It is complex system with around 10 billion nerve cells and connective tissue neuroglia. Transmission of impulses from one nerve cell to other cell is with the help of chemical substances (acetylcholine, adrenaline, and nor adrenaline). Impulses are finally transmitted to brain and spinal cord. Here they are recognized and interpreted. Based on the function, nerve fibers are divided into:
- Afferent or sensory: Carry impulses from organs to CNS.
- Efferent or motor: Carry impulses from CNS to organs.
- Mixed nerves: These nerves possess the characters of both sensory
Nervous system is classified into:
- Central nervous system formed by the brain and spinal cord.
- Peripheral nervous system which includes:
- Cranial nerves.
- Spinal nerves.
- Autonomic nervous system.
BRAIN: Brain is the part of central nervous system, which lies within the cranial cavity. It consists of the following parts:
- Cerebrum (made of two cerebral hemispheres).
- Medulla oblongata.
Cerebrum: It is the largest part of the brain.
Cerebrum consists of two hemispheres, the right and the left hemispheres. These two hemispheres are separated by
- Falx cerbri (a fold of dura mater) in the midline.
- Corpus callosum (a bridge of white matter) below.
Lobes: Each cerebral hemisphere has five lobes. They are:
- Frontal lobe.
- Two temporal lobes.
- Parietal lobe.
- Occipital lobe.
Surface of the brain has got numerous folds. The elevations are called convolution or gyri and the depressions are called fissures or sulci. Each hemisphere is made of outer grey matter an inner white matter. Inside of the cerebral hemisphere is open and form cavities or spaces which are known as ventricles (lateral). Cerebrospinal fluid flows through these ventricles.
Grey matter: It consists of nerve cells, which constitute the surface of hemispheres. It is also called as cerebral cortex.
White matter: It is present in the interior of the hemispheres. It contains nerve fibers.
Functions of Cerebrum:
- Motor functions like control of voluntary movements.
- Sensory functions which include:
- Analysis of touch, temperature, pain, pressure, shapes etc.
- Governing of conditional reflexes.
- Control of intelligence, memory, etc. through higher center of cerebrum.
These functions are governed by two parts of the cerebral cortex namely motor cortex and sensory cortex. The central sulcus divides the cerebral cortex to form these two parts.
- Motor Cortex: It lies in front of central sulcus. The motor cortex controls voluntary movements of the body. The controlling areas are arranged from above downwards (feet, hip, trunk, arms, and head in that order).
- Sensory Cortex: It lies behind the central sulcus. It deals with sensation like touch, pressure and temperature.
A large mass of gray matter deeply situated in the forebrain. There is one on either side of the midline. Sometimes they are interconnected at the massa intermedia.
It relays to the cerebral cortex information received from diverse brain regions. Sort of a requisite ‘last pit stop’ for information going to cortex.
Axons from every sensory system (except olfaction) synapse here as the last relay site before the information reaches the cerebral cortex.
There are other thalamic nuclei that receive input from cerebellar-, basal ganglia- and limbic-related brain regions.
The hypothalamus links the nervous system to the endocrine system via the pituitary gland (hypophysis). The hypothalamus, (from Greek it means under the thalamus) is located below the thalamus, just above the brain stem. This gland occupies the major portion of the ventral region of the diencephalon. It is found in all mammalian brains. In humans, it is roughly the size of an almond.
The hypothalamus regulates certain metabolic processes and other activities of the Autonomic Nervous System. It synthesizes and secretes neurohormones, often called hypothalamic-releasing hormones, and these in turn stimulate or inhibit the secretion of pituitary hormones.
The hypothalamus controls body temperature, hunger, thirst, fatigue, anger, and circadian cycles.
Cerebellum: It lies below the cerebrum. It is situated in the posterior cranial fossa behind the pons and medulla. Tentorium cerebelli is a layer of dura matter, which separates the cerebrum and cerebellum. Cerebellum consists of two hemispheres. The two-cerebellar hemispheres are separated by a partition of dura matter called falx cerebelli. The cerebellum also contains:
- An outer grey matter which has numerous convolutions.
- An inner white matter.
