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NEUR3905 > Weeks 7 to 9 > Flashcards

Weeks 7 to 9 Flashcards

1
Q

What are upper motor neurons? Include structure, neurotransmitter, location and projection

A

• Upper motor neurons- pyramidal cells (excitatory, glutamatergic) found mainly in the motor areas of the cerebral cortex projecting to lower motor neurons
o Neurons projecting to the lower motor neurons from subcortical regions (brainstem) should also be referred to as upper motor neurons

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2
Q

Where do upper motor neurons predominantly synapse and what are the implications of this?

A

o Upper motor neurons (excitatory, glutamatergic) synapse predominantly on the inhibitory interneurons (local circuit neurons with GABAergic/glycinergic neurons), that is the supraspinal input produces inhibition of the lower motor neuron

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3
Q

What occurs when there is loss of supraspinal input from upper motor neurons and what are the consequences of this

A

 Loss of supraspinal input from upper motor neurons results in spastic paralysis (lose control of lower motor neurons and movements- but increased tension in muscles as inhibition will be lost)
• Spastic paralysis may include increased spinal reflexes

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4
Q

What are lower motor neurons? Describe structure, neurotransmitter, location and projection

A

• Lower motor neurons
o Cholinergic neurons found in the ventral horn of the spinal cord and cranial nuclei of the brainstem
o Send myelinated axons terminating as neuromuscular junctions (NMJs) on fibres of skeletal muscles (alpha motor neurons) or on muscle spindles (gamma motor neurons)

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5
Q

How are lower motor neurons organised in the ventral horn of the spinal cord?

A

o Are organised somatotopically in the ventral horn of the spinal cord

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6
Q

What neurons are lower motor neurons surrounded by/ receive synaptic input from?

A

o Lower motor neurons are surrounded by and receive synaptic input from inhibitory interneurons (GABAergic/glycinergic)
 Glycinergic nerve endings predominate in the spinal cord but there are also a few GABAergic nerve endings
 Receive predominantly indirect signalling, although also receive direct signalling

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7
Q

What is a motor unit?

A

• Motor unit- one alpha motor unit and the muscle fibre it innervates

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8
Q

What is the structure of alpha motor neurons?

A

o Structure-
 Are large neurons with large cell bodies (perikaryal) and extensive dendritic tree
 Receive many synapses (about 10,000 to 20,000)
 Myelinated axons

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9
Q

How do alpha motor neurons leave the spinal cord and what do they terminate on?

A

 Alpha motor neurons leave the spinal cord through the ventral root of the spinal nerve and terminate on fibres of skeletal muscles at neuromuscular junctions (NMJs)

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10
Q

How do alpha motor neuron axons travel in the brainstem?

A

 In the brainstem the axons travel in the motor cranial nerves (or in the motor components of cranial nerves in the case of complex cranial nerves)

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11
Q

What are neuromuscular junctions?

A

• NMJs are very large specialized cholinergic synapses

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12
Q

How do gamma motor neurons leave the spinal cord and what do they terminate on?

A

 Gamma motor neurons leave through the ventral root and terminate on muscle spindles

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13
Q

What are muscle spindles?

A

• Muscle spindles are receptors monitoring the length of the fibres (muscles) and providing feedback to the alpha motor neurons via sensory axons entering through the dorsal root

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14
Q

What is the function of gamma motor neurons?

A

o Gamma motor neurons preset the sensitivity of the spindles thus regulating the muscle tension

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15
Q

What neurons are alpha motor neurons influenced by? Name the tract and function

A

o Alpha motor neurons tend to be influenced by cortical upper motor neurons
 Lateral cortico-spinal tract, mediating voluntary skilled movement

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16
Q

What tracts are gamma motor neurons influenced by? Name the function

A

o Gamma motor neurons tend to be influenced by tracts originating in the brain stem and regulating the muscle tension
 Gamma motor neurons create structural basis for intrinsic spinal reflexes

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17
Q

In what sections is the ventral horn enlarged along the length of the spinal cord and why?

A

• The shape and size of the ventral horn varies along the length of the spinal cord
o Cervical enlargement
 Prominent enlargement of grey matter in ventral horn
 Contains lower motor neurons for the upper limb
o Lumbosacral enlargement
 Prominent enlargement of grey matter in ventral horn
 Contains lower motor neurons for the lower limb

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18
Q

How are lower motor neurons organised in the ventral horn? Give details about position/ organisation of lower motor neurons innervating the trunk and arm

A

• Lower motor neurons are organised somatotopically
o The lower motor neurons are arranged in columns with more lateral columns corresponding to more distal parts of the limb
 From medial to lateral, motor neurons are somatotopically organised in:
• Neurons that innervate the trunk
• Neurons that innervate the shoulder
• Neurons that innervate the arm
• Neurons that innervate the forearm
• Neurons that innervate the hand
o Those targeting flexors (dorsolateral- important for fine control of skilled movement) are segregated from those innervating extensors (ventromedial- posture and antigravity)

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19
Q

Where are flexors located in the ventral horn?

A

 Flexors are more dorsal/lateral in ventral horn

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20
Q

Where are extensors located in the ventral horn?

A

 Extensors are more ventral/medial in ventral horn

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21
Q

What are the developmental origins of the segregation between sensory and motor neurons?

