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 are subcortical nuclei Caudate nucleus + putamen = Associated with subthalamic nuclei (diencephalon) and (midbrain) Caudate and putamen not completely separate – actually single nucleus with fibers from cortex passing through

12 is bunched up corona radiata

13 Corona radiate are 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 bundles between cortex, basal ganglia, thalamus, 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 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 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. —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 neurons in motor pathway Visceral pain afferents travel along same pathways as somatic pain fibers, contributing to phenomenon of referred pain

49 Functional classification Somatic reflexes Activate skeletal muscle Autonomic (visceral) reflexes Activate visceral effectors (smooth or cardiac muscle or glands)

50 Composed of 3–10 modified skeletal muscle fibers - intrafusal muscle fibers - wrapped in connective tissue capsule Effector fibers – extrafusal muscle fibers

51 Noncontractile in central regions (lack myofilaments) Two types of afferent endings Anulospiral endings (primary sensory endings) Endings wrap around spindle; stimulated by rate and degree of stretch Flower spray endings (secondary sensory endings) Small axons at spindle ends; respond to stretch

52 Contractile end regions innervated by gamma () efferent fibers - maintain spindle sensitivity Note: extrafusal fibers (contractile muscle fibers) innervated by alpha () efferent fibers

53 Excited in two ways 1. External stretch of muscle and muscle spindle 2. Internal stretch of muscle spindle Activating  motor neurons stimulates ends to contract, thereby stretching spindle

54 Stretch causes increased rate of impulses to spinal cord

55 Contracting muscle reduces tension on muscle spindle Sensitivity lost unless muscle spindle shortened by impulses in  motor neurons – coactivation maintains tension and sensitivity of spindle during muscle contraction

56 Contracting muscle reduces tension on muscle spindle Sensitivity lost unless muscle spindle shortened by impulses in  motor neurons – coactivation maintains tension and sensitivity of spindle during muscle contraction

57 Spinal somatic reflexes Integration center in spinal cord Effectors are skeletal muscle

58 Maintains muscle tone in large postural muscles, and adjusts it reflexively Causes muscle contraction in response to increased muscle length (stretch)

How stretch reflex works Stretch activates muscle spindle Sensory neurons synapse directly with  motor neurons in spinal cord  motor neurons cause stretched muscle to contract All stretch reflexes are monosynaptic and ipsilateral

Reciprocal inhibition also occurs—IIa fibers synapse with interneurons that inhibit  motor neurons of antagonistic muscles Example: In patellar reflex, stretched muscle (quadriceps) contracts and antagonists (hamstrings) relax

59 60 Polysynaptic reflexes Helps prevent damage due to excessive stretch Important for smooth onset and termination of muscle contraction

61 Produces muscle relaxation (lengthening) in response to tension Contraction or passive stretch activates tendon reflex Afferent impulses transmitted to spinal cord Contracting muscle relaxes; antagonist contracts (reciprocal activation) Information transmitted simultaneously to cerebellum and used to adjust muscle tension

62 Flexor (withdrawal) reflex Initiated by painful stimulus Causes automatic withdrawal of threatened body part Ipsilateral and polysynaptic Protective; important Brain can override E.g., finger stick for blood test

63 Crossed extensor reflex Occurs with flexor reflexes in weight-bearing limbs to maintain balance Consists of ipsilateral withdrawal reflex and contralateral extensor reflex Stimulated side withdrawn (flexed) Contralateral side extended e.g., step barefoot on broken glass

64 Startle reflex in newborn

65 66 Elicited by gentle cutaneous stimulation Depend on upper motor pathways and cord-level reflex arcs Best known: Plantar reflex Abdominal reflex

67 Test integrity of cord from L4 – S2 Stimulus - stroke lateral aspect of sole of foot Response - downward flexion of toes Damage to motor cortex or corticospinal tracts  abnormal response = Babinski's sign Hallux dorsiflexes; other digits fan laterally Normal in infant to ~1 year due to incomplete myelination

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