Marieb Human Anatomy & Physiology Chapter 13 Lecture Notes PDF

Marieb Human Anatomy & Physiology Twelfth Edition Chapter 13 The Peripheral Nervous System and Reflex Activity PowerPoint® Lecture Slides...

Marieb Human Anatomy & Physiology Twelfth Edition Chapter 13 The Peripheral Nervous System and Reflex Activity PowerPoint® Lecture Slides prepared by Ashley Spring, Ph.D., Eastern Florida State College Copyright © 2025 Pearson Education, Inc. All Rights Reserved Why This Matters Understanding the peripheral nervous system help you to recognize and treat nerve damage Copyright © 2025 Pearson Education, Inc. All Rights Reserved Video: Why This Matters (Career Connection) Click here to view ADA compliant video: Why This Matters (Career Connection) https://mediaplayer.pearsoncmg.com/assets/secs_wtm_ch_13_christian_v2 Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Peripheral Nervous System PNS provides links from and to world outside our body Consists of all neural structures outside brain and spinal cord that can be broken down into four parts: Part 1—Sensory Receptors and Sensations Part 2—Transmission Lines: Nerves and Their Structure and Repair Part 3—Motor Endings and Motor Activity Part 4—Reflex Activity Copyright © 2025 Pearson Education, Inc. All Rights Reserved Place of the PNS in the Structural Organization of the Nervous System Figure 13.1 Place of the PNS in the structural organization of the nervous system. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Part 1—Sensory Receptors and Sensation Copyright © 2025 Pearson Education, Inc. All Rights Reserved 13.1 Sensory Receptors Sensory receptors: specialized to respond to changes in environment (stimuli) – Activation results in graded potentials that trigger nerve impulses Awareness of stimulus (sensation) and interpretation of meaning of stimulus (perception) occur in brain Three ways to classify receptors: – Type of stimulus – Body location – Structural complexity Copyright © 2025 Pearson Education, Inc. All Rights Reserved Classification by Stimulus Type Mechanoreceptors—respond to touch, pressure, vibration, and stretch Thermoreceptors—sensitive to changes in temperature Photoreceptors—respond to light energy (e.g., retina) Chemoreceptors—respond to chemicals (e.g., smell, taste, changes in blood chemistry) Nociceptors—sensitive to pain-causing stimuli (e.g., extreme heat or cold, excessive pressure, inflammatory chemicals) Copyright © 2025 Pearson Education, Inc. All Rights Reserved Classification by Location Exteroceptors – Respond to stimuli arising outside body – Receptors in skin for touch, pressure, pain, and temperature – Most special sense organs Interceptors (visceroceptors) – Respond to stimuli arising in internal viscera and blood vessels – Sensitive to chemical changes, tissue stretch, and temperature changes – Sometimes cause discomfort but usually person is unaware of their workings Proprioceptors – Respond to stretch in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles – Inform brain of one’s movements Copyright © 2025 Pearson Education, Inc. All Rights Reserved Classification by Receptor Structure (1 of 8) Majority of sensory receptors belong to one of two categories: – Simple receptors of the general senses ▪ Modified dendritic endings of sensory neurons ▪ Are found throughout body and monitor most types of general sensory information – Receptors for special senses ▪ Vision, hearing, equilibrium, smell, and taste ▪ All are housed in complex sense organs Copyright © 2025 Pearson Education, Inc. All Rights Reserved Classification by Receptor Structure (2 of 8) Simple receptors of the general senses – General senses include tactile sensations (touch, pressure, stretch, vibration), temperature, pain, and muscle sense ▪ No “one-receptor-one-function” relationship – Receptors can respond to multiple stimuli – Receptors have either: ▪ Nonencapsulated (free) nerve endings or ▪ Encapsulated nerve endings Copyright © 2025 Pearson Education, Inc. All Rights Reserved Classification by Receptor Structure (3 of 8) – Nonencapsulated (free) nerve endings ▪ Abundant in epithelia and connective tissues ▪ Most are nonmyelinated, small-diameter group C fibers; distal terminals have knoblike swellings ▪ Respond mostly to temperature, pain, or light touch Copyright © 2025 Pearson Education, Inc. All Rights Reserved Classification by Receptor Structure (4 of 8) – Nonencapsulated (free) nerve endings (cont ) inued ▪ Thermoreceptors – Cold receptors are activated by temps from 10 to 40 C – Located in superficial dermis – Heat receptors are activated from 32 to 48 C located in in deeper dermis – Outside those temperature ranges, nociceptors are activated and interpreted as pain Copyright © 2025 Pearson Education, Inc. All Rights Reserved Classification by Receptor Structure (5 of 8) – Nonencapsulated (free) nerve endings (cont ) inued ▪ Nociceptors: pain receptors triggered by extreme temperature changes, pinch, or release of chemicals from damaged tissue – Vanilloid receptor: protein in nerve membrane is main player Acts as ion channel that is opened by heat, low pH, chemicals (e.g., capsaicin in red peppers) Itch receptors in dermis: can be triggered by chemicals such as histamine Copyright © 2025 Pearson Education, Inc. All Rights Reserved Classification by Receptor Structure (6 of 8) – Nonencapsulated (free) nerve endings (cont ) inued ▪ Tactile (Merkel) discs: function as light touch receptors – Located in deeper layers of epidermis ▪ Hair follicle receptors: free nerve endings that wrap around hair follicles – Act as light touch receptors that detect bending of hairs Example: Allows you to feel a mosquito landing on your skin Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.1-1 General Sensory Receptors Classified by Structure and Function Table 13.1 General Sensory Receptors Classified by Structure and Function. Nonencapsulated Structural Class Illustration Functional Classes According to Body Location Location (L) and Stimulus Type (s) Free nerve endings L: Exteroceptors, interoceptors, and Most body tissues; most of sensory neurons proprioceptors dense in connective tissues neur ons a ppe An ilust r at ionsh ar asantenn owsFreene a-like structures,en r veend ingsofsen dingbranchese sory xtend ingt h ro ugh outt h et issue. S: Thermoreceptors (warm and cool), (ligaments, tendons, dermis, chemoreceptors (itch, pH, etc.), joint capsules, periostea) and mechanoreceptors (pressure), nociceptors epithelia epidermis, cornea, (pain) mucosae, and glands) Modified free nerve L: Exteroceptors Basal layer of epidermis endings: Epithelial S: Mechanoreceptors (light pressure); tactile complexes An ilust r at ionsh owsMod if iedfr een erveen dings.At a ctile ep it he lial cell iswit h in a nepithelial tactilecomp synapse wit hatactileepithelial cel. lex. Axonendsinanep it he lial t a ctile co mplex,whichinclud esa slowly adapting (Merkel cells and discs) Hair follicle L: Exteroceptors Surrounding hair follicles receptors S: Mechanoreceptors (hair deflection); An ilust r at ionsh owstheha ir f o licle r eceptorwit han te n-na likestr u ctur e satt a che dt otheroo t oft h ehair folicle. End ingbr a nch eswraparoun dahair folicle. rapidly adapting Copyright © 2025 Pearson Education, Inc. All Rights Reserved Classification by Receptor Structure (7 of 8) – Encapsulated dendritic endings ▪ Almost all are mechanoreceptors whose terminal endings are encased in connective tissue capsule ▪ Vary greatly in shape and include: – Tactile (Meissner’s) corpuscles: small receptors involved in discriminative touch Found just below skin, mostly in sensitive and hairless areas (fingertips) – Lamellar (Pacinian) corpuscles: large receptors respond to deep pressure and vibration when first applied (then turn off) Located in deep dermis Copyright © 2025 Pearson Education, Inc. All Rights Reserved Classification by Receptor Structure (8 of 8) – Encapsulated dendritic endings (cont ) inued – Bulbous corpuscles (Ruffini endings): respond to deep and continuous pressure Located in dermis – Muscle spindles: spindle-shaped proprioceptors that respond to muscle stretch – Tendon organ: proprioceptors located in tendons that detect stretch – Joint kinesthetic