Voluntary Motor Pathways- Wilson Flashcards
What are the voluntary motor pathways?
- corticospinal
- corticobulbar
involved in skilled movement
What are the basic types of movements?
- reflexive movements: ie. monosynaptic reflexes in Unit 1
- voluntary movements: purposeful and goal directed
- rhythmic motor patterns: the in between reflexive and voluntary movements; such as walking, running, and chewing
cortex can initiate a movement but the reflexive circuits in the SC and brainstem will take over
Describe reflexive movements.
autonomic: the motor response is stimulus dependent
stereotypic: there is no learning involved
fast: fastest movement going from stimulus to response
Describe circuits for voluntary movements
- response to stimulus is context dependent: voluntary movement is not necessarily stimulus dependent;
- sensory stimuli are not necessary (may be internally evoked)
- improved by learning and experience: initially voluntary movements are slow and clumsy but as you practice you can get to skilled movements (learning to play a piano)
- flexibility of strategy: motor equivalence ( ie. i can write letters using my right or left hand, different arms performing the same movement
What are the four major components of the motor system?
- Spinal cord
- Primary motor and premotor cortex
- Cerebellum
- Basal ganglia
What is the difference between upper and lower motor neurons?
UPPER motor neurons as all signals coming from cortex cannot reach skeletal muscles directly and instead give commands to lower motor neurons to execute:
- primary motor cortex
- premotor cortex
LOWER motor neurons work directly on the muscle to contract them :
- alpha: go to extrafusal fibers
- gamma: go to muscle spindles to regulate the threshold and sensitivity of the muscle
What is the function of the cerebellum?
- cerebellum coordinates voluntary movements such as posture, balance, coordination, and speech, resulting in smooth and balanced muscular activity
- relays their motor commands through the thalamus and then to cortex
What is the function of the basal ganglia?
-is involved particularly in the gate-keeper of movements and decide which movements to depress and which ones to execute
information is relayed through the thalamus then to cortex
Why are lower motor neurons also known as the final common pathway?
regardless of where a motor signal comes from all that information have to go to the lower motor neuron and all motor signal commands must converge at the lower motor neuron
Many of the basic circuits of movement are located where?
in the spinal cord
If you lesion the spinal cord below the brachial plexus and above S4 what happens?
result in paraplegia
-brachial plexus C5-T1
If you lesion the spinal cord at the origin of the brachial plexus what happens?
results in quadriplegia (paralysis of both lower and motor limbs)
If you lesion the spinal cord at the origin of the phrenic nerve or above what happens?
results in asphyxiation and death (without medical intervention) ‘’
-you interrupt the commands for breathing and get negative motor negative signs: cannot walk, breathe, etc.
Lesions of the supraspinal motor structures can produce positive symptoms. What does this mean?
upper motor neurons in the cerebellum or cortex can suppress certain movements that should not normally occur
-our nervous system not only produces the movements we want to make but it also suppress movements that are not wanted resulting in positive sign
Describe the pathway of corticospinal tract from the cortex to the spinal cord.
- the cell bodies are located in motor cortex which have very long axons that will go through the internal capsule, crus cerebri of midbrain, basilar pons, then to the medulla where they will form the pyramids
- once at the intersection between medulla and spinal cord 90% of the fibers will decussate to the other side
What is the difference between the lateral and medial corticospinal tract?
once the fibers reach the spinal cord the descending corticospinal tract is made up of two parts:
- the lateral corticospinal tract are those that decussated
- anterior corticospinal tract does not decussate and remains on the same side
If there is lesion of the lateral corticospinal tract in the cortex prior to decussation, what are the resulting symptoms?
contralateral symptoms
Where is the primary motor cortex?
- in the precentral gyrus AKA Brodmann’s area 4
- also had portions on the medial side of the precentral gyrus
-this area is most important in initiating and controlling skilled movements
What is the primary sensory cortex?
in the postcentral gyrus AKA Brodmann’s area 312
What is found immediately rostral to the primary motor cortex?
the premotor region AKA area 6
What are the 2 subregions of the premotor region and what are their directionality?
- premotor cortex is found more laterally in area 6
- supplementary cortex is found more medially in area 6
There are 6 cortical layers. The thickness of each layers changes depending upon what?
whether they are sensory or motor or in between associational
Compare area 4 and area 6 in terms of cortical layer content.
- area 4 and 6 lack layer 4 which is the inner granular cortex and thus they are often called the primary and secondary agranular cortex
- area 4 and 6 are THICK with layer 5 that is loaded with pyramidal projection cells; area 4 in particular has very large pyramidal cell bodies
Remember area 4 and 6 make up the precentral gyrus and the portions rostral to it respectively
The cell bodies of the corticospinal tract are found in what layer of the cortex?
layer 5