A

• 14-21 days into brain development
o Dorsal-ventral
 Patterns of differentiation
• Midline mesoderm (and later the notochord which sits at midline of neural groove and is positioned ventrally) produces a signalling molecule called Sonic Hedgehog (SHH) which causes neuroblasts in close proximity to mesoderm to become motor neurons
• Ectoderm next to the neural plate produces an opposing signalling molecule Bone Morphogenetic Proteins (BMPs) which causes neuroblasts to differentiate into sensory neurons

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22
Q

What is the Bell-Magendia law in the spinal cord?

A
  • The principle that the ventral roots of the spinal cord are motor in function and the dorsal roots are sensory
  • Back in, front out
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23
Q

Describe the segregation of sensory and motor neurons during development in the spinal cord

A

o Different gradients of signalling molecules establish a functional organisation which persists in adult spinal cord
o In spinal cord, alar (dorsal) derivatives become sensory neurons, whilst basal (ventral) derivatives become motor
 Sulcus limitans divides the alar and basal plates during development of spinal cord but sulcus limitans in adult spinal cord disappear

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24
Q

In the spinal cord, what columns does the alar plate divide into?

A

o In spinal cord, alar plate divides into:
 General somatic afferent column
 General visceral afferent column

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25
Q

In the spinal cord, what column does the basal plate divide into?

A

o In spinal cord, basal plate divides into:
 General visceral efferent column
 General somatic efferent column

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26
Q

What are corticobulbar fibres and their relative number comapred to corticospinal fibres?

A

• Upper motor neurons targeting lower motor neurons in the brainstem are referred to as corticobulbar fibres, more numerous than the corticospinal fibres, generally do not form distinct easily traceable tracts

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27
Q

Where is the alar plate positioned in the brainstem and what columns does it give rise to?

A 
•	Alar plate (sensory structures) is lateral. Divides into:
o	Special sensory afferent column
o	General somatic afferent column 
o	Special visceral afferent column
o	General visceral afferent column
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28
Q

Where is the basal plate positioned in the brainstem and what columns does it give rise to? Where are the locations of these columns?

A

• Basal plate (motor structures) is medial. Divides into:
o General visceral efferent column
o Special visceral efferent column
 Lateral to general somatic efferent column in developing brainstem
 In adult brainstem, migrates away the floor of the ventricle
o General somatic efferent column
 Present close to midline

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29
Q

Where is the sulcus limitans in the brainstem and what division does it mark?

A

• In the brainstem, the sulcus limitans will continue to separate sensory neurons (incoming, afferent) from motoneurons (outgoing, efferent) but it will run along the rhomboid fossa (floor of the 4th ventricle)
o Therefore, the sulcus limitans will divide lateral (afferent, sensory) from medial (efferent, motor) groups of nuclei, not dorsal vs ventral as in the spinal cord
 This division does not extend rostrally into mesencephalon and forebrain
 Sulcus limitans is present in both developing and adult brain stem

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30
Q

Where is the general somatic efferent column in the brainstem and what structures does it generally innervate? What structure in the spinal cord is it homologous to?

A
  • Closest to the midline
  • Lower motor neurons supplying innervation to extraocular muscles (oculomotor, trochlear and abducens) and the tongue (hypoglossal)
  • Homologous to the ventral horn of the spinal cord
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31
Q

What nuclei does the general somatic efferent column contain, where are the nuclei located, where do their fibres leave and what muscles do they innervate?

A 
•	Includes the:
o	Oculomotor nuclear complex (midbrain)
	Fibres of the oculomotor nerve (III) leave midbrain into the inter-peduncular fossa
	Innervates extraocular muscles 
o	Trochlear nucleus (midbrain)
	Fibres of the trochlear nerve (IV) leave dorsal midbrain just caudally of the tectum 
	Innervates superior oblique muscles 
o	Abducens nucleus (caudal pons)
	Fibres of the abducens nerve (VI) leave the brainstem at the ponto-medullary junction
	Innervates lateral rectus muscles
o	Hypoglossal nucleus (medulla)
	Innervates muscles of the tongue
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32
Q

What nuclei does the general visceral efferent column in the brainstem contain and where are these nuclei located?

A

General visceral efferent (GVE)-
• Preganglionic parasympathetic neurons
• Includes the:
o Accessory oculomotor nucleus (a.k.a. Edinger-Westphal) (midbrain)
o Superior and inferior salivatory nucleus (scattered in caudal pons/rostral medulla)
o Dorsal motor nucleus of vagus (short fat,just lateral to the hypoglossal in the medulla)

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33
Q

What group of muscles do the lower motor neurons in the special visceral efferent innervate?

A

• Lower motor neurons from the special visceral efferent nuclei supply muscles derived from the branchial arches/branchiomeric muscles, absent in spinal cord

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34
Q

What nuclei does the special visceral efferent column include, the location of these nuclei and what muscles they supply

A

o Motor trigeminal nucleus (pons)
 Supplies innervation for muscles of mastication
o Motor Facial nucleus (caudal pons)
 Supplies innervation for muscles of facial expression
o Ambiguus nucleus (medulla)
 Supplies innervation for muscles of larynx and pharynx
o Accessory nucleus (caudal medulla to upper cervical spinal cord)
 Supplies sternocleidomastoid and trapezius muscles

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35
Q

What is morphometry?

A

• Morphometry- study of size and shape of the brain and its structures

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36
Q

What is voxel based morphommetry?

A

• Voxel Based Morphometry

o When an individual’s brain T1-weighted image is warped to match a standard template

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37
Q

How is voxel based morphometry performed?

