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most movements are combinations of closed loop and open loop systems. It could be argued that all movements begin in an open loop manner. Most motor behavior includes some degree of corrected responses. Basal ganglia receives sensory information and processes motor commands from the frontal cortex. It refines the commanss and loops them back through thalamus to the frontal cortex, generating a closed loop system
rhythmic activity is initiated and modulated by the brain. It is actively fine-tuned by sensory input. A lot of fine tuning behavior occurs at the lower levels of the motor system, including features like pattern generators in the spinal cord. The brain may turn it on and monitor its execution, but the intrinsic wiring of the portions of a motor system determine features of movement like rhythymic alternation between opposing muscle groups within a limb and even rhythmic alternation between activities of the limbs to accomplish feats like walking.
What are the basic components of muscles?skeletal muscles are composed of many myofibers. Myofibers are composed of many myofibrils. Myofibrils are composed of actin and myosin filaments (protein complexes), which are organized in repeating sacomeres (subunit). The repetition gives the muscles a striped appearance, and therefore also known as striated muscles. They are connected to bones via tendons, strong bands of connective tissueHow to actin and myosin interact to accomplish muscle contractionmuscle contraction occurs when heads of the myosin filaments row against the actin filaments within each sarcomere, effectively shortening the length of the sacromere. When length is shortened, the contractile force of the muscle is increased, allowing movement. Biochemical activities within the sacromere produce energy dependent changes in the interaction between the head of the myosin and specific sites along the actin filament.What are flexorsflexion: a movement of a limb that tends to bend its joints; opposite of extension; produced by a contraction of a flexor muscle; decreases angle of articulation of the limbWhat are extensorsextension: a movement of a limb that tends to straighten its joints; opposite of a flexion; produced by a contraction of an extensory muscle; increases angle of articulation of the limb
Muscles do not flec. limbs flexWhat is meant by reciprocal innervation of antagonist muscles and how does it contribute to coordinated activity?skeletal muscles are arranged in opposing anatagonistic pairs. the ability to smoothy regulate of muscle pairs is wired into the neuroanatomy of the spinal cord. IF a descending signal from the brain is sent, the action potential in the descending spinal motor neuron can simultaneously activate one muscle and at the same time send an axon collateral to signal inhibitory interneuron to decrease the contraction of the antagonistic muscle. This neural wiring is used to regulate the reciprocal activation of antagonistic muscle pair in varied activitieswhat is a motor unita motor neuron and its associated muscle fibers, smallest unit of motor activitywhat is a motor poolall innervation of muscle, total set of motor units
Skeletal muscles typically contain a combination of slow and fast motor units in the motor pool, but the distribution of the motor units differs from one muscle to anotherwhich muscles have motor units with the highest innervation ratios-eyes: there is about 1 axon per 3 myofibers
-biceps: about 1 axon for more than 100 myofibers
-postural muscles of the trunk and legs contain more motor units
- muscles of the arms fingers and face contain more fast motor unitsdescribe the neuromuscular junctionthe synapse between the terminal buttons of an axon and a muscle fiber, occurs around the midpoint of the muscle fiber, releases acetylcholinedescribe motor endplatethe postsynaptic membrane of a neuromuscular junction, contain nicotinic receptors (ionotropic Na+ channels) that acetylcholine binds todescribe endplate potentialthe postsynaptic potential that occurs in the motor endplate in response to the release of acetylcholine by the terminal button (depolarizing)how do action potentials in motor neurons related to myofibers contractionswhen acetylcholine binds to the nicotonic receptors, an EPSP is produced in the motor endplate, called