THE NERVOUS SYSTEM (1)

THE NERVOUS SYSTEM : 

THE NERVOUS SYSTEM

What is the Nervous System? : 

What is the Nervous System? It enables the body to gather information from different environment and respond quickly. It transmits information to the processing areas in the brain and spinal cord. It sends information to muscles, glands and organs so they can respond correctly.

NEURON- The Message –carrying unit of the Nervous System : 

The Nervous system is constantly alive with activity. Every second, hundreds of these messages are carried by strings cells called “neurons or nerve cells”. These are the basic functional units of structure and function of the nervous system. Neurons carry information through the nervous system in the form of nerve impulses. They Are very different from all other cells. Nerve cells, once Damaged, they cannot be replaced. But the number of neurons that you are born with is so large that you will Have more than to last your entire life. NEURON- The Message –carrying unit of the Nervous System

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PARTS OF A NEURON

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Neurons also share certain characteristics or feature. Like other cells, the cell body of the neuron also consist of nucleus, a cytoplasm and/or organelles. The cytoplasm of the neuron extends into two types of fiberlike structure. CELL BODY – this is the largest part of the neuron. This contains the nucleus, which controls all the activities of the cell. DENDRITES – tiny, branching, threadlike structures, which the neurons runs into. AXONS - a protoplasmic protrusion that can extend to distant parts of the body and make thousands of synaptic contacts. They frequently travel through the body in bundles called nerves.

THE GLIAL CELLS : 

THE GLIAL CELLS Glial cells are non-neuronal cells that provide support and nutrition,, form myelin(Myelin is a dielectric material that forms a layer, the myelin sheath, usually around only the axon of a neuron ), and participate in signal transmission in the nervous system.Among the most important functions of glial cells are to support neurons and hold them in place; to supply nutrients to neurons; to insulate neurons electrically; to destroy pathogens and remove dead neurons; and to provide guidance cues directing the axons of neurons to their targets. A very important type of glial cell(oligodendrocytes in the central nervous system, and Schwann cells in the peripheral nervous system) generates layers of a fatty substance called myelin that wraps around axons and provides electrical insulation which allows them to transmit action potentials much more rapidly and efficiently.

PERIPHERAL NERVOUS SYSTEM : 

PERIPHERAL NERVOUS SYSTEM -consists of the nerves and ganglia outside of the brain and spinal cord. The main function of the PNS is to connect the central nervous system (CNS) to the limbs and organs. The Peripheral nervous system is divided into the : Somatic Nervous System & Autonomic Nervous System SOMATIC NERVOUS SYSTEM- is responsible for Coordinating the body movements, and also for receiving external stimuli. It is the system that regulates activities that are under conscious control.

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AUTONOMIC NERVOUS SYSTEM -acts as a control system functioning largely below the level of consciousness, and controls visceral functions The autonomic nervous system is then split into the sympathetic division, parasympathetic division SYMPATHETIC DIVISION - Its general action is to mobilize the body's nervous system fight-or-flight response. It is, however, constantly active at a basal level to maintain homeostasis. PARASYMPATHETIC DIVISION -is responsible for stimulation of "rest-and-digest" activities that occur when the body is at rest, including sexual arousal, (tears), urination, digestion, and defecation.

CENTRAL NERVOUS SYSTEM : 

CENTRAL NERVOUS SYSTEM The central nervous system (CNS) is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian .It contains the majority of the nervous system and consists of the brain and the spinal cord. Some classifications also include the retina and the cranial nerves in the CNS. Together with the peripheral nervous system, it has a fundamental role in the control of behavior. The CNS is contained within the dorsal cavity, with the brain in the cranial cavity and the spinal cord in the spinal cavity. In vertebrates, the brain is protected by the skull, while the spinal cord is protected by the vertebrae, and both are enclosed in the meninges.

BRAIN : 

BRAIN The brain is the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the primary sensory organs for such senses as vision, hearing, balance, taste, and smell. the function of the brain is to provide coherent control over the actions of an animal. A centralized brain allows groups of muscles to be co-activated in complex patterns; it also allows stimuli impinging on one part of the body to evoke responses in other parts, and it can prevent different parts of the body from acting at cross-purposes to each other.

