Task 1 - The Basics Flashcards
Lateral pathways
Involved in voluntary movement of the distal musculature and are under direct cortical control
1. Corticospinal tract
2. Rubrospinal tract
Ventromedial pathways
Involved in the control of posture and locomotion and are under brain stem control
1. Vestibular tracts
2. Tectospinal tracts
3. Reticulospinal tracts (2)
Corticospinal tract
5 steps
- Starts in motor cortex
- Through the cerebral peduncle
- Forms the medullary pyramid
- Decussates when going over into spinal cord
- Collect in lateral column of spinal cord
Rubrospinal tract
3 steps
- Starts in the red nucleus
- Axons decussate in the pons
- Join the corticospinal tract in the lateral column of the spinal cord
Vestibulospinal tracts
3
- Originates in the vetsibular nuclei of the medulla
- Then either to the spinal cord where it activates cervical spinal circuits
- Or to the lumbar spinal cord which then facilitates motor neuron in legs
Tectospinal tracts
- Originates in the superior colliculus
- Through the medulla
- Ends in the spinal cord
Pontine (medial) reticulospinal tract
- Starts in pontine reticular formation
- Through medulla
- End in cervical spinal cord
Medullary reticulopinal tract
- Starts in medullary reticular formation
- Ends in cervical spinal cord
Origin of the corticospinal tract
- Corticospinal tract evolved as primates became more dexterous with their hands.
- As primates developed precision grip, the corticospinal tract increased in its overall size.
- This was accompanied by the emergence of corticospinal terminations in the ventral horn where the lateral motor nuclei are located
Motor cortex
A region of the frontal lobe, including areas 4 and 6.
Area 4
- Also known as primary motor cortex, motor strip or M1.
- It lies just anterior to the central sulcus.
- Electrical stimulation of area 4 invokes twitches of the muscles in a particular region of the body on the contralateral side
Area 6
- Lies just anterior to area 4. It includes the premotor area (PMA) laterally and the supplementary motor area (SMA) medially
- Electrical stimulation of area 6 can evoke more complex movements of either side of the body; it is a higher motor area in humans
Coding of movement in Area 4
- Pyramidal cells in area 4 show individual direction tuning (direction vector)
- The actual direction seems to be determined by population coding, specifically by a population vector
Hemiplegia
Paralysis that occurs only on one side of the body, usually affects the most distal effectors (e.g. fingers or hand).
Paraplegia
Paralysis that involves only the legs
Quadriplegia
Paralysis that involves all 4 limbs
Spasticity
A condition, which is often permanent, characterized by a dramatic & sometimes painful increase of muscle tone (hypertonia) and spinal reflexes (hyperreflexia)
Babinski sign
- An indication of motor tract damage
- Sharply scratching the sole of the foot from the heel toward the toes causes reflexive upward flexion of the big toe and an outward fanning of the other toes.
Apraxia
A selective inability to perform complex (but not simple) motor acts.
Two types:
1. Ideomotor apraxia
2. Ideational apraxia
Ideomotor apraxia
The patient has a rough sense of the desired action but has problems executing it properly
Ideational apraxia
The patient’s knowledge about the intent of an action is disrupted, the more severe type
Function of the dorsal premotor area
- Important for making associations involving motor stimuli
- PM neurons fir after presentation of cue that instructs a motor response
Meaning it can direct movement based on sensory information
Function of Ventral premotor area
- Hand movement required for manipulation of an object
- PMv neuron fire when monkeys view or grab objects
- In some monkeys it also contains mirror neurons which are important for understanding actions made by others
How do premotor areas influence primary motor area?
- All nonprimary motor areas have some direct connection to the spinal cord, challenging hierarchy assumption
- M1 i connected to nonprimary motor areas but not really with the rest of the cortex, so nonprimary areas are important for connection to sensory information
What does the SMA do?
While premotor cortex is more about sensory guided action, the SMA is more about action guided by personal preferences and goals
Function of the Corticospinal tract
Responsible for voluntary movement and skilled motor control
Function of Rubrospinal tract
Facilitates fine motor control, especially of the distal muscles, and regulates muscle tone.
Function of Vestibulospinal tract
Maintains balance, posture, and head stabilization by integrating information from the vestibular system.
Function of Tectospinal tract
Mediates reflexive head and eye movements in response to visual and auditory stimuli.
Function of Reticulospinal tract
Regulates muscle tone, posture, and autonomic functions (one enhances antigravity effect and one liberates antigravity effect)
