Transcript Chapter 1
CHAPTER 11 The Body Senses and Movement The Body Senses Movement Phantom pain • Phantom pain: – Pain that is experienced as being located in the missing (amputated) limb. – 70% of amputees experience – Phantom pain IS a real sensation: brain not know that limb is missing – Significant problem in post-amputation pain management. Phantom pain • The phantom “pain” originates in the brain. – Neural circuits for movement involve many movement areas • After amputation: missing limb still has neural contribution to a movement • When move your body, those circuits are stimulated – Brain is interpreting the state of the “missing” limb via the stimulation of those old remaining circuits • Awareness of the details of limb's shape/perceived ability to move it tend to fade with time. – Over time, old neural connections fade (no longer stimulated because the limb associated with them is gone) – New circuits form that do not include the neural stimulation caused by the missing limb • Most amputees report continuing to feel some phantom sensations throughout the remainder of their lives. Phantom pain • Neural mechanisms which permit perception of phantom limbs are well recognized: – Major muscles in residual limb tense up several seconds before cramping phantom limb pain begins • • • Muscles remain tense for much of duration of episode. – – – – • Remember: those muscles associated with movement in missing limb Brain interprets this as if the missing limb itself was cramping Muscle fatigue sets in Reduced blood supply Eventually, pain sensation in remaining muscles But, because circuits are tied to missing limb, feel as if missing limb is painful! Burning phantom limb pain closely associated with reduced blood flow in residual limb- is a sensation of a lack of circulation – Brain acting like limb still there: interprets residual limb activity as if it was activity in the missing limb – Assumes that if residual muscle is “hurting”, the missing limb must be too! Phantom pain • What is brain doing? Investigated brain activity for missing arm – Researchers noted that stimulating the amputee’s face often produces sensations in phantom (missing) arm – Team of researchers in Germany used brain imaging to map face and hand somatosensory areas in upper-limb amputees. • In phantom limb pain patients: neurons from one area invade the area dedicated to the missing limb – E.g.: Neurons from the face area appear to invade the area that normally receives input from the missing hand. – Thus, as face moves, brain processes this as movement of limb, and pain reaction to movement • As if neurons for one area of the body spread and take over the neurons for the missing limb…except the body doesn’t know it ISN’T the missing limb Phantom pain: Treatment • Main treatment is NOT pain meds, but fixing the miscommunication in the brain through BIOFEEDBACK • Why is biofeedback helpful? – Teach the amputee’s brain to recognize that limb is missing – The specific aim of the treatment: • teach amputees with phantom pain to habitually and unconsciously keep their residual limbs as warm and as relaxed as the intact limb. • Teach them to increase muscle temperature • Teach them to reduce cramping and muscle tension in surrounding area – Disconnect neural patterns involving the missing limb! Phantom pain: Treatment • Have to explicitly TEACH the relationship between sensation and the missing limb: – Feel the muscle tension/temp changes in the tissue surrounding the missing limb – Relate those sensations to the pain sensations “in the missing limb” • Muscle tension and temperature awareness training – Often use mirrors or biosensors: – Show muscle tension in surrounding muscle areas – Have amputee identify pain sensation that goes with the tensing of surrounding muscles: SEE the tension and FEEL the pain – Have them learn to relax surrounding muscles and feel lessening of pain • SEE the relaxation and FEEL the lessening of pain • Begin to learn to control these parameters…..lots and lots of trials and practice movement Muscles and detecting movement Three categories of muscles • Skeletal muscles – move the body and limbs. – Are called striated muscles: have striped appearance. • Smooth muscles – produce the movements of the internal organs. – E.g., small intestine, colon • Cardiac muscles: are the muscles that make up the heart. MUSCLE CELLS • Muscle fibers. – – – – Muscles made up of individual muscle cells or fibers Muscle fiber made up of myosin filaments and actin filaments. Muscles controlled by motor neurons Motor neurons synapse with muscle cell at the neuromuscular junction. • When a motor neuron releases acetylcholine: – The muscle fiber is depolarized, which opens calcium channels. – The calcium influx initiates a series of actions by the myosin that contract the muscle. Detecting Muscle Movement • Muscle spindles: Muscle stretch receptors • Golgi tendon organs: Receptors that detect tension in a muscle. • Central pattern generators – Neuronal networks – Produce rhythmic patterns of motor activity, • E.g., walking, swimming, flying, and breathing. – Central pattern generators may be located in the spinal cord or brain. Agonistic and Antagonistic muscles • Agonist muscles: cause a movement to occur through own contraction • Antagonist muscles: oppose a specific movement. – Controls a motion, slows it down, and returns a limb to its initial position. – If a motion is reversed, agonist and antagonist muscles switch roles. • Simultaneous activation of antagonistic muscles contributes to • smoother movements, • precise stopping and starting of movements • reduction of tremor Pushups: Agonistic and Antagonistic muscles • Look at Push ups: both agonist and antagonist movement • The triceps contracts during push-ups: act as AGONIST – during the up phase of a push-up: controls elbow flexion to move up. – Triceps relax during the down phase of a push-up: Controls elbow flexion while relaxing – In both cases, triceps continues to be the prime mover, or controller, of the joint action. • The elbow flexor muscles are the ANTAGONISTS during pushups – during both the up phase and