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
Which cortical layer does the corticospinal tract originate from?
layer 5
The corticospinal tract consist of 1 million axons. About 30,000 axons are contributed from what cells?
very large pyramidal cells called Betz cells that contribute approximately 30,000 to the 1 million axons
Where are the large Betz neurons found?
in the layer 5 ONLY in the primary motor cortex
Where do axons of the corticospinal tract originate? List the abundance of each origin.
- 1/2 of the axons originate in the primary motor cortex (Brodmann’s area 4)
- most of the other axons come from the medial supplementary motor cortex
- smaller portion from the lateral premotor cortex
- small number of axons come from the area 5 and area 3, 2, 1 (these target the dorsal horn to modulate sensory activity) in the parietal cortex
What is the evidence that the precentral gyrus is the “primary motor cortex”?
- electrical stimulation of the motor cortex (area 4) evokes movements of:
- individual or a few muscles
- the lowest threshold (in the nanoamp range) for producing movement is in the motor cortex
- short latency: time of stimulation to movement of muscle is short
How does latency relate to the number of synapses in a pathway?
the more synapses in a pathway the longer the latency is between the stimulus and response
The primary motor cortex contains a motor map of the body AKA it is somatotopically organized.
The medial bank of the primary cortex controls movements of what parts of the body?
-legs: hip, knee, ankle, toes
gluteal region is the transition between the medial and lateral bank of the primary motor cortex
The primary motor cortex contains a motor map of the body AKA it is somatotopically organized.
The lateral bank of the primary cortex controls movements of what parts of the body?
- trunk
- upper limbs
- hands
- face
- oral cavity
Which regions of the body have the highest cortical representation? What does this mean?
hands and mouth
they have highest motor control (both involve intricate movements) whether its speech, swallowing, holding things, writing
the regions of the body which have the highest motor control have the largest representation
What supplies the cortical region supplying the lower limb?
anterior cerebral artery
-monoplegia will result if there is stroke
What supplies the cortical region supplying the hand and face?
middle cerebral artery
What artery is most often infarcted in the brain when there is a clot, etc.?
middle cerebral artery
Monoplegia may result from stroke of what artery?
anterior or middle cerebral
How does the activity of the corticospinal neurons correlate with flexor and extensor movements????
corticospinal neurons codes force NOT change of position
eccentric contraction has no
The upper motor neurons in the primary motor cortex (area 4) central in the production of precision, skilled movements. What aspects of movement do they control?
- direction: extension or flexion
- force: the faster UMN fire the more force is generated meaning more force it can take
- speed
How does electrical stimulation of area 6 differ with stimulation of area 4 in evoking movements ?
-in contrast to single muscles, stimulation of supplementary cortex produces complex movements involving several joints (ie. opening and closing the hands), often bilaterally
-lesion of area 6 results in apraxia,
difficulty carrying out complex purposeful movement such as dressing
