Nervous Tissue and Nervous System

Zhong Jinjie 0017152@zju.edu.cn

Nervous System

Central nervous systemBrainSpinal cord

Peripheral nervous systemGangliaNervesNerve endings

Deep color –

grey matter (cortex) , more

nuclei, less nerve fibers

Light color –

white matter (medulla) , less

nuclei, more nerve fibers

In the histological slide

grey matter

white matter

Dark blue dots: nuclei of nerve cells

Nerve tissue is distributed throughout the body as an integrated communications network.

Nerve fiber : formed by neurons and neuroglial cells together.Nerve ganglia : small aggregates of nerve cells.

Nerve Tissue

Nerve tissue consists of two cell types: nerve cells, or neurons, which

usually show numerous long processes, and several types of glial cells

(neuroglia cells), which have short processes, support and protect neurons,

and participate in neural activity, neural nutrition, and the defense

processes of the central nervous system.

Neurons consist of three parts : 1. Dendrites, which are multiple elongated processes specialized in receiving stimuli from the environment, sensory epithelial cells, or other neurons; 2. Cell body, which is the center for the whole nerve cell and is also receptive to stimuli; 3. Axon, which is a single process specialized in generating or conducting nerve impulses to other cells (nerve, muscle, and gland cells).

Neuron - Neuroglia cell - Nerve fiber – Synapse - Another neuron

Nerve : formed by many nerve fibers.

Classification of neurons

I Number of processes: pseudounipolar/bipolar/multipolar neuronsⅡ Length of axons: Golgi type Ⅰ / Ⅱ neuronsⅢ Functions: sensory (afferent) neurons / motor (efferent) neurons/ interneuronsⅣ Chemical substances: cholinergic / adrenergic / peptidergic neurons

Neuron

Cell membrane is excitable one.Axon and dendrite have different functions.

synapse

glial

Nissl body

synapse

synapse

axon hillock microtubule

Nissl body

glial

microfilament

microfilament

dendrite

dendrite

Ultrastructure of a neuron

Chromophil Substance(Nissl bodies)LM: strongly basophilic,

throughout the cytoplasm of the cell

body and dendrites, but absent from

the axon hillocks and axons).

EM: RER(rough endoplasmic

reticulum), free ribosomes.

Functions: synthesis proteins

Neurofibrils

consisting of aggregates of microtubules and microfilaments.

abundant in cell bodies and axons and dendrites.

silver impregnation : black

function: supporting neurons as cell skeleton transportation of substances

processes numbers shape hillock spines functions

dendrites 1~numerous branched, like trees

no Yes, numerous

reception of information from other neurons

axons 1 longer, thinner, not branched

yes no conducting impulses away from cell body to other

neurons, or effectors structures

Comparison Between Axon and Dendrite

Chemical Synapse

A synapse is a specialised area of contact where the transmission of nerve impulses occurs from one neuron to another in one direction.

Presynaptic element:axonal terminals/terminal buttons, mitochondria, synaptic vesicles,presynaptic membrane(neurotransmitters)

Synaptic cleft:10-30nm wide

Postsynaptic element:postsynaptic membrane(receptor molecules)

Structure of Chemical snapses

Neuroglia cells

a-d In central nervous systeme In peripheral system

Glial cells are 10 times more abundant in the brain than neurons; they surround neurons that occupy the interneuronal spaces.

Nerve tissue has only a very small amount of extracellular matrix, and glial cells furnish a microenvironment suitable for neuronal activity.

Glial Cell Type Origin Location Main Functions

Oligodendrocyte Neural tube Central nervous system Myelin production, electric insulation

Schwann cell Neural tube Peripheral nerves Myelin production, electric insulation

Astrocyte Neural tube Central nervous system Structural support, repair processes Blood–brain barrier, metabolic exchanges

Ependymal cell Neural tube Central nervous system Lining cavities of central nervous system

Microglia Bone marrow Central nervous system Macrophagic activity

Origin and Principal Functions of Neuroglial Cells

Neuroglia cells in central nervous system astrocyte oligodendrocyte

unmyelinated axon

myelin

capillary

myelinated axonneurons

microglia cell

ependymal cell

nodes

Grey matter White matter

myelin sheath in internode

Spinal cord

astrocytes oligodenrocytes

microglia

Blood-brain barrier A. the continuous endothelium of capillaries. B. a continuous basal membrane around the endothelium. C. the vascular foot processes of astrocytes.

Formation and organization of a nerve in PNS

Formation and organization of myelinated fibers

Myelin is formed by Schwann cells in the peripheral nervous system (PNS) and oligodendrocytes in the central nervous system (CNS). Each Schwann cell forms a single myelin sheath around an axon. In contrast, each oligodendrocyte forms multiple sheaths (up to 30 or more) around different axon.

Saltatory conduction (from the Latin saltare, to hop or leap) is the propagation of action potentials along myelinated axons from one node of Ranvier to the next node, increasing the conduction velocity of action potentials. The uninsulated nodes of Ranvier are the only places along the axon where ions are exchanged across the axon membrane, regenerating the action potential between regions of the axon that are insulated by myelin, unlike electrical conduction in a simple circuit.

