Neurophysiology- Motor System PDF

NEUROPHSIOLOGY- MOTOR SYSTEM  MOTOR CENTRES INCLUDE Spinal cord Brain stem Basal Ganglia Cerebellum Motor Cortex Motor system control voluntary muscles. Muscle contraction brought about by impulses from the following sources:  α-motor neurons...

NEUROPHSIOLOGY- MOTOR SYSTEM  MOTOR CENTRES INCLUDE Spinal cord Brain stem Basal Ganglia Cerebellum Motor Cortex Motor system control voluntary muscles. Muscle contraction brought about by impulses from the following sources:  α-motor neurons γ-motor neurons Interneurons Sensory or afferent signals Motor system commonly divided into: Upper motor neurons Lower motor neurons Lesion of upper motor neuron causes spastic paralysis and hyperactive stretch reflexes Lesion of lower motor neuron causes flaccid paralysis, muscular atrophy and absence of reflex responses.  Motor unit Definition: This is a motor neuron and all the muscle fibres it innervates. Some motor units contain few muscle fibres while others contain large number of fibres. The function of the muscle determines the number of fibres per motor unit.  Factor involved in the gradation of muscle tension Recruitment of motor units. This is the first factor required in the gradation of muscle tension. More and more motor units are brought into play as the required muscle tension increases. Changes in firing frequency of motor units. Different motor units have different firing frequencies and the firing frequency of a single motor unit may vary from time to time as muscle tension varies.  Length of the muscle: The tension developed in a muscle increases as the length of the muscle increases. Maximum tension is obtained at the resting length Asynchronous discharge of motor units: Muscle fibres discharge out of phase with one another. Asynchronous discharge prevents jerky movement, thus allowing for smooth contraction. Individual muscle fibre response merge into smooth contraction of the whole muscle  NEURONAL NETWORK Divergence Convergence Temporal and spatial facilitation Synaptic potentiation Occlusion Simple inhibitory circuits Some neuronal networks boost weak signals while others suppress over activity. Neuronal network recall often in various parts of the brain.  Divergence Axons divide into collateral branches that synapses with few or many other neurons. Functional importance: (i)Information is made available simultaneously to all parts of CNS (ii) Boost incoming signals (iii) Serves as a safety factor that ensures that information get to their destination. Convergence Some neurons receive input from many other neurons-this is called convergence Functional importance is that motor neurons integrates both excitatory and inhibitory events occuring at its memebrane.  Temporal and spatial facilitation Temporal: The effect of several stimuli occuring in quick succession is greater than the sum of their individual stimuli. It is an increase in excitability brought about by several EPSPs. Spatial: The effect of several stimuli occurring simultaneously is greater than the sum of their individual stimuli. Similarly, many small IPSPs may add up to produce a large IPSP. EPSPs and IPSPs from different sources may cancel each other out so that the result is the net sum of both, or even zero  Synaptic Potentiation: Repeated use of a synapse leads to considerable increase in synaptic potential. Important in learning and memory. Occurs mainly in the hippocampus. Occlusion: Response of 2 or more stimuli less than sum of their individuals responses.  Simple inhibitory circuits Antagonist inhibition Renshaw inhibition Surround inhibition  REFLEXES Definition: A stereotyped reaction of the CNS to sensory stimuli. Components: Reflex arc made up of: -Receptors -Afferent pathway -Integration centre -Efferent pathway -Effectors  Types of Reflexes Monosynaptic reflexes - Have only one central synapse e.g Stretch reflexes Bisynaptic reflexes - Have 2 central synapses e.g Golgi Tendon Organ reflex Polysynaptic reflexes - Have more than 2 central synapses e.g. Withrawal, respiratory, cardiovascular, sexual, cough, micturition, defeacation reflexes etc,  Monosynaptic Reflexes Stimulus: Stretch of the muscle Receptors: Muscle spindle Afferent: Ia and II fibres Int. Centre: Spinal cord Efferent: Aα motor neurons Effectors: Extrafusal fibres of the muscle Response: Contraction of the extrafusal muscles of the affected muscle.  