THE SPINAL CORD Flashcards
sensory information
sensory information comes
into the spinal cord at the
DORSAL horn.
* information about the body
such as:
* fine touch.
* proprioception
* vibration.
* pain.
* temperature
motor neurons
are located in the VENTRAL
spinal cord.
* these neurones make direct
contact onto the muscles.
* stimulation of these neurones
causes movement.
* each cell is part of a motor
unit.
motor pools
All the motor neurones that
innervate a single muscle are
called a motor pool.
* Because there are more muscle
fibres than neurones, each
muscle fibre is innervated by a
single neurone, but a single
motor neurone may innervate
many fibres in the same muscle.
* The size of this innervation is
important as muscles that are
capable of fine movements are
innervated by more neurones.
what is somatotopy
Maps are referred to as
‘somatotopic’ when that
space is related to
locations on the body, such
that adjacent neurons in
the neural tissue respond
selectively to stimuli
presented to adjacent
locations on the body.
what are the 2 major descending systems
Lateral descending system
Medial descending system
the tracts of Lateral descending system
The corticospinal and rubrospinal
tracts
the tracts of the medial descending system
The vestibulospinal and reticulospinal
tracts
what is the lateral descending system
he corticospinal and rubrospinal
tracts make up the the lateral
descending system
* fibres of the lateral system are in the dorso-
lateral part of the spinal cord.
* they connect to motor neurones in the
lateral part of the ventral horn.
* this system influences lateral musculature.
lateral system – round up
Corticospinal fibers strongly influence movement of every part of the
body and is particularly useful for individual finger use.
2. Other descending fibers, primarily the rubrospinal tract, can compensate
almost completely for the loss of descending corticospinal input.
3. The one ability of the descending corticospinal tract for which no other
tract can compensate is the ability to use the fingers individually.
Individual finger movements are the sole province of the corticospinal
system.
what is the medial descending system
The vestibulospinal and reticulospinal
tracts make up the the medial descending
system.
* fibres of the medial system are in the
ventro-medial part white matter.
* they connect to motor neurones in the
medial part of the ventral horn.
* this system influences medial musculature
medial systems – round up
the medial systems are involved in the control of balance and
posture.
2. these functions happen with little conscious control.
3. the vestibulospinal tract retains balance when the body is
moved – external disturbance.
4. the reticulospinal tract helps us retain posture and balance
during our own volitional movements – internal disturbance.
what is the dorsal column pathway
carries sensory information
from the joint and skin about:
* fine touch.
* vibration.
* two-point discrimination.
* proprioception (position) from
the skin and joints.
what is the Spinothalamic pathway
The lateral spinothalamic tract
conveys
* crude touch.
* a sense of being touched
without knowledge of where.
* pain.
* temperature.
what is the dorsal root ganglion
The cell bodies of incoming sensory neurones lie outside the spine in a
series of ganglion
This is unlike the motor neurones that have their cell bodies in the
ventral horn
how many spinal nerves are there
31 pairs of spinal nerves.
* The positions in the spine these
nerves will determine what part of
the body each spinal nerve serves.
* Because some parts of the body
have more muscles and more
sensory receptors. The size of the
nerve and the amount of
information carried by the nerve will
be different.
what are dermatomes
an area of the skin
supplied by nerves
from a single spinal
root.
what is shingles
Chickenpox is caused by
the varicella zoster virus ).
After recovery the virus
remains in your DRG.
* Sometimes in later life the
virus can reactivate
producing a painful or
itchy rash that is isolated
to a single dermatome
what is 2 point discrimination
is the ability to
discern that two
nearby objects
touching the
this ability reflects
how finely innervated
an area of skin is
how are muscles stimulated
All the motor neurones that
innervate a single muscle are
called a motor pool.
* Because there are more muscle
fibres than neurones, each
muscle fibre is innervated by a
single neurone, but a single
motor neurone may innervate
many fibres in the same muscle.
* The size of this innervation is
important as muscles that are
capable of fine movements are
innervated by more neurones.
what are motor units
a lower motor neurone (or alpha
motor neurone) in the spinal
cord innervates a muscle.
* each motor neuron synapses
with multiple fibres within the
muscle. The motor neurone
and all the muscle fibres it
contacts define the motor unit.
* cross section through the muscle
shows the relatively diffuse
distribution of muscle fibres (dark
fibres) contacted by a single
motor neuron.
Motor pools are made of motor units.
what is spinal enlargements
the arms and legs (particularly the
hands and feet) have many highly
innervated muscles and have a
high density of sensory receptors.
Because of this the portions od
the spinal cord that provide the
spinal nerves to the arms and
legs are enlarged.
information flow in spinal cord
dorsal horn - contains sensory
neurones. these receive
sensory information and send
this up to the brain.
* Ventral horn – contain
neurones that send messages
directly to the muscles.
* intermediate zone –contain
interneurones. these integrate
information. e.g – inhibition.
what does the stimulus intensity determine
stimulus intensity determines size of receptor potential & thus
frequency of action potentials
what does the firing frequency code for
firing frequency codes for intensity (“rate code”)
very non-linear
usually codes for intensity
of contrast between two
levels.