Connective tissue

Blood vessel

Nerve

Nodes of Ranvier

Each Schwann cell myelinates about 100 µm of an axon. Gaps between neighboring Schwann cells are called nodes of Ranvier. Action potentials jump from node to node while traversing an axon.

Myelinated Unmyelinated

Nerve Endings

Sensory nerve endings

Motor nerve endings

Sensory nerve endings in the finger

Encapsulated nerve endings consist of branched axon enclosed in a discrete connective tissue capsule.Free nerve endings are the branched terminations of the axons. Myelinated nerves lose their myelin sheath, and end in a number of branches that penetrate the area being innervated.

Meissner’s corpuscles

1. Are found in thick skin of the palms and soles, and in the skin of the nipples and genitalia.

2. Are sensitive to discriminatory touch.

3. Are critically located in the dermal papillae where the overlying epidermis is thinnest

4. Are oval structures

5. Have branched, unmyelinated nerve terminals within their core

6. Have transversely arranged, flat cells around the nerve terminals, considered to be modified Schwann cells of Neural crest origin.

7. Are enclosed within an external connective tissue sheath

epidermis

Meissner’s corpuscles

Pacinian corpuscles1. Are found in the deep tissues, particularly in the deep layers of the dermis, subcutaneous tissue, around joints, in the parietal pleura and peritoneum

2. Are sensitive to deep touch, pressure and vibration

3. Are large structures measuring 1-2 mm in diameter

4. Have branched, unmyelinated nerve terminals in the core of the corpuscle

5. Have concentric lamellae of flattened cells arranged longitudinally along the corpuscle

6. Are enclosed within an external connective tissue sheath

Golgi tendon organs

1. Are situated at musculo-tendinousjunctions. 2. Are enclosed within a capsule3. Have a core of intracapsular tendon bundles4. Have elaborately branched nerve endings twisted around the tendon core5. Have skeletal muscle fibres inserted into them6. Signal the strength of muscle contraction7. Are involved in reflexes that inhibit the homonymous (agonist) muscle and stimulate antagonistic muscles Tendon

Dendrite

Axon

Neuromuscular spindles

Neuromusclar spindles are abundant in antigravity muscles, muscles of the neck and intrinsic muscles of the hand.

They consist of a group of 6 to 12 intrafusal muscle fibres, surrounded by connective tissue continuous with the perimysium.

The intrafusal muscle fibres are modified skeletal muscle fibres that have the characteristic striations but do not have their nuclei situated below the sarcolemma.

Nerve endings on smooth muscle, cardiac muscle and secretory cells

1. These are the nerve endings of postganglionic autonomic nerves.2. They are always free nerve endings and do not have motor end plates or other specialised endings.3. They may be cholinergic or adrenergic.4. Gastrointestinal smooth muscle and cardiac muscle contract independently of motor nerve stimulation. The autonomic endings on these two types of muscle may affect the rate of contraction of the muscles.

Brain - Cerebrum

gray matter

white matter

Dark blue dots: nuclei of nerve cellsGray matter (Cortex) : 6 layers

Gray matter contains neuronal cell bodies, dendrites, and the initial unmyelinated portions of axons and glial cells.

Cerebral cortex: 6 layers

Neurons in gray matter

The cerebellar cortex has three layers: an outer molecular layer, a central layer of large Purkinje cells, and an inner granule layer. The Purkinje cells have a conspicuous cell body and their dendrites are highly developed, assuming the aspect of a fan.

The Purkinje cells

In cross sections of the spinal cord, white matter is peripheral and gray matter is central, assuming the shape of an H. In the horizontal bar of this H is an opening, the central canal, which is a remnant of the lumen of the embryonic neural tube. It is lined with ependymal cells.

Glial cell Neuron

Nerve fiber

PoliomyelitisPoliomyelitis, often called polio or infantile paralysis, is an infectious disease caused

by the poliovirus. In about 0.5% of cases there is muscle weakness resulting in an inability to move.

Polio vaccine

Nervous Tissue and Nervous System Nervous System幻灯片编号 3幻灯片编号 4幻灯片编号 5幻灯片编号 6幻灯片编号 7Nerve Tissue 幻灯片编号 9幻灯片编号 10幻灯片编号 11幻灯片编号 12幻灯片编号 13幻灯片编号 14幻灯片编号 15幻灯片编号 16幻灯片编号 17幻灯片编号 18 Structure of Chemical snapses幻灯片编号 21幻灯片编号 22幻灯片编号 23幻灯片编号 24Blood-brain barrier 幻灯片编号 26幻灯片编号 27幻灯片编号 28幻灯片编号 29幻灯片编号 30幻灯片编号 31幻灯片编号 32幻灯片编号 33幻灯片编号 34幻灯片编号 35幻灯片编号 36幻灯片编号 37幻灯片编号 38幻灯片编号 39幻灯片编号 40幻灯片编号 41幻灯片编号 42幻灯片编号 43幻灯片编号 44幻灯片编号 45幻灯片编号 46幻灯片编号 47幻灯片编号 48幻灯片编号 49