Motor systems Flashcards
1
Q
What is the somatic motor system?
A
• Concerned with skeletal or somatic muscle under conscious control
2
Q
What are the two types of somatic muscles?
A
• Somatic muscles are either flexors or extensors
3
Q
Do flexors and extensors work together?
A
o Flexors and extensors work in antagonist function and work against each other- have contraction in either one of those 2 sets at one moment
o Flexors are synergists of one another, and extensors are synergists of one another
4
Q
Where in the spinal cord can lower motor neurons be found and what can they do?
A
• Ventral horn of spinal cord where lower motor neurons reside and control contraction of muscle (control voluntary movement)
o Somatic musculature is innervated by the somatic motor neurons in the ventral horn of the spinal cord
5
Q
Where can extensors be found in the ventral horn of the spinal cord?
A
o Extensors-found more ventrally within ventral horn
6
Q
Where can flexors be found in the ventral horn of the spinal cord?
A
o Flexors lower motor neurons-found more dorsally within ventral horn
7
Q
What are distal muscles?
A
Distal muscles are those that control hand, feet and digit movement which is specialised for manipulation of objects
8
Q
Where are distal muscle lower motor neurons found?
A
o Distal muscle lower motor neurons- found more laterally in the ventral horns
9
Q
What are axial muscles?
A
- control trunk movement which is vital for posture
10
Q
What are proximal muscles?
A
Proximal muscles- control shoulder, elbow, pelvis and knee movement which is critical for locomotion
11
Q
Where are axial and proximal lower motor neurons found?
A
o Lower motor neurons that control axial and proximal muscles- found in medial position in ventral horn of spinal cord
12
Q
What are upper motor neurons and where are they found?
A
• Upper motor neuron- supplies input to the spinal cord
o Comes from brain and synapses onto lower motor neuron
13
Q
What is the role of lower motor neurons?
A
• Lower motor neuron
o Control the muscle contraction
o Cell body of neuron is in ventral horn
o Generate force of contraction within muscle fibres
14
Q
What is a motor unit?
A
• Motor unit-one alpha motor neuron and all the muscle fibers it innervates
15
Q
Is the motor unit size for distal muscles and axial/proximal muscles the same?
A
o Distal muscles have smaller motor units for fine dexterity
o Large motor units for axial/proximal muscles for anti-gravity muscles of the leg
16
Q
What is the motor neuron pool?
A
• Motor neuron pool- collection of alpha motor neurons that innervates a single muscle
17
Q
What is the role of alpha/lower motor neuron?
A
• Alpha/lower motor neuron-controls muscle force or length in whole muscle
18
Q
What is the role of the gamma motor neuron?
A
• Gamma motor neuron-control tension within muscle spindle fibres separately to make sure there’s always tension in muscle spindle
19
Q
What is the relationship in position between cells innervating the axial muscles vs the distal muscles?
A
• Cells innervating the axial muscles are medial to those innervating the distal muscles
20
Q
What is the relationship in position between cells innervating the flexors vs the extensors?
A
• Cells innervating flexors are dorsal to those innervating extensors
21
Q
How do axons of lower motor neurons form spinal nerves?
A
• Axons of lower motor neurons bundle together to form ventral roots: each ventral root joins with a dorsal root to form a spinal nerve that exits the cord through the notches between vertebrae
22
Q
Describe the ventral horn at the cervical level of the spinal cord
A
• Cervical level of spinal cord- controls movement of upper limbs and hence has very large ventral horn at that level (C3-T1)
23
Q
Describe the ventral horn at the thoracic level of the spinal cord
A
• Thoracic level of spinal cord- controls movement of trunk and hence has less lower motor neurons and smaller ventral horn at that level
24
Q
Describe ventral horn of the the lumbar level of spinal cord
A
• Lumbar level of spinal cord- large ventral horn as controlling muscles of lower limbs (L1-S3)
25
What controls lower motor neurons?
• Control over lower motor neuron is from several points
o Get input from upper motor neurons in the brain giving voluntary command to move
o Get input from spinal cord interneurons
o Get input from muscle spindles themselves
26
What is proprioception?
Awareness of limb position
27
What type of receptor is the muscle spindle?
Proprioreceptor
28
Describe the neuromuscular spindle and what neurons it is innervated by
Muscle spindle is in parallel with the muscle fibres
• Tough fibrous capsule on outside
• Within it has intrafusal muscle fibres (small muscle fibres)
o These are innervated by gamma motor neurons
• Muscle spindles-consists of several types of specialised skeletal muscle fibres contained in a fibrous capsule
29
Describe extrafusal fibres and what neuron innervates them
• Extrafusal fibres- the muscle itself
| o Only innervated by alpha motor neurons
30
What is the difference between 1a sensory fibres and 1b sensory fibres in terms of muscle information?
1a activity from the spindle encodes muscle length formation, while 1b activity from the golgi tendon organ encodes muscle tension information
31
Describe the role of group1a sensory fibres in the motor system and how they carry out this role
o Group 1a axons enter the spinal cord via the dorsal roots, branch repeatedly and form excitatory synapses upon both interneurons and alpha motor neurons of the ventral horns
o Group 1a sensory fibre (neuronal fibres wrapped around intrafusal fibres in muscle spindle) transmits feedback (length of muscle) to dorsal horn and project back to ventral horn
Get information from length of muscle when contracting/relaxing
As muscle contracts/relaxes, muscle spindle will be contracted/relaxed as well which will be detected by group 1a sensory fibres
• Sensory fibres are detecting level of relaxation/contraction in muscle spindle itself
32
Describe the role of gamma motor neurons and how they do this
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o Gamma (lower) motor neuron maintains tone in intrafusal fibre, even when muscle is relaxed
Muscle spindle itself has intrafusal fibres in it which can also contract when overall muscle tension is reduced just to ensure that muscle spindle remains taught and can still detect overall length of muscle when the muscle itself is relaxed
Keeps the 1a sensory axons active
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33
What is the gamma loop in the motor system?
o Gamma loop:
| Gamma motor neuron-> intrafusal muscle fiber-> 1a afferent axon-> alpha motor neuron-> extrafusal muscle fibers
34
Describe the stretch feedback loop in the motor system
o Stretch feedback loop-
Set point is determined (desired muscle length), deviations from set point are detected by a sensor (1a axon endings) and deviations are compensated for by an effector system (alpha motor neurons and extrafusal muscle fibers), returning the system to set point
Changing the activity of the gamma motor neurons changes the set point of the stretch feedback loop
35
At what timing are alpha and gamma motor neurons activated by descending commands form the brain during normal movements?
