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Midterm

KINE 3020 Midterm 1- Readings Topic 1-9 and Answers

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Department
Kinesiology & Health Science
Course
KINE 3020
Professor
Merv Mosher
Semester
Fall

Description
Topic 1-pg 47-51 Pg. 47 Motor Control Theories and Physiology  It has been suggested that movement control is achieved through cooperative effort of many brain structures that are organized both hierarchically and in parallel  Hierarchical processing in conjunction with Parallel Distributed Processing (PDP) occurs in the Perception, Action, and Cognitive systems of movement control Pg. 48  In Perception system hierarchical processing means that higher brain centers integrate inputs from many sense and interpret incoming sensory information  On Action side- higher levels of brain function form motor plans and strategies for action  Higher levels select the specific response to accomplish task  Lower levels would carry out the detailed monitoring and regulation of response execution  Many structures of the brain (eg.spinal cord, brainstem, cerebellum, and association cortex) have both perception and action components  In PDP the same signal is processed simultaneously among many different brain structures but for different purposes Overview of Brain Function  Multiple processing levels including the Spinal Cord, the Brainstem (medulla, pons, midbrain), and Diencephalon (Thalamus and Hypothalamus), the Cerebellum, and Cerebral Hemispheres, Cerebral cortex and three deep structures, Basal ganglia, Amygdala, Hippocampus Spinal Cord  The lowest level of Perception/ Action Hierarchy  It is involved in initial reception and processing of Somatosensory information (from muscles, joints, skin) and the reflex and voluntary control of posture and movement through motor neurons  At level of Spinal cord processing- simple relationship between sensory input and motor output- we also have organization of reflexes- flexion and extension patterns  Sherrington called the motor neurons of the spinal cord the “Final Common Pathway” since they are the last processing level before muscle activation occurs  Afferent input send information to the Spinal cord (segmental spinal networks) and higher parts of the brain, the output modulates skeletal muscles Brainstem  Spinal cord extends rostrally to join onto the next processing level, the brainstem  The Brainstem contains important nuclei for postural control and locomotion, including the vestibular nuclei, the red nucleus, and reticular nuclei  It has Ascending and Descending pathways which send Motor and Sensory information  Brainstem receives Somatosensory information from skin and muscles of the head as well as sensory input from the vestibular (spatial/balance) and visual systems  Brainstem controls output to neck, face , and eyes, and critical to the function of hearing and taste  All Descending Motor Pathways except the Corticospinal tract originate in the Brainstem  Reticular formation- regulates our arousal and awareness is also found in the Brainstem Division of Brainstem from Caudal to Rostral: Medulla, Pons, and Midbrain Cerebellum  Located behind the Brainstem and connected to it are tracts called Peduncles Pg. 49  Cerebellum receives inputs from Spinal cord (about movements) and from Cerebral cortex (about planning movements), and outputs to the Brainstem  Cerebellum adjusts out motor responses by comparing the intended output with sensory signals and then to update the movement commands if they deviate from the intended trajectory  Also regulates the force and range of movements and is involved with motor learning Diencephalon  Moving rostrally in the brain we find the Diencephalon which contains the Thalamus and Hypothalamus  Thalamus- processes most of the information coming to the cortex from many parallel input pathways from the spinal cord, cerebellum, and brainstem o Pathways stay segregated Pg. 50 Cerebral Hemispheres (Cerebral Cortex and Basal Ganglia)  Higher in the processing level is the Cerebral hemispheres, which include the cerebral cortex and basal ganglia  Basal ganglia is located at the base of the Cerebral cortex- it receives input from most areas of Cerebral cortex and sends output to the Motor cortex through the Thalamus o Some of its functions involve higher order cognitive aspects of motor control like planning of motor strategies  Cerebral cortex- often considered the highest level of motor control hierarchy  The Parietal and Premotor areas, along with other parts of the Nervous system are involved in identifying targets in space, choosing a course of action, and programming movements  Premotor areas outputs mainly to the Motor cortex which sends its commands to the Brainstem and Spinal cord through the Corticospinal tract and the Corticobulbar system  The Nervous system is organized both controls: Hierarchically and “in Parallel”  Highest