1
Q
What is the general definition of the Nervous System?
A
It is a communication and control network that allows an organism to interact with its environment.
2
Q
What are the two main sections of the overall nervous system?
A
Central Nervous System (CNS) (highlighted in red in the figure). Peripheral Nervous System (PNS) (highlighted in blue in the figure).
3
Q
What is the Central Nervous System (CNS) and what does it include?
A
It is the processing center for the entire nervous system. It includes the brain and the spinal cord.
4
Q
What is the Peripheral Nervous System (PNS) and what does it consist of?
A
It includes the rest of the nervous system located in the periphery. It consists of nerves and ganglia (groups of nerve cell bodies located outside the brain and spinal cord).
5
Q
What parts of the body does the PNS serve?
A
It serves the limbs (legs and arms) and internal organs.
6
Q
How is the PNS divided based on the direction of information flow?
A
Afferent Division (Sensory) Efferent Division (Motor)
7
Q
What is the function of the Afferent Division (Sensory System)?
A
It is responsible for sending afferent info (sensory detection) towards the nervous system (CNS).
8
Q
What are the two types of information carried by the Afferent Division?
A
Info from the external environment (e.g., light and sound). Info from the internal environment (e.g., blood pressure).
9
Q
What is the function of the Efferent Division (Motor Division)?
A
It sends information from the nervous system to the organs of the body, which then carry out the appropriate response (expression of behavior).
10
Q
In summary, what are the three general functions of the Nervous System?
A
Sensory detection (by the afferent/sensory division). Information processing (by the brain/CNS). Expression of behavior (by the efferent/motor division).
11
Q
What are the three functional parts the Cerebral Cortex is commonly described as?
A
Motor Areas Sensory Areas Association Areas
12
Q
How many motor areas are there and what is/are it/they called?
A
There is only one primary motor area: the Somatomotor Cortex
13
Q
Where is the Somatomotor Cortex located?
A
In the Frontal Lobe, specifically in the Precentral Gyrus (just anterior to the central sulcus).
14
Q
What is the function of the Somatomotor Cortex and its association areas?
A
They are involved in the planning, control, and execution of voluntary movements.
15
Q
Where are the important Motor Association areas located relative to the primary motor cortex?
A
They lie just anterior to the primary motor cortex.
16
Q
What are two specific examples of Motor Association areas mentioned?
A
The Supplemental Motor Area The Premotor Cortex
17
Q
Where is the Somatosensory Cortex located?
A
In the Parietal Lobe, specifically in the Postcentral Gyrus (just posterior to the central sulcus).
18
Q
What is the function of the Somatosensory Cortex and its association area?
A
They are important for the sense of touch, temperature, nociception (pain), and taste.
19
Q
Where is the Visual Cortex located?
A
In the Occipital Lobe
20
Q
What is the function of the Visual Cortex and its association area?
A
They are responsible for the sense of light (vision).
21
Q
Where are the Auditory Cortex and Olfactory Cortex located?
A
In the Temporal Lobe
22
Q
What are the functions of the Auditory and Olfactory cortices?
A
Auditory: Responsible for the sense of sound. Olfactory: Responsible for the sense of smell.
23
Q
What anatomical landmark divides the Frontal Lobe from the Parietal Lobe?
A
The Central Sulcus.
24
Q
What general principle governs the relationship between primary sensory/motor areas and their association areas?
A
Primary areas receive/send the raw signal, while association areas (which often lie adjacent to them) are important for higher-order processing or planning. Association areas project to or receive input from their respective primary cortices.
25
What is the Spinal Cord?
It is a part of the CNS located in the vertebral column, extending from the base of the skull to the first lumbar vertebra (L1). It is the most caudal portion of the CNS.
26
What are the 5 subdivisions (segments) of the spinal cord and how many segments are in each?
Cervical: 8 segments Thoracic: 12 segments Lumbar: 5 segments Sacral: 5 segments Coccygeal: 1 segment Total: 31 segments.
27
How many pairs of spinal nerves are there?
31 pairs (corresponding to the 31 segments).
