CNS consists of brain and spinal cord PNS consists of nerves

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1 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

2 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

3 Adult brain regions 1. Cerebral hemispheres 2. Diencephalon 3. Brain stem (midbrain, pons, and medulla) 4. Cerebellum

4 areas of gray matter (cell bodies) in brain organized in the cerebral hemispheres and cerebellum Outer gray matter called cortex 4

5 Main aspects of gyral patterns similar from person to person Central sulcus identifiable 5

6 Precentral gyrus frontal continuation goes towards the front. Note left right asymmetry 6

7 Five lobes Frontal Parietal Temporal Occipital Insula

8 Cortical areas functionally distinct. Motor areas in frontal lobe most posterior aspect near primary sensory cortex. 8

9 Obvious difference between motor and sensory cortex across central sulcus 9

10 (Korbinian) Brodmann s areas based on location and cytoarchitecture. Intuition that different cell arrangements had different functions turns out to have been correct 10

11 The basal ganglia are subcortical nuclei Caudate nucleus Putamen Globus pallidus Caudate nucleus + putamen = striatum Associated with subthalamic nuclei (diencephalon) and substantia nigra (midbrain)

12 Caudate and putamen not completely separate actually single nucleus with fibers from cortex passing through 12

13 Internal capsule is bunched up corona radiata 13

14 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

15 Internal capsules are axon bundles between cortex, basal ganglia, thalamus, brainstem and spinal cord

16 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)

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). 17

18 Corona radiate (internal capsule) include axons PROJECTING to other parts of nervous system corticopontine, corticobulbar, corticospinal tracts

19 Three paired structures Thalamus Hypothalamus Epithalamus Encloses third ventricle 19

20 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

21 [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

22 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

23 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

24 Controls autonomic nervous system (e.g., blood pressure, rate and force of heartbeat, digestive tract motility, pupil size)

25 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

26 11% of brain mass Dorsal to pons and medulla Input from cortex, brain stem and sensory receptors Allows smooth, coordinated movements

27 Each hemisphere has three lobes Anterior, posterior, and flocculonodular Arbor vitae treelike pattern of cerebellar white matter

28 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

29 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

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 30

31 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

32 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

33 Deliver efferent impulses from brain to spinal cord Two groups Direct pathways pyramidal tracts Indirect pathways all others 33

34 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

35 Impulses from pyramidal neurons in precentral gyri pass through pyramidal (corticospinal)l tracts Descend without synapsing 35

36 Axons synapse with interneurons or ventral horn motor neurons Direct pathway regulates fast and fine (skilled) movements 36

37 Complex and multisynaptic Includes brain stem motor nuclei, and all motor pathways except pyramidal pathways 37

38 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

39 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

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43 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

44 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

45 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

46 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

47 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

48 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

49 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

50 Functional classification Somatic reflexes Activate skeletal muscle Autonomic (visceral) reflexes Activate visceral effectors (smooth or cardiac muscle or glands) 50

51 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

52 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

53 Contractile end regions innervated by gamma ( ) efferent fibers - maintain spindle sensitivity Note: extrafusal fibers (contractile muscle fibers) innervated by alpha ( ) efferent fibers 53

54 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

55 Stretch causes increased rate of impulses to spinal cord 55

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 56

57 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

58 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

59 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

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61 Polysynaptic reflexes Helps prevent damage due to excessive stretch Important for smooth onset and termination of muscle contraction 61

62 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

63 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

64 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

65 Startle reflex in newborn 65

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67 Elicited by gentle cutaneous stimulation Depend on upper motor pathways and cord-level reflex arcs Best known: Plantar reflex Abdominal reflex 67

68 Test integrity of cord from L 4 S 2 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 68

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The Nervous System: Sensory and Motor Tracts of the Spinal Cord

15 The Nervous System: Sensory and Motor Tracts of the Spinal Cord PowerPoint Lecture Presentations prepared by Steven Bassett Southeast Community College Lincoln, Nebraska Introduction Millions of sensory