Download ANATOMICAL TERMS

ANATOMICAL TERMS
Anatomical stance
Is a stance in which a person stand erect with the feet flat on the floor and close together, arms at
their sides and the palms and face directed forwards?
Body Planes
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Sagittal Plane – Passes vertically though the body or an organ and it divides it into
right and left positions
Midsagittal (median) plane – The sagittal plane that divides the body or organ into
equal halves
Parasagittal Planes – Sagittal planes that are parallel to the medium and divide into
unequal right and left portions
Frontal (coronal) planes - Extends vertically but is perpendicular to the sagittal plane
and divides the body into anterior and posterior positions
Horizontal (cross-sectional or transverse) planes - Passed across the body or an
organ perpendicular to its long axis; it divides the body or organ into superior
(upper) and inferior(lower) portions
Direction
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Plane – Frontal (Coronal)
 Anterior (ventral) – towards the front or belly
 Posterior (dorsal) – Towards the back or spine
Plane – (Horizontal (Transverse)
 Superior (cranial) – Above
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 Inferior (caudal) – Below
Plane – (Sagittal)
 Medial – Towards the median plane
 Lateral – Away from the medial plane
Superficial – Closer to the body surface
Deep – further from the body surface
Proximal – Closer to the point of attachment of origin
Distal – Further from the point of attachment of origin
Movements
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Flexion – Movement that usually decreases a joint angle, usually in the sagittal plane
 Eg: Bending elbow or knee
Extension – Movement that straightens a joint and generally returns a body point to
the zero position
 Eg: Straightening the elbow or knee
Hyperextension – further extension of the joint passed through the zero position
 Eg: Whiplash
Abduction – the movement of a body part in the frontal plane away from the
midline of the body
 Eg: Moving feet apart to stand spread legged or raising one arm to one side
of the body
Adduction – movement in the frontal plane back towards the midline of the body
 Eg: Closing arms back to the chest
Rotation – Movement in which a bone spins on its longitudinal axis
Pronation – Movement causing the palm to face posteriorly or downwards
Supination – Movement that turns the palm to face anteriorly or upwards
Circumduction - One end of an appendage remains stationary while the other end
makes a circular motion
 Eg: A baseball player throwing a ball
Elevation – Movement that raises a body part vertically in the frontal plane
 Eg: Raising your eyebrows
Depression – Lowers a body part in the same plane
 Eg: Lowering your eyebrows
Inversion – Foot movement that tips the soles medially, somewhat facing each other
Eversion – movement that tips the soles laterally away from each other
NERVOUS SYSTEM
Overview
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Central Nervous System – consists of the brain and the spinal cord, which are enclosed and
protected by the cranium and vertebral column
Peripheral Nervous System – consists of all the rest (somatic and motor), it is composed of
nerves and ganglia
o Nerves – a bundle of nerve fibres (axons) wrapped in fibrous connective tissue (CT)
o Ganglia – a knot like swelling in a nerve where the cell bodies of neurons are
concentrated
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Sensory (afferent) division – carriers signals from various receptors to the CNS
 Somatic sensory division – carriers signals from receptors in the skin,
muscles, bone and joints
 Visceral sensory division – carriers signals mainly from the viscera of the
thoracic and abdominal cavities
Motor (efferent) division – carriers signals from the CNS to gland and muscle cells
that carry out the body’s responses
 Somatic motor division – carriers signals to the skeletal muscles
 Visceral motor division (autonomic nervous system) – carriers signals to
glands, cardiac muscles and smooth muscles
 Sympathetic division – tends to arouse body for action, accelerating
the heartbeat
 Parasympathetic division – tends to have a calming effect, slowing
the heartbeat
a) Describe the embryological development of the nervous system.
