May 20, 2024

Introduction to Nervous System

Introduction to Nervous System

The organisation of the Nervous system

The nervous system is one of the smallest and yet the most complex of the 11 body systems.

Its subdivisions include the central nervous system and the peripheral nervous system.

Neurology deals with normal functioning and disorders of the nervous system.

A neurologist is a physician who diagnoses and treats disorders of the nervous system.

Functions of the Nervous System

Gathers information from both inside and outside the body – Sensory Function Transmits information to the processing areas of the brain and spine Processes the information in the brain and spine – Integration Function

Sends information to the muscles, glands, and organs so they can respond appropriately – Motor Function


DIVISIONS OF NERVOUS SYSTEM

  1. CENTRAL NERVOUS SYSTEM
  2. PERIPHERAL NERVOUS SYSTEM

CENTRAL NERVOUS SYSTEM

The central nervous system (CNS) consists :

BRAIN

The brain is the part of the CNS that is located in the skull and contains about 85 billion neurons.

SPINAL CORD

The spinal cord is connected to the brain through the foramen magnum of the occipital bone and is encircled by the bones of the vertebral column. The spinal cord contains about 100 million neurons.

The CNS processes many different kinds of incoming sensory information. It is also the source of thoughts, emotions, and memories. Most signals that stimulate muscles to contract and glands to secrete originate in the CNS.

THE PERIPHERAL NERVOUS SYSTEM

Sensory (afferent) division –

Nerve fibres that carry information to the central nervous system

Motor (efferent) division –

Nerve fibres carry impulses away from the central nervous system.

This division is further subdivided into a

  • Somatic nervous system
  • Autonomic nervous system.

THE SOMATIC NERVOUS SYSTEM (SNS)[VOLUNTARY] :

conveys output from the CNS to skeletal muscles only. Because its motor responses can be consciously controlled, the action of this part of the PNS is voluntary.

THE AUTONOMIC NERVOUS SYSTEM [INVOLUNTARY]:

conveys output from the CNS to smooth muscle, cardiac muscle, and glands. Because its motor responses are not normally under conscious control, the action of the ANS is involuntary.

The ANS is comprised of two main branches, the sympathetic nervous system and the parasympathetic nervous system.


Structure of a Nerve

A nerve is a bundle of neuron fibres found outside the CNS.

Endoneurium.

Each fibre is surrounded by a delicate connective tissue sheath, an endoneurium.

Perimeurium.

Groups of fibres are bound by a coarser connective tissue wrapping, the perineurium, to form fibre bundles or fascicles.

Epineurium.

Finally, all the fascicles are bound together by a tough fibrous sheath, the epineurium, to form the cordlike nerve.

Mixed nerves.

Nerves carrying both sensory and motor fibres are called mixed nerves.

Sensory nerves.

Nerves that carry impulses toward the CNS only are called sensory, or afferent, nerves.

Motor nerves.

Those that carry only motor fibres are motor, or efferent, nerves.


Basic Cells of the Nervous System


Neuron

The basic functional cell of the nervous system Transmits impulses (up to 250 mph)

Parts of a Neuron

Dendrite – receive stimulus and carries it impulses toward the cell body

Cell Body with nucleus-nucleus & most of cytoplasm

Axon – fibre which carries impulses away from the cell body

Schwann Cells- cells that produce myelin or fat layer in the Peripheral Nervous System

Myelin sheath – dense lipid layer which insulates the axon – makes the axon look grey

A node of Ranvier – gaps or nodes in the myelin sheath. Impulses travel from dendrite to cell body to axon

Three Types of Neurons

Sensory neurons – bring messages to CNS

Motor neurons – carry messages from CNS

Interneurons – between sensory & motor neurons in the CNS


Impulses

A stimulus is a change in the environment with sufficient strength to initiate a response.