DIFFERENT PARTS OF A BRAIN : 

DIFFERENT PARTS OF A BRAIN CEREBRUM - The cerebrum or cortex is the largest part of the human brain, associated with higher brain function such as thought and action. The cerebral cortex is divided into four sections, called "lobes": the frontal lobe, parietal lobe, occipital lobe, and temporal lobe. What do each of these lobes do? Frontal Lobe- associated with reasoning, planning, parts of speech, movement, emotions, and problem solving Parietal Lobe- associated with movement, orientation, recognition, perception of stimuli Occipital Lobe- associated with visual processing Temporal Lobe- associated with perception and recognition of auditory stimuli, memory, and speech

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CEREBELLUM - The cerebellum, or "little brain", is similar to the cerebrum in that it has two hemispheres and has a highly folded surface or cortex. This structure is associated with regulation and coordination of movement, posture, and balance. LIMBIC SYSTEM - The limbic system, often referred to as the "emotional brain", is found buried within the cerebrum. Like the cerebellum, evolutionarily the structure is rather old. This system contains the hippocampus, thalamus, hypothalamus, and amygdala, HIPPOCAMPUS - the portion of the cerebral hemispheres in basal medial part of the temporal lobe. This part of the brain is important for learning and memory .

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THALAMUS - a large mass of gray matter deeply situated in the forebrain at the topmost portion of the diencephalon. Almost all sensory information enters this structure where neurons send that information to the overlying cortex. Axons from every sensory system (except olfaction) synapse here as the last relay site before the information reaches the cerebral cortex. HYPOTHALAMUS - part of the diencephalon, ventral to the thalamus. The structure is involved in functions including homeostasis, emotion, thirst, hunger, circadian rhythms, and control of the autonomic nervous system. AMYGDALA - part of the telencephalon, located in the temporal lobe; involved in memory, emotion, and fear. medial part of the temporal lobe where it causes the bulge on the surface called the uncus.

BRAIN STEM : 

BRAIN STEM Underneath the limbic system is the brain stem. This structure is responsible for basic vital life functions such as breathing, heartbeat, and blood pressure. Scientists say that this is the "simplest" part of human brains because animals' entire brains, such as reptiles resemble our brain stem. The brain stem is made of the midbrain, pons, and medulla.

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MIDBRAIN - the rostral part of the brain stem, which includes the tectum and tegmentum. It is involved in functions such as vision, hearing, eyemovement, and body movement. The anterior part has the cerebral peduncle, which is a huge bundle of axons traveling from the cerebral cortex through the brain stem and these fibers are important for voluntary motor function. PONS - part of the metencephalon in the hindbrain. It is involved in motor control and sensory analysis.. It has parts that are important for the level of consciousness and for sleep. Some structures within the pons are linked to the cerebellum, thus are involved in movement and posture. MEDULLA OBLONGATA - this structure is the caudal-most part of the brain stem, between the pons and spinal cord. It is responsible for maintaining vital body functions, such as breathing and heartrate .

SPINAL CORD : 

SPINAL CORD The spinal cord is a long, thin, tubular bundle of nervous tissue and support cells that extends from the brain. The spinal cord begins at the occipital bone and extends down to the space between the first and second lumbar vertebrae; it does not extend the entire length of the vertebral column. The enclosing bony vertebral column protects the relatively shorter spinal cord.

FUNCTIONS : : 

FUNCTIONS : transmission of neural signals between the brain and the rest of the Serve as a conduit for motor information, which travels down the spinal cord. Serve as a conduit for sensory information, which travels up the spinal cord. Serve as a center for coordinating certain reflexes .

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The spinal cord is protected by three layers of tissue, called spinal meninges, that surround the canal. The dura mater is the outermost layer, and it forms a tough protective coating. Between the dura mater and the surrounding bone of the vertebrae is a space called the epidural space. The epidural space is filled with adipose tissue, and it contains a network of blood vessels. The arachnoid mater is the middle protective layer. Its name comes from the fact that the tissue has a spiderweb-like appearance.

TISSUES SURROUNDING THE SPINAL CORD : 

TISSUES SURROUNDING THE SPINAL CORD SPINAL MENINGES - is the system of membranes which envelopes the central nervous system. The meninges consist of three layers: the dura mater, the arachnoid mater, and the pia mater. The primary function of the meninges and of the cerebrospinal fluid is to protect the central nervous system. DURA MATER - , is the outermost of the three layers of the meninges surrounding the brain and spinal cord. It is derived from Mesoderm. The other two meningeal layers are the pia mater and the arachnoid mater. The dura surrounds the brain and the spinal cord and is responsible for keeping in the cerebrospinal fluid.

