Transcript pathways - LearningSpace

Pathways: movement and
sensation
The pathways:
• The motor pathways:
Direct and indirect activation pathways
• The white matter pathways
• The sensory pathways
Movement overview:
• Is complex and incompletely understood
• Is planned in sensorimotor areas of the cortex
• Is effected by pathways of descending neurons,
under the control of the cerebellum and the basal
ganglia
• Control is achieved through sensory feedback
from muscles/joints
• And information from the eyes and ears (vision
and balance) also influences the motor pathways
Control circuits
• The cerebellum: coordinates motor and
sensory information
• Gets info from the cortex about what muscles
SHOULD be doing, and compares this with
what is ACTUALLY happening
• The basal ganglia: involved in control of
background movement, and initiation of
movement patterns
Voluntary movement
• Although skeletal movement is under our
voluntary control, much of it is automatic
• Speech, chewing, swallowing comes under the
heading of automatic movements that can be
altered voluntarily
• These ‘automated’ movements are acquired
developmentally
• Can be affected by developmental
abnormalities, or ABI
Pathways: functional divisions of the
motor system
• Direct activation pathway (pyramidal tracts):
– UMNs: corticobulbar and corticospinal tracts
• Indirect activation pathway (extrapyramidal
tracts):
– Also UMNs: corticorubral, corticoreticular,
rubrospinal, reticulospinal, vestibulospinal and related
tracts
• Final common pathway (FCP):
• LMNs: generates activity in skeletal (voluntary)
muscles
Lateral premotor cortex
The motor cortex
• http://thebrain.mcgill.ca/flash/i/i_06/i_06_cr/
i_06_cr_mou/i_06_cr_mou.html
The cortical areas responsible for
movement and sensation
• What is meant by a motor/sensory
homunculus?
– What areas have the most representation?
– What are the main differences you notice between
the two homunculi?
Structural classification of neurons
Pyramidal cells
The direct pathways:
So..the Direct Activation pathway….
• Originates in the (predominantly) frontal cortex of each
hemisphere where 1x106 pyramidal cells are located
• Directly connects this cortex to the lower motor neurons
• The upper motor neurons synapse on:
– anterior horn cells (corticospinal tract)
– cranial nerve nuclei (corticobulbar tract)
• The lower motor neurons emerge at the spinal and bulbar
levels, and activate skeletal muscle
• The direct activation pathway is primarily facilitative
• Activity leads to finely controlled, skilled and discrete
movements
• The ‘express’ route
The corticospinal tract:
The Corticospinal tract
• http://thebrain.mcgill.ca/flash/i/i_06/i_06_cl/
i_06_cl_mou/i_06_cl_mou.html
www.studyblue.com
The corticobulbar tract
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The corticobulbar tract:
The axons of the UMN s follow
the same path as those of the
corticospinal tract until they reach
the brainstem, there some cross over,
others remain uncrossed
The UMNs terminate in the nuclei of
CN
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IV
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VII
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X
Hind brain (diencephalon) and brain stem showing major structures and the
origins of the cranial nerves
CN nuclei lie at the same level that the nerve enters or leaves the brainstem
Indirect activation pathways
Sometimes called extrapyramidal pathway
• Complex and incompletely understood (esp with
regard to speech pathways)
• Originates in motor, premotor and sensory cortex,
and brainstem
• Composed of numerous short pathways and
interconnected structures (so are polysynaptic)
involving the motor cortex, the bsal ganglia, the
limbic system, the thalamus, the cerebellum, the
reticular formation AND nuclei in the brainstem
• UMNs synapse
• Helps regulate reflexes & mediates
subconscious automatic muscle activities e.g.
posture and tone.
• Many of its activities are inhibitory (i.e.
prevent too much tone/movement)
• The ‘local’ route
Examples of indirect pathways
• Rubrospinal - large muscle movement as well as fine motor control.
Terminates cervical spinal cord. Facilitates flexion in the upper extremities
• Reticulospinal - descends from reticular formation in two tracts to act
on the motor neurons supplying the trunk and proximal limb muscles.
Involved mainly in locomotion and postural control
• Tectospinal - coordinates head and eye movements. Connects midbrain
tectum and spinal cord. Mediates reflex postural movements of head in
response to visual and auditory stimuli.
• Vestibulospinal – Vestibular nuclei receive information through
vestibulocochlear nerve about changes in orientation of head. The nuclei
relay motor commands through the vestibulospinal tract.