receptors: proprioceptors that monitor joint position and motion Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.1-2 General Sensory Receptors Classified by Structure and Function (1 of 2) Table 13.1 General Sensory Receptors Classified by Structure and Function. Encapsulated Structural Illustration Functional Classes According to Body Location Class Location (L) and Stimulus Type (s) Tactile L: Exteroceptors Dermal papillae of hairless (Meissner’s) S: Mechanoreceptors (light pressure, skin, particularly nipples, corpuscles discriminative touch, vibration of low external genitalia, fingertips, An ilust r at ionsh owsatactile corpusclecon ta iningspir a ls o f ne r vef ibe r sen cap sulatedwithinacap sule. frequency); rapidly adapting soles of feet, eyelids Lamellar L: Exteroceptors, interoceptors, and Dermis and hypodermis; (Pacinian) some proprioceptors periostea, mesentery, tendons, corpuscles An ilust r at ionsh owsalamellar co rp uscle containingconcentr iclaye r so f lamellaeencapsulatingaf lataxo nt e r minal. S: Mechanoreceptors (deep pressure, ligaments, joint capsules; most stretch, vibration of high frequency); abundant on fingers, soles of rapidly adapting feet, external genitalia, nipples Bulbous L: Exteroceptors and Proprioceptors Deep in dermis, hypodermis, corpuscles An ilust r at ionsh owsabu lbouscorpusclecompo sedo f asing le, bran chingsensor yfiberin athinca psu le sur rou nde dbyco lagenfiber s. S: Mechanoreceptors (deep pressure and joint capsules (Ruffini endings) and stretch); slowly or nonadapting Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.1-2 General Sensory Receptors Classified by Structure and Function (2 of 2) Table 13.1 General Sensory Receptors Classified by Structure and Function. Nonencapsulated Structural Illustration Functional Classes According to Body Location Class Location (L) and Stimulus Type (s) Muscle spindles L: Proprioceptors Skeletal muscles, S: Mechanoreceptors(muscle stretch, particularly in the An ilust r ationsho wsamuscle spindleco ntainingne r vee nding swr a ppe dar o undintrafusa l fiber s,whicha r ee nca sedinaca psu le. length) extremities Tendon organs L: Proprioceptors Tendons S: Mechanoreceptors (tendon stretch, An ilust r ationsho wsat e ndo norgancontainingn er ve-end ingbr a nch esthatwr a par o undtheten dona ndareall e nca sedinaco nne ctivet issueca psu le o f thetend on. tension) Joint kinesthetic L: Proprioceptors Joint capsules of receptors Blank S: Mechanoreceptors and nociceptors synovial joints Copyright © 2025 Pearson Education, Inc. All Rights Reserved 13.2 Sensory Processing Survival depends upon: – Sensation: the awareness of changes in the internal and external environment – Perception: the conscious interpretation of those stimuli Copyright © 2025 Pearson Education, Inc. All Rights Reserved General Organization of the Somatosensory System (1 of 7) Somatosensory system: part of sensory system serving body wall and limbs Receives inputs from: – Exteroceptors, proprioceptors, and interoceptors Input is relayed toward head, but processed along the way Copyright © 2025 Pearson Education, Inc. All Rights Reserved General Organization of the Somatosensory System (2 of 7) Levels of neural integration in sensory systems: 1. Receptor level: sensory receptors 2. Circuit level: processing in ascending pathways 3. Perceptual level: processing in cortical sensory areas Copyright © 2025 Pearson Education, Inc. All Rights Reserved Three Basic Levels of Neural Integration in Sensory Systems Figure 13.2 Three basic levels of neural integration in sensory systems. Copyright © 2025 Pearson Education, Inc. All Rights Reserved General Organization of the Somatosensory System (3 of 7) Processing at the receptor level – Generating a signal: For sensation to occur, the stimulus must excite a receptor, and the AP must reach CNS ▪ Stimulus energy must match receptor specificity (touch receptors do not respond to light) ▪ Stimulus must be applied within receptive field ▪ Transduction must occur—energy of stimulus is converted into graded potential called generator potential (in general receptors) or receptor potential (in special sense receptors) ▪ Graded potentials must reach threshold → AP Copyright © 2025 Pearson Education, Inc. All Rights Reserved General Organization of the Somatosensory System (4 of 7) Processing at the receptor level (cont ) inued – Adaptation: Change in sensitivity in presence of constant stimulus ▪ Receptor membranes become less responsive ▪ Receptor potentials decline in frequency or stop ▪ Phasic receptors: (fast-adapting) send signals at 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 Copyright © 2025 Pearson Education, Inc. All Rights Reserved General Organization of the Somatosensory System (5 of 7) Processing at the circuit level – Pathways of three neurons conduct sensory impulses received from receptors upward to appropriate cortical regions – First-order sensory neurons ▪ Conduct impulses from receptor level to spinal reflexes or second-order neurons in CNS – Second-order sensory neurons ▪ Transmit impulses to third-order sensory neurons – Third-order sensory neurons ▪ Conduct impulses from thalamus to the somatosensory cortex (perceptual level) Copyright © 2025 Pearson Education, Inc. All Rights Reserved General Organization of the Somatosensory System (6 of 7) Processing at the perceptual level – Interpretation of sensory input depends on specific location of target neurons in sensory cortex – Aspects of sensory perception: ▪ Perceptual detection: ability to detect a stimulus (requires summation of impulses) ▪ Magnitude estimation: intensity coded in frequency of impulses ▪ Spatial discrimination: identifying site or pattern of stimulus (studied by two-point discrimination test) Copyright © 2025 Pearson Education, Inc. All Rights Reserved General Organization of the Somatosensory System (7 of 7) Processing at the perceptual level (cont ) inued – Feature abstraction: identification of more complex aspects and several stimulus properties – Quality discrimination: ability to identify submodalities of a sensation (e.g., sweet or sour tastes) – Pattern recognition: recognition of familiar or significant patterns in stimuli (e.g., melody in piece of music) Copyright © 2025 Pearson Education, Inc. All Rights Reserved Perception of Pain (1 of 3) Warns of actual or impending tissue damage so protective action can be taken Stimuli include extreme pressure and temperature, histamine, K + , ATP, acids, and bradykinin Impulses travel on fibers that release neurotransmitters glutamate and substance P Some pain impulses are blocked by inhibitory endogenous opioids (e.g., endorphins) Copyright © 2025 Pearson Education, Inc. All Rights Reserved Perception of Pain (2 of 3) Pain tolerance – All perceive pain at same stimulus intensity – Pain tolerance varies – “Sensitive to pain” means low pain tolerance, not low pain threshold – Genes help determine pain tolerance as well as response to pain medications ▪ Research in use of genetics to determine best pain treatment is ongoing Copyright © 2025 Pearson Education, Inc. All Rights Reserved Perception of Pain (3 of 3) Visceral and referred pain – Visceral pain results from stimulation of visceral organ receptors ▪ Felt as vague aching, gnawing, burning ▪ Activated by tissue stretching, ischemia, chemicals, muscle spasms – Referred pain: pain from one body region perceived as coming from different region ▪ Visceral and somatic pain fibers travel along same nerves, so brain assumes stimulus comes from common (somatic) region – Example: left arm pain during heart attack Copyright © 2025 Pearson Education, Inc. All Rights Reserved Map of Referred Pain Figure 13.3 Map of referred pain. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Clinical—Homeostatic Imbalance 13.1 Long-lasting or intense pain, such as limb amputation, can lead to hyperalgesia (pain amplification), chronic pain, and phantom limb pain – NMDA receptors (same receptors that strengthen neural connections during certain kinds of learning) are activated by long-lasting or intense pain ▪ Allow spinal cord to “learn” hyperalgesia ▪ Early pain management critical to prevent Phantom limb pain: pain felt in limb that is no longer present – Blocking pain transmission during and after surgery reduces – Rerouting cut nerves to innervate surround muscle reduces Copyright © 2025 Pearson Education, Inc. All Rights Reserved Part 2—Transmission Lines: Nerves and Their Structure and Repair Copyright © 2025 Pearson Education, Inc. All Rights Reserved 13.3 Nerves Nerve: cordlike organ of PNS Bundle of myelinated and nonmyelinated peripheral axons enclosed by connective tissue Two types of nerves: spinal or cranial, depending on where they originate Copyright © 2025 Pearson Education, Inc. All Rights Reserved Structure and Classification (1 of 4) Connective tissue coverings include: – Endoneurium: loose connective tissue that encloses axons and their myelin sheaths (Schwann cells) – Perineurium: coarse connective tissue that bundles fibers into fascicles – Epineurium: tough fibrous sheath around all fascicles to form the nerve Copyright © 2025 Pearson Education, Inc. All Rights Reserved Structure of a Nerve (1 of 2) Figure 13.4a Structure of a nerve. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Structure of a Nerve (2 of 2) Figure 13.4b Structure of a nerve. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Structure and Classification (2 of 4) Most nerves are mixtures of afferent and efferent fibers and somatic and autonomic (visceral) fibers Nerves are classified according to the direction they transmit impulses – Mixed nerves: contain both sensory and motor fibers ▪ Impulses travel both to and from CNS – Sensory (afferent) nerves: impulses only toward CNS – Motor (efferent) nerves: impulses only away from CNS Copyright © 2025 Pearson Education, Inc. All Rights Reserved Structure and Classification (3 of 4) Pure sensory (afferent) or pure motor (efferent) nerves are rare; most nerves are mixed Types of fibers in mixed nerves: – Somatic afferent (sensory from muscle to brain) – Somatic efferent (motor from brain to muscle) – Visceral afferent (sensory from organs to brain) – Visceral efferent (motor from brain to organs) Copyright © 2025 Pearson Education, Inc. All Rights Reserved Structure and Classification (4 of 4) Ganglia: contain neuron cell bodies associated with nerves in PNS – Ganglia associated with afferent nerve fibers contain cell bodies of sensory neurons ▪ Dorsal root ganglia (sensory, somatic) – Ganglia associated with efferent nerve fibers contain autonomic motor neurons ▪ Autonomic ganglia (motor, visceral) Copyright © 2025 Pearson Education, Inc. All Rights Reserved Regeneration of Nerve Fibers (1 of 2) Mature neurons are amitotic, but if the soma (cell body) of the damaged nerve is intact, the peripheral axon may regenerate in PNS; does not occur in CNS CNS axons – Most CNS fibers never regenerate – CNS oligodendrocytes bear growth-inhibiting proteins that prevent CNS fiber regeneration – Astrocytes at injury site form scar tissue – Treatment: neutralizing growth inhibitors, blocking receptors for inhibitory proteins, destroying scar tissue components Copyright © 2025 Pearson Education, Inc. All Rights Reserved Regeneration of Nerve Fibers (2 of 2) PNS axons – PNS axons can regenerate if damage is not severe 1. Axon fragments and myelin sheaths distal to injury degenerate (Wallerian degeneration); degeneration spreads down axon 2. Macrophages clean dead axon debris; Schwann cells are stimulated to divide 3. Axon filaments grow through regeneration tube 4. Axon regenerates, and new myelin sheath forms Copyright © 2025 Pearson Education, Inc. All Rights Reserved Regeneration of a Nerve Fiber in a Peripheral Nerve (1 of 4) Figure 13.5 Regeneration of a nerve fiber in a peripheral nerve. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Regeneration of a Nerve Fiber in a Peripheral Nerve (2 of 4) Figure 13.5 Regeneration of a nerve fiber in a peripheral nerve. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Regeneration of a Nerve Fiber in a Peripheral Nerve (3 of 4) Figure 13.5 Regeneration of a nerve fiber in a peripheral nerve. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Regeneration of a Nerve Fiber in a Peripheral Nerve (4 of 4) Figure 13.5 Regeneration of a nerve fiber in a peripheral nerve. Copyright © 2025 Pearson Education, Inc. All Rights Reserved 13.4 Cranial Nerves 12 pairs of cranial nerves are associated with brain – Two attach to forebrain, rest with brain stem Most are mixed nerves, but two pairs purely sensory Each numbered (I through XII) and named from rostral to caudal “On occasion, our trusty truck acts funny—very good vehicle anyhow” “Oh once one takes the anatomy final, very good vacations are heavenly” Copyright © 2025 Pearson Education, Inc. All Rights Reserved Location and Function of Cranial Nerves (1 of 4) Figure 13.6a Location and function of cranial nerves. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Location and Function of Cranial Nerves (2 of 4) Figure 13.6b Location and function of cranial nerves. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Overview of Cranial Nerves (1 of 12) CN I : Olfactory nerves Sensory nerves of smell Run from nasal mucosa to olfactory bulbs Pass through cribriform plate of ethmoid bone Fibers synapse in olfactory bulbs Pathway terminates in primary olfactory cortex Purely sensory (olfactory) function Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.2-1 Cranial Nerves (1 of 2) I Olfactory Nerves (ol-fak’to-re) Origin and course: Fibers arise from olfactory sensory neurons located in olfactory epithelium of nasal cavity and pass through cribriform plate of ethmoid bone to synapse in olfactory bulb. Fibers of olfactory bulb neurons extend posteriorly as olfactory tract, which runs beneath frontal lobe to enter cerebral hemispheres and terminates in primary olfactory cortex. See also Figure 15.20, p. 576. Function: Purely sensory; carry afferent impulses for sense of smell. Clinical Testing: Ask subject to sniff and identify aromatic substances, such as oil of cloves and vanilla. Homeostatic Imbalance Fracture of ethmoid bone or lesions of olfactory fibers may result in partial or total loss of smell, a condition known as anosmia (an-oz’me-ah). Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.2-1 Cranial Nerves (2 of 2) Copyright © 2025 Pearson Education, Inc. All Rights Reserved Overview of Cranial Nerves (2 of 12) CN II : Optic nerves Arise from retinas; really a brain tract Pass through optic canals, converge, and partially cross over at optic chiasma Optic tracts continue to thalamus, where they synapse Optic radiation fibers run to occipital (visual) cortex Purely sensory (visual) function Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.2-2 Cranial Nerves (1 of 2) II Optic Nerves Origin and course: Fibers arise from retina of eye to form optic nerve, which passes through optic canal of orbit. The optic nerves converge to form the optic chiasma (ki - az’mah) where fibers partially cross over, continue on as optic tracts, enter thalamus, and synapse there. Thalamic fibers run (as the optic radiation) to occipital (visual) cortex, where visual interpretation occurs. See also Figure 15.19, p. 574. Function: Purely sensory; carry afferent impulses for vision. Clinical Testing: Assess vision and visual field with eye chart and by testing the point at which the person first sees an object (finger) moving into the visual field. View fundus of eye with ophthalmoscope to detect papilledema (swelling of optic disc, the site where the optic nerve leaves the eyeball) and examine optic disc and retinal blood vessels. Homeostatic Imbalance Damage to optic nerve results in blindness in eye served by nerve. Damage to visual pathway beyond the optic chiasma results in partial visual losses. Visual defects are called anopsias (ah-nop’se-ahz). Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.2-2 Cranial Nerves (2 of 2) Copyright © 2025 Pearson Education, Inc. All Rights Reserved Overview of Cranial Nerves (3 of 12) CN III : Oculomotor nerves Fibers extend from ventral midbrain through superior orbital fissures to four of six extrinsic eye muscles Function in raising eyelid, directing eyeball, constricting iris (parasympathetic), and controlling lens shape Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.2-3 Cranial Nerves (1 of 2) III Oculomotor Nerves (ok”u-lo-mo’tor) Origin and course: Fibers extend from ventral midbrain (near its junction with pons) and pass through bony orbit, via superior orbital fissure, to eye. Function: Chiefly motor nerves (oculomotor = motor to the eye); contain a few proprioceptive afferents. Each nerve includes the following: Somatic motor fibers to four of the six extrinsic eye muscles (inferior oblique and superior, inferior, and medial rectus muscles) that help direct eyeball, and to levator palpebrae superioris muscle, which raises upper eyelid. Parasympathetic (autonomic) motor fibers to sphincter pupillae (circular muscles of iris), which cause pupil to constrict, and to ciliary muscle, which controls lens shape for visual focusing. Some parasympathetic cell bodies are in the ciliary ganglia. Sensory (proprioceptor) afferents, which run from the skeletal muscles served to the midbrain. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.2-3 Cranial Nerves (2 of 2) Clinical Testing: Examine pupils for size, shape, and equality. Test pupillary reflex with penlight (pupils should constrict when illuminated). Test convergence for near vision and subject’s ability to follow objects with the eyes. Homeostatic Imbalance In oculomotor nerve paralysis, eye cannot be moved up, down, or inward. At rest, eye rotates laterally [external strabismus (strah-biz’mus)] because the actions of the two extrinsic eye muscles not served by cranial nerves III are unopposed. Upper eyelid droops (ptosis), and the person has double vision and trouble focusing on close objects. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Overview of Cranial Nerves (4 of 12) CN IV : Trochlear nerves Fibers from dorsal midbrain enter orbits via superior orbital fissures to innervate superior oblique muscle Primarily motor nerve that directs eyeball Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.2-4 Cranial Nerves IV Trochlear Nerves (trok’le-ar) Origin and course: Fibers emerge from dorsal midbrain and course ventrally around midbrain to enter orbit through superior orbital fissure along with oculomotor nerves. Function: Primarily motor nerves; supply somatic motorfibers to (and carry proprioceptor fibers from) one of the extrinsic eye muscles, the superior oblique muscle, which passes through the pulley-shaped trochlea. Clinical Testing: Test with cranial nerve III (oculomotor). Homeostatic Imbalance Damage to a trochlear nerve results in double vision (diplopia) and impairs ability to rotate eye inferolaterally. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Overview of Cranial Nerves (5 of 12) CN V : Trigeminal nerves Largest cranial nerves; fibers extend from pons to face Three divisions – Ophthalmic (V1 ) passes through superior orbital fissure – Maxillary (V2 ) passes through foramen rotundum – Mandibular (V3 ) passes through the foramen ovale Convey sensory impulses from various areas of face (V1 and V2 ) Supply motor fibers (V3 ) for mastication Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.2-5 Cranial Nerves (1 of 4) V Trigeminal Nerves Largest cranial nerves; fibers extend from pons to face, and form three divisions (trigemina = threefold): ophthalmic (V1 ), maxillary (V2 ), and mandibular (V3 ) divisions. As main general sensory nerves of face, transmit afferent impulses from touch, temperature, and pain receptors. Cell bodies of sensory neurons of all three divisions are located in large trigeminal ganglion. The mandibular division also contains motor fibers that innervate chewing muscles. Dentists desensitize upper and lower jaws by injecting local anesthetic (such as procaine) into alveolar branches of maxillary and mandibular divisions, respectively. Since this blocks pain-transmitting fibers of teeth, the surrounding tissues become numb. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.2-5 Cranial Nerves (2 of 4) Bl ank Ophthalmic division (V1 ) (V s ub 1) Maxillary division (V2 ) (V s ub 2) Mandibular division (V3 ) (V sub 3 ) Origin and Fibers run from face to Fibers run from face to Fibers pass through skull via course pons via superior orbital pons via foramen foramen ovale. fissure. rotundum. Function Conveys sensory impulses Conveys sensory Conveys sensory impulses from skin of anterior scalp, impulses from nasal from anterior tongue (except upper eyelid, and nose, cavity mucosa, palate, taste buds), lower teeth, skin of and from nasal cavity upper teeth, skin of chin, temporal region of scalp. mucosa, cornea, and cheek, upper lip, lower Supplies motor fibers to, and lacrimal gland. eyelid. carries proprioceptor fibers from, muscles of mastication. Clinical Corneal reflex test: Test sensations of pain, Assess motor branch by asking Testing Touching cornea with wisp touch, and temperature person to clench their teeth, of cotton should elicit with safety pin and hot open mouth against resistance, blinking. and cold objects. and move jaw side to side. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.2-5 Cranial Nerves (3 of 4) Homeostatic Imbalance Trigeminal neuralgia (nu-ral’je-ah), or tic douloureux (tik doo”loo-roo’; tic = twitch, douloureux = painful), caused by inflammation of trigeminal nerve, is widely considered to produce most excruciating pain known. The stabbing pain lasts for a few seconds to a minute, but it can be relentless, occurring a hundred times a day. Usually provoked by some sensory stimulus, such as brushing teeth or even a passing breeze hitting the face. Thought to be caused by a loop of artery or vein that compresses the trigeminal nerve near its exit from the brain stem. Several drugs are used to treat this frustrating condition. In severe cases, traditional or gamma knife surgery relieves the agony—either by moving the compressing vessel or by destroying the nerve. Nerve destruction results in loss of sensation on that side of face. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.2-5 Cranial Nerves (4 of 4) Copyright © 2025 Pearson Education, Inc. All Rights Reserved Overview of Cranial Nerves (6 of 12) CN VI : Abducens nerves Fibers from inferior pons enter orbits via superior orbital fissures Primarily a motor, innervating lateral rectus muscle Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.2-6 Cranial Nerves VI Abducens Nerves (ab-du’senz) Origin and course: Fibers leave inferior pons and enter orbit via superior orbital fissure to run to eye. Function: Primarily motor; supply somatic motor fibers to lateral rectus muscle, an extrinsic muscle of the eye. Convey proprioceptor impulses from same muscle to brain. Clinical Testing: Test in common with cranial nerve III (oculomotor). Homeostatic Imbalance In abducens nerve paralysis, eye cannot be moved laterally. At rest, eyeball rotates medially (internal strabismus). Copyright © 2025 Pearson Education, Inc. All Rights Reserved Overview of Cranial Nerves (7 of 12) CN VII : Facial nerves Fibers from pons travel through internal acoustic meatuses and emerge through stylomastoid foramina to lateral aspect of face Chief motor nerves of face with five major branches Motor functions include facial expression, parasympathetic impulses to lacrimal and salivary glands Sensory function (taste) from anterior two-thirds of tongue Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.2-7 Cranial Nerves (1 of 3) VII Facial Nerves Origin and course: Fibers issue from pons, just lateral to abducens nerves (see Figure 13.6), enter temporal bone via internal acoustic meatus, and run within bone (and through inner ear cavity) before emerging through stylomastoid foramen. Nerve then courses to lateral aspect of face. Function: Mixed nerves that are the chief motor nerves of face. Five major branches: temporal, zygomatic, buccal, mandibular, and cervical (see c). Convey motor impulses to skeletal muscles of face (muscles of facial expression), except for chewing muscles served by trigeminal nerves, and transmit proprioceptor impulses from same muscles to pons (see b). Transmit parasympathetic (autonomic) motor impulses to lacrimal (tear) glands, nasal and palatine glands, and submandibular and sublingual salivary glands. Some of the cell bodies of these parasympathetic motor neurons are in pterygopalatine (ter”eh-go- pal’ah-tīn) and submandibular ganglia on the trigeminal nerve (see a). Convey sensory impulses from taste buds of anterior two-thirds of tongue; cell bodies of these sensory neurons are in geniculate ganglion (see a). Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.2-7 Cranial Nerves (2 of 3) Clinical Testing: Test anterior two-thirds of tongue for ability to taste sweet (sugar), salty, sour (vinegar), and bitter (quinine) substances. Check symmetry of face. Ask subject to close eyes, smile, whistle, and so on. Assess tearing with ammonia fumes. Homeostatic Imbalance Bell’s palsy is characterized by paralysis of facial muscles on affected side and partial loss of taste sensation. May develop rapidly (often overnight). Caused by inflamed and swollen facial nerve, possibly due to herpes simplex 1 viral infection. Lower eyelid droops, corner of mouth sags (making it difficult to eat or speak normally), tears drip continuously from eye and eye cannot be completely closed (conversely, dry-eye syndrome may occur). Treated with corticosteroids. Recovery is complete in 70% of cases. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.2-7 Cranial Nerves (3 of 3) Copyright © 2025 Pearson Education, Inc. All Rights Reserved Overview of Cranial Nerves (8 of 12) CN VIII : Vestibulocochlear nerves Afferent fibers from hearing receptors (cochlear division) and equilibrium receptors (vestibular division) pass from inner ear through internal acoustic meatuses and enter brain stem at pons-medulla border Mostly sensory function; small motor component for adjustment of sensitivity of receptors Formerly auditory nerve Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.2-8 Cranial Nerves (1 of 2) VIII Vestibulocochlear Nerves (ves-tib”u-lo-kok’le-ar) Origin and course: Fibers arise from hearing and equilibrium apparatus located within inner ear in petrous part of temporal bone and pass through internal acoustic meatus to enter brain stem at pons-medulla border. Afferent fibers from hearing receptors in cochlea form the cochlear division (cochlear nerve); those from equilibrium receptors in semicircular canals and vestibule form the vestibular division (vestibular nerve). The two divisions merge to form vestibulocochlear nerve. Function: Mostly sensory. Vestibular division transmits afferent impulses for sense of equilibrium, and sensory nerve cell bodies are located in vestibular ganglia. Cochlear division transmits afferent impulses for sense of hearing, and sensory nerve cell bodies are located in spiral ganglion within cochlea. Small motor component adjusts the sensitivity of sensory receptors. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.2-8 Cranial Nerves (2 of 2) Clinical Testing: Check hearing by air and bone conduction using tuning fork. Homeostatic Imbalance Lesions of cochlear nerve or cochlear receptors result in central, or nerve, deafness. Damage to vestibular division produces dizziness, rapid involuntary eye movements, loss of balance, nausea, and vomiting. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Overview of Cranial Nerves (9 of 12) CN IX : Glossopharyngeal nerves Fibers from medulla leave skull via jugular foramen and run to throat Motor functions: innervate part of tongue and pharynx for swallowing and provide parasympathetic fibers to parotid salivary glands Sensory functions: fibers conduct taste and general sensory impulses from pharynx and posterior tongue, and impulses from carotid chemoreceptors and baroreceptors Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.2-9 Cranial Nerves (1 of 2) IX Glossopharyngeal Nerves (glos”o-fah-rin’je-al) Origin and course: Fibers emerge from medulla and leave skull via jugular foramen to run to throat. Function: Mixed nerves that innervate part of tongue and pharynx. Provide somatic motor fibers to, and carry proprioceptor fibers from, a superior pharyngeal muscle called the stylopharyngeus, which elevates the pharynx in swallowing. Provide parasympathetic motor fibers to parotid salivary glands (some of the nerve cell bodies of these parasympathetic motor neurons are located in otic ganglion) Sensory fibers conduct taste and general sensory (touch, pressure, pain) impulses from pharynx and posterior tongue, impulses from chemoreceptors in the carotid body (which monitor O 2 and CO 2 levels in the blood and help regulate respiratory rate and depth), and impulses from baroreceptors of carotid sinus (which monitor blood pressure). Sensory neuron cell bodies are located in superior and inferior ganglia. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.2-9 Cranial Nerves (2 of 2) Clinical Testing: Check position of uvula; check gag and swallowing reflexes. Ask subject to speak and cough. Test posterior third of tongue for taste. Homeostatic Imbalance Injured or inflamed glossopharyngeal nerves impair swallowing and taste. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Overview of Cranial Nerves (10 of 12) CN X : Vagus nerves Only cranial nerves that extend beyond head and neck region Fibers from medulla exit skull via jugular foramen Most motor fibers are parasympathetic fibers that help regulate activities of heart, lungs, and abdominal viscera Sensory fibers carry impulses from thoracic and abdominal viscera, baroreceptors, chemoreceptors, and taste buds of posterior tongue and pharynx Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.2-10 Cranial Nerves (1 of 3) X Vagus Nerves (va’gus) Origin and course: The only cranial nerves to extend beyond head and neck region. Fibers emerge from medulla, pass through skull via jugular foramen, and descend through neck region into thorax and abdomen. See also Figure 14.4, p. 536. Function: Mixed nerves. Nearly all motor fibers are parasympathetic efferents, except those serving skeletal muscles of pharynx and larynx (involved in swallowing). Parasympathetic motor fibers supply heart, lungs, and abdominal viscera and are involved in regulating heart rate, breathing, and digestive system activity. Transmit sensory impulses from thoracic and abdominal viscera, from the aortic arch baroreceptors (for blood pressure) and the carotid and aortic bodies (chemoreceptors for respiration), and from taste buds on the epiglottis. Also carry general somatic sensory information from small area of skin on external ear. Carry proprioceptor fibers from muscles of larynx and pharynx. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.2-10 Cranial Nerves (2 of 3) Clinical Testing: As for cranial nerve IX (glossopharyngeal); IX and X are tested in common, since they both innervate muscles of throat and mouth. Homeostatic Imbalance Since laryngeal branches of the vagus innervate nearly all muscles of the larynx (“voice box”), vagal nerve paralysis can lead to hoarseness or loss of voice. Other symptoms are difficulty swallowing and impaired digestive system motility. These parasympathetic nerves are important for maintaining the normal state of visceral organ activity. Without their influence, the sympathetic nerves, which mobilize and accelerate vital body processes (and shut down digestion), would dominate. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.2-10 Cranial Nerves (3 of 3) Copyright © 2025 Pearson Education, Inc. All Rights Reserved Overview of Cranial Nerves (11 of 12) CN XI : Accessory nerves Formed from ventral rootlets from C1 to C 5 region of spinal cord (not brain) Rootlets pass into cranium via each foramen magnum Accessory nerves exit skull via jugular foramina to innervate trapezius and sternocleidomastoid muscles Formerly spinal accessory nerve Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.2-11 Cranial Nerves (1 of 2) XI Accessory Nerves Origin and course: Unique in that they form from rootlets that emerge from the spinal cord, not the brain stem. These rootlets arise laterally from superior region ( C1 − C 5 ) of spinal cord, pass upward along spinal cord, and enter the skull as the accessory nerves via foramen magnum. The accessory nerves exit from skull through the jugular foramen together with the vagus nerves, and supply two large neck muscles. Until recently, these nerves were considered to have both a cranial and a spinal portion, but the cranial rootlets are actually part of the vagus nerves. This raises an interesting question: Should the accessory nerves still be considered cranial nerves? Some anatomists say “no” because they don’t arise from the brain. Others say “yes” because their origin is different from a typical spinal nerve and they pass through the skull. Stay tuned! Function: Mixed nerves, but primarily motor in function. Supply motor fibers to trapezius and sternocleidomastoid muscles, which together move head and neck, and convey proprioceptor impulses from same muscles. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.2-11 Cranial Nerves (2 of 2) Clinical Testing: Check strength of sternocleidomastoid and trapezius muscles by asking person to rotate head and shrug shoulders against resistance. Homeostatic Imbalance Injury to one accessory nerve causes head to turn toward the injured side as a result of sternocleidomastoid muscle paralysis. Shrugging that shoulder (role of trapezius muscle) becomes difficult. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Overview of Cranial Nerves (12 of 12) CN XII : Hypoglossal nerves Fibers from medulla exit skull via hypoglossal canal Innervate extrinsic and intrinsic muscles of tongue that contribute to swallowing and speech Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.2-12 Cranial Nerves (1 of 2) XII Hypoglossal Nerves (hi”po-glos’al) Origin and course: As their name implies (hypo = below; glossal = tongue ), hypoglossal nerves mainly serve the tongue. Fibers arise by a series of roots from medulla and exit from skull via hypoglossal canal to travel to tongue. See also Figure 13.6. Function: Mixed nerves, but primarily motor in function. Carry somatic motor fibers to intrinsic and extrinsic muscles of tongue, and proprioceptor fibers from same muscles to brain stem. Hypoglossal nerve control allows tongue movements that mix and manipulate food during chewing, and contribute to swallowing and speech. Clinical Testing: Ask subject to protrude and retract tongue. Note any deviations in position. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.2-12 Cranial Nerves (2 of 2) Homeostatic Imbalance Damage to hypoglossal nerves causes difficulties in speech and swallowing. If both nerves are impaired, the person cannot protrude tongue. If only one side is affected, tongue deviates (points) toward affected side; eventually paralyzed side begins to atrophy. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Location and Function of Cranial Nerves (3 of 4) Figure 13.6a Location and function of cranial nerves. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Location and Function of Cranial Nerves (4 of 4) Figure 13.6b Location and function of cranial nerves. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Composition of Cranial Nerves Olfactory and optic nerves – Neuron cell bodies located within special sense organs Other nerves with sensory information (V, VII, IX, and X) – Neuron cell bodies located in cranial sensory ganglia Some mixed nerves contain both somatic and autonomic fibers – Most motor neuron cell bodies in ventral gray matter of brain stem – Some autonomic motor neurons in ganglia To remember primary functions of cranial nerves as sensory, motor, both: – “Some say marry money, but my brother believes (it’s) bad business (to) marry money.” Copyright © 2025 Pearson Education, Inc. All Rights Reserved 13.5 Spinal Nerves (1 of 5) 31 pairs of spinal nerves All are mixed nerves named for point of issue from spinal cord Supply all body parts except head and part of neck – 8 pairs of cervical nerves (C1 − C 8 ) – 12 pairs of thoracic nerves (T1 − T12 ) – 5 pairs of lumbar nerves (L1 − L 5 ) – 5 pairs of sacral nerves (S1 − S 5 ) – 1 pair of tiny coccygeal nerves (C 0 ) Copyright © 2025 Pearson Education, Inc. All Rights Reserved 13.5 Spinal Nerves (2 of 5) 7 cervical vertebrae give rise to 8 pairs of cervical spinal nerves because: – Each of the first 7 pairs (C1 to C 7 ) exits the vertebral canal superior to vertebra for which it is named – Last spinal nerve (C 8 ) exits canal inferior to C 7 ▪ So vertebra C 7 has a nerve that leaves above it and one that leaves below it Each of the other spinal nerves exits inferior to vertebra for which it is named Copyright © 2025 Pearson Education, Inc. All Rights Reserved Spinal Nerves Figure 13.7 Spinal nerves. Copyright © 2025 Pearson Education, Inc. All Rights Reserved 13.5 Spinal Nerves (3 of 5) Each spinal nerve is connected to spinal cord via two roots: – Ventral roots ▪ Contain motor (efferent) fibers from ventral horn motor neurons that innervate skeletal muscles – Dorsal roots ▪ Contain sensory (afferent) fibers from sensory neurons in dorsal root ganglia that conduct impulses from peripheral receptors Both ventral and dorsal roots are branched medially as rootlets that then join laterally to form spinal nerve Copyright © 2025 Pearson Education, Inc. All Rights Reserved Formation of Spinal Nerves and Rami Distribution (1 of 2) Figure 13.8a Formation of spinal nerves and rami distribution. Copyright © 2025 Pearson Education, Inc. All Rights Reserved 13.5 Spinal Nerves (4 of 5) Spinal nerves emerge from vertebral column via their respective intervertebral foramina Spinal roots become progressively longer superiorly to inferiorly down cord – Lumbar and sacral roots are very long and extend through lower vertebral canal as cauda equina Copyright © 2025 Pearson Education, Inc. All Rights Reserved 13.5 Spinal Nerves (5 of 5) Spinal nerves are quite short (  1− 2 cm) Almost immediately after exiting foramen, spinal nerves divide into three branches: – Dorsal ramus: smaller branch – Ventral ramus: larger branch – Meningeal branch: tiny branch that reenters vertebral canal to innervate meninges and blood vessels Rami communicantes contain autonomic nerve fibers that join ventral rami in thoracic region Copyright © 2025 Pearson Education, Inc. All Rights Reserved Formation of Spinal Nerves and Rami Distribution (2 of 2) Figure 13.8b Formation of spinal nerves and rami distribution. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Innervation of Specific Body Regions (1 of 11) Spinal nerve rami and their main branches supply entire somatic region of body from neck down – Dorsal rami supply posterior body trunk – Ventral rami supply rest of trunk and limbs Difference between roots and rami: – Roots lie medial to and form spinal nerves ▪ Each root is purely sensory or motor – Rami lie distal to and are lateral branches of spinal nerves ▪ Can carry both sensory and motor Copyright © 2025 Pearson Education, Inc. All Rights Reserved Innervation of Specific Body Regions (2 of 11) All ventral rami except T2 − T12 form interlacing nerve networks called nerve plexuses – Found in cervical, brachial, lumbar, and sacral areas – Only ventral rami form plexuses Within plexus, fibers crisscross so that: 1. Each branch contains fibers from several different spinal nerves 2. Fibers from ventral ramus go to body periphery via several routes ▪ Means each limb muscle is innervated by more than one spinal nerve, so damage to one does not cause paralysis Copyright © 2025 Pearson Education, Inc. All Rights Reserved Innervation of Specific Body Regions (3 of 11) Cervical plexus and the neck – First four ventral rami (C1 − C 4 ) form looping cervical plexus ▪ Most branches of this form cutaneous nerves – Innervate skin of neck, ear, back of head, and shoulders – Other branches innervate neck muscles – Phrenic nerve ▪ Major motor and sensory nerve of diaphragm, major muscles for breathing ▪ Phrenic nerve receives fibers from C 3 to C 5 Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Cervical Plexus Figure 13.9 The cervical plexus. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.3 Branches of the Cervical Plexus Table 13.3 Branches of the Cervical Plexus (See Figure 13.9 ) Nerves Ventral Rami Structures Served blank Blank Cutaneous Branches (Superficial) C sub 2 (C sub 3) Lesser occipital C 2 (C 3 ) Skin on posterolateral aspect of head and neck C sub 2, C sub 3 Greater auricular C 2 ,C 3 Skin covering ear and anterior to ear (over parotid Transverse cervical C 2 ,C 3 C sub 2, C sub 3 gland) Supraclavicular (medial, Skin on anterior and lateral aspect of neck C 3 ,C 4 C sub 3, C sub 4 intermediate, and lateral) Skin of shoulder and clavicular region blank blank Motor Branches (Deep) Ansa cervicalis (superior C1 − C 3 C sub 1 to C sub 3 Infrahyoid muscles of neck (omohyoid, sternohyoid, and inferior roots) and sternothyroid) Segmental and other C1 − C 5 C sub 1 to C sub 5 Deep muscles of neck (geniohyoid and thyrohyoid) muscular branches and portions of scalenes, levator scapulae, trapezius, and sternocleidomastoid muscles C3 − C5 Phrenic Diaphragm (its only motor nerve supply) C sub 3 to C sub 5 Copyright © 2025 Pearson Education, Inc. All Rights Reserved Clinical—Homeostatic Imbalance 13.2 Irritation of the phrenic nerve causes spasms of the diaphragm, also called hiccups If both phrenic nerves are severed, or if C 3 − C 5 region spinal cord is destroyed, diaphragm becomes paralyzed – Respiratory arrest occurs – Victim requires mechanical respirators to stay alive ▪ Air is mechanically forced into the lungs—literally breathing for them Copyright © 2025 Pearson Education, Inc. All Rights Reserved Innervation of Specific Body Regions (4 of 11) Brachial plexus and upper limb – Formed by ventral rami of C 5 − C 8 and T1 (and often C 4 and/or T2 ) – Gives rise to nerves that innervate upper limb – Four major branches of this plexus: ▪ Roots—five ventral rami (C 5 − T1 ) unite to form… ▪ Trunks—upper, middle, and lower, which unite to form… ▪ Divisions—anterior and posterior, which unite to form… ▪ Cords—lateral, medial, and posterior Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Brachial Plexus (1 of 4) Figure 13.10a The brachial plexus. Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Brachial Plexus (2 of 4) Figure 13.10b The brachial plexus. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Innervation of Specific Body Regions (5 of 11) Brachial plexus and upper limb (cont ) inued Cords of brachial plexus give rise to nerves of the upper limb, five of most important being: – Axillary: innervates deltoid, teres minor, and skin and joint capsule of shoulder – Musculocutaneous: innervates biceps brachii and brachialis, coracobrachialis, and skin of lateral forearm – Median: innervates skin, most flexors, forearm pronators, wrist and finger flexors, thumb opposition muscles – Ulnar: supplies flexor carpi ulnaris, part of flexor digitorum profundus, most intrinsic hand muscles, skin of medial aspect of hand, wrist/finger flexion – Radial: innervates essentially all extensor muscles, supinators, and posterior skin of limb Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Brachial Plexus (3 of 4) Figure 13.10c The brachial plexus. Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Brachial Plexus (4 of 4) Figure 13.10d The brachial plexus. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.4 Branches of the Brachial Plexus (1 of 2) Table 13.4 Branches of the Brachial Plexus. (See Figure 13.10) Nerves Cord and Ventral Structures Served Rami Musculocu Lateral cord (C 5 − C 7 ) Muscular branches: flexor muscles in anterior arm (biceps brachii, brachialis, (C s u b 5 to C su b 7) taneous coracobrachialis) Cutaneous branches: skin on lateral forearm (extremely variable) Median By two branches, Muscular branches to flexor group of anterior forearm (palmaris longus, flexor one from medial carpi radialis, flexor digitorum superficialis, flexor pollicis longus, lateral half of cord (C 8 ,T1 ) and(C s ub 8, T s ub 1) flexor digitorum profundus, and pronator muscles); intrinsic muscles of lateral one from the lateral palm and digital branches to the fingers cord (C 5 − C 7 ) ( C sub 5 toCsub7 ) Cutaneous branches: skin of lateral two-thirds of hand on ventral side and dorsum of fingers 2 and 3 Ulnar Medial cord (C 8 ,T1 ) ( C sub 8,Tsub1 ) Muscular branches: flexor muscles in anterior forearm (flexor carpi ulnaris and medial half of flexor digitorum profundus); most intrinsic muscles of hand Cutaneous branches: skin of medial third of hand, both anterior and posterior aspects Radial Posterior cord Muscular branches: posterior muscles of arm and forearm (triceps brachii, (C 5 − C 8 ,T1 ) (C sub 5 to C sub 8, T sub 1) anconeus,supinator, brachioradialis, extensors carpi radialis longus and brevis, extensor carpi ulnaris, and several muscles that extend the fingers) Cutaneous branches: skin of posterolateral surface of entire limb (except dorsum of fingers 2 and 3) Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.4 Branches of the Brachial Plexus (2 of 2) Nerves Cord and Ventral Rami Structures Served Axillary Posterior cord (C 5 ,C 6 ) (C s u b 5 , C su b 6) Muscular branches: deltoid and teres minor muscles Cutaneous branches: some skin of shoulder region Dorsal scapular Branches of C 5 rami C sub 5 Rhomboid muscles and levator scapulae Long thoracic Branches of C5 − C7 C sub 5 to C sub 7 rami Serratus anterior muscle Subscapular Posterior cord; branches Teres major and subscapularis muscles of C 5 and C 6 rami C s ub 5 C sub 6 Suprascapular Upper trunk (C 5 ,C 6 ) (C s u b 5 , C su b 6) Shoulder joint; supraspinatus and infraspinatus muscles Pectoral (lateral and Branches of lateral and Pectoralis major and minor muscles medial) medial cords (C 5 − T1 ) (C s u b 5 to T s ub 1 ) Copyright © 2025 Pearson Education, Inc. All Rights Reserved Clinical—Homeostatic Imbalance 13.3 Injuries to brachial plexus are common Severe injuries can weaken or paralyze entire upper limb Injuries may occur if upper limb is pulled too hard, stretching plexus – Example: when football tackler yanks arm of running back – Blows to top of shoulder can force humerus inferiorly Copyright © 2025 Pearson Education, Inc. All Rights Reserved Clinical—Homeostatic Imbalance 13.4 Injury to median nerve makes it difficult to use pincer grasp (opposed thumb and index finger) to pick up small objects Seen in carpal tunnel syndrome, when median nerve is compressed – Also, frequent casualty of wrist-slashing suicide attempts Copyright © 2025 Pearson Education, Inc. All Rights Reserved Clinical—Homeostatic Imbalance 13.5 Severe or chronic damage to ulnar nerve can lead to sensory loss, paralysis, and muscle atrophy – Affected individuals have trouble making a fist and gripping objects – Little and ring fingers become hyperextended at the knuckles and flexed at distal interphalangeal joints – Causes hand to contort into a clawhand Striking the “funny bone,” the spot where this nerve rests against medial epicondyle, can make the little finger tingle. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Clinical—Homeostatic Imbalance 13.6 Trauma to the radial nerve results in wrist drop, inability to extend the hand at the wrist Improper use of a crutch can compress radial nerve and impair its blood supply – “Saturday night paralysis”: An intoxicated person falls asleep with an arm draped over the back of a chair or sofa edge, cutting off blood supply to radial nerve Copyright © 2025 Pearson Education, Inc. All Rights Reserved Innervation of Specific Body Regions (6 of 11) Lumbosacral plexus and lower limb – Lumbar and sacral plexuses have significant overlap ▪ Fibers of lumbar plexus contribute to sacral plexus via lumbosacral trunk ▪ Lumbosacral plexus serves mostly lower limb, but also sends some branches to abdomen, pelvis, and buttocks Copyright © 2025 Pearson Education, Inc. All Rights Reserved Innervation of Specific Body Regions (7 of 11) Lumbosacral plexus and lower limb (cont ) inued – Lumbar plexus ▪ Arises from L1 to L 4 ▪ Innervates thigh, abdominal wall, and psoas muscle ▪ Femoral nerve: innervates quadriceps and skin of anterior thigh and medial surface of leg ▪ Obturator nerve: passes through obturator foramen to innervate adductor muscles Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Lumbar Plexus (1 of 2) Figure 13.11a The lumbar plexus. Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Lumbar Plexus (2 of 2) Figure 13.11b The lumbar plexus. