Muscular Tissue

Prof. Dr. Xiaoxun Xie

2006.10

Component of muscular tissue

- numerous muscular cells;

- containing few CT;

- enrich capillary network,

lymphatic vessel, and

terminal nerve fiber.

Classification

Morphologic type Functional type

Skeletal m.

Cardiac m.

Smooth m

Striated m.

Unstriated m.

Voluntary m.

Involuntary m.

Nomenclature in muscular cell

Muscular cell------------------------muscular fiber

Membrane of muscular C.--------sarcolemma

Cytoplasm of muscular C.--------sarcoplasm

Smooth endoplasmic reticulum--sarcoplasmic reticulum

Organization of skeletal muscle

*muscle-------------------epimysium

*fascicle------------------perimysium

*muscular fiber (cell)---endomysiun

Skeletal muscleLM：Shape: long cylindrical shape

Nuclei: ovoid & flattened; multinucleated,

located at the periphery of cell;

Sarcoplasm: * regular transverse / longitudinal striation * myofibrils

myofibril

Muscular cell

nucleus

EM:

1. Myofibril

2.Transverse tubule

3. Sarcoplasmic reticulum

4. Other inclusions

mitochodria

myoglobin

glycogen

ribosome

1

2

3

Muscle fiber & myofibril

———muscular fiber (muscular cell)

myofibrildark band (A band)

Light band （ I band)

Myofibril

* long , parallel , cylindrical filamentous bundles

*consisting of two types of myofilament (thin & thick).

Sarcomere: A segment between two adjacent Z line.

It is a structural and basic contractile unit.

Banding

I band： only thin filament

H band (central region of A band): only thick

filament without cross bridges

Extremities of A band： both thin & thick filament

Z Z

Molecular configuration of myofilaments

* thick filament ----myosin

* thin filament: actin, tropomyosin, tropnin.

Myosin (thick filament)

—head (adenosine triphosphatase, ATPase ） —shaft

Thin filament

TropninActin Tropmyosin

Components of a thin filament

—binding site to myosin

Two strands of actin molecule arranged in a helix

Actin

Actin

Tropomyosin

双股螺旋丝状多肽链 ,

嵌于 actin 双螺旋链的浅沟内

Tropnin

—TnT

—TnI

TnC—binding Ca2+

Transverse tubule

* invaginations of the surface

sarcolemma

* lying as rings around each

myofibril

* located at A-I junction

* providing for the rapid spread

throughout the entire muscle

fiber of surface membrane

excitation.

A

I

Z

myofibril

Sarcoplasmic reticulun * RER forming cylindrical sheaths

around each myofibril

(longitudinal tubule)

* at A-I junction, tubules connect to channels of larger caliber called terminal cisternae

Triad

* A T tubule is sandwiched

between two terminal cisternae.

myofibrils in transverse section through the end of the A-band 。Mitochondrea (M) sarcoplasmic reticulum (SR)

Muscular Dystrophy

- a group of diseases involving muscle deterioration.

-Duchenne muscular dystrophy related to deletions in a huge gene coding for the protein dystrophin.

-The gene is linked to the X chromosome, so it appears predominantly in males.

Guillaume-Benjamin  Duchenne de Boulogne

LM

-short cylindrical shape

- to be branched- the central location of the nucleus, one or two nucleus per fiber

- cross striation

-myofibril

-intercalated disks

Cardiac muscle

Cardiac muscle（ transverse section）

Cardiac muscle

intercalated disk

nucleus

EM:*myofibril is not well defined;

*sarcoplasmic reticculum less developed;

*T tubeles much wider;

located in the Z lines;

*Diad

* intercalated disk

T tubulez

z

terminal cisternae

M

Intercalated disc

*Specialized cell junctions located at Z lines

*Stepwise pattern:

transverse region: intermidiate/desmosomes j.

longitudinal region: gap junction

z G.J.

I.J.

D.J.

Intercalated dis: Stepwise pattern

Transverse region : desmosome, intermediate J.

Longitudial region : Gap J

Smooth muscle* spindle-shape with single central nucleus

* sarcoplasm appears acidophilic

* no transverse striation and intercalated disc.

EM:

* invagination of sarcoplasm

* sarcoplasmic reticulum poorly developed

* there are myofilaments, but no myofibrils

caveola

Dense patch

Dense body

myofilaments

Heart muscle with purkinje fibers

NERVOUS TISSUE

Introduction

Nervous System

• nervous system consists of all nervous tissue

• divided anatomically into:

Central NS-------brain (encephalon),spinal cord

Peripheral NS

Functions of NS

• monitors changes occurring both inside & outside of the body;

• processes & interprets information, makes decisions about what should be done at each

moment;

• carries the order of what should be done

to muscles and glands.

Histological characteristics of NT

• many cells packed closely together ( little extracellular material);

• Most of cells are strongly branching

• two main groups of cells:

-nerve cells (neurones): * accept stimuli,

* conduct N impulses

-glia (Neuroglia): support, protect & nourish neuron

NeuronClassified based on

1. Number of processes (3 types)

2. Function (3 types)

3. Long or Short of axon (2 types) Golgi I

Golgi II

4. Chemical substances released

• Cholinergic neurons• Aminergic neurons• Peptidergic neurons• Aminoacidergic neurons

Pseudounipolar Neuron

*Anatomically, only one cell process arising from the soma.

*Developmentally, begin as bipolar, then grow together and fuse.