28
What types of nerves do spinal nerves contain?
They contain both sensory nerves and motor nerves.
29
What is the function of Sensory nerves in the spinal cord?
They carry information to the spinal cord from the skin, joints, muscles, and visceral organs in the periphery
30
Via what structures do sensory nerves enter the spinal cord?
Via the dorsal root and cranial nerve ganglia.
31
What is the function of Motor nerves in the spinal cord?
They carry information from the spinal cord to the periphery.
32
What structures do Motor nerves innervate?
Skeletal muscle Cardiac muscle Smooth muscle Glands Secretory cells
33
What are the two pathways by which information travels up and down the spinal cord?
Ascending pathways Descending pathways
34
What is the function of Ascending pathways?
They carry sensory information from the periphery to higher levels of the CNS.
35
What is the function of Descending pathways?
They carry motor information from higher levels of the CNS to the motor nerves that innervate the periphery.
36
What is the "simple words" description of the spinal cord's function?
It is the "information highway of the body" that helps in connecting the various organs of the body to the brain (sending messages back and forth).
37
What is the shape of the Central Gray Matter in the spinal cord?
It is "H" or butterfly-shaped.
38
What surrounds the central gray matter?
Ascending and descending white matter columns.
39
What are the three main zones of the central gray matter?
Dorsal Horn Intermediate Zone Ventral Horn
40
What is the primary function of the Dorsal Horn?
It is involved mainly in sensory processing.
41
What does the Intermediate Zone contain?
Interneurons and certain specialized nuclei.
42
What does the Ventral Horn contain?
Motoneurons.
43
How do Motoneurons send their axons out of the spinal cord?
Via the Ventral Nerve Root.
44
Where are the cell bodies of Sensory Neurons located?
In the Dorsal Root Ganglia.
45
How do Sensory Neurons send their axons into the spinal cord?
Via the Dorsal Nerve Root.
46
Describe the bifurcation (splitting) of Sensory Neuron axons in the periphery.
They bifurcate into a Ventral Ramus and a Dorsal Ramus.
47
What information does the Ventral Ramus (sensory) convey?
Sensory information from the periphery (extremities/limbs) and the ventral trunk to the dorsal horn.
48
What information does the Dorsal Ramus (sensory) convey?
Sensory information from the dorsal trunk (back) to the dorsal horn.
49
Describe the bifurcation of Motoneuron axons.
They also bifurcate into a Ventral Ramus and a Dorsal Ramus.
50
What information does the Ventral Ramus (motor) convey?
Motor information to the limbs and ventral trunk.
51
What information does the Dorsal Ramus (motor) convey?
Motor information to the dorsal trunk.
52
Why does the spinal cord vary in size and shape along its length?
Because of the two enlargements (Cervical and Lumbosacral) which give rise to the nerve plexuses for the arms and legs, respectively.
53
How does the amount of gray matter differ at the enlargement levels?
There is more gray matter (particularly in the ventral horns) at the cervical and lumbosacral levels than at the thoracic levels, to accommodate the motor control of the limbs.
54
What are the four common organizational features shared by sensory and motor pathways?
Synaptic Relays Decussation Different types of nerve fibers Topographic Organization
55
What is a Synaptic Relay?
It is a feature where the nervous system uses synapses in relay nuclei to integrate converging information.
56
Where are relay nuclei found, and where are they especially prominent?
They are found throughout the CNS, but they are especially prominent in the thalamus.
57
What is the role of the thalamus in synaptic relays?
Almost all information going to and coming from the cerebral cortex is processed in relay nuclei in the thalamus
58
What is Decussation?
The crossing of information from one side to the other side of the brain or spinal cord.
59
What is the functional result of decussation?
Almost all sensory and motor pathways are bilaterally symmetric. Sensory/motor activity on one side of the body is relayed to/controlled by the contralateral (opposite) cerebral hemisphere.
60
What determines the Conduction Velocity of nerve fibers?
The size (diameter) of the fibers and the presence or absence of myelination.
61
Which nerve fibers have the fastest conduction velocities?