Functions of cerebellum:
- Co-ordination of muscular movements.
- To keep the muscles in a normal state of tension.
- Maintenance of balance and equilibrium.
That part of the brainstem developing from the middle of the three primary cerebral vesicles of the embryo (the caudal of these being the rhombencephalon or hindbrain, the rostral the prosencephalon or forebrain). In the adult, the mesencephalon is characterized by the unique conformation of its roof plate, the lamina tecti (tectal plate or quadrigeminal plate composed of the bilaterally paired superior and inferior colliculus, and by the massive paired prominence of the crus cerebri at its ventral surface. On transverse section, its patent central canal, the cerebral aqueduct, is surrounded by a prominent ring of gray matter poor in myelinated fibers; the periaqueductal gray is ventrally and laterally adjoined by the myelin-rich mesencephalic tegmentum, and covered dorsally by the mesencephalic tectal plate. Prominent cell groups of the mesencephalon include the motor nuclei of the trochlear and oculomotor nerves, the red nucleus, and the substantia nigra..
Pons: It lies under the cerebellum. It contains both grey matter and white matter. It forms a bridge between the two lobes of cerebellum. Nerve fibers pass through pons to midbrain above and medulla oblongata below. Pons contains nuclei for the 5th, 6th, 7th, 8t cranial nerves.
Medulla Oblongata: It is part of the brain, which forms the upward continuation of the spinal cord. It lies on the base of the skull just in front of foramen magnum. The medulla oblongata contains two ridges on the ventral surface called pyramids. The pyramids are formed by a number of nerve fibers which descend from cerebral hemispheres into the spinal cord. Before they enter into the spinal cord, the fibers of one side cross with those of the other side. This crossing of nerve fibers is called ‘decussation of pyramids’. Because of this crossing, injury to one side of the brain produces paralysis of the muscles of the opposite side.
The medulla oblongata contains nuclei for 9th, 10th, 11th and 12th cranial nerves.
The Spinal Cord is connected to the brain and is about the diameter of a human finger. From the brain the spinal cord descends down the middle of the back and is surrounded and protected by the bony vertebral column. The spinal cord is surrounded by a clear fluid called Cerebral Spinal Fluid (CSF), that acts as a cushion to protect the delicate nerve tissues against damage from banging against the inside of the vertebrae.
The anatomy of the spinal cord itself consists of millions of nerve fibers which transmit electrical information to and from the limbs, trunk and organs of the body, back to and from the brain. The brain and spinal cord are referred to as the Central Nervous System, whilst the nerves connecting the spinal cord to the body are referred to as the Peripheral Nervous System.
The nerves within the spinal cord are grouped together in different bundles called Ascending and Descending tracts.
Ascending tracts within the spinal cord carry information from the body, upwards to the brain, such as touch, skin temperature, pain and joint position.
Descending tracts within the spinal cord carry information from the brain downwards to initiate movement and control body functions.
Nerves called the spinal nerves or nerve roots come off the spinal cord and pass out through a hole in each of the vertebrae called the Foramen to carry the information from the spinal cord to the rest of the body, and from the body back up to the brain
There are four main groups of spinal nerves which exit different levels of the spinal cord.
These are in descending order down the vertebral column:
Cervical Nerves “C” : (nerves in the neck) supply movement and feeling to the arms, neck and upper trunk.
Thoracic Nerves “T”: (nerves in the upper back) supply the trunk and abdomen.
Lumbar Nerves “L”
Sacral Nerves “S”: (nerves in the lower back) supply the legs, the bladder, bowel and sexual organs.
The spinal nerves carry information to and from different levels (segments) in the spinal cord. Both the nerves and the segments in the spinal cord are numbered in a similar way to the vertebrae. The point at which the spinal cord ends is called the conus medullaris, and is the terminal end of the spinal cord. It occurs near lumbar nerves L1 and L2. After the spinal cord terminates, the spinal nerves continue as a bundle of nerves called the cauda equina. The upper end of the conus medullaris is usually not well defined.
