been mapped according to their specific functions, such as vision, hearing, speech, emotions, language, and other aspects of perceiving, thinking, and remembering. Associative cortex (cortical regions) is responsible for integrating multiple inputs, processing the information, and carrying out complex responses.

2. / Cerebellum

The cerebellum coordinates body movements. The cerebellum provides the basis for organizing and smoothing gestures because it consists of a distinctive set of neural circuits well suited to this task -- including inputs from both the cerebral cortex and the spinal cord. Located at the lower back of the brain beneath the occipital lobes, the cerebellum is divided into two lateral (side-by-side) lobes connected by a fingerlike bundle of white fibers called vermis. The cerebellum coordinates voluntary movements by fine-tuning commands from the motor cortex in the cerebrum. The cerebellum also maintains posture and balance by controlling muscle tone and sensing the position of the limbs. All motor activity depends on the cerebellum.

3. / Brain Stem

The brain stem controls our most basic functions, many of which happen without our thinking about them at all. The brain stem is evolutionarily the most primitive part of the brain and is responsible for sustaining the basic functions of life, such as breathing and blood pressure. It includes three main structures lying between and below the two cerebral hemispheres—the midbrain, pons, and medulla oblongata. There are twelve sets of cranial nerves, one of each pair for each side of the body. Most of them originate in the brain stem. These nerves control important things like swallowing, facial movement, the senses, and neck and shoulder muscles. Major nerves carrying information to and from the rest of the body pass through the brain stem. The nerve axons cross over in the medulla so that the left side of the brain controls the right side of the body and vice versa. Tumors on one side of the brain may well affect movement and sensation on the opposite side of the body.

Question 4: Draw and label the three major parts of your brain.

A. Cerebrum

Picture 1: Superior cerebrum

Picture 2: Lobes of the cerebrum

B. Cerebellum

Picture 3: Cerebellum

C. Brain stem

Picture 4: The three main structures of the brain stem.

Student 2: Lazaridis Panagiotis

Question 1: Describe the five sensory organs.

Question 2: Draw and label the parts of each.

Our sensory organs take in information and send it through the nerves to the brain for processing. Each sense collects information from the world around us and detects changes in the body. We have five main sensory organs: The eyes (sight), ears (hearing), nose (olfaction), tongue (taste) and skin (touch).

Each eye consists of the eyeball, which weighs 7.3-7.8 g and has a volume of approximately 6.5cm3.

The eyeball has a number of protective features. The eyelids, eyelashes and eyebrows are all designed to protect the eye from dirt and dust that might enter it and cause damage. The eyeball sits inside the orbital cavity, a bony pocket lined with fatty tissue as a cushion. Together these provide additional protection against injury. The six extraocular muscles - 4 rectus (medial, lateral, superior, inferior) and 2 oblique (superior, inferior) - attach at various points to the sclera and enable the globe to move in many directions inside the orbit.

Parts of the eyeball

·  Cornea

As light enters the eye, it is refracted by the cornea, a spherically curved, transparent sturdy layer that covers the front part of the eyeball. The cornea is the main eye’s focusing element.

·  Iris

It is a circular pigmented tissue that consists of circular and radial smooth muscle fibers arranged so as to form a doughnut shaped structure (the hole in the middle is called the pupil) containing a stroma, itself containing the sphincter and two layers of epithelia. The sphincter makes the pupil expand and contract, thus regulating the intensity of light that enters the eye. The iris attaches to the ciliary body.

·  Pupil

It is the central opening of the eyeball that permits light into the interior of the eye.

·  Lens

It is clear and flexible focusing element behind the pupil. Its curvature is controlled by muscles. By changing the curvature of the lens, the eye can focus at different "depths of field". It refracts light entering the eye and projects it onto the retina.

·  Retina

It is a photosensitive membrane lining the back of the eyeball and forming its innermost layer. It translates the visual image into a neural signal. It terminates the optic nerve to the photoreceptive cells, retinal receptors (known as rods and cones), which translate the light coming into the eye into biochemical signals and finally to nerve (electric) impulses sent back up along the optic nerve to an area of the cortex at the back of the brain for processing. Cones -short cone-like cells that detect colour- are less numerous than rods and are most densely concentrated in the fovea centralis, a small depression in the center of a yellowish area, the macula lutea, found near the center of the retina. They become less and less dense from the fovea outward. Rods -longer cells that respond to dim light- are absent entirely from the fovea and macula and increase in density toward the periphery of the retina.