During most normal movements, alpha and gamma motor neurons are simultaneously activated by descending commands from the brain
36
What is the role of Golgi tendon organ?
o Golgi tendon organ-involved in detecting force of contraction within the muscle
37
Where is the Golgi tendon located and what axons is it innervated by?
Located at the tendon region of the muscle and is organised in series with the muscle
Innervated by group Ib sensory axons
38
Why is the Golgi tendon organ arrangement and the muscle spindle arrangement different?
• Different to in parallel spindle arrangement as different anatomical arrangement helps to determine the types of information these two sensors provide the spinal cord
39
What allows control of flexors and extensors antagonistically?
• Synaptic interconnections allow control of flexors and extensors antagonistically
40
What input does synaptic interneurons receive?
• Synaptic interneurons receive synaptic input from primary sensory axons, descending axons from the brain and collaterals of lower motor neuron axons
41
What is reciprocal inhibition?
• Reciprocal inhibition- contraction of one set of muscles accompanied by the relaxation of their antagonist muscles
42
What is the crossed-extensor reflex and how does it occur?
• Crossed-extensor reflex allows coordinated movements of the opposite limb (that is flexion on one side extension of the other)
o Involves sensory input of spinal cord-only occurs at level of spinal cord
o Activation of flexor and relaxation of extensor in affected limb, as well as respreading of weight and rebalancing gravity
o Interneuron will drive increase in activity of extensor and inhibition of flexor in opposite limb so don’t fall over when it happens
43
What are central pattern generators?
• Central pattern generators-circuits that give rise to rhythmic motor activity
o Neurons within the spinal cord which generate rhythmic patterns of activity
44
What are pacemaker neurons and what can they do?
Pacemaker neurons within spinal cord make bursts of activity which can drive lower motor neurons in a very complex pattern that looks like walking
Pacemaker neurons- individual neurons whose membrane properties endow them with pacemaker properties
45
What are the 2 broad classes of major pathways that control lower motor neurons which come from the brain? What is the function of these pathways and what are they controlled by?
o Lateral pathways- control voluntary movements, particularly of distal musculature-> under direct cortical control (neocortex)
Found in lateral ferniculus
o Ventromedial pathways-unconscious functions control posture and locomotion via axial and proximal musculature under brain stem control
46
What are the 2 lateral pathways?
Rubrospinal tract
| Corticospinal tract
47
Describe the rubrospinal tract process
• Rubrospinal tract- vestigial in humans (has no useful function) but useful for other species
o Originates at red nucleus-nucleus found in the midbrain-same input as corticospinal tract
Input from primary motor cortex (M1)
Decussates (Crosses over) in the pons and then travels down into the lateral column of spinal cord
48
Is the rubrospinal tract useful in humans?
o Overtime, the corticorubrospinal tract can compensate for corticospinal lesions
o Largely vestigial in humans-
Mainly activates flexors of the upper limb
Remains important in other mammals, but not important in humans
49
Describe the corticospinal tract -process
• Corticospinal tract-most important voluntary control tract
o 2/3 of axons in the tract originate in areas 4 and 6 of the frontal lobe (motor cortex) and the rest from somatosensory areas
o Starts in motor cortex and finishes at spinal cord
Travels through diencephalon and internal capsule
Traverses through midbrain in cerebral peduncle
Goes through pons
Gets to level of medulla and crosses over from once side to the other -pyramidal decussation
• Corticospinal tract which originates in the right hemisphere actually crosses into left side of body at the level of the medulla
o Right hemisphere controls the left body and vice-versa
Travels within the lateral feniculus of the spinal cord and travels down spinal cord until it gets to level of motor neuron which controls muscle (dorsolateral region of ventral horn-location of the motor neurons that control the distal muscles, specifically the flexors)
50
What are the consequences of partial lesion in the upper motor neuron part of the corticospinal tract?
Partial lesion
• Slow, weak movements
• Loss of fractioned movements
51
What are the consequences of complete lesion in the upper motor neuron part of the corticospinal tract?
Complete lesion
• Spastic paralysis-increase in muscle tone but no voluntary control of the limb
o Lower motor neuron left to its own devices-leads to increase in muscle tone as normally one lower motor neuron is inhibited
• Increased muscle tone
• Increased reflexes
• Mild atrophy
o Muscles still being innervated by lower muscle neuron
52
When are upper motor neuron lesions in corticospinal tract ipsilateral/contralateral?
Contralateral if above medulla (e.g. stroke)
• Deficit on opposite side of the body as hasn’t decussated
Ipsilateral if below medulla (e.g. spinal injury)
53
Describe the symptoms of lower motor neuron partial lesion in corticospinal tract
Partial lesion
| • Muscle weakness
54
Describe the symptoms of lower motor neuron complete lesion in corticospinal tract
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Complete lesion
• Flaccid paralysis
• Decreased muscle tone
o Muscle group not getting any input at all from lower motor neuron
• Decreased reflexes
• Severe atrophy
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55
Are lower motor neuron lesion in corticospinal tract contralateral or ipsilateral?
Always ipsilateral
56
What neurons make up the corticospinal tract?
Betz cells (large pyramidal cells)
57
What are the two ventromedial motor pathways?