levels of control also can affect the Spinal Motor Neurons  The combination of using both controls allows an overlap of functions so that one system is able to take over from another when environmental or task conditions require it o It also allows a certain amount of recovery from neural injury by the use of alternative pathways Pg. 51 The Pathways of the Nervous system for Planning and Execution example  You are thirsty and want to pour some milk from the milk carton in front of you into a glass 1. Sensory inputs come in from the periphery to tell you what is happening around you, where you are in space, and where your joints are relative to each other, they give you a map of your body in space o Sensory information gives you critical information about the task you are to perform: how big the glass is, what size the milk carton is, and how heavy it is 2. Higher centers in the Cortex make a plan to act on this information in relation to the goal: reaching for the milk carton 3. From your Sensory map you make a Movement plan (using maybe the Parietal lobes and Supplementary and Premotor Cortices) o You are going to reach over the box of corn flakes in front of you 4. The plan is sent to the Motor cortex and muscle groups are specified 5. The plan is also sent to the Cerebellum and Basal ganglia, and they modify it to refine the movement 6. The Cerebellum sends an update of the movement output plan to the Motor cortex and Brainstem 7. Descending pathways from the Motor cortex and Brainstem then activate Spinal cord networks 8. Spinal cord networks activate the muscle- you reach for the milk 9. If milk carton is full when you expected it to be empty Spinal reflex pathways will compensate for the extra weight that you did not expect and activate more Motor neurons 10. The Sensory consequences fo your reach will be evaluated and the Cerebellum will update the movement to accommodate for the heavier milk Topic 2- pg 51-52 Neuron the Basic Unit of CNS  Lowest level in the Hierarchy is the Single Neuron in Spinal cord  The Neuron at rest always has a negative electrical charge on the inside of the cell compared to outside o The Resting Potential is about -70 mV  This electrical potential is caused by an unequal concentration of chemical ions on the inside versus the outside. K+ high on the inside and Na+ high on the outside  The is an electrical pump in the cell membrane that keeps ions in their appropriate concentrations o At rest the K+ channels are open and keep neuron at this negative potential  Action Potential are jumps in voltage across the cell membrane- it does not go to zero voltage but to +30mV- the inside becomes positive o AP are about 1msec in duration and the membrane is quickly repolarized o The height of AP is always about the same -70 to +30mV= 100mV jump  Synaptic Transmission- process of information passing onto the next cell  Each AP in a neuron releases small amount of transmitter substance o Diffuses across the cleft and goes to receptor o Which open up channels and depolarize the cell  One AP makes only a small depolarization called an Excitatory Post Synaptic Potential (EPSP)~ it normally dies after 3-4 msec, so it is not enough to activate the next cell  Summation- If a cell fires enough AP then a series of EPSPs occur and build up for a big enough depolarization to meet the threshold voltage so that another AP can be fired to the next neuron  Two types of Summation- Temporal and Spatial  Temporal Summation is depolarizations that occur close together in time  Spatial Summation- produces depolarizations because of multiple cells synapsing at the same time  Spatial summation is an example of Parallel Distribution Processing since multiple pathways are affecting the same neuron  Synaptic Facilitation- neuron releases more transmitter; therefore, more easily depolarizes next cell  Defacilitation or Habituation- cell is depleted of transmitter; thus, less effective in depolarizing next cell Topic 3 & 4- pg. 52-62 Pg. 52 Sensory/ Perceptual Systems  Sensory inputs serve as the stimuli for reflexive movement organized at the Spinal cord level of the Nervous System  Sensory system plats a vital role in modulating the output of movement that results from the activity of pattern generators in the Spinal cord like Locomotor pattern generators  The reason that sensation can modulate all these types of movement is that Sensory receptors converge on the Motor neurons considered the Final Common Pathway  Another role of Sensory information in movement control is accomplished through Ascending Pathways which contribute to the control of movement in more complex ways Somatosensory system  From the lowest to the highest level of the CNS hierarchy going from the reception of signals in the periphery to the integration and interpretation of those signals relative to other sensory systems in Association cortex Pg. 53 Peripheral Receptors Muscle Spindle  Most Muscle