nervous system easy introduction

• General anatomy of nervous system

Nervous system

• Nervous system integrates these sensory information, store information as memory

Nervous system receives sensory information •From external environment (temperature, vision, sound etc.) •From body (touch, pressure, pain etc.)

Nervous system makes an appropriate response, ex: movement of muscles

Simple flowchart of nervous system function

Skin > touch > nerve (sensory nerve/afferent

fibre/ascending tract) Brain nerve(motor nerve/efferent

fibres/descending tract) muscle> movement

CNS : PRINCIPLES ROLES

• Integrate and coordinate incoming and outgoing neural signals

• Carry out higher mental functions such as thinking and learning

Division of nervous system

• Structurally,• Central nervous

system

Brain Spinal cord

• Peripheral nervous system

Cranial nerves,

Spinal nerves, Autonomic nerves

Functional divisionSomatic nervous system, is the part of nervous system which control voluntary activities

Autonomic nervous system,

is the part of nervous system concerned with the innervation of involuntary structures, such as the heart, smooth muscle, and glands within the body

What is the composition of nervous tissue?

1. Neuron ( nerve cell ) 2. Neuroglia

Nerve cell body Processes Dendrite Axon

Nerve cell body

Nerve cell processesDendrite Axon

Histological feature of neuronnerve cell body

A centrally placed spherical, unusually large , euchromatic (pale-staining) nucleus with a prominent nucleolus,

Nissl body unique feature of neuron

Nissl bodies are basophilic granular areas formed by the rER , iron & free ribosomes.

Golgi complex arranged around the periphery of the nucleus.

Mitochondria are found through out of the cell body,

dendrites, and axons. They are spherical or rod shaped.

Axon hillock :

it is the area of cell body which is free of large cytoplasmic organelles. It is a landmark to distinguish between axons and dendrites in both light & TEM microscopes.

• Dendrites are receptor processes that receive stimuli from other neurons or from the external environment

• Axon are effector processes that transmit stimuli to other neurons or effector cells

What is gray matter and white matter?

Grey matter Nerve cell body Neuroglia Blood vessel White matter Nerve processes Neuroglia Blood vessels

Neuroglia Blood vessels

• Gray matter: Neuron cell bodies Neuroglial cells Blood vessels • White matter: Processes of neuron Neuroglial cells Blood vessels

Location of gray & white matter in the CNS

• Cerebrum and cerebellum ,

• Outer gray matter

• Inner white matter

• Spinal cord,• outer part

white matter• Inner gray

matter

Gray matter matter

Classification of neuronAccording to the polarity

According to function

Sensory neuron

Motor neuron

Neuroglia

• The neuron of the central nervous system are supported by several varieties of non excitable cells, which together are called neuroglia.

• They are smaller than the neuron • Number of them 5-10 times greater than the

neuron

There are four types of neuroglial cells in CNS & two types in PNS:

CNS1. Astrocytes (a) fibrous (b) protoplasmic 2. Oligodendrocytes3. Microglia4. Ependyma

• PNS1. Schwann cells2. Satellite cells.

Protoplasmic Astrocytes Fibrous Astrocytes

Oligodendrocytes Microglia

Ependyma

Schwann cells:

It have the same function as oligodendrocytes but are located around axons in the peripheral NS.

Axon

Functions of neuroglia Name of the neuroglia Functions

Astrocytes Formation of blood brain barrier

Oligodendrocyte Myelination of nerve fibers in the CNS

Ependymal cells secrete, circulate and absorbed CSF

Microglia Phagocytic function in inflamed brain (They are inactive in normal brain)

Schwann cells Myelination of nerve fibers in the PNS

Development of neuroglia

Name of the neuroglia

Functions

Astrocytes Neuroectoderm

Oligodendrocyte Neuroectoderm

Ependymal cells NeuroectodermMicroglia Mesodermal in origin

Schwann cells Neural crest

What is myelin sheath?

• Axon of neuron is covered by

sheaths which are modified cell

membranes of schwann cells in

PNS and oligodendrocytes in

CNS

Schwann cells

Axon

Schwann cells undergo spiraling around the axon

Myelination in the CNS by oligodendrocyte

Function of myelination

• It acts as an insulator• Helps in impulse conduction

Ganglia a collection of nerve cell bodies out

side the CNS

1. sensory ganglia of spinal nerves (posterior root ganglia) and cranial nerves

2. autonomic ganglia

Nucleus: a collection of nerve cell bodies of neuron in the CNS is called nucleus

Example: Dorsal nucleus of vagus nucleus ambiguous, nucleus of tractus solitarius

Grey matter

White matter

Nucleus

What is synapse?

• The synapse is the specialised junctions between two or more adjacent neurons.

How impulse go from one neuron to another ?

What are the types of synapses?According to the location of synapse in the post

synaptic neurons

• How nervous system is worked ?

Simple reflex arc

Reflex arc

• A reflex may be define as an involuntary response to a stimulus. It depends on the integrity of the reflex arc .

A reflex arc consists of the following anatomical structures:

Location

1) a receptor organ Skin, muscle, or tendon

2) an afferent neuron Posterior root ganglion

3) an effector neuron Example: Lower motor neuron located in the ventral horn of spinal cord

4) an effector organ Example: Skeletal muscle

Structural organization of reflex may be two types

•Monosynaptic reflex

Incoming axons of the unipolar primary sensory neurons synapse directly on a motor neuron.Example: tendon jerks

•Polysynaptic reflex

In these reflex one or more interneurons, excitatory or inhibitory, intervene between sensory and motor neurons.

Polysynaptic reflex

Types of reflex • Reflex may be divided into 4 groups:1) superficial (or skin and mucous membrane) reflexes

Corneal reflexes, gag reflexes2) deep (or myotatic) reflexes Jaw jerk, knee jerk3) visceral ( or organic) reflexes Pupillary reflex4) pathological (or abnormal) reflexes Ankle clonus, Babinski’s sign