down phase of the movement: – Are opposing the movement of the triceps • But: Need brain control to tell muscles how to move! Motor cortices • The motor cortex consists of three main areas: – Primary motor cortex – TWO major secondary motor areas: • supplementary motor area • premotor cortex. • Both primary and secondary areas form a tonotopic map of the body – Again, remember the Homunculus – Greater amounts of cortex devoted to the parts of the body that produce finer movements. Motor cortex functions • Prefrontal cortex: Initial step in motor planning – Integrates auditory and visual information about the world with information about the body • Body information comes from posterior parietal cortex • Auditory information from temporal area • Visual information from occipital areas – Holds information in memory while selecting appropriate movement and its target. Movement control • Premotor cortex – begins programming a movement by combining information from the prefrontal cortex and the posterior parietal cortex. • Supplementary motor area – Output from the prefrontal cortex flows to SMA – SMA assembles sequences of movements – E.g., eating or playing the piano. • Primary motor cortex responsible for – execution of voluntary movements: – cells fire most during the movement instead of prior to it. Basal ganglia: inhibitory control • Basal ganglia: includes several brain areas – – – – the Striatum: putamen and caudate nucleus Globus pallidus including Subthalamic nuclei (STN), Substantia nigra (SN). • Basal ganglia uses information from – Primary motor cortex areas – Secondary motor areas – Somatosensory cortex Basal ganglia: inhibitor motor control • Basal ganglia send output directly to – – – – Primary motor cortex Supplementary motor area Premotor cortex Sent via the thalamus. • Basal ganglia smooths movements by – facilitating outputs to thalamus – inhibiting outputs to the thalamus • Two major pathways: Direct and Indirect pathways – Have opposite net effects on their thalamic target structures: – One works directly – The other works indirectly Direct vs. indirect Pathway • The direct pathway – Makes excitatory connections on the thalamic neurons – Thalamic neurons in turn make excitatory connections onto neurons in motor and cognitive areas of the cortex. • Indirect pathway – Produces the net effect of inhibiting thalamic neurons. – When inhibited, the thalamic neurons are then unable to excite motor cortex neurons. • Within normally functioning basal ganglia, a proper balance is achieved between these two pathways. Basal ganglia • That is: A delicate balance must be formed – Direct pathway selectively facilitates a particular motor or cognitive behavior that is necessary for a present task, – Indirect pathway simultaneously inhibits neurons which control competing motor behaviors. • Extra Pyramidal Syndrome: – Upsetting the balance between these two motor pathways – Results in motor dysfunctions – Symptoms include stationary tremor, uncontrollable limb movements, difficulty walking and poor motor control – Includes Parkinson's, Tardive Dyskinesia and related motor disorders Cerebellum: Yep, more motor control • Cerebellum – Receives information from the motor cortex about an intended movement – Determines the order of muscular contractions and their precise timing. • Cerebellum also uses information from the vestibular system to – Maintain posture and balance – Refine movements – Control eye movements that compensate for head movements cerebellum • Cerebellum composed of two control loops critical for controlling and processing motor behavior • Cerebellum functions: – improves accuracy of movements – creates smooth muscle movements – Does this by comparing descending motor commands with information regarding current motor actions. • Cerebellar system makes corrections as necessary to equate current with desired motor sequences, – acting on the brain stem and cortical motor areas. cerebellum • Because cerebellum receives input from most body senses: Serves as distinct feed-back loop for sensory-motor coordination • Cerebellum can be said to – compare what the body is doing to – what should the body be doing – and signals the brain to make changes as necessary. • Damage to the cerebellum typically results in – loss of ability for both sensory and motor coordination – Results in disruptions of equilibrium, motor coordination and postural control. – E.g., cerebral palsy Specialized areas within cerebellum • Vestibulocerebellum – This area regulates both balance and eye movements. – damage to the vestibulocerebellum results in disruptions of balance and gait. • Spinocerebellum – Anticipates and adjusts for body and limb movements. – Critical for modulation of the descending motor systems. – Role is to elaborate proprioceptive input, allowing the system to anticipate future body position. Specialized areas within cerebellum • Cerebrocerebellum: – Critical for planning movement and evaluating sensory information required for action. – also plays a critical role for planning anticipated motor movements and modulating at least some cognitive functions. • Cerebellar deep nuclei: – unique (and only) set of output structures – embedded within the center of each cerebellar hemisphere. – send outputs to the superior and inferior cerebellar peduncles, and on to various areas of the cerebral cortex. – Sends information regarding other specialized areas….thus exerts control on basal ganglia, cortex, etc. So: What part of the brain controls movement? • MANY brain areas control movement: – Prefrontal cortex: selects the motor response – Premotor cortex : • combines information from prefrontal and parietal cortex. • Selects individual responses for movement – Supplementary motor area : Assembles sequences of movements – Primary motor cortex: Executes voluntary movements: – Basal Ganglia: • Direct and indirect pathways • maintain voluntary movement while suppressing unwanted movement – Cerebellum: • Integrates movements; helps precise timing • Smoothes, refines, makes sure what is = what should be. • Note the redundancy and dual control of processing! • Why!?!