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BIO 435
Motor System
| Question | Answer | |
|---|---|---|
| Which neurons innervate the muscles/muscle fibers? | motor neurons | |
| What does the ventral horn shape reflect? | The number of motor neurons | |
| What does it mean that motor units and motor neurons vary in size? | Larger muscles will have more motor units | |
| What are the two ways that motor neuron activity controls muscle force production? | 1. firing rate of motor neurons by changing action potential frequencies (if the AP are close enough it can result in temporal summation) 2. recruitment of motor units (first recruit small motor neurons then large) | |
| How many types of fibers does each motor unit have? | One | |
| How many different types of muscle fibers are there? | 3 | |
| Describe slow muscle fibers | -sustain low force -for long periods of time -are used in aerobic conditions | |
| Describe fast fatigable muscle fibers | -provide the MOST FORCE (at first) -only lasts for about a minute | |
| Describe fast-fatigable resistant muscle fibers | -provides LOT of force -lasts for a while (a little less than 60 minutes) -eventually dissipates | |
| What determines muscle biochemistry? | Motor neuron type | |
| Describe normal innervation | where slow motor neurons connect directly to slow muscles types and vice versa for fast motor neurons and fast muscle types | |
| Describe cross innervation | whenever you change the connection of the muscle neuron, it changes the muscle type, how many mitochondria it expresses, capillary density, etc. | |
| What type of motor units are recruited first? | small | |
| Why are small motor units recruited first? | It is easier to get them to action potential threshold | |
| In what order are the types of motor units recruited for locomotion? | 1. slow 2. fast-fatigue resistant 3. fast fatigable | |
| What type of responses are mediated by the spinal cord? | Simple, stereotyped responses | |
| What type of neurons do spinal reflexes and proprioception require? | sensory neurons (priprioceptors) | |
| How many types of proprioceptor neurons do muscle spindles contain? | 1 | |
| What type of sensory neurons do stretch muscles activate? | 1a (Aa) [stretch-activated channels] | |
| Describe neuron activity during stretch reflexes | 1. hammer tap stretches tendon 2. sensory receptors in leg extensor muscle are stretched 3. sensory neuron activated and releases glutamate which excites the motor neuron in the spinal cord 4. Sensory neuron also excite spinal interneuron | 5. Interneuron synapse inhibits flexor motor neuron 6. Motor neuron conductions action potential to synapses on extensor muscle fibers and causes contraction 7. Leg extends |
| How does reciprocal inhibition work? | Reciprocal inhibition allows for the relaxation of antagonist muscles; 1a neurons synapse on inhibitory motor neurons in order to alternate contraction and relaxation | |
| What type of neurons do gamma motor neurons maintain the sensitivity of? | 1a neurons | |
| Which muscle fibers do gamma motor neurons synapse onto and how does the synapse control the muscle fiber? | intrafusal muscle fibers to control their length | |
| How do gamma motor neurons work? | 1. The alpha motor neuron becomes excited 2. Extrafusal muscle fibers shorter in response to the alpha motor neuron | 3. Gamma motor neuron activates in response to the muscle spindle becoming slack after shortening of extrafusal muscle fibers 4. The activation of gamma motor neurons results in the intrafusal fibers becoming taut again |
| What does the stretch reflex allow you to do? | Stretch reflex allows us to make adjustments based on our movements (especially for unexpected weight load) | |
| Which type of proprioceptors do Golgi tendon organs have? | 1b axons located in the junction between the muscle and the tendon | |
| How are 1b axons activated? | 1b axons are activated by an increase in muscle tension/when muscle contracts | |
| Describe the function of 1b axons | 1. synapse onto inhibitory interneurons in the spinal cord 2. inhibits motor neurons to maintain optimal tension 3. prevents overcontraction | |
| Describe polysynaptic reflexes | - more complicated - slower | |
| What provides support of the body during the flexor reflex? | Flexor reflex and crossed-extension reflex | |
| Describe how the flexion and crossed-extension reflex work? | Extensor motor neurons in the opposite legs are excited and the flexor motor neurons are inhibited | |
| What can affect the reflex pathway activity? | Gating from the central nervous system; descending input from the brain can inhibit reflex pathways during voluntary movements | |
| Which provides input to the brain? | Proprioceptors | |
| Describe how proprioceptors affect gating of the reflex pathway activity. | 1a and 1b neurons ascend to the brain and give feedback to the cerebellum to alter the direction of movement; these neurons also allow for conscious perception of body position | |
| What type of systems are critical for initiating movements | Sensory systems | |
