Peripheral Nervous System

Place of the PNS in the structural organization of the nervous system CNS PNS Sensory division Motor division Sympathetic division Autonomic nervous system Somatic nervous system Parasympathetic division

Axon Blood vessels Perineurium Myelin sheath Endoneurium Perineurium Structure of a nerve Axon Blood vessels Perineurium Myelin sheath Endoneurium Perineurium Epineurium Fascicle Fascicle Blood vessels Endoneurium Nerve fibers (a) (b)

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 Cervical nerves C1– C8 Brachial plexus Cervical enlargement Intercostal Thoracic nerves T1– T12 nerves Lumbar enlargement Lumbar plexus Lumbar nerves L1– L5 Sacral plexus Sacral nerves S1– S5 Cauda equina Coccygeal nerve C0

Formation of spinal nerves and rami distribution Dorsal ramus Ventral ramus Spinal nerve Intercostal nerve Rami communicantes Dorsal root ganglion Ventral root Sympathetic trunk (chain) ganglion Dorsal root Thoracic cavity Lateral cutaneous Branches of intercostal nerve Anterior cutaneous Sternum (b)

The cervical plexus Key: = Ventral rami Segmental branches Hypoglossal nerve (XII) Ventral rami: Lesser occipital nerve C1 Greater auricular nerve C2 Transverse cutaneous nerve C3 Ansa cervicalis C4 Accessory nerve (XI) C5 Phrenic nerve Supraclavicular nerves

The brachial plexus Roots: Key: C4 Dorsal scapular = Roots C5 Nerve to subclavius = Trunks C6 Suprascapular Upper = Anterior division Posterior divisions C7 Middle Trunks = Posterior division C8 Lateral Lower T1 Cords Posterior Long thoracic Medial Medial pectoral Lateral pectoral Axillary Upper subscapular Musculo- cutaneous Lower subscapular Thoracodorsal Radial Medial cutaneous nerves of the arm and forearm Median (a) Ulnar

Trunks Humerus Radial nerve Musculo- cutaneous nerve Ulna Radius The brachial plexus Trunks Humerus Radial nerve Musculo- cutaneous 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 nerve Digital branch (c)

Ventral rami: L1 Iliohypogastric Ilioinguinal L2 Iliohypogastric The lumbar plexus Ventral rami: L1 Iliohypogastric Ilioinguinal L2 Iliohypogastric Femoral Ilioinguinal Lateral femoral cutaneous Genitofemoral L3 Obturator Lateral femoral cutaneous Anterior femoral cutaneous L4 Saphenous Obturator L5 Femoral Lumbosacral trunk (a) Key: = Ventral rami (b)

Ventral rami: L4 Superior gluteal Superior gluteal L5 Inferior gluteal The sacral plexus Ventral rami: L4 Superior gluteal Superior gluteal L5 Inferior gluteal Lumbosacral trunk Pudendal S1 Inferior gluteal Sciatic Posterior femoral cutaneous Common fibular S2 Tibial Common fibular S3 Posterior femoral cutaneous Tibial S4 Sural Pudendal Deep fibular S5 Sciatic C0 Superficial fibular (a) Key: Plantar branches = Ventral rami (b)

Activity 2 Activity 3 Identify spinal chord tracts 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 Motor division Sympathetic division Autonomic nervous system Somatic nervous system Parasympathetic division

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 Norepinephrine Smooth muscle (e.g., in gut) Ganglion Sympathetic division Acetylcholine Epinephrine and norepinephrine Autonomic nervous system Blood vessel Glands Adrenal medulla Acetylcholine Cardiac muscle Para- sympathetic division Ganglion Key: = Preganglionic axons (sympathetic) = Postganglionic axons (sympathetic) = Myelination = Preganglionic axons (parasympathetic) = Postganglionic axons (parasympathetic)

Overview of the subdivisions of the ANS Parasympathetic Sympathetic Eye Eye Brain stem Salivary glands Skin* Cranial Salivary glands Sympathetic ganglia Heart Cervical Lungs Lungs T1 Heart Stomach Thoracic Stomach Pancreas Liver and gall- bladder Pancreas L1 Liver and gall- bladder Adrenal gland Lumbar Bladder Bladder Genitals Genitals Sacral

Parasympathetic (craniosacral) division of the ANS Eye CN III Lacrimal gland CN VII CN IX Nasal mucosa CN X III: Oculomotor VII: Facial IX: Glossopharyngeal X: Vagus Ciliary ganglion Submandibular and sublingual glands Pterygopalatine ganglion Parotid gland Submandibular ganglion Heart Cardiac and pulmonary plexuses Otic ganglion Lung Liver and gallbladder Celiac plexus Stomach S2 Pancreas S4 Large intestine Pelvic splanchnic nerves Small intestine Inferior hypogastric plexus Rectum Urinary bladder and ureters Genitalia (penis, clitoris, and vagina)