Examples of Stretch Reflexes Knee jerk reflex Stimulus: Tapping of the patellar tendon Response: Extension of the Knee Efferent: C5- C6 segments of the spinal cord Biceps jerk reflex Stimulus: Tapping the biceps tendon Response: Extension of the elbow/Twitch of the biceps Efferent: C5- C6 segments of the spinal cord  Triceps jerk reflex Stimulus: Tapping the triceps tendon Response: Extension of the elbow Efferent: C6- C8 segments of the spinal cord Brachioradialis jerk reflex Stimulus: Tapping the tendon 4cm above wrist Response: Flexion of the elbow Efferent: C5- C6 segments of the spinal cord Ankle jerk reflex Stimulus: Tapping the achilles tendon Response: Plantarflexion of the foot Efferent: S1- S2 segments of the spinal cord Muscle Spindle  Structure of the Muscle Spindle Muscle spindle made up of 2-10 intrafusal fibres Intrafusal fibres lie in parallel with extrafusal fibres 2 Types of intrafusal fibres: (i)Nuclear Bag and (ii)Nuclear Chain fibres Nuclear bag fibres have dilated central portion that contain many nuclei. Nuclear chain fibres are thinner and shorter Each intrafusal fibre has contractile ends and central portion which is not contractile  Innervation of the muscle spindle Afferent : Groups Ia and II fibres Ia-Primary/dynamic afferent, have annulospiral endings on both nuclear bag and nuclear chain fibres II- Secondary/static afferent, have flower-spray ending only on nuclear chain fibres Efferent: 2 types: β and γ efferents β-efferent innervate both intrafusal and extrafusal fibres. γ-efferent innervate only intrafusal fibres, made up of dynamic and static gamma efferents. Dynamicγ innervate mainly nuclear bag fibres while static γ innervate mainly nuclear chain fibres  Central connections of the muscle spindle Has only 1 central synapse i.e afferents end directly on motor neurons supplying extrafusal fibres Time b/w application of stimulus and response is called reaction time e.g. in humans, reaction time for knee jerk reflex is 19-24ms Central delay: The time taken for the reflex activity to pass through the spinal cord e.g. central delay for knee jerk is 0.6-0.9ms  Functions of muscle spindle Muscle spindle and its reflex connections constitute a feedback device that operate to maintain muscle length i.e they detect changes in muscle length. They also detect rate of change in muscle length. Ia fibres carry impulses concerning changes and rate of change in muscle length while group II fibres carry impulses about changes in muscle length only.  BISYNAPTIC REFLEXES Golgi tendon organ reflex is a good example GTO reflex also called inverse stretch or jack-knife reflex Stimulus: Muscle tension or load on the muscle Receptors: Golgi tendon organ. They lie in series with extrafusal muscle fibres and also in series with the load which the muscle bears. Thus, their stretch is proportional to the tension developed by the muscle. They have low threshold. Afferent: Group Ib fibres  Integrating centre : Spinal cord. Ib fibres end on inhibitory interneurons in the spinal cord Efferents: α motor neurons Effectors: Homonymous extrafusal muscle fibres Response: Relaxation of the muscle fibres i.e inhibition of the homonymous extrafusal fibres. Function: A tension control system that prevents overloading of the muscle, thus preventing damage by forces pulling on them  POLYSYNAPTIC REFLEXES Withdrawal reflex is a good example Stimulus: Painful or noxious stimulus Receptors: Free nerve endings Afferents: Aδ and C fibres Integration centre: Spinal cord Efferent: α motor neurons Effectors: Extrafusal muscle fibres Response: (i) Contraction of the ipsilateral flexor muscle, thus producing flexion or withdrawal of part of the body from the stimulus. (ii) Inhibition of the ipsilateral extensor muscle through inhibitory interneurons  Application of a strong stimulus will produce the following additional responses: (iii) contraction of contralateral extensor muscles, hence the reflex is called cross extensor reflex (iv) Relaxation of the contralateral flexor muscle through inhibitory interneurons Responses (iii) and (iv) in turn support the body and position the subject to run away from the offending stimulus Characteristics of Withdrawal reflex It is protective in function; the limbs are flexed away from the offending stimulus Withrawal reflex is pre-potent i.e. they prevent the spinal pathways from any other reflex activity occuring at that time. Strong painful stimulus causes after-discharge i.e. prolonged and repeated firing associated with continous bombardment of motor neurons by impulses arriving from complicated and circuitous polysynaptic pathways Spatial and temporal facilitation may occur Local sign may occur i.e. exact response depends on the location of the stimulus Occlusion may occur  VENTRAL HORN CELLS These are nerve cells within the spinal cord that are concerned with motor function They are located in the ventral horn of the spinal cord and are collectively known as the ‘final common pathway’ They represent the final output from CNS to the skeletal muscle They also serve as terminals for descending pathways from higher centres and afferents from receptors. Distribution of ventral horn cells is as follows: Medially arranged neurons innervate muscles of the trunk The most lateral neurons innervate the extremities The most dorsal neurons innervate the flexors The most ventral neurons innervate the extensors.  