Neurophysiology, Part 3 PDF Lecture Notes

1 PRINCIPLES OF NEUROPHYSIOLOGY, PART 3 Dr. Samantha Solecki, DC, MS Instructor, Biology Thinker. Learner. Motivator. Lover of Anatomy & Physiology [email protected] © 2019 Pearson Education, Inc. ...

1 PRINCIPLES OF NEUROPHYSIOLOGY, PART 3 Dr. Samantha Solecki, DC, MS Instructor, Biology Thinker. Learner. Motivator. Lover of Anatomy & Physiology [email protected] © 2019 Pearson Education, Inc.  2 Learning Objectives *Acquired from the Human Anatomy and Physiology Society (HAPS) with personal additions Explain and integrate concepts of neurological integration. Analyze types of circuits and apply types of circuits to examples. Explain the generator potential that occurs when receptors for general senses are stimulated. Explain the phenomenon of adaptation. List cranial nerves by name and number. Describe the specific functions of each of the cranial nerves and classify each as sensory, motor or mixed. Propose how knowledge of the anatomy of cranial nerve nuclei can be used to help pinpoint damage to particular regions of the brain stem. Distinguish between ascending and descending tracts in the spinal cord. Describe the concept of dermatomes and why they are clinically significant. Define the term reflex. Describe reflex responses in terms of the major structural and functional components of a reflex arc. Distinguish between each of the following pairs of reflexes: intrinsic (inborn) reflexes vs. learned reflexes, somatic vs. visceral reflexes, monosynaptic vs. polysynaptic reflexes and ipsilateral vs. contralateral reflexes. Explain the term spinal reflex. Describe a stretch reflex, a flexor (withdrawal) reflex, and a crossed-extensor reflex, and name all components of each reflex arc.  3 Learning Objectives *Acquired from the Human Anatomy and Physiology Society (HAPS) with personal additions Demonstrate a stretch reflex (eg. Patellar or plantar) Propose how specific reflexes would be used in clinical assessment of nervous system function. Describe locations and functions of the upper and lower motor neurons in a motor pathway. Explain how decussation occurs in sensory and motor pathways & predict how decussation impacts the correlation of brain damage and symptoms in stroke patient. Provide specific examples to demonstrate how the nervous system responds to maintain homeostasis in the body. Explain how the nervous system relates to other body systems to maintain homeostasis. Predict factors or situations affecting the nervous system that could disrupt homeostasis. Predict the types of problems that would occur in the body if the nervous system could not maintain homeostasis.  4 NEURAL INTEGRATION  5 Neural Integration Neural integration: neurons functioning together in groups Groups contribute to broader neural functions There are billions of neurons in CNS Must have integration so that the individual parts fuse to make a smoothly operating whole  6 Organization of Neurons: Neuronal Pools Neuronal pool: functional groups of neurons Integrate incoming information received from receptors or other neuronal pools Forward processed information to other destinations  7 Patterns of Neural Processing Serial processing Input travels along one pathway to a specific destination One neuron stimulates next one, which stimulates next one, etc. System works in all-or-none manner to produce specific, anticipated response Best example of serial processing is a spinal reflex Rapid, automatic responses to stimuli Particular stimulus always causes same response  8 Patterns of Neural Processing Parallel processing Input travels along several pathways Different parts of circuitry deal simultaneously with the information One stimulus promotes numerous responses Important for higher-level mental functioning Example: A sensed smell may remind one of an odor and any associated experiences  9 Types of Circuits Circuits: patterns of synaptic connections in neuronal pools Four types of circuits Diverging Converging Reverberating Parallel after-discharge  10 Types of Circuits in Neuronal Pools Figure 11.20a Types of circuits in neuronal pools.  