CNS consists of brain and spinal cord PNS consists of nerves 1 As with sensory input, motor output is organized in central nervous system Peripheral Nervous system divides efferent signals somatotopically Signals to skeletal muscles (including those transmitting voluntary movements) originate and are carried in SOMATIC NERVOUS SYSTEM Signals to other effector cells and organs - viscera, smooth and cardiac muscle-containing structures, glands – originate and are carried in AUTONOMIC NERVOUS SYSTEM Adult brain regions 1. Cerebral hemispheres 2. Diencephalon 3. Brain stem (midbrain, pons, and medulla) 4. Cerebellum areas of gray matter (cell bodies) in brain organized in the cerebral hemispheres and cerebellum Outer gray matter called cortex 4 Main aspects of gyral patterns similar from person to person Central sulcus identifiable 5 Precentral gyrus – frontal continuation goes towards the front. Note left right asymmetry 6 Five lobes Frontal Parietal Temporal Occipital Insula Cortical areas functionally distinct. Motor areas in frontal lobe – most posterior aspect – near primary sensory cortex. 8 Obvious difference between motor and sensory cortex across central sulcus 9 (Korbinian) Brodmann’s areas based on location and cytoarchitecture. Intuition that different cell arrangements had different functions turns out to have been correct 10 The basal ganglia are subcortical nuclei Caudate nucleus Putamen Globus pallidus Caudate nucleus + putamen = striatum Associated with subthalamic nuclei (diencephalon) and substantia nigra (midbrain) Caudate and putamen not completely separate – actually single nucleus with fibers from cortex passing through 12 Internal capsule is bunched up corona radiata 13 Corona radiate are axons to and from cortex to lower areas Association fibers are axons between areas of the same cortical hemisphere Commisural fibers are axons between areas of the two different hemispheres Internal capsules are axon bundles between cortex, basal ganglia, thalamus, brainstem and spinal cord Functions thought to be Influence muscle movements Role in cognition and emotion Regulate intensity of slow or stereotyped movements Filter out incorrect/inappropriate responses Inhibit antagonistic/unnecessary movements 16 Direct circuitry is cortex to putamen to globus pallidus (interna) to thalamus to cortex – inhibition of inhibition of excitation leads to enhanced thalamic drive of cortical activity (excitatory) Indirect circuitry is cortex to putamen to globus pallidus (externa) to subthalamic nucleus to globus pallidus (interna) to thalamus to cortex - inhibition of inhibition of excitation of inhibition of excitation leads to reduced thalamic stimulation of cortex (inhibitory). 17 Corona radiate (internal capsule) include axons PROJECTING to other parts of nervous system – corticopontine, corticobulbar, corticospinal tracts Three paired structures Thalamus Hypothalamus Epithalamus Encloses third ventricle 19 Thalamus (singular) main sensory path to cortex (third order neurons) Major component of motor circuitry 20 [Repeat of slide 17] Direct circuitry is cortex to putamen to globus pallidus (interna) to thalamus to cortex – inhibition of inhibition of excitation leads to enhanced thalamic drive of cortical activity (excitatory) Indirect circuitry is cortex to putamen to globus pallidus (externa) to subthalamic nucleus to globus pallidus (interna) to thalamus to cortex - inhibition of inhibition of excitation of inhibition of excitation leads to reduced thalamic stimulation of cortex (inhibitory). 21 Controls autonomic nervous system (e.g., blood pressure, rate and force of heartbeat, digestive tract motility, pupil size) Physical responses to emotions (limbic system) Perception of pleasure, fear, and rage Biological rhythms and drives - Suprachiasmatic nucleus (biological clock) Regulates body temperature – sweating/shivering Regulates hunger and satiety in response to nutrient blood levels or hormones Regulates water balance and thirst Regulates sleep-wake cycles Suprachiasmatic nucleus (biological clock) Controls endocrine system Controls secretions of anterior pituitary gland Produces posterior pituitary hormones Controls autonomic nervous system (e.g., blood pressure, rate and force of heartbeat, digestive tract motility, pupil size) Corpora quadrigemina— dorsal protrusions Superior colliculi—visual reflex centers Inferior colliculi—auditory relay centers Substantia nigra—functionally linked to basal nuclei Red nucleus—relay nuclei for some descending motor pathways; part of reticular formation 11% of brain mass Dorsal to pons and medulla Input from cortex, brain stem and sensory receptors Allows smooth, coordinated movements Each hemisphere has three lobes Anterior, posterior, and flocculonodular Arbor