Peripheral Nervous System PDF

Peripheral Nervous System  Topic Outline Introduction about Peripheral Nervous System Anatomy of Neurons and Nerves Autonomic Nervous System (ANS) Somatic Nervous System Cranial Nerves Nerves in the Forelimb and Hindlimb Reproductive and Urinary Nerves Enteric Nervous System  PERIPHER...

Peripheral Nervous System  Topic Outline Introduction about Peripheral Nervous System Anatomy of Neurons and Nerves Autonomic Nervous System (ANS) Somatic Nervous System Cranial Nerves Nerves in the Forelimb and Hindlimb Reproductive and Urinary Nerves Enteric Nervous System  PERIPHERAL NERVOUS SYSTEM Connects CNS (brain and spinal cord) to the rest of the body Consists of nerves outside the brain and spinal cord Peripheral Nervous System Enteric “Gut Brain” Peripheral Nervous System Enteric  Peripheral Nervous System Divided into two main parts: 1. Sensory Division (Afferent): Carries signals from the body to the CNS Divided into: Somatic Sensory: Detects external stimuli (skin, muscles, joints, special senses) Conscious sensations like touch, temperature, and pain Peripheral Nervous System Visceral Sensory: Monitors internal stimuli (organs like heart, lungs, stomach) Usually unconscious (e.g., hunger, internal pain)  Peripheral Nervous System Divided into two main parts: 2. Motor Division (Efferent): Carries signals from the CNS to the body: Divided into: Somatic Nervous System: Controls voluntary movements (skeletal muscles) Autonomic Nervous System (ANS): Controls involuntary functions (smooth muscle, cardiac muscle, glands)  Peripheral Nervous System Autonomic Nervous System (ANS) further divided into: Sympathetic Division: Fight or flight response Parasympathetic Division: Rest and digest response Peripheral Nervous System Anatomy of Neurons and Nerve  What is a Neuron? Building blocks of the nervous system Receive and transmit signals to different parts of the body Anatomy of a Neuron  Anatomy of a Neuron Soma (Cell Body) Contains the nucleus and organelles. Maintains neuron structure and provides energy. Dendrites Branching fibers that receive signals from other neurons. Can form multiple dendritic trees.  Anatomy of a Neuron Axon Long projection that transmits electrical signals away from the cell body. Joins the cell body at the axon hillock. Insulated by the myelin sheath for faster signal conduction.  Anatomy of a Neuron Myelin Sheath Fatty layer covering axons. Insulates nerve cells and speeds up impulse conduction. Nodes of Ranvier Gaps in the myelin sheath. Facilitate saltatory conduction, speeding up signal transmission. Schwann Cells Myelinate axons of peripheral neurons and support nerve function and repair.  Anatomy of a Neuron Parts of a Neuron Description Soma Contains genetic info, maintains structure, provides energy, and has a nucleus. Dendrite Branch-like structures that receive signals from other neurons. Axon Long projection, transmits signals, insulated by myelin, connects at axon hillock Myelin Sheath Fatty layer insulating axons, speeds up nerve impulse conduction. Nodes of Ranvier Gaps in myelin that speed up signal transmission. Schwann Cell Glial cell, supports neurons, forms myelin in the peripheral nervous system.  What is a Nerve? Composed of bundles of nerve fibers (axons or dendrites) surrounded by connective tissue.  Anatomy of Nerve Endoneurium Surrounds each individual axonal fiber and Schwann cells. Perineurium Surrounds groups of axons, forming bundles called fascicles.  Anatomy of Nerve Fascicle A bundle of nerve fibers organized for efficient signal transmission.  Anatomy of Nerve Epineurium The outermost layer that encases the entire nerve. Paraneurium (Mesoneurium) Loose areolar tissue surrounding the epineurium for added support.  