Introdutory anatomy.

There follows the text of the overhead transparencies used by Dr Johnson for introductory lectures in anatomy. These cover terminology, bones, joints, segmentation and muscles.

THE ANATOMICAL POSITION

Standing erect Face and eyes forwards Hands at sides, palms forwards Heels together, great toes adjacent

PLANES OF THE BODY

Three, mutually at right angles

Median or sagittal - sagitta, an arrow Divides the body into equal right and left halves Parasagittal divides the body into unequal right and left parts

Coronal (corona, a crown): any vertical plane at right angles to the sagittal: divides the body into anterior and posterior parts

Horizontal (horizon, the horizon): any plane at right angles to the other two: divides the body into superior and inferior parts

Oblique: any other plane

TERMS

In order to define the planes we needed three pairs of other terms:

1. medial - closer to the midline lateral - father from the midline

2. anterior - nearer the front surface of the body
posterior - nearer the back surface of the body

3. superior - nearer the crown of the head inferior - nearer the soles of the feet

TERMS IN ZOOLOGY AND EMBRYOLOGY

The human system is inappropriate for other mammals where zoological terms are used. These are also used in embryology and comparative anatomy.

1. ventral = anterior
dorsal = posterior

2. rostral, cranial,
cephalic = towards the head = superior
caudal = towards the tail = inferior

SPECIAL TERMS FOR SPECIAL BITS

In the limbs we need some special terms. These need care: look at the limbs in the anatomical position.

1. proximal - nearer the trunk, the soggy end
distal - further from the trunk

2. preaxial - the lateral border (thumb or big toe side)
postaxial - the medial border (little finger, little toe side)

3. flexor - anterior of upper limb, posterior of lower limb
extensor - other side of the limb

TERMS OF MOVEMENT

1. to flex - to bend or make an angle to extend - to straighten

2. to abduct - to draw away from the median plane
to adduct - to move towards the median plane

A combination of abduction, adduction, flexion and extension is called circumduction

3. to protrude or protract - move forwards to (retrude) or retract - move backwards

4. to pronate - turn the hand so the palm faces backwards to supinate - turn the hand so the palm faces forwards

5. to medially rotate - to turn a limb around its long axis - so the palm faces inwards to laterally rotate - to turn a limb around its long axis the other way

ODDS AND PIECES OF TURF

1. inside, interior, internal
outside, exterior, external

2. invaginations - bulges into
evaginations - bulges out from

3. superficial - near the surface
deep - further below the surface

ANATOMY

Greek to cut up = anatomy
Latin to cut up = dissection

SUBDIVISIONS OF ANATOMY

Embryology - development from egg to adult

Cytology - about cells Histology - about groups of cells, tissues and organs

Neuroanatomy - about nerve cells, and nervous tissues

Gross anatomy - anything you can see and handle without a microscope.

METHODS OF STUDY

Dissection:-

• whole body
• prosections
• plastination
• pots
• bones
• Living anatomy, surface anatomy
• Scopes and imaging
• endoscopes
• proctoscopes
• bronchoscopes
• fibre optics
• Radiographs, X rays
• contrast media
• radio isotopes
• Tomography
• computer aided tomography (CAT)
• ultrasound
• magnetic resonance imaging (MRI)

BONES

Bone vs Bones

Bone - a connective tissue impregnated with minerals

Bones - pieces of the skeleton

Misconception

That bones are dead

They have:

• cells
• nerves
• blood supply
• pain receptors

If broken they hurt, bleed and bruise

They metabolise at a fairly rapid rate: turnover inorganic matrix and collagen.

Strength

High: in standing still the weight on the hip is about 3x bodyweight due to muscular pull.
In a fracture bone ends overlap because of force applied by muscles.
A running man can exert forces = a dead-weight of 270kg.

Strength is high due to:-

the material - organic and inorganic extracellular matrix

and to the structure.

Structure of bones

Outer casing of cortical bone acts like a bicycle frame.

Inner trabecular bone is arranged along lines of force. Calcified fibres run out into tendons.