Large, myelinated nerve fibers.
62
Which nerve fibers have the slowest conduction velocities?
Small, unmyelinated nerve fibers.
63
What are the two classification systems for nerve fibers mentioned?
The Letter system (e.g., A, B, C). The Roman numeral system (e.g., I, II, III, IV).
64
What is Topographic Organization?
A feature where information from a specific area of the body travels in a particular pathway and terminates in a specific area of the cortex that is different from information from other parts of the body.
65
Which cortices are specifically noted as being topographically organized?
The Somatosensory cortex and the Primary Motor cortex
66
How many major pathways are there for transmitting somatosensory info to the CNS, and what are they?
Two: Dorsal Column-Medial Lemniscus System (shown in blue/green). Anterolateral (or Spinothalamic) System (shown in red).
67
What is the general structure of the neurons involved in these pathways?
A series of sensory afferent neurons (First-order, Second-order, Third-order, Fourth-order) are responsible for transmission.
68
What is the First-order neuron (Primary Afferent Neuron)?
Cell Body Location: Dorsal root ganglia. Axon Type (Dorsal Column): Large, myelinated axons. Axon Type (Anterolateral): Lightly myelinated and unmyelinated small fibers.
69
Where are the cell bodies of the Second-order neurons located?
Anterolateral System: In the Spinal Cord. Dorsal Column System: In the Brain Stem.
70
What is a key characteristic of the Second-order neurons regarding their axons?
Their axons cross the midline (decussate) (either in the spinal cord or brain stem) and ascend to the thalamus.
71
Where are the cell bodies of the Third-order neurons located?
In one of the somatosensory nuclei of the Thalamus.
72
Where do Third-order neurons project?
They synapse on the Fourth-order neuron located in the Somatosensory Cortex.
73
What is the function of Higher-order neurons in the cortex?
They integrate complex information and translate it into conscious perception.
74
Which sensory modalities are carried by the Dorsal Column Pathway?
Fine touch, pressure, vibration, and two-point discrimination.
75
Which sensory modalities are carried by the Anterolateral System?
Pain, temperature, and crude touch.
76
What is the definition of Spinocerebellar Pathways?
They are nerve tracts originating in the spinal cord and terminating in the same side (ipsilateral) of the cerebellum.
77
What type of information do the Spinocerebellar tracts carry?
They carry unconscious proprioceptive information (e.g., positions and movement of body parts).
78
What types of sensory receptors provide this proprioceptive information?
Proprioceptors, specifically Golgi tendon organs and muscle spindles.
79
What does the cerebellum use this information for?
Motor coordination functions.
80
How many individual tracts are within the spinocerebellar pathways?
Four. (Dorsal, Ventral, Cuneocerebellar, Rostral).
81
What is the function of the Dorsal/Posterior Spinocerebellar Tract?
It carries proprioceptive information from the lower limbs and trunk to the ipsilateral cerebellum.
82
Describe the pathway of the Dorsal Spinocerebellar Tract.
1st Order Neuron: Dorsal root ganglion axon enters spinal cord. Synapse: In the dorsal horn at the Nucleus Dorsalis (Clarke’s Column). 2nd Order Neuron: Projects up (does not decussate) to form the tract. Entry: Enters cerebellum via the Inferior Cerebellar Peduncle.
83
What is the function of the Ventral/Anterior Spinocerebellar Tract?
It carries proprioceptive information from the lower limbs.
84
Describe the pathway of the Ventral Spinocerebellar Tract (specifically the decussations).
1st Decussation: In the spinal cord (axons cross to opposite side). Ascent: Travels up to the brainstem. Entry: Enters cerebellum via the Superior Cerebellar Peduncle. 2nd Decussation: In the cerebellar white matter. Result: Terminates in the ipsilateral cerebellum (due to double crossing).
85
What is the function of the Cuneocerebellar Tract?
It carries proprioceptive information from the upper limbs to the ipsilateral cerebellum.
86
Describe the pathway of the Cuneocerebellar Tract.