vitae—treelike pattern of cerebellar white matter Cerebellar hemispheres connected by vermis Folia—transversely oriented gyri All fibers in cerebellum are ipsilateral Three paired fiber tracts connect cerebellum to brain stem Superior cerebellar peduncles connect cerebellum to midbrain Middle cerebellar peduncles connect pons to cerebellum Inferior cerebellar peduncles connect medulla to cerebellum Cerebellum receives impulses from cerebral cortex of intent to initiate voluntary muscle contraction Signals from proprioceptors and visual and equilibrium pathways continuously "inform" cerebellum of body's position and momentum Cerebellar cortex calculates the best way to smoothly coordinate muscle contraction "Blueprint" of coordinated movement sent to cerebral motor cortex and brain stem nuclei 30 Cerebellum receives impulses from cerebral cortex of intent to initiate voluntary muscle contraction Signals from proprioceptors and visual and equilibrium pathways continuously "inform" cerebellum of body's position and momentum Cerebellar cortex calculates the best way to smoothly coordinate muscle contraction "Blueprint" of coordinated movement sent to cerebral motor cortex and brain stem nuclei Role in thinking, language, and emotion May compare actual with expected output and adjust accordingly 31 Motor pathways (somatic and autonomic) with nuclei embedded in white matter Controls automatic behaviors necessary for survival Contains fiber tracts connecting higher and lower neural centers Nuclei associated with 10 of the 12 pairs of cranial nerves 32 Deliver efferent impulses from brain to spinal cord Two groups Direct pathways—pyramidal tracts Indirect pathways—all others 33 Motor pathways involve two neurons: Upper motor neurons Pyramidal cells in primary motor cortex – yellow in picture Lower motor neurons Ventral horn motor neurons – blue in picture Innervate skeletal muscles 34 Impulses from pyramidal neurons in precentral gyri pass through pyramidal (corticospinal)l tracts Descend without synapsing 35 Axons synapse with interneurons or ventral horn motor neurons Direct pathway regulates fast and fine (skilled) movements 36 Complex and multisynaptic Includes brain stem motor nuclei, and all motor pathways except pyramidal pathways 37 These pathways regulate Axial muscles maintaining balance and posture Muscles controlling coarse limb movements Head, neck, and eye movements that follow objects in visual field 38 Reticulospinal and vestibulospinal tracts—maintain balance Rubrospinal tracts—control flexor muscles Superior colliculi and tectospinal tracts mediate head movements in response to visual stimuli 39 40 41 42 Cerebellum and basal nuclei are ultimate planners and coordinators of complex motor activities Complex motor behavior depends on complex patterns of control Segmental level Projection level Precommand level 43 Precommand Level Neurons in cerebellum and basal nuclei Regulate motor activity - Precisely start or stop movements - Coordinate movements with posture Block unwanted movements - Monitor muscle tone Perform unconscious planning and discharge in advance of willed movements Cerebellum - acts on motor pathways through projection areas of brain stem - acts on motor cortex via thalamus to fine-tune motor activity Basal nuclei - inhibit various motor centers under resting conditions 44 Projection Level consists of Upper motor neurons that initiate direct (pyramidal) system to produce voluntary skeletal muscle movements Brain stem motor areas that oversee indirect (extrapyramidal) system to control reflex and CPG-controlled motor actions Projection motor pathways send information to lower motor neurons, and keep higher command levels informed of what is happening 45 Segmental level Lowest level of motor hierarchy Reflexes and automatic movements Central pattern generators (CPGs): segmental circuits that activate networks of ventral horn neurons to stimulate specific groups of muscles Controls locomotion and specific, oft-repeated motor activity 46 Components of a reflex arc (neural path) 1. Receptor—site of stimulus action 2. Sensory neuron—transmits afferent impulses to CNS 3. Integration center—either monosynaptic or polysynaptic region within CNS 4. Motor neuron—conducts efferent impulses from integration center to effector organ 5. Effector—muscle fiber or gland cell that responds to efferent impulses by contracting or secreting 47 Inborn (intrinsic) reflex - rapid, involuntary, predictable motor response to stimulus Example – maintain posture, control visceral activities Can be modified by learning and conscious effort Learned (acquired) reflexes result from practice or repetition, Example – driving skills 48 Visceral reflex arcs have same components as somatic reflex arcs But visceral reflex arc has two