The structure of the nervous system

The Nervous System

VOCABULARY

neuron нейрон

brain мозок

spinal cord спинний мозок (стрижень)

meninx оболонка мозку

dendrites дендрити (розгалужені відростки нервових клітин)

cell nucleus ядро клітини

axon аксон ( відросток нервової клітини)

to carry the impulse away from… проводити імпульси від…

myelin sheath мієлінова оболонка

cerebrum головний мозок

cerebral cortex кора головного мозку

cerebrospinal fluid спинномозкова рідина

synapse синапс

gyrus звивина мозку

fissue щілина; борозна

sulcus борозна

thalamus таламус, зоровий горбок

hypothalamus гіпоталамус

Read and memorize some interesting facts about the brain.

1) Your brain uses 20 % of oxygen that enters your bloodstream. The brain only makes up about 2 % of our body mass, yet consumes more oxygen than any other organ in the body, making it extremely susceptible to damage related to oxygen deprivation. So breathe deep to keep your brain happy.

2) Nerve impulses to and from the brain travel as fast as 170 miles per hour. Ever wonder how you can react so fast to things around you? It’s due to the super-speedy movement of nerve impulses from your brain to the rest of your body and vice versa, bringing reaction at the speed of a high powered luxury sports car.

3) The brain itself cannot feel pain. While the brain might be the pain center when you cut your finger or burn yourself, the brain itself does not have pain receptors and cannot feel pain. That doesn’t mean your head can’t hurt. The brain is surrounded by loads of tissues, nerves and blood vessels that are plenty receptive to pain and can you pounding headache.

Read and memorize the English idioms containing the word brain. Make your own sentences with the idioms.

BRAIN

To beat/rack one’s brain(s) (about smth) – to think very hard of for a long time to try to find a solution to a problem.

To have smth on the brain - to think repeatedly or constantly about it.

A brain-wave – a good thought, idea or suggestion which comes unexpectedly or suddenly.

To turn smb’s brain – to disturb smb mentally.

Match the following English word combination and the Ukrainian ones:

1. mental activity a) сіра речовина

2. impulse transmission b) спинномозкова речовина

3. gray matter c) розумова діяльність

4. voluntary control d) передача імпульсів

5. spinal fluid e) свідомий контроль

Read and translate the text.

THE STRUCTURE OF THE NERVOUS SYSTEM

The nervous system is the major controlling, regulatory, and communicating system in the body. It is the center of all mental activity including thought, learning, and memory.

Though its receptors, the nervous system keeps us in touch with our environment, both external and internal.

Like other system in the body, the nervous system is composed of organs, principally the brain, spinal cord, nerves, and ganglia. These, in turn, consist of various tissues, including nerve, blood, and connective tissue. Together these carry out the complex activities of the nervous system.

The system is composed of specialized cells, termed nerve cells or neurons, that communicate with each other and with other cells in the body. A neuron has three parts:

1) the cell body, contacting the nucleus;

2) dendrites, hair-like structure surrounding the cell body, which conduct incoming signals;

3) the axon (or nerve fiber), varying in length from a millimeters to a meter, which conduct outgoing signals emitted by the neuron. Axons are encased in a fat-like sheath, called myelin, which acts like an insulator and speeds impulse transmission.

Typically a given neuron is connected to many thousands of neurons. The specific point of contact between the axon of one cell and dendrite of another is called a synapse. Messages passed to and from the brain take the form of electrical impulses, produced by a chemical change that progresses along the axon. At the synapse, the release of neurotransmitters and this, in turn, drives the impulse to the next neuron. These impulses travel very fast along these chain of nervous – up to 250 miles per hour. This contract with other system, such as the endocrine system, which may take hours to respond with hormones.

The nerve cell bodies are generally located in groups. Within the brain and spinal cord, the collections of neurons are called nuclei and constitute the gray matter, so called because of their colour. Outside the brain and spinal cord the groups are called ganglia. The remaining areas of the nervous system are tracts of axons, the white matter, so-called because of white myelin sheath.

The Nerves of the body are organized into two major systems:

- the central nervous system (CNS), consisting of the brain and spinal cord;

- the peripheral nervous system (PNS), the vast network of spinal and cranial nerves linking the body to the brain and spinal cord. The PNS is subdivided into:

1) the autonomic nervous system (involuntary control of internal organs blood vessels, smooth and cardiac muscles), consisting of the sympathetic NS and parasympathetic NS;

2) the somatic nervous system (voluntary control of skin, bones, joints and skeletal muscle).

The two systems function together, with nerves from the periphery entering and becoming part of the central nervous system, and vise versa.

The brain, the body’s “control center”, is one of the largest of adult organs, consisting of over 100 billion neurons and weighing 3 pounds. It is typically divided into four parts:

1) the cerebrum;

2) the cerebellum;

3) the diencephalon (thalamus, hypothalamus, sometimes classed as cerebral structure);

4) the brain stem (medulla oblongata, pons, midbrain), which is an extension of the spinal cord.

The largest division of the brain, the cerebrum, consists of two sides, the right and left cerebral hemispheres, which are interconnected by the corpus callosum. The two hemispheres are “twins”, each with centres for receiving sensory (afferent) information and for initiating motor (efferent) responses. The left side sends and receives information to/from the right side of the body, and vise versa. The hemispheres are covered by a thin layer of gray matter known as the cerebral cortex. The interior portion consists of white matter, tract, and nuclei (gray matter) where synapses occur. Each hemisphere of the cerebral cortex is divided onto four “lobes” by various sulci and gyri. The sulci (or fissures) are the grooves and gyri are the “bumps” on the brain’s surface.

The cerebellum, the second largest brain structure, sits below the cerebrum. Like the cerebellum has an outer cortex of gray matter and two hemispheres. It receives/relays information via the brain stem. The cerebellum perform 3 major function, all of which have to do with skeletal muscle control:

- balance of the trunk;

- muscle tension, spinal nerve reflexes, posture and balance of the limbs;

- fine motor control, eye movement.

The diencephalon, located between the cerebrum and midbrain, consists of several important structures, two which are the:

- thalamus: large, bilateral (right thalamus/left thalamus) egg-shaped mass of gray matter serving as main synaptic relay center;

- hypothalamus: are collection of ganglia located below the thalamus and intimatetly associated with the pituitary gland. It has a variety of functions: senses changes in body temperature; control autonomic activites and hence regulates the sympathetic and parasympathetic nervous systems; links to the endocrine system/ controls the pituitary gland; regulates appetite; functions as part of the arousal or alerting mechanism: and links the mid (emotions) to the body – sometimes, unfortunately, to the degree of producing “psychosomatic disease”.

The medulla oblongata, pons and midbrain – often referred to collectively as the brain stem – control the most basic life functions. Of these three, the medulla is the most important. In fact, so vital is the medullas to survival diseases or injuries affecting it often prove fatal. All functions of the brain stem are associated with cranial nerved III-XII. Functions:

- breathing/respiration (pons, medulla);

- heart rate/action (medulla);

- blood pressure/blood vessel diameter (medulla);

- reflex centers for papillary reflexes and eye movements (midbrain, pons); and for vomiting, coughing sneezing, swallowing, and hiccupping (medulla).

The spinal cord lies within the spinal cavity, consisting of the vertebral column, the meninges, spinal nerves, spinal fluid, blood vessels, and a cushion of adipose/fat tissue. The spinal cord has two general functions; 1) It provides the two-way conduction routes to/from (afferent/efferent) the brain; and 2) it serves as the reflex center for all spinal reflexes.