1st Order Neuron: Fibers from cervical spinal levels ascend to the medulla. Synapse: In the External Cuneate Nucleus. 2nd Order Neuron: Axons form the tract (does not decussate). Entry: Enters cerebellum via the Inferior Cerebellar Peduncle.
87
What is the function of the Rostral Spinocerebellar Tract?
It carries proprioceptive information from the upper limbs to the ipsilateral cerebellum (not shown in figure).
88
What is the "general rule" for spinocerebellar tracts regarding laterality?
Each half of the cerebellum is functionally related to the ipsilateral side of the body.
89
What is the clinical presentation of a spinocerebellar tract lesion?
An ipsilateral loss of muscle coordination.
90
Does proprioceptive information only go to the cerebellum?
No. It is also sent to the cerebral cortex (via dorsal column pathway for upper limb, dorsal spinocerebellar for lower limb).
91
What is the function of proprioceptive information sent to the cerebral cortex?
It forms the basis for Kinesthesia: the conscious awareness of our body parts (e.g., position of our hand).
92
Where is somatosensory information eventually sent?
To the Somatosensory Cortex.
93
What principle dictates how body parts are represented in the Somatosensory Homunculus?
Each part is represented in proportion to its number of sensory neural connections (or sensory receptors), not its actual physical size.
94
What determines the size of a region in the Homunculus?
The number of sensory receptors in that area of the body.
95
What does the large size of the hand on the homunculus represent?
It indicates an extensive proportion of touch receptors in the hand, meaning the hands are a lot more sensitive to touch than the rest of the body.
96
Describe the general visual appearance of the homunculus.
It looks like an oddly proportioned human with: Oversized: Face, hands, fingers, lips, feet, and tongue. Skinny: Arms and legs.
97
Based on the slide diagram, list the body parts mapped on the homunculus from the top (medial) to the bottom (lateral).
Genitals Toes / Foot / Leg Hip / Trunk / Neck / Head Shoulder / Arm / Elbow / Forearm / Wrist Hand / Fingers (Little, Ring, Middle, Index, Thumb) Eye / Nose / Face Lips (Upper, Lower) Teeth, gums, jaw / Tongue Pharynx / Intraabdominal
98
In which cerebral lobe is the Somatosensory Cortex (and thus the homunculus) located?
In the Parietal Lobe, just posterior to the Central Sulcus .
99
What type of nerve fibers does the Dorsal Column System use?
It uses large, myelinated, fast conduction axons (group Aα and Aβ)
100
Describe the path of the 1st order neuron (axons) in the Dorsal Column System.
The axons ascend ipsilaterally (on the same side) in the spinal cord to the dorsal column nuclei in the medulla.
101
Where do the 2nd order neurons decussate (cross the midline)?
They cross to the contralateral side in the medulla of the brainstem before synapsing in the thalamus.
102
Where are the 3rd order neurons located?
In the Ventral Posterior Lateral (VPL) nucleus of the thalamus.
103
Where do the 3rd order neurons project to?
They ascend to the Somatosensory Cortex.
104
What specific sensory modalities are carried by the Dorsal Column System?
Accurate (fine) touch Pressure Vibration Two-point discrimination Conscious proprioceptive information (muscle and joint sense)
105
Describe the path of the first-order neurons in the Dorsal Column System
The axons ascend ipsilaterally (on the same side) in the spinal cord to the dorsal column nuclei in the medulla.
106
Where do the second-order neurons of the Dorsal Column System decussate?
They cross to the contralateral side in the medulla before synapsing in the thalamus.
107
Where are the third-order neurons of the Dorsal Column System located and where do they project?
They are in the Ventral Posterior Lateral (VPL) nucleus of the thalamus and ascend to the somatosensory cortex.
108
What sensory modalities does the Dorsal Column System carry?
Accurate (fine) touch, vibration, and conscious proprioceptive (muscle and joint) information.
109
What type of nerve fibers does the Anterolateral System use?
It uses lightly myelinated and unmyelinated, small and slow axons (Group Adelta and C).
110
Describe the path and decussation of the second-order neurons in the Anterolateral System.
