HUMAN NERVOUS SYSTEM

Human NERVOUS system

Nervous system controls and regulates the work of all body parts, from simple finger movement till very complex heartbeat

The nervous system contains a complex

network of nerve cells, or neurons.

Neurons are specialized cells that transmit information throughout the body.

Structure of a neuron

Dendrites which extend from the cell body of the neuron, are the “antennae” of the neuron. Dendrites receive information from other cells.

An axon is a long membrane-covered extension of the cytoplasm that conducts nerve impulses.

Its membrane is called as myelin sheath

Bundles of axons are called nerves.

Neuron structure

Types of neurons Neurons can be classified according to their

projections and functions:

a. Unipolar – sensory neuron, They transmit information from sensory organs (eyes, ears, skin, etc) to the central nervous system.

b. Bipolar - interneurons are generally found in the central nervous system. Their main function is interpretation of information.

c. Multipolar - motor neurons carry impulses from central nervous system to muscles or glands.

Neuron function Neurons receive and transmit signals

as weak electrical impulses

These signals are called as nerve impulses and they travel like wave from dendrite to axon

Na+ and K+ ions take role in carrying impulse.

Communication between neurons Neurons communicate

by means of synapse, where signals are transmitted from axon of one neuron to dendrite of another

Synapse is a space between neurons and there is no direct connection

Neurotransmitters Impulse passes from axon of one neuron to

dendrite of another by means of special neurotransmitters

Neurotransmitters diffuse across the synapse and carry impulse from a nerve cell to another.

They are released by 1st cell axon end and received by 2nd cell dendrite

Examples: adrenaline, histamine, acetylcholine etc.

Parts of human nervous system

Human nervous system includes 2 parts:

a. Central Nervous System (CNS): includes brain and spinal cord, control center of body

b. Peripheral nervous system (PNS): contains sensory neurons, receive information (eye, skin, ear …) and transmit it to CNS; and motor neurons which send commands from CNS to muscles and organs

CNS: brain Brain, body’s main processing and

controlling center which is protected by skull and includes about 100 billion neurons

All body activities, emotions, thought, memories are controlled by brain

Its size in males about 1200-1350 grams and in females 1000-1250 grams

The brain consists of three main parts:

1. Forebrain

2. Midbrain

3. Hindbrain

BRAIN: 1. Forebrain (передний мозг) Largest portion of brain, composed of 2 main parts:

a. Cerebrum (конечный мозг)

Upper covering part, has many folds, divided into 2 hemispheres

Responsible for thought, skeletal muscles movement, skin feel, vision, hearing and smell and etc.

b. Diencephalon (промежуточный мозг)

Regulates body temperature, responsible for anger, pain, pleasure, hunger, thirst, also maintains homeostasis and etc.

BRAIN: 2. Midbrain

Coordinates head and eye movement, eye focus, helps for hearing

BRAIN: 3. Hindbrain (задний мозг)

Composed of medulla oblongata (продолговатый мозг), cerebellum(мозжечок) and pons (мост)

a. Medulla oblongata:

Located in the border of spinal cord and brain

Regulates respiratory, circulatory and excretory activities, swallowing, sneezing, vomiting and etc.

b. Cerebellum:

Located in posterior end of brain

Regulates balance, posture and movement

c. Pons:

Bridge-like structure

Controls certain respiratory functions

CNS: spinal cord Spinal cord is a dense cable coming out from

brain and protected by vertebral column

Spinal cord transmits signals from brain and to brain and functions in reflexes

A reflex is a sudden, involuntary contraction of muscles in response to a stimulus.

Spinal cord contains a core of grey matter covered by white matter, grey matter mainly neuron bodies and interneurons, white matter axons

Peripheral nervous system PNS PNS connects CNS to the rest of the body

From brain 12 pair of nerves projected, from spinal cord 31 pairs that go to all body parts

Body is controlled by 2 ways of PNS:

a. Somatic nervous system (soma means body)

b. Autonomic nervous system

1. Somatic nervous system

Most motor neurons that stimulate skeletal muscles are UNDER OUR CONSCIOUS CONTROL, like running, writing, swimming …

They coordinate the voluntary action of our body

Some activity such as reflexes are involuntary, because they are to protect our body and very fast

2. Autonomic nervous system

Motor neurons that regulate smooth muscles and NOT UNDER OUR CONSCIOUS CONTROL, like heartbeat, peristalsis, blood vessels contraction …

They action involuntarily

It is divided to PARASYMPATHETIC and SYMPATHETIC nervous systems which maintain stability in our body

The effects of parasympathetic and sympathetic nervous system are opposite.

Generally sympathetic system helps the body deal with emergency situations by accelerating some body activities.

Parasympathetic system promotes normal relaxed body functioning.