Lecture Human anatomy and physiology - Chapter 13: The peripheral nervous system and reflex activity (part d)

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Chapter 13 (part d) provides knowledge of motor endings and motor activity. In this chapter, students will be able to compare and contrast the motor endings of somatic and autonomic nerve fibers, outline the three levels of the motor hierarchy, compare the roles of the cerebellum and basal nuclei in controlling motor activity.

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Nội dung Text: Lecture Human anatomy and physiology - Chapter 13: The peripheral nervous system and reflex activity (part d)

PowerPoint® Lecture Slides prepared by Janice Meeking, Mount Royal College CHAPTER 13 The Peripheral Nervous System and Reflex Activity: Part D Copyright © 2010 Pearson Education, Inc.
Motor Endings • PNS elements that activate effectors by releasing neurotransmitters Copyright © 2010 Pearson Education, Inc.
Review of Innervation of Skeletal Muscle • Takes place at a neuromusclular junction • Acetylcholine (ACh) is the neurotransmitter • ACh binds to receptors, resulting in: • Movement of Na+ and K+ across the membrane • Depolarization of the muscle cell • An end plate potential, which triggers an action potential Copyright © 2010 Pearson Education, Inc.
Myelinated axon Action of motor neuron potential (AP) Axon terminal of neuromuscular Nucleus junction 1 Action potential arrives Sarcolemma of at axon terminal of motor the muscle fiber neuron. 2 Voltage-gated Ca2+ channels open and Ca2+ enters the axon terminal. Ca2+ Synaptic vesicle Ca2+ containing ACh 3 Ca2+ entry causes Mitochondrion Axon terminal some synaptic vesicles to of motor neuron Synaptic cleft release their contents (acetylcholine) Fusing synaptic by exocytosis. vesicles 4 Acetylcholine, a ACh Junctional neurotransmitter, diffuses folds of sarcolemma across the synaptic cleft and binds to receptors in Sarcoplasm of the sarcolemma. muscle fiber Na+ K+ Postsynaptic membrane 5 ACh binding opens ion ion channel opens; channels that allow ions pass. simultaneous passage of Na+ into the muscle fiber and K+ out of the muscle ACh Degraded ACh fiber. Na+ Postsynaptic membrane ion channel closed; 6 ACh effects are ions cannot pass. terminated by its K+ enzymatic breakdown in Acetylcholinesterase the synaptic cleft by acetylcholinesterase. Copyright © 2010 Pearson Education, Inc. Figure 9.8
Review of Innervation of Visceral Muscle and Glands • Autonomic motor endings and visceral effectors are simpler than somatic junctions • Branches form synapses en passant via varicosities • Acetylcholine and norepinephrine act indirectly via second messengers • Visceral motor responses are slower than somatic responses Copyright © 2010 Pearson Education, Inc.
Varicosities Autonomic Smooth nerve fibers muscle innervate cell most smooth muscle fibers. Synaptic Mitochondrion Varicosities release vesicles their neurotransmitters into a wide synaptic cleft (a diffuse junction). Copyright © 2010 Pearson Education, Inc. Figure 9.27
Levels of Motor Control • Segmental level • Projection level • Precommand level Copyright © 2010 Pearson Education, Inc.
Precommand Level (highest) • Cerebellum and basal nuclei • Programs and instructions (modified by feedback) Internal Feedback feedback Projection Level (middle) • Motor cortex (pyramidal system) and brain stem nuclei (vestibular, red, reticular formation, etc.) • Convey instructions to spinal cord motor neurons and send a copy of that information to higher levels Segmental Level (lowest) • Spinal cord • Contains central pattern generators (CPGs) Sensory Reflex activity Motor input output (a) Levels of motor control and their interactions Copyright © 2010 Pearson Education, Inc. Figure 13.13a
Segmental Level • The lowest level of the motor hierarchy • 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 Copyright © 2010 Pearson Education, Inc.
Projection Level • Consists of: • Upper motor neurons that direct the direct (pyramidal) system to produce voluntary skeletal muscle movements • Brain stem motor areas that oversee the indirect (extrapyramidal) system to control reflex and CPG-controlled motor actions • Projection motor pathways keep higher command levels informed of what is happening Copyright © 2010 Pearson Education, Inc.
Precommand Level • Neurons in the 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 Copyright © 2010 Pearson Education, Inc.
Precommand Level • Cerebellum • Acts on motor pathways through projection areas of the brain stem • Acts on the motor cortex via the thalamus • Basal nuclei • Inhibit various motor centers under resting conditions Copyright © 2010 Pearson Education, Inc.
Precommand Level (highest) • Cerebellum and basal nuclei • Programs and instructions (modified by feedback) Internal Feedback feedback Projection Level (middle) • Motor cortex (pyramidal system) and brain stem nuclei (vestibular, red, reticular formation, etc.) • Convey instructions to spinal cord motor neurons and send a copy of that information to higher levels Segmental Level (lowest) • Spinal cord • Contains central pattern generators (CPGs) Sensory Reflex activity Motor input output (a) Levels of motor control and their interactions Copyright © 2010 Pearson Education, Inc. Figure 13.13a
Precommand level • Cerebellum • Basal nuclei Projection level • Primary motor cortex • Brain stem nuclei Segmental level • Spinal cord (b) Structures involved Copyright © 2010 Pearson Education, Inc. Figure 13.13b
Reflexes • Inborn (intrinsic) reflex: a rapid, involuntary, predictable motor response to a stimulus • Learned (acquired) reflexes result from practice or repetition, • Example: driving skills Copyright © 2010 Pearson Education, Inc.
Reflex Arc • Components of a reflex arc (neural path) 1. Receptor—site of stimulus action 2. Sensory neuron—transmits afferent impulses to the CNS 3. Integration center—either monosynaptic or polysynaptic region within the CNS 4. Motor neuron—conducts efferent impulses from the integration center to an effector organ 5. Effector—muscle fiber or gland cell that responds to the efferent impulses by contracting or secreting Copyright © 2010 Pearson Education, Inc.
Stimulus Skin 1 Receptor Interneuron 2 Sensory neuron 3 Integration center 4 Motor neuron 5 Effector Spinal cord (in cross section) Copyright © 2010 Pearson Education, Inc. Figure 13.14
Spinal Reflexes • Spinal somatic reflexes • Integration center is in the spinal cord • Effectors are skeletal muscle • Testing of somatic reflexes is important clinically to assess the condition of the nervous system Copyright © 2010 Pearson Education, Inc.
Stretch and Golgi Tendon Reflexes • For skeletal muscle activity to be smoothly coordinated, proprioceptor input is necessary • Muscle spindles inform the nervous system of the length of the muscle • Golgi tendon organs inform the brain as to the amount of tension in the muscle and tendons Copyright © 2010 Pearson Education, Inc.
Muscle Spindles • Composed of 3–10 short intrafusal muscle fibers in a connective tissue capsule • Intrafusal fibers • Noncontractile in their central regions (lack myofilaments) • Wrapped with two types of afferent endings: primary sensory endings of type Ia fibers and secondary sensory endings of type II fibers Copyright © 2010 Pearson Education, Inc.