Lecture 13 - Posture and Movement

Question 1

Why are abnormalities of posture and movement more important than sensory disorders?

Name brain structures associated with posture and movement

Answer 1

because animals readily express motor behavior but hardly report their feelings

reticular formation, vestibular nuclei, red nucleus, tectum, substantia nigra, subthalamus, basal nuclei

Question 2

1) Describe anatomy of reticular formation
2) Where does it receive synaptic input from?

Answer 2

1) mixture of gray and whtie matter, found thru out midbrain and hindbrain
2) from collateral branches of ascending tracts (spinothalamic tract)

Question 3

1) Describe physiology of reticular formation
2) Damage of this area leads to what?

Answer 3

1) spintaneously active neuronal circuits
- ascending system to alert cerebral cortex (via non-specific thalamic nuclei)
- vegetative centers: regulate HR, resp, GI, micturition
- standing posture and muscle tone via two pathways to alpha and gamma neurons
2) coma

Question 4

1) What are the two pathways that lead to alpha and motor neurons? (descending tracts)
2) What’s the origin of the pontine reticulospinal tract?
3) What’s its fn?
4) What’s the origin of medullary reticulospinal tract?
5) What’s its fn?

Answer 4

1) pontine reticulospinal tract and medullary reticulospinal tract
2) arises from neurons located laterally in pons and medulla
3) dominant and spontaneously active;

activates alpha and gamma neurons to extensor muscles of proximal joints

4) arises from neurons located medially in medulla
5) not spontaneously active –> driven by cerebral cortex to preset movement posture

inhibits neurons to extensor muscles and excites neurons to flexor muscles

Question 5

1) What are the two descending tracts used by vestibular nuclei?
2) What else does vestibular nuclei use?

Answer 5

1) lateral vestibulospinal tract - drives standing posture

medial vestibulospinal tract - controls neck nuscles

2) two reticulospinal tracts to adjust muscle tone

Question 6

1) What do the neurons of the red nucleus form?
2) What is it composed of?
3) Describe the pathway of the rubrospinal tract
4) What do rubrospinal tract fibers synapse on? resulting actions?

Answer 6

1) give rise to rubrospinal tract - principal descending tract for voluntary movement in domestic animals
2) collection of projection neurons
- axons from motor area of cerebral cortex synapse on large projection neurons in red nucleuus –> control their activity
3) decussates in midbrain and descends in dorsal half of LF
4) synapse on spinal interneurons –> produce independent movements of shoulder/hip and elbow/stifle; carpus/hock

Question 7

1) What is the tectum?
2) What structures make up tectum?
3) What are the rostral and caudal colliculi?
4) Where are they located?

Answer 7

1) roof of midbrain
2) rostral and caudal colliculi
3) reflex centers which orient head, eyes and ears toward sudden visual and auditory stimuli
4) btw visual and somatic sensory layers

Question 8

1) What do the neuros in intermediate layer of RC give rise to?
2) describe path of tectospinal fibers
3) describe path of textobulbar fibers
4) What are the horizontal and vertical gaze centers in reticular formation?
5) Using these centers, what can the tectum do?
6) What’s a saccade?

Answer 8

1) two tracts –> tectospinal fibers and tectobulbar fibers
2) descend to cervial spinal cord –> head turning
3) to cranial nerve nuclei –> control ear and eye movement
4) horizontal - pons

vertical - midbrain

5) rapidly shifts the eyes to focus on novel stimuli
6) quick eye movement used to shift focus to new visual feature; visual perception occurs during stops following saccades

Question 9

1) What results in the degeneration of substantia nigra?
2) What does subthalamic nucleus participate in?
3) What does damage of the subthalamus result in?

Answer 9

1) Parkinson’s disease
2) basal nuclei circuits –> regulate voluntary movement
3) hyperkinetic movements –> hemiballismus

Question 10

1) What’s the anatomy of basal nuclei?
2) What are the two anatomic groups of basal nuclei?
3) What are the physiological groups of basal nuclei?
4) What are the input and output nuclei?

