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Peripheral Nervous System Place of the PNS in the structural organization of the nervous system CNS PNS Sensory division Sympathetic division Parasympathetic division Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Motor division Autonomic nervous system Somatic nervous system Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. Structure of a nerve Axon Blood vessels Perineurium Myelin sheath Endoneurium Perineurium Epineurium Fascicle Fascicle Blood vessels (a) Endoneurium Nerve fibers (b) Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. Spinal Nerves and Nerve Plexuses • Characteristics: – Somatic sensation (conscious) and somatic motor control (voluntary control) of skeletal muscles. – Includes cranial nerves: I, II, IV-VI, VIII, XI and XII. – Spinal nerves: 31 • • • • • Cervical: 8 (above C1, and below C1-C7) Thoracic: 12 (below T1-T12) Lumbar: 5 (below T1-T5) Sacral: 5 ( below S1-S5) Coccygeal: 1 exit coccyx – Mixed nerves • Sensory • Motor – Dorsal and ventral rami (nerve branches) plexuses (network of nerves) Distribution of spinal nerves Cervical plexus Brachial plexus Cervical nerves C1– C8 Cervical enlargement Intercostal nerves Thoracic nerves T1– T12 Lumbar enlargement Lumbar plexus Sacral plexus Cauda equina Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Lumbar nerves L1– L5 Sacral nerves S1– S5 Coccygeal nerve C0 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. Formation of spinal nerves and rami distribution Dorsal ramus Ventral ramus Spinal nerve Rami communicantes Intercostal nerve Dorsal root ganglion Ventral root Sympathetic trunk (chain) ganglion Dorsal root Thoracic cavity Lateral cutaneous Anterior cutaneous Sternum (b) Branches of intercostal nerve The cervical plexus Key: = Ventral rami Segmental branches Hypoglossal nerve (XII) Lesser occipital nerve Ventral rami: C1 Greater auricular nerve C2 Transverse cutaneous nerve C3 Ansa cervicalis C4 Accessory nerve (XI) Phrenic nerve Supraclavicular nerves C5 The brachial plexus Roots: Key: Dorsal scapular = Roots Nerve to subclavius Suprascapular = Trunks = Anterior division = Posterior division Cords C4 C5 C6 Upper Posterior divisions C7 Lateral C8 Posterior T1 Middle Trunks Lower Long thoracic Medial Medial pectoral Lateral pectoral Axillary Musculocutaneous Radial Median (a) Ulnar Upper subscapular Lower subscapular Thoracodorsal Medial cutaneous nerves of the arm and forearm The brachial plexus Trunks Humerus Radial nerve Musculocutaneous nerve Ulna Radius Ulnar nerve Median nerve Radial nerve (superficial branch) Dorsal branch of ulnar nerve Superficial branch of ulnar nerve Digital branch of ulnar nerve Muscular branch Median Digital nerve branch (c) Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. The lumbar plexus Ventral rami: L1 Iliohypogastric Ilioinguinal Iliohypogastric Ilioinguinal Genitofemoral L2 Femoral Lateral femoral L3 cutaneous Obturator Lateral femoral cutaneous Anterior L4 femoral cutaneous Saphenous Obturator Femoral L5 Lumbosacral trunk (a) Key: = Ventral rami (b) Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. The sacral plexus Ventral rami: L4 Superior gluteal L5 Lumbosacral trunk Inferior gluteal Common fibular Tibial Posterior femoral cutaneous Pudendal Sciatic (a) Key: = Ventral rami Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn S1 S2 S3 S4 S5 C0 Superior gluteal Inferior gluteal Pudendal Sciatic Posterior femoral cutaneous Common fibular Tibial Sural Deep fibular Superficial fibular Plantar branches (b) Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. • Activity 2 – Identify spinal chord tracts • Activity 3 – Identify Major nerve plexuses and Peripheral nerves The Autonomic Nervous System (ANS) Place of the ANS in the structural organization of the nervous system CNS PNS Sensory division Sympathetic division Parasympathetic division Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Motor division Autonomic nervous system Somatic nervous system Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. Characteristics of the ANS • Regulates body function unconsciously. – Cardiac muscle, smooth muscle, glands. • Consists of chains of 2 motor neurons. – Preganglion neuron: located in the CNS. – Ganglion neuron: synapses with pregalnglion, outside the CNS and its axon synapses with the effector organ. • Sympathetic (fight or flight) functions are antagonistic to the Parasympathetic (resting and digesting) functions. Comparison of somatic and autonomic nervous systems Central nervous system Peripheral nervous system Effector organs Acetylcholine Somatic nervous system Skeletal muscle Acetylcholine Sympathetic division Norepinephrine Smooth muscle (e.g., in gut) Ganglion Acetylcholine Autonomic nervous system Epinephrine and norepinephrine Blood vessel Glands Adrenal