A

o Creates a deformation field-
 Map of how far each voxel in the input image must move to land at the matching point in the template image
o Segmented into tissue classes- based on intensity of image and probability map
 Grey matter
 White matter
 Cerebrospinal fluid
o Images are modulated by scaling the image intensities by amount of contraction/expansion that occurred during spatial normalization
 Results in image where each voxel’s value represents its volume
o Images are smoothed-> blurs segmented image

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38
Q

Why are morphometry images smoothed?

A

 Makes data more normally distributed
 Increases validity of parametric tests
 Reduces intersubject anatomical variability
 Increases sensitivity to detect changes

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39
Q

Describe the process and limitation of cortical thickness analysis?

A

• Cortical thickness-
o Uses T1- weighted anatomical images to explore regional cortical thickness
o Surfaced based analysis
 Remove the skull from the image
 Determine borders of cortical gray matter
 Measure thickness of cortical gray matter
 Spatial normalization
 Smoothing
o Cannot be used for subcortical structures

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40
Q

What is tractography?

A

• Tractography- tracing tracts by visualising fibres

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41
Q

What is diffusion tensor imaging based on?

A

• DTI- based on use of diffusion of water molecules to generate different pixel intensities that can contain information about direction of water movement

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42
Q

How is diffusion tensor imaging used?

A

• To use DTI to explore fibre bundles, it is typical to take series of images in which water direction in 32 or more directions are calculated
o These images are compared to reference image

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43
Q

What is mean diffusivity and what is it affected by?

A

o A measure of the average molecular motion independent of any tissue directionality.
o It is affected by cellular size and integrity
o Anything that changes the physical structure of the area will alter mean diffusivity

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44
Q

Describe the principles behind fractional anisotropy and diffusion tensor imaging depending on tissue type

A

o Diffusion of protons depends on freedom of movement in tissue
 Protons move differently in different brain compartments
 Membranes restrict movement
 CSF
• Isotropic
o Moves in all directions
• Water
• High diffusivity
 Grey matter
• Isotropic
• Low diffusivity (move in any direction but constrained-in smaller space)
• Lots of water in cells but also lipid, cell membranes
 White matter
• Anisotropic
o Constrained direction- can only move in very narrow space along longitudinal axis of axons
• High diffusivity
• Mostly myelin but also axonal membranes
o In fibre tracts, combination of movement in axonal membrane and surrounding oligodendrocyte membrane (myelin) restricts movement of protons

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45
Q

What can cause increased mean diffusivity?

A

 Increased mean diffusivity can mean:
• Loss of neurons
• Dendritic pruning
• Inflammation

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46
Q

What can cause decreased mean diffusivity?

A

 Decreased mean diffusivity can mean:
• Dendritic sprouting
• Astrocyte activation

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47
Q

What is fractional anisotropy?

A

• FA fractional anisotropy- scalar value between zero and one that describes the degree of anisotropy of a diffusion process- a value of zero means that diffusion is unrestricted and value of one means that diffusion is fully restricted

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48
Q

What can diffusion matrices provide us information of?

A

• The diffusion matrix (tensors) can be used to generate a 3D image of the tracts
o Outline squares in the matrix where protons can’t move much: these will be the fibre tracts
o In the myelin of oligodendrocytes, there is directionality: can tell moving from anterior to posterior/ superior or inferior
 Hence, DITs can show which direction the fibres are projecting in

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49
Q

Compare the autonomic nervous system vs somatic motor system i terms of:

  • Speed of conduction
  • Specificity
  • Targets
  • Location
  • Number of synapses in pathway
A

Somatic:

  • Rapid (fibres are well myelinated) and accurate
  • Only peripheral targets
  • Commands only skeletal muscle
  • Within CNS
  • Monosynaptic pathway

Autonomic:

  • Actions multiple, widespread and slow (fibres are not well myelinated)
  • Wide, coordinated and graded control
  • Commands all tissue and organ except skeletal muscle
  • Outside the CNS
  • Disynaptic pathway
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50
Q

What are the two divisions of the autonomic nervous system and their overall function?

A 
•	Two divisions of the autonomic nervous system
o	Sympathetic division 	
	Fight or flight 
o	Parasympathetic division 
	Rest and digest
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51
Q

Describe the difference in pre-ganglionic and post-ganglionic neurons in the sympathetic nervous system vs parasympathetic nervous system

A

• Autonomic nervous system organisation
o Preganglionic neuron- found in CNS
o Post-ganglionic neuron-found in periphery
o Sympathetic nervous system
 Post-ganglionic neurons found close to central nervous system
 Pre-ganglionic fibres are short
 Post-ganglionic fibres are long
o Parasympathetic nervous system
 Post-ganglionic neurons found close to innervated organ
 Pre-ganglionic fibres are long
 Post-ganglionic fibres are short

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52
Q

What organs does the sympathetic nervous system innervate and what is the result of this?

A
  • Increased heart rate, force of contraction and rate of conduction (heart innervation)
  • Bronchodilation (lungs innervation)
  • Increased blood pressure (blood vessel innervation)
  • Piloerection and sweating (skin innervation)
  • Pupil dilation (eye innervation)
  • Depressed digestive function (guts innervation)
  • Mobilized glucose reserves (liver innervation)
  • Orgasm (gonads innervation)
  • Relaxation of destrusor and contraction of urethral sphincter (bladder innervation)
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53
Q

Where are sympathetic preganglionic neurons found in the spinal cord?