an endplate potential. THe neuromuscular junction produces a very large depolarization, which produces an action potential in a muscle fiber. A large depolarization occurs because the endplate contains voltage gates Na+ channels at the site where nicotinic receptors respond to the release of acetylcholine from the motor neuron. Na+ channels are triggered, and an action potential is reliably propagated in both directions down the muscle fiber, causing contraction at each sacromere along the length of the fiber. If the magnitude of the contractile force has to be increased, a sustained contraction of may muscle fibers would need to be produced.proprioceptorssensory receptors that are sensitive to position, movement, or acceleration of a body part (joints, ligaments, muscles, or tendons) they can exert powerful influences over the function of associated muscles to initiate and regulate movements. It functions largely outside of conscious awareness partly because sensory mechanisms exhibit rapid adaptationjoint proprioceptorssensory receptors located in the fibrous capsule that surrounds the joint (type 1 and 2) , or in the ligaments within the joint (type 3) or distributed broadly around the joint (type 4)type 1 joint proprioceptorsignal position of the joint, have tuning curves in relation to position, each receptor activates a maximal rate of firing of action potentials when the limb is in the best position for that particular receptor, different proprioceptors are tuned for different positions, contributes to awareness of where the limb is in space, tells about starting positionType 2 Joint proprioceptorsignal movement of the joint, indicates acceleration and speed of the change in the angle of the jointstype 3 proprioceptorimportant in extremes of movement, high threshold for activation, activated when joint is moved beyond the usual range of motion, important in protective functions to prevent hyperextensiontype 4 proprioceptorsfine, unmyelinated fibers, signal pain in the joint, extremes of movement, and other problems like joint inflammation and arthritis.muscle and tendon proprioceptorssecond class of proprioceptorswhat is a muscle spindlelocated within every skeletal muscle, sensory stretch receptors that wrap around a subset of muscle fibers, respond to changes in muscle length (not tension), fire action potentials if a muscle is stretchedintrafusal muscle fibersmuscle fiber that functions as a stretch receptor, arranged parallel to extrafusal muscle fibers, thus detecting changes in muscle length, set of muscle fibers in contact with muscle spindle afferent neurons and gamma-motor neurons, inside sensory receptors, small subset of total number of contractile fibers, do not contribute greatly to the force of strength of the muscle, innervated by gamma motor neurons (specialized neurons that activate intrafusal fibers in parrallel with main fibers of the muscle so the length of the intrafusal fiber is a good approximation of the length of extrafusal fibers during movement execution)extrafusal muscle fibersmuscle fiber that is responsible for the force exerted by contraction of a skeletal muscle, provide the bulk of the muscle and are principally responsible for the contractile dorce of muscles, innervated by alpha-motor neurons (convey commands to contract whenever the muscle is called to engage in a reflexive or voluntary movement) outside muscle spindle mechanismalpha motor neuronsneruons whose axon forms synapses with extrasual muscle fibers of a skeletal muscle; activation contracts the muscle fibersgamma motor neuron:neuron whose axons form synapses with instrafusal muscle fibers of a skeletal muscleto what kind of stimulus does a muscle spindle respond?when a muscle is stretched, primary type 1a fibers of the muscle spindle responds to both changes in muscle length and velocity and transmit this activity to the spinal cord in the form of changes in the rate of action potentialsExplain the monosynaptic stretch flexreflex in which a muscle contracts in response to it being quickly stretched; involves a sensory neuron and a motor neuron, with one synapse between them. If an unexpected stretch is experienced by the muscle, the increase in length of the extrafusal muscle fiber activates muscle spindle afferents in the stretched muscle. Afferents convey an increased rate of firing of