TEXTBOOK CHAP 17,20,27,33 PDF

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➔ Chapter 17 - Upper Motor Neuron Control of the Brainstem andSpinal Cord:Upper Motor Neurons: - Arise from cell bodies in higher centres and descend to influence local circuits in the brainstem and spinal cord - These circuits organise movement by coordinating the activity of the lower motor neuron...

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➔ Chapter 17 - Upper Motor Neuron Control of the Brainstem and Spinal Cord: Upper Motor Neurons: - Arise from cell bodies in higher centres and descend to influence local circuits in the brainstem and spinal cord - These circuits organise movement by coordinating the activity of the lower motor neurons that innervate different muscles - Organisation of descending motor control: The Corticospinal and Corticobulbar Tracts: - Corticospinal Tract: Pathway carrying motor information from the motor cortex to the spinal cord, is essential for performance of discrete voluntary movements i.e. hands and feet - Corticobulbar Tract: Pathway carrying motor information from the motor cortex to brainstem nuclei Functional Organisation of the Primary Motor Cortex: - Topographic or somatotopic organisation of primary motor cortex which means neighbouring body parts represented in neighbouring cortical tissue - Wilder Penfiled was the first to systematically map somatotopic organisation of human primary motor cortex - Somatotopic organisation also occurs in other cortical areas including the premotor area (PMA) - Can be distinguished from other motor areas in 2 primary ways: - Architectonics - output layer V contains distinctive large diameter pyramidal neurons ( Batz cells) - Electrophysiology - low intensity electrical stimulation elicits movement What do Motor Maps Represent? - Early experiments implied fine-scale topographic representation of individual muscles but recent work instead suggests that this map represents movement and not muscles - One to many mapping - individual M1 sites control multiple muscle groups that contribute to the generation of meaningful actions - Many to one mapping - stimulation of many individual sites spread over a relatively wide region (2-3mm) of M1 can generate contractions in a single muscle

M1 represents movements, not muscles: - Evidence from microstimulation studies suggests this notion - The most powerful evidence is that M1 represents movements not muscles is as each time the monkey is stimulated and the hand comes to the mouth, very different muscles are associated with that movement Spike-triggered Averaging: - Measures the effects and influence of upper motor neurons on lower motor neurons in the brainstem and spinal cord - Correlates timing of cortical neuron discharge with onset times of muscle contractions - Measures influence of individual cortical neurons on a population of lower motor neurons in the spinal cord and on muscle activity and movement - Individual upper motor neurons contact a number of lower motor neuron pools in the spinal cord and are involved in producing activations in a number of different muscles - The group of muscles activated by an individual upper motor neuron is called the muscle field - Provides further evidence for movement representation not muscle representation in the primary motor cortex Spatial or Directional Tuning: - Individual neurons are tuned to different spatial locations Premotor Cortex: - Many other frontal and parietal cortical areas support motor functions including the premotor cortex - Premotor neurons help control movement both indirectly via reciprocal connections with primary motor cortex and directly via axons projecting through corticobulbar and corticospinal tracts - 30% of axons in the corticospinal tract originate in premotor cortex - Many premotor neurons involved in motor preparation rather than the initiation of movement - Elevated firing with the appearance of a trained visual cue indicating an upcoming reach

Mirror Neurons:

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Subset of neurons in the ventrolateral portion of premotor cortex responding both in preparation for upcoming movement and when the same action is observed being performed by another individual Involved in imitation learning

Brainstem Circuits Supporting Posture Maintenance and Control: - The reticular formation; complex network of circuits in brainstem and vestibular nuclei that provides feedback to the spinal cord essential for posture maintenance and control e.g if posture has changed - Direct projections from vestibular nuclei to spinal cord provide sensory feedback about postural changes detected by vestibular labyrinth - Neurons in the reticular formation initiate anticipatory or feedforward postural adjustments based on outbound motor commands originating in the cortex Damage to Descending Motor Path - Upper Motor Neuron Syndrome: - Damage to the descending motor pathways gives rise to symptoms referred to as upper motor neuron syndrome - Damage cases an immediate flaccidity of muscles on the contralateral side of the lower face and body, hypotamia. The Babinski sign (stroking sole of foot elicit extension of big toe but also fanning of other toes), spasticity (increased muscle tone, hyperactive stretch reflexes and clonus), loss of ability to perform fine movements

Chapter Summary: - One set of UMN originated from neurons in the frontal lobe and includes projections from the primary motor cortex and the nearby premotor area - Premotor cortices responsible for planning, initiating and controlling complex sequences of voluntary movements - Primary Motor Cortex influences movement directly by contracting LMN and local circuit neurons in the spinal cord and brainstem and indirectly by innervating neurons in the brainstem centres which in turn project to LMN and circuits - Another set of UMN originate from brainstem circuits i.e. reticular formation and the vestibular nuclei - Reticular formation is important in feedforward control of posture - The neurons in vestibular nuclei project to the spinal cord and are important in feedback postural mechanisms

