1BioSci107Lecture 4 Muscle and Nerve Tissue2015

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Objectives

Describe general features of muscle tissue Understand location, structure, function

Describe general features of nervous tissue Understand the function of its component

cells.

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2Muscle Tissue

Consists of elongated cells (muscle fibres or myocytes) that use energy from the hydrolysis of ATP (adenosine triphosphate) to generate force.

The Tissues of the Body (iii):Muscle and Nervous

As a result of contraction, muscle tissue produces body movements, maintains posture and generates heat. 3

Muscle Tissue

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There are three types of muscle comprising ~50% of the body tissue mass:

i. Skeletal Muscle

ii. Cardiac Muscle

iii.Smooth Muscle

3i. Skeletal Muscle There are about 650 named skeletal muscles in

the body

Usually attached to bones via tendons.

Appear striated under the microscope.

Contraction is under conscious control (voluntary; sometimes not always - posture)

Fibres (remember = cells) cylindrical

www.dbtechno.com5

Smallest: 1.25 mm stapedius (in the ear; prevent hyperacusis; Bells Palsy; facial n)

Longest: up to the 60 cm sartorius (Checking for gum! : hip: flexor, abductor, lateral rotator; knee: flexor).

*Hyperacusis stapedius n damage - extra loud sound perception.

Stapedius

Sartorius

Type Location Structure ControlSkeletal Attached to bones

by tendons Long cells; Striated; Multinucleate (many peripheral nuclei pushed to side)

Voluntary

Skeletal Muscle Tissue

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Functions: Motion, Posture, Heat, Protection

Note: cylindrical cells

4The striations of skeletal muscle fibres (cells) are due to the highly organised arrangement of myofibrils within the cells

Myofibrils (2 m diam) more or less fill the cytoplasm (sarcoplasm) of the muscle fibre and extend its entire length within the cell

Myofibrils are composed of two types of filaments (myofilaments): Thin filaments: mostly actin; 8 nm diam; 1-2 m long Thick filaments: myosin; 16 nm diam; 1-2 m long

Myofilaments do not extend the length of the muscle fibre, but are arranged in compartments called sarcomeres

Z discs (Z lines) separate sarcomeres

The sarcomere is the basic functional unit of a myofibril

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Connective tissue of skeletal muscle

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Epimysium: surrounds anatomical muscle

Perimysium: fascicles

Endomysium: muscle fibres (cell)

5The thick and thin filaments overlap to produce the striations:A band: dark, middle part ; contains all the thick filamentsI band: thin filaments, but no thick filamentsH zone: thick filaments, but no thin filamentsM line: middle of sarcomere (holds thick filaments together)Z disc: passes through centre of I band (between sarcomeres) made up of actinins that link filaments of adjacent sarcomeres

9Titin: links Z to M; provides resting tension in I band, molecular spring

ii Cardiac MuscleStriated. Branched. Single central nucleus.Fibres join end-to-end through intercalated discs.

Gap junction

Intercalated disc TEM

GJD

Intercalated discs contain: 1. Desmosomes (bind intermediate filaments) Provide adhesion in contraction 2. Gap junctions (communication) (co ordinated; rapid conduction).

Desmosome10

6Type Location Structure ControlCardiac Heart Striated; branched;

single central nucleus; intercalated discs

Involuntary

Cardiac Muscle Tissue

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Still have actin and myosin

iii. Smooth Muscle (no striations)Located in the walls of hollow internal structures

e.g. intestines (peristalsis); blood vessel walls (constriction); also : Iris of eye, reproductive; digestive; respiratory; urinary; skin

erector pili

Short, Small, spindle-shaped, about 30-200 m long; 3-8 m thickest in the middle

InvoluntaryNon-striated (smooth)Single central nucleus

Single smooth muscle cell Generalised blood vessel12

7 Smooth muscle fibres are non-striated, but still have bundles of thin (e.g. actin) and thick (e.g myosin) filaments.

Thin filaments (e.g. actin) attach to dense bodies, functionally similar to Z discs. (Dense body: a major protein is Actinin).

Intermediate filaments (non-contractile elements) also connect to dense bodies

During contraction tension is transmitted to the intermediate filaments (dont contract), and the cell twistsas it contracts about these stable rods.