- Tectospinal tract
- Vestibulospinal tract
- Pontine (medial) reticulospinal tract
- Medullary (lateral) reticulospinal tract
58
Describe the tectospinal tract and its function
• Originates in the superior colliculus, also known as the optic tectum
• Superior colliculus receives visual and auditory input
• Sudden visual or auditory stimuli causes activation of the tectospinal pathway
o Orienting response which directs the head and eyes towards stimulus
• Controls unconscious reflexes
• Direct projection of midline into cervical regions of the spinal cord to control head and neck movement
59
Describe the vestibulospinal tract and its function, as well as the two tracts that compose the vestibulospinal tract
• Concerned with controlling balance
• Originates in the vestibular nuclei of the medulla (input from semi-circular canal in inner ear (cranial nerve VIII))-on right side
• If cells start in medial vestibular nuclei then medial vestibulospinal tract-projects to cervical spinal cord (bilateral projection-both sides of the spinal cord)
o Controls head and neck position
o Crucial for maintaining stability of the eyes
• If cells start in later vestibular nuclei then lateral vestibulospinal tract
o Projects to lumbar spinal cord (ipsilateral)
Controls upright and balanced posture via extensors of the legs
60
Describe the pontine (medial) retibulospinal tract and its function
• Works in antagonistic fashion from medullary reticulospinal tract
• Subconscious
• Ipsilateral connections
• Arise from the reticular formation in pons
o Enhances the anti-gravity muscles, maintaining standing posture
o Activates extensors of the lower limbs
61
Describe the medullary (lateral) retibulospinal tract and its function
Medullary (lateral) reticulospinal tract
• Subconscious
• Ipsilateral connections
• Arise from the reticular formation in medulla
o Liberates anti-gravity muscles, to allow movement
o Activates flexors of the lower limbs
62
Sketch the location of the ventromedial pathways and lateral motor pathways on a spinal cord crossection
-Tectospinal tract
-Vestibulospinal tract
-Pontine reticulospinal tract
-Medullary reticulospinal tract
-Rubrospinal tract
-Corticospinal tract
Timestamp: 4:40pm at 31/08
63
Describe the cerebral cortex areas responsible for the 3 aspects of movement (strategy, setting the scene and making movement occur)
o Parietal and frontal lobes- high order strategy/planning-selection of different potential options
o Supplementary and pre-motor areas (area 6) as well as basal ganglia-sets the scene for movement: before movement occurs
o Area 6/are 4 (M1) and cerebellum- initiates movement command-> movement occurs
64
What is the function of the posterior parietal cortex in motor movement?
Where does it receive information from during motor movement?
o Parietal association areas (areas 5 and 7) important for spatial orientation/perception
o Area 5- inputs from areas 3,1 and 2 (SI)
o Area 7-inputs from higher-order visual cortical areas such as MT
65
What is the function of the prefrontal cortex in motor movement?
o Abstract thought, decision making and anticipating consequences of actions
66
What Brodmann areas make up the motor cortex?
- Brodmann area 4 of the frontal lobe
| - Brodmann area 6 of the frontal lobe
67
Describe Brodmann area 4 in terms of its name, its location in the brain and its function (as well as how that function was confirmed)
o Brodmann area 4 of the frontal lobe
Primary motor cortex (M1)
Anterior to central sulcus (pre-central gyrus)
Body map represented in area 4-controls every part of the body but different area= different muscle stimulation
• Somatotopic representation
Area 4 has the lowest threshold for eliciting movement
• Electrical stimulation of M1
o Region with the lowest threshold to elicit movement
o Focal contraction of small group of muscles
68
Describe the sources of input to M1 (area 4) of the cortex
• Two sources of input to Betz cells
o Cortical areas (area 6 and S1)
S1 (primary somatosensory cortex)- posterior to area 4
o Thalamus (relaying cerebellar input)
Caudal ventral lateral nucleus, which relays info from the cerebellum
69
Describe the cells in M1 (area of 4) of the cortex and what they project to
• Betz cells: Pyramidal cells in cortical layer 5
o Project to spinal cord
o Project to brainstem-control of ventromedial pathways
Cells in area 4 are called the Betz cells
• Very large cell body neurons (100um) and very long axons that project to ventral horn of spinal cord
70
How is the direction of movement determined in cells in area 4?
Each cell is tuned to a specific direction -has preferences to specific directions
• However, movements are encoded by a collective activity of a population neurons
o Direction of movement is determined by a tally (and averaging) of all activity in population of neurons (population vector)
o Movement in a particular direction is not dependent on activity on a single neuron, but dependent on tuning of all neurons and their specific amount of activation
71
Where is Brodmann area 6 of the frontal lobe found?
o Brodmann area 6 of the frontal lobe
| Anterior to area 4
72
What are the two regions of area 6 in the cortex and what is their function?
Two regions-
• Lateral region-Premotor area (PMA)
• Medial region-Supplementary motor area (SMA)
Motor maps in PMA and SMA
• Similar functions; different groups of muscles innervated
• SMA-Distal (directly innervates)
• PMA- Axial and Proximal (via reticulospinal)
73
Describe the role of area 6 and experiments which proved that role
* Plans movement before it occurs, and relays information to area 4 which actually drives that movement
* Area 6- desired actions converted into signals specifying how actions will be performed
* Per Roland monitored cortical activation accompanying voluntary/rehearsal of movement in humans
* Evarts recorded activity in SMA of awake, behaving animals increase in activity 1 second before movement of either hand
* Results demonstrated the importance of area 6 in planning movement
74
What brain regions output to area 6?
Area 6 receives input from prefrontal and posterior parietal cortex
75
What brain structure are areas 4 and 6 connected to?
o Areas 4 and 6 are also connected to the basal ganglia
76
Describe the knee-jerk reflex and how it works
o Quadriceps muscle stretches out, which causes an increase in length in the muscle which is detected in the muscle spindle
o Group 1a sensory fibre within the muscle sends information back to spinal cord and goes through dorsal root and dorsal horn and continues to project onto the lower motor neurons in the ventral horn which controls the muscle
o Group 1a sensory fibre will also project to interneuron in spinal cord (GABAergic interneuron) which will inhibit lower motor neuron that controls antagonistic muscle to quadricep (the hamstring)
o Hence, get contraction of quadricep but inhibition of hamstring, which facilitates the knee movement kicking up
Contraction in the extensor (quadriceps) and inhibition of the flexor simultaneously (hamstring)
o Brain is not involved at all- just spinal cord involved
77
What inputs to the basal ganglia, and what does the basal ganglia output to?