➔ Chapter 20 - Eye Movements and Sensory Motor Integration: What Eye Movements Accomplish: - Important as they are behaviourally important e.g most animals have eye movements which is behaviourally important in their motor repertoire - Important in survival i.e searching for food, scanning for dangers and risks - Important in social settings and contexts and can be used to divert attention or engage/grasp attention - Eye movements have several major advantages as model system for investigating sensorimotor integration; eye movements can be accurately measures, only 6 muscles control the position of each eye (each of which plays specific roles in adjusting eye position) and neural circuits controlling eye movements do not need to compensate for variable loads (eyes essentially maintain same volume over life span) - To pick up high resolution about things in the world and not just the fovea (which would be limited from the rest of the visual features of the environment) - Visual fades when retinal images are stabilised Actions and Innervations of Extraocular Muscles: - Three antagonistic pairs responsible for controlling all eye movement; each movement controlled by a separate pair of muscles - These muscles are responsible of movements of the eye along three different axes; horizontal (either toward the nose; adduction, or away from the nose; abduction), vertical (either elevation or depression) and movements that bring the top of the eye toward to nose (intorsion) or away from the nose (extorsion) - Horizontal movements are controlled by the medial and lateral rectus muscles; medial rectus muscle is responsible for adduction while the lateral rectus muscle is responsible for abduction - Vertical movements are controlled through co-ordinated action of two pairs of muscles; the superior and inferior rectus muscles are activated depending on whether the person is looking up or down as well as inferior and superior obliques - Elevation (vertical movement); due to action of superior rectus and inferior oblique muscles - Depression (vertical movement); due to action of inferior rectus and superior oblique muscles Types of Eye Movements and their Functions:

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Stabilising vs Shiing Gaze: - Stabilizing eye movements include the vestibulo-ocular and optokinetic, which stabilize gaze in response to body motion, world motion or both - Shiing gaze eye movements include saccades, smooth pursuit and vergence, which allow to destabilise gaze and move gazr to options of interest in the environment

Stabilising:

Vestibulo-ocular: - Stabilizing gaze due to self motion e.g. allowing you to stabilize your gaze on a merked cross whilst moving head from side to side - Reflex Response to automatically compensate for head moment by moving the eyes the same distance (at the same velocity) but in the opposite direction Optokinetic: - Optokinetic system is sensitive to global or full-field visual motion produced by slow rotational movements - This system plays an essential role in stabilizing the visual image on the retina by producing compensatory eye movements in the direction of global visual motion - Stabilizing gaze due to world motion

Shiing:

Saccades: - Shiing gaze to objects of interest e.g. diverting gaze to faces - Saccades are rapid, ballistic, highly stereotyped movement that change the direction of gaze of fixation - Can be voluntary or occur involuntary whenever the eyes are open - Can reflect knowledge of a task domain (task specific) - Saccades are ballistic; ballistic movement cannot be modified by new information once it is initiated, so the saccade generating system doesn't respond to subsequent changes in target position during a saccade Smooth Pursuit: - Shiing gaze to track moving objects e.g a bouncing ball - Under voluntary control (observer can decide whether or not to

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track a moving stimuli) Difficult to make a smooth pursuit movement in the absence of a moving visual target

Vergence: - Shiing gaze in depth - Vergence movements align fovea of each eye with targets located at different depths - Unlike other eye movements, where both eyes in same direction (conjugate), mergence movements involve both eyes move in different directions (disconjugate)

Chapter Summary: - The reticular formation of the pons and midbrain provides the basic circuitry that mediates movements of the eye - Descending projections from upper motor neurons in the superior colliculus and the frontal eye field enervate gaze centres in the brainstem - this provides a basis for integrating eye movements with sensory information which indicates the location of objects in space - Eye movements are also under the control of the basal ganglia and cerebellum which ensures the proper initiation and successful execution of motor behaviours which allows use to interact efficiently with visual environment

➔ Chapter 27 - Cognitive Functions and Organisation of the Cerebral Cortex: A Primer on Cortical Structure: - Most of the cortex that covers the cerebral hemisphere is neocortex (cortex that has six layers or laminae) - Each layer of the neocortex has more or less distinctive populations of cells based on their densities, sizes, shapes, inputs and outputs - Cytoarchitectonic areas are subdivisions of the cerebral cortex - Each cortical layer has a primary source of inputs and a primary output target and each area has connections in the vertical axis (called columnar or radial connections) and connections in the horizontal axis (called lateral or horizontal connections) - Cells with similar functions tend to be arrayed in radially aligned groups that span all the cortical layers and receive inputs that oen are segregated into radial bands (or columns) Unique Features of the Associated Cortices: - Receive input from thalamic nuclei that receive input from the cortex (instead of peripheral sensory) - information has already been processed in the primary sensory areas - Majority of input comes from corticocortical connections (between cortical regions) - ipsilateral and inter hemispheric - Subcortical inputs from brainstem (dopaminergic, noradrenergic, cholinergic) - Each association area has a distinct (but overlapping) subset of thalamic, corticocortical and sub-cortical connections The Parietal Association Cortex: - Responsible for mediating attention and has the capacity to select what is relevant and to ignore what is not - Critical for bringing information together for awareness and is crucial for mapping space - The right parietal lobe is more important for attention than the le; patient studies tell us that the right parietal lobe is particularly important for mediating attention - Both parietal lobes are essential and are involved in representing space; need parietal function to know where something is and to integrate multiple sources of information to guide attention and movement