spindles are encapsulated spindle shaped sensory receptors o Consist of specialized very small muscle fibres called Intrafusal fibres (Extrafusal fibres are the regular muscle fibres) o Sensory neurons endings ( Group 1a and 2 afferents) wrap around the central regions of these small Intrafusal muscle fibres o Gamma motor neuron endings that activate the polar contractile regions of the Intrafusal muscle fibres (Nuclear chain, and Nuclear bag) Pg. 54  In humans the muscles with the highest spindle density are the extraocular, hand, and neck muscles Intrafusal Muscle Fibres  There are two types of this fibre: Nuclear bag (divided into static and dynamic types) and Nuclear chain (static type)  The Nuclear bag has many spherical nuclei in its central noncontractile region which stretches quickly when lengthened because of its elasticity  Nuclear chain has a single row of nuclei, and is less elastic and also stretched slowly Groups Ia and II Afferent Neurons  Cell bodies are in the Dorsal root ganglia of the Spinal cord, wrap around the Intrafusal muscle fibres o The Ia fibre sensory endings wrap around the equatorial region of both bag and chain, and thus respond quickly to stretching, sensing the rate of change of the muscle length o Group II endings wrap around the region next to the equator which is less elastic and thus less responsive o Ia afferents go to both Bag and Chain while group II go mainly to the Chain o Group Ia is most sensitive to change or dynamic muscle length o Group II is most responsive to steady state or static muscle length Gamma Motor Neurons  Both bag and chain muscle fibres are activated by axons of the Gamma Motor Neurons  Cell bodies of the GMN are inside the Ventral horn of the Spinal cord, intermingled with Alpha Motor Neurons innervating the Extrafusal fibres  Two types of GMN- Gamma dynamic activating only the dynamic Bag fibres and Gamma Static innervating both static Bad and Chain fibres  Activation of Gamma dynamic MN enhances the dynamic responses of the Ia afferent neurons while the activation of Gamma static MN enhances the responses of the Group II afferent neurons signalling the steady state length of the muscles Stretch Reflex Loop  When a muscle is stretched it stretches the muscle spindle, exciting the Ia afferents  Two types of reflex responses can be triggered by this Ia afferent excitation, a Monosynaptic spinal reflex and a Long loop or Transcortical reflex  Spinal stretch reflex is activated by Excitatory Monosynaptic connections from the Ia afferent neurons to the Alpha Motor eurons which activate their own muscle and synergistic muscles  Ia afferent also excite the Ia inhibitory interneurons which then inhibit the AMN to the antagonist muscles  The Long loop or Transcortical reflex is a more modifiable reflex and therefor is called a Functional stretch reflex o Easily modified by environmental conditions  Whenever there is a voluntary contraction there is coactivation of both Alpha( activating the main muscle that is the Extrafusal muscle) and Gamma (activating the Spindle muscle that is Intrafusal fibre) Pg. 55  Without this coactivation the Spindle sensory neurons would be silent during voluntary muscle contractions  Gamma efferent motor neurons cause polar regions of the Nuclear Bag and Chain contract and this the central region of the muscle spindle cannot go slack  Because of this coactivation if there is unexpected stretch during the contraction the Group Ia and II afferents will be able to sense it and compensate Golgi Tendon Organs  Spindle shaped and located at the muscle tendon junction- they connect 15 to 20 muscle fibres  Afferent information from the GTP is carried to the nervous system through the Ib afferent fibres, unlike muscle spindles they have no efferent connections this are not subject to CNS modulation  GTO is sensitive to tension changes that come from either stretch or contraction of muscle- it responds to as little as 2-25 g of force- GTP reflex is an inhibitory disynaptic reflect inhibiting its own muscle and exciting the antagonist  Newly hypothesized function of the GTO is that it modulates muscle output in response to fatigue. When muscle tension is reduced because of fatigue the GTO output is reduced lowering its inhibitory effect on its own muscle  Extensor muscles of the leg are active during the stance phase of locomotion and act to excite the extensor muscles and inhibit the flexor muscles until the GTO is unloaded Joint receptors  Different types of receptors in joints: Ruffin- type endings, Spray endings, Piciniform endings, Ligament receptors and Free nerve endings- they share the same characteristics as receptors found in the Nervous ststem o Ligament receptors are almost identical to GTOs  Joint receptor information are used at several levels of Hierarchy of sensory processing  Joint receptors seem to only be sensitive to extreme joint angles so this may suggest that these joint