nervous system pdf, classification of nervous system

NERVOUS SYSTEM

• Introduction Nervous system is a highly advanced network of specialised cells called neurons.

• By the help of millions of neurons, nervous system coordinates body functioning and transmits signals between the different body parts.

• A single nerve is a collection of various neurones. These bundles of neurons are covered by a protective layer of connective tissue; and

this layer can be divided into:

 1) Endoneurium: It surrounds each individual neuron. It is a delicate tissue. continuous with the septum that passes inwards from the perineurium.

2) Perineurium: It is a smooth connective tissue that bundle of fibres.

3) Epineurium: It is a fibrous tissue that surrounds and encloses numerous nerve fibre bundles.

CNS is the main control centre of the whole system. all external and internal internal stimuli passes to the CNS by means of sense and receptors. 

• CNS interpret these stimuli and if necessary response to them example moving away from fire etc.

PNS forms the second major part of the nervous system and PNS further subdivided into many smaller units.

 • it comprises of all not connecting the brain and spinal cord to the sensory receptor muscles and glands.

PERIPHERAL NERVOUS SYSTEM (PNS)

• The peripheral nervous system include nerve extending between the CNS and other parts of the body muscles glands and sense organs.

• It mainly act to control the voluntary function of the body.

• The peripheral nervous system is further subdivided into somatic nervous system and autonomic nervous system.

• pns comprises of 

1) Sensory Neurons :-  sensory neurones carry information in the form of extremely from the sensory tissue and receptors to the CNS.

2) Motor neurones - motor neurones carry bag the information from the CNS to the effector organs for action

3) somatic nervous system- this system control the skeletal muscle and external sensory organs.

4) Autonomic Nervous system :-  this system control the involuntary actions of the body by controlling the involuntary muscles like the smooth muscle and the cardiac muscle it further include sympathetic and parasympathetic systems.

CRANIAL NERVES :-

• 12 pairs of cranial nerves are present in humans. Pass through the form in the skull and mainly supply the peripheral tissue of the head.

• The vagus nerves is an exception as it extends to the abdomen.

• 3rd and 4th cranial nerves arise from the midbrain while the remaining 10 pair of cranial nerves originate from the brainstem.

 • the naming of cranial nerves is based on their origin, the organ supplied the nature and the function they are as follow :- 

I - Olfactory 

II - Optic

III - Motor oculi 

IV - Trochlear (pathetic)

V - Trivial (Trigeminus) 

VI - Abducent 

VII - Facial (portio dura )

VIII - Auditory (portion mollis ) 

IX - Glosso

ORIGIN :-

Amongst all the twelve cranial nerves mentioned above: 

1) Three pairs of nerves (I, II, and VII) are sensory in nature.

 2) Five pairs of nerves (IUI, IV, VI, XI and XII) are motor in nature.

3) Four pairs of nerves (V, VII, IX and X) are mixed in nature.

SPINAL NERVES :-

• Nerves originating from the spinal cord are termed as spinal nerves. 

• They transmit through the intervertebral foramina, located on either side of the spinal cord.

• The number of spinal nerves is equal to the number of vertebrae present in that region, except for the cervical and coccygeal nerves. 

• Cervical region comprises of only seven vertebrae, though the cervical nerves are eight in number.

• Every spinal nerve passes through two roots, one dorsal or motor root and one ventral or sensory root . 

• The sensory root shows the presence of a ganglion, the spinal ganglion.

• The spinal nerve runs a short course and divides into a dorsal primary ramus and a ventral primary ramus.

•  The dorsal ramus is smaller than the ventral ramus. 

• The dorsal ramus passes backwards and divides into medial and lateral branches that innervate the muscles and skin of the back. 

• The ventral ramus passes forwards.

ORIGIN

FUNCTIONS

The functions of spinal nerves are: 

1) Sensory Function: Sensory information is carried by posterior or dorsal roots of the spinal nerves from the areas innervated by them, back to the brain.

2) Motor Function: Motor impulses are carried from the brain to the muscles by the anterior, or ventral, roots of the spinal nerves, thus responding to the stimulus. Any injury to a nerve may cause weakness or paralysis of muscles that it supplies. .