RETICULAR FORMATION Occupies the mid-ventral portion of medulla and midbrain It consists of large number of small neurons arranged in a complex intertwining network Centres located in reticular formation are important for vegetative functions such as: Control of blood pressure Control of respiration Control of heart rate Adjustment of endocrine secretions Regulation of sensory input Consciousness, etc  RETICULAR ACTIVATING SYSTEM Acomplex polysynaptic pathway that receives input from the following sources: Long ascending sensory tracts Trigeminal nerve Auditory system Visual system Olfactory system All these systems funnel and shoot into RAS. RAS is non-specific in function, neurons are activated with equal facility by different sensory stimuli. Many neurons converge in RAS i.e. it is a very highly complex neuronal network It is considered to be the brain attention centre and the main centre for motivation.  RAS is the place where thoughts, internal feelings and the outside influences converge. RAS consists of ascending and descending components. The ascending part is connected to the cerebral cortex, hypothalamus and thalamus. The descending component is connected to the cerebellum and sensory nerves. The functions of RAS are under the control of some cholinergic (acetylcholine) and adrenergic (Adrenaline) neurotransmitters.  Part of RAS by-pass the thalamus to project profusely to the cerebral cortex Another part of RAS end in intralaminar and related thalamic nuclei where it projects diffusely and non-specfically to the cortex. RAS is intimately connected with the electrical activity of the whole cortex, it keeps the brain at an alert state.  ELECTROENCEPHALOGRAM (EEG) Introduction: This is background electrical activity in the brain It is a record of variations in potential and represents the algebraic summations of the points on the surface at which measurements are made. It is a record of potentials resulting from current flow between the dendrites and the cell bodies in the underlining brain cells. It is due to EPSP and IPSP; AP does not contribute to EEG. The magnitude ot the potential recorded is attenuated reflecting the fact that electrical changes have been conducted through a volume conductor.  Recording of EEG EEG can be recorded extracellularly or intracellularly In extracellular recording, the recording electrodes are placed on the skull whereas in intracellular recording, it is positioned in the brain. Such recording could be achieved via unipolar or bipolar recording method. Bipolar recording shows fluctations in potential between 2 cortical electrodes while unipolar shows the difference between a cortical electrode and a theoritically indifferent electrode maintained at zero potential.  Records obtained from EEG 1. α waves: They are large slow waves with frequency of 8-13Hz They have amplitude of about 50mV. They are obtained when the individual is at rest, eyes closed and mind wondering. They are most prominent in frontal and occipital lobes. They are called ‘synchronized EEG’. 2. β waves: They are recorded with the eyes open. They have high frequency (30-40Hz) and low amplitude They are mostly found in the frontal lobe especially precentral gyrus They are probably harmonics of α waves.  3. Theta waves They are seen during sleep They have a low frequency of about 4-7Hz and a high amplitude of about 50mV. They occur in normal children. They are probably generated in the hippocampus of the limbic system. 4. δ waves: They have high amplitude (50mV) and very low frequency of about 0.3-2.5Hz. They reflect slow changes in membrane potential of cortical neurons.  The frequency of α waves is reduced by the following: Low blood glucose level Low body temperature High arteria PCO2 Low level of glucocorticoids Forced hyperventilation Note: The frequency of α waves is increased when the conditions above are reversed. α- block (Desynchronization of EEG): This is abolition of α waves. It occurs when the eyes are open and the α waves are replaced by fast irregular low voltage waves called ‘α –block’ or ‘desynchronization of EEG’. Desynchronization is produced by sensory stimulation and correlated with arousal-alert state. In terms of neuronal arrangement, desynchronization requires stimulation up to the level of midbrain  Clinical uses of EEG Used in the diagnosis of epilepsy Useful in detecting tumors in the brain Used in detecting accumulation of fluid in the brain e.g. subdural haematoma. EEG is also useful in the diagnosis of the following: Encephalitis (an inflammation of the brain) encephalopathy (a disease that causes brain dysfunction) memory problems sleep disorders Stroke dementia  Human Sleep An awake individual is in active contact with his environment. During sleep, this is greatly interrupted Sleep Patterns There are 2 different sleep patterns: (i) REM Sleep (ii) Non-REM Sleep  REM Sleep This is called paradoxical sleep. EEG activity resemble that seen in alert/awake individuals when their eyes are open, however, sleep is not interrupted. It is marked by intense brain activity. Dreams mostly occur during REM sleep. REM sleep is thought to play a role in memory consolidation, the synthesis and organization of cognition, and mood regulation.  