A

• Sympathetic preganglionic neurons found from T1-L2/3

o Found in an area called the lateral horn (otherwise known as intermediolateral grey matter)

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54
Q

Describe the pathway of sympathetic preganglionic neurons from the spinal cord to their post-ganglionic neuron

A

• Sympathetic preganglionic neurons leave the spinal cord through ventral roots and join the spinal nerve and get to sympathetic post-ganglionic neurons in rami, then supply to different structures

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55
Q

What forms the white communicating ramus?

A

o Incoming pre-ganglionic fibres form the white communicating ramus
 Because they are myelinated

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56
Q

What forms the grey communicating ramus?

A

o Leaving post-ganglionic fibres form the grey communicating ramus
 Because they are unmyelinated

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57
Q

What is the location of the sympathetic trunk/chain?

A

 Entire length of the vertebral column

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58
Q

What are paravertebral ganglia?

A

 Ganglia that lie parallel to vertebral column- paravertebral ganglia

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59
Q

What is the relationship between sympathetic ganglia and intervertebral foramen?

A

• Ganglia (paravertebral) associated with vertebral levels

o Sympathetic ganglia found in association with intervertebral foramen (with some exceptions)

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60
Q

What is the terminal ganglion impar?

A

• Terminal “ganglion impar”

o Where the two parallel sides of sympathetic trunk join together to form one ganglion

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61
Q

Where is the superior cervical ganglia located?

A

o Superior cervical ganglia- closest to the skull

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62
Q

Where is the middle cervical ganglia located?

A

o Middle cervical ganglia- between superior and inferior ganglia

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63
Q

Where is the inferior cervical ganglia located?

A

o Inferior/stellate cervical ganglia- adjacent to thoracic ganglia

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64
Q

What are prevertebral ganglia?

A

 Ganglia found on aorta or organ of innervation- prevertebral ganglia

65
Q

What ganglia can be found on the abdominal aorta?

A

• On abdominal aorta, can find celiac ganglion, superior mesenteric ganglion and inferior mesenteric ganglion
o Named after aorta found on

66
Q

What ganglion does the greater splanchnic nerve supply?

A

o Greater splanchnic nerve-supplies the celiac ganglion

67
Q

What ganglion does the lesser/least splanchnic nerve supply?

A

o Lesser/least splanchnic nerve-supplies superior mesenteric ganglion

68
Q

What ganglion does the lumbar splanchnic nerve supply?

A

o Lumbar splanchnic nerve-supplies the inferior mesenteric ganglion

69
Q

How does the sympathetic nervous system innervate local structures (T1-L2/3)

A

• Sympathetic supply to local (T1-L2/3 structures)
o Sympathetic neurons leave lateral horn
o Travel in ventral roots
o Join spinal nerve
o Enter sympathetic ganglion
o Synapse on sympathetic post-ganglionic cell
o Leave and enter spinal nerve
o Enter dorsal and ventral primary rami
o Supply local structures (blood vessels to muscles)

70
Q

How does the sympathetic nervous system innervate distant structures (above T1-below L2/3)

A

• Sympathetic supply to distant structures (above T1- below L2/3)
o Sympathetic neurons leave lateral horn and travel in ventral roots
o Join spinal nerve
o Enter and traverse sympathetic ganglion
o Leave and enter the sympathetic chain (trunk)
o Ascend or descend then synapse on ganglion cell
o Enter dorsal and ventral primary rami
o Supply distant structures (head, lower extremities)

71
Q

How does the sympathetic nervous system innervate medial deep visceral structures?

A

• Sympathetic supply to medial deep visceral structures
o Leave lateral horn and travel in ventral roots
o Join spinal nerve
o Enter sympathetic ganglion
o Can synapse on sympathetic paravertebral post-ganglionic cell (heart) or not (guts and gonads)
o Leave and enter either cardiac or splanchnic (guts and gonads) nerves
o Synapse on prevertebral ganglia or the adrenal medulla (exception)
 Adrenal medulla is a modified ganglion- splanchnic nerve synapses immediately on adrenal medulla
 Adrenal medulla then releases noradrenaline into circulation to augment activity of the sympathetic nervous system
o Supply organ

72
Q

What organs does the parasympathetic nervous system innervate and what is the result of this?

A
  • Decrease heart rate, force of contraction and rate of conduction (heart innervation)
  • Bronchoconstriction and increased bronchial secretion (lungs innervation)
  • Some vasodilation (blood vessel innervation)
  • Salivation and mucus production (secretory tissue innervation)
  • Pupil constriction (eye innervation)
  • Stimulates digestive function (guts innervation)
  • Storage of glucose (liver innervation)
  • Erection and lubrication (gonads innervation)
  • Contraction of detrusor and relaxation of urethral sphincter (bladder innervation)
73
Q

Where does the parasympathetic system originate from?

A
  • Brainstem

* Sacral parts of the spinal cord

74
Q

In what cranial nerves are there parasympathetic preganglionic fibres, what do these nerves innervate and what is the name of ganglia associated with these nerves?

A

o Parasympathetic preganglionic fibres in cranial nerves III (oculomotor), VII (facial), IX (glossopharyngeal) and X (vagus)
 CNIII- eyes innervation
• Ciliary ganglion- contains parasympathetic postganglionic neurons associated with CNIII
 CNVII- lacrimal, salivary, mucous membranes innervation
• Submandibular and pterygopalatine ganglion-contains parasympathetic postganglionic neurons associated with CNVII
 CNIX- parotid innervation
• Otic ganglion- contains parasympathetic postganglionic neurons associated with CNIX
 CNX-thorax and abdomen innervation
• Most vagal postganglion neurons are found on surface of organ that will be innervated- most preganglionic fibres of the vagus will synapse on postganglionic neuron that sits on the organ that it’s controlling

75
Q

How is the nucleus ambiguus mapped for parasympathetic neurons?

