Descending Pathways Flashcards
two modes of control
external and internal control
external control
sensory guided (visual or auditory system is needed to execute movements)
which parts of the brain relate to external control
parietal cortex, premotor cortex, cerebellum
internal control
non-sensory guided - proprioceptors
what parts of the brain relate to internal control
prefrontal cortex, supplementary motor area, basal ganglia
what are motor projection fibres
Neurons in the motor cortex give rise to axons that travel through the corona radiata and the internal capsule
what are commissural fibres
the axons of neurons that join the two cerebral hemispheres
what are association fibres
axons of neurons that unite different parts of the same cerebral hemisphere
upper motor neuron
- cell body originates in the cerebral cortex or brainstem
- does not transmit impulses directly to muscles
- glutamatergic
what are upper motor neurons also known as
first order neurons
lower motor neuron
- cell body originates in the anterior grey column of spinal cord, brainstem or cranial nerve nuclei
- transmits impulses directly to muscles
- uses neurotransmitter acetylcholine
what are lower motor neurons also known as
second order neurons
whar is the spinal reflex arc
reflexes that occur without spinal input
name two reflexes
- patellar reflex
- abdominal skin reflex
how do reflexes work
sensory neuron synapses with interneuron which then synapses with motor neuron - interneuron is the connection not spinal cord
pyramidal tracts vs extrapyramidal tracts
pyramidal tracts pass through the medullary pyramids
extrapyramidal tracts do not
what do the fibres do in pyramidal tracts
- originate in motor cortex
- most cross to contralateral side
where do fibres of extrapyramidal tracts originate
brainstem
name two types of pyramidal tract
- corticospinal
- corticobulbar
where are cell bodies of pyramidal tracts located
precentral gyrus of frontal lobe (primary motor cortex)
where do corticospinal tracts originate
five layers of cortex - internal pyramidal layer, contains large pyramidal neurons
where do corticospinal tracts recieve input from
motor and premotor cortical areas: somatosensory cortex, parietal lobe and cingulate gyrus
where do corticospinal tracts travel to
through internal capsule to the cerebral peduncles and then tbey come to lie on the ventral surface of the medulla (pyramids)
what do anterior corticospinal tracts control
central axial and proximal muscles involved in postural control
where do the fibres of anterior corticospinal tracts decussate
in spinal cord
what do lateral corticospinal tracts control
appendicular muscles for fine movement of ipsilateral limbs
where do lateral corticospinal tract fibres decussate
in the pyramids
what are corticobulbar tracts also known as
corticonuclear tracts
what nerves do the corticobulbar tracts synapse with
synapse with motor nuclei of cranial nerves beginning at the level of the upper pons
do all corticobulbar tract fibres decussate
no
corticobulbar tracts function
- responsible for voluntary movement of face (CN VIII), head and neck (CN IX)
- involved in phonation, swallowing and facial expression (CN VII and IX)
upper motor neuron lesion
- causes spastic paralysis (muscles become tight, stiff and contracted, hypertonia)
- in the absence of UMN control the LMN exhibits hyperactivity
lower motor neuron lesion
- causes flaccid paralysis (muscles are limp and lack firmness, hypotonia)
- loss of reflexes
- muscle atrophy (later symptom)
example of LMN lesion
bulbar lesion of facial nerve
lesion A
bulbar lesion of facial nerve
upper face is spared because both hemispheres contribute to movements of upper face and unaffected hemisphere can compensate
Lesion B
bulbar lesion of facial nerve
entire face is affected on one side
causes of other bulbar lesions
injury to cranial nerve nuclei or axons of glossopharyngeal, vagus and/or hypoglossal nerves
due to brainstem stroke or tumor
what do bulbar lesions cause
bulbar palsy
bulbar palsy symptoms
- nucleus of glossopharyngeal/vagus nerve: pharyngeal muscle weakness and posterior 1/3 of tongue - ie. swallowing issues
- nucleus of hypoglossal nerve: progressive loss of speech and tongue muscle atrophy ie. dysarthria
what is amyotrophic lateral sclerosis (ALS)
- upper and lower motor neuron disease
- Leads to muscle weakening, twitching, and an inability
to move the arms, legs, and body. - The condition slowly gets worse as more and more muscle groups are affected.
- When the muscles in the chest area stop working, it becomes hard or impossible to breath on one’s own.
- ALS does not affect the senses (sight, smell, taste,
hearing, touch). It only rarely affects bladder or bowel
function, or a person’s ability to think or reason - no known cure
function of extrapyramidal tracts
involuntary and automatic control of movements, posture and muscle tone - more control of over muscles in the midline than those in the periphery ie. gross motor more than fine motor
structures involved in extrapyramidal tracts
- basal ganglia
- red nucleus
- substantia nigra
- reticular formation
- cerebellum
name the four extrapyramidal tracts
- vestibulospinal
- reticulospinal
- rubrospinal
- tectospinal
where does the vestibulo spinal tract arise
vestibular nuclei
vestibulospinal tract function
conveys balance information to spinal cord
is the vestibulospinal tract contralateral or ipsilateral
ipsilateral
where does the reticulospinal tract arise
in reticular formation of the pons
reticulospinal tract function
medial fibres: exites voluntary movements
lateral fibres: inhibits voluntary movements
where does the rubrospinal tract arise
red nuclei
is the rubrospinal tract contralateral or ispsilateral
contralateral
rubrospinal tract function
plays a role in fine control of the hand
where does the tectospinal tract arise
in the superior colliculi
tectospinal tract function
coordinates head movements in relation to visual stimuli (recieves input from optic nerves)
what are extrapyramidal syndromes
collections of symptoms that usually occur after long-term use of psychiatric medication
name four extrapyramidal syndromes
- akathisia
- dystonia
- parkinsonism
- tardive dyskinesia
what are extrapyramidal diseases
impairments of the central nervous system
name three extrapyramidal diseases
- parkinsons disease
- huntingtons chorea
- tourettes syndrome
akathisia
motor recklessness
dystonia
involuntary contraction of muscles (eye, neck, tongue, limbs)
parkinsonism
parkinsons like signs (tremor, rigidity, bradykinesia)
tardive dyskinesia
repetitive, involuntary movements (chewing, tongue protrusion, lip puckering)