receptors provide a danger signal about extreme joint motion  Other researchers say that they respond to limited range of joint motion o Called Range Fractionation- with multiple receptors being activated in overlapping ranges  Afferent information from Joint receptors ascends to the Cerebral cortex and contributes to our perception of position in space Cutaneous Receptors  Several types of Cutaneous receptors Detecting Mechanical stimuli: Merkel’s disks, Meissner’s corpuscles, Ruffini endings, and Lanceolate endings around hair follicles  Detecting Temperature change: Thermoreceptors  Detecting Potential Damage to the skin: Nociceptors  Skin, tips of fingers have a very high amount of receptors  Cutaneous information gives rise to reflex movements, and provide spatial information  Placing rection- light touch to the bottom of foot, produces extension of the limb  Flexor Withdrawal Reflex- sharp focal stimulus produce withdrawal or flexion- protect from injury Pg. 56  Ipsilateral flexion, and Contralateral extension- allows you to support your weight on the opposite limb  Reflexes are modulated by higher centers and outcomes depends on situation  Pg. 57 Role of Somatosensation at the Spinal Cord Level  Grillner and Wallen performed experiments in which they cut the dorsal roots to the cat Spinal cord to eliminate Sensory feedback from the Periphery. They stimulated the Spinal cord and were able to activate the Neural pattern generator for Locomotor patterns o They found that low rates of repetitive stimulation gave rise to a walk and higher rates to a trot and then a gallop o This suggests that complex movements such as locomotion can be generated at the spinal cord level without Supraspinal influences or inputs from the Periphery  Hans Forssberg and his colleagues have shown that Sensory information modulates Locomotor output in a very elegant way Ascending Pathways  Information from the Trunk and Limbs is also carried to the Sensory cortex and Cerebellum  Two systems ascend to the Cerebral cortex: the Dorsal Column- Medial Lemniscal (DC- ML) system and the Anterolateral system o These are examples of Parallel Ascending Systems  DC-ML- send information containing touch and pressure receptors  Anterolateral system- pain, temperature, crude touch, and pressure  Advantage of Parallel system- they give extra subtlety and richness to perception by using multiple modes of processing information and give a measure of insurance of continued function in case of injury Pg. 59 Dorsal Column- Medial Lemniscal System  The DC are formed mainly by Dorsal root neurons, thus are First order neurons  They send information about muscle, tendon, and joint sensibility up to the Somatosensory cortex and other higher brain centres  There is an exception- Leg proprioceptors have their own private pathways to the brainstem, the lateral column  DC also contains information from touch and pressure and codes especially for discriminative fine touch  The pathway synapses at multiple levels in the nervous system, including the medulla where Secondary neurons become the ML pathway and cross over to the thalamus, synapsing with the Third order neurons, which go to the Somatosensory cortex  Every level of Hierarchy has the ability to modulate the information coming into it from below o There is the ability to enhance or shut off ascending information  Receptive field is enlarged at each successive neuron to allow meaningful interpretation of information Anterolateral system  Consist of Spinothalamic, Spinoreticular, and Spinomesencephalic tracts- they cross over upon entering the Spinal cord and then ascend to Brainstem centres  The AL system has a dual function o Transmits information on crude touch and pressure, thus contributes to touch and limb proprioception in a minor way o Plays a major role in relaying information related to Thermal and Nociception to higher brain centres  All levels of the Sensory processing Hierarchy act on the AL system in the same ways as for the DCML system  There is redundancy of information in both tracts, a lesion in one tract does not cause complete loss of discrimination in any of these sense, but in both causes severe loss  Example: Hemisection of the Spinal cord (caused by a serious accident) would cause tactile sensation and proprioception in the arms to be lost on the Ipsilateral side (fibres have not crossed yet), while pain and temperature sensation would be lost on the Contralateral side (fibres have already crossed upon entering the Spinal cord) Thalamus  Information from both the Ascending Somatosensory tracts like information from virtually all Sensory systems goes though the Thalamus  It also receives information from Basal ganglia and Cerebellum  Thus it is a major processing centre  Lesion in this area will cause severe Sensory and motor problems  It has become a target for treatments aimed at decreasing tremor in patients with Parkinson’s disease