Anatomy of a Neuron Parts of a Nerve Description Surrounds each individual axonal fiber and Schwann cells. Endoneurium Surrounds groups of axons, forming bundles called fascicles. Perineurium A bundle of nerve fibers organized for efficient signal transmission. Fascicle The outermost layer that encases the entire nerve. Epineurium Paraneurium (Mesoneurium) Loose areolar tissue surrounding the epineurium for added Autonomic Nervous System  Definition of Autonomic NS Part of the peripheral nervous system responsible for regulating involuntary bodily functions Controls essential functions such as heart rate, digestion, respiratory rate, and blood pressure Divided into two main branches: Sympathetic Nervous System (SNS): Activates "fight or flight" responses during stress Parasympathetic Nervous System (PNS): Supports "rest and digest" activities during relaxation Operates unconsciously to maintain homeostasis and respond to internal and external changes Sympathetic Nervous System Sympathetic NS Anatomy Origins in T1-L2 (thoracolumbar region) Sympathetic Chain Ganglia runs parallel to the vertebral column Preganglionic fibers are short, while postganglionic fibers are long Pathways differ based on whether the postganglionic neuron reenters the spinal nerve, joins a sympathetic nerve, or forms splanchnic nerves A unique pathway leads to the adrenal medulla, releasing adrenaline (epinephrine) and norepinephrine  Pathway 1: Spinal Nerve to Blood Vessels Preganglionic Neurons: Located in the lateral horn of the spinal cord segments T1-L2 Preganglionic neuron synapses in the sympathetic chain ganglia Postganglionic neuron exits via gray rami and reenters the spinal nerve Target: Skin and blood vessels throughout the body Pathway 2: Sympathetic Nerve to Thoracic Cavity Similar to Pathway #1, but postganglionic neurons enter sympathetic nerves Target: Organs in the thoracic cavity (e.g., heart, lungs)  Pathway 3: Sphlanchnic Nerves and Colateral Ganglia Preganglionic neurons bypass the sympathetic chain ganglia They form splanchnic nerves and synapse at collateral ganglia Target: Organs, glands, and vessels of the abdominopelvic cavity Splanchnic Nerves: Greater Splanchnic Nerve (T5-T9): Supplies the adrenal medulla and visceral organs like the stomach, liver, and kidneys Lesser Splanchnic Nerve (T10-T11): Innervates the small intestine and portions of the kidney Least Splanchnic Nerve (T12): Supplies parts of the kidney and ureter  Pathway 4: Direct Pathway to the Adrenal Medulla Preganglionic neurons do not synapse at any ganglia They directly stimulate cells in the adrenal medulla, leading to the release of adrenaline and norepinephrine This is part of the body's rapid "fight or flight" hormone response Sympathetic Nervous System Pathways Parasympathetic Nervous System Parasympathetic NS Anatomy Responsible for conserving energy and returning the body to homeostasis (rest and digest) Origin : Craniosacral division (brainstem and sacral spinal cord). Cranial outflow: From cranial nerves III, VII, IX, and X Sacral outflow: From sacral spinal cord segments S2-S4 Parasympathetic Cranial Nerves CN III (Oculomotor): Pupil constriction, lens accommodation CN VII (Facial): Stimulates tear and saliva production CN IX (Glossopharyngeal): Stimulates salivation in parotid glands CN X (Vagus): Major parasympathetic input to thoracic and abdominal organs Vagus Nerve (CN X) 75-80% of parasympathetic fibers are in the vagus nerve Supplies parasympathetic input to most thoracic and abdominal viscera Key functions: Slows heart rate, promotes digestion Sacral Region Preganglionic neurons in S2-S4 travel through pelvic splanchnic nerves Target: Bladder, rectum, and reproductive organs Parasympathetic Cranial Nerves  Comparison of Sympathetic NS and Parasympathetic NS  Aspect Sympathetic Nervous System (SNS) Parasympathetic Nervous System (PNS) SNS vs PNS General Function "Fight or flight" "Rest and digest" Craniosacral region (brainstem and Origin of Nerves Thoracolumbar region (T1-L3) sacral segments) Neurotransmitters Norepinephrine, epinephrine Acetylcholine Heart Rate Increases