Shape

Determined by many factors:

• genetic - primary shape is genetic: organ culture grows rough, recognisable, replicas of bones
• mechanical - final fine tuning of shape is by muscular action: training and paralysis
• metabolic - calcium, phosphorous, vitamins A,C,D, - pituitary, thyroid, parathyroid, adrenal, gonadal hormones (osteoporosis) involved.

Growth involves remodelling:

• osteoblasts
• osteocytes
• osteoclasts
• growth in length

Function

1. As a lever
2. As a calcium store
3. Protective?
4. As a marrow holder

Origin of bone

Bone is either:-

preformed in cartilage - replacement or endochondral bone
or
formed in membranous connective tissue - membrane bone

Centres of ossification

Destruction of cartilage to make replacement bone

Why two types? History lesson

Classification of bones

Purely for our entertainment - not functional

Long bones:- epiphysis, diaphysis, plywood
In limbs
metacarpals, metatarsals

Short bones

Flat bones

Irregular bones

Sesamoid bones - tendons turning corners

Surface markings on bones

articular surfaces
foramina- holes for vessels/nerves humps and hollows for muscles

STRENGTH

JOINTS

Joints occur where 2 bones meet

They may:

1. join two bones with as little flexibility as possible
2. join two bones with a little ' give'
3. join two bones with a maximum flexibility

The first two are called synarthroses (sing. synarthrosis) and have no cavity
The third are called diarthroses (sing. diarthrosis) and have a cavity

TYPES OF JOINT

Synarthrosis bone - solid connective tissue - bone

1. Fibrous connective tissue

sutures bone - collagenous sutural ligament - bone
syndesmosis bone - collagenous interosseous ligament - bone
gomphosis bone - complex periodontium - bone

2. Cartilage

synchondrosis bone - hyaline cartilage - bone
symphysis bone - hyaline cartilage - fibrocartilage disc - hyaline cartilage - bone

3. Synostosis

rigid bony union

Diarthrosis bone - cavitated connective tissue - bone

Synovial joints bone - articular cartilage - fluid in cavity - articular cartilage - bone

EXAMPLES

Fibrous joints

Sutures - in skull
Gomphoses - around teeth
Syndesmoses - inferior tibia-fibula

Cartilaginous joints

primary synchondroses - named in skull (and unnamed elsewhere)
secondary synchondroses, symphyses, - bounded by fibrocartilage - pubis, menti

Synovial joints

SYNOVIAL JOINT COMPONENTS

Bone attached to articular cartilage.

Articular cartilage has:
no pain receptors
no blood vessels
very low coefficient of friction

Articular cartilage on each bone is separated by synovial fluid

Synovial fluid - dialysate of plasma secreted by synovial membrane (specialised connective tissue)
watery lubricant - viscous, elastic, plastic maintains articular cartilage cells
few cells - mainly immune system
pH buffer

Leakage prevented by fibrous capsule which forms a cuff
local thickenings - joint ligaments
local apertures - bursae

INCLUSIONS IN JOINTS

Non-articular bony surface
tendons and ligaments passing through

articular disc or meniscus
may split the cavity completely into two joints -TMJ
or be partial and partly divide cavity - menisci of the knee

labra or lips - cartilage around the edge of an articular margin which may deepen a concavity and add stability

fat pads

CLASSIFICATION OF SYNOVIAL JOINTS

1.Complexity

Two articular surfaces - simple.
Usually:
one convex, male
one concave, female
More than 2 articular surfaces - compound

2. Degrees of freedom

Moves in one plane (elbow) uniaxial
Moves in two planes biaxial
Moves in three planes triaxial

3. Shape

• hinge joints
• pivot joints
• plane joints
• condylar joints
• saddle joints
• ball and socket
• ellipsoid

SHAPES OF JOINT SURFACES

Classification by function

Movements at two bone ends are made up of:
gliding of one surface over another - slide
angulation of one surface over another - roll
rotation about bone axis - spin

THE FIT OF JOINTS

Surfaces are spheroids, egg shaped

Because of this there will be a better fit at some positions of the joint than others