A

 More superior part of nucleus ambiguus supply superior visceral structures
 More inferior part of nucleus ambiguus supply inferior structures
 Somatotopic map in nucleus ambiguus

76
Q

Where do parasympathetic preganglionic neurons that control parasympathetic supply to the heart originate in

A

nucleus ambiguus

77
Q

Where do parasympathetic preganglionic neurons that control parasympathetic supply to thoracic and abdominal area originate from

A

o Parasympathetic preganglionic neurons that control parasympathetic supply to thoracic and abdominal area originate from dorsal motor nucleus of vagus and nucleus ambiguus (somatotopic map applicable)
 Dorsal motor nucleus of vagus primary supply to digestive tract

78
Q

What are preganglionic neurons of both the sympathetic and parasympathetic regulated by?

A

• Preganglionic neurons of both sympathetic and parasympathetic divisions are regulated by nuclei within the CNS
o These can be considered similar to the upper motor neurons of the somatic motor system

79
Q

Do all regions innervate both sympathetic and parasympathetic preganglionic neurons? Give an example

A

• Some regions will innervate both sympathetic and parasympathetic preganglionic neurons, others show selectivity
o Patterned excitation and inhibition of lower medullary regulatory centres drive sympathetic activity of preganglion neurons found in the spinal cord

80
Q

Why is it important that different levels of the neuraxis play functionally distinct roles in regulation of the autonomic preganglionic neural populations?

A

o Critical for functions from sustaining homeostatic tonic function, through basic integrative functions to complex behaviourally-coupled outputs, which can be preparatory or executive

81
Q

Describe the relationship of the visceral motor system with the somatic motor system

A

• The visceral motor system has to work in parallel with somatic motor system-has to work on an integrated fashion as both systems drive behaviour to deal with context you find yourself in

82
Q

What are examples of higher cortical regions that integrate motor activity in the parasympathetic and sympathetic motor system?

A

• Integration of motor activity in parasympathetic and sympathetic nervous system by higher cortical regions to allow for functional whole of vegetative functions, such as hypothalamus, parabrachial nucleus, amygdala, cortex and periaqueductal grey matter

83
Q

What are the two main types of movement and what muscle group are they performed by?

A
  • Skilled movement- tend to innervate distal somatic muscles

* Basic movement- tend to innervate proximate somatic muscles

84
Q

What brain areas controls movement?

A

• Higher centres such as the cortex and brainstem control movement

85
Q

How do descending movement pathways control movement type and performance?

A

• Descending movement pathways:
o Excitation (descending pathway directly synapses on alpha or gamma motor neuron) or inhibition (descending pathway directly synapses on interneuron, which synapses on alpha or gamma motor neuron)
 Excitation- descending pathway
o If synapse on alpha neuron, pathway more likely to be skilled, but if synapse directly on gamma neuron, pathway more likely to be basic

86
Q

What are the two main types of movement pathways?

A 
•	Two types of movement pathways
o	Basic (medial set)
o	Skilled (lateral set)
87
Q

Describe the phylogenetic age of the basic movement pathway

A

 Features: phylogenetically older, crucial for life

88
Q

Where is the basic movement pathway located in the spinal cord?

A

 More medial in the spinal cord

89
Q

What are the functions of the basic movement pathway?

A

 Functions: basic (gross, proximal) movements
• Posture (muscle tone)
• Locomotion
• Balance/equilibrium

90
Q

What two main regions does the basic movement pathway originate from and what is the respective function of the basic movement pathways from these areas?

A 
•	Brainstem
o	Function: posture/locomotion/balance/equilibrium
•	Hypothalamus
o	Function-
	Maintains homeostasis 
	Somatic motor and visceral link 
	Emotional/emergency expression of basic pathways
	Controls brainstem
91
Q

What two main pathways are is the brainstem basic movement pathway composed of?

A

 Reticulospinal tract

 Vestibulospinal tract (mainly innervate extensors)

92
Q

Describe the origin of the reticulospinal tract and the termination of the reticulospinal tract

A
  • Originates from brainstem reticular formation

* Will descend ipsilateral and mainly synapse on gamma motor neurons

93
Q

What is the function of the brainstem reticular formation?

A 
o	Maintains arousal 
o	Controls visceral functions
	Cardiovascular reflex
	Respiratory reflex
	Urogenital reflex 
	Gastrointestinal reflex
94
Q

What is the function of the reticulospinal tract?

A

• Function:
o Maintains posture
o Maintains locomotion

95
Q

What is the origin and termination of the vestibulospinal tract?

A

• Comes from vestibular nuclei in brainstem
o Receive input from inner ear
• Descends and mostly innervate gamma motor neurons

96
Q

What is the function of the vestibulospinal tract?

A

• Function:

o Controls posture and locomotion but mainly balance and equilibrium

97
Q

What two main pathways are is the hypothalamus basic movement pathway composed of?

A
  • Hypothalamoreticular tract

* Hypothalamospinal tract

98
Q

Describe the origin and termination of the hypothalamoreticular tract and its purpose

A

• Hypothalamoreticular tract
o Originates from hypothalamus, goes down to reticular formation and controls the reticulospinal tract from the brainstem

99
Q

Describe the origin and termination of the hypothalamospinal tract and its purpose

A

o Originates from hypothalamus, goes directly to spinal cord to synapse mainly on gamma motor neurons

100
Q

What is the phylogenetic age of the skilled movement pathway?

