Nervous Coordination
Is brought aboutthrough various elements of the nervous system which are:

• Receptors
• Sensory Neurons
• CNS---Central Neurons System(Brain and Spinal Cord), made of associative neurons(intr neurons)
• Motor Neurons(nerves)
• Effector organs

The stimuli are recieved by the receptors which convey the messages to the CNS through sensory neurons or nerves.CNS consolidates the information of stimuli, comprehends it and formulates the type of response to be produced. The message of type of response are passed via motor meurons or nerves to the particular effectors which produce specific response.
COMPONENTS OF NERVOUS SYSTEM

1.Neurons(nerve cells)
The structural and functional unit of the nervous system in all animal including human is neurons.This is highly specialized cell which contins the typical orgenells found in most eukaryotic cell.This is cell highly adapted for communication because of its wire like projection, the dendrites which are often further branchedand carry impulses towards the central cell cell body.The cell body is thicker region of neurons containing the nucleus and most of sytoplasm. The axon is the projection, generally very long that carries impulses away from the cell body. Usually neurons has a single axon. Fatty substance covering the axon is myellin along with the short regions of exposed axons are called nodes of Ranvier.Many axons and dendrites combines to form a single nerve.

TYPES

• Sensory Neurons:They carry nerve impulsion (messages) from receptors to central nervous system.
• Motor Neurons:They carry nerves impulsion (orders) from central nervous system to effectors.
• Assocaited Neurons:They form central nercous system and are responsible for analyzing the message and issuing orders.

2.BRAIN
The brain is encased in a bony shell and a further protected by three membranes or meninges.The inner part of these covers the brain and richely supplied with blood vessels. It brings Oxygen and nutritions to underlying brain and protects it. The cerebrospinal fluid(CSF) lies between the inner and middle layers which provides cushioning and ions to the brain and spinal cord. The outer most layer is tough and fibrous and provide mechanical support.

The vertebrate brain is divided into three basic region
a)The Hindbrain
b)The Midbrain
c)The forebrain

a)The Hindbrain
The Hindbrain is chiefly concerned with involuntary, mechanical process. It consists of three primary structures.

1. The Medulla Oblangta: which lies on the top of the spinal cord and contains many of the centres that controls onvoluntary process like breathing,blood pressure and heart beat.All communication betweeb brain and spinal cord pass through the medulla.
2. The Pons: that is present on the top of the medulla oblangta and contains the longitudinal bundles of mylinated fibers running between brain and spinal cord and cenrols balance and muscles coordination
3. The Cerebellum: lies behind the medulla and controls balance and muscle coordination

b.The midbrain
The mid brain lies between the hindbrain and forebrain and connects the two.It processes the visual and auditory information from eyes and ears before sending them to forebrain.


c.The Forebrain
The forebrain is most advance in human. Its lower most part which lies above the midbrain is called Hypothalamus.

• Hypothalamus:
  which controls, heart rate, blood pressure, body temprature,hunger, thirst,sex and anger in addition to its harmonial role.
• Thalamus:provides connection between many parts of brain and between sry system and cerebrum. It may also controls moods and feelings. Sleep may be influenced ny thalamus centre along with the midbrain and hindbrain.It concerned to keep the body alert.
  
  The Cerebrum i the top mosst part of forebrain. It is divided into two hemishpere, comrising 1.5 billions nerve cells. Each hemisphere is divided into four major lobes.
  
  1. At the back are occipital lobes which recieves and analyze visual indormation.
  2. At the lower sides of the brain are temporal lobe which are primarly concerned with hearing.
  3. At the front of brain are the frontal lobes which regulates fine motor control including movement involoved in speech.

Spinal Cord

The spinal cord extends from the foramen magnum at the base of the skull to the level of the first lumbar vertebra. The cord is continuous with the medulla oblongata at the foramen magnum. Like the brain, the spinal cord is surrounded by bone, meninges, and cerebrospinal fluid.

The spinal cord is divided into 31 segments with each segment giving rise to a pair of spinal nerves. At the distal end of the cord, many spinal nerves extend beyond the conus medullaris to form a collection that resembles a horse's tail. This is the cauda equina. In cross section, the spinal cord appears oval in shape.

The spinal cord has two main functions:

• Serving as a conduction pathway for impulses going to and from the brain. Sensory impulses travel to the brain on ascending tracts in the cord. Motor impulses travel on descending tracts.
• Serving as a reflex center. The reflex arc is the functional unit of the nervous system. Reflexes are responses to stimuli that do not require conscious thought and consequently, they occur more quickly than reactions that require thought processes. For example, with the withdrawal reflex, the reflex action withdraws the affected part before you are aware of the pain. Many reflexes are mediated in the spinal cord without going to the higher brain centers.

The Peripheral Nervous System
The peripheral nervous system consists of the nerves that branch out from the brain and spinal cord. These nerves form the communication network between the CNS and the body parts. The peripheral nervous system is further subdivided into the somatic nervous system and the autonomic nervous system. The somatic nervous system consists of nerves that go to the skin and muscles and is involved in conscious activities. The autonomic nervous system consists of nerves that connect the CNS to the visceral organs such as the heart, stomach, and intestines. It mediates unconscious activities.


A nerve contains bundles of nerve fibers, either axons or dendrites, surrounded by connective tissue. Sensory nerves contain only afferent fibers, long dendrites of sensory neurons. Motor nerves have only efferent fibers, long axons of motor neurons. Mixed nerves contain both types of fibers.

A connective tissue sheath called the epineurium surrounds each nerve. Each bundle of nerve fibers is called a fasciculus and is surrounded by a layer of connective tissue called the perineurium. Within the fasciculus, each individual nerve fiber, with its myelin and neurilemma, is surrounded by connective tissue called the endoneurium. A nerve may also have blood vessels enclosed in its connective tissue wrappings.

• Cranial Nerves:Twelve pairs of cranial nerves emerge from the inferior surface of the brain. All of these nerves, except the vagus nerve, pass through foramina of the skull to innervate structures in the head, neck, and facial region.
• Spinal Nerves:Thirty-one pairs of spinal nerves emerge laterally from the spinal cord. Each pair of nerves corresponds to a segment of the cord and they are named accordingly. This means there are 8 cervical nerves, 12 thoracic nerves, 5 lumbar nerves, 5 sacral nerves, and 1 coccygeal nerve.
• Autonomic Nervous System:The autonomic nervous system is a visceral efferent system, which means it sends motor impulses to the visceral organs. It functions automatically and continuously, without conscious effort, to innervate smooth muscle, cardiac muscle, and glands. It is concerned with heart rate, breathing rate, blood pressure, body temperature, and other visceral activities that work together to maintain homeostasis.

To be continued.......

__________________
Always do what you are afraid to do
Saqib Riaz(TIPO KHAN)