Changes that occur during REM sleep: Rapid eye movement Occurence of large but phasic potential occuring in groups of 3-5. These potentials originate from the pons, pass through the geniculate body to the occipital cortex. Hence they are called ‘Ponto-geniculo-occipital spikes’. Hypotonia despite the rapid eye movement. Hypotonia may be caused by activation of reticular inhibiting area in the medulla which decreases stretch and polysynaptic reflexes. There is increase in BP, hear rate and respiration. REM sleep is frequently associated with penile erection.  Non-REM Sleep This is divided into 4 stages: Stage 1: α waves appear in the drowsy state as one goes to sleep. It is replaced by θ waves of frequency 4-6 Hz with high amplitude of 50mV. Stage 2: Marked by fast waves called ‘sleep spindles’ with frequency of 10-14 Hz and amplitude of 50mV. They appear as sleep becomes deeper and deeper. HR and body temp. fall. Stage 3: This is marked by the appearance of high amplitude δ waves and ‘K-complex’. Also called slow wave sleep. Stage 4: Maximum slowing of frequency occurs at this stage. Marked by the presence of δ waves with frequency of 1-2 Hz and high amplitude of 50mV. Note: In the course of the night, an individual passes each stage 3-4 times. Thus the characteristics of deep sleep is rythmic slow waves indicating synchronization  CEREBELLUM Anatomy of Cerebellum: Cerebellum sits beside the main sensory and motor systems in the brain stem. It is connected to the brainstem on each side by superior, middle and inferior peduncles. Weighs 10% as much as cerebral cortex; surface area is 75 % that of cerebral cortex. Functionally, cerebellum is divided into 3 parts: 1. Archicerebellum/Vestibulocerebellum/ Flocculonodular lobe: - This is the oldest part of cerebellum - It has connection with the vestibular system. - It is concerned with maintenance of balance and equilibrium 2. Spinocerebellum: - Receives propioceptive input from the body and motor plan from the motor cortex. - It co-ordinates and smoothens ongoing movements; it achieves this by comparing plans with performance. 3. Neocerebellum: - This is the newest part of the cerebellum. - It is highly developed in humans. - It interacts with motor cortex in the planning and programming of movements.  Histology of the cerebellum Cerebellum has a regular and beautiful neuronal structure, hence it is often described as a ‘neuronal machine’. Cerebellar cortex contains 5 types of neurons: Purkinje, Granule, Basket, Golgi and Stellate cells. Purkinje cells are the main cells, they have huge dendrites and about 30 million of them are found in the cerebellar cortex. Purkinje cells project to the deep nuclei found in the core of the cerebellum. They are 4 deep nuclei found in the cerebellum: Fastigial, Emboliform, Globose and Dentate nuclei. Deep nuclei have huge receptive areas and Purkinje cells project to them in a systematic manner: -Purkinje cells in the medial area project to Fastigial nuclei. -Purkinje cells on the lateral area project to emboliform nuclei while those in the intervening area project to globose and dentate nuclei. The deep nuclei in turn project to various motor structures such as: vestibular nuclei, thalamus, cerebral cortex, etc.  Afferents to the cerebellum is via the: i) Climbing fibres- Specific to cerebellar function, they originate from the inferior olivary nucleus. ii) Mossy and Parrellel fibres- Non-specific in function, they provide propioceptive input from all parts of the body and motor cortex. They transmit via the pontine nuclei to the cerebellar cortex Granule cell receive input from mossy and parallel fibres and project to purkinje cells which forms the sole output of the cerebellar cortex. Basket, stellate and golgi cells are examples of inhibitory interneurons found in the cerebellum. They provide lateral inhibition and assist in making information sharper.  