11 Types of Circuits in Neuronal Pools Figure 11.20b Types of circuits in neuronal pools.  12 Types of Circuits in Neuronal Pools Figure 11.20c Types of circuits in neuronal pools.  13 Types of Circuits in Neuronal Pools Figure 11.20d Types of circuits in neuronal pools.  14 SENSORY PHYSIOLOGY Figure 13.4b Structure of a nerve. 15 Axon Myelin sheath Endoneurium Perineurium Epineurium Fascicle Blood vessels  16 Classification of Nerves Most nerves are mixtures of afferent and efferent fibers and somatic and autonomic (visceral) fibers Classified according to direction transmit impulses Mixed nerves – both sensory and motor fibers; impulses both to and from CNS Sensory (afferent) nerves – impulses only toward CNS Motor (efferent) nerves – impulses only away from CNS  17 From Sensation to Perception Survival depends upon sensation and perception Sensation - the awareness of changes in the internal and external environment Perception - the conscious interpretation of those stimuli  18 Processing at the Receptor Level To produce a sensation Receptors have specificity for stimulus energy Stimulus must be applied in receptive field Transduction occurs Stimulus changed to graded potential Generator potential or receptor potential Graded potentials must reach threshold  AP  19 Processing at the Receptor Level In general sense receptors, graded potential called generator potential Stimulus  Generator potential in afferent neuron  Action potential  20 Adaptation of Sensory Receptors Adaptation is change in sensitivity in presence of constant stimulus Receptor membranes become less responsive Receptor potentials decline in frequency or stop Phasic (fast-adapting) receptors signal beginning or end of stimulus Examples - receptors for pressure, touch, and smell Tonic receptors adapt slowly or not at all Examples - nociceptors and most proprioceptors  21 SPINAL CORD PHYSIOLOGY Figure 12.26a Gross structure of the spinal cord, dorsal view. 22 Cervical Cervical spinal enlargement nerves Dura and arachnoid mater Thoracic spinal nerves Lumbar enlargement Conus medullaris Cauda Lumbar equina spinal nerves Filum terminale Sacral spinal nerves The spinal cord and its nerve roots, with the bony vertebral arches removed. The dura mater and arachnoid mater are cut open and reflected laterally.  Figure 12.28b Anatomy of the spinal cord. 23 Dorsal median sulcus Dorsal funiculus Gray commissure Dorsal horn White Ventral funiculus Gray Ventral horn matter columns Lateral funiculus Lateral horn Dorsal root ganglion Spinal nerve Central canal Dorsal root (fans out into Ventral median fissure dorsal rootlets) Pia mater Ventral root (derived from several ventral rootlets) Arachnoid mater Spinal dura mater The spinal cord and its meningeal coverings  Figure 12.30 Major ascending (sensory) and descending (motor) tracts of the spinal cord, cross-sectional 24 view. Ascending tracts Descending tracts Ventral white Dorsal Fasciculus gracilis commissure white Fasciculus cuneatus Lateral column reticulospinal tract Dorsal Lateral spinocerebellar tract corticospinal tract Ventral Rubrospinal tract spinocerebellar tract Medial Lateral spinothalamic reticulospinal tract tract Ventral corticospinal tract Ventral spinothalamic tract Vestibulospinal tract Tectospinal tract  25 Ascending Pathways Three main pathways: Two transmit somatosensory information to sensory cortex via thalamus Dorsal column–medial lemniscal pathways Spinothalamic pathways Spinocerebellar tracts Figure 12.31a Pathways of selected ascending spinal cord tracts. (2 of 2) 26 Dorsal Medial lemniscus (tract) spinocerebellar (axons of second-order neurons) tract (axons of Nucleus gracilis second-order neurons) Nucleus cuneatus Medulla oblongata Fasciculus cuneatus (axon of first-order sensory neuron) Joint stretch receptor Axon of (proprioceptor) first-order Cervical spinal cord neuron Muscle Fasciculus gracilis spindle (axon of first-order sensory neuron) (proprioceptor) Lumbar