heart rate (tachycardia) Decreases heart rate (bradycardia) Bronchoconstriction (reduces airflow, Respiratory System Bronchodilation (increases airflow) increases mucus secretion) Dilates pupils (mydriasis) for improved Constricts pupils (miosis) for close Pupillary Response vision during stress vision during rest Inhibits digestion (decreases Stimulates digestion (increases Digestive System secretions, reduces peristalsis) secretions, promotes peristalsis) No significant effect on most blood Constricts most blood vessels Blood Vessels vessels (exception: dilation in genital (increases blood pressure) tissues during arousal) Liver Stimulates glucose release for energy No significant effect Bladder Function Relaxes bladder (inhibits urination) Contracts bladder (stimulates urination) Promotes ejaculation and vaginal Promotes erection and vaginal Reproductive System contraction during orgasm lubrication Sweat Glands Activates sweat production No effect Energy Use Increases energy expenditure Conserves energy SNS vs PNS Innervations SNS and PNS Neurons Somatic Nervous System SOMATIC NS aka voluntary nervous system responsible for contraction and movement of skeletal muscles Includes all of the nerves that extend from the brain and spinal cord Cranial nerves and spinal nerves CRANIAL NERVES Olfactory Nerve (CN I) Function: Detects chemical molecules (odorants) (Purely sensory nerve; doesn't control any muscles or other motor functions). Optic Nerve (CN II) Optic Nerve Function: Carries sensory signals (Purely sensory nerve; doesn't control any muscles or other motor functions)  Oculomotor Nerve (CN III) Function: Controlling most of the eye's movements Innervated Muscles: Extraocular Muscles Superior Rectus - elevates the eyeball Levator Palpabrae Superioris - raises the upper eyelid Inferior Rectus – depresses the eyeball Medial Rectus – adducts the eyeball Inferior Oblique – elevates, abducts and laterally rotates the eyeball Trochlear Nerve (CN IV) Function: Helps maintain stable vision Innervated Muscle: Superior Oblique Muscle - depress and intort the eyeball Trigeminal Nerve (CN V) Function: Responsible for sensation in the face and controlling the muscles involved in chewing. The peripheral aspect of the trigeminal ganglion gives rise to 3 divisions: ophthalmic (V1), maxillary (V2) and mandibular (V3). Innervated Muscles: Masseter: Elevates the jaw to close the mouth. Temporalis: Assists in closing the mouth and retracting the jaw. Medial pterygoid: Assists in jaw closure. Lateral pterygoid: Helps to open the jaw and move it side to side. Trigeminal Nerve (CN V) Abducens Nerve (CN VI) Function: Crucial for lateral eye movement. Innervated Muscle: Lateral Rectus - abduct the eyeball (i.e. to rotate the gaze away from the midline) Facial Nerve (CN VII) Function: Expressing emotions, tasting food, and regulating essential glands in the face. Innervated Muscles: Frontalis: Raises the eyebrows. Orbicularis oculi: Closes the eyelids. Orbicularis oris: Controls the movement of the lips. Buccinator: Helps in chewing by compressing the cheeks. Vestibulocochlear Nerve (CN VIII) Function: Responsible for hearing and balance. It has two distinct components. 1. Cochlear Nerve (Hearing): Transmits sound information from the inner ear to the brain. 2.Vestibular Nerve (Balance): Transmits information from the vestibular organs in the inner ear. It does not control any muscles but rather transmits sensory input related to hearing and balance.  