There are 31 pairs of spinal nerves which branch off from the spinal cord. In the cervical region of the spinal cord, the spinal nerves exit above the vertebrae. A change occurs with the C7 vertebra however, where the C8 spinal nerve exits the vertebra below the C7 vertebra. Therefore, there is an 8th cervical spinal nerve even though there is no 8th cervical vertebra. From the 1st thoracic vertebra downwards, all spinal nerves exit below their equivalent numbered vertebrae.
The spinal nerves which leave the spinal cord are numbered according to the vertebra at which they exit the spinal column. So, the spinal nerve T4, exits the spinal column through the foramen in the 4th thoracic vertebra. The spinal nerve L5 leaves the spinal cord from the conus medullaris, and travels along the cauda equina until it exits the 5th lumbar vertebra.
The level of the spinal cord segments do not relate exactly to the level of the vertebral bodies i.e. damage to the bone at a particular level e.g. L5 vertebrae does not necessarily mean damage to the spinal cord at the same spinal nerve level.
The Meninges: The brain and spinal cord are protected by three coverings called Meninges. They are:
- Dura matter: which forms the outer layer.
- Arachnoid membrane: which forms the middle layer.
- Pia mater: which forms the inner layer.
Ventricles of Brain: They are cavities in the brain which are filled with cerebrospinal fluid (CSF). The ventricles are four in number. They are:
- The right and the left lateral ventricles which lies one in each cerebral hemisphere.
- The third ventricle, which is present in the mid line. The third ventricle communicates with the two lateral ventricles and also with fourth ventricle.
- The fourth ventricle lies in front of the cerebellum and behind pons and medulla oblongata. It is continuous below with the central canal of spinal cord.
PERIPHERAL NERVOUS SYSTEM
Cranial Nerves: They are 12 pairs of nerves attached to the brain. These nerves may be:
- Sensory – carrying impulses to the brain.
- Motor – Carrying impulses from the brain to the periphery.
- Mixed – Containing both sensory and motor fibers.
List of cranial nerves
# Name Function
- 0 Cranial nerve zero (CN0 is not traditionally recognized.) Still controversial
New research indicates CN0 may play a role in the detection of pheromones
- I Olfactory nerve
Transmits the sense of smell
- II Optic nerve
Transmits visual information to the brain
- III Oculomotor nerve
Innervates levator palpebrae superioris, superior rectus, medial rectus, inferior rectus, and inferior oblique, which collectively perform most eye movements
IV Trochlear nerve
Innervates the superior oblique muscle, which depresses, pulls laterally, and intorts the eyeball
V Trigeminal nerve
Receives sensation from the face and innervates the muscles of mastication
VI Abducens nerve
Innervates the lateral rectus, which abducts the eye
VII Facial nerve
Provides motor innervation to the muscles of facial expression and stapedius, receives the special sense of taste from the anterior 2/3 of the tongue, and provides secretomotor innervation to the salivary glands (except parotid) and the lacrimal gland
VIII Vestibulocochlear nerve (or auditory-vestibular nerve or statoacustic nerve) Senses sound, rotation and gravity (essential for balance & movement)
IX Glossopharyngeal nerve
Receives taste from the posterior 1/3 of the tongue, provides secretomotor innervation to the parotid gland, and provides motor innervation to the stylopharyngeus (essential for tactile, pain, and thermal sensation). Sensation is relayed to opposite thalamus and some hypothalamic nuclei.
X Vagus nerve
Supplies branchiomotor innervation to most laryngeal and pharyngeal muscles; provides parasympathetic fibers to nearly all thoracic and abdominal viscera down to the splenic flexure; and receives the special sense of taste from the epiglottis. A major function: controls muscles for voice and resonance. Symptoms of damage: dysphagia (swallowing problems).
XI Accessory nerve (or cranial accessory nerve or spinal accessory nerve) Controls muscles of the neck and overlaps with functions of the vagus. Examples of symptoms of damage: inability to shrug, weak head movement, velopharyngeal insufficiency)
XII Hypoglossal nerve
Provides motor innervation to the muscles of the tongue and other glossal muscles. Important for swallowing (bolus formation) and speech articulation.