Close packed:

end of range of movement
position of best fit
ligaments stretched, joint screwed home by spin
approached but not fully realised: comfortable, energy saving

Loose packed:

loose fitting surfaces can spin, roll and slide
reduced area of contact, little friction
wedge shaped gaps circulate fluid like peristaltic pump

LIMITATION OF JOINT MOVEMENT

by using up articular surface

by adjacent soft tissues

by pain and stretch receptors in ligaments and muscles Hilton's law says that joints and muscles share a nerve supply

muscle paralysis affects joints spastic paralysis - movement restricted other paralyses - joints become flails

SEGMENTATION

What is it?

Serial repetition of similar structures along body axis.

Who needs it?

Invertebrates

• Worms
• Crustacea
• Insects

Pro-vertebrates and Vertebrates

• Sea squirts
• Amphioxus
• Fishes, amphibia, reptiles, birds, mammals
• MAN

What causes segmentation?

Tissues close to the notochord segment.

Mainly mesoderm (middle stuff) which fills the gap between
ectoderm (outside stuff) which forms skin etc.
and endoderm (inside stuff) which forms gut.

The mesoderm nearest notochord forms somites.

Other parts (kidneys, genitalia, blood supply) get involved either because they are near the notochord too, or secondarily

Somites - segmental paired blocks of mesoderm, each side of the notochord

Break up immediately into sclerotome (hard slice) and dermomyotome (skin/muscle slice)

Each dermomyotome splits again into dermatome and myotome

Sclerotome forms axial skeleton - vertebral column

Myotome forms axial muscles (back, rib, body wall, limb muscles, voluntary muscles of genitals, anus) and skin of trunk

Mesoderm more lateral (so further from the notochord) forms unsegmented muscle - smooth muscle around gut, blood vessels etc.

Segmented axial muscles originally moved the vertebrae from side to side (as in fish tail)

To do this they need to be out of step

This is achieved by making a vertebra from: The inferior half of one sclerotome plus the superior half of the one behind

This allows:

1. Muscles to attach between vertebrae

2. Spinal cord (which is inside vertebrae) to run nerve roots between vertebrae to myotomes and from dermatomes

and

3. Notochord obliterated within vertebrae but survives between vertebrae as intervertebral disc.

Because of this vertebrae (named and numbered according to where they are i.e. C6, T4, L2, S1) lie immediately below nerve with the same number.

NERVOUS SYSTEM AND SEGMENTATION

Nerve tube (neural tube, brain + spinal cord) is affected by the somites.

Primitively nerves to muscles derived from the myotome are a. segmental - between vertebrae b. ventral in the cord

When dermomyotomes split sensory nerves from skin tend to be dorsal.

Dorsal and ventral roots unite as mixed spinal nerves.

Dermatomes of the skin form a series of bands around the embryo, one to each segment.

Segmental muscles also tend to form groups with common nerve supply

UNSEGMENTED MUSCLE

What about muscle that didn't segment but formed smooth muscle of the viscera?

New stuff. Ancestral forms had gut cilia, not muscles. Later forms had a system like this:

The autonomic nervous system:-
To gut: motor nerves leaving the cord at the head (brain) and tail ends.

To genitalia, heart, glands etc.: - same thing but between the head and tail sections.

Originally only one part received nerves from both sets - the heart. Stimulation of both systems makes the heart beat faster in the Lamprey.

SITUATION IN MAN

Anatomically as already described: Parasympathetic (Gk alongside the sympathetic) outflow in head and tail. Sympathetic outflow between the two.

Functionally now different: most areas (except the limbs) have both sympathetic and parasympathetic supplies.

ACTION OF SYMPATHETIC AND PARASYMPATHETIC

Sympathetic (originally to heart, glands, genitalia) perks thing up - fear and anger, dry mouth, cramped gut, rapid heartbeat, pallor, sweaty palms, goosepimples.

Parasympathetic (originally to the gut, associated with peace, tranquillity, digestion) slows the heart, increases salivation, peristalsis, secretion of stomach juices etc.