Glossopharyngeal Nerve (CN IX) Function: Essential for taste, swallowing, salivation, and monitoring key cardiovascular functions. innervated Muscle: Stylopharyngeus - assists in elevating the pharynx during swallowing and speech. Vagus Nerve (CN X) Function: Helps regulate involuntary bodily functions Innervated Muscle: Pharyngeal Muscles Superior, Middle and Inferior pharyngeal constrictor Palatopharyngeus Salpingopharyngeus Levator veli palatini Laryngeal Muscles Recurrent Laryngeal Nerve (Thyro-arytenoid, Posterior and Lateral crico-arytenoid, Transverse and Oblique arytenoids, and Vocalis) External Branch of the Superior Laryngeal Nerve Vagus Nerve (CN X) Accessory Nerve (CN XI) Function: Essential for controlling key neck and shoulder movements in dogs. Innervated Muscle: Trapezius Sternocleidomastoid Hypoglossal Nerve (CN XII) Function: Essential for various activities, including eating, drinking, and vocalization. Innervated Muscle: Extrinsic muscles Genioglossus Hyoglossus Styloglossus Intrinsic muscles Superior longitudinal Inferior longitudinal Transverse muscle of the tongue Vertical muscle of the tongue  TRACING OF THE FORELIMB NERVES  RADIAL NERVE Description: A.K.A. n. radialis Composed of superficial and deep branches Innervated Muscle: Triceps brachii (all heads) Tensor fasciae antebrachii Function: Controls extension of the elbow, carpus, and digits, supination of the paw Provides sensation to the forelimb and paw. RADIAL NERVE radial nerve DEEP BRANCH OF RADIAL N. A.K.A. ramus profundus Passes under the extensor carpi radialis and supinator muscles Divides to supply the extensors of the carpus and digits. Innervated Muscle: extensor carpi radialis m. common digital extensor m. lateral digital extensor m. Function: anconeus innervate the extensor muscles of the forelimb, allowing supinator extension of the carpus (wrist) and digits. abductor digiti I longus/external carpi obliquus provides sensory input to the antebrachiocarpal (wrist) joint. DEEP BRANCH OF RADIAL N. SUPERFICIAL BRANCH OF RADIAL N. A.K.A. ramus superficialis Lies beneath the lateral head of the triceps brachii Runs along the brachialis muscle and splits into lateral and medial branches. Innervated Muscle: none Function: provides sensory innervation, not motor innervation to muscles. It supplies the skin on the cranial surface of the antebrachium and the dorsum of the paw. SUPERFICIAL BRANCH OF RADIAL N. Function: provides sensory innervation, not motor innervation to muscles. It supplies the skin on the cranial surface of the antebrachium and the dorsum of the paw.  MEDIAN NERVE A.K.A n. medianus travels deep to the pronator teres muscle and supplies several flexor muscles, including the flexor carpi radialis, superficial digital flexor, and parts of the deep digital flexor. Innervated Muscle: Pronator Teres Pronator Quadratus Flexor Carpi Radialis Flexor Digitorum Superficialis/superficial digital flexor Radial Head of Flexor Digitorum Profundus/deep digital flexor Function: flex muscles of the forearm, allowing for flexion at the carpal and digital joints. provides sensory innervation to the skin on the palmar side of the forepaw and part of the dorsal surface. MEDIAN NERVE median nerve  ULNAR NERVE A.K.A n. ulnaris runs caudally through the forelimb, crossing the elbow behind the medial epicondyle. Innervated Muscle: Flexor Carpi Ulnaris Flexor Digitorum Profundus (medial head) Superficial Digital Flexor (humeral head) Deep Digital Flexor (ulnar portion) Function: flex the wrist (carpus) and digits. sensory innervation of the forepaw and the fifth digit.  ULNAR NERVE Innervated Muscle: Flexor Carpi Ulnaris Flexor Digitorum Profundus/deep digital flexor Function: flex the wrist (carpus) and digits. sensory innervation to the skin on the medial aspect of the forepaw and the fifth digit.  CAUDAL CUTANEOUS ANTEBRACHIAL N. A.K.A. n. cutaneus antebrachii caudalis travels over the medial surface of the olecranon and supplies the proximal two-thirds of the caudolateral forelimb. Innervated Muscle: None Function: it is purely a sensory nerve. Its function is to provide sensation to the skin of the antebrachium (forearm). MUSCULAR BRANCHES OF THE ULNAR NERVE A.K.A. rami musculares arise as the ulnar nerve passes caudal to the medial epicondyle of the humerus.  