3) Autonomic Function: A proper functioning of internal organs is also

regulated by the spinal nerves.

• Any disruption in the functioning of the

autonomic nervous system (ANS) can result in life-threatening conditions.

Difference b/w cranial nerves and spinal cord:- 

AUTONOMIC NERVOUS SYSTEM

Introduction

• Involuntary functions of the body (e.g., activity of heart muscles, smooth muscles, glands and muscles) are controlled by the autonomic nervous system.

ANS is further categorised into:

1) Sympathetic (thoracolumbar outflow) system, and

 2) Parasympathetic (craniosacral outflow) system.

1. Sympathetic Nervous System (SNS)

•Sympathetic nervous system controls physical or emotional stress like stress

due to work or exercise, pain and unfavourable living conditions (like too cold and hot weather), etc.

 • The preganglionic fibres of the sympathetic nervous system arise from the cell bodies from the Thoracic (Tl) to the Lumbar (L2) region of the spinal cord. Hence, the sympathetic nervous system is also known as thoracolumbar outflow.

Structure 

Sympathetic Trunks: The sympathetic trunk represent a pair of long cords located on either side of the vertebral column. 

• They extend from the foramen magnum to coccyx.

• Every sympathetic trunk comprises of 21 lateral or chain ganglia (3 cervical, 12 thoracic, 5 lumbar and 1 sacral) interconnected to each other in a sequential manner. 

• Every ganglion is a collection of neuronal cell bodies.

•  A white ramus communicans connects the ganglia to the spinal cord while a grey ramus communicans connects the ganglia to the spinal nerve. 

• Preganglionic Sympathetic Fibres: 

• The preganglionic sympathetic fibres represent small sized neuronal axons located along the lateral funiculus of the spinal cord.

• These fibres generally exit from the ventral foot of the spinal nerves and form synapses with neuronal dendrons located along all the thoracic and upper three lumbar chain ganglia, thus

forming thoracolumbar outflow.

Postganglionic Sympathetic Fibres: 

• The postganglionic sympathetic fibres represent long sized neuronal axons of chain ganglia. 

• Their effect is widespread as they innervate the smooth muscles and glands of visceral organs such as the heart, ciliary muscles and iris of eyes, lungs. gut, liver, urinary and reproductive systems.

Collateral Ganglia: 

Three collateral ganglia are present namely, collateral ganglia coeliac, superior mesenteric and inferior mesenteric ganglia. Postganglionic fibres spread from neurons of collateral ganglia to visceral organs.

2. PARASYMPATHETIC NERVOUS SYSTEM (PSNS) 

• The preganglionic fibres of the parasympathetic nervous system arise from the cell bodies of the CNS. 

• The preganglionic fibres originate from the nuclei of the third, seventh, ninth and tenth cranial nerves (CN III, VII, IX, and X) and the fourth sacral segments (S2 to S4) of the spinal cord.

• Hence the parasympathetic nervous system is said to have the craniosacral outflow.

Structure

Preganglionic Parasympathetic Fibres:

• The preganglionic parasympathetic fibres are neuronal axons.

•  These long sized fibres are present in the midbrain, brain stem and lateral funiculus of the sacral part of the spinal cord.

• They form the cranio-sacral outflow as they come out either through some cranial nerves such as occulomotor (III), facial (VII). glossopharyngeal (IX) and vagus (X), or through the 2nd, 3rd and 4th sacral spinal nerves. 

• They synapse with neurons of the parasympathetic ganglia.

Parasympathetic Ganglia: 

The parasympathetic ganglia are either located inside the visceral organs, or close to them.

 • Every ganglion is made up of a mass of neurons. The parasympathetic ganglia do not interlink to form a chain.

Postganglionic Parasympathetic Fibres:

• The postganglionic parasympathetic fibres are neuronal axons. 

• These small sized neurons supply the smooth muscles and glands of visceral organs. 

• The parasympathetic nervous system involves energy conservation and is responsible for the feeling of comfort, relaxation, pleasure, etc, at the time of rest.

DIFFERENCE BETWEEN SNS AND PSNS