They cross immediately in the spinal cord and ascend contralaterally before synapsing in the thalamus.
111
Where are the third-order neurons of the Anterolateral System located?
In the Ventral Posteroinferior (VPI) nucleus of the thalamus.
112
What sensory modalities does the Anterolateral System carry?
Pain, temperature, and crude touch information.
113
What type of nerve fibers does the Spinocerebellar System use?
It uses large, myelinated, fast conduction axons (Aalpha-beta).
114
Describe the decussation pattern of the Spinocerebellar System.
Second-order neurons have either no decussation or double decussation (once in spinal cord, once in cerebellum).
115
Is the Spinocerebellar system ipsilateral or contralateral?
It is generally ipsilateral (information ends up on the same side).
116
What is the path of the Spinocerebellar System?
It ascends from the spinal cord to the cerebellum.
117
What sensory modalities does the Spinocerebellar System carry?
Unconscious proprioceptive information from muscle and joints.
118
What is the function of the cerebellum using this information?
It is involved in movement coordination and balance.
119
What anatomical landmark separates the primary sensory and motor areas?
The Central Sulcus, which divides the frontal lobe from the parietal lobe.
120
Where is the Primary Motor Cortex located?
In the Precentral Gyrus of the Frontal Lobe.
121
What signals does the Primary Motor Cortex handle?
Motor signals.
122
What signals does the Somatosensory Cortex handle?
Tactile sensory signals.
123
Where are the important Motor Association areas located?
Just anterior to the primary motor cortex.
124
What are two specific examples of Motor Association areas?
The Supplemental Motor Area The Premotor Cortex
125
What is the function of the Motor Association areas?
They are involved in higher-order motor planning.
126
Where do the Motor Association areas project to?
They project to the Primary Motor Cortex.
127
In summary, how many primary motor areas are there?
Only one: the Somatomotor Cortex (Primary Motor Cortex).
128
What is the overall function of the Somatomotor Cortex and its association areas?
They are involved in the planning, control, and execution of voluntary movements.
129
How is information from specific areas of the body represented in the sensory and motor cortices?
It is represented in specific areas of the cortex, typically as a homunculus (a map of the body). The primary motor cortex is somatotopically organized, just like the sensory cortex.
130
What is the Motor Homunculus used for?
It is used to assist in understanding broadly that specific regions of the motor cortex correspond to specific regions for body movement.
131
Describe the physical appearance of both the sensory and motor homunculi.
They appear as a grotesquely distorted (or disfigured) human with disproportionately huge hands, fingers, lips, tongue, and face in comparison to the rest of the body.
132
Why are the hands, lips, tongue, and face represented as being larger on the Motor Homunculus?
Because of the fine motor skills found in these particular parts of the body. Their size on the map is proportional to the complexity of movement/control, not physical size.
133
How is a body part with fewer motor connections to the brain represented on the homunculus?
It is represented as being smaller.
134
Unlike the sensory system, how many motoneurons do Somatic Motor Pathways involve?
Two motoneurons: An Upper Motoneuron A Lower Motoneuron
135
Where are the cell bodies of Upper Motoneurons located?
In a central nervous system processing center like the Cerebrum or Brainstem.
136
Where are the cell bodies of Lower Motoneurons located?
In a nucleus of the brainstem (if related to cranial nerves). In the spinal cord (if related to spinal nerves).
137
How does the Upper Motoneuron communicate with the Lower Motoneuron?
It synapses on the lower motoneuron directly or indirectly via interneurons.
138
What does the Lower Motoneuron innervate?
A Skeletal Muscle.
139
What is the result of the activation of a Lower Motoneuron?
It triggers a contraction in the innervated muscle.
140
s the "Upper Motoneuron" strictly a motoneuron in the functional sense?
No. It is not really a true motoneuron; it is actually an interneuron.
141
What effect can activity in the Upper Motoneuron have on the Lower Motoneuron?
It may facilitate (excite) or inhibit the lower motoneuron.
142
What do the axons of Upper Motoneurons form?