Achieved by 2 different neurotransmitters:- sympathetic - norepinephrine parasympathetic - acetylcholene

THE HEAD

The head is different because:

a. It is fairly recent (vertebrates, Amphioxus -, lamprey +)

b. The notochord doesn't go that far forward

c. Only a few somites in the tongue and eye muscles

d. Cranial nerves represent dorsal (sensory) and ventral (motor) roots which do not unite

Motor group III, IV, VI, IX
Sensory group V, VII, VIII, X, XI, XII.

n.b. I and II are both oddballs, associated with nose and eyes.
V-XII have picked up motor fibres to the 'new' pharyngeal arches which make up most of the face

MUSCLES

Muscles contract

Types of muscle: Smooth Skeletal and cardiac - both striated

Innervation

Smooth not under voluntary control

Striated (cardiac) not under voluntary control

Striated (skeletal) under voluntary control

OCCURRENCE

Smooth:

flat sheets

wrapped around a viscus (pl. viscera) in so called circular and longitudinal layers (gut) forming a sphincter to close off a tube (anus)
regulated by sympathetic/parasympathetic (autonomic) nervous system

Cardiac:

specialised: only in heart walls histologically distinct
own conducting system/ beat producer regulated by sympathetic/parasympathetic (autonomic) nervous system

Striated or skeletal:

usually attached to bone
regulated by central/ peripheral (voluntary) nervous system

SKELETAL MUSCLE

Name from musculus, little mouse
Mouse shaped?
Layman's muscle

Attachment to bone

Usually attached to skeleton at two bony points (one at each end) which are brought together by muscular contraction

ATTACHMENTS

1. tendon. Cords or strips of collagen fibres (white) - flexible, resists stretch. Integral part of muscle. Mainly parallel bundles, visible to naked eye
arise from occasional fibroblasts poor blood supply - heals slowly (Achilles' heel)
stretch/pain receptors.

May be circular in cross section, oval or flattened sheet (aponuerosis). Aponeuroses often have plywood-like crossed fibres

Friction reduced by bursae or sheaths

2. fleshy insertion

Muscle joined to bone without visible tendon. Collagen still there as inclusion within muscle.

Fleshy and tendinous insertions have Sharpey's fibres running through - continuous with collagen of bone

ORIGINS AND INSERTIONS

Origin at one end
Insertion at the other

Classically origin (which moves least on contraction) proximal, insertion distal

Muscles often arise from two, three or four places (bicipital, tricipital, quadricipital) and so has more than one head

In some circumstances origin and insertion get confused, so talk of attachments

FORM OF MUSCLES

Wide functional variation in size and shape. Bundles (fascicles) of muscle fibres (10-60µm diameter, 15-30cm length) arranged in series/parallel for power/range of contraction

Strap muscles. Flat. Short with one set of fibres, long with fibres in series (tendinous insertions between) or wide with fibres in parallel

Fusiform muscles. Spindle shaped classic, three dimensional for more fibres. One or more bellies (digastric), one or more heads.

Unipennate, bipennate, multipennate. Relations are as quill pen barbs to shaft. Unipennate (like multi headed) often unbalanced. Bipennate balanced, multipennate a variation

Spiralised impart twist

MUSCLE ACTION

Muscle tone. All muscle fibres cycle. At a given time some will be:
contracting,
relaxing,
in stasis,
Net result is muscle tone

When a muscle contracts tends to approximate ends

This opposed by
passive resistance of muscle
ditto articular tissues
opposing muscles
opposing soft tissues
inertia
load
gravity

If the force exerted exceeds this limb accelerated from rest: lower force will maintain movement

TYPES OF MUSCLE ACTION

Prime mover or agonist (to start movement) Antagonists in opposition (to control or stabilise)

If movement is abolished joint is stable - better to close pack or use gravity

Action of agonist often produces unwanted movement (in wrong direction) opposed by other muscles

MUSCLE MECHANICS

With two bones linked by a joint across which a muscle acts movement is resolved:
swing - moving the mobile bone
shunt - compressing joint
spin - rotating mobile bone

Relative size of each varied by moving attachments

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