Answer 10

1) non-cortical gray matter of telencephalon
2) striatum = accumbens, caudate and putamen

internal capsule gray matter striations

Lentiform nucleus = putamen and globus pallidus

together have shape of a lens

3) motor role = accumbens, caudate, putamen, globus pallidus and endopeduncular nuclei –> circuits that involve thalamus and cerebral cortex
4) input nuclei = accumbens, caudate and putamen

output nuclei = globus pallidus and endopeduncular nucleus

Question 11

1) What’s the fn of basal nuclei?
2) What does the motor cortex do?
3) What are voluntary movements initiated by?

Answer 11

1) suppress unwanted movements –> regulate the selection, onset and cessation of voluntary movement b y participating in thalamocortical circuits involving motor-related areas of cerebral cortex
2) executes actual movements via pyramidal or extrapyramidal descending tracts (basal nuclei do not give rise to these tracts)
3) regions of cerebral cortex responsible for emotionally driven behavior (limbic cortex) or goal driven decisions (association cortex)

Question 12

4) T or F: Initiating areas of cerebral cortex do not communicate their movement needs directly to motor-related cortex
5) How do the initiating cortices communicate?
6) What are forebrain circuits the mechanism for?
7) What are the two fnal categories of voluntary movement circuits?

Answer 12

4) True
5) via circuits involving basal nuclei and thalamus
6) selection/execution of desired movements and suppression of unwanted movements
7) 1= involves caudate nucleus –> active in selecting and assembling movements (during leanring)

2=involves putamen –> controls amplitude and durations of movements –> habitually performed movements performed with minimal thinking

Question 13

1) All projection neurons of basal nuclei are what?
2) The output basal nuclei are what?
3) The input basal nuclei require what?
4) What needs to happen to activate desired movements?
5) Damage leads to?
6) What do lesions produce?

Answer 13

1) inhibitory
2) tonically active in suppressing movement
3) require excitatory input from cerebral cortex
4) input nuclei disinhibit the output nuclei
5) impairs either movement onset (hypokinetic syndromes) or movement cessatino (hyperkinetic syndromes)
6) circling toward damaged side, pacing and muscle hypertonia

Question 14

1) basal nuclei contain what type of neurons that produce what?
2) output basal nuclei contain what type of neurons?
3) What is the role of basal nuclei?
4) Cerebral cortex project to which basal nuclei?

Answer 14

1) GABAergic; inhibitory output
2) spontaneous active inhibitory neurons
3) to facilitate desired voluntary movements (initiated by cerebral cortex) and dampen unwanted movements via participation in thalamocortical circuits
4) accumbens, caudate adn putamen = input nuclei, the anatomical striatum

Question 15

5) How does striatum control spontaneously active output nuclei? fn?

6) What modulates the two striatal pathways?
7) What does the cerebral cortex suppress?

Answer 15

5) via two pathways

direct pathway = facilitates desired movements by inhibiting endopeduncular nucleus (and substantia nigra reticulata)

indirect pathway = suppresses unwanted movement by inhibiting globus pallidus which tonically inhibited endopeduncular and subthalamus nuclei

6) substantia nigra compacta –> favors movemnet via dopamine release
7) movements direclty via subthalamic nucleus –> enhances endopeduncular inhibition

Question 16

1) What is the motor area of cerebral cortex involved in?
2) What are the other motor-related areas involved in?
3) Where is the motor area located?
4) Main source of what?
5) each output neuron from motor cortex innervates what?
6) Why is cerebral cortex organized?

Answer 16

1) executing voluntary movement
2) planning/learning/selecting voluntary movement
3) aroudn cruciate sulcus
4) two descending pathway systems: direct pyramidal and indirect extrapyramidal tract
5) multiple motor nuclei
6) to control movements not muscles

Question 17

1) What comprises premotor area?
2) What’s it involved in?
3) What is the supplementary motor area?
4) When is it active?