• Cerebral cortex (all) projects to basal ganglia
• Cerebral cortex (area 6 specifically) receives information back from basal ganglia
o Basal ganglia processes information and then projects to the ventral lateral (VLo) thalamic nucleus
o Provides major input only to SMA (area 6)
78
How does information to the basal ganglia flow?
From lateral to medial
79
What are the input nuclei of the basal ganglia and what areas exactly do they receive projections from?
o Striatum (caudate nucleus, putamen)
Large subcortical structures under cerebral cortex
Caudate nucleus and putamen are technically joined together at the anterior portion
Caudate nucleus-Projections from other areas such as prefrontal cortex
• Has tail in temporal lobe
• Temporal lobe and cortical areas also project to caudate nucleus
Putamen- Projections from motor area
80
What are the processing nuclei in the basal ganglia (those that don't receive or relay information)
o External globus pallidus (GPe)
Downstream of striatum
o Subthalamic nucleus (STN)
o Substantia nigra pars compacta (SNpc)
81
What are the output nuclei of the basal ganglia?
• Output nuclei-output to ventral lateral part of the thalamus
o Internal globus pallidus (GPi)
o Substantia nigra pars reticulata (SNpr)
82
What are the nuclei of the basal ganglia? Sketch their position on a coronal section of the brain
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o Striatum (caudate nucleus, putamen)
o External globus pallidus (GPe)
o Subthalamic nucleus (STN)
o Substantia nigra pars compacta (SNpc)
o Internal globus pallidus (GPi)
o Substantia nigra pars reticulata (SNpr)
Timestamp: 5:18pm on 31/08
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83
What are the two pathways of the motor loop of the basal ganglia and what are they responsible for?
o Direct pathway-selection and initiation of willed movements
o Indirect pathway-suppression of movement (resting state)
84
Describe the pathway of the direct motor loop of the basal ganglia
Inhibitory pathway
Input from cortex to cells in putamen
Direct projection from putamen to output structures (GPi and SNpr)
• GABAergic putamen neurons inhibit the basal ganglia output nuclei (internal globus pallidus (GPi) and substantia nigra pars reticulata (SNpr))
• Skips medial structures (Globus pallidus externus and subthalamic nucleus)
Releases cells in thalamus (VLo) from inhibition by output nuclei
o Prevents output structures from inhibiting thalamus (which they normally do) so increase in activity in thalamus
Activity in ventro-lateral nucleus activates supplementary motor area and initiates movement
• More active thalamus-glutamergic pathway back to cortex
85
Describe the pathway of the indirect motor loop of the basal ganglia
Indirect pathway passes through the external globus pallidus (GPe), then the subthalamic nucleus (STN) before reaching the output nuclei
Activity in indirect pathway activates the output nuclei (through glutamate pathway), which inhibits the ventral-lateral nucleus
• Putamen reduces activity of the GPe (which normally inhibits subthalamic nucleus)
• Subthalamic nucleus activates output structures through glutamate pathway
• Causes more inhibition of output structures onto thalamus, and hence switches off thalamic projection back to the cortex
Inhibition of the ventral-lateral nucleus decreases excitatory output projecting to the SMA and prevents movement
86
Describe the impact of dopamine on basal ganglia pathways, and where that dopamine comes from
• Direct and indirect pathways are antagonistic
| o Dopamine from SNpc activates direct and inhibits indirect pathways, initiating movement
87
Describe how dopamine facilitates movement
• Increase in activity in direct pathway at the same time as decrease in activity in indirect pathway
• Projection from SNpc (which is dopaminergic) to putamen and release dopamine in putamen at exact moment where want to select and initiate movement
• Neurons for direct pathway in putamen have D1 receptors (dopaminergic receptors) and they are excitatory
o When dopamine binds to these D1 receptors, increases activity in direct pathway direction and results in more GABA being released in output structures, which switches off inhibition of thalamic relay nuclei and increases thalamus activity to area 6
• Neurons for indirect pathway in putamen have D2 receptors (inhibitory dopamine receptor)
o When D2 is bound by dopamine, get reduction of activity of indirect pathway (which will allow movement to occur)
88
Describe the anatomy of the cerebellum and sketch it (both saggital view and lateral view)
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• Folia and lobules
o Ridges-folia
o Lobules-there are 10 of them
• Floculus and nodules
• Vermis (spinocerebellum)
• Cerebellar hemispheres
o Lateral hemispheres (Cerebrocerebellum)
• Deep cerebellar nuclei
• Cerebellar peduncles
• Lobes
Timestamp: 5:35 at 31/08
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89
Describe the vermis of the cerebellum in terms of position and function
• Vermis (spinocerebellum)
o Midline of cerebellum
o Contributes to ventromedial pathways (regulates-particular reticulospinal pathway)
o Involuntary movement-posture
90
Describe the lateral hemispheres of the cerebellum in terms of function and input
o Lateral hemispheres (Cerebrocerebellum)
Contributes to lateral pathways
• In particular, the corticospinal tract
Voluntary movement
• Once voluntary movement has been selected by basal ganglia and area 6, info will go to cerebellum to get sequence of muscle movements calculated for movement to occur in correct manner
Gets input from cerebral cortex
91
Describe the function of the deep cerebellar nuclei of the cerebellum and each of their names
• Deep cerebellar nuclei
o Relay cerebellar output
o In the middle of the cerebellum
o Nuclei (from lateral to more medial)
Dentate nucleus (relay to cerebrocerebellum)
Globose and emboliform nuclei (relay to spinocerebellum)
Fastigial nucleus (relay to vestibulocerebellum)
• Smallest deep nucleus because vestibulocerebellum itself is smallest subdivision of cerebellum
92
What are peduncles?
o Peduncles- stalks of axons that rise form the pons
93
Describe the 3 cerebellar peduncles in the cerebellum and their roles/inputs
o Inferior cerebellar peduncle
Most information in the inferior cerebellar peduncle is incoming information from spinal cord and is involved in proprioception
• Cerebellum gets info from the body via the spinocerebellar pathways and enters for the most part in the inferior cerebellar peduncle
o Middle cerebellar peduncle
Largest cerebellar peduncle
Information is coming from the cerebral cortex and is involved in planning movements
o Superior cerebellar peduncle
Information leaving the cerebellum back to the cerebral cortex
94
Describe the lobes of the cerebellum
• Lobes-
o Made up of several folia
o Anterior lobe
o Posterior lobe
o Primary fissure-separates anterior lobe from posterior lobe
o Floculonodular lobe (vestibulocerebellum)
Contributes to ventromedial pathways (regulates)
Involuntary-balance and eye
95
Does the cerebellum have lots of neurons? What are the neurons in the cerebellum?