Somatosensory Cortex  Major processing centre for all Somatosensory modalities and marks the beginning of conscious awareness of Somatosensation  Divided into two major areas: Primary Somatosensory cortex(SI) (Brodmann’s areas 1,2,3a, and 3b) and Secondary Somatosensory Cortex (SII)  In SI kinaesthetic and touch information from the contralateral side of the body is organized in a somatotopic manner and spans four Cytoarchitectural areas, Brodmann’s areas 1,2,3a, and 3b  It is in this area that we begin to see Cross-modality processing- information from joint receptors, Muscle spindles, and Cutaneous receptors is now integrated to give us information about movement in a given body area  It provides Spatial processing which is essential to coordination of movements in space o Information like position of the body relative to the environment and position of one body segment relative to another Pg. 60  Contrast sensitivity is very important to movement control since it allows the detection of the shape and edges of objects  The Somatosensory cortex processes incoming information to increase contrast sensitivity so that we can easily identify and discriminate between different objects through touch o Receptive fields of the Somatosensory neurons have an excitatory centre and inhibitory surround  The Inhibitory surround aids in two point discrimination through Lateral inhibition  Lateral inhibition- the cell that is excited inhibits the cells next to it thus enhancing contrast between excited and nonexcited regions of the body  Comes in at the level of Dorsal columns and at each subsequent step in the relay Pg. 61  Receptive fields of neurons in the Somatosensory cortex are not fixed in size- injury and experience can change their shape Association Cortices  In Association Cortices we see the transition from perception to action, you also see the interplay between cognitive and perceptual processing  It is found in Parietal, Temporal, and Occipital lobes, include centres for higher level sensory processing and higher level abstract cognitive processing  Area 5 of the parietal cortex is a thin strip posterior to the Postcentral gyrus  After intermodality processing has taken place within are SI, outputs re sent to Area 5 which integrates information between body parts  Area 5 connects to Area 7 of the Parietal lobe  Area 7 also receives processed visual information thus it combines eye-limb processing in most visually triggered or guided activities  Lesion in Area 5 or 7 in either humans or animals cause problems with the learning of skills that use information regarding the position of the body in space, and affect the ability to interpret this type of information also  The Parietal love participates in processes involving attention to the position of and manipulation of objects in space  Damage to the Parietal lobe have problems with body image an perception of spatial relations which may be very important in both postural control and voluntary movement  Agnosia- lesions in the right Angular gyrus (nondominant hemisphere) show complete neglect of the contralateral side of body, objects and drawings, inability to recognize. Ex if they see their own hand they may not recognize it Pg. 62  Constructional Apraxia- larger lesions may cause the inability to operate and orient in space or the inability to perform complex sequential tasks. o If asked to copy a picture, only half of the figure might be drawn  Right handed patients that have lesions in the Left Angular gyrus (dominant hemisphere) may show symptoms like confusion of left and right  If lesions in both sides they have problems with Visual stimuli, in using vision to grasp an object and making voluntary eye movement to a point in space Topic 5- Pg. 62, 64-67 Visual System  Vision allows us to identify objects in space and to determine their movement, considered an Exteroceptive sense  Visual Proprioception- it gives us information not only about the environment but also about our own bodies- where our body is in space, about the relation of one body part to another and about the motion of our bodies  Vision plays a key role in control of posture, locomotion, and manipulatory function Peripheral Visual System Photoreceptor Cells  Light enters the eye through the Cornea and is focused by the Cornea and Lens on the Retina at the back of the eye  Light must pass through all layers of the Retina before it reaches the Photoreceptors  There are two types of Photoreceptors: the Rods and Cones  Cones are functional for vision in normal daylight and re responsible for colour vision  Rods are responsible for vision at night, when the amount of light is very low and too weak to activate the cones  Right at the Fovea the rest of the layers are pushed aside so the Cones can receive the light in it clearest form  The Blind spot- where the optic nerved leave the retina has no photoreceptors, thus we are blind in this one part of the