Spinal Nerves: There are 31 pairs of spinal nerves, which arise from the spinal cord. Each spinal nerve contains an anterior root and posterior root. These two roots unite to form a single nerve trunk, which comes out of the vertebral column. The posterior nerve root contains the posterior root ganglion. One spinal nerve on each side corresponds with each segment of the vertebral column.
Autonomic nervous system:
Autonomic nervous system is divided into:
1. Sympathetic system: Activated in stress and crisis. Neurotransmitter is adrenaline which increase heart rate increases the force of contraction and dilates the air ways.
2. Parasympathetic system: Neurotransmitter is acetylcholine. When stimulated slows down the heart rate, lowers blood pressure, and increase the secretions.
Syncope Sudden decrease in blood supply to brain and subsequent loss of consciousness
Headache Diffuse pain in various regions of the head
Vertigo A sensation of irregular/whirling motion either of oneself or external objects
Paralysis Loss of power of voluntary movement in muscle
Ataxia Inability of coordinate the muscles in the execution of voluntary movement
Convulsion A series of jerkings of face, trunk/extremities
Hydrocephalus is a term derived from the Greek words “hydro” meaning water, and “cephalus” meaning head, and this condition is sometimes known as “water in the brain”. People with this condition have abnormal accumulation of cerebrospinal fluid (CSF) in the ventricles, or cavities, of the brain. This may cause increased intracranial pressure inside the skull and progressive enlargement of the head, convulsion, and mental disability.
Hydrocephalus is usually due to blockage of CSF outflow in the ventricles or in the subarachnoid space over the brain. In a normal healthy person, CSF continuously circulates through the brain and its ventricles and the spinal cord and is continuously drained away into the circulatory system. In a hydrocephalic situation, the fluid accumulates in the ventricles, and the skull may become enlarged because of the great volume of fluid pressing against the brain and skull. Alternatively, the condition may result from an overproduction of the CSF fluid, from a congenital malformation blocking normal drainage of the fluid, or from complications of head injuries or infections.
Alzheimer’s disease (AD, named after the German psychiatrist Alois Alzheimer), also called Alzheimer disease or simply Alzheimer’s, is a neurodegenerative disease that, in its most common form, occurs in people over 65 years old. Alzheimer’s disease is the most common cause of dementia, which afflicts 24 million people worldwide.
Clinical signs of Alzheimer’s disease include progressive cognitive deterioration, together with declining ability to perform activities of daily living and neuropsychiatric symptoms or behavioral changes. Plaques which contain misfolded peptides called amyloid beta (Aβ) are formed in the brain many years before the clinical signs of Alzheimer’s are observed. Together, these plaques and neurofibrillary tangles form the pathological hallmarks of the disease. These features can only be discovered at autopsy and help to confirm the clinical diagnosis. Medications can help reduce the symptoms of the disease, but they cannot change the course of the underlying pathology.
Amyotrophic lateral sclerosis (ALS):
Amyotrophic lateral sclerosis (ALS, sometimes called Lou Gehrig’s Disease, or Maladie de Charcot) is a progressive, usually fatal, neurodegenerative disease caused by the degeneration of motor neurons, the nerve cells in the central nervous system that control voluntary muscle movement. As one of the motor neuron diseases, the disorder causes muscle weakness and atrophy throughout the body as both the upper and lower motor neurons degenerate and die, ceasing to send messages to muscles. Unable to function, the muscles gradually weaken, develop fasciculations (twitches) because of denervation, and eventually atrophy due to that denervation. The patient may ultimately lose their ability to initiate and control all voluntary movement except of the eyes.
Epilepsy is defined as a group of disorders in which there is altered cerebral function with a sudden excessive discharge of electrical activity in the brain. Types of seizures:
- Partial seizures: In this type of seizure only a limited part of cerebrum discharges excessive electrical activity.
- Generalized seizures: In this seizure larger areas of both the cerebral hemispheres simultaneously and synchronously discharge electrical activity.
- Tonic-clonic (grandmal) seizure: Phases of tonic-clonic seizure include aura in which a peculiar sensation appears before the onset of definite symptoms. Tonic phase in which contractions of muscles takes place. Clonic phase in which violent jerking of face and limbs, tongue biting and incontinence are present.