• Anatomy allows cerebellum to be neuron-dense
| o Most of these neurons are granule cells (whose somata lies in the granule cell layer)
96
Describe the function of cerebellum and how it achieves this function
• Programming of the cerebellum
o Process of learning new skill and enact skill with accuracy
o New motor program created to ensure smooth movement
Need to exhibit plasticity and learning
Long term changes in cerebellum which allow motor learning to occur but also allows it to be revised when motor movement is changed
o After action has occurred, there is feedback regarding the level of success of action which build on motor learning in cerebellar circuits
• Function-execution of planned, voluntary and multi-joint movements
o Sequence, timing and force of muscle contractions
Allows simultaneous multi-join movement
Heavily reliant on proprioceptive input
o Motor learning
Predictions are made from previous movements
Failure in a movements execution results in compensatory changes in cerebellar circuits
97
Describe the cerebellum (corticopontine tract) pathway
o Cerebral cortex-> cerebellum
Cortex in left hemisphere projects down to pons in region called the corticopontine tract
Pontine nuclei receive input from axons in layer V pyramidal cells in sensorimotor cerebral cortex on the left and then projects to cerebellum in the right hemisphere (crosses over).
Computation in lateral hemispheres of cerebellum
• Timing, contraction, force of each individual muscle
o Lateral cerebellar hemisphere -> dentate nucleus
o Dentate nucleus across to ventrolateral caudal part of thalamus (in the opposite hemisphere-> Right dentate nucleus left thalamus (and vice versa)
o Thalamus Area 4
98
Why does crossing over occur between the sensorimotor cerebral cortex and the cerebellum during information transfer
* Information in cerebellum is ipsilateral because all proprioceptive information which goes to the cerebellum remains on same side of body (ipsilateral) (doesn’t cross)
* If cerebral cortex (which has contralateral information) wants to exchange information with cerebellum (ipsilateral information), information needs to uncross before it reaches cerebellum
99
Compare the number of neurons in the corticopontine tract to the corticospinal tract and what this implies
Number of neurons that make the corticopontine tract are 20 times more numerous than those that form the corticospinal tract
• Cortico-pontocerebellar projection requires more processing than corticospinal tract
o More important plan than to move
100
Describe the impact of cerebrocerebellar dysfunction
• Cerebrocerebellar dysfunction
o Ataxia- uncoordinated and inaccurate movements ipsilateral to lesion
Dyssynergia-complex multi-joint movement cannot be enacted in synchronisation -breaking down in individual movement
Dysmetria-inability to regulate distance of a movement
Intention tremor-tremor of being too far or too near of object
o Caused by lateral cerebellar lesions
o Ipsilateral body affected
101
Describe the impact of spinocerebellar dysfunction
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• Spinocerebellar dysfunction
o Truncal ataxia- drunken sailor gait
Characterised by uncertain starts and stops, lateral deviations and unequal steps
Affects posture and axial muscles
o Damaged to spinocerebellum
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102
What does root mean?
term is used to refer to the axons entering or exiting the
| spinal cord
103
Describe the potential locations of lower motor neurons
o Lower motor neurons of the somatic motor system are located in the ventral horn
o Lower motor neurons of the autonomic sympathetic motor system are located I the lateral horn (or intermediolateral cell column)
Lateral horn- only present in thoracic and lumbar segments (T1-L2) where the autonomic flow is sympathetic
Pre-ganglionic parasympathetic LMNs are located in the sacral spinal cord S3-4
o Lower motor neurons of the parasympathetic nervous system are found in the brainstem
104
What does funiculus mean?
Bundles of myelinated axons
105
What are the two tract directions in funiculi and what function are they associated with?
- Ascending: carry somatosensory information from the periphery to the brain
- Descending: carry motor inforamtion to synpase on lower motor neurons, and lower motor neurons will then send axons to innervate muscles
106
How is a tract usually named?
A tract is frequently named for the origin (location of cell body) and target (location of axon terminal)
107
What are pathways?
Several tracts connected by synapses
108
Describe what makes the difference between the lateral corticospinal tract and the anterior corticospinal tract in terms of dessucation of upper motor neurons
o Lateral corticospinal tract- approximately 90% of the upper motor neuron axons from the cortex decussate in the caudal medulla at the motor decussation, then synapse on lower motor neurons in the ventral horn of the spinal cord
o Anterior corticospinal tract- the remaining 10% of the upper motor neuron axons from the cortex cross in the spinal cord at the ventral white commissure and then synapse on lower motor neurons in the ventral horn
109
Describe the two motor systems in the emotional motor system that regulate emotion and what they do
• Emotional motor system has two motor systems to regulate emotion-
o Lateral component
Specific emotional behaviours (being happy, sad…)
o Medial pathway
Gain setting systems including triggering mechanisms of rhythmical and other spinal reflexes
110
Is emotion the same in all species?
o Continuity between emotional expressions in animals and humans
111
Describe what influences emotion and how emotion can be detected
• Cognition (can change expression of emotional state) and visceral sensation both feed emotion, which can be exhibited through cognition (meaning we attribute to expression of movement and expression of physiological changes), behavioural momentum (behaviour and quality of movement by person) and integrated/physiological response (endocrine, autonomic, somatic changes which change our physiology)
112
How can emotion be defined?
o Emotion can be defined by particular classes of physiological response and changes in quality and expression of behaviour (which is contraction of somatic muscles)
113
What is the James-Lange theory of emotion and how is emotion caused?
o Emotion is the interpretation of behavioural and physiological changes triggered by external stimuli
Experience emotion in response to physiological changes in our body
o See stimulus, which triggers physiological changes and causes brain to interpret physiological changes as the emotion and leads to emotional response
o Each emotion produces a different set of physiological responses- this is why two different emotions feel different
114
What is the Cannon-Bard theory of emotion and how is emotion caused?