Excitability is the ability of a neuron to respond to the stimulus and convert it into a nerve impulse

All of Nothing Rule –

The stimulus is either strong enough to start an impulse or nothing happens

Impulses are always the same strength along a given neuron and they are self-propagating – once it starts it continues to the end of the neuron in only one direction- from dendrite to cell body to axon

The nerve impulse causes a movement of ions across the cell membrane of the nerve cell.


Synapse

Synapse – small gap or space between the axon of one neuron and the dendrite of another – the neurons do not actually tough at the synapse

It is the junction between neurons that uses neurotransmitters to start the impulse in the second neuron or an effector (muscle or gland) The synapse ensures oneway transmission of impulses 


Neurotransmitters

These are the chemicals in the junction which allow impulses to be started in the second neuron

“Neurotransmitter is a type of chemical messenger that transmits signals across a chemical synapse, from one neuron to another.”

A neurotransmitter is the body’s chemical messenger. They are molecules that transmit signals from neurons to muscles, or between different neurons. The transmission of signals between two neurons occurs in the synaptic cleft.

The electrical signals that travel along the axon are briefly converted into chemical signals through neurotransmitters.

Types of Neurotransmitter

There are the following different types of neurotransmitters:

Excitatory neurotransmitters

These types of neurons increase the chances of the neuron firing an action potential. Epinephrine and norepinephrine are the two excitatory neurotransmitters.

Inhibitory neurotransmitters

These have inhibitory effects on the neurons and have fewer chances of the neuron firing an action potential. For eg., serotonin and gamma-aminobutyric acid (GABA).

Modulatory neurotransmitter

These can affect a large number of neurotransmitters at the same time. These can also influence the effect of other chemical messengers.


Reflex Activity

Reflex is an involuntary and sudden response to stimuli. It happens to be an integral component of the famed survival instinct.

Most of the common reflexes are a response to all the well-trained, accumulated knowledge of caution that we have internalized. It could be anything and ranges from the reflex action of abruptly withdrawing the hand as it comes in contact with an extremely cold or hot object. This action is termed as the reflex action. It has a subtle relation to instinct.

A point to be thought upon is that we all have our instincts differently depending on our past experiences and understanding. A reflex is a reaction triggered by this instinct. At times, we have no prior knowledge if the pan is hot or not. In other words, instinct has little to do with reflex.


References:

Principles of Anatomy and Physiology by Tortora Grabowski. Palmetto, GA, U.S.A.; fifteenth edition;pg no: 403-440

Ross  and   Wilson   Anatomy   And   Physiology   In   Health   And   Illness;12TH EDITION;Pg no: 143-190

https://www.weber.edu/wsuimages/mollysmith/3510Presentations/Nerve.PPT


First Year B Pharm Notes, Syllabus, Books, PDF Subjectwise/Topicwise

First Year B Pharm Notes, Syllabus, Books, PDF Subjectwise/Topicwise

F Y B Pharm Sem-IF Y B Pharm Sem-II
BP101T Human Anatomy and Physiology I TheoryBP201T Human Anatomy and Physiology II – Theory
BP102T Pharmaceutical Analysis I TheoryBP202T Pharmaceutical Organic Chemistry I Theory
BP103T Pharmaceutics I TheoryBP203T Biochemistry – Theory
BP104T Pharmaceutical Inorganic Chemistry TheoryBP204T Pathophysiology – Theory
BP105T Communication skills TheoryBP205T Computer Applications in Pharmacy Theory
BP106RBT Remedial BiologyBP206T Environmental sciences – Theory
BP106RMT Remedial Mathematics TheoryBP207P Human Anatomy and Physiology II Practical
BP107P Human Anatomy and Physiology PracticalBP208P Pharmaceutical Organic Chemistry I Practical
BP108P Pharmaceutical Analysis I PracticalBP209P Biochemistry Practical
BP109P Pharmaceutics I PracticalBP210P Computer Applications in Pharmacy Practical
BP110P Pharmaceutical Inorganic Chemistry Practical
BP111P Communication skills Practical
BP112RBP Remedial Biology Practical