retina  Except for the fovea there are 20 times more Rods than Cones in the Retina  Cones are more important than Rods for normal vision because their loss causes Legal blindness while total loss of Rods causes only night blindness  The Visual system has to identify if objects are moving  There are two separate pathways to process them  Contrast sensitivity enhances the edges of objects, giving us greater precision in perception Vertical Cells  In addition to Rods and Cones, the Retina contains Bipolar cells, and Ganglion cells which can be consider Vertical cells since they connect in series to one another but have no lateral connection  Rods and Cone synaptic contact with Bipolar cells  Ganglion cells relay information to the CNS by sending axons to the Lateral Geniculate Nucleus and Superior Colliculus as well as to Brainstem nuclei Pg. 63 Horizontal cells  Another class of cells in the Retina  These neurons modulate the flow of information within the Retina by connecting the Horizontal and Amacrine cells  Horizontal cells mediate interactions between the receptors and bipolar cells  Amacrine cells mediate interactions between Bipolar and Ganglion cells  The Horizontal and Amacrine cells are critical for achieving Contrast sensitivity Pg. 64  There are two types of pathways that involve Bipolar cells, Direct pathway and a Lateral pathway  In the Direct pathways, cones (or rods) connect directly to Bipolar cells with either “on- centre” or “ off centre” Receptive fields  Receptive field (RF) of a cell is the specific area of the Retina to which the cell is sensitive, when the part of the retina is illuminated o This can be either Excitatory or Inhibitory, increasing or decreasing the cell’s membrane potential o Receptive fields of Bipolar and Ganglion cells are circular  On centre means that the cell has an excitatory central portion on the RF o Gives very few AP in the dark and are activated when their RF is illuminated, when illuminated it inhibits the effect of stimulating the centre  Off centre refers to the opposite case of an inhibitory centre and excitatory surround o Also shows inhibition when light is applied to the centre of their RF, and fire at the fastest rate just after the light is turned off  Ganglion cells are also influenced by the activity of Amacrine cells- transmits inhibitory inputs from nearby Bipolar cells to the Ganglion cell, ioncreasing contrast sensitivity  These two types of pathways (on- off centres) for processing retinal information are two examples of PDP  Ganglion cells send their axons, via the Optic nerve, to three different regions in the Brain, the Lateral Geniculate Nucleus, the Pretectum, and the Superior Colliculus Central Visual Pathways Lateral Geniculate Nucleus  Left half of the visual field projects on the Nasal (medial next to the nose) half of the Retina of the left eye and the Temporal (lateral) half of the Retina of the right eye  Right visual field projects on the Nasal half of the Retina on the right eye and the Temporal half of the Retina of the left eye  Optic nerves from the Left and Right eyes leave the retina at the Optic disk in the back  They travel to the Optic chiasm where the nerves from each eye come together, and axons from the Nasal side of the eyes cross, while Temporal side do not cross  At this point the Optic nerve becomes the Optic tract b/c of this cross both Tracts have images of both eyes  One of the targets of cells in the Optic tract is the LGN of the Thalamus  LGN has 6 layers that map the Contralateral visual field  The Fovea of the Retina which we use for high acuity vision is represented much more than the Peripheral area  Each layer of LGN only gets input from one eye  First two layers (most ventral) are the Magnocellular (large cell) layers, and layers four to six are called the Parvocellular (small cell) layers Pg. 65  Magnocellular layers appear to be involved in the analysis of movement of the visual image (they have high temporal resolution, detecting fast pattern changes) and the course details of an object (they have low spatial resolution), with no response to colour o More important for motor functions such as balance for which movement of the visual field gives us information about body sway and in reaching for moving objects  Parvocellular layers function in color vision and more detailed structural analysis (high spatial resolution and low temporal resolution) o Important for final phases of reaching for an object when we need to grasp it accurately  Only 10-20% of input to LGN comes from the Retina with the rest coming from the Cortex and reticular formation of the Brainstem  One of the most important aspects of Sensory processing is choosing the inputs that are most important for an individual to attend to in a given moment and that each individual may have very different perceptions of a given event according to the sensory inputs their system allowed to move to higher