Neurophysiology (Part 3)

Question 1

Descending motor pathways are divided among what 2 tracts?

Answer 1

pyramidal and extrapyramidal tracts

Question 2

What are the 2 types of pyramidal tracts?

Answer 2

• corticospinal tract

- corticobulbar tract

Question 3

Where do the pyramidal tracts descend down to?

Answer 3

They pass through the medullary pyramids and descend directly onto lower motor neurons in the spinal cord

Question 4

What are the 5 types of extrapyramidal tracts?

Answer 4

• rubrospinal tract
• potine reticulospinal tract
• medullary reticulospinal tract
• lateral vestibulospinal tract
• tectospinal tract

Question 5

Where does the rubrospinal tract originate from and where does it project to?

Answer 5

It originates in the red nucleus and projects to the motoneurons in the lateral spinal cord

Question 6

Stimulation of the red nucleus (rubrospinal tract) produces what?

Answer 6

activation of flexor muscles and inhibition of extensor muscles

Question 7

Where does the pontine reticulospinal tract originate from and where does it project to?

Answer 7

It originates in nuclei of the pons and projects to the ventromedial spinal cord

Question 8

Stimulation of the pontine reticulospinal tract produces what?

Answer 8

General activation of both flexor and extensor muscles, with its predominant effect on extensors

Question 9

Where does the medullary reticulospinal tract originate from and where does it project to?

Answer 9

It originates in the medullary reticular formation and projects to motoneurons in the spinal cord

Question 10

Stimulation of the medullary reticulospinal tract produces what?

Answer 10

General inhibition of both flexor and extensor muscles, with its predominant effect on extensors

Question 11

Where does the lateral vestibulospinal tract originate from and where does it project to?

Answer 11

It originates in the lateral vestibular nucleus and projects to the ipsilateral motoneurons in the spinal cord

Question 12

Stimulation of the lateral vestibulospinal tract produces what?

Answer 12

Activation of extensors and inhibition of flexors

Question 13

Where does the tectospinal tract originate from and where does it project to?

Answer 13

It originates in the superior colliculus and projects to the cervical spine

Question 14

What is the tectospinal tract involved in?

Answer 14

Control of neck muscles

Question 15

If a brainstem lesion occurs above the pontine reticular formation and lateral vestibular nucleus, but below the midbrain what will occur and why?

Answer 15

It will cause a dramatic increase in extensor tone (called decerebrate rigidity) because the pontine reticular formation and lateral vestibular nucleus have powerful excitatory effects on extensor muscles

Question 16

Will lesions above the midbrain cause decerebrate rigidity?

Answer 16

No

Question 17

What does the cerebellum regulate and play a role in?

Answer 17

movement and posture and plays a role in certain kinds of motor learning

Question 18

What does the cerebellum help to control?

Answer 18

The rate, range, force, and direction of movements (collectively called synergy)

Question 19

The cerebellum is connected to the brainstem via what?

Answer 19

3 cerebellar peduncles that contain both afferent and efferent nerve fibers

Question 20

What are the 3 main divisions of the cerebellum?

Answer 20

• vestibulocerebellum
• spinocerebellum
• pontocerebellum

Question 21

What is the vestibulocerebellum dominated by and what does it control?

Answer 21

It is dominated by vestibular input and controls balance and eye movements

Question 22

What is the spinocerebellum dominated by and what does it control?

Answer 22

It is dominated by spinal cord input and controls synergy of movement

Question 23

What is the pontocerebellum dominated by and what does it control?

Answer 23

It is dominated by cerebral input and controls the planning and initiation of movements

Question 24

How many layers are there to the cerebellar cortex and how are they described?

Answer 24

3, all of which are described in relaation to its output cells, the Purkinje fibers

Question 25

List the 3 layers of the cerebellar cortex staring with the innermost layer

Answer 25

- granular layer - Purkinje cell layer - molecular layer

Question 26

What does the granular layer contain?

Answer 26

the granule cells, Golgi II cells, and glomeruli

Question 27

Mossy fibers from which 2 tracts synapse on dendrites of the granule and Golgi type II cells in the granular layer of the cerebellar cortex?

Answer 27

spinocerebellum and pontocerebellum tracts

Question 28

What does the Purkinje cell layer contain?

Answer 28

Purkinje cells

Question 29

Output from the Purkinje cell layer is always ______.

Answer 29

inhibitory

Question 30

What does the molecular layer contain?

Answer 30

Outer stellate cells, basket cells, dendrites of Purkinje and Golgi II cells, and axons of granule cells

Question 31

What 2 input systems provide excitatory input to the cerebellar cortex?