MUSCULAR BRANCHES OF THE ULNAR NERVE Muscle: Flexor Carpi Ulnaris Flexor digitorum profundus/deep digital flexor Function: innervate the muscles responsible for flexing the carpus and digits.  TRACING OF THE HINDLIMB NERVES FEMORAL NERVE Description: Runs between the sartorius and iliopsoas m. Lies lateral to the femoral artery Innervated Muscle: Sartorius m. Iliacus m. Quadriceps femoris m. Function: Helps the muscles straighten the leg and move the hip TIBIAL NERVE Description: Continuation of sciatic n. Runs between the gastrocnemius m. and passes on the medial aspect of the thigh Innervated Muscle: Gastrocnemius m. Superficial Digital Flexor m. Deep Digital Flexor m. Popliteus m. Function: Supplies movement to the lower leg COMMON PERONEAL N. Description: Aka Common Fibular n. Descends obliquely along the lateral side of the popliteal fossa to the fibular head Innervated Muscle: Cranial Tibial m. Long Digital Extensor m. Peroneus Longus m. Function: Supplies movement in the lower leg SURAL NERVE Description: Descends lateral to the calcaneal tendon Near the short saphenous vein Innervated Muscle: None Function: Detect foot position Purely sensory nerve  SAPHENOUS NERVE Description: Terminal branch of the femoral nerve Innervated Muscle: Sartorius m. Function: Provides sensation to the medial aspect of the lower leg and the medial foot Purely sensory nerve PLANTAR NERVE Description: Compromised the medial and lateral divisions Lateral Plantar n. Medial Plantar n. -branches in the posterior part of the tibial n. Medial Plantar n. Lateral Plantar n. - branches laterally from the tibial n. Innervated Muscle: Palmar m. (e.g. plantar fascia m.) Function: Provides sensation in the foot SUMMARY REPRODUCTIVE AND URINARY NERVES  Reproductive Nerve Supply: Male System: Sympathetic: Hypogastric nerve controls ejaculation and prevents retrograde ejaculation. Parasympathetic: Pelvic nerve promotes erection via vasodilation. Somatic: Pudendal nerve aids in erection and ejaculation. Female System: Sympathetic: Hypogastric nerve influences uterine contractions and reproductive tract tone. Parasympathetic: Pelvic nerve facilitates clitoral and vaginal vasodilation for arousal. Somatic: Pudendal nerve manages external genitalia control.  Urinary Nerve Supply: HYPOGASTRIC NERVE Sympathetic Innervation: Hypogastric nerve(L1–L4) Controls bladder relaxation and internal urethral sphincter contraction, promoting urine retention.  Pelvic nerve(S1–S3) Parasympathetic Innervation: Pelvic nerve(S1–S3) Stimulates detrusor muscle contraction and relaxes the internal urethral sphincter, facilitating urination.  PUDENDAL NERVE Somatic Innervation: Pudendal nerve(S1–S3) Manages voluntary control of the external urethral sphincter. Sensory Afferents: Pelvic and hypogastric nerves relay bladder fullness to the CNS.  Sensory Afferents: Sensory Afferents: Pelvic and hypogastric nerves relay bladder fullness to the CNS. ENTERIC NERVOUS SYSTEM ENTERIC NERVOUS SYSTEM Local nervous system of the gut Composed of two ganglionated plexuses: 1. Myenteric (Auerbach) 2. Submucosal (Meissner) plexuses Self-contained, functioning through local reflex activity, but often receives input from, and provides feedback to SNS and PNS May receive input from postganglionic sympathetic neurons or preganglionic parasympathetic neurons ENS neurons use over 30 neurotransmitters that are similar to those of the CNS, with cholinergic and nitrergic transmitters being the most common AUERBACH’S PLEXUS / MYENTERIC PLEXUS Sits in between the longitudinal and circular smooth muscle of the GI tract Coordinates the contractility of the circular and longitudinal muscle cells of the gut to produce peristalsis MEISSNER’S PLEXUS / SUBMUCOSAL PLEXUS Submucosal plexus is present within the submucosa Governs the movement of water and electrolytes across the intestinal wall Enteric neurons can be bipolar, pseudounipolar, and multipolar MYENTERIC PLEXUS AND SUBMUCOSAL PLEXUS ILLUSTRATION OF ENS THANK YOU FOR LISTENING Ohhh yeahhh!