Nervous tissues

brain, spinal cord, peripheral nerves

Win components of NS which regulates and controls bodily functions

Nervous Tissues

Composed of neurons which transmit impulses, and neuroglial cells (glia from Greek word meaning glue) which assist in the propagation of nerve impulses as well as providing nutrients to the neurons

Axon

All types of nerve cells have that sends action potential signal to the next cell

1.Sensory input

2.Integration

3.Control of muscles and glands

4.Homeostasis

5.Mental activity

Functions of the nervous system

Cell body

enclosed by a cell/plasma membrane and has a central nucleus

Nissl bodies

granules found in the cytoplasm of the cell body

Neurofibrils

extremely fine fibers within the cell body  from the dendrites to the axon

Myelin sheath

whitish, non-cellular fatty layer that surrounds the axon

Neurilemma or sheath of Schwann cells

cellular layer outside of the myelin sheath

Medullary sheath

Myelin sheath together with the neurilemma

Nodes of Ranvier

interrupted intervals along the medullary sheath

True

All living cells have ability to react to stimuli

Stimuli

Where does the Nervous tissue specialized to react and conduct impulses to various organs in the body which bring about response

Neurons

easily stimulated and transmit impulses very rapidly

connective tissue

Nerve made up of nerve fibers bound together by what

Epineurium sheath of dense connective tissue

which surrounds the nerve and penetrates the nerve to form the perineurium which surrounds  bundles of nerve fibers

Yes

Blood vessels in the epineurium

Endoneurium

a thin layer of loose CT which surrounds individual nerve fibers

Before birth

When does the Neuron ( Nerve cell) generated

Persisting stem cells

give rise to new neurons throughout lifetime

True

Additional neurons is important  for maintenance and plasticity but insufficient to replace neurons that die

mitotically divide

Mature neurons do not

cell body (perikaryon or soma)

Where does Long processes that extend around the nucleus

Dendrites

part of receptive surface of neuron

smooth  or studded with small, mushroom-shaped appendages called spines

Texture of dendrites

Axon

never more than one

Axon hillock

Point of origin from perikaryo

oMay branch like dendrites

o“Transmitting” process of the neuron

oSmall bulb-shaped swellings called boutons at the end (terminal boutons) or along the course (boutons en passant)

Texture of axon

Synapse

specialized contacts  between a bouton formed by one neuron (presynaptic neuron) and the cell surface of another neuron (postsynaptic neuron)

Synaptic vesicles

accumulate close to point of contact between bouton and postsynaptic neuron

neurotransmitters

Information transmitted across gap

impulses

Messages carried by nervous system are electrical signals

Transmitters

Excite or inhibit postsynaptic neurons

L-glutamate

Most prominent excitatory transmitter of CNS

amino butyric acid (GABA)

Most prominent inhibitory transmitter is gamma

dopamine, serotonin, acetylcholine, noradrenaline  and glycine

Other main neurotransmitters are

One

How many transmitter uses by each neurons.?

Astrocytes (astroglia)

oStar-shaped cells which processes are often in contact with blood vessels (perivascular foot processes)

oProvide mechanical and metabolic support to the neurons of the CNS

oParticipate in maintenance of composition of ECF

oMaybe involved in removal of transmitters from synapses and metabolism of transmitters

oScar-forming cells of CNS

Oligodendrocytes (oligoglia)

oFewer and shorter processes

oForm myelin sheath around axons in the CNS, homologue of peripheral Schwann cells

oUnlike Schwann cells, may form parts of myelin sheath of several axons

Microglia

oSmall cells with complex shapes

oOf mesodermal origin

oDerived from cell lines which gives rise to monocytes

oIn case of tissue damage, microglia can proliferate and differentiate into phagocytic cells

Ependymal cells

oForm tight junctions and control exchange of substances between these regions and surrounding nervous tissue or CSF

● Many glial cells express neurotransmitter receptors

● Neuronal activity may regulate glial functions by spillover of transmitter from synaptic sites surrounded by fine processes of glial cells

● Occasionally, neurons may make synapse-like contact with glial cells

● Glial cells may communicate with each other via the gap junctions

Amphycytes or satellite cells (gliocytes of the PNS)

Oval or spindle-shaped cells with scanty cytoplasm and round nucleus at expanded part of the cell

●Form rosary-like capsule around individual cell bodies of neurons located in cranial and spinal ganglia

Neurolemmocytes of Schwann cells

Cells enclosing both the unmyelinated and myelinated axons in the PNS

●Single can invest one to several nerve fibers

●Produce myelin sheath of myelinated fibers in the PN

Unipolar neuron

type of neuron in which only one protoplasmic process (neurite) extends from the cell body

Most neurons multipolar

having several dendrites and an axon

Unipolar neuron

Present in developing or embryonic nervous system and is also common in insects

Pseudounipolar neuron

has 2 processes, one axon and one dendrite that fuse close to the cell body but separate at some distance from it

Pseudounipolar neuron

Soma is large with large, round, centrally located nucleus

Both processes appear structurally as axons but functionally, afferent and efferent

Bipolar neuron

has 2 processes, one axon and one dendrite that originate at opposite poles of the soma

●Ex. Photoreceptor cells of the retina and olfactory hair cells of the olfactory epithelium

Multipolar neuron

has many processes, one axon and several dendrites that arise from an oval, pyramidal or stellate soma