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If this part of the brain is damaged; can lead to visual neglect syndrome or contralateral neglect which is a deficit of attention to one side of space Damage to both sides of the parietal lobe can lead to Balint’s syndrome; optic ataxia - losing the ability to map space, cannot perceive more than one object at a time, cannot reach for things in space

The Temporal Association Cortex: - Responsible and involved in recognising and identifying stimuli - Damage to the temporal lobe can lead to difficulty recognising, identifying and naming objects (which is known as agnosia; not knowing - different from neglect as patients are aware of objects but are unable to report what they are) The Frontal Association Cortex: - Essential and allows for planning, decision making and execution - Involved in selecting, planning and executing appropriate behaviour - Involved in highly important functions that allow us to operate functionally in society - The largest brain lobe and contains the most cytoarchitectonic areas - The most elaborate lobe in humans relative to other animals and is the last the mature; not fully developed until about the age of 25 - Damage to this lobe leads to devastating and diverse clinical effects - Damage to the frontal lobe causes a wide range of cognitive deficits including impaired restraint, disordered thoughts, perseveration and inability to plan Chapter Summary: - The association cortices mediate cognitive functions - ability to attend to, identify and act meaningfully in response to complex external or internal stimuli - The purpose of association areas of the brain have been established through descriptions of patients with cortical lesions, functional brain imaging and behavioural and electrophysiological studies of non-human primates i.e monkeys - Parietal cortex - involved in attention and awareness of the body and stimuli they - Temporal cortex - involved in recognition and identification - Frontal cortex - important in guiding complex behaviour by planning responses, matching behaviour to demands of situation

➔ Chapter 33 - Speech and Language: Representation of Language in the Brain: - Frontal and temporal association cortices of the le central hemisphere are important for verbal aspects of human language - Language abilities are both lateralized and localised - Language in the brain is concerned with the motor planning and control of the larynx, pharynx, mouth and tongue - structures that produce speech sound

Aphasias: - A collection of syndromes that diminish or abolish the ability to comprehend and/or to produce language to communicate meaningfully while sparing the ability to perceive the relevant stimuli and to produce intelligible words - These syndromes can occur as a result of damage to specific brain regions, compromising essential language functions while leaving the sensory and motor characteristics of communication intact - Patients will be unable capacitate, recognise or employ the meaning of words correctly - depriving these individuals of linguistic understanding, grammatical and syntactic organisation Motor or Expressive Aphasia or Broca’s Aphasia:

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Lesion of the le frontal lobe in a region called Broca’s area Affects ability to produce language efficiently

Sensory or Receptive Aphasia or Wernicke’s Aphasia:

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Damage to the le temporal lobe Causing difficulty understanding spoken language

Conduction Aphasia:

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Lesions to the pathways connective the relevant temporal and frontal regions i.e. the arcuate fasciculus linking the broca’s and wernicke’s area Resulting in inability to produce appropriate responses to heard communication even though the communication is understood

Split Brain: - Roger Sperry and colleagues in the 1960s and 1970s - discovered that patients were able to name objects held in the right hand without difficulty but when an object was placed in their le hand, it could not be named Sign Language: - Brain areas are broadly organised for processing symbols needed for social communication - Sign language has various components of spoken and head language; grammar, syntax and emotional tone - A critical period of language acquisition - Neural circuitry is susceptible to modification during early development - this gradually diminishes with maturation - The window for extensive neural modification supporting a behaviour is referred to as the critical period (which is also known as the sensitive period)

Reading and Dyslexia: - Dyslexia is a common problem that affects a child’s ability to read; they are poor readers and have difficulty in processing speech sounds and translating visual to verbal information - this does not mean that they cannot be normal or above normal in intelligence - They may have problems with writing, may be poor spellers and may be prone to errors arising from letter transposition - Subtypes; surface dyslexia, phonological, poor comprehenders/hyperlexia, letter identification/neglect dyslexia, letter position dyslexia, deep dyslexia, attentional dyslexia, fluency dyslexia Do other animals have language? - There is evidence of highly sophisticated systems of communication in animals such as; bees, birds, monkeys and whales - Humans language is unique in its ability to associate specific meanings with arbitrary symbols and infinitum Chapter Summary: - Clinical observations of patients with split brain patients, mapping prior to neurosurgery, transient anaesthesia of a single hemisphere and non-invasive imaging techniques such as PET and fMRI have extended knowledge - Perisylvian cortices of the le hemisphere are important for normal language in the vast majority of humans - The right hemisphere contributes to language and gives emotional tone...