- Absence or petitmal seizure: Minor form of seizures consisting of temporary clouding of consciousness and los of contact with environment.
- Treatment includes evaluation of seizures and lookout for an organic cause and antiepileptic drugs.
Huntington’s disease is a progressive, degenerative disease that causes certain nerve cells in your brain to waste away. As a result, you may experience uncontrolled movements, emotional disturbances and mental deterioration.
Huntington’s disease is an inherited disease. Signs and symptoms usually develop in middle age. Younger people with Huntington’s disease often have a more severe case, and their symptoms may progress more quickly. Rarely, children may develop this condition.
Also called Huntington’s chorea, Huntington’s disease was documented in 1872 by American physician George Huntington. The name “chorea” comes from the Greek word for “dance” and refers to the incessant quick, jerky, involuntary movements that are characteristic of this condition.
It is demyelinating white matter lesion. Natural course of this disease is variable with relapses and remissions. Clinical features include paresthesia, muscle weakness, unsteady gait (manner of walking) and paralysis. Etiology is unknown and there is no effective treatment.
Myasthenia gravis (literally “serious muscle-weakness”; abbreviated MG) is a neuromuscular disease leading to fluctuating muscle weakness and fatiguability. It is an autoimmune disorder, in which weakness is caused by circulating antibodies that block acetylcholine receptors at the post-synaptic neuromuscular junction, inhibiting the stimulative effect of the neurotransmitter acetylcholine. Myasthenia is treated medically with cholinesterase inhibitors or immunosuppressants, and, in selected cases, thymectomy.
Paralysis (partial or complete loss of motor function).
Cerebral palsy (CP) is an umbrella term for a group of disorders affecting body movement, balance, and posture. Loosely translated, cerebral palsy means “brain paralysis.” Cerebral palsy is caused by abnormal development or damage in one or more parts of the brain that control muscle tone and motor activity (movement). The resulting impairments first appear early in life, usually in infancy or early childhood. Infants with cerebral palsy are usually slow to reach developmental milestones such as rolling over, sitting, crawling, and walking.
Common to all individuals with cerebral palsy is difficulty controlling and coordinating muscles. This makes even very simple movements difficult.
Cerebral palsy may involve muscle stiffness (spasticity), poor muscle tone, uncontrolled movements, and problems with posture, balance, coordination, walking, speech, swallowing, and many other functions.
Mental retardation, seizures, breathing problems, learning disabilities, bladder and bowel control problems, skeletal deformities, eating difficulties, dental problems, digestive problems, and hearing and vision problems are often linked to cerebral palsy.
The severity of these problems varies widely, from very mild and subtle to very profound.
Although the magnitude of the problems may wax and wane over time, the condition does not get worse over time.
Parkinsonism (also known as Parkinson’s syndrome, atypical Parkinson’s, or secondary Parkinson’s) is a neurological syndrome characterized by tremor, hypokinesia, rigidity, and postural instability. The underlying causes of parkinsonism are numerous, and diagnosis can be complex. While the neurodegenerative condition Parkinson’s disease (PD) is the most common cause of parkinsonism, a wide-range of other etiologies can lead to a similar set of symptoms, including some toxins, a few metabolic diseases, and a handful of non-PD neurological conditions.
Inflammation of the Meninges. This condition could be the result of infection with bacteria like E.coli, streptococcus, pneumococcus. H.influenza, or viruses like echovirus and polio. Symptoms are fever, vomiting, headache and signs of meningeal irritation include photophobia and stiffness of neck. Treatment includes broad septum antibiotics.
It is a viral disease affecting the peripheral nerves. The neurons of the sensory ganglia in spinal cord and brain stem are affected by herpes virus (Herpes zoster), the same virus which causes chicken pox. Clinical features include vesicular (blister) skin eruption and pain distributed along with course of the nerve. Treatment includes anti viral drugs like acyclovir etc.
Imperfect union of vertebral body during the development of embryo results in spina bifida (bi-two: fida-spilt) there are several forms.
- Spina bifida occulta: Vertebral lesion is covered by skin. The only evidence of its presence is a small dimple with a tuft of hair, there may be no neurological deficit.