They form the descending pathways (tracts).
143
What is the general function of these descending pathways?
To voluntarily control body movement and some sensory-driven reflex actions.
144
From which structures do descending tracts carry motor information?
From cortical structures like the Cerebrum, Cerebellum, and Brainstem.
145
Where do descending tracts transmit this motor information to?
To Lower Motoneurons located in the ventral horn of the spinal cord (or equivalent neurons in the brainstem).
146
ow are Descending Motor Pathways classified?
As Lateral and Medial pathways.
147
What is the basis for this Lateral vs. Medial classification?
It is based on the sites of termination in the spinal cord and the consequent differences in their roles in controlling movement and posture.
148
Where do Lateral Pathways terminate?
In the lateral portions of the gray matter of the spinal cord.
149
What muscles do Lateral Pathways control?
Both proximal and distal muscles.
150
What is the primary functional responsibility of Lateral Pathways?
They are responsible for most voluntary movements of the arms and legs.
151
What are the two specific Lateral Pathways mentioned?
Lateral Corticospinal Tract Rubrospinal Tract
152
Do Lateral Pathways typically cross (decussate)?
Yes. Most cross over from their site of origin and descend in the contralateral spinal cord to control contralateral extremities. (This is why the left brain controls the right body).
153
Where do Medial Pathways terminate?
In the medial ventral horn of the spinal cord, innervating the medial group of interneurons.
154
What muscles do Medial Pathways control?
Axial muscles, proximal limbs, and muscles for head and neck movement.
155
What are the primary functional responsibilities of Medial Pathways?
They contribute to balance and posture (via axial muscles) and head/neck movement.
156
What are the specific Medial Pathways mentioned?
Ventral Corticospinal Tract
Vestibulospinal Tracts (lateral and medial)
Reticulospinal Tracts (pontine and medullary)
Tectospinal Tracts
Corticobulbar Tracts
157
What two tracts make up the Lateral Pathway?
Lateral Corticospinal Tract Rubrospinal Tract
158
What are Betz Cells?
Giant pyramidal cells found only in the primary motor cortex. They are the largest neurons in the human nervous system.
159
What percentage of corticospinal neurons do Betz cells account for?
About 3%. (They are Upper Motoneurons).
160
Describe the descending path of the Corticospinal Tract (axons from the cortex).
Cortex -> Internal Capsule -> Cerebral Peduncle (midbrain) -> Basilar Pons -> Pyramids (medulla).
161
Where do the Pyramids form?
On the ventral surface of the medulla. (This is why it's sometimes called the Pyramidal Tract).
162
What happens at the Pyramidal Decussation?
About 90% of the fibers cross over to the contralateral side.
163
After crossing, where do these fibers go and what do they form?
They enter the lateral white matter columns of the spinal cord, forming the Lateral Corticospinal Tract.
164
Where do the remaining 10% of fibers go?
They continue into the spinal cord ipsilaterally (without crossing) and enter the ventral white matter columns.
165
What tract is formed by the uncrossed 10% of fibers?
The Ventral Corticospinal Tract (which belongs to the Medial Pathway).
166
What is the function of the Corticospinal Tract system (Lateral + Ventral)?
It voluntarily controls skeletal muscles of the limbs.
167
Where does the Rubrospinal Tract begin?
In the Red Nucleus of the midbrain.
168
Does the Rubrospinal Tract decussate?
Yes, fibers immediately decussate (in the midbrain) before descending.
169
What inputs does the Red Nucleus receive?
From the Cerebellum and the Motor Cortex. It is an area of integration for these two systems.
170
What muscles does the Rubrospinal Tract preferentially affect?
Motoneurons controlling distal muscles (similar to corticospinal fibers).
171
What is the believed function of the Rubrospinal Tract?
It plays a role in the subconscious regulation of limb muscle movement, particularly motor function after corticospinal tract injury.
172
How are Medial Pathways grouped?
Pathways that begin in the Motor Cortex. Pathways that begin in the Brainstem.
173
What is the unifying characteristic of all Medial Pathways (despite different origins)?