Answer 17

1) collection of cortical regions that project to motor area
2) involved in assembling complex movements and generating learned, rapid-sequence movements (pattern generator circuits)
3) specialized premotor cortex located medially
4) when thinking about proposed movements

Question 18

1) Where do volulntary movements originate?
2) What do the forebrain circuits do?
3) Describe the voluntary movement process

Answer 18

1) in forebrain from circuits involving basal nuclei, thalamus and motor areas of cerebral cortex
2) select and execute movements decided by association cortex in response to stimuli and emotional drive
3) External cue (sensory cortex)/internal urge (limbic system) –> decision (association neocortex) –> selection (premotor and caudate) –> execution (motor area and putamen)

Question 19

1) What are the two descending pathways for voluntary movement?
2) Describe anatomy of pyramidal tract
3) Where do the axons travel?
4) What does it control?
5) Where do most axons decussate?
6) remaining axons form what?

Answer 19

1) pyramidal and extrapyramidal tracts
2) direction connection from motor and premotor areas of cerebral cortex to motor unit efferent neurons (generally via local interneurons)
3) in pyramids of medulla oblongata
4) particulary musculature of manus and pes; esp concerned with precise movements of individual digits (lips and tonue too)
5) at medullary-spinal jn and form lateral corticospinal tract –> terminate in lateral motor nuclei of VH enlargements (limb muscles)
6) ventral corticospinal tract which crosses at level of termination in spinal cord and innervates medial motor nuclei (postural muscles)

Question 20

1) Extrapyramidal tracts is applied to what?
2) What does this tract control?
3) Which tract most important in domestic animals?
4) What are the principal extrapyramidal tracts?
5) Voluntary movements engage what?
6) What does a specific voluntary movement involve?

Answer 20

1) non-pyramidal voluntary movement tracts
2) trunk and proximal limb musculature, generating coarse components of posture/movement/locomotion
3) extrapyramidal tract
4) rubrospinal, pontine reticulospinal and medullary reticulospinal tracts
5) multiple descending tracts
6) rubrospinal and pyramidal tracts and require associated postural adjustments involving reticulospinal tracts

Question 21

1) What does upper motor neuron damage result in?

Answer 21

1) loss of only pyramidal tract = paresis of manus and pes, inability to move digits and lips independently and rapidly

loss of motor cortex = disappearnce of learned movement skills

loss of whole forebrain = persistent standing posture, exhibit phasic actions

loss of forebrain and midbrain = limbs rigidly extended constantly ; no locomotion or righting capability

loss of whole brain = temporary areflexia evident with abrupt injury; paralysis w/o spasticity; local spinal reflexes intact; crossed extention accompanies withdrawal reflex

Question 22

1) What does lower motor neuron damage result in (spinal cord or peripheral nerve)?
2) What does forebrain circuits involve?
3) What does hindbrain circuits involve?

Answer 22

1) paralysis an dareflexia (flaccid paralysis); severe atrophy (denervation atrophy) of skeletal muscles over weeks
2) basal nuclei, pyramidal and extrapyramidal tracts
3) reticular formation and vestibular nucli plus midbrain tectum

Question 23

1) What produces posture and movement?
2) What is a motor unit?
3) What do interneurons do?
4) Nearly all descending pathway axons synapse on what?
5) T or F: both voluntary and reflex pathways compete for control of same interneurons and motor units
6) Cerebellum continuously modulates what?

7)

Answer 23

1) excited alpha and gamma motor neurons
2) one alpha motor nueorns plus all muscle fibers innervated
3) hardwire motor neurons so that logical movement patterns are produced
4) interneurons; small minority of descending axons synapse directly on motor neurons
5) True; to gain control, voluntary neurons must suppress reflex activity and vice versa
6) modulates neuronal activity in motor centers (based on info from motor centers and proprioceptive feedback about body position and acceleration)