• Cannon-Bard theory of emotion
o Stimuli are registered in the thalamus which then triggers combined experiential, behavioural and physiological changes, which comprise emotion
o See stimuli, thalamus is activated, produces experience, drives physiological changes which produces emotion and hence emotional expression
Character of emotion is determined by the pattern of activation of the thalamus irrespective of the physiological response to the sensory input
o Emotional experience can occur independently of emotional expression
115
What is the Schachter-Singer 2 factor theory of emotion?
• Schachter-Singer 2 factory theory of emotion
o Stimuli trigger physiological arousal, we become aware of physiological arousal, then there is cognitive appraisal of the situation to determine the most appropriate emotion
o Emotion is derived from how you appraise the source of the arousal that you’re experiencing
o Suggests that lower mammalian species may not experience emotion in the same way we do
116
Describe Broca's limbic lobe and how it pertains, both now and originally, to emotion
• Broca’s Limbic lobe
o Broca didn’t think it was originally involved in emotion
o All areas around ventrical are limbic lobe
Cingulate gyrus, hippocampus, cortex on the medial surface of the temporal lobe and parahippocampal gyri responsible for cognitive appraisal for emotion
117
Describe the 1937 Papez circuit
| Sketch the location of structures involved in it
• Papez circuit (1937)
o Neocortex (emotional colouring) connected to cingulate cortex and vice versa
Emotional experience influences cognitive state and vice versa
o Cingulate cortex (regulation of emotional experience) connected to hypothalamus (regulation of emotional expression) via the hippocampus and fornix
o Hypothalamus connected back to cingulate cortex by anterior nuclei of the thalamus
• Hence, Papez circuit suggests that emotional experience has capacity to drive emotional expression, and emotional expression has capacity to drive/influence emotional experience
Timestamp: 11:13pm at 7/09/2019
118
Describe what two systems comprise the limbic system and why the idea of a limbic system is a problem
• Due to the correlation between elements composing the Papez circuit and Broca’s limbic lobe, these structures were referred to as the limbic system
o But some structures involved in emotions are also involved in other functions- not a one-to-one relationship between structure and function
o Also thought that there is not a single discrete, emotion system
119
What is the basic theory of emotion and who is a big player in it?
• Basic theories of emotion-Basic emotions encapsulated by the brain (Ekman)-expressed by all people and recognised by all people and controlled by somatic muscles (emotional system can tune the responses given by somatic muscles to give expression which characterises a particular feeling state)
120
What are the basic emotions and the signs of these basic emotions?
- Sadness
- Fear
- Surprise
- Anger
- Disgust
- Happiness
121
Describe the signs of sadness
Drooping upper eyelids
Losing focus in eyes
Slight pulling down of lip corners
122
Describe the signs of fear
Eyebrows raised and pulled together
Raised upper eyelids
Tensed lower eyelids
Lips slightly stretched horizontally back to ears
123
Describe the signs of surprise
Eyebrows raised
Eyes widened
Mouth open
124
Describe the signs of anger
Eyebrows down and together
Eyes glare
Narrowing of lips
125
Describe the signs of disgust
Nose wrinkling
| Upper lip raised
126
Describe the signs of happiness
Crow’s feet wrinkles
Pushed up cheeks
Movement from muscle that orbits the eye
127
Describe Kluver and Bucy's 1937 and 1939 experiment and results
o Kluver and Bucy (1937 and 1939)
Resection of the temporal lobe in animal models triggers complex behavioural changes
• Female cat with this resection treated other species as appropriate receptors of her sexual behaviours (which were of a male cat)
An effect replicated in other mammalian species
Resection of temporal lobe (especially the amygdala after further investigation) results in:
• Psychic blindness- inability to recognise common objects
• Oral tendencies- examine the environment with the mouth not eyes
• Hypermetamorphosis- irresistible desire to examine everything
• Altered sexual behaviours- dramatic increases
• Emotional changes- little emotion in facial expression or vocalisation, decreased fear and aggression
128
What does resection of the amygdala result in?
* Psychic blindness- inability to recognise common objects
* Oral tendencies- examine the environment with the mouth not eyes
* Hypermetamorphosis- irresistible desire to examine everything
* Altered sexual behaviours- dramatic increases
* Emotional changes- little emotion in facial expression or vocalisation, decreased fear and aggression
129
Where is the amygdala, what inputs to it and what are its nuclei (and their respective roles)
Sketch their positions in the amygdala
o Amygdala-
Located in the anterior pole of the temporal lobe
Each sensory system has a different projection pattern to the amygdala nuclei, and interconnections within the amygdala allow the integration of information from different sensory modalities
Subdivided into several subregions, including:
• Corticomedial nuclei
o Closely associated with the cortex
• Basolateral nuclei
o Get inputs from everywhere (visual, auditory, somatosensory….)