Functions of the Cerebellum It is involved in the maintenance of balance and posture. It receives input from vestibular nuclei and propioceptors and modulates commands to motor neurons. It is primarily concerned with co-ordination, adjustment and making movements smooth; it has the ability to programme rapid movements. It corrects the course of movements. It acts as centre for motor learning. It is involved in adapting and fine-tuning motor programs to make accurate movements. The cerebellum is involved at all levels of muscle control i.e at the spinal cord, brainstem and cerebral cortex. Cerebellum is involved in certain cognitive functions such as language.  Effects of lesion of the cerebellum 1. Difficulty in postural co-ordination such as: standing upright, Tendency to dizziness, staggering gait while walking. 2. Ataxia: Difficulty in general movements and such movements are largely unco-ordinated. 3. Hypotonia: Low tone of muscles due to loss of facilitatory inputs from the cerebellum to the cerebral cortex and brain stem. 4. Dysmetria/Overshooting/Pastpointing: This is poor prediction of movements which cause overshooting beyond intended marks. 5. Adiadochokinesia: This is inability to perform rapid alternating movements e.g rotation of wrist between pronation and supination. 6. Intension tremor: This is trembling that appears during movements, it not seen at rest. 7. Rebound: This slowness to react to changing circumstances. 8. Asynergia: This is inability to achieve balanced activation of muscle during movements leading to jerky movements. 9. Dysarthria/Scanningor Slurring of speech: This causes jumbled vocalization leading to speech that is poorly audible and sometimes unintelligent. 10. Cerebellar Nystagmus: This is tremor of the eyeballs which occurs when one tries to fixate the eyes on an object by the side of the eye. 11. Decomposition of movement.  BASAL GANGLIA Basal ganglia consists of 5 structures on each side of the brain: Caudate nucleus Putamen Globus pallidus Substantia nigra Subthalamus The caudate nucleus and putamen are collectively called corpus striatum. The putamen and globus pallidus are collectively called lentiform nucleus Globus pallidus is divided into internal and external segments. Substantia nigra is divided into pars compacta and pars reticularis. Parts of the thalamus is closely associated with the basal ganglia.  The Putamen Circuit This is used to describe the various connections of the basal ganglia. The main afferents into the basal ganglia originates from the cerebral cortex and synapse in the corpus striatum (corticostriate fibres). The corpus striatum also receives afferents from the centromedial nucleus of the thalamus. The various parts of the basal ganglia are connected to one another. The pars compacta of the substantia nigra sends fibres (nigrostriatal) to the corpus striatum. These fibres release dopamine i.e dopaminergic fibres. The corpus striatum in turn sends fibres that release GABA i.e GABAergic fibres to the pars reticularis of substantia nigra. The corpus striatum also projects fibres to both segments of globus pallidus.  The external segment of globus pallidus project to subthalamus which in turn project to both segments of globus pallidus. The subthalamus also sends fibres to both parts of substantia nigra. The main output (efferent) from the basal ganglia is from the internal segments of globus pallidus, via the thalamic fasciculus to the thalamus (centromedial, ventroanterior and ventrolateral nuclei). Substantia nigra also project fibres to the thalamus. From these thalamic nuclei, fibres project to the cerebral cortex, completing the circuit. Note: Diagram of the putamen circuit  Functions of basal ganglia Little is known about the precise functions of the basal ganglia, however, they are associated with the following functions: 1. They participate in the conversion of plans for movement arising in the association cortex into programmes for movement e.g as in writing 2. They participate in the initiation and perhaps in large scale planning and execution of movements. 3. They are involved in the process by which abstract thought is converted into voluntary action. 4. The basal ganglia especially the caudate nucleus plays a role in cognitive processes. The limbic part of basal ganglia is involved in motivation and decision making. 5. The basal ganglia is involved in changing the timing and scaling of the intensity of movements. 6. It is involved in the control of eye movement via impulses from substantia nigra. 7. The basal ganglia has been suggested to be the gate regulating what enters and what doesn't enter working memory.  