A

 Features
• Phylogenetically newer
• Quality of life

101
Q

Where is the skilled movement pathway located in the spinal cord?

A

 More lateral in the spinal cord

102
Q

What is the function of the skilled movement pathway?

A

• Skilled (fine, distal musculature) movement

o Goal-driven, voluntary

103
Q

What are the two types of tracts for skilled movement?

A
  • Corticospinal tract

* Rubrospinal tract

104
Q

What cortical areas does the corticospinal tract originate from?

A

 Motor (M1,2) cortex
 Sensory (S1) cortex
 Higher-order/association cortex (eg cingulate)

105
Q

What is the homunculus of the motor cortex?

A

• Homunculus of motor cortex
o Muscles of the head close to lateral sulcus
o From more to most medially, have hand, trunk and finally legs

106
Q

Describe the pathway of the corticospinal tract

A

 Goes from cortical areas through corona radiata
 From corona radiata, goes through internal capsule
 Gets to cerebral peduncle of the midbrain
 Goes to the medulla into the pyramid and decussates
• Corticospinal tract is the only tract in the pyramid
• Pyramidal decussation- 90% axons decussate (makes up the lateral corticospinal tract) and 10% axons don’t decussate (makes up ventral corticospinal tract)
o Those that don’t decussate in the pyramidal decussation decussate in the ventral white commissure
 Axons from motor cortex terminate mainly in ventral spinal cord (most will terminate at cervical level) and directly innervate mainly alpha motor neurons (although some gamma motor neurons are also innervated)
 Axons from sensory cortex terminate in dorsal spinal cord

107
Q

What is the function of the corticospinal tract and how does it achieve these functions?

A 
	Skilled/fine movement
	Learning movement 
•	Happens using the cerebellum 
	Sensory gating for focus of sensation 
•	Corticospinal tract dampens inputs from areas of non-relevant areas of the spinal cord (not involved in the focused sensation) which amplifies those receiving the sensation in question
108
Q

Describe the rubrospinal tract pathway

A

o Origin- red nucleus
o Course:
 Comes from red nucleus and decussates at ventral tegmental decussation and descends in lateral funiculus to terminate in ventral spinal cord
 Will innervate mainly alpha motor neurons (but also some gamma motor neurons)

109
Q

Describe the function of the rubrospinal tract

A

o Function:
 Skilled movement
 Carries out learnt movement
 Helps corticospinal tract in skilled movement

110
Q

Where are learnt movements stored?

A

• Learnt movement stored in basal ganglia

111
Q

What are the main cortical areas involved in movement and where are they?

A
  • Caudal Parietal lobe
  • Secondary motor: supplementary motor area and premotor area (caudal frontal lobe)
  • Prefrontal (rostral frontal lobe)
  • Primary motor (precentral gyrus/paracentral lobe)
112
Q

What is the function of the parietal cortex in motor movement?

A

Focus/attention/integration of sensation

113
Q

What is the impact of a lesion of the parietal cortex in motor movement?

A

Attention and recognition loss

114
Q

What is the function of the supplementary motor area and premotor area in motor movement?

A
  • Plan (complex)

- Posture/ muscle tone/global coordination

115
Q

What is the impact of a lesion of the supplementary motor area and premotor area in motor movement?

A
  • No complex movement/no coordination/ forced grasp reflex (grasping at sensory stimuli- this reflex is only switched on in babies)
  • Posture/tone issues (akinesia, spasticity)
116
Q

What is the function of the prefrontal area in motor movement?

A

Moral/social skills

117
Q

What is the impact of a lesion of the prefrontal area in motor movement?

A

No moral/social skills: delinquent behaviour

118
Q

What is the function of the primary motor area in motor movement?

A

Simple movement

119
Q

What is the impact of a lesion of the primary motor area in motor movement?

A

No movement but there can be a degree of recovery

120
Q

Describe the 4 essential steps we have to perform for movement to occur and what cortical/subcortical areas are responsible for these

A
  1. Focus attention
    a. Cortical area: Parietal (caudal)
    b. Subcortical areas: thalamus (pulvinar)
  2. Plan/program movement
    a. Cortical area: M2
    b. Subcortical area: Basal ganglia
  3. Select appropriate movement
    a. Cortical area involved: Prefrontal
    b. Subcortical area: Basal ganglia
  4. Execute movement
    a. Cortical area involved: M1
    b. Subcortical area: Cerebellum
121
Q

Where is the cerebellum and what is it covered by?

A
  • Positioned in the posterior cranial fossa

* Superiorly covered by tentorium cerebelli (dural reflection)

122
Q

What percent of total brain volume does the cerebellum account for?

A

• Accounts for about 10-12% of total brain volume

123
Q

What supplies the blood to the cerebellum?

A
  • Blood supply is from posterior inferior and the anterior inferior cerebellar arteries (PICA and AICA) and from the superior cerebellar artery (ISCA, all vertebral artery systems)
  • Cerebellar blood supply highly variable
124
Q

What is the roof of the fourth ventricle formed by?

A

• Roof of the fourth ventricle formed by superior and inferior medullary velum

125
Q

What are the lobes of the cerebellum?

A

• Lobes:
o Anterior
o Posterior
o Flocculonodular

126
Q

What is the general function of the superior cerebellar peduncle?

