descending pathways Flashcards
motor system evolution
-as animals evolved with more complex nerous systems and motor capabilities more pathways evolved
steps of motor system evolution
- reticular formation
- vestibular system
- development of tectum
- development of red nucleus
- development of cerebral cortex to control the above systems
- then the devlopment of the pyramidal tract
how are the descending pathway neurons of the limbs organized in the ventral horn
- example
- somatotopic organization
- more medial you are in the spinal cord the more medial the muscles are
what are the 2 groups of descending pathways
lateral ( lateral cortico spinal tract) and medial pathways ( vestibulo spinal tract, reticulospinal, tectospinal)
why are the lateral cortico spinal tract lateral?
◼ Control of distal musculature
- such as hands and fingers
why are vestibulo spinal , reticulospinal, and tectospinal tracts medial
◼ Control of axial and proximal
musculature
- such as balance and equilibrium
what cells are located in the cortex
Giant pyramidal cells
- (betz cells)
when does the motor cortex fire
Fires impulses prior to muscle
movement
how is the motor cortex organized to produce
◼ Organized to produce simple
movements of individual body parts
what does the motor cortex determine
Determines direction, amplitude,
speed, and force of movement
the motor cortex is not organized to control ______ muscles
individual
what is the somatotopic organization of of the primary motor cortex
More area given to parts of body that perform
more precise and delicate movements as compared
to those that perform less precise movements.
what is the efferent patheay
pathway:
-axons travel through white matter internal capsule
cruscerebri/cerebral peduncle
pyramidal fibers pierce the pons pyramids of medulla
lateral
corticospinal tract
where is the the crus ceribri and sunstantia ( cerbral peduncle )
where are the pyranidal fibers in the pons ( cortical spinal tract)
what does the premotor cortex produce movements in response to
- what types of movements does it direct?
- visual and other stimuli
- Directs reaching and grasping
movements
what is the supplementary motor cortex concerned with
Concerned with movement that is
self- generated
what is included in the motor asscocaiation cortex
- premotor cortex
- supplementary motor cortex
photo of premotor and primary motor cortex
what is the corticobulbart tract pathway
◼ Cell bodies in motor cortex (lateral
convexity)
◼ Fibers leave through internal capsule
◼ Exit in midbrain, pons and medulla
◼ Innervate cranial nerve motor nuclei
◼ Crossed and uncrossed fibers
what nuclei are innervated by the corticobulbar tract
Trigeminal motor nucleus
Nucleus ambiguus
Facial motor nucleus (upper face)
Facial motor nucleus (lower face)
Hypoglossal nucleus
what are the functions of:
Trigeminal motor nucleus
Nucleus ambiguus
Facial motor nucleus (upper face)
Facial motor nucleus (lower face)
Hypoglossal nucleus
responsible for
trigeminal: muscles of mastication
- Ambiguus: pharynx and larynx muscles
- 2 subnuclei for facial nucleus upper face and lower face
- Hypoglossal: tongue muscles
what is the organization of the fibers of the corticobulbar tract
- how is this different than corticospinal
- crossed and uncrossed fibers
- completely crossed - cortico spinal
how are the nerves of the lower face and tongue organized
- ex
- what does this resemble
- theyre completely crossed
- so left buccinators are controlled by the right motor cortex
-similar to corticospinal r=tract
what is bells palsy produced by
- lesion to the facial nerve and facial nucleus
what does a lession to the left facial nerve cause
- paralysis to the left half of the face including the eye, mouth, and forehead
what happens when you get a lesion to the cortex before it gets to the motor nucleus of 7 on the right side
- the axons will degenerate and pt loses control of the lower part of the face of the left side
what does it mean a pt has paralysis to the lower half of the face vs the whole half
- lower half = stroke ( central weakness/lesion)
- whole half = bells palsey (peripheral weaknes/lesion)
how many neurons in the upper face vs lower face
- what happens if there is a stroke in the right side
- upper face has 2 neurons ( one goes right the other goes left)
- lower face has 1
- lower left face droops but upper doesnt since the left neuron is still functional
what are the 2 categories of pahthophysiology of the motor cortex
epilepsy
lesions
jacksonian march
- observed epileptic seisures
and observed the pattern of spread of the convulsion - he came up with a somatatopic map of the motor cortex
- he observed the convulsion would spread to different body parts ( this is the jacksonian march)
what occurs in LMN lesions
Severee muscle atrophy
fasciculation ( rippling)
hyporeflexia
decreased/ flacid muscle tone
what occurs in UMN lesions
- slight muscle atrophy
- no fasciculation
- hyperreflexia
- increased/spastic muscle tone
why should their be spasticity in the UMN lesion
cerebral cortec acts on the reticuloformation in a inhibatory way.
- if inputs of the cerebral cortex are removed the reticuloformation is no longer inhibited causing spasticity
spastic hemiplegia
- paralysis of the lower half of the face
- arm has excess tone ( flexion in the elbow,)
- excess tone in the lower limb as well
babinski response
- what is normal and abnormal
- response that appears with a person with a stroke
- if you stroke the the sole of the foot you get flaring of the foot ( midly interitating stimulus that induces withdrwal response)
- normal would cause toes to curl
how does the babinski respose affect babies? what does this mean?
what occurs if you have stroke
- babies flare toes when you touch the foot but get surpessed as you begin to walk and become an adult. however if you have a stroke this resposne will reappear