medulla Acetylcholine Parasympathetic division Cardiac muscle Ganglion Key: = Preganglionic axons (sympathetic) Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn = Postganglionic axons (sympathetic) = Myelination = Preganglionic axons (parasympathetic) = Postganglionic axons (parasympathetic) Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. Overview of the subdivisions of the ANS Parasympathetic Sympathetic Eye Brain stem Salivary glands Heart Eye Skin* Cranial Cervical Sympathetic ganglia Salivary glands Lungs Lungs T1 Heart Stomach Stomach Thoracic Pancreas Liver and gallbladder Pancreas L1 Liver and gallbladder Adrenal gland Lumbar Bladder Bladder Genitals Genitals Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Sacral Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. Parasympathetic (craniosacral) division of the ANS Eye Lacrimal gland Nasal mucosa Submandibular and sublingual glands CN III CN VII CN IX CN X III: Oculomotor Ciliary ganglion VII: Facial Pterygopalatine ganglion IX: Glossopharyngeal X: Vagus Parotid gland Submandibular ganglion Cardiac and pulmonary plexuses Otic ganglion Celiac plexus S2 Heart Lung Liver and gallbladder Stomach Pancreas S4 Pelvic splanchnic nerves Inferior hypogastric plexus Large intestine Small intestine Rectum Urinary bladder and ureters Genitalia (penis, clitoris, and vagina) Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. Characteristics of the Parasympathetic Division • Preganglion axons are located in the cranial nerves in the immediate area to be stimulated. • Terminal or intramural ganglion, which emits a short axon to the organ, synapse with the preganglion ganglion. • Sacral region ganglions synapse to pelvic splanchnic nerves that travel to the pelvic cavity. Sympathetic (thoracolumbar) division of the ANS Midbrain Superior cervical Pons ganglion Eye Lacrimal gland Nasal mucosa Sympathetic trunk (chain) ganglia Blood vessels; skin (arrector pili muscles and sweat glands) Medulla Middle cervical ganglion Inferior cervical ganglion T1 Salivary glands Heart Cardiac and pulmonary plexuses Lung Greater splanchnic nerve Lesser splanchnic nerve Liver and gallbladder Celiac ganglion L2 Stomach Superior mesenteric White rami communicantes ganglion Spleen Aortic plexus on aorta Lumbar splanchnic nerves Inferior mesenteric ganglion Adrenal gland Kidney Small intestine Large intestine Rectum Sympathetic division (thoracolumbar) Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Inferior hypogastric plexus Genitalia (uterus, vagina, and penis) and urinary bladder Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. Characteristics of the Sympathetic Division • Preganglion are located in the lateral ramus of the spinal chord T1 – L2. Axon leaves the chord via ventral root the spinal nerve the ventral ramus white ramus communicans paravertrebral ganglion in the sympathetic chain. • Preganglion axon may: – Synapse with a same level sympathetic ganglion chain neuron. – Travel up or downward through the sympathetic chain in the paravertebral region to another ganglion. • (Postganglionic reenter spinal nerve through gray ramus communicans to travel in dorsal or ventral ramus to innervate organs). – Skip the ganglion and form part of the splanchnic nerves, which travele to the organ to synapse with prevertebral or collateral ganglion. • Celiac, superior mesenteric, inferior mesenteric, hypogastric ganglia. Sympathetic trunks and pathways Dorsal root Ventral root Sympathetic trunk (chain) ganglion Lateral horn (visceral motor zone) Spinal cord Sympathetic trunk ganglion Body of a vertebra Dorsal white column Dorsal root ganglion Sympathetic trunk Ventral ramus of spinal nerve Gray ramus communicans Thoracic splanchnic nerves Intercostal nerve Intercostal muscle of thorax Rib (a) 2 White ramus communicans Ventral root Dorsal ramus of spinal nerve 3 1 1.Synapse in paravertebal region at the same level 2. Synapse in chain ganglion at different level 3. Synapse in prevertebral region anterior to vertebral column Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn 2 1 Splanchnic nerve Blood vessels Skin (arrector pili muscles and sweat glands) To effector Collateral (prevertebral) ganglion such as the celiac 3 Target organ (in abdomen) (b) Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. • Activity 4 – Locate the ANS chains in the models. Human Reflex Physiology • Definition: – Rapid, predictable and involuntary motor response to stimuli through pathways called reflex arcs. • Two systems – Autonomic reflexes (unconscious): digestion, sweating etc. – Somatic reflexes: activate skeletal muscles. Hierarchy of motor control Interactions Control level Programs and instructions (modified by feedback) Structures involved Highest (precommand) Cerebellum and basal nuclei Internal feedback Feedback Middle