L18 Postural Reflexes and Higher Motor Areas

Question 1

Sensory/motor pathways that PASS through the brainstem

Answer 1

• Dorsal column-medial lemniscus pathway, anterolateral (spinothalamic) pathway (S)
• Corticospinal tract and corticobular tracts (M)

Question 2

Motor pathways that originate from the brainstem, lateral and medial

Answer 2

Lateral: rubrospinal tract
Medial: pontine and medullary reticulospinal, lateral/medial vestibulospinal, tectospinal tracts

Question 3

Functions of the postural reflexes

Answer 3

Maintain the body in an upright, balanced position at rest, provide adjustments necessary to maintain a stable position during voluntary movement.

Question 4

Vestibular reflexes

Answer 4

Elicited by head movement and sensory receptors, such as the semicircular canals in the vestibular apparatus.

Question 5

Tonic neck reflexes

Answer 5

Elicited by head movement that activates stretch receptors, such as the muscle spindles in the neck.

Question 6

Righting reflexes

Answer 6

Elicited when the body goes off balance and falls, activating receptors in the vestibular apparatus, stretch receptors, and mechanoreceptors. Coordinate muscles to restore an altered position of the head and body toward normal.

Question 7

Postural reflexes: reflex arc

Answer 7

1) Afferent pathways from the vestibular apparatus, eye, and proprioreceptors.
2) Integration in the brainstem and spinal cord, nuclei and reticular formation.
3) Efferent pathways and the a-motoneurons that supply the skeletal muscles

Question 8

Brainstem in controlling locomotion

Answer 8

Spinal cord contains central pattern generators and the cerebral cortex controls the CPG activation and shutdown.

Question 9

Central pattern generators

Answer 9

In spinal cord, produce regular rhythmic output for locomotion, controlled by the cerebral cortex.

Question 10

Connection fibers from the cerebral cortex to CPG/motoneurons

Answer 10

Cerebral cortex connects brainstem locomotor regions through corticobulbar fibers.
Brainstem connects CPG through reticulospinal fibers.
CPG then innervates motoneurons.

Question 11

Cortical motor areas (3) motivation, planning, and execution.

Answer 11

Premotor area (PMA) and supplementary motor area (SMA): plan movement.
Primary motor cortex: execute movement.
Posterior parietal cerebral cortex: motivation.

Question 12

Inputs of motor control

Answer 12

Other cortical areas, thalamus, posterior parietal cortex, cerebellum, and basal ganglia

Question 13

What are the upper motoneurons known as?

Answer 13

Betz cells

Question 14

Cerebellar anatomy
1. Hemispheres connected via _______
2. Connects brainstem via _____, _____, _____ peduncles.
3. Nuclei (4) are _____, _____, _____, _____.
4. Lobes (3) are _____, _____, _____.
5. Tissues (2) are _____, _________ fissure.

Answer 14

1. Vermis
2. Superior, middle, and inferior peduncles
3. Fastigial, globose, emboliform, dentate nuclei
4. Anterior, posterior, and flocculonodular lobes
5. Primary, posterolateral fissure

Question 15

Nucleus associated with each of the 3 peduncles

Answer 15

Superior: Red
Middle: Pontine
Inferior: Inferior olivary

Question 16

Cerebellum granular layer cells

Answer 16

Granule cells, golgi II cells, glomeruli; (lugaro cells, unipolar brush cells)

Question 17

Cerebellum purkinje cell layer

Answer 17

Purkinje cells with extensive dendritic trees that project to the molecular layer, (candelabrum cells)

Question 18

Cerebellum molecular layer

Answer 18

Outer stellate cells, basket cells, and dendrites of other inner cells, and parallel fibers

Question 19

Two excitatory cerebellar inputs

Answer 19

Mossy fibers excite granule cells which excite purkinje cells. Climbing fibers directly excite purkinje cells. BOth send collaterals to cerebellar nuclei.

Question 20

One inhibitory cerebellar output

Answer 20

Purkinje cell axons terminate in cerebellar nuclei.

Question 21

Interneurons in cerebellar cortical circuitry

Answer 21

Granule cells and unipolar brush cells are glutamatergic (excitatory). Golgi, stellate, basket, lugaro, and candelabrum cells are GABAergic (inhibitory).

Question 22

Mossy fibers, activity and function

Answer 22

Excite granule cells, causing purkinje cells to discharge single APs (simple spikes).
Simple spike: fires at 20Hz to 100Hz, depending on the balance of excitation and inhibition.
Involved in motor control.

Question 23

Climbing fiber cells

Answer 23

Cause purkinje cells to discharge a high frequency burst of APs (complex spikes), because in makes hundreds of excitatory synapses along the dendrites of the cell.
Firing rate of 1Hz means they do not change the firing rate of purkinje cells substantially; they are not involved in motor control but may alter purkinje cell’s responsiveness to parallel fibers.

Question 24

Inferior peduncle (aff/eff, tracts, connection)

Answer 24

Mainly afferent
Spinocerebellar (mossy fibers) and olivocerebellar (climbing fibers) tracts
Spinal cord and medulla connect the cerebellum

Question 25

Middle peduncle (aff/eff, tracts, connection)

Answer 25

Only afferent
Pontocerebellar tract (mossy fibers)
Motor cortex connects pontine nuclei connects the cerebellum

Question 26

Superior peduncle (aff/eff, tracts, connection)

Answer 26

Interposed nuclei and red nucleus
Dentate nucleus connects thalamus connects the motor cortex

Question 27

Is cerebellar function and consequences ipsilateral or contralateral?

Answer 27

Ipsilateral, and the vermis tends to control coordination and muscle tone of the trunk

Question 28

Ataxia

Answer 28

Cerebellar lesions

Question 29

Dysmetria

Answer 29

the inability to the control the speed, distance, and range of motion necessary

Question 30

Dysdiadochokinesia

Answer 30

The inability to perform rapid, alternating movements

Question 31

Decomposition of movements

Answer 31

A movement is accomplished in a series of discrete steps rather than as a smooth sequence

Question 32

Intention tremors

Answer 32

the affect limb develops tremors that increase in magnitude as a target is approached

Question 33

Basal ganglia organisation: striatum, globus pallidus, substantial nigra

Answer 33

Striatum: caudate nucleus and putamen
Globus pallidus: external segment (Gpe), and internal segment (Gpi)
Substantia nigra: pars reticulata, pars compacta

Question 34

Basal ganglia inputs and outputs

Answer 34

Input: cerebral cortex to the striatum (glutamatergic)
Output: Gpi and pars reticulata project to the thalamus (GABAergic)

Question 35

Basal ganglia circuits: communication between the striatum and thalamus

Answer 35

Indirect: globus pallidus, subthalamic nuclei (inhibitory)
Direct: Gpi (excitatory)

Question 36

Parkinson’s causes

Answer 36

Bradykinesia
Loss of dopaminergic neurons in the pars compacta and substantia nigra. Reduced activity of the direct pathway and increase of the indirect pathway causing less activation of motor cortical areas.

Question 37

Huntington’s causes

Answer 37

Hyperkinetic
Loss of GABAergic and cholinergic neurons in the striatum, disinhibiting neurons in the thalamus via the indirect pathway. This increases the activity in the motor cortex causing choreiform movements.