Effects of lesion of the Basal ganglia 1. Parkison’s disease (paralysis agitans): The main symptoms occur if the dopaminergic fibres that connect the substantia nigra to the corpus striatum particularly the putamen is lesioned i.e. damage to nigrostriatial fibres. Symptoms of parkison’s disease include: a) Akinesia- general poverty of movement as examplified by the following: - Absence or impairment of movement - Expressive movements such as the usual mobility of the face may be lost giving the face a lifeless and apathetic look. – There may be loss of associated movements i.e. loss of movement that occurs with a particular primary activity that is not strictly necessary e.g swinging of arms when walking. - The patient blinks less often. - Shuffling gait often occurs. - Patient may be slow in walking about (bradykinesia) b) Rigidity or Rigor: This may occur due to increase in muscle tone and it is present regardless of joint position or movement. c) Postural difficulty (vague) may be present. d) Passive tremor (tremor at rest) is usually present. 2. Huntington’s disease (chorea): This is less energetic spontaneous movement. It is characterized by rapid, involuntary ‘dancing’ movement. It is a hereditary disorder that results in death of brain cells. 3. Ballismus: This is involuntary movement that affects the proximal limb muscles. It is characterized by the patient throwing his arm around in a violent manner when walking. It is caused by lesion of the subthalamus. When one side of the body is involved, it leads to hemiballismus. 4. Athetosis: This is characterized by slow, involuntary, convoluted writhing movement of the fingers, hands, toes and feet and in some cases arms, legs, neck and tongue. Lesion of the corpus striatum may be the possible cause. 5. Fahr Disease- Idiopathic calcification of basal ganglia by calcium deposits in motor areas of the brain.  HYPOTHALAMUS Hypothalamus is a structure in the diencephalon which lies the thalamus. It is involved in the control endocrine, autonomic and behavioural functions of the body. It has the highest blood supply in the brain. It is divided into 3 parts: Posterior, Anterior and Lateral hypothalamus. Each of these parts contain several nuclei. Posterior hypothalamus: posterior hypothalamus nuclei, dorsomedial nuclei, perifrontal nucleus, ventromedial nucleus, mamillary body. Anterior hypothalamus: Paraventricular nucleus, medial preoptic nuclei, supraoptic nucleus, posterior preoptic nucleus and anterior hypothalamic area. Lateral hypothalamus: Contain nuclei that control hunger, thirst and emotions.  Functions of Hypothalamic nuclei: Posterior: Posterior hypothalamic nuclei: Stimulation increases BP, causes pupillary dilatation, shivering, and corticotrophin release. Dorsomedial nucleus: GIT stimulation Perifrontal nucleus: stimulation causes hunger, increase BP and rage Ventromedial nucleus: Stimulation causes satiety Mamillary body: stimulation initiates feeding reflexes Anterior: Paraventricular nucleus: Stimulation causes oxytocin release, water conservation. Medial preoptic nuclei: Bladder contraction, decrease in HR, decrease in BP. Supraoptic nucleus: Stimulation causes ADH release (water conservation) Posterior preoptic and anterior hypothalamic area: Controls body temperature,, panting, sweating and thyrotropin inhibition.  The hypothalamus sends signal in 2 directions: 1. Downwards into the brainstem and reticular formation 2. Upwards into the thalamus, cerebral cortex and limbic cortex The hypothalamus is closely related with motor output of the limbic system The hypothalamus controls vegetative functions of the body as well as many aspects of emotional behaviour.  Summary of the functions of the hypothalamus The hypothalamus: (1) controls the release of 8 major hormones by the pituitary gland It is involved in: (2) temperature regulation (3) control of food and water intake (4) sexual behaviour and reproduction (5) control of daily cycles in physiological state and behaviour (6) mediation of emotional responses. 1. Regulation of feeding: Feeding is controlled by feeding centre in lateral hypothalamus while the satiety centre is located in the ventromedial nucleus. Stimulation of the feeding centre stimulates hunger while that of ventromedial nucleus causes satisfaction. Destruction of the satiety centre causes voracoius feeding leading to hypothalamic obesity. Whereas destruction of the feeding centre leads to lethal starvation called anorexia.  2. Regulation of body water: Hypothalamus regulates body water via 2 ways: i. Stimulation of thirst receptors which causes the animal to drink water ii. Regulation of water excretion in the urine- mainly via the action of ADH. 3. Regulation of uterine contraction: The PVN secretes oxytocin which causes uterine contraction and contraction of the breast to empty milk to the nipple. 4. Control of the Pituitary gland: Regulates anterior pituitary via releasing and inhibiting hormones. Also regulates posterior pituitary via hypothalamohypophyseal neural tracts. 5. Regulation of body temperature: Body temperature is regulated in the anterior hypothalamus especially posterior preoptic area. 6. CVS regulation: Posterior and lateral hypothalamus contain centres that regulate BP. Regulation is exerted through CV centres and reticular formation. 