Projection areas Motor cortex (pyramidal system) and brain stem nuclei (vestibular, red, reticular formation, etc.) Segmental motor controls (CPG) Lowest Spinal cord Sensory input Reflex activity Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Motor output CNG: central pattern generator Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. The basic components of all human reflex arcs Spinal cord (in cross section) Stimulus 2 Sensory neuron 1 Receptor 4 Motor neuron Skin 3 Integration center Interneuron 5 Effector Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. The reflex arc • Characteristics: Structurally (number of neurons involved) – Monosynaptic arc: one synapse – Polysynaptic arc: one or more association neurons. • Somatic Reflexes (skeletal muscle effectors) – Stretch reflexes: Postural and locomotion reflexes. • Muscle spindle stimuli/Golgi organ in tendons (stretching) initiates reflex. – Reciprocal inhibition: antagonistic efferent muscles are relaxed (damped). – Patellar reflex (activity 1). The stretch reflex Interneuron 1 Afferent impulses from stretch receptor to spinal cord Initial stimulus: muscle stretch Cell body of sensory neuron Motor neuron serving quadriceps 2 Efferent impulses to alpha (a) motor neurons cause contraction of the stretched muscle that resists/reverses the stretch Motor neuron serving antagonist muscle group (hamstrings) – Spinal cord (L2–L4) Patella Muscle spindle Quadriceps (extensors) Muscle spindle Patellar ligament 3 Efferent impulses to antagonist muscles are damped (reciprocal inhibition) Hamstrings (flexors) Key: + Excitatory synapse – Inhibitory synapse (a) (b) Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. The Golgi tendon reflex Quadriceps (extensor) Golgi tendon organ Hamstrings (flexor) Spinal cord Interneurons + + + – Key: + Excitatory synapse – Inhibitory synapse Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Afferent fiber from Golgi tendon organ Efferent fiber to muscle associated with stretched tendon Efferent fiber to antagonistic muscle Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. Operation of the muscle spindle Muscle spindle Intrafusal muscle fiber Primary sensory (la) nerve fiber Extrafusal muscle fiber Time Time Time Time (a) Unstretched muscle; AP frequency constant (b) Stretched muscle; AP frequency increased (c) a Motor neuron stimulation only; no APs, unable to signal length changes (d) a - g Neuron coactivation; AP frequency constant AP: Action Potential Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. Anatomy of the muscle spindle and Golgi tendon organ g Efferent motor fiber to spindle Secondary sensory endings (type II fiber) Primary sensory endings (type Ia fiber) Muscle spindle Connective tissue capsule Capsule a Efferent motor fiber to extrafusal muscle fibers Extrafusal muscle fiber Intrafusal muscle fibers Sensory fiber Tendon Golgi tendon organ Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. Somatic Reflexes • Crossed extensor reflex: Withdrawal reflex, followed by extension of the opposite limb. • Activity 2? The crossed-extensor reflex Interneurons + + – Afferent fiber Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn – + Efferent fibers Efferent fibers Extensor inhibited Flexor stimulated Key: + Excitatory synapse – Inhibitory synapse + Flexor inhibited Extensor stimulated Arm movements Right arm (site of stimulus) Left arm (site of reciprocal activation) Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. Somatic Reflexes • Autonomic Reflexes – Pupillary reflexes – Salivary reflex • Reaction time of a reflex – Relative to the myelination of an axon andits length relative to the interneuron or association center. – Visual stimulus 150-300 ms. Somatic Reflexes • Superficial cord reflex: Abdominal, cremaster and plantar reflexes. • Plantar reflex. Normal pyramidal activity, toes flex and move close together. Activity 3. – Cranial nerve reflex: optical (motor) nerves. • Corneal reflex (V). Activity 4 Autonomic reflexes • Pupillary reflexes. – Cranial nerve II, III. • Actvity 6: Contralateral response, ipsilateral response. – Ciliospinal reflex. Pupilary. – Salivary reflex. Smooth/skeletal muscles. Visceral reflexes Sensory receptor in viscera Dorsal root ganglion Stimulus Central nervous system Visceral Visceral reflex arc (sensory) (Autonomic reflex) fiber Postganglionic axon Response Visceral effector Ganglionic neuron Autonomic ganglion Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Integration center (may be preganglionic neuron) Preganglionic axon Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. Referred pain Heart Lungs and diaphragm Liver Gallbladder Gallbladder Heart Appendix Liver Stomach Pancreas Small intestine Ovaries Colon Kidneys Urinary bladder Ureters Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings.
