Descending Neural Pathways

Question 1

what is the definition of a lower motor neurone

Answer 1

there cell bodies are in the brain stem or spinal cord and project outside the CNS to muscle

Question 2

what is the definition of an upper motor neurone

Answer 2

cell bodies are in the brain or brainstem and DO NOT project outwit the CNS

Question 3

Role of interneurones

Answer 3

coordinate groups of muscles

Question 4

what is the role of an upper motor neurone

Answer 4

orchestrate complex directed movements

Question 5

what is the role of lower motor neurones

Answer 5

single muscle innervation, cell bodies are located in the ventral horn of the spinal cord or the motor nuclei of the brainstem

Question 6

what are the two major systems of the descending pathway from the cortex to the motor centres

Answer 6

1. lateral pathways

2. ventromedial (medial) pathways

Question 7

what is the role of the lateral pathway

Answer 7

• control voluntary movements
• control distal muscles
• mainly controlled by cerebral cortex (via the corticospinal tracts

Question 8

what is the role of the medial pathway

Answer 8

• Mainly control posture and locomotion
• Control the axial and proximal muscles
• Mainly controlled by the brainstem
• Mainly uncrossed

Question 9

what are the 4 characteristics of a voluntary movement

Answer 9

1. Purposeful goal directed
2. Triggered either by imagination or by a wilful decision
3. Where the goal could be achieved by different strategies.
   e.g. writing on a small piece of paper or writing on a blackboard (example of motor equivalence
4. Often learned
   may initially need much concentration (Driving or playing a guitar) but
   with practice movement can be achieved fluently. Efficiency and accuracy improves

Question 10

Motor Equivalence

Answer 10

illustrates multiple levels of control of movement

Question 11

what is the structure of a voluntary movement

Answer 11

1. Sensory integration: Target identification
2. Planning; movements required
3. Execution; commands from cortical and brainstem centres are needed

Each phase involves the involvement of distinct areas of the cerebral cortex as well as feedback from basal ganglia and cerebellum

Question 12

what is area 4 on Brodmanns cortical map

Answer 12

primary motor cortex

Question 13

what is immediately posterior to the primary motor cortex

Answer 13

primary somatosensory cortex

Question 14

on what map is the primary motor cortex somatotopically organised

Answer 14

the somatotopic homunculus

Question 15

what is immediately anterior to the primary motor cortex

Answer 15

the premotor cortex

Question 16

what is the role of the pre-motor cortex

Answer 16

this area produces stronger more prolonged stimuli, which implies a less direct route to the lower MN’s

the movements are more complex:

• they can involve more than one joint
• can be bilateral movement

important in orientating the body in preparation for a voluntary movement (contributing to an established postural set)

Question 17

where does the premotor cortex’s fibres project to ?

Answer 17

1. the brainstem motor nuclei

2. spinal circuits controlling proximal and axial muscles (mainly postural)

Question 18

which area of the brain controls the plasticity of complex sequences of movements based on prior experience, and is influenced by memory and the limbic system

Answer 18

premotor cortex

Question 19

If primary motor area is destroyed

Answer 19

initially electrical stimulation of either premotor areas has no effect

this means the their principles action are mediated through the primary motor cortex

Question 20

Damage to the premotor areas

Answer 20

produces more complex deficits

Question 21

an example of a deficit which has resulted from damage to the premotor cortex

Answer 21

Apraxia -cannot perform tasks that involve a complex sequence of movements like brushing one’s hair or drawing a quick sketch

Question 22

3 Major sources of input:

Answer 22

• Sensory receptors
via the somatic sensory area, the premotor areas or the posterior parietal association cortex
• From the Cerebellum
-Both planning (feed forward) movement and corrective feedback from proprioception etc.
• From the Basal Ganglia
-Both initiating complex movement and motor correction plus an overlay of an emotional component
from limbic circuits.

Question 23

when the corticospinal tract enters the brain stem it has an initial branch, what is this called

Answer 23

corticobulbar tracts - these influence facial muscles and descending postural pathways of the brainstem

Question 24

where fo corticobulbar tracts then go

Answer 24

Multiple cranial nuclei outputs and relays:

Vestibulospinal - balance
Reticulospinal – muscle tone, orientation, breathing Rubrospinal – cerebellar influenced upper limb movement
Tectospinal pathways – head movements to follow sight

Question 25

there are then the two other ‘main’ branches

Answer 25

the anterior corticospinal and lateral corticospinal tract (this veing around 85% of nerve fibres)

Question 26

anterior corticospianl tract

Answer 26

this tract descends ipsilaterally and at the level of their central root, innervates bilaterally

Question 27

lateral corticospinal tract

Answer 27

this tracts descends and then crosses over to innervate, this is the voluntary control of distal muscles

Question 28

Lesions of corticospinal - upper motor neurone

Answer 28

• common as they are so long
• most commonly caused by infarcts related to cerebrovascular incidents, trauma, tumours and demyelinating diseases can also cause damage.
• middle cerebral artery (this supplys the lateral surface of the hemispheres and the internal capsule) is particularly vulnerable

Question 29

what is a negative sign

Answer 29

loss of function (weakness or paralysis)

Question 30

what is a positive sign

Answer 30

this is the appearance of an abnormal response

Question 31

UMN pattern weakness

Answer 31

• Arm extensors weaker than flexors (flexors are stronger)

* Leg flexors weaker than extensors (extensors are stronger)

Question 32

Posture is

Answer 32

the position of a body and its parts relative to each other, its vitally important in balance and is adjusted predominantly by involuntary movement

Question 33

how is posture adjusted

Answer 33

predictively (postural set)
and
Reflexively (compensation)

Question 34

Compensatory responses are based on

Answer 34

information sent from

1. Muscle proprioceptors (detect changes in muscle length and or tension)
2. Sense of balance derived from movements of the head relative to the Earths gravitational field (vestibular apparatus)
3. Visual inputs (detecting movements in visual field representing movement of the body)

These nuclei all receive information from the voluntary circuit collaterals which provides feed forward information

Question 35

postural set is generated where

Answer 35

These sensory inputs converge on nuclei in the brainstem