7. Regulation of behaviour: Hypothalamus is involved in the control of emotional behaviour. Stimulation of lateral hypothalamus leads to rage and fighting while stimulation of the preoptic nucleus cuses tranquility. Stimulation of certain areas of the hypothalamus stimulates sexual drive e.g lateral part of medial hypothalamus Stimulation of certain areas of the hypothalamus leads to reward and punishment. Reward and punishment can be described as pleasant and unpleasesant sensation or satisfaction and aversion. Stimulation along the course of medial forebrain bundle in lateral and ventromedial nuclei leads to pleasantness or reward. Stimulation of the periventricular areas of the hypothalamus and thalamus leads to unpleasantness or punishment. Tranquilizers inhibit both reward and punishment areas, thus decreasing the affective reactivity of the animal or human. Reward and punishment function is important because it drives life and gives motivation. It helps in learning/ experience.  LIMBIC SYSTEM This consists of brain structure that lie in the border region between the hypothalamus and its related structures and the cerebral cortex. It consists of the entire basal system of the brain that controls one’s emotional behaviour and drive e.g. rage, fear, pleasure, sexual behaviour, control of appetite, etc. The limbic system constitute a route whereby emotional influences can produce autonomic, endocrine or reflex changes. The limbic system is made of the following parts: 1. Limbic cortex 2. Subcortical structures 3. Hypothalamus Limbic cortex consists of the following: temporal cortex, orbitofrontal area, cingulate gyrus, parahippocampal gyrus, pyriform area and uncus.  Subcortical structures include: Preoptic area, anterior thalamic nuclei, parts of the basal ganglia, hippocampus and amygdala. Hypothalamus: Already described. Afferent and Efferent Connections of the Limbic System (Papez Circuit): There is a closed system of information flow between the limbic system and the hypothalamus and thalamus, this is called the ‘Papez circuit’. In this circuit, the fornix connects the hippocampus to the mamillary bodies which in turn project to the anterior nuclei of the thalamus which in turn sends fibres to the cingulate gyrus which the completes the circuit by sending fibers to hippocampus. Through these connections, the limbic system and hypothalamus control emotional behaviour. The functions of various parts of the limbic system have been obtained via electrical stimulation, ablation or surgical removal or destruction of such specific areas.  Functions of specific parts of the limbic system 1. Limbic cortex: Function as cerebral association area for control of behaviour. Ablation of the temporal cortex causes the animal to develop consumatory behaviour, have intense sex drive and loses all fear. Ablation of the orbitofrontal cortex: Bilateral ablation of this area causes insomnia and motor restlessness Ablation of the subcallosal gyri: Bilateral ablation of this area releases the rage centre in the septum and hypothalamus and produces fits of rage in the animal. 2. Functions of the Amygdala: The amygdala receives impulses from all portions of the limbic cortex. Because of its multiple connections, the amygdala has been referred to as the window through which the limbic system sees the place of a person in the world. The amygdala in turn transmits signals to: same cortical areas; hippocampus; septum; thalamus and mostly to the hypothalamus. Amygdala patterns the behavioural response of an individual so that is appropriate for each occasion.  Stimulation of the amygdala elicit the same response as stimulating the hypothalamus plus additional effects such as: Increase in BP, Increase in HR, increase or decrease in GIT secretion and motility, defeacation, micturition, pupillary dilatation and secretion of anterior pituitary hormones. Stimulation of the amygdala also elicits sexual activities such as; erection, copulatory movements, ejaculation, ovulation, uterine activity and premature labour. Bilateral ablation of the amygdala causes Kluver Bucy Syndrome: This syndrome was described in 1939 by Kluver and Bucy from studies done in monkeys. It is associated with changes in behaviour which include the following: Excessive tendency to examine objects orally Loss of fear Decreased aggresiveness Change in dietary habits e.g. hebivorous animal can become canivorous Sometimes psychic blindness i.e inability to distinguish between edible and non-edible objects. Often excessive sex drive e.g. attempt to copulate with immature animals, animals of wrong sex or even of different species  Functions of the hippocampus: Hippocampus has numerous connections with the sensory cortex and basic structures of the limbic system such as the amygdala, hypothalamus, septum and mamillary bodies. It responds to almost all sensory experiences. It sends its output through the fornix to the hypothalamus and other parts of the limbic system. Stimulation causes rage, passivity, excess sex drive, etc. Weak electrical stimulation causes epileptic seizures. Bilateral lesion of the hippocampus causes inability to learn something new but can perform previously learned activities. New names and faces of people that they come in contact with everyday cannot be remembered.  