- Spina bifida cystica: It involves, protrusion of meninges (meningocele) or protrusion of meninges and spinal canal (meningomyelocele).
A brain tumor is any intracranial tumor created by abnormal and uncontrolled cell division, normally either in the brain itself (neurons, glial cells (astrocytes, oligodendrocytes, ependymal cells), lymphatic tissue, blood vessels), in the cranial nerves (myelin-producing Schwann cells), in the brain envelopes (meninges), skull, pituitary and pineal gland, or spread from cancers primarily located in other organs (metastatic tumors). Primary (true) brain tumors are commonly located in the posterior cranial fossa in children and in the anterior two-thirds of the cerebral hemispheres in adults, although they can affect any part of the brain. In the United States in the year 2005, it was estimated that there were 43,800 new cases of brain tumors (Central Brain Tumor Registry of the United States, Primary Brain Tumors in the United States, Statistical Report, 2005 – 2006), which accounted for 1.4 percent of all cancers, 2.4 percent of all cancer deaths, and 20–25 percent of pediatric cancers. Ultimately, it is estimated that there are 13,000 deaths/year as a result of brain tumors.
In this type of injury to brain there is no structural damage to the brain tissue. Temporary loss of consciousness is usually present which cleared within 24 hours.
In the case of severe injuries there is a structural damage of brain tissue resulting in neurological deficit persisting longer than 24 hours.
Cerebrovascular Accident (CVA):
This condition also known as stroke or cerebral infarction is the result of disruption of blood supply (ischemia) to the brain tissue. There are three types of strokes.
- Thrombotic: Atherosclerosis of cerebral blood vessels leads to thrombus (clot) formation which in turn occlude the vessel. Before total occlusion occurs patient may experience symptoms of gradual occlusion. These short episodes of neurological dysfunction are called TIAs or (Transient Ischemic Attacks).
- Emboli: Embolus (clot that breaks off from any area of the body travels to the cerebral arteries and can block the blood supply.
- Hemorrhagic: Bursting forth of blood form cerebral artery. This results form atherosclerosis or hypertension causing degeneration of blood vessels. If the hemorrhage is small it is usually reabsorbed and the patient’s recovery will be full. If the hemorrhage is large, it may turn out to be fatal.
Clinical procedures and laboratory tests:
Electroencephalography, (EEG): A graphic record of electrical currents developed in the brain that are detected by placing electrodes on skull.
Electromyography (EMG): Graphic record of electrical current generated in an active muscle. Useful in diagnosing disorders of the nerves, supplying the muscles and in disorders affecting the muscle tissue.
Magnetic resonance imaging (MRI): It is primarily used in medical imaging to visualize the structure and function of the body. It provides detailed images of the body in any plane. MR has much greater soft tissue contrast than Computed tomography (CT) making it especially useful in neurological, musculoskeletal, cardiovascular and oncolological diseases. Unlike CT it uses no ionizing radiation
Myelography: X-ray image of the spinal cord after injection of a contrast medium. Used to identify and study spinal distortions caused by tumors, cysts, herniated intervertebral disks, or other lesions.
DRUGS USED IN CNS DISORDERS
- ANTIEPLILEPTIC DRUGS
- Phenobar bitone,
- primidone (a deoxybarbiturate)
- Trimethadione (Troxidone)
- Valproic Acid (sodium valproate)
- ANTI-PARKINSONIAN DRUGS
- Levodopa (l-dopa)
- Amant adine,
- Selegiline (Deprenyl)
- Triexyphenidyl (Benzhexol),
- OPIOID ANALGESICS
- OPIOIDS ANTAGONISTS
AFP : Alpha-fetoprotein
ALS : Amyotrophic lateral sclerosis
CNS : Central nervous system
CSF : Cerebrospinal fluid
CT : Computed tomography
CVA : Cerebrovascular accident
EEG : Electroencephalogram
ICP : Intracranial pressure
LP : Lumbar Puncture
MRI : Magnetic resonance imaging
MS : Multiple sclerosis
PET : Positron emission tomography
RIND : Reversible, ischemic neurological deficit
TENS : Transcutaneous electrical nerve stimulation
TIA : Transient ischemic attack