They all end on the medial group of interneurons in the spinal cord and on equivalent neurons in the brainstem.
174
What is the first medial pathway that originates in the Motor Cortex?
The Ventral Corticospinal Tract
175
What percentage of corticospinal fibers travel in the Ventral Corticospinal Tract?
About 10% (the uncrossed fibers).
176
Do fibers in the Ventral Corticospinal Tract decussate in the pyramids?
No. They continue down to the spinal cord on the ipsilateral side of the brainstem.
177
Where do most axons of the Ventral Corticospinal Tract eventually decussate?
In the spinal cord, just before they synapse with lower motoneurons.
178
What is the function of the Ventral Corticospinal Tract?
It controls the movements of axial muscles of the trunk.
179
What is the second medial pathway that originates in the Motor Cortex?
The Corticobulbar Tract
180
From which specific part of the primary motor cortex does the Corticobulbar Tract arise?
From the lateral aspect of the primary motor cortex (where the face/head are mapped).
181
Where does the Corticobulbar Tract terminate?
In the brainstem at the motor nuclei (rather than continuing to the spinal cord).
182
What do the Corticobulbar fibers synapse on in the brainstem?
On the Cranial Nerve Motor Nuclei (which are Lower Motoneurons).
183
What is the decussation pattern for the Corticobulbar Tract?
About 50% of the fibers decussate above the relevant cranial motor nuclei.
184
What is the function of the Corticobulbar Tract?
It supplies bilateral innervation to the muscles of the head and neck.
185
In summary, what type of muscles do both the Ventral Corticospinal and Corticobulbar tracts primarily control?
Axial muscles, which often contract bilaterally to provide postural support or bilateral functions (e.g., swallowing).
186
Where does the second group of medial system pathways originate?
In the brainstem.
187
What are the three specific tracts included in the brainstem-originating medial pathways?
Reticulospinal Tracts Vestibulospinal Tracts Tectospinal Tract
188
What are the two separate pathways of the Reticulospinal Tract?
Pontine Reticulospinal Tract (originating from the Pontine Reticular Formation in the Pons). Medullary Reticulospinal Tract (originating from the Medullary Reticular Formation in the Medial Medulla).
189
Do the Reticulospinal tracts decussate?
No. Both tracts remain uncrossed (ipsilateral).
190
Where do the Reticulospinal tracts terminate?
They end on the medial group of interneurons, eventually terminating on motoneurons affecting axial and limb muscles.
191
What is the specific function of the Pontine Reticulospinal Tract
It facilitates voluntary and reflex responses and influences muscle tone.
192
What is the specific function of the Medullary Reticulospinal Tract?
It has an inhibitory effect on voluntary and reflex responses of axial and limb muscles.
193
What is the overall function of the Reticulospinal Tracts?
They are involved mainly in locomotion and postural control.
194
Where do the Vestibulospinal Tracts originate?
In the Lateral and Medial Vestibular Nuclei in the Pons and Medulla.
195
Do the Vestibulospinal Tracts decussate?
No. They do not decussate; they descend ipsilaterally.
196
Where do the Vestibulospinal Tracts terminate?
On the medial group of interneurons.
197
What is the general function of the Vestibulospinal Tracts?
They control ipsilateral postural and tone adjustments in response to the vestibular apparatus.
198
What is the specific function of the Medial fibers of the Vestibulospinal tract?
Positioning of the head and neck.
199
What is the specific function of the Lateral fibers of the Vestibulospinal tract?
Balance.
200
Where does the Tectospinal Tract originate?
In the Tectum of the Midbrain
201
Does the Tectospinal Tract decussate?
Yes. The axons cross to the contralateral side.
202
Where does the Tectospinal Tract terminate?
On the medial group of interneurons in the upper cervical spinal cord.
203
What is the function of the Tectospinal Tract?
It regulates head movement in response to visual, auditory, and somatic stimuli.
204
How are the primary descending motor pathways classified based on their location in the spinal cord?
They are divided into Lateral and Medial motor systems
205
What are the two Lateral Motor Systems?