o Input area for the amygdala
• Central nucleus
o Primarily an output area for the amygdala
o All neurons
Timestamp: 11:23pm at 7/09/2019
130
Describe who expanded on the limbic system and what structures were added to it, as well as their connections to the Papz circuit
The limbic system (preferentially called emotional motor system) after Maclean-
• Expansion and modification of Papez circuit
o Addition of prefrontal cortex, amygdala (and later the association cortex, septum)
• Amygdala gets input from hippocampus and outputs to hypothalamus (key for producing emotional expression)
• Critical region interconnected in the neocortex include the prefrontal cortex and the association cortex (important for bidirectional communication with emotional circuit)
131
Sketch the Maclean limbic system
Timestamp at: 11:25pm at 7/09/2019
132
Described LeDoux and Phillip 1992 two part experiment
• LeDoux and Phillip 1992
o White rats are placed into a chamber and allowed to explore for 2 minutes
o A tone or noise is presented for 30 seconds
o When the tone terminates, the rat receives footshock
High increase in blood pressure and movement changes (freezing due to direct neural and endocrine contributions)
o Rats taken back out of chamber after a few trials then placed back in to test for fear of the context
o Rats are tested for fear of the tone in a novel context
o The defensive response time of freezing is used to measure fear
o Show that rats show fear through conditioning through context
o Lesioned hypothalamus of rats-> when played conditioned sound, exhibited physical fear response (froze) but no high blood pressure as expected
o Lesioned periaqueductal gray matter in brain stem-> animals didn’t freeze but blood pressure went up
133
Describe the nuclei in the amygdala
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o Basolateral nucleus
Lateral nucleus
Basal nucleus
Accessory-basal nuclei
o Corticomedial amygdala
o Central nuclei
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134
Describe how all the nuclei in the amygdala connect to each other in terms of input and output and how the output of the central nucleus influences learning
Lateral nucleus receives information from the temporal and frontal cortex , as well as the medial geniculate nucleus (medial division) and posterior intralaminar nucleus from the thalamus
• Appears to play an important role in acquisition and storage of memory associated with fear conditioning
Lateral nucleus sends projections to the basal and the accessory basal nucleus, as well as the central nucleus before they are sent to the brain stem and other areas of the brain – also send back to the frontal cortex and the cerebral cortex
• Basaloateral nuclei project to cerebral cortex, which makes the emotional emotional experience
All nuclei project to central nucleus
Central nucleus connects to parts of the brain which generate emotional responses, including the nucleus basalis which contains acetyl choline neurotransmitters
• If animal thinks stimulus is important, nucleus basalis floods the cortex with acetyl choline -> in the presence of acetyl choline, learning happen: changes in synaptic strength that enhance the amygdala’s response to the tone after conditioning
• Central nucleus also connects to the hypothalamus, which produces the autonomic response, and periaqueductal gray matter in the brain stem, which drives the behavioural reaction
135
Describe how the amygdala is important in fear conditioning
o Process:
Information about the unconditional stimulus enters the lateral nucleus and this can automatically excite the outputs of the central nucleus
If this fires at the same time the neurons are firing that encode the conditioned stimulus (context), they bind together through process of long-term potentiation
After repeated pairings, the conditioned stimulus can excite the same neurons in the lateral nucleus as the unconditioned stimulus
136
Why is neuroplasticity in the amygdala important and what facilitates it?
• Fear conditioning requires neuroplasticity in the amygdala
o Pavlovian fear conditioning is based upon neuroplasticity within the lateral nucleus of the amygdala
Plasticity in LA depends on calcium entry through NMDA receptors and voltage gated calcium channels
Elevated calcium triggers a number of intracellular cascades involving kinase mediated enzymatic reactions
137
Describe Morris et al's 1996 experiment
• Morris et al. 1996
| o Recognition of fearful faces is done by the amygdala, but only on one side (lateralised on the left)
138
What are viscera?
• Viscera- smooth muscles of blood vessels, the heart, the glandular structures…
o Everything that is not a somatic muscle
139
Describe the somatic motor system in terms of:
- Accuracy and speed of signals
- Targets
- Neuron location
- Synaptic pathway
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Rapid and accurate signals
Only peripheral targets
Commands only skeletal muscle
All neurons that regulate skeletal muscles are within CNS
Monosynaptic pathway
• Single synapse
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140
Describe the autonomic motor system in terms of:
- Accuracy and speed of signals
- Targets
- Neuron location and identity
- Synaptic pathway
Actions multiple, widespread, slow
Wide coordinated and graded control
Commands all tissue and organ except skeletal muscle
Neurons that control viscera are found outside CNS (in body cavities)
• Cell bodies of all autonomic lower motor neurons lie outside the central nervous system in autonomic ganglia
• Neurons in these ganglia are called postganglionic neurons
• Postganglionic neurons are driven by preganglionic neurons
Disynaptic pathway
• Two synapses in the pathway
o One synapse on the viscera (from neurons to body cavity)
From autonomic ganglion along postganglionic neurons
o Another synapse on the neurons in the body cavity from the brain and spinal cord
To autonomatic ganglion (groups of neurons) through preganglionic neurons
• Regulated by CNS neurons
141
Describe the effects of the sympathetic system and hence what organ it innervates
o Sympathetic division-excites behaviour
Effects-
• Increased heart rate and blood pressure (innervate blood vessels and heart)
• Depressed digestive function (innervates guts)
• Mobilised glucose reserves (innervates liver)
• Orgasm (innervates gonads)
• Inhibits micturition (innervates gonads)
142
What are the 2 divisions of the visceral motor system/autonomic nervous system?
- Sympathetic division
| - Parasympathetic division
143
What is the origin of pre-ganglionic sympathetic neurons?
* Origin- spinal cord (T1)
| * Lateral horn of spinal cord-location of sympathetic preganglionic neurons
144
Compare the pre-ganglionic fibres to the length of the pre-ganglionic fibres, as well as the location of the autonomic ganglion in the sympathetic nervous system
• Short preganglionic fibres, autonomic ganglion is close to brain/spinal cord and longer post-ganglionic fibres
145
Describe the sympathetic trunk
- What it is
- Where it is
Sympathetic ganglia are connected together from superior to inferior aspect of the body and run parallel to spinal cord
• Run parallel entire length of vertebral column outside in body cavity
• Bilateral structure
• Ganglia (paravertebral)associated with vertebral levels
146
What is the ganglion impar?
• Once get to tailbone, both sides of sympathetic ganglia join together and end at sacral spinal segment known as terminal “ganglion impar”
147
What are landmark features of the sympathetic trunk in the cervical region?