Embryonic Development
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The nervous systems develops from the ectoderm
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Within the first 3 weeks the neural plate forms along the midline of the embryo and sinks
into the tissue to form the neural groove, with raised neural folds
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The neural folds’ roll towards each other and fuse
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By day 26 the neural folds form the neural tube
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As the neural tube develops it forms a neural crest
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Neural crest cells give rise to the peripheral nervous system, including the sensory and
automatic nerves
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By the fourth week the neural tube forms the forebrain, midbrain and hindbrain
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Neural tube
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Everything on the dorsal side is sensory
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Everything on the ventral side is motor
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Failure of the neural tube to close results in spina bifida
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Somites are regular repeating pattern along the tube
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Each segment has a spinal nerve
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The spinal nerve is protected by vertebrae’s
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Shingles is a viral infection that affects neurons
Embryological Development Failure
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Spina Bifida
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Indicates a failure of the dorsal portions of the vertebrae to fuse with each other
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More severe forms, involve failure to close of more than one or two vertebrae,
resulting in the meninges bulging through (meningocele) the opening or the
meninges, spinal cord and nerves bulging out (meningomyelocele)
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The more sever forms involve gradation of neurological symptoms which may
include paralysis, loss of bladder and anal control and absence of reflexes
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To prevent this condition females should have a high level of folic acid, when trying
to have a child
Anencephaly
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Results from failure of the cephalic part of the neural tubes to close
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The fore and mid brain do not develop fully
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The cranial vault is also absent, resulting in the infant not surviving past birth
Hydrocephaly
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The circulation or drainage of CSF is obstructed resulting in a build-up in pressure
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This result in abnormal skull in infants, as there skull is not yet fused, which can lead
to possible retardation
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This can be treated before birth by inserting a shunt which drains the fluid from the
ventricles into a vein in the neck
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In adults the skull is unable to grow and the brain is compressed causing pain, coma
and then death if not treated
b) Describe and identify gross anatomical features of the nervous system.
Structure of a Neuron
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The control centre of a neuron is the soma/neurosoma/cell body
o The soma usually gives rise to the dendrites, long, thin like branches
 They are the primary site for receiving signals from other neurons
 The more dendrite a neuron has the more information it can receive
 5 to 135 micro metres in diameter
o Axon - a cylindrical and relatively unbranched for most of its length
 Specialised for rapid conduction of nerve signals to points remote from the
soma
 1 to 20 micro metres long
Neuron Classifications
o Multipolar Neurons – one axon and multiple dendrites
o Bipolar Neurons – one axon and one dendrite
o Anaxonic Neurons – multiple dendrites and no axons
Axonal Transport
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Axonal transport – the two-way passage of proteins, organelles and other materials along an
axon
Anterograde transport – movement away from the soma down the axon
Retrograde transport – movement up the axon toward the soma
Fast axonal transport – occurs at a rate of 20 to 400 mm/day and may either be anterograde
or retrograde
o Fast anterograde transport – moves mitochondria, synaptic vesicles
o Fast retrograde transport – returns used synaptic vesicles and other material to the
soma and informs the soma of the conditions of the axon terminals
Slow axonal transport – an anterograde process that works in a stop and go fashion, moves
at 0.5 to 10 mm/day
o Moves enzymes and cytoskeletal components down the axon
Types of Neuroglia
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Neuroglia of CNS
o Oligodendrocytes – form myelin in brain and spinal cord
o Ependymal cells – line cavities of brain and spinal cord
o Microglia – destroys microorganisms, foreign matter and dead nervous tissue
o Astrocytes – cover brain surface
Neuroglia of PNS
o Schwann cells – forms a myelin sheath around nerve in the PNS
o Satellite cells – surround somas of neurons in the ganglia
Myelin
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Myelin sheath is a spiral layer of insulation around a nerve fibre, formed by oligodendrocytes
in the CNS and Schwann cells in the PNS
Production of the myelin sheath is called myelination, begins at the 14th week of foetal
development
Conduction speed of Nerve Fibres
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The speed at which a nerve signal travels along a nerve fibre depends on two facts, the
diameter of the fibre and the presence or absence of myelin
o Travel fast in the presence of myelin
Local Potentials