perceptual centres Superior Colliculus  Ganglion cells axons in the Optic tract also terminate here  Superior Colliculus is located posterior to the Thalamus, in the roof of the Midbrain  Hypothesized that it maps the visual space around us in terms of not only visual but also auditory and Somatosensory cues  Not mapped in terms of density of receptors in a particular area but in terms of their relationship to the Retina  Areas closer to the Retina (nose) are given more representation than areas far away (hands)  Controls Saccadic eye movements that cause the eye to move toward a specific stimulus  Superior colliculus then sends outputs to (a) regions of the brainstem that control eye movements (b) the tectospinal tract, mediating the reflex control of the neck and head (c) the tectopontine tract, which projects to the cerebellum for further processing of eye- head control Pretectal Region  Ganglion cells also terminate here which is just anterior to the Superior Colliculus  Important for visual reflex centre involved in Pupillary eye reflexes in which the pupil constricts in response to light shining on the Retina Primary Visual Cortex  From LGN axons project to the Primary Visual Cortex(V1) (also called Striate cortex) to Brodmann’s area 17 which is in the Occipital lobe  Ocular dominance columns- inputs from the two eyes alternate throughout the Striate cortex  From V1 to Brodmann’s area 18 (V2), neurons from V2 project to Medial temporal (MT)(Area 19) to Inferotemporal cortex (Areas 20,21) and Posterior Parietal cortex (Area 7)  Outputs also go to the Superior colliculus and project back to the LGN (feedback control)  Receptive fields in the Visual cortex are Linear, the light must be in the shape of a line, bar, or an edge to excite them- these Cells are classified as Simple or Complex  Simple cells- respond to bars with an Excitatory centre and Inhibitory surround  They also have specific Axis of orientation for which the bar is most effective in exciting the cell- All Axis of orientation for all parts of the Retina are represented in the Visual Cortex  For many Complex cells the most useful stimulus is movement across the field  Pg. 66  Blobs- cells organized in a cylindrical shape that respond t colour stimuli  Visual cortex is divided into Orientation columns with each column consisting of cells with one Axis of orientation, Blobs, which are activated more by colour than orientation, and Ocular dominance columns receiving input from the Left versus the Right eye  Hypercolumns coined by Hubel & Wiesel are horizontally connected to the other columns with same response properties- depending on inputs the Axis of orientation may change thus it is responsive to the context/ environmental changes Higher Order Visual Cortex  Higher order cortices are involved in the integration of Somatosensory and Visual information underlying Spatial orientation, an essential part of all actions  Ungerleider and Mishkin have proposed a model of two visual systems with Parallel pathways through which visual information is processed  Proposed that these two systems to can be traced back to the two main subdivisions of the Retinal Ganglion cells, Magnocellular layers and Parvocellular layers  One of the pathways is called the Dorsal stream which terminates in the Posterior Parietal region o Impaired when solving tasks involving spatial visual cues and less for visual pattern discrimination and recognition  Ventral stream terminates in the Inferotemporal cortex o Monkeys with lesion in the Inferotemporal cortex was very impaired in visual pattern discrimination and recognition, but less impaired in solving tasks involving spatial visual cues  Pg. 67  Patients with Optic Ataxis (due to lesions in the Parietal areas) have problems not only with reaching in the right directions, but also with positioning their fingers or adjusting the orientation of their hand when reaching toward an object, and trouble with adjust grasp to reflect size of the object they are picking up  Ventral stream plays a major role in the perceptual identification of objects, while Dorsal stream mediates the required sensorimotor transformations for visually guided actions directed at those objects  Binding problem- the process by which the brain recombines information processed in its different regions  Recombination of information requires attention  One neural mechanism hypothesized to contribute to binding everything into one cohesive experience is that information from neural events in many different parts of the cortex (visual, auditory, kinaesthetic, memory) is integrated by the cortex to produce perceptual binding through synchronizing their neural activation patterns, leaving all other neural activations nonsynchronized. This creates a Global neuronal workspace  Multiple inputs compete for access to an Attentional network and those that win become the contents of conscious experience Pg. 70 Topic 6- Pg. 