spinal cord Touch receptor Spinocerebellar pathway Dorsal column–medial lemniscal pathway Figure 12.31a Pathways of selected ascending spinal cord tracts. (1 of 2) 27 Primary somatosensory cortex Axons of third-order neurons Thalamus Cerebrum Midbrain Cerebellum Pons Spinocerebellar pathway Dorsal column–medial lemniscal pathway Figure 12.31b Pathways of selected ascending spinal cord tracts. (2 of 2) 28 Lateral spinothalamic tract (axons of second-order neurons) Medulla oblongata Pain receptors Cervical spinal cord Axons of first-order neurons Temperature Lumbar spinal cord receptors Spinothalamic pathway Figure 12.31b Pathways of selected ascending spinal cord tracts. (1 of 2) 29 Primary somatosensory cortex Axons of third-order neurons Thalamus Cerebrum Midbrain Cerebellum Pons Spinothalamic pathway Figure 12.31a Pathways of selected ascending spinal cord tracts. (2 of 2) 30 Dorsal Medial lemniscus (tract) spinocerebellar (axons of second-order neurons) tract (axons of Nucleus gracilis second-order neurons) Nucleus cuneatus Medulla oblongata Fasciculus cuneatus (axon of first-order sensory neuron) Joint stretch receptor Axon of (proprioceptor) first-order Cervical spinal cord neuron Muscle Fasciculus gracilis spindle (axon of first-order sensory neuron) (proprioceptor) Lumbar spinal cord Touch receptor Spinocerebellar pathway Dorsal column–medial lemniscal pathway Figure 12.31a Pathways of selected ascending spinal cord tracts. (1 of 2) 31 Primary somatosensory cortex Axons of third-order neurons Thalamus Cerebrum Midbrain Cerebellum Pons Spinocerebellar pathway Dorsal column–medial lemniscal pathway  32 Descending Pathways and Tracts Motor pathways involve two neurons: Upper motor neurons Pyramidal cells in primary motor cortex Lower motor neurons Ventral horn motor neurons Innervate skeletal muscles Figure 12.32a Three descending pathways by which the brain influences movement. (1 of 2) 33 Pyramidal cells (upper motor neurons) Primary motor cortex Internal capsule Cerebrum Midbrain Cerebral peduncle Cerebellum Pons Pyramidal (lateral and ventral corticospinal) pathways Figure 12.32a Three descending pathways by which the brain influences movement. (2 of 2) 34 Ventral corticospinal tract Medulla oblongata Pyramids Decussation of pyramids Lateral corticospinal tract Cervical spinal cord Skeletal muscle Lumbar spinal cord Somatic motor neurons (lower motor neurons) Pyramidal (lateral and ventral corticospinal) pathways  35 REFLEX PHYSIOLOGY  36 Reflexes 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  37 Reflex Arc 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 Figure 13.15 The five basic components of all reflex arcs. 38 Stimulus Skin 1 Receptor Interneuron 2 Sensory neuron 3 Integration center 4 Motor neuron 5 Effector Spinal cord (in cross scetion)  39 Reflexes Functional classification Somatic reflexes Activate skeletal muscle Autonomic (visceral) reflexes Activate visceral effectors (smooth or cardiac muscle or glands)  40 Spinal Reflexes Spinal somatic reflexes Integration center in spinal cord Effectors are skeletal muscle Testing of somatic reflexes important clinically to assess condition of nervous system If exaggerated, distorted, or absent  degeneration/pathology of specific nervous system regions  41 Stretch and Tendon Reflexes To smoothly coordinate skeletal muscle nervous system must receive proprioceptor input regarding 1. Length of muscle From muscle spindles 2. Amount of tension in muscle From tendon organs  42 Stretch and Tendon Reflexes Stretch reflex Brain sets muscle’s length via stretch reflex Example: knee-jerk reflex is a stretch reflex that keeps knees from buckling when you stand upright Stretch reflexes maintain muscle tone in large postural muscles and adjust it reflexively Causes muscle contraction on side of spine in response to increased muscle length (stretch) on other side of spine  43 Stretch and Tendon Reflexes Stretch reflex (cont.) How stretch reflex works: Stretch activates muscle spindle Sensory neurons