In the Thoracic/Abdominal Region:* Cervical nerves- The cervical nerves are the spinal nerves from the cervical vertebrae. there are eight cervical nerves (C1-C8). All nerves except C8 emerge above their corresponding vertebrae, while the C8 nerve emergesbelow the C7 vertebra. (In the other portions of the spine, the nerve emerges below the vertebra with the same name.) : 

In the Thoracic/Abdominal Region:* Cervical nerves- The cervical nerves are the spinal nerves from the cervical vertebrae. there are eight cervical nerves (C1-C8). All nerves except C8 emerge above their corresponding vertebrae, while the C8 nerve emergesbelow the C7 vertebra. (In the other portions of the spine, the nerve emerges below the vertebra with the same name.) THE MAJOR NERVES OF THE BODY:

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Thoracic nerves - The thoracic nerves are the spinal nerves emerging from the thoracic vertebrae. Branches also exit the spine and go directly to the Sympathetic Chain Ganglia of the Autonomic Nervous System where they are involved in the functions of organs and glands in the head, neck, thorax and abdomen. Lumbar nerves - are the five spinal nerves emerging from the lumbar vertebrae. Sacral nerves - also termed sacral neuromodulation, involves the implantation of a programmable stimulator subcutaneously which delivers low amplitude electrical stimulation via a lead to the sacral nerve, usually accessed via the S3 foramen.

MAJOR NERVES IN THE ARMS : 

MAJOR NERVES IN THE ARMS Musculocutaneous nerve - arises from the lateral cord of the brachial plexus, opposite the lower border of the Pectoralis major, its fibers being derived from C5, C6 and C7. Brachial plexus - a network of nerve fibers, running from the spine, formed by the ventral rami of the lower four cervical and first thoracic nerve roots .It proceeds through the neck, the axilla (armpit region), and into the arm.

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Median nerve - a nerve in humans and other animals. It is in the upper limb. It is one of the five main nerves originating from the brachial plexus. Radial nerve - a nerve in the human body that supplies the upper limb. It supplies the medial and lateral heads of the triceps brachii muscle of the arm, as well as all 12 muscles in the posterior osteofascial compartment of the forearm and the associated joints and overlying skin. Ulnar nerve -  a nerve which runs near the ulna bone. The ulnar collateral ligament of elbow joint is in relation with the ulnar nerve.

MAJOR NERVES IN THE PELVIC REGION/ LEGS : 

MAJOR NERVES IN THE PELVIC REGION/ LEGS Sacral plexus -  a nerve plexus which provides motor and sensory nerves for the posterior thigh, most of the lower leg, the entire foot, and part of the pelvis. It is part of the lumbosacral plexus and emerges from the sacral vertebrae. Femoral nerve -  the largest branch of the lumbar plexus, arises from the dorsal divisions of the ventral rami of the second, third, and fourth lumbar nerves.

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Sciatic nerve -  large nerve fiber in humans and other animals. It begins in the lower back and runs through the buttock and down the lower limb. Common peroneal nerve -the smaller of the branches into which the sciatic nerve dividespassing obliquely outward and downward from the popliteal space and to the neck of the fibula where it divides into the deepperoneal nerve and the superficial peroneal nerve. Tibial nerve -a branch of the sciatic nerve. The tibial nerve passes through the popliteal fossa to pass below the arch of soleus.

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EXAMPLES OF DISEASES IN NERVOUS SYSTEM

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ALZHEIMER’S DISEASE - Alzheimer disease (AD) is the most common cause of dementia in western civilization. It affects more women than men, and the clinical course generally lasts approximately five years. There is no cure for the disease, which worsens as it progresses, and eventually leads to death . PARKINSON’S DISEASE - is characterized by a slowing of voluntary movements, bradykinesia, muscular rigidity and tremor at rest.  LOCKED IN SYNDROME - This syndrome is due to stroke, tumor or trauma to the ventral part of the rostral pons.  Lesions there render the individual quadriplegic, unable to speak and incapable of facial movement. One would think these individuals were in a coma except that they are able to move their eyes and if given an eye communicating device they can communicate.