• Superior, Middle and Inferior/stellate cervical ganglia
| o Only in cervical region- cervical ganglia join together to form these 3 large ganglia
148
Describe the sympathetic ganglia on top of the anterior abdominal aorta
o On top of abdominal aorta, there are 3 sympathetic ganglia that leave this aorta
One lies next to celiac artery (celiac ganglion)
One lies close to superior mesenteric artery (superior mesenteric ganglion)
One lies by the inferior mesenteric artery (inferior mesenteric ganglion)
o These are called the prevertebral ganglia (in front of vertebral column)
149
What is the destination of sympathetic nerves?
* Locally (T1-L2/3)
* Above and below body representation (above T1 and below L2/3)
* Deep into core of body cavities (medial visceral structures)
150
Describe the sympathetic pathway when sympathetic nerves go locally
• Locally (T1-L2/3)
o Sympathetic pre-ganglionic neuron -> sympathetic pre-ganglionic fibre which leaves the lateral horn, goes to ventral horn and leaves through ventral root
o Joins spinal nerve
o Enters sympathetic ganglion
o Synapses on sympathetic post-ganglionic cell
o Rejoins spinal nerve
o Travels with spinal nerve through dorsal and ventral primary rami to axial-skeletal muscles/blood vessels on body surface
151
Describe how sympathetic neurons reach the heart-upper thoracic spinal cord
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• The heart-upper thoracic spinal cord
o Lateral neurons project into ventral roots
o Into the spinal nerve
o Jumps out of spinal nerve
o Into the sympathetic trunk
o Synapses on post-ganglionic neuron
o Special set of nerves (cardiac sympathetic nerves) plunge into thoracic area and supply the heart
Cardiac sympathetic nerves
• Superior
• Inferior
• Middle
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152
Describe how sympathetic neurons reach above T1 or below L2/3
o Preganglion neuron-> fibre leave lateral horn and travel in ventral roots
o Join spinal nerve
o Enter and traverse sympathetic ganglion
o Leave and enter sympathetic trunk
o Ascend or descend then synapse on sympathetic ganglion cell
o Post ganglionic fibre enter dorsal and ventral primary rami
o Supply distant structures (head, lower extremities)
153
Describe how sympathetic nerves reach deep into core of body cavities
talk about the difference when reaching the heart vs guts and gonads
• Deep into core of body cavities (medial visceral structures)
o Prepanglion neuron-> fibre leave lateral horn and travel in ventral roots
o Join spinal nerve
o Enter sympathetic ganglion
o Enters sympathetic trunk
o Descends/ascends a little bit
o Can synapse on sympathetic post-ganglionic (heart) and enters cardiac nerves, or not (guts and gonads)
o If not (guts and gonads)
Leaves sympathetic trunk as a pre-ganglionic fibre and enters splanchnic nerves
Head to anterior surface of abdominal aorta and Synapse on prevertebral ganglia and post-ganglionic neuron
Supply organ
154
Describe the effects of the parasympathetic system and hence what organs it acts on
Effects-
• Slower heart rate (but there are no parasympathetic nerves innervating the blood vessels)
• Increased digestive functions (acts on guts)
• Decreased sweating (acts on skin)
• Store glucose (acts on liver)
• Erection and lubrication (acts on gonads)
• Triggers micturition (acts on gonads)
155
What structures get input from the parasympathetic nervous system
All visceral structures (WITH EXCEPTION OF BLOOD VESSELS) get input from parasympathetic nervous system
156
Where do parasympathetic nerves originate from?
• Origin-within brain stem (within nucleus ambiguus and dorsal motor nucleus of vagus)
157
Compare the pre and post-ganglionic fibre sizes in parasympathetic nervous system, as well as the location of the autonomic ganglia
• Long preganglionic fibres, autonomic ganglion is far away from brain/spinal cord and short post-ganglionic fibres
158
What is the vagus nerve and where is it found?
• Vagus nerve (cranial nerve X) is primary parasympathetic nerve from everything to the neck below and above the splenic flexure
o Goes from base of the brain to abdominopelvic junction innervating all structures in body cavities
o Bundle of fibres (some of which are parasympathetic preganglionic fibres, some of which are sensory fibres)- it is a mixed nerve
159
Where are preganglionic neurons found in the brainstem?
The preganglionic neurons are found in the brainstem. In 2 major regions:
• The nucleus ambiguus
• The dorsal motor nucleus of the vagus
160
Describe the composition of the nucleus ambiguus and what structures it supplies
o Contains only parasympathetic preganglionic neurons which supply structures in larynx and pharynx, the oesophagus, heart, abdominal viscera and supply small portions of certain aspects of reproductive organs
o Rostral to caudal organisation
Neurons in rostral portion control rostral structures
Neurons in caudal portion control caudal structures
o Viscerotropic maps selective for gastrointestinal tract
161
Describe the structures of the dorsal motor nucleus of the vagus and what structures it regulates
• The dorsal motor nucleus of the vagus
o Contains parasympathetic preganglionic neurons
o Regulate the gastrointestinal tract
162
Where are the ganglia of body structures innervated by the vagus
• All body structures that receive parasympathetic input from the vagus have their ganglia sitting on organ surface, followed by really short post-ganglionic fibre
163
Describe how the sympathetic and parasympathetic act on the heart
o Both work together
E.g. the heart gets sympathetic post-ganglionic fibres from the stellate ganglion and parasympathetic post-ganglionic fibres from the cardiac plexus on its surface- dual innervation
164
Describe how the autonomic ganglia develop
o Development of autonomic ganglia
When neural tube was closing, some neurons squeezed out of neural tube as it closed and sat in body cavity
Embryological composition identical to every neuron
165
What higher brain regions is the visceral motor system regulated by?
• Visceral motor system is regulated by higher brain regions
o These regions include:
Parabrachial nucleus
Periaqueductal grey region
Hypothalamus, amygdala and cingulate cortex
166
Describe how the emotional motor system works with the autonomic nervous system and what the impact of this is
• All the emotional motor system plugs into parasympathetic and sympathetic motor neuronal pools to produce physiological changes to support the expression of emotional behaviours
o Basis of integrated output
Feeling state
Somatic motor output
Sympathetic and parasympathetic outflow