70-74 Motor Cortex Primary Motor Cortex and Corticospinal Tract  Motor cortex is located in the Frontal lobe and consists of a number of different processing areas including the Primary motor cortex (M1) and four pre-motor cortical areas, including Supplementary motor area (SMA), Cingulate motor area (MII)(inferior to the SMA), two Lateral premotor areas, the Ventral and Dorsal premotor cortex  These areas interact with Sensory processing areas in the Parietal lobe and also with Basal ganglia and Cerebellar areas to identify where we want to move, to plan movement, and to execute our actions  All three of these areas have their own Somatotopic maps of the body, so that if different regions are stimulated, different muscles and body parts move  Primary motor cortex (Brodmann’s Area 4) contains very complex map of the body  Early experiments suggested a one to one correspondence between cells stimulated in the Primary motor cortex and the activation of individual Gamma motor neurons in the Spinal cord HOWEVER more recently it has been shown that the same muscles can be activated from several sites in the cortex, suggesting that neurons from several motor cortex areas project to the same muscle  Stimulation of the neurons in the Premotor areas typically activate multiple muscles at multiple joints giving rise to more coordinated movements  The Motor map or Motor homunculus is similar to the Sensory map in the way it distorts the representation of the body Pg. 71  Areas that require more detailed control are highly represented  Suggested that Transcortical pathway might be used in parallel with the Spinal reflex pathway to give additional force output in the muscles when an unexpected load is encountered during movement  Outputs from the Primary motor cortex contribute to the Corticospinal tract (Pyramidal tract) and often make excitatory monosynaptic connections onto Alpha motor neurons Pg. 72  The Corticospinal tract descends ipsilaterally from the cortex through the Midbrain, and the Medulla, near the junction of the Medulla and Spinal cord, most (90%) cross to form the Lateral Corticospinal tract, the remaining 10% continue uncrossed to form the Anterior Corticospinal tract, the AC tract cross just before they terminate in the Ventral horn  Primary Motor cortex controls both absolute force and the speed of a movement  Specific neurons in the Cortex, activated when we pick up an object, may remain totally silent when we make a similar movement, such as a gesture in anger. There are parallel pathways for carrying out an action sequence o So when training a patient in one situation we cannot assume that it will carry to other activities requiring the same set of muscles Supplementary Motor and Premotor Areas  Movements that are initiated internally are controlled primarily by the SMA o Also contributes to activating the motor programs involved in learned sequences o Learning of these sequences involve the Pre-supplementary motor area o Pre-SMA is rostral extension of the SMA o When sequences become overlearned with extensive training, the control of the movement sequence can be transferred to the Primary motor cortex  Movements that are activated by external stimuli (visual cue: traffic light changing) are controlled by the Lateral Premotor area (Dorsal and Ventral premotor cortex) o Associating a given sensory event with a movement to be made o Also defined as Associative learning o Monkey’s with lesions in this area are unable to learn new tasks involving associating a specific stimulus with a movement they are to make, although they can execute movement without a problem  Premotor neurons were more active when a sequential task was visually guided  SMA neurons were more active when the sequence was remembered and self-initiated  SMA specialized for controlling internally referenced motor output o Lesions disrupt retrieval of self-initiated movements  PMA specialized for control of externally referenced motor acts o Lesions cause impairment of movements in accordance to visual cues  SMA receives inputs from the Putamen of the Basal ganglia  Parkinson’s disease patients have a depletion of dopamine in the Putamen, these patients have difficulty with self-initiating movements such as walking  Parkinson’s causes impaired input to the Supplementary cortex which results in Bradykinesia or slowness in initiating movement  Blood flow increase in Primary motor and Sensory cortex- Simple task (1 finger)  Blood flow increase in the SMA, bilaterally, PM and Sensory cortex- Complex task (4 fingers touching the thumb in different ways)  Blood flow increase in SMA- just rehearse but not perform task  Two separate pathways from the Parietal cortex to the Premotor areas control reaching and grasping  Reaching pathway originates in the Parieto-occipital area (PO) and terminates in the Dorsal premotor area (PMd) o Uses visual informa
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