Lateral Corticospinal Tract Rubrospinal Tract
206
What body parts do the Lateral Motor Systems control?
Movements of the limbs
207
Do Lateral Motor Systems decussate?
Yes. Most of these pathways cross over from their site of origin and descend in the contralateral spinal cord
208
What is the functional consequence of the lateral system's decussation?
The left side of the brain controls the right side of the body (and vice versa)
209
What are the five Medial Motor Systems?
Ventral Corticospinal Tract Corticobulbar Tract Vestibulospinal Tract Reticulospinal Tract Tectospinal Tract
210
What muscles do the Medial Motor Systems control?
Proximal axial and girdle muscles
211
What specific functions are the Medial Motor Systems involved in?
Postural tone Balance Movements of the head and neck Automatic gait-related movements
212
Do Medial Motor Systems decussate?
They descend ipsilaterally or bilaterally (they do not strictly cross over to just the contralateral side like the lateral system)
213
Where do Medial Motor Systems tend to terminate in the spinal cord?
On interneurons that project to both sides of the spinal cord
214
What is the clinical consequence of the bilateral termination of Medial Motor Systems?
Unilateral lesions of the medial motor systems produce no obvious deficits (because the other side can compensate)
215
Table Summary: Where do the Lateral Corticospinal upper motoneurons originate and where do they decussate?
Origin: Primary Motor Cortex. Decussation: Pyramids of the Medulla.
216
Table Summary: Where do the Rubrospinal upper motoneurons originate and where do they decussate?
Origin: Red Nuclei of the Midbrain. Decussation: Brainstem (midbrain).
217
Table Summary: Where do the Ventral Corticospinal upper motoneurons originate and where do they decussate?
Origin: Primary Motor Cortex. Decussation: Spinal Cord.
218
Table Summary: Where do the Corticobulbar upper motoneurons originate and where do they terminate?
Origin: Primary Motor Cortex. Termination: Cranial nerve nuclei of the brainstem.
219
Table Summary: Where do the Reticulospinal tracts originate and do they decussate?
Origin: Pontine and Medullary Reticular Formation. Decussation: None.
220
Table Summary: Where do the Vestibulospinal tracts originate and do they decussate?
Origin: Vestibular Nuclei. Decussation: None.
221
Table Summary: Where do the Tectospinal tracts originate and where do they decussate?
Origin: Tectum of the Midbrain. Decussation: Brainstem.
222
What is a common cause of motor impairment in humans described in this slide?
Interruption of the cerebral cortical efferent fibers in the internal capsule, resulting in a disorder termed Pyramidal Tract Syndrome or Upper Motoneuron Disease
223
What specific tracts are damaged in Pyramidal Tract Syndrome?
The Corticospinal Tracts
224
What are the common causes of Upper Motoneuron Disease?
Stroke Traumatic brain or spinal injury Cerebral palsy Multiple sclerosis Amyotrophic lateral sclerosis (ALS)
225
If there is a unilateral lesion of the left or right corticospinal tract, where will the symptoms appear?
On the contralateral side of the body
226
What is the first motor change characteristic of this disorder (Hyperreflexia)?
Hyperreflexia: Increased muscle reflexes. Example: Rubbing your hand over your belly might cause your abdominal muscles to tighten up
227
What is the second motor change characteristic of this disorder (Hypertonia)?
Hypertonia: An increased muscle tone. The muscles become rigid and hard to move
228
What is the third motor change characteristic of this disorder (Muscle weakness)?
Muscle weakness, usually of the distal muscles, especially the finger muscles
229
What is the fourth motor change characteristic of this disorder (Clonus)?
Clonus: A muscular spasm that involves repeated, often rhythmic, contractions
230
What is the fifth motor change characteristic of this disorder (Pathological Reflexes)?
Pathological reflexes, such as the Sign of Babinski (Babinski sign)
231
Describe the Babinski Sign.
Extension of the hallux (big toe pulls back) and spreading out of the other toes in response to blunt stimulation (stroking) of the sole of the foot