Answer 31

- the climbing fiber system | - the mossy fiber system

Question 32

Excitatory projections from the cerebellar cortex modulates the output of what? How?

Answer 32

These excitatory projections activate secondary circuits, which modulate the output of the cerebellar nuclei via the Purkinje cells

Question 33

Which of the 2 fiber systems constitutes the majority of the cerebellar input?

Answer 33

the mossy fiber system

Question 34

Describe the synapses between the climbing fibers and the Purkinje cells

Answer 34

Each Purkinje cell receives input from only one climbing fiber, however a single AP from a climbing fiber can elicit multiple excitatory bursts (complex spikes) in the dendrites of the Purkinje cell

Question 35

Describe the synapses between the mossy fibers and the Purkinje cells

Answer 35

Mossy fibers project to excitatory granule cells, that ascend to the molecular layer and give rise to parallel fibers that contact the dendrites of many Purkinje cells

Question 36

In summary one climbing fiber activates __ Purkinje cell and one mossy fibers activates ___ Purkinje cells

Answer 36

one many

Question 37

In summary climbing fibers cause ____ spikes that produce multiple action potentials whereas mossy fibers cause _____ spikes that produce single action potentials.

Answer 37

complex simple

Question 38

What is the function of cerebellar intenreurons?

Answer 38

to modulate Purkinje cell output

Question 39

With the exception of the granule cells, all of the cerebellar interneurons are ______.

Answer 39

inhibitory

Question 40

The only output of the cerebellar cortex is via what?

Answer 40

axons of Purkinje cells

Question 41

Purkinje cell output is always inhibitory, why?

Answer 41

Because the NT released at these synapses is GABA which is an inhibitory neurotransmitter

Question 42

What do cerebellar lesions result in?

Answer 42

an abnormality of movement called ataxia

Question 43

Cerebellar ataxia is a lack of coordination due to what?

Answer 43

errors in rate, range, force, and direction of movement

Question 44

What are the 5 ways in which ataxia can be exhibited?

Answer 44

- Delayed onset - Overshoot - Dysdiadochokinesia - Intention tremors - Rebound phenomenon

Question 45

Describe delayed onset ataxia

Answer 45

Movement or poor execution of the sequence of a movement is delayed causing the movement to appear uncoordinated

Question 46

Describe overshoot ataxia

Answer 46

A limb may overshoot its target or stop before reaching its target

Question 47

Describe dysdiadochokinesia ataxia

Answer 47

A person is unable to perform rapid, alternating movements

Question 48

Describe intention tremors

Answer 48

These are tremors that occur perpendicular to the direction of a voluntary movement, increasing near the end of the movement

Question 49

Intention tremors are seen in what type of pathology?

Answer 49

Parkinson's disease

Question 50

Describe the rebound phenomenon

Answer 50

A person is unable to stop a movement

Question 51

The basal ganglia are the deep nuclei of the telencephalon, list the 4 nuclei

Answer 51

- Striatum which consists of the caudate nucleus and the putamen - Globus pallidus - Amygdala

Question 52

What are the associated nuclei of the basal ganglia?

Answer 52

- Ventral anterior and ventral lateral nuclei of the thalamus - Subthalamic nulceus of the diencephalon - Substantia nigra of the midbrain

Question 53

What is the major function of the basal ganglia?

Answer 53

to influence the motor cortex via pathways through the thalamus

Question 54

What are the 2 other functions of the basal ganglia?

Answer 54

To aid in planning and execution of smooth movements, and to also contribute to affective and cognitive functions

Question 55

What are the 2 pathways into and out of the basal ganglia?

Answer 55

- indirect | - direct

Question 56

The overall output of the indirect pathway is ______, whereas the overall output of the direct pathway is _____.

Answer 56

inhibitory excitatory

Question 57

What are 2 diseases of the basal ganglia?

Answer 57

Parkinson's disease and Huntington’s disease

Question 58

Describe Parkinson's disease

Answer 58

Occurs when cells of the pars compacta of the substantia niagra degenerate, which reduces inhibition via the indirect pathway and reducing excitation via the direct pathway

Question 59

What are the characteristics of Parkinson's disease?

Answer 59

- resting tremor - slowness and delay of movement - shuffling gait

Question 60

How is Parkinson's disease treated?

Answer 60

By replacing dopamine by treatment with L-dopa or administration of dopamine agonists

Question 61

Describe Huntington’s disease

Answer 61

It is a hereditary disorder caused by destruction of striatal and cortical cholinergic neurons and inhibitory GABAergic neruons

Question 62

What are the symptom of Huntington’s disease?

Answer 62

choreic (writhing) movements and dementia

Question 63

Where are voluntary movements directed by?