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Stimulation of neuron causes local disturbances in membrane potential
Depolarization – any such case in which the voltage shifts to a less negative value
Local Potential – Short range change in voltage
Characteristics
o Graded – they vary in magnitude (voltage) per the strength of the stimuli
 An intense or prolonged stimulus opens more ion channels than a weaker
stimulus
o Decremental – they get weaker as they spread from the point of stimulation
o Reversible – if stimulation ceases, cation diffusion out of the cell quickly returns the
membrane voltage to its resting potential
o Either excitatory or inhibitory
Action Potentials
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Action potential – a more dramatic change produced by voltage-gated ion channels in the
plasma membrane
Characteristics
o All or non-law – the neuron will only fire if the threshold has been reached
o Non-decremental – they do not get weaker with distance
o Irreversible – if a neuron reaches threshold, the action potential goes to completion,
it cannot be stopped once it begins
Threshold – the minimum needed to open voltage-gated channels
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Refractory period – during an action potential and for a few milliseconds after, it is difficult
or impossible to stimulate that region of a neuron to fire again
o Absolute refractory period – no stimulus of any strength will trigger a new action
potential
o Relative refractory period – it is possible to trigger a new action potential, but only
with an unusually strong stimulus
Local vs Action Potential
Local Potential
Produced by gated channels of the dendrites
and Soma
May be positive (depolarizing) or negative
(hyperpolarizing) voltage change
Graded; proportion to stimulus strength
Reversible
Local
Decremental
Action Potential
Produced by voltage-gated channels on the
trigger zone and axon
Always begins with depolarization
All or none
Irreversible
Self-propagating
Nondecremental
Spinal Cord – Structure
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A cylinder of nervous tissue that arises from the brainstem at the foramen magnum of the
skull
45cm long and 1.8cm thick
During embryological development, the spinal cord extends for the full length of the
vertebrae, but since the vertebrae grows faster than the spinal cord, the cord only extends
to L3 by the time of birth and to L1 in an adult
31 pairs of spinal nerves
o The part supplied by each pair of nerves is called a segment
Region of Spinal Cord
Cervical
Thoracic
Lumbar
Sacral
Coccygeal
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Number of pairs of nerves
8
12
5
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Spinal cord is divided into cervical, thoracic lumbar and sacral regions
Thicker in two areas
o In the inferior cervical region, a cervical enlargement gives rise to nerves of the
upper limbs
o In the lumbosacral region, lumbar enlargement that issues nerves to the pelvic
region and lower limbs
Cauda equine is a bundle of nerve roots
Spinal cord is enclosed by three fibrous membranes called meninges, that separate the soft
tissue of the central nervous system from the bones of the vertebrae and skull
o Dura mater – forms a loose-fitting sleeve called the Dural sheath around the spinal
cord
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Tough, collagenous membrane
Epidural space – space between the sheath and vertebral bones, that is
occupied by blood vessels, adipose tissue and loose connective tissue
 Epidural anaesthesia – anaesthetics introduced to this space to block pain
signals during childbirth or surgery
o Arachnoid mater – a loose mesh of collagenous and elastic fibers spanning the gap
between the arachnoid membrane and the pia mater
 Simple squamous epithelium
 Subarachnoid space – gap between the arachnoid membrane and the pia
mater that is filled with cerebrospinal fluid
o Pia mater
 Delicate, transparent membrane that closely follows the contours of the
spinal cord
Cross sectional anatomy
o Consists of two kinds of nervous tissue called grey and white matter
 Grey matter – relatively dull colour because it contains little myelin
 White matter – bright, pearly white appearance due to an abundance of
myelin
 There is more white matter on sections of the spinal cord that are
closer to the brain since there are more ascending and descending
tracts closer to the brain
o Axons run through white matter
 Surrounds the grey matter
Spinal tracts
o Ascending tracts – carry sensory information up the cord
 Example
 Gracile fasciculus – carries signals from the mid thoracic and lower
parts of the body
 Cuneate fasciculus – joins the gracile fasciculus at the T6 level
 Spinothalamic tract – carriers signals for pain, temperature,
pressure, tickle, itch and touch
 Spinoreticular tract – carries pain signals resulting from tissue injury
 Posterior and anterior spinocerebellar tracts – carry proprioceptive
signals from the limbs and trunk to the cerebellum at the rear of the
brain
o Descending tracts – conduct motor impulses down
 Example
 Corticospinal tract – carry motor signals
 Tectospinal tract – involved in reflex turning of the head
 Lateral and medial reticulospinal tract – control muscle of the upper
and lower limbs
 Lateral and medial vestibulospinal tract – control of extensor
muscles of the brain
o Decussation – the tracts cross over from the left side of the body to the right
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As a result the left side of the brain receives sensory information from the
right side of the body and sends motor commands to that side
Neurons
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Neurons are cells
10^10 neurons
Predominantly the same structure
A living cell with a nucleus
Neurons cannot divide
The Brain
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Rostral – towards the forehead
Caudal – towards the spinal cord
Three major portions of the brain (Major parts of CNS)
o Cerebrum
 83% of brains volume
 Grey matter on outside
 Marked by thick folds called gyri and separated by shallow grooves called
sulci
 The longitudinal fissure separates the right and left portion
 The hemispheres are connected by a thick bundle of nerve fibers called the
corpus callosum