descending pathways Flashcards
function
- modify all the activity of ascending stimuli
- control conscious and reflex response to stimuli
modes of control
- internal control
- external control
external control
- sensory guided
- parietal cortex, premotor cortex, cerebellum
internal control
- non-sensory guided
- prefrontal cortex, supplementary motor area, basal ganglia
key features of the primary motor cortex
- inverse
- disproportionate
- contralateral
motor projection fibers
neurons in the motor cortex that give rise to axons that travel through the corona radiate and internal capsule
commissural fibers
axons of neurons that join two cerebral hemispheres
association fibers
axons of neurons that unite different parts of the same cerebral hemispheres
first order neurons
- upper motor neurons
- cell body originates in the cerebral cortex or brainstem
- does not transmit impulses directly to muscles
- glutamatergic
second order neurons
- lower motor neurons
- cell body originates in the anterior grey column of the spinal cord, brainstem, or cranial nerve nuclei
- transmit impulses directly to muscles
- acetylcholine
spinal reflex arc examples
- patellar reflex
- abdominal skin reflex
- plantar reflex
plantar reflex
big toe curls with stimuli
pyramidal tracts
- pass through the medullary pyramids (some corticobulbar tracts may not)
- synapse on cranial nerves or with neurons in the anterior horn of the spinal cord
- voluntary movement
- most fibers originate in motor cortex
- most fibers cross to contralateral side
extrapyramidal tracts
- do not pass through the medullary pyramids
- coordination of movements, posture control and muscle tone
- most fibers originate in the brainstem
pyramidal tract examples
- lateral corticospinal tract
- anterior corticospinal tract
extrapyramidal tract examples
- rubrospinal tract
- reticulospinal tract
- olivospinal tract
- vestibulospinal tract
pyramidal tracts are either …
corticospinal or corticobulbar tracts
where are most of the cell bodies of the pyramidal tracts located
on the precentral gyrus of the frontal lobe (primary motor cortex)
pyramidal tract input
- supplementary motor area
- premotor cortex fibers
- parietal lobe
- cingulate gyrus
where do corticospinal tracts originate
- layer 5 of cortex
- internal pyramidal layer contains large pyramidal neurons
corticospinal tract input
- from motor and pre-motor cortical areas
- somatosensory cortex
- parietal lobe
- cingulate gyrus
where do corticospinal tracts travel through
- internal capsule to the cerebral peduncles
- come to lie on ventral surface of the medulla (the pyramids)
types of corticospinal tracts
- anterior corticospinal tracts
- lateral corticospinal tracts
anterior coticospinal tracts
- controls central axial and proximal muscles involved in postural control
- fibers decussate in the spinal cord
lateral corticospinal tracts
- controls appendicular muscles for fine movement of ipsilateral limbs
- fibers decussate in the pyramids
corticobulbar tract other name
corticonuclear tract
corticobulbar tract
- initially follows the same pathway as corticospinal tracts
- synapse with the motor nuclei of the CN beginning at upper pons
- some fibers decussate
corticobulbar tract function
- responsible for voluntary movement of the face muscles (CNVII) and head/neck (CNXI)
- involved in phonation, swallowing, facial expression (CNVII and IX)
pyramidal disorders
- upper motor neuron lesion (UMN)
- lower motor neuron lesion (LMN)
upper motor neuron lesion (UMN)
- causes spastic paralysis (muscles tighten, stiffen, contract)
- hypertonia
- absence of UMN control, LMN exhibits hyperactivity
- caused by neuritis, direct trauma, spinal cord accident, or tbi
lower motor neuron lesion (LMN)
- causes flaccid paralysis (muscles are limp, lack firmness)
- hypotonia
- loss of reflexes
- muscle atrophy
example of lmn lesion
bulbar lesion of the facial nerve
bulbar lesions
- injuries to the cranial nerve nuclei or axons of the glossopharyngeal, vagus, and/or hypoglossal nerve
- caused by lesions to the lower motor neurons, brainstem stroke, tumor
bulbar palsy
- paralysis produced by bulbar lesions
- nucleus of the glossopharyngeal or vagus nerve (pharyngeal muscle weakness and posterior 1/3 of the tongue)
- nucleus of the hypoglossal nerve (progressive loss of speech and tongue muscle atrophy)
lou gehrig’s disease (ALS)
- pyramidal disorder
- upper and lower motor neuron disease
- muscle weakening, twitching
- inability to move arms, legs, body
- progressive deterioration
- muscles in chest stop working, it becomes hard to breath alone
- caused by genetic defect in 10% of cases, idiopathic
- breathing or swallowing muscles usually affected first
- does not affect senses
- rarely affects bladder, bowel, or cognition
- no cure
extrapyramidal tract function
- involuntary and automatic control of movement, posture, and muscle tone
- more control over medial muscles than periphery (more gross motor movements than fine motor)
structures involved in extrapyramidal tracts
- basal ganglia
- red nucleus
- substantial nigra
- reticular formation
- cerebellum
how many extrapyramidal tracts are there
- vestibulospinal
- reticulospinal
- rubrospinal
- tectospinal
vestibulospinal tract
- arises from vestinular nuclei
- conveys balance information to spinal cord
- ipsilateral
reticulospinal tract
- arises in the reticular formation of the pons
- medial fibers (excites voluntary movements)
- lateral fibers (inhibits voluntary movements)
rubrospinal tract
- arises from the red nuclei
- contralateral
- plays a role in fine control of the hand
tectospinal tract
- arises in the superior colliculi
- receives input from optic nerves
- coordinates head movements in relation to visual stimuli
extrapyramidal syndrome
collections of symptoms that usually occur after long-term use of psychiatric medication
extrapyramidal syndrome examples
- akathisia
- dystonia
- parkinsonism
- tardive dyskinesia
akathisia
motor restlessness
dystonia
involuntary muscle contraction (eyes, tongue, neck, limbs)
parkinsonism
parkinson-like signs (tremor, rigidity, bradykinesia)
bradykinesia
slowness of movement and speed (or progressive hesitations/halts) as movements are continued
tardive dyskinesia
- repetitive, involuntary movements
- chewing, tongue protrusion, lip puckering
extrapyramidal disease
impairments of the central nervous system
extrapyramidal disease examples
- parkinson’s disease
- huntington’s chorea
- tourette syndrome
parkinson’s disease
a brain disorder that causes unintended or uncontrollable movements, such as shaking, stiffness, and difficulty with balance and coordination
huntington’s chorea
- movement disorders associated with Huntington’s disease
- both involuntary movement problems and impairments in voluntary movements
- involuntary jerking or writhing movements (chorea)
- muscle problems (rigidity or muscle contracture)
- slow or unusual eye movements
tourette syndrome
- neurodevelopmental disorder
- characterized by involuntary movements and sounds (tics)