Answer 63

the motor cortex via descending pathways

Question 64

What is the function of the motor plan

Answer 64

The motivation and ideas necessary to produce voluntary activity are organized in the cerebral cortex and then transmitted to the supplementary motor and premotor cortices to develop the plan. This plan will identify the specific muscles that need to contract, how much they need to contract, and in what sequence

Question 65

After the motor plan is developed, where is it transmitted?

Answer 65

to upper motoneurons in the primary motor cortex, which send it through descending pathways to lower motoneurons in the spinal cord

Question 66

What are the planning and execution stages of the motor plan influenced by?

Answer 66

motor control systems in the cerebellum and basal ganglia

Question 67

What are the 3 areas of the motor cortex?

Answer 67

- primary motor cortex - supplementary motor cortex - premotor cortex

Question 68

The supplementary motor cortex and premotor cortex are responsible for what?

Answer 68

generating a plan of movement

Question 69

When is the supplementary motor complex active?

Answer 69

during "mental rehearsal" of a movement

Question 70

Once the plan of movement is generated is transferred to the primary motor cortex, for what?

Answer 70

execution

Question 71

Describe what happens as programmed patterns of motoneurons are activated from the primary motor cortex

Answer 71

This activation excites upper motoneurons which transmits the plan to the brain stem and spinal cord, where lower motoneurons are activated and produce coordinated contraction of the appropriate muscles

Question 72

The primary motor cortex is topographically organized and is described as what?

Answer 72

the motor homunculus

Question 73

The topographic organization of the primary motor cortex is dramatically illustrated by what type of seizures?

Answer 73

jacksonian seizures

Question 74

The brain is composed of 80% fluid, most of which is what?

Answer 74

cerebrospinal fluid (CSF)

Question 75

CSF is formed at a rate of ___ml/day by what cells?

Answer 75

500 by the epithelial cells of the choroid plexus

Question 76

Describe the path the CSF takes after it is produced by the choroid plexus

Answer 76

It flows into the ventricles and the subarachnoid spaces, which surround the brain and spinal cord

Question 77

The rate at which CSF is transferred to venous blood is equivalent to what?

Answer 77

the rate of CSF formation

Question 78

How is CSF sampled?

Answer 78

Using a lumbar puncture in the lumbar cistern

Question 79

What is the barrier between the cerebral capillary blood and CSF called?

Answer 79

the choroid plexus

Question 80

What are the 3 layers of the choroid plexus?

Answer 80

- capillary endothelial cells and basement membrane - neuroglial membrane - epithelial cells of the choroid plexus

Question 81

What is the barrier between the cerebral capillary blood and the interstitial fluid of the brain called?

Answer 81

blood-brain barrier

Question 82

What are the 2 ways in which the blood-brain barrier differs from the analogous barrier in other tissues?

Answer 82

- the junctions between endothelial cells in the brain are so "tight" that few substances can cross between the cells - only a few substances can pass through the endothelial cells (lipid-soluble substances can; water-soluble substances cannot)

Question 83

What is CSF formed by?

Answer 83

the epithelial cells of the choroid plexus

Question 84

What molecules are excluded from CSF?

Answer 84

Protein and cholesterol because of their large molecular size

Question 85

Which molecules move freely and equilibrate between the CSF and the brain interstitial fluid?

Answer 85

Lipid-soluble substances such as oxygen and carbon dioxide

Question 86

What substances are present at approximately the same concentration in the CSF and in the brain interstitial fluid?

Answer 86

- sodium - chloride - bicarbonate - osmolarity

Question 87

What substances are present at higher concentrations in the CSF compared to in the brain interstitial fluid?

Answer 87

- magnesium | - creatinine

Question 88

What substances are present at higher concentrations in the brain interstitial fluid compared to in the CSF?

Answer 88

- potassium - calcium - glucose - amino acids - pH

Question 89

What are the functions of the CSF?

Answer 89

- provide a constant, controlled environment for the brain cells - to protect the brain from endogenous or exogenous toxins - prevent escape of local transmitters into the general circulation

Question 90

Do ionized or nonionized drugs readily penetrate the brain readily and why?

Answer 90

nonionized drugs do because they are lipid-soluble

Question 91

What things may increase the permeability of the blood-brain barrier and allow substance normally excluded to enter the brain?

Answer 91

inflammation, irradiation, and tumors

Question 92

What part of the brainstem do the rubrospinal and tectospinal tracts originate?

Answer 92

midbrain

Question 93

What part of the brainstem does the pontine reticulospinal tract originate?

Answer 93

Pons

Question 94

What part of the brainstem do the medullary reticulospinal lateral vestibulospinal tracts originate?

Answer 94

medulla