* Found in peripheral sensory ganglia, such as dorsal root ganglia.

Bipolar Neuron

• A single axon and dendrite arise at opposite poles of the cell body.

• Found only in sensory neurons, such as in the retina, olfactory and auditory systems.

Multipolar Neuron

• Multiple dendritic processes, one axon

• Most numerous and common cell type in the body

• found in brain, peripheral autonomic nervous

system and spinal cord.

Sensory(afferent) NC

involved in the reception of sensory stimuli from environment & from within body

Motor (efferent ) NC

conducts impulses to effectors (muscle, glands) & controls their functions

Interneuron

establishes interrelationshipes among other neurons, modifies and integrates nerve impulses

* 99% of neurons are interneurons

Organization of neuron

Cell body (soma)

Processes(neurites)

Dendrites

Axon

membrane

perikaryon

nucleus

• Large

• Spherical

• Pale-staining

• Prominent nucleolus

• In the center of soma

Nucleus of neuron

H&E

Silver impregnation

LM EM Function

Nissl bodies

Basophilic

RER +Free ribosomes

Synthesize proteins

neurofibrilsMicrotubules +Neurofilaments

skeletontransportation

Cytoplasm (perikaryon)

Cytoplasm (perikaryon)

Besides Nissl body and neurofilaments,there are other organelles :

• well-development Golgi apparatus

• Scattered mitochondria

• Less lysosmes

• Lipid droplets

• Pigment granules, etc.

Processes (neurite)

Axon

Dendrites

Axon• single long process

• Membrane—plasmaleman

• Cytoplasm (axoplasm): neurotubules + neurofilaments, some mitochondria

• Axon hillock: the site where an axon arises from the cell body

• Terminal buttons: small, bulb-shaped swellings at the ends

• conducting signals from one nerve cell to another.

hillock

Dendrite

• numerous, short processes

• become attenuated and branch with distance from the perikaryon.

• structures same as the perikaryon

• Dendritic spine: studded with small,

mushroom-shaped appendages

• carrying impulses to the soma.

Synapse

Definition: point of contact between neurons(usually between axon terminals and dendrites).

Types: Chemical synapse* Electrical synapse = Gap junction

Forms: 9 types (B-body; D-dendrite; A-axon)

Neuron B D A

Another neuron B D A

A—D and A—B are more often

Structure of chemical synapse

- Synaptic vesicles (neurotransmitters)

-Presynaptic membrane

Presynaptic element

Cleft

Postsynaptic element

-Postsynaptic membrane-receptor: specific molecules in the membrane

Movement of Nerve Impulse:

Impulses (electrical activity) always move from dendrite

--->cell body--->axon--->axon terminal--->synapse

--->dendrite of next neuron.

Neuroglia• 5 ~ 10 times of neurons

• smaller than neuron,

• presence of processes (no

dendrites and axon),

• lack of nucleoli

• functional difference

•Types: 4 in CNS: astrocyte, oligodendrocytes microglia: act as macrophage

ependymal cell

2 in PNS: Capsular and Neurolemmal cell

Astrocyte• star-shaped, most numerous in gray matter • end feet attach to the wall of capillaries; • forming BBB; regulating composition of intercellular environment in CNS.

Blood-Brain Barrier components

Endoepithelium of capillariesand tight junction

Basement membrane under epithelium

End feet of astrocytes surrounding capillaries

Pericyte between epithelium & end feet of astrocytes*

Oligodendrocyte

- fewer processes;

- form myelin sheath if surround axon

• lining at the ventricles of the brain

• lining at the central canal of the spinal cord

• lacking of tight junctions between cells allows a free exchange between cerebrospinal fluid and nervous tissue.

Ependymal cell

Review

• Characteristic of nerve tissue

• Morphological Characteristics of the neuron

• synapse

• neuroglia: types, function,

and relate structures

• BBB

Neuroglia of PNS

Capsular cells (satellite cells):around the neuron’s soma

Neurolemmal cells (Schwann cells): form myelin sheath of myelinated n.f. in PNS

Nerve Fiber

• consists of an axon (or long dendrites) and its nerve sheath formed by neuroglia (schwann cell in PNS, or oligodendrocyte in CNS).

Type:

myelinated nerve fiber unmyelinated nerve fiber

Myelinated & Unmyelinated Fiber

Structure of myelinated nerve fiber

Node of Ranvier: between two segment

Internodal segment: between two nodes

Myelinsheath

Components: lipids, protein

Formed: by the successive layering of Schwann cell plasmalemma

Function as: an insulation layer,increased velocity of action potential

Saltatory conduction of myelinated nerve fiber

Unmyelinated Nerve Fiber

Schwann cell

Axons

* Axons are housed within infoldings of cytoplasm & membrane;

* An individual Schwann cell surround up to 30 separate axons.

Nerve & its Organization

What is nerve?

Nerve is composed of nerve fibers.

Epineurium

A fascicle

A nerve fiberand

endoneurim

perineurium

Connective tissue

Nerve Ending* terminals of n. f. are termed nerve ending

* two groups according to the function:

- Sensory nerve endings

Free nerve endings

Tactile corpuscles

Lamellated corpuscles

Muscular spindles

- Motor nerve endings

Sensory Nerve Endings

Free nerve endings

Tactile corpuscle

Lamellated corpuscle

Epithelium

Muscular spindle

Lamellated corpuscle

Tactile corpuscle

Motor nerve endings—skeletal muscle

Motor nerve endings—skeletal muscle