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Innervation of Specific Body Regions (8 of 11) Lumbosacral plexus and lower limb (cont ) inued – Sacral plexus ▪ Arises from L 4 to S 4 ▪ Serves the buttock, lower limb, pelvic structures, and perineum ▪ Sciatic nerve – Longest and thickest nerve of body – Innervates hamstring muscles, adductor magnus, and most muscles in leg and foot – Composed of two nerves: tibial and common fibular Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Sacral Plexus (1 of 3) Figure 13.12a The sacral plexus. Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Sacral Plexus (2 of 3) Figure 13.12b The sacral plexus. Copyright © 2025 Pearson Education, Inc. All Rights Reserved The Sacral Plexus (3 of 3) Figure 13.12c The sacral plexus. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.5 Branches of the Lumbar Plexus Table 13.5 Branches of the Lumbar Plexus (See Figure 13.11) Nerves Ventral Rami Structures Served L2 − L4 L s u b 2 to L s ub 4 Femoral Skin of anterior and medial thigh via anterior femoral cutaneous branch; skin of medial leg and foot, hip and knee joints via saphenous branch; motor to anterior muscles (quadriceps and sartorius) of thigh and to pectineus, iliacus L2 − L4 L s u b 2 to L s ub 4 Obturator Motor to adductor magnus (part), longus, and brevis muscles, gracilis muscle of medial thigh, obturator externus; sensory for skin of medial thigh and for hip and knee joints Lateral femoral L2 , L3 L s u b 2 , L su b 3 Skin of lateral thigh; some sensory branches to peritoneum cutaneous Iliohypogastric L1 L s ub 1 Skin on side of buttock and above pubis; muscles of anterolateral abdominal wall (internal obliques and transversus abdominis) Ilioinguinal L1 L s ub 1 Skin of external genitalia and proximal medial aspect of the thigh; inferior abdominal muscles Genitofemoral L1, L 2 L s u b 1 , L su b 2 Skin of scrotum in males, of labia majora in females, and of anterior thigh inferior to middle portion of inguinal region; cremaster muscle in males Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.6 Branches of the Sacral Plexus Table 13.6 Branches of the Sacral Plexus (See Figure 13.12) Nerves Ventral Rami Structures Served L 4 , L 5 , S1 − S 3 L s u b 4 , L su b 5 , Ss ub 1 to S su b 3 Sciatic nerve Composed of two nerves (tibial and common fibular) in a common sheath; they diverge just proximal to the knee Tibial (including sural, L 4 − S3 L s u b 4 to S sub 3 Cutaneous branches: to skin of posterior surface of leg and sole of foot medial and lateral Motor branches: to muscles of back of thigh, leg, and foot [hamstrings (except short plantar, and medial head of biceps femoris), posterior part of adductor magnus, triceps surae, tibialis calcaneal branches) posterior, popliteus, flexor digitorum longus, flexor hallucis longus, and intrinsic muscles of foot] Common fibular L 4 − S2 L s u b 4 to S sub 2 Cutaneous branches: to skin of anterior and lateral surface of leg and dorsum of foot (superficial and deep Motor branches: to short head of biceps femoris of thigh, fibular muscles of lateral branches) compartment of leg, tibialis anterior, and extensor muscles of toes (extensor hallucis longus, extensors digitorum longus and brevis) Superior gluteal L 4 ,L 5 ,S1 L s u b 4 , L su b 5 , Ss ub 1 Motor branches: to gluteus medius and minimus and tensor fasciae latae Inferior gluteal L5 − S2 L s u b 5 to S sub 2 Motor branches: to gluteus maximus Posterior femoral cutaneous S1 − S 3 S s u b 1 to S su b 3 Skin of inferior buttock, posterior thigh, and popliteal region; length varies; may also innervate part of skin of calf and heel Supplies most of skin and muscles of perineum (region encompassing external S2 − S4 genitalia and anus and including clitoris, labia, and vaginal mucosa in females, and Pudendal S s u b 2 to S su b 4 scrotum and penis in males); external anal sphincter Copyright © 2025 Pearson Education, Inc. All Rights Reserved Table 13.7 Summary of Major Spinal Nerve Plexuses Plexus Ventral Rami Major Nerves Cervical C1 − C 4 (some C 5 ) Phrenic C s u b 1 to Cs ub 4 (s ome C su b 5 ) Brachial C 5 − T1 C s u b 5 to T su b 1 Axillary, musculocutaneous, median, radial, ulnar Lumbar L1 − L 4 Femoral, obturator L s u b 1 to L s ub 4 Sacral L4 − S4 Sciatic (composed of tibial and common L s u b 4 to S sub 4 fibular) Copyright © 2025 Pearson Education, Inc. All Rights Reserved Clinical—Homeostatic Imbalance 13.7 When spinal roots of lumbar plexus are compressed, gait problems occur Other symptoms are pain or numbness of the anterior thigh Femoral nerve serves prime movers that flex hip and extend knee – Damage can be caused by a herniated disc If obturator nerve is impaired, person experiences pain in the medial thigh Copyright © 2025 Pearson Education, Inc. All Rights Reserved Clinical—Homeostatic Imbalance 13.8 Sciatica, a common problem, is characterized by stabbing pain radiating over course of the sciatic nerve – Injury could be caused by a fall, disc herniation, or badly placed injection into the buttock If the nerve is transected, leg is nearly useless and cannot be flexed because hamstrings are paralyzed Foot and ankle cannot move at all, so foot drops into plantar flexion, a condition called footdrop Recovery from sciatic nerve injury is usually slow and incomplete – For lesions below knee, thigh muscles are spared – If tibial nerve is injured, paralyzed calf muscles cannot plantar flex foot, and a shuffling gait develops Copyright © 2025 Pearson Education, Inc. All Rights Reserved Innervation of Specific Body Regions (9 of 11) Anterolateral thorax and abdominal wall – Ventral rami of T12 − T12 are intercostal nerves that supply muscles of ribs, anterolateral thorax, and abdominal wall – Give off cutaneous branches to skin along course – Two special thoracic nerves: ▪ Tiny T1 ▪ T12 , which is a subcostal nerve – Back ▪ Back is innervated by dorsal rami via several branches – Each branch innervates a strip of muscle and skin in line with where it emerges from spinal cord Copyright © 2025 Pearson Education, Inc. All Rights Reserved Innervation of Specific Body Regions (10 of 11) Innervation of skin: dermatomes – Dermatome: area of skin innervated by cutaneous branches of single spinal nerve – All spinal nerves except C1 participate in dermatomes – Extent of spinal cord injuries ascertained by affected dermatomes – Most dermatomes overlap, so destruction of a single spinal nerve will not cause complete numbness Copyright © 2025 Pearson Education, Inc. All Rights Reserved Map of Dermatomes Figure 13.13 Map of dermatomes. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Innervation of Specific Body Regions (11 of 11) Innervation of joints – To remember which nerves serve which synovial joint, use: ▪ Hilton’s law: Any nerve serving a muscle that produces movement at a joint also innervates that joint and skin over that joint Copyright © 2025 Pearson Education, Inc. All Rights Reserved Part 3—Motor Endings and Motor Activity Copyright © 2025 Pearson Education, Inc. All Rights Reserved 13.6 Peripheral Motor Endings Motor endings: PNS elements that activate effectors by releasing neurotransmitters These element innervate skeletal muscle, visceral muscle, and glands Copyright © 2025 Pearson Education, Inc. All Rights Reserved Innervation of Skeletal Muscle Takes place at neuromuscular junction Neurotransmitter acetylcholine (ACh) is released when nerve impulse reaches axon terminal ACh binds to receptors, resulting in: – Movement of Na + and K + across membrane – Depolarization of muscle cell – An end plate potential, spreads to adjacent areas of sarcolemma, which triggers opening of Na + voltage-gated channels – Results in an action potential, which leads to muscle contraction Copyright © 2025 Pearson Education, Inc. All Rights Reserved Events at the Neuromuscular Junction Focus Figure 9.1 Events at the Neuromuscular Junction. Copyright © 2025 Pearson Education, Inc. All Rights Reserved Innervation of Visceral Muscle and Glands Autonomic motor endings and visceral effectors are simpler than somatic junctions Branches form synapses en passant (“synapses in passing”) with effector cells via varicosities Acetylcholine and norepinephrine act indirectly via second messengers Visceral motor responses are slower than somatic responses Copyright © 2025 Pearson Education, Inc. All Rights Reserved 13.7 Levels of Motor Control Cerebellum and basal nuclei are the ultimate planners and coordinators of