PYRAMIDAL AND EXTRA PYRAMIDAL TRACTS Two types of motor fibres that originate from the motor cortex to the spinal cord: 1. Pyramidal tract 2. Extrapyramidal tract PYRAMIDAL TRACT (SYSTEM) This include: (i) Corticospinal tract (ii) Corticobulbar tract  CORTICOSPINAL TRACT Extends from the motor cortex to the spinal cord as a single fibre i.e without synapsing At the level of the medulla, 80% of the fibres decussate and run in large pyramids or paired bundles near the ventral sulcus. These structures are referred to as pyramids, hence the name pyramidal tract. The fibres that decussate form the lateral corticospinal tract. The remaining 20% (ipsilateral) fibres form the anterior or ventral corticospinal tract. They end on spinal on spinal motor neurones on the same side of the body.  Anterior corticospinal tract control the axial and proximal limb muscles. Anterior corticospinal tract end in either the cervical or thoracic segments of the spinal cord. Lateral corticospinal tract runs through the entire length of the spinal cord. Most of the pyramidal tract fibres end on interneurones with only a few ending directly on motor neurones. The pyramidal tract is the primary pathway for movement, forced commands are sent to the spinal cord through it.  CORTICOBULBAR TRACT They extends from the motor cortex to the brain stem They synapse on interneurones which in turn synapse on motor nuclei of cranial nerves Note: The ventral corticospinal tract do not run through the pyramids in the medulla. Hence, there is no rigid division between pyramidal and extrapyramidal tracts.  Functions of pyramidal tract The pyramidal tract is concerned with fine-skilled voluntary movement, particlarly those associated with manipulation e.g cloth weaving Forced commands are sent to the spinal cord through the pyramidal tract.  EXTRAPYRAMIDAL TRACT This is used clinically to denote those part of the motor system that are not part of the direct corticospinal tract. These include pathways through the basal ganglia, reticular formation, vestibular and red nuclei. Extrapyramidal tract contain 2 types of fibres: (1) Fibres from motor cortex to brain stem (2) Fibres from brain stem to spinal cord  Fibres from motor cortex to brain stem The 4 most important ones include: (i) Fibres from motor cortex directly to brain stem through internal capsule. (ii) Fibres that synapse in corpus striatum before going to the brain stem (iii) Those that synapse in globus pallidus before going to the brain stem (iv) Those that first synapse in corpus striatum, then in globus pallidus before going to the brain stem. These fibres synapse on the same side of the brain stem, decussation only occurs after they have synapsed.  Fibres from brainstem to spinal cord The most important ones include the following: (i) Medial reticulospinal tract which originate from pontine reticular formation (ii) Lateral reticulospinal tract which originate from medullary reticular formation (iii) Vestibulospinal tract which originate from vestibular nuclei (iv) Rubrospinal tract which originate from red nucleus or nucleus ruba (v) Tectospinal tract which originate from tectum of the fourth ventricle  Their terminations Medial reticulospinal tract end in the medial part of spinal cord Lateral reticulospinal tract end in dorsal /posterior part of the spinal cord Vestibulospinal tract end on the ventral part of the spinal cord Tectospinal tract on the ventral part of the spinal cord Rubrospinal tract end on the lateral part of the spinal cord. Most of these fibres end on interneurones with only a few ending directly on motor neurones  Functions of the Extrapyramidal tract Both medial and lateral reticulospinal tract function in the control of basic instinctual reactions e.g. startled reaction to gun shot. They are also involved in the control of posture. Vestibulospinal tract is involved in the control of posture. They also support the body against gravity. The tract is associated with the cerebellum which may control the spinal cord through it. Tectospinal tract act as integration centre for coordination of vision and learning especially in orienting responses. The function of rubrospinal tract is not clear, however, stimulating it electrically produces flexion i.e it may be involved in the control of flexor muscles