| How are sensory systems used to initiate movement | - determine the body's starting point - provides sensory feedback to adjust the movement - provides sensory feedback for adjusting the next movement | |
| How is the sensory system used for motor learning? | The sensory system sends feedback to the brain in order to adjust the body for the next movement | |
| What is used to help create rhythmic movements such as walking, running, and swimming? | The central pattern generators | |
| What are the two descending motor pathways | 1. lateral pathways 2. ventromedial pathways | |
| Describe the lateral pathway | The lateral pathway is in charge of voluntary movement/skilled movements of the distal body parts --is directly controlled by the cortex | |
| Describe the ventromedial pathway | The ventromedial pathway controls posture and balance of the trunk, head and neck -controls locomotion -moves body to focus on relevant stimuli -is controlled by the brainstem | |
| What is the most important component of the lateral pathway? | The corticospinal tract (the longest and largest CNS tract and 2/3 of the axons in the tract originate in the motor cortex) | |
| What do lesions in the lateral pathways affect? | The lateral pathway affects fine detail and coordinated movements which makes it harder to grasp anything | |
| Where does the ventromedial tract originate? | The vestibular nuclei, superior colliculi, and the reticular formation | |
| What brain area are all motor pathways influenced by? | Motor cortex | |
| Describe are 4 of the motor cortex | - known as M1 (the primary motor cortex) - directs the movements of specific parts of the body - this is the last stop in the cortex before moving to the spinal cord- projects motor neurons through the corticospinal tract | |
| Describe area 6 of the motor cortex | - called the premotor cortex - contains the premotor area (PMA) and supplementary motor area (SMA) - stimulates complex movements- "plans" movements -has some connections with the motor neurons and some projections to M1 | |
| Which layer of neurons in the M1 contribute to the corticospinal tract and also project to the brainstem | Layer V neurons | |
| Describe the primary motor cortex | - receives input from the cerebellum and sensory areas (visual feedback) - neurons encode force and directions of movements (where force is based on the action of potential of motor neurons) | |
| What is the somatotopic map? | This is a map in the primary motor cortex (M1) that is based on the movements of the body (there are clusters of cells that were active during specific types of movements) | |
| Do neurons in M1 have direction preference? | Yes | |
| Describe how neurons in the M1 have direction preference? | When you move your hand to the left, there are specific cells that have a higher firing rate. All M1 cells are active but some are more active than others | |
| Describe how plasticity is prevalent in the motor cortex? | If you cut the neurons connected to whiskers, the cells that were predominately for whisker movement now becomes cells that affect periocular/eye movements instead. Therefore, cells are able to adopt new functions and new synapses | |
| What type of information converges in the premotor cortex? | Somatosensory, proprioceptive, visual, and motivational information | |
| What does the premotor cortex do with the information it receives? | The premotor cortex converts the desired goal into a specific plan | |
| What is the premotor cortex important for? | motor planning; activity in one side of the premotor cortex can occur before movement of either hand | |
| What can lesions in the premotor cortex affect? | Lesions affect visually-cued movements and movements that require the coordination of both hands | |
| What are mirror neurons? | Neurons in the premotor cortex that respond when someone else performs the same movement or the same type of movement | |
| What determines if a planned movement will occur? | The loop through the basal ganglia and ventral lateral thalamus | |
| Describe the basal ganglia motor loop | 1. striatum receives excitatory input from the cortex and the substantia nigra 2. The striatum forms inhibitory synapses on the globus pallidus | 3. The globus pallidus= inhibitory connections with cells in the ventral lateral nucleus of the thalamus, the inhibition of the globus pallidus frees the thalamus from inhibition 4. The VL forms excitatory connections with the supplementary motor cortex |
| Describe Parkinson's Disease | - occurs from selective loss of dopaminergic neurons in the substantia nigra (dopamine inhibits the striatum and prevents inhibitory output being sent to globus pallidus) - has two symptoms | |
| Which pathway of the basal ganglia is more important for maintaining inhibition of unwanted movements (suppressed competing and inappropriate, motor programs)? | the indirect basal ganglia | |
| Describe Huntington's disease | - involves loss of neurons in the striatum that project to the globus pallidus (via the indirect pathway) | |
| What is the cerebellum important for? | Sequencing movements, coordination, and motor learning |
Created by:
keiannaowens
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