Function of these motors commands = to alter muscle tone,
extend, and change the position of the limbs and head with
the goal of supporting posture and maintaining balance of the
body and head.
Summary of direct and indirect
activation pathways
• Both pathways end on LMNs
• These LMNs receive both excitatory and inhibitory
stimulation from both pathways
• The sum of this input determines the final response of
an individual neuron in the pathway
• The indirect pathway provides the framework (muscle
tone, posture, regulation of reflex activity)
• The direct pathway accomplishes the skilled, discrete
muscle actions
• The LMNs are referred to as the final common
pathways or FCP
White Matter pathways
There are three types of white matter pathway:
• Commisural
• Association
• Projection
White and Grey matter
• White matter = highways for information flow
in the NS
• Grey matter = receives and integrates
incoming and outgoing information
...Commissural White Matter Pathways
• Commissural white matter pathways connect the 2
hemispheres. The largest is the corpus callosum,
with its posterior splenium, central body or trunk,
anterior genu, and ventrally directed rostrum.
• Besides the corpus callosum, commisural white
matter pathways include the anterior commisure
which connects the olfactory &
temporal regions,
and the posterior commisure
...Projection White Matter Pathways
• White matter projections consist of long tracts
which connect the cortex with the brainstem and
spinal cord
• These long tracts both ascend and descend.
• The corona radiata consists of projection tracts
running to and from the cortex
• The projections converge at the internal capsule
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...Association White Matter Pathways
• Connect cerebral areas within each hemisphere.
• Association pathways are generally bidirectional.
• Association pathways contain short association fibres known
as "U" or arcuate fibres that link adjacent cortical gyri.
• Long association fibres, all of which terminate in the frontal
lobe, include these 5 types: the cingulate, the arcuate
fasciculus, the superior occipitofrontal fasciculus, the inferior
occipitofrontal fasciculus, and the uncinate fasciculus.
• The degree and integrity of neural myelination significantly
influences the speed and efficiency of action potential
propagation.
Study the stretch reflex
• Revise the structure and function of the
muscle spindle (see lecture 3, Nerves, Muscles
and How They Work)
• Watch the video or review the pathways
involved in the stretch reflex:
• http://www.youtube.com/watch?v=HfuhVWK
8C0U
Note the terms:
• Agonist/antagonist
• Interneuron
• Reciprocal innervation
• If you are unfamiliar with these terms through
your reading, then look them up and write
some definitions now
Particular relevance to SLT:
• To perform accurate movements, information re
the range, rate and force of contraction, and
position of the muscles, is essential.
• Muscle spindle actions are involved in controlling
the rapid and fine muscle movements required
for speech.
• Sensory nerves from muscle spindles send out a
continuous stream of impulses to the CNS
• Muscle tone is maintained via these feedback
mechanisms
Jane, 17, suffered a C7 spinal cord
injury after falling from her horse.
• Will she exhibit a knee jerk reflex when the
patellar tendon is stretched?
• What will she feel when her knee is tapped?
Some Clues
• You will need to refer to the pathway in this
particular stretch reflex, and consider the spinal level
involved
• You will need to research the main sensory
pathways which run from the periphery
to the cortex
• Then consider how spinal injury might
affect these pathways
• The next diagram contains some clues
The diagram illustrates the position of the major ascending
(sensory) and descending (motor) tracts in the upper spinal cord
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Joyce, 74, has had a stroke.
The CT scan shows an infarct in the anterior
limb of the left internal capsule
What will be the likely effects of this stroke?
Will her signs and symptoms be of upper
motor neuron or lower motor neuron
damage?
Will they be contralateral or ipsilateral to the
lesion side?
List the common signs of both upper and
lower motor neuron damage
The clue
• Lies in the direct pathway..study this closely
and identify the internal capsule….you may
need to magnify (hint!)
“Elementary, my dear Watson!”
George, 11, Bell’s palsy
Or he could be any one of a number of young people
with this condition
https://www.youtube.com/watch?v=PpIjB5TmMx4
Bell’s palsy
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Why is it called Bell’s palsy?
What causes it?
Where is the lesion?
Use the ppt slides supplied, your texts and
watch the You Tube materials on the following
slides to help you
• Can it be treated?
Here is you clue:
www.nature.com
And more clues…..
Unilateral UMN v Bells’ palsy
http://www.youtube.com/watch?v=L8hIWPYm6
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