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 Eye Lacrimal gland Nasal mucosa Sympathetic trunk (chain) ganglia Midbrain Superior cervical ganglion Pons Blood vessels; skin (arrector pili muscles and sweat glands) Medulla Middle cervical ganglion Salivary glands Heart Inferior cervical ganglion Cardiac and pulmonary plexuses Lung T1 Greater splanchnic nerve Lesser splanchnic nerve Liver and gall- bladder Celiac ganglion Stomach L2 Superior mesenteric ganglion White rami communicantes Spleen Adrenal gland Aortic plexus on aorta Kidney Lumbar splanchnic nerves Small intestine Inferior mesenteric ganglion Large intestine Rectum Sympathetic division (thoracolumbar) Inferior hypogastric plexus Genitalia (uterus, vagina, and penis) and urinary bladder

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 Spinal cord Dorsal root Ventral root Dorsal white column Sympathetic trunk ganglion Sympathetic trunk (chain) ganglion Body of a vertebra Lateral horn (visceral motor zone) Dorsal root ganglion Sympathetic trunk Thoracic splanchnic nerves Ventral ramus of spinal nerve Gray ramus communicans Intercostal nerve 2 Intercostal muscle of thorax White ramus communicans Rib (a) Ventral root Dorsal ramus of spinal nerve 3 2 1 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 Splanchnic nerve Blood vessels Collateral (prevertebral) ganglion such as the celiac 3 To effector Skin (arrector pili muscles and sweat glands) Target organ (in abdomen) (b)

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 Structures involved Programs and instructions (modified by feedback) Highest (precommand) Cerebellum and basal nuclei Internal feedback Feedback Projection areas Middle Motor cortex (pyramidal system) and brain stem nuclei (vestibular, red, reticular formation, etc.) Segmental motor controls (CPG) Lowest Spinal cord Sensory input Reflex activity Motor output CNG: central pattern generator

The basic components of all human reflex arcs Spinal cord (in cross section) Stimulus 2 Sensory neuron 3 Integration center 1 Receptor Motor neuron Interneuron Skin 4 5 Effector

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).

Interneuron Cell body of sensory neuron 1 Afferent impulses The stretch reflex Interneuron Cell body of sensory neuron 1 Afferent impulses from stretch receptor to spinal cord 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) – Initial stimulus: muscle stretch Spinal cord (L2–L4) Muscle spindle Patella Quadriceps (extensors) Muscle spindle Patellar ligament Hamstrings (flexors) 3 Efferent impulses to antagonist muscles are damped (reciprocal inhibition) Key: + Excitatory synapse – Inhibitory synapse (a) (b)

The Golgi tendon reflex organ Quadriceps (extensor) Hamstrings (flexor) Spinal cord Interneurons + + Afferent fiber from Golgi tendon organ – + Efferent fiber to muscle associated with stretched tendon Key: + Excitatory synapse – Inhibitory synapse Efferent fiber to antagonistic muscle

Operation of the 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

Anatomy of the muscle spindle and Golgi tendon organ  Efferent motor fiber to spindle Secondary sensory endings (type II fiber) a Efferent motor fiber to extrafusal muscle fibers Primary sensory endings (type Ia fiber) Extrafusal muscle fiber Muscle spindle Intrafusal muscle fibers Connective tissue capsule Sensory fiber Capsule Tendon Golgi tendon organ

Somatic Reflexes Crossed extensor reflex: Withdrawal reflex, followed by extension of the opposite limb. Activity 2?

The crossed-extensor reflex Interneurons + + – + + – Efferent fibers Afferent fiber Efferent fibers Extensor inhibited Flexor inhibited Flexor stimulated Flexes Arm movements Extensor stimulated Extends Key: + Excitatory synapse – Inhibitory synapse Right arm (site of stimulus) Left arm (site of reciprocal activation)

Somatic Reflexes Autonomic Reflexes Reaction time of a reflex 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.

Dorsal root ganglion Sensory receptor in viscera Central nervous Visceral reflexes Dorsal root ganglion Sensory receptor in viscera Central nervous system Stimulus Visceral (sensory) fiber Visceral reflex arc (Autonomic reflex) Postganglionic axon Visceral effector Response Integration center (may be preganglionic neuron) Ganglionic neuron Autonomic ganglion Preganglionic axon

Heart Lungs and diaphragm Liver Gallbladder Gallbladder Heart Liver Referred pain Heart Lungs and diaphragm Liver Gallbladder Gallbladder Heart Appendix Liver Stomach Pancreas Small intestine Ovaries Colon Kidneys Urinary bladder Ureters