INTRODUCTION TO NEUROLOGY

CENTRAL (CNS) & PERIPHERAL NERVOUS SYSTEM (PNS) NEUROLOGY • Neurology is the study of nervous system. This system is a complex mechanism by which the organism is brought into functional relation with the environment and the functions of the various systems are co-ordinated. • The activity of the nervous system controls two spheres of activity. It is through the nervous system that the animal is enable to react to alterations in the external environment and to various external stimuli. • The part of the nervous system controlling this is known as the somatic component and it is through the nervous system that all the other systems in the body are co-ordinated, so that their activities are directed towards the benefit of the organism as a whole and this part is termed as the visceral component of the autonomic nervous system. Nervous System

• Central Nervous System (CNS) • Peripheral Nervous System (PNS) • Brain, - Cranio spinal Autonomic Nervous System (ANS) • Cranial Spinal -Sympathetic, Parasympathetic (Thoraco-lumbar) (Cranio-sacral)

What is CNS:

• The CNS consists of the brain and spinal cord. • The brain is protected by the (the cranial cavity) and the spinal cord travels from the back of the brain, down the center of the spine, stopping in the lumbar region of the lower back. • The brain and spinal cord are both housed within a protective triple-layered membrane called the meninges. • The central nervous system has been thoroughly studied by anatomists and physiologists, but it still holds many secrets; it controls our thoughts, movements, emotions, and desires. It also controls our breathing, heart rate, the release of some hormones, body temperature, and much more. • The retina, optic , olfactory nerves, and olfactory epithelium are sometimes considered to be part of the CNS alongside the brain and spinal cord. This is because they connect directly with brain tissue without intermediate nerve fibers.

• The brain • The brain is the most complex organ in the body; the cerebral cortex. • In total, around 100 billion neurons and 1,000 billion glial (support) cells make up the . Our brain uses around 20 percent of our body's total energy. • The brain is roughly split into four lobes:

• Temporal lobe: important for processing sensory input and assigning it emotional meaning. • It is also involved in laying down long-term memories. Some aspects of language perception are also housed here. • Occipital lobe visual processing region of the brain, housing the visual cortex. • Parietal lobe : the parietal lobe integrates sensory information including touch, spatial awareness, and navigation. • Touch stimulation from the skin is ultimately sent to the parietal lobe. It also plays a part in language processing. • Frontal lobe positioned at the front of the brain, the frontal lobe contains the majority of dopamine-sensitive neurons and is involved in attention, reward, short-term memory, motivation, and planning.

• Brain regions • Basal ganglia: involved in the control of voluntary motor movements, procedural learning, and decisions about which motor activities to carry out. • Cerebellum: mostly involved in precise motor control, but also in language and attention. • Broca's area: this small area on the left side of the brain (sometimes on the right in left-handed individuals) is important in language processing. • Corpus callosum: a broad band of nerve fibers that join the left and right hemispheres. It is the largest white matter structure in the brain and allows the two hemispheres to communicate. oblongata: extending below the skull, it is involved in involuntary functions, such as vomiting, breathing, sneezing, and maintaining the correct blood pressure. • Hypothalamus: sitting just above the brain stem and roughly the size of an almond, the hypothalamus secretes a number of neurohormones and influences body temperature control, thirst, and hunger. • Thalamus: positioned in the center of the brain, the thalamus receives sensory and motor input and relays it to the rest of the cerebral cortex. It is involved in the regulation of consciousness, sleep, awareness, and alertness. • Amygdala: two almond-shaped nuclei deep within the temporal lobe. They are involved in decision-making, memory, and emotional responses; particularly negative emotions. Spinal cord

• The spinal cord, running almost the full length of the back, carries information between the brain and body, but also carries out other tasks. • From the brainstem, where the spinal cord meets the brain, 31 spinal nerves enter the cord. • Along its length, it connects with the nerves of the peripheral nervous system (PNS) that run in from the skin, muscles, and joints. • Motor commands from the brain travel from the spine to the muscles and sensory information travels from the sensory tissues — such as the skin — toward the spinal cord and finally up to the brain.

• White and gray matter • The CNS can be roughly divided into white and gray matter. As a very general rule, the brain consists of an outer cortex of gray matter and an inner area housing tracts of white matter. • Both types of tissue contain glial cells, which protect and support neurons. White matter mostly consists of axons (nerve projections) and oligodendrocytes — a type of glial cell — whereas gray matter consists predominantly of neurons.

• • Of these 12 pairs, the olfactory and optic nerves arise from the forebrain and are considered part of the central nervous system: • Olfactory nerves (cranial nerve I): transmit information about odors from the upper section of the nasal cavity to the olfactory bulbs on the base of the brain. • Optic nerves (cranial nerve II): carry visual information from the retina to the primary visual nuclei of the brain. Each consists of around 1.7 million nerve fibers.

