The Nervous Tissue - Nervous The Nervous Tissue - Nervous SystemSystemThe Nervous Tissue - Nervous The Nervous Tissue - Nervous SystemSystem

Human nervous system is the most complex system in the body formed by a network of many billion of nerve cell called neuron and all assisted by many more supporting glial cell

Neurons (nerve cell ) long processes respond to environmental change

(stimuli)

Glial cell (Neuroglia ) “glue cell” short processes and support protect neurons participate in neural activity neural nutrition defence of cell in Central nervous system

Development of nerve Development of nerve tissuetissue

Nerve system develop from the outer embryonic layer (ectoderm) 3rd week of human embryonic life

1. Central nervous system (CNS) Component: Brain (cerebrum and cerebellum)

and Spinal cord Function : Overall “command center” processing

and integrating information Location: CNS nerve cell bodies are present only

in the gray matter

2. Peripheral nervous system (PNS) Component: nerve (Cranial and spinal) and

ganglia Function: receives and projects information to

and from the CNS Location: found in ganglia and in some sensory

region like olfactory mucosa

Two Anatomical Divisions of the nervous system

Neuron structure

1. Cell body (perikaryon) Trophic center for the entire

nerve cell and is receptive to stimuli

2. Dendrites Many elongated process

specialized to receive stimuli from the environment

3. Axon Single process specialized in

generating and conducting nerve impulse to other cell(nerve,muscles gland cell)

Synapse:

interact with other neurons or nonnerve cells

Responsible for the transmission of nerve impulse

Contact between neurons and other effector cell by releasing neurotransmitters

Structural classes of neurons :

• Anaxonic neurons

no anatomical clues to determine axons from dendrites

functions unknown

• Multipolar neuron

multiple dendrites & single axon

most common type• Bipolar neuron

two processes coming off cell body – one dendrite & one axon only found in eye, ear & nose

• Pseudounipolar (Unipolar) neuron

single process coming off cell body, giving rise to dendrites (at one end) & axon (making up rest of process)

3 Main Types of Neuron1. Sensory (afferent)

involved in the reception of sensory stimuli from the environment and from within the body through presence of receptors

transmit sensory information from receptors of PNS towards the CNS

most sensory neurons are unipolar, a few are bipolar

2. Association (interneurons)

interpretation of sensory information (information processing); complex (higher order) functions

are all multipolar

3.Motor (efferent)

control muscle contraction and glandular secretion (muscles/glands/adipose tissue)

all are multipolar

Neuroglia (glial cells)

CNS neuroglia:• Astrocytes create supportive framework for neuronscreate “blood-brain barrier”monitor & regulate interstitial fluid surrounding neuronsMetabolic exchangesOrigin : neural tube•Oligodendrocytescreate myelin sheath around axons of neurons in the CNS,Myelinated axons transmit impulses faster than unmyelinated axonsOrigin: neural tube

•Microglia “brain macrophages” phagocytize cellular wastes & pathogensImmune-related activityOrigin: bone marrow

•Ependymal cells produce, monitor & help circulate CSF (cerebrospinal fluid)Lining of CNSOrigin:Neural tube

PNS neuroglia:•Schwann cells (Neurolemmocytes)

surround all axons of neurons in the PNS creating a neurilemma around them. Neurilemma allows for potential regeneration of damaged axons

creates myelin sheath around most axons of PNS

Orgin : neural tube

Satellite cells

support groups of cell bodies of neurons within ganglia of the PNS

Things to know:Things to know:The axons of neurons are

bundled together to form nerves in the PNS & tracts/pathways in the CNS. Most axons are myelinated so these structures will be part of “white matter

The cell bodies of neurons are clustered together into ganglia in the PNS & nuclei/centers in the CNS. These are unmyelinated structures and will be part of “gray matter”

Ganglia

•Most axons of the nervous system are surrounded by a myelin sheath (myelinated axons)

•The presence of myelin speeds up the transmission of action potentials along the axon

•Myelin will get laid down in segments (internodes) along the axon, leaving unmyelinated gaps known as “nodes of Ranvier”

•Regions of the nervous system containing groupings of myelinated axons make up the “white matter”

•“gray matter” is mainly comprised of groups of neuron cell bodies, dendrites & synapses (connections between neurons)

Blood brain barrierFuction : shields the brain from toxic substances in the blood, supplies brain tissues with nutrients, filters harmful compounds from the brain back to the bloodstream.Compotents :Capillary endotheliumMeningesThe skull and the vertebral column protect the CNSBetween the bone and nervous tissue are membranes of connective tissueThree layer:1.Dura mater : outer layer lining of skull2.Arachnoid mater : contain blood vessel

subarachoid space : filled with CSF3.Pia mater : cover the brain

Choroid plexusFuction :remove water from blood and release it as CSF

Microscopic specimen Microscopic specimen

Cross section of a nerveCross section of a nerve

Peripheral nerve connective Peripheral nerve connective tissuetissue

Cross section of the spinal Cross section of the spinal cordcord

Neuron and neuroglia Neuron and neuroglia

AstrocytesAstrocytes

Microglia Microglia

ependymal cellsependymal cells

GangliaGanglia

Cerebral cortexCerebral cortex

cerebellumcerebellum

Choroid plexusChoroid plexus

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