action potentials through the dorsal roots and into the central gray of the spinal cord.what signal is sent to the antagonistic muscle in a monosynaptic reflex?a signal is sent to inhibit the antagonistic muscle to prevent muscles from locking up. The signal consists of activation of inhibitory interneurons that regulate the alpha motor neurons that innervate the antagonistic muscle. There are two synapses in this process so it is slightly slower. It is mediated at the level of the spinal cord, so it is known as a spinal reflexwhat are the important functions mediated by monosynaptic reflexes? Is it only protective responses?it is important in protective responses after something goes wrong with holding something or walking. It can also help with planned behaviors like catching a ball or picking up an objectexplain how a golgi tendon organ is stimulated and describe the the polysynaptic reflex that occurs- golgi tendon organ: receptor organ at the junction of the tendon and muscle that is sensitive to tension, responds to increases in muscle tension (not stretch lenght) , provides information to CNS regarding load on muscle and acts as a brake to prevent overly vigorous contraction, prevents damage to muscles, tendon pulled by a muscle contraction, active in mormal movement by encoding amount of force on muscle over a broad range muscle loads
- when a load is added to a muscle, the force of the muscle is increased and golgi tendon organ is activated. Afferent neuron signals through the dorsal root ganglion and activates an inhibitory interneuron in the gray matter of the spinal cord. The inhibitory interneuron decreases the number of action potentials in the alpha motor neuron that innervates the muscle that is assocaited with the golgi tendon orgran. Contractile force is decreased and tension on the tendon is reduceddistinguish monosynaptic stretch reflex from polysynaptic refelxes- opposite effects
- monosynaptic stretch reflexes causes contraction of the stretched muscle. The polysynaptic reflex is a slightly slower mechanism that can cause a decrease in the contraction of the muscle when the load is increased on the muscle. Both work together to signal the status of muscles, and to organize and correct movements during executionwhat kind of reflex is the patellar (knee jerk) reflex?the patellar reflex is a monosynaptic stretch reflex. When it is tested, the tendon that attaches the quadricep muscles is distorted and pulls on/ stretches the quadricep muscles, activating the muscle spindle afferents from those muscles. The muscle spindle afferents excite the alpha motor neurons that innervate the quadricepts muscle, and those muscle neurons cause a contraction of the quadriceps muscle group. At the same time, the muscle spindle afferent activates an interneuron that synapses on the alpha motor neuron that connects the antagonistic hamstring muscles. The interneuron inhibits the activity of the alpha motor neuron so the contraction of the antagonistic muscle is decreased, and the stretch reflex can effectively shorten the quadriceps muscle back to its original position.what is a police officer testing in a field sobriety test?field sobriety tests proprioceptive integrity and evaluates alcohol intoxication. the subject has to reach outward, and touch the nose with both eyes closed. Intoxicated individuals have difficulty locating their limbs in space relative to noses. Adolescence, sudden body wight, extreme fatigue, migrane auras, or epilepsy can also impair proprioception transiently. More severe impairments occur in mutliple scleorsis and spinal cord lesionsthe prefrontal cortex receives sensory inputs from which areas?the prefrontal cortex is rostral to the premotor cortex and supplementary motor area. Sensory inputs come from the temporal and parietal lobes. It is important for organizing movement plans.describe the roles of the prefrontal cortex, in motor activitty- neurons in the medial parietal cortex integrate highly processed visual, auditory, and somatosensory information. They participate in organizing the manner a person will reach out and interact with an object. THey process the characteristics of the stimuli you can interact with so the appropriate response is engaged in. The integrated information is conveyed to the prefrontal cortex and other areas of the frontal lobes.