Diseases of CNS

• Below are the major causes of disorders that affect the CNS: • Trauma: depending on the site of the injury, symptoms can vary widely from paralysis to mood disorders. • Infections: some micro-organisms and viruses can invade the CNS; these include fungi, such as cryptococcal meningitis; protozoa, including malaria; bacteria, as is the case with leprosy, or viruses. • Degeneration: in some cases, the spinal cord or brain can degenerate. One example is Parkinson's disease which involves the gradual degeneration of dopamine-producing cells in the basal ganglia. • Structural defects: the most common examples are birth defects; including anencephaly, where parts of the skull, brain, and scalp are missing at birth. • Tumors: both cancerous and noncancerous tumors can impact parts of the central nervous system. Both types can cause damage and yield an array of symptoms depending on where they develop. • Autoimmune disorders: in some cases, an individual's immune system can mount an attack on healthy cells. For instance, acute disseminated encephalomyelitis is characterized by an immune response against the brain and spinal cord, attacking myelin (the nerves' insulation) and, therefore, destroying white matter. • Stroke: a stroke is an interruption of blood supply to the brain; the resulting lack of oxygen causes tissue to die in the affected area. •Peripheral Nervous System(PNS) • The peripheral nervous system (PNS) is one of two components that make up the nervous system of bilateral animals, with the other part being the central nervous system (CNS). The PNS consists of the nerves and gangliaoutside the brain and spinal cord.The main function of the PNS is to connect the CNS to the limbs and organs, essentially serving as a relay between the brain and spinal cord and the rest of the body. Unlike the CNS, the PNS is not protected by the and skull, or by the blood–brain barrier, which leaves it exposed to toxins and mechanical injuries.

• Cervical spinal nerves (C1–C4) • Further information: • The first 4 cervical spinal nerves, C1 through C4, split and recombine to produce a variety of nerves that serve the and back of head. • C1 is called the suboccipital nerve, which provides motor innervation to muscles at the base of the skull. C2 and C3 form many of the nerves of the neck, providing both sensory and motor control. • Lumbosacral plexus (L1Co1) • The anterior divisions of the , sacral nerves, and coccygeal nerve form the lumbosacral plexus, the first lumbar nerve being frequently joined by a branch from the twelfth thoracic. For descriptive purposes this plexus is usually divided into three parts: • • • pudendal plexus • (C5–T1) • Further information: Brachial plexus • The last four cervical spinal nerves, C5 through C8, and the first thoracic spinal nerve, T1, combine to form the brachial plexus, or plexus brachialis, a tangled array of nerves, splitting, combining and recombining, to form the nerves that subserve the upper-limb and upper back

• Autonomic nervous system • The autonomic nervous system controls involuntary responses to regulate physiological functions. The brain and spinal cord from the central nervous system are connected with organs that have smooth muscle, such as the heart, bladder, and other cardiac, exocrine, and endocrine related organs, by ganglionic neurons. The autonomic nervous system is always activated, but is either in the sympathetic or parasympathetic state.Depending on the situation, one state can overshadow the other, resulting in a release of different kinds of neurotransmitters. • Sympathetic nervous system • The sympathetic system is activated during a “fight or flight” situation in which great mental stress or physical danger is encountered. Neurotransmitters such asnorepinephrine, and epinephrine are released, which increases heart rate and blood flow in certain areas like muscle, while simultaneously decreasing activities of non-critical functions for survival, like digestion. The systems are independent to each other, which allows activation of certain parts of the body, while others remain rested. • Parasympathetic nervous system • Primarily using the neurotransmitter acetylcholine (ACh) as a mediator, the parasympathetic system allows the body to function in a “rest and digest” state. Consequently, when the parasympathetic system dominates the body, there are increases in salivation and activities in digestion, while heart rate and other sympathetic response decrease. Unlike the sympathetic system, humans have some voluntary controls in the parasympathetic system. The most prominent examples of this control are urination and defecation. Diseases of PNS

• Diseases of the peripheral nervous system can be specific to one or more nerves, or affect the system as a whole. • Any peripheral nerve or nerve root can be damaged, called a mononeuropathy. Such injuries can be because of injury or trauma, or compression. Compression of nerves can occur because of a tumour mass or injury. Alternatively, if a nerve is in an area with a fixed size it may be trapped if the other components increase in size, such as carpal tunnel syndrome and tarsal tunnel syndrome. Common symptoms of carpal tunnel syndrome include pain and numbness in the thumb, index and middle finger. In peripheral neuropathy, the function one or more nerves are damaged through a variety of means. Toxic damage may occur because of diabetes (diabetic neuropathy), alcohol, heavy metals or other toxins; some infections; autoimmune and inflammatory conditions such as amyloidosis and sarcoidosis.Peripheral neuropathy is associated with a sensory loss in a "glove and stocking" distribution that begins at the peripheral and slowly progresses upwards, and may also be associated with acute and chronic pain. Peripheral neuropathy is not just limited to the somatosensory nerves, but the autonomic nervous system too (autonomic neuropathy).