1.8 Motor and Sensory Pathways Flashcards
What are the three types of motor movements?
- Reflexive
- Rhythmic
- Voluntary
Give two examples of rhythmic movement
- Walking
- Breathing
Explain the role of the primary motor cortex in motor movement
- Receives input from premotor and association areas
- Projects to spinal cord through corticospinal tract
Explain the role of the basal ganglia in motor movement
- Modifies movement indirectly through planning areas
- Initiates movement and postural adjustments
Explain the role of the cerebellum in motor movement
Compares planned action to actual action, and corrects disparity to aid coordination
True or false: motor neurons and interneurons integrate sensory inputs from the periphery during motor movement
True.
What are the three levels of the hierarchy of motor control?
- Highest level: planning (cortical association areas, basal ganglia, cerebellum)
- Middle level: commanding (motor cortex and descending pathways)
- Lowest level: executing (spinal interneurons and motor neurons)
Which areas of the parietal lobe are important for integrating sensory information to inform motor movement?
Posterior parietal cortex
What is the role of the premotor cortex?
Selection of appropriate motor plans
What is the role of the supplementary motor area?
Active during the planning and coordinating of internally-guided movements (and coordinating bilateral movements)
True or false: somatotopic organization of the motor cortex is plastic (i.e. it can be changed)
True; this is how we learn physical skills
The cell bodies of motor neurons that are proximal are ___ in the ventral horn, and those of motor neurons that are more distal are more ___in the ventral horn.
Proximal muscle: medial soma
Distal muscle: lateral soma
What is the name given to neurons that interconnect motor nuclei across vertebral segments?
Propriospinal neurons.
What occurs if there is a lesion in motor association areas? What is this called?
- Called apraxia
- Strength is intact, but higher-order planning and execution is disrupted
True or false: rhythmic movements can be generated at the level of the spinal cord
- True
- This is how they disconnected a cat’s brain, and got it to walk on a treadmill
What neurotransmitter do lower motor neurons release?
Acetylcholine
Isotonic vs isometric contractions
Isometric: no change in muscle length
Isotonic: change in muscle length
What is a motor nucleus?
A group of motor neurons that are all responsible for the control of a specific muscle/muscle group.
Describe the arrangement of muscle fibres, motor neurons, and motor units in a muscle
- There are multiple muscle fibres in a muscle
- Each motor neuron innervates multiple muscle fibres
- The combo of all muscle fibres innervated by a motor neuron is called a motor unit
What is meant by innervation ratio? How does it change in finer movements?
- The number of muscle fibres innervated by a single neuron
- The finer the movement, the smaller the ratio
Which of extra/intrafusal muscle fibres are innervated by alpha/gamma motor neurons?
Extrafusal: alpha
Intrafusal: gamma
What’s the deal with Renshaw cells
- The axons of alpha motor neurons not only attach to extrafusal muscle fibres, but also interneurons called Renshaw cells
- These Renshaw cells are inhibitory
- This creates a negative feedback loop, preventing overcontraction of muscle
In which area of the internal capsule does the corticospinal tract travel?
Posterior
Would an UMN vs LMN result in ipsilateral/contralateral side?
UMN: Contralateral
LMN: Ipsilateral
(Anything in the lateral corticospinal tract would be ipsilateral)
What’s the deal with the DCML pathway?
- Sensory neurons transmit information about fine touch and vibration from the lower limb (fasiculus gracilis) and upper limb (fasiculus cuneatus) in the dorsal columns
- In the medulla, they synapse at the nucleus gracilis/cuneatus, and deucssate to form the medial lemniscus (upper + lower in one bundle on each side)
- Synapse at thalamus + head out to primary somatosensory cortex
What’s the deal with the spinothalamic tract?
- Carries information about crude touch (anterior) and temp/pain (lateral).
- First order neurons immediately synapse, decussate, and head up to the thalamus.
- Head out into the primary somatosensory cortex.
How does the sensory cortical map change in response to amputation or training?
Areas grow/shrink depending on how much they are needed (amputation: gone, trained to use, increased in size)
Explain phantom limbs
- When cortical areas are remapped in response to loss of body parts, adjacent areas on the homunculus grow bigger
- Touching these adjacently-mapped areas can lead to the feeling of an adjacent limb