- the prefrontal cortex is implicated ina wide variety og high level cognitive functions (executive functions). The activities of the prefrontal cortex represent the highest level of cognitive organization of motor behavior. It then innervates additional parts of the frontal lobes that translate the higher level cognitive decisions into more concrete motor plans. As the processing of information moves from the most rostral pole of the frontal lobes through the supplementary motor area and premotor cortex to the primary motor cortex, the functions move from abstract organization to more and more concrete motor commandsdescribe the role of the supplementary cortex in motor activitythe supplementary motor area and the premotor cortex lie in the frontal lobes, just caudal to the prefrontal cortex. They both receive inputs from the prefrontal cortex, and they are involved in the basic organization and execution of the movements required to execute the goal-directed behaviors that are planned by the prefrontal cortex. The principle output of these two regions is the primary motor cortex, M1. The supplementary motor area resides in a very dorsal part of the cortex that lies just outside of and even folds into the longitudinal fissure. The supplementary motor area is important in initiating and sequencing movements that are executed in complex behaviors. Patients with damage to this area are often unable to initiate voluntary behavior, and are left with only reflexive responses. It is less involved in the actual execution of the behavior, but rather plays a role in activating and in anticipating what the next movement will be in a sequence of movements.describe the role of the premotor cortex in motor activitythe premotor cortex is important in voluntary behavior, particularly gross coordination of limb movements. An important function is control of reaching, shaping the forepaw during grasping, interactions between the hand and mouth, making particular kinds of movements in response to presentation of stimuli, and sensory guidance of locomotion (especially movement of the body toward nearby objects in personal space). The premotor cortex is not focused on activation of individual muscles. Area F5 receives integrated sensory information from the parietal and temporal lobes. Neurons in area F5 are activating when observing and when performing particular motor behaviors (mirror neurons)what are mirror neuronsneurons located in the ventral premotor cortex and inferior parietal lobule that respond when the individual makes a particular movement or sees another individual making that movement. They appear to have both sensory and motor functions that can be activated by sight or sound of someone engaging in an activity. They are important in practicing a motor response, engaging observational learning, and interpreting intentions of others.Describe the organization of the primary motor cortex (M1). What is somatotopic organization?the primary motor cortex is the precentral gyrus or most caudal gyrus of the frontal lobes. It contains the primary motor homunculus. Early studies indicated that brief stimulation caused brief, jerky movements, and prolonged stimulation caused complex movement, implicating M1 in activating individual muscles to produce organized movemnts. About 1/3 of M1 cells encode single muscle movement, and the rest encode complex functionsDescribe the directional tuning of M1neurons in M1 have tuning curves for the direction of movementdescribe the plasticity of tuning M1plasticity in M1 when learning motor tasks with areas involved with motor learning expandingwhat brain structures comprise the basal ganglia?basal ganglia are interconnected set of subcortical forebrain and midbrain structures, consisting of the striatum (caudate nucelus, putamen), globus pallidus, and substantia nigra. It is in the dicenphalon and mesencephalon. The activity of neurons correlate with movement, and its principal function seems to be fine-tuning motor activityThe basal ganglia receives input from which areas in the brain? to where does it project?The caudate and putamen receive extensive input from all over the cortex, and a little from the thalamus. The subthalamic nucleus receives corticol input from motor cortices. Outputs of basal ganglia originate from internal subdivisions of globus pallidus, and substantia nigra pars reticulata. Outputs are inhibitory and GABAergic and they project back to thalamus and brainstem nuclei that are involved in motor behavior regulation. It is thought to reduce excess unwanted motor activity. As motor information is processed through the loops, it can be compared with other signals processed by the basal ganglia, such as sensory influences and learned motor patterns. They can exert a profound influence over descending motor function even if they do not have direct contact with spinal cord circuitry.
- the three pathways determine the manner in which basal ganglia processing adds or subtracts from particular aspects of motor commands to sharpen signals sent to lower levelsBasal Ganglia indirect pathwaycortex->caudate->Gpe-> Gpi/Snrbasal ganglia direct pathwaycortex-> caudate-> GPi/SNrbasal ganglia hyper direct pathwaycortex-> STN-> Gpe-> and GPi/SNrdescribe the cerebellumthe cerebellum houses more than 50% of neurons even though it is only 10% of total brain volume. It is comprised of two hemispheres, each with a cortex overlaying a layer of white matter. Cortex only has three layers. Outputs of the cerebellum are inhibitory and are funneled through three deep cerebellar nuclei and the brainstem vestibular nuclei. It is situated at the base of the brain near the top of the spinal cord so it can receive ascendnig sensory input and process descending motor output. It does not control, but influences the timing and coordination of motor commands.