A

o Superior cerebellar peduncle- mainly output

127
Q

What is the general function of the middle cerebellar peduncle?

A

o Middle cerebellar peduncle- pontocerebellar fibres

128
Q

What is the general function of the inferior cerebellar peduncle?

A

o Inferior cerebellar peduncles- input/output

129
Q

What are the functional divisions of the cerebellum and their age?

A 
•	Functional divisions-
o	Archicerebellum/vestibulocerebellum
	Most ancient
	Function is to maintain balance
o	Paleocerebellum/ spinocerebellum
	Formed more recently
o	Neocerebellum/ cerebrocerebellum/pontocerebellum
	Most recent addition 
o	Visuocerebellum 
o	Audiocerebellum
130
Q

Describe the pathway of the cerebrocerebellum

A

• Cerebrocerebellum
o Cerebral cortex sends descending fibres to the pontine nuclei
o Pontine nuclei project to contralateral cerebellum (decussation)
o Output from cerebellum goes to the thalamus (decussation)
o Thalamus information goes back to the cortex
o This processed information is projected from the cortex to the spinal cord through corticospinofibres

131
Q

Describe the pathway of the spinocerebellum

A

 Cerebellum receives information from the spinal cord and from the cortex via pontine nuclei
 Information received decussates to the thalamus and the red nucleus
 From the thalamus, information is transported to the cortex
 Cortex sends information to the spinal cord through corticospinotract and red nucleus sends information back to the spinal cord via the rubrospinal tract
 Red nucleus also send information to the inferior olivary complex back into the cerebellum
• Possibly involved in cerebellar learning
• Climbing fibres- output of the inferior olivary complex targeting the cerebellar cortex

132
Q

What is the function of the spinocerebellum

A

 Compares information from cortex and spinal cord- sees if motor neurons are doing what the cortex is telling them to do

133
Q

What is the origin of spinocerebellar fibres in the spinal cord?

A

 Proprioceptive (Ib) fibres, (Golgi tendon organs; tension in muscles, position of joints…)
 Relayed in nucleus dorsalis (Clarke’s nucleus, nucleus thoracicus) in spinal cord
 Runs ipsilaterally

134
Q

What is the origin of rubrospinal fibres and where does the decussation for the rubrospinal tract occur?

A

o Original of rubrospinal fibres
 Origin- red nucleus (n. rubrus) in midbrain
 Crosses immediately at the level of the red nucleus

135
Q

What is the pathway of the vestibulocerebellum?

A

o Pathway-
 Cerebellum mainly outputs to lateral vestibular nucleus, which outputs to the spinal cord, although it also follows the same circuit as the cerebrocerebellar tract

136
Q

What is the function of the vestibulocerebellum?

A

o Function-
 Muscle tone
 Balance

137
Q

What is the origin of lateral vestibulospinal fibres, where do they project to, what is their function and when do they decussate?

A

o Lateral vestibulospinal tract
 Lateral vestibular nucleus in the brain stem (Deiter’s n.)
 Uncrossed (ipsilateral)
 Targets ventral horn
 Important for maintaining posture (antigravity muscles)

138
Q

What are the layers of the cerebellar cortex?

A 
•	Layers- from surface to deep 
o	Molecular layer on surface
o	Purkinje cell layer
o	Granule cell layer
o	White matter of folium
139
Q

Describe the internal circuity in the cerebellar cortex (input, the stuff that happens in it and the resulting output)

A

o Mossy fibres input to the cerebellum and contact the granule cell layer
 Mossy fibres (excitatory, +) bifurcate many times and form rosettes
 Each rosette synapses with about 20 granule cells
o Granule cells produce parallel fibres (excitatory, +) and sends fibre to molecular layer which bifurcates and produces parallel fibres
o Parallel fibres (PF) contact Purkinje cells (PC), Golgi cells and basket cells (GC and BC, both inhibitory, -) in an excitatory manner
 Golgi cells- inhibitory to granule cells
• Parallel fibres also contact Golgi cells which send inhibitory feedback to the rosette and cut off the signal
 Basket cells- inhibitory to purkinje cells
• Send axons across the rows next to them and inhibit Purkinje cells in neighbouring parallel rows
 Each parallel fibre excites the purkinje cells in its path and inhibits the purkinje cells (through basket in the path of the parallel fibre next to it: the strongest parallel fibre- the most excited parallel fibre will win
• This process sharpens the signal in space and time
 Climbing fibres (excitatory) from the contralateral inferior olivary complex contact purkinje cells
• Each climbing fibre excites about 2-10 purkinje cells
• Each purkinje cell receives only on climbing fibre
• Repeated firing of climbing fibre will slow down the activity of purkinje cell (long term depression)- physiological substrate for cerebellar learning
o The only output from the cerebellar cortex is via GABAergic inhibitory Purkinje cells
 Target- deep (central) cerebellar nuclei
• Dentate (cerebrocerebellum) projects to the contralateral ventrolateral nucleus of the thalamus, then the cortex
• Globose, emboliform, fastigial (spinocerebellum) project to contralateral red nucleus and reticular formation
• Lateral vestibular (Deiters) nucleus (vestibulocerebellum): project through vestibulospinal tract and reticular formation

140
Q

What happens if the vestibulocerebellum is lesioned?

A 
•	Archicerebellum/vestibulocerebellum: 
o	Unsteadiness
o	Swaying
o	Falling 
o	Tendency to fall backwards when walking 
o	Muscle tone not changed all the time
o	No asynergy or tremor in the limbs
o	Signs are usually bilateral
141
Q

What happens if the spinocerebellum is lesioned?