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Smooth Muscle Tissue

Type Location Structure ControlSmooth In the walls of hollow

internal structures e.g. blood vessels, intestines, skin

Non-striated (smooth);single, central nucleus

Involuntary

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Lots of gap junctions: e.g. gut; or no gap junctions: e.g Iris

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Nervous Tissue

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9The nervous system helps to:maintain homeostasis (along with the endocrine system), initiates voluntary movementsresponsible for perception, behaviour and memory.

4. Nervous Tissue

Nervous tissue is the essential component of the nervous system.

The nervous system has two main subdivisions: Central nervous system (CNS): brain and spinal cord Peripheral nervous system (PNS): all nervous tissue outside CNS

Activities grouped under three major functions:

i. Sensory: Detection of internal and external stimuli and transfer to CNSii. Integrative: analysis and storing of informationiii. Motor: stimulation of effectors (e.g. muscle and glands) through PNS i.e.

motor here means effector17

Nervous tissue consists of two types of cells: neurons (nerve cells) neuroglia (supportive cells).

Neurons are longest cells in body (up to 1m spinal cord to toe)Conscious and unconscious control

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Neurons Have a cell body into which short, branched dendrites convey nerve impulses (action potentials) and from which a longer, single axonconducts nerve impulses to another neuron or tissue.

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Multipolar Neurons Have 2 or more dendrites

and a single axon. Most common neurons in

CNS All motor neurons (control

skeletal muscle) are in this class

Some of longest (spinal cord to toe muscles)

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Bipolar Neurons Two distinct processes

1 dendritic processes (can branch at tip but not at cell body)

And 1 axon

Has cell body between axon and dendrite

Rare and small (30m) Special sense organs

(sight, smell, hearing) relay information from receptor to neurons

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Unipolar Neuron

The dendrites and axon are continuous

Cell body off to one side Whole thing from where

dendrites converge called axon

Most sensory nerves are unipolar

Very long (1m) like motor nerves CNS-toe tip.

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Anaxonic neuron

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Rare and function poorly understood

Anatomy cannot distinguish dendrites from axons

Found in brain and special sense organs

Neuroglia Found in both CNS and PNS. Make up about half the volume of the CNS (glue). Smaller than neurons but more numerous (5-50x) Do not propagate action potentials, but can communicate. Can divide within the mature nervous system

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Functions Physical structure of nervous tissue Repair framework of nervous tissue Undertake phagocytosis Nutrient supply to Neurons Regulate interstitial fluid in neural tissue.

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Classification of Neuroglia

1. CNS Neuroglia

i. Astrocytes:

a. Star-shaped; largest; most numerous. Syncytium network.

b. Support (have microfilaments) and repair (scar).

c. Communicate with neurons via gliotransmitters e.g. glutamate

d. Maintain environment around neuron by eg regulating ions.

e. Maintain blood-brain barrier via endothelium. Wrap around vessels and influence their permeability

ii. Oligodendrocytes: Form insulating multilayered myelin sheath ( protein lipid layer) around CNS axons. Can myelinate more than one neuron cells axon. Accelerate the action potential.

iii. Microglia: Phagocytic (resident macrophages) - protection

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http://drgominak.com

Oligodendrocyte Inactive microglia Active microglia

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IV. Ependymal cells: Produce cerebrospinal fluid (CSF).

Line the CSF-filled ventricles in the brain and the central canal of the spinal cord.

These single layer of predominantly cuboidal cells have cilia (flow) and microvilli (sampling).

Located in ventricles and in other locations where CSF found.

Ependymal cells

Martin Hasselblatt

Blausen.com staff

2. Peripheral Nervous System Neurogliai. Schwann cells: form insulating myelin sheath around axons or can just

support and surround several non-myelinated axons. (Note: One schwanncell per axon for myelination but more axons/cell if just support).

ii. Satellite cells: surround neuron cell bodies. Support and fluid exchange (equiv. to astrocytes in CNS).

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Myelinating Schwann

Non-Myelinating Schwann

NOTE: Text Book Resources

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Tortora and Derrickson: (See lecture notes in Course guide)

Martini and Ober:(See lecture notes in Course guide)

Image Acknowledgements: Various editions of these 2 text books above or Wikipedia (free creative commons) were the sources for the images used in BioSci 107 Lectures 1-5 in 2015; unless otherwise stated.