- IMportant in language tasks, working memory, motivated behavior, forms of classical conditioning, experience of pain, and allocation of attention.describe the flocculondular lobe (vestibulocerebellum)receives inputs from vestibular nuclei of brainstem and projects back to them, important in balance, regulation of eye movements (with superior colliculus and frontal eye fields)describe the posterior lobe (cerebrocerbellum)important in planning a skilled voluntary behavior and for storage of skilled patterns (procedural memory)describe the anterior lobe (spinocerebellum)important in skilled movements, coordination, gait, regulation of muscle tone, coordination of skilled voluntary movement planning and modulation of voluntary activity, storage of procedural memories, matienance of balance, eye controlDescribe the function of the medial longitudinal zone in the cerebellum (vermis)receives vestibular/auditory/visual/somatosensory input from the tectum and the spinal cord, outputs back to one of the three deep cerebellar nuclei (fastigial nucleus) to regulate posture, gait, and balance of the medial aspects of the body, fastigial nucleus innervates vestibular nuclei to return information about balance and posturedescribe the function of the intermediate cerebellum longitudinal zonereceives input from motor cortex and somatosensory input from spinal cord, outputs to interpostius nucleus, interpoitus nucleus sends projections to motor nucleus (red nucleus in the brainstem) and back through the thalamus to the motor cortex to control proximal limb movementsdescribe the function of the lateral cerbellumreceives input from motor cortex and somoatosensory input from spinal cord, outputs to denate nucleus, denate nucleus innervates red nucleus and provides reafferent input to thalamus and motor cortex, regulates control of distal portions of the limbs, independent limb movement, timing of open-loop ballistic movementswhat are ballistic movements and how does the cerebellum play a role in these movementsa rapid muscular movement that is generally preprogrammed .
- the cerebellum modulate the activities of the control systems of the body which may be routed to the thalamus in a loop back to the cortexdescribe the two groups of descending tracts involved in the control of motor functionsLateral and ventromedial groupsVentromedial Tracts:- inputs from midbrain and brainstem nuclei and from M1- regulate postural control, stance, walking- vestibulospinal tract- originate in brainstem vestibular nuclei; terminate in spinal cord- controls trunk and legs- posture- tectospinal tract- originate in superior colliculi; terminate in spinal cord- controls neck and trunk- coordinates eye/head movements- ventral corticospinal tract- originate in trunk and proximal leg region of M1; terminatein spinal cord- controls hands (not fingers), lower arms, feet, lower legs- walking and posturedescribe the general features of amyotrophic lateral sclerosisrapidly progressive, fatal disorder,, destruction of the CNS and PNS motor neurons, one of the most common neuromusucclar diseases, 90-95% sporadic, but some familia due to genetic error, death typically from respitory failure in 3-5 years, wasting of skeletal muscle, no sensory impairment, no cognitive decline but may exhibit depression and alterations in decision-making and memorydescribe the general features of the apraxiasacquired disorder of motor planning, not incoordination, sensory or comprehension deficit
- ideomotor apraxia: incorrect organization of seqeuncing movement, left frontal or parietal lesions
constructional apraxia: skilled movements are intact, but inability to draw or assemble, right parietal damagedescribe the general features of cerebellar ataxiacerebellar disease or damage causing ataxia, hypotonia, astasia, and/or intention tumordescribe the general features of huntington's diseaseautosomal dominant disorder, chromosome 4-CAG, usually onsets in early-middle age (35-50), loss of striatal neurons, atrophy of caudate, characteristic boxcar ventricles, generally characterized by choeroid movements, psychiartric disturbances, and intellectual deteriorationdescribe the general features of parkinsons diseasedestruction of dopaminergic neurons of SN and VTA, loss of more than 70% of neurons, cause unkown- possibly genetics and toxicity, tremor, ridgidty, akinesia/bradykinesia, postural instability, treatments include levodopa and carbidopa, it is converted to dopamine by remaining axon terminals, selegiline (deprenyl), MAO-B inhibitor, deep brain stimulation
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