synapse directly with α motor neurons in spinal cord  motor neurons cause extrafusal muscles of stretched muscle to contract  44 Stretch and Tendon Reflexes Stretch reflex (cont.) Reciprocal inhibition also occurs—afferent fibers synapse with interneurons that inhibit  motor neurons of antagonistic muscles Example: In patellar reflex, stretched muscle (quadriceps) contracts, and antagonists (hamstrings) relax  45 Stretch and Tendon Reflexes All stretch reflexes are monosynaptic and ipsilateral (motor activity is on same side of body) Positive reflex reactions provide two pieces of info: Proves that sensory and motor connections between muscle and spinal cord are intact Strength of response indicates degree of spinal cord excitability  46 Stretched Muscle Spindles Initiate a Stretch Reflex, Causing Contraction of the Stretched Muscle and Inhibition of its Antagonist FOCUS FIGURE 13.1 Stretch Reflex.  47 Stretch Reflexes Positive reflex reactions indicate Sensory and motor connections between muscle and spinal cord intact Strength of response indicates degree of spinal cord excitability Hypoactive or absent if peripheral nerve damage or ventral horn injury Hyperactive if lesions of corticospinal tract Grading Reflexes: 0 : Areflexia - no response (always abnormal) 1+: Slight response (correlate clinically) 2+: Normal and brisk 3+: “Hyper”normal - more brisk but usually normal (correlate clinically) 4+: Hyperreflexia – without clonus (always abnormal) 5+: Hyperreflexia – with clonus (always abnormal)  48 Stretched Muscle Spindles Initiate a Stretch Reflex, Causing Contraction of the Stretched Muscle and Inhibition of its Antagonist FOCUS FIGURE 13.1 Stretch Reflex.  49 Stretch and Tendon Reflexes Tendon reflex Involves polysynaptic reflexes Helps prevent damage due to excessive stretch Important for smooth onset and termination of muscle contraction  50 Stretch and Tendon Reflexes Tendon reflex (cont.) 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  Figure 13.19 The tendon reflex. 51 Slide 1 1 Quadriceps strongly contracts. 2 Afferent fibers synapse with Tendon organs are activated. interneurons in the spinal cord. Interneurons + + Quadriceps (extensors) – + Tendon organ Spinal cord Hamstrings (flexors) 3a Efferent 3b Efferent impulses impulses to muscle to antagonist muscle with stretched cause it to contract. + Excitatory synapse tendon are damped. – Inhibitory synapse Muscle relaxes, reducing tension.  52 Clinical – Homeostatic Imbalance Stretch reflexes can be hypoactive or absent if peripheral nerve damage or ventral horn injury has occurred Reflexes are absent in people with chronic diabetes mellitus or neurosyphilis and during coma Stretch reflexes can be hyperactive if lesions of corticospinal tract reduce inhibitory effect of brain on spinal cord  53 The Flexor and Crossed-Extensor Reflexes 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  54 Flexor and Crossed-Extensor Reflexes 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  Figure 13.20 The crossed-extensor reflex. 55 + Excitatory synapse Interneurons – Inhibitory synapse + + – + + – Afferent Efferent fiber fibers Efferent fibers Extensor Flexor inhibited inhibited x es Flexor Fle Arm movements Extensor stimulated stimulated s t e nd Ex Site of stimulus: Site of reciprocal A noxious stimulus activation: At the causes a flexor same time, the reflex on the same extensor muscles side, withdrawing on the opposite that limb. side are activated.  56 Superficial Reflexes Elicited by gentle cutaneous stimulation Depend on upper motor pathways and cord-level reflex arcs Best known: Plantar reflex Abdominal reflex  57 Superficial Reflexes: Plantar Reflex Test integrity of cord from L – S 4 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  58 Superficial Reflexes: Abdominal Reflexes Test integrity of cord from T8 – T12 Cause contraction of abdominal muscles and movement of umbilicus in response to stroking of skin Vary in intensity from one person to another Absent when corticospinal tract lesions present