CNS/Motor II Flashcards
What is the function of gamma neurons?
They aim to maintain the sensitivity of the stretch receptor in the muscle spindle when muscle fibers shorten during contraction.
Is the stretch reflex considered monosynaptic or polysynaptic? Why?
It is considered to have both mono- and polysynaptic components. The primary afferent part is considered monosynaptic, while the secondary afferent part is considered polysynaptic.
Muscle spindles report […]
Muscle length
Do muscle spindles contribute to the force of muscle contraction?
NO
What is the purpose of the stretch reflex.
To control muscle length.
What is the purpose of the inverse stretch reflex?
To control muscle tension.
What organ primarily responds to muscle tension?
The Golgi apparatus.
Is the Golgi tendon more active when the muscle stretches or contracts? Why?
It will send more action potentials for both, but will be more active during muscle contraction, as this is when tension is the highest. It will send fewer action potentials during stretching.
Describe the structure of the Golgi tendon orgon.
It connects the tendons to the muscle fibers. It consists of collagen fibers wrapped around free nerve endings, all wrapped in a capsule. The nerve endings form 1b afferents.
How does transduction take place in the golgi tendon?
When a muscle contracts and pulls the golgi tendon, this causes the collagen fibers to mechanically deform the nerve endings of the 1b afferents, mechanically opening ion channels.
Describe the 5 steps of the inverse stretch reflex (Golgi tendon organ reflex).
- Increased tension in extensor muscle due to contraction
- Activation of Golgi tendon organ
- Increased afferent activity from Golgi organ tendon
- Inhibition of motor neurons innervating the ipsilateral extensor.
- Excitation of motor neurons innvervating the ipsilateral flexor.
The inverse stretch reflex contains a […] feedback. Explain how.
Negative. This is because when the muscle contracts and activates the Golgi tendon, this causes an inhibition of the same extensor, stopping it from generating force
The Golgi tendon organ has what kind of afferents?
1b
Is the inverse stretch reflex considered monosynaptic or polysynaptic?
Polysynaptic
The pathways involved in motor control are [ascending/descending]
Descending
What are the two motor control pathways? What do they control?
Corticospinal: skilled movements
Extrapyramidal: trunk and posture
What are the 3 levels of the motor control hierarchy? Describe the major components of each.
Highest level: higher centers
Middle level: sensorimotor cortex, basal nuclei, thalamus, brainstem, cerebellum
Local level: brainstem and spinal cord
What are the two major functions of the middle level in motor control?
- Executes the individual muscle contractions
- Makes corrections based on sensory information.
The corticospinal pathway goes from the […] to the […]
Sensorimotor cortex, brainstem and spinal cord
The extrapyramidal pathway goes from the […] to the […]
Brainstem, brainstem and spinal cord.
Name the major parts of the brain involved in voluntary control of movement and the order in which they get activated.
After consciously initiating a movement, first the premotor cortex starts breaking down the movement into smaller steps and contractions. Then, the primary motor cortex is activated and sends information down descending pathways.
The somatosensory cortex is also involved, as it receives information from the contralateral side of the body about muscle tension, length, etc.
Where are the primary motor cortex and the somatosensory cortex located relative to one another?
They are right next to each other and are separated by the central sulcus.
Describe the organization of the primary motor cortex.
It is set up in the same way as the somatotopic map, going from legs to arms to head as you move outwards from the midline.
What parts of the body take up more space in the primary motor cortex? What does this imply about them?
The hands and face take up a lot of space. This is because we have very detailed control of our hands and face, meaning that more neurons are dedicated to their motor control and more skill is required to operate that area of the body.
The size of body structures in the primary motor cortex is proportional to […]
Number of neurons dedicated to their motor control, degree of skill
Describe the corticospinal pathway.
Starts in the motor system, goes down the brainstem and crosses at the medulla. Descends to spinal segment and synapses with alpha and gamma motor neurons, sending the signal to the contralateral side of the body from where it started.
Is the corticospinal pathway ipsilateral or contralateral?
It is contralateral.
What parts of the body does the corticospinal pathway control?
It controls the extremities (mainly hands and feet) and also the mouth.
What kinds of movements does the corticospinal pathway control?
Skilled voluntary movements.
What types of neurons are involved in the corticospinal pathway?
Alpha and gamma motor neurons.
Describe the extrapyramidal pathway.
It starts in the brainstem and travels down to the spinal segment along various different pathways, both ipsilateral and contralateral. It activates interneurons.
What parts of the body does the extrapyramidal pathway control?
The trunk and postural muscles.
What types of movements does the extrapyramidal pathway control?
It controls less conscious movements, like upright posture, balance, and walking.
What is muscle tone?
It is the resistance of skeletal muscle to stretch.
Muscle tone in normal individuals can be described as […]
Slight and uniform
How does damage to descending pathways affect muscle tone?
It leads to hypertonia, meaning abnormally high muscle tone.
What are the symptoms of hypertonia?
Spasticity (overactive motor reflexes) and rigidity (constant muscle contraction)
How does damage to motor neurons affect muscle tone?
It leads to hypotonia, meaning abnormally low muscle tone.
What are the symptoms of hypotonia?
Atrophy (loss of muscle mass) and decreased or missing reflexes.
What is the function of the basal nuclei in motor control?
They help to determine the specific sequence of movements needed to accomplish a desired action.
Give 2 examples of disorders related to the basal nuclei.
Parkinson disease and Huntington disease.
What is the cause of Parkinson disease?
Reduced dopamine input to the basal nuclei.
What are the 4 symptoms of Parkinson’s disease?
- Akinesia: reduced movements
- Bradykinesia: slow movements
- Muscular rigidity
- Resting tremor
How is Parkinson’s disease treated?
Increasing dopamine concentrations in the brain or deep brain stimulation.
What is the cause of Huntington’s disease?
Genetic mutation that causes widespread loss of neurons in the brain (mainly basal nuclei).
What are the two symptoms of Huntington’s disease?
- Hyperkinetic disorder: excessive motor movements
- Choreiform movements: jerky, random involuntary movements of the limbs and face
What is the role of the cerebellum in motor control?
It adjusts movement timing, planning, and error correction. It is also involved in the learning of new motor skills.
How does the cerebellum regulate movement?
It receives sensory information from the vestibular, visual, auditory, somatosensory, and proprioceptive systems and uses it to adjust movement.
Name the 5 symptoms of cerebellar deficits.
- Asynergia: smooth movements subdivided into their separate components
- Dysmetria: unable to target movements correctly (can’t point accurately)
- Ataxia: incoordination of muscle groups (awkward gate)
- Intention tremor during voluntary movements
- No paralysis or weakness
What is akinesia?
Reduced movements
What is bradykinesia?
Slow movements
What is hyperkinetic disorder?
Excessive motor movements
What are choreiform movements?
Jerky, random involuntary movements of limbs and face
What is asynergia?
Smooth movements subdivided into their separate components.
What is dysmetria?
The inability to target movements correctly “past pointing”
What is ataxia?
Incoordination of muscle groups (awkward gate)