A

• Paleocerebellum/spinocerebellum

o No specific deficits known in humans but could be similar to decerebration in animal experiments

142
Q

What happens if the cerebrocerebellum is lesioned?

A

• Neocerebellum/cerebrocerebellum (includes paravermal regions)
o Loss of muscle tone and fatigue
o Asynergia
o Dysmetria (hypermetria, pastpointing)
o Intention tremor
o Dysdiadochokinesia (inability to perform rapid successive movements)
o Nystagmus
o Speech disturbances (slurred speech, separating of syllables)

143
Q

What are the possible functions of the cerebellum and the functional parts of the cerebellum responsible for these?

A

• Maintaining posture and balance while standing and moving (vestibulocerebellum)
• Monitoring the movement as it is executed (spinocerebellum)
• Coordinating synergy of muscle activity in groups of muscles to generate complex movements (cerebrocerebellum)
• Integrating of sensory input to help to plan and execute complex and precise movement essential in activities (spinocerebellium, visuoccerebellum, audiocerebellum, cerebrocerebellum)
o Automation of movements through cerebellar learning

144
Q

Compare the basal ganglia with the cerebellum in terms of:

  • Input
  • Output
  • Function
  • Mechanism
A

Basal ganglia:
>Receive significant input from prefrontal areas
>Output focused to supplementary motor area
>Conscious decision making, planning and initation of movement
>Mechanism by changing balance between direct and indirect loop

Cerebellum:
>Significant input from association and somatosensory areas
>Output focused on area 4 (primary motor cortex)
>
-Automated movement (mainly cerebrocerebellum)
-Comparing intended and actual movement (spinocerebellum)
>
-Automation (learning) of movement by long term depression of Purkinje cell activity by climbing fibres from the inferior olivary complex
-Spatial and temporal sharpening of signal: parallel fibres excite the purkinje cells in its path, inhibits purkinje cells in the neighbouring rows and cuts of its own input via Golgi cells

145
Q

What are the components of the basal ganglia?

A 
•	Components of the basal ganglia
o	Striatum- Putamen and caudate nucleus
o	Globus Pallidus- external and internal
o	Subthalamic nucleus 
o	Substantia nigra
	 Pars compacta 
	Pars reticulata 
o	Peduculopontine nucleus in brain stem
146
Q

What are the two loops of the basal ganglia?

A
  • Direct loop

- Indirect loop

147
Q

Describe the direct pathway of the basal ganglia

A

o Direct loop
 The cortex projects to the striatum with excitatory glutamatergic fibres
 The striatum then projects to the globus pallidus internal with inhitory GABAergic fibres
 Globus pallidus (internal) projects to the thalamus with inhibitory GABAergic fibres
 Thalamus projects to the cortex with excitatory glutamatergic fibres

148
Q

Describe the function of the basal ganglia

A

 Function-
• Increases input back to cortex
• Direct loop is excitatory
• Associated with planning

149
Q

Describe the indirect pathway of the basal ganglia

A

 The cortex projects to the striatum with excitatory glutamatergic fibres
 The striatum projects to the globus pallidus external with inhibitory GABAergic fibres
 The globus pallidus external projects to the subthalamic nucleus with inhibitory GABAergic fibres
 The subthalamic nucleus projects to the globus pallidus internal with excitatory glutamatergic fibres
 The globus pallidus internal projects to the thalamus with inhibitory GABAergic fibres
 The thalamus projects to the cortex with excitatory glutamatergic fibres

150
Q

Describe the function of the indirect loop

A

 Function-
• Decreases input back to cortex
• Indirect loop is inhibitory

151
Q

What are the inputs of the basal ganglia?

A

• Receives input from several cortical areas (wide)-
o Primary motor
o Premotor
o Somatosensory
o Other areas (particularly prefrontal cortex)

152
Q

What are the outputs of the basal ganglia?

A

• Output to the:
o Supplementary motor area (SMA)
o Premotor area
o Primary motor area

153
Q

How does the substantia nigra influence the activity of the basal ganglia direct and indirect loop?

A

• Substantia nigra (pars compacta)
o Substantia nigra pars compacta sends dopaminergic neurons to the striatum to potentiate direct loop and inhibit indirect loop
o Dopaminergic neurons of substantia nigra pars compacta stimulate the signalling through the basal ganglia

154
Q

What are the inputs and outputs of the pedunculopontine nucleus in the basal ganglia?

A

• Pedunculopontine nucleus (mesencephalon/pons) receives inhibitory input from globus pallidus internal
o Cholinergic projects from pedunculopontine nucleus to the reticular formation of the brainstem may control muscle tone

155
Q

What are the functions of the basal ganglia?

A
  • Appears to sculpt and sharpen the cortical activity by funnelling signals to certain areas
  • Encode fragments of movement that are assembled in supplementary motor area and sent to the primary motor area for execution
  • Help with planning of movement and will of movement
  • Influence muscle tone
  • Control undesirable activities (tremor) in the thalamus
156
Q

How does parkinsonism occur?

A

• Parkinsonism- loss of dopaminergic input from substantia nigra pars compacta

157
Q

How does huntington’s chorea occur?

A

• Huntington’s chorea- neurodegeneration in striatum (mainly in caudate nucleus)

158
Q

How does hemiballism occur?

A

• Hemiballism- unilateral damage to subthalamic nucleus, uncontrolled flailing movements in contralateral limb

NEUR3905 (5 decks)

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