Anatomy and Physiology Chapter 13
Terms in this set (86)
Peripheral Nervous System (PNS)
All neural structures outside the brain including, Sensory receptors, Peripheral nerves and associated ganglia, and Motor endings.
Specialized to respond to changes in their environment (stimuli). Activation results in graded potentials that trigger nerve impulses. Sensation (awareness of stimulus) and perception (interpretation of the meaning of the stimulus) occur in the brain.
Classification of receptors is based on:
Stimulus type, Location, and Structural complexity
respond to touch, pressure, vibration, stretch, and itch
sensitive to changes in temperature. classified by stimulus type
respond to light energy (e.g., retina). classified by stimulus type
respond to chemicals (e.g., smell, taste, changes in blood chemistry). classified by stimulus type.
Nociceptors—sensitive to pain-causing stimuli (e.g. extreme heat or cold, excessive pressure, inflammatory chemicals). classified by stimulus type.
Respond to stimuli arising outside the body. Receptors in the skin for touch, pressure, pain, and temperature. Most special sense organs. Classification by Location
Respond to stimuli arising in internal viscera and blood vessels. Sensitive to chemical changes, tissue stretch, and temperature changes. Classification by Location
Respond to stretch in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles. Inform the brain of one's movements. Classification by Location.
Unencapsulated Dendritic Endings
Thermoreceptors, Nociceptors (Pain Receptors), and Light Touch Receptors (Tactile "merkel" discs, hair follicle receptors)
Meissner's (tactile) corpuscles
mechanoreceptor. discriminative touch. encapsulated dendritic endings.
Pacinian (lamellated) corpuscles
mechanoreceptor. deep pressure and vibration. encapsulated dendritic endings.
mechanoreceptor. deep continuous pressure. encapsulated dendritic endings.
mechanoreceptors. muscle stretch. Encapsulated Dendritic Endings.
golgi tendon organs
mechanoreceptor. stretch in tendons. encapsulated dendritic endings.
Joint kinesthetic receptors
mechanoreceptor. stretch in articular capsules. encapsulated dendritic endings.
Location of Meissner's corpuscles
dermal papillae of hairless skin, particularly nipples, external genitalia, fingertips, soles of feet, eyelids.
Location of Pacinian corpuscles
dermis and hypodermic; periostea, mesentary, tendons, ligaments, joint capsules; most abundant on fingers, soles of feet, external genitalia, nipples
Location of Ruffini Endings
deep in dermis, hypodermis,and joint capsules.
Processing at the Receptor Level
stimulus --> receptor/generator potential in afferent neuron --> action potential at first node of Ranvier
Processing at the Receptor Level (Special Sense Organs)
stimulus --> receptor potential in receptor cell --> release of neurotransmitter --> generator potential in first-order sensory neuron --> action potentials (if threshold is reached)
Adaptation of Sensory Receptors
Adaptation is a change in sensitivity in the presence of a constant stimulus. Receptor membranes become less responsive. Receptor potentials decline in frequency or stop.
Processing at the Circuit Level
Pathways of three neurons conduct sensory impulses upward to the appropriate brain regions
Conduct impulses from the receptor level to the second-order neurons in the CNS
Transmit impulses to the thalamus or cerebellum
Conduct impulses from the thalamus to the somatosensory cortex (perceptual level)
Structure of a Nerve
Bundle of myelinated and unmyelinated peripheral axons enclosed by connective tissue
loose connective tissue that encloses axons and their myelin sheaths
coarse connective tissue that bundles fibers into fascicles
tough fibrous sheath around a nerve
Contain neuron cell bodies associated with nerves. Dorsal root ganglia (sensory, somatic). Autonomic ganglia (motor, visceral).
Twelve pairs of nerves associated with the brain. Most are mixed in function; two pairs are purely sensory. Each nerve is identified by a number (I through XII) and a name
I: The Olfactory Nerves
Arise from the olfactory receptor cells of nasal cavity. Pass through the cribriform plate of the ethmoid bone. Fibers synapse in the olfactory bulbs. Pathway terminates in the primary olfactory cortex. Purely sensory (olfactory) function.
II: The Optic Nerves
Arise from the retinas. Pass through the optic canals, converge and partially cross over at the optic chiasma. Optic tracts continue to the thalamus, where they synapse. Optic radiation fibers run to the occipital (visual) cortex. Purely sensory (visual) function
III: The Oculomotor Nerves
Fibers extend from midbrain through the superior orbital fissures to the extrinsic eye muscles. Functions in raising the eyelid, directing the eyeball, constricting the iris (parasympathetic), and controlling lens shape.
IV: The Trochlear Nerves
Fibers from midbrain enter the orbits via the superior orbital fissures to innervate the superior oblique muscle. Primarily a motor nerve that directs the eyeball.
V: The Trigeminal Nerves
Largest cranial nerves; fibers extend from pons to face. Three divisions. Convey sensory impulses from various areas of the face (V1) and (V2), and supplies motor fibers (V3)
passes through the superior orbital fissure
passes through the foramen rotundum
passes through the foramen ovale
VI: The Abducens Nerves
Fibers from the inferior pons enter the orbits via the superior orbital fissures. Primarily a motor, innervating the lateral rectus muscle
VII: The Facial Nerves
Fibers from pons through the internal acoustic meatuses, and emerge through the stylomastoid foramina to the lateral aspect of the face. Chief motor nerves of the face with 5 major branches. Motor functions include facial expression, parasympathetic impulses to lacrimal and salivary glands. Sensory function (taste) from the anterior two-thirds of the tongue
VIII: The Vestibulocochlear Nerves
Afferent fibers from the hearing receptors (cochlear division) and equilibrium receptors (vestibular division) pass from the inner ear through the internal acoustic meatuses, and enter the brain stem. Mostly sensory function; small motor component for adjustment of sensitivity of receptors
IX: The Glossopharyngeal Nerves
Fibers from the medulla leave the skull via the jugular foramen and run to the throat. Motor functions: innervate part of the tongue and pharynx for swallowing, and provide parasympathetic fibers to the parotid salivary glands. Sensory functions: fibers conduct taste and general sensory impulses from the pharynx and posterior tongue, and impulses from carotid chemoreceptors and baroreceptors .
X: The Vagus Nerves
The only cranial nerves that extend beyond the head and neck region. Fibers from the medulla exit the skull via the jugular foramen. Most motor fibers are parasympathetic fibers that help regulate the activities of the heart, lungs, and abdominal viscera. Sensory fibers carry impulses from thoracic and abdominal viscera, baroreceptors, chemoreceptors, and taste buds of posterior tongue and pharynx.
XI: The Accessory Nerves
Formed from ventral rootlets from the C1-C5 region of the spinal cord (not the brain). Rootlets pass into the cranium via each foramen magnum. Accessory nerves exit the skull via the jugular foramina to innervate the trapezius and sternocleidomastoid muscles
XII: The Hypoglossal Nerves
Fibers from the medulla exit the skull via the hypoglossal canal. Innervate extrinsic and intrinsic muscles of the tongue that contribute to swallowing and speech
31 pairs of mixed nerves named according to their point of issue from the spinal cord. 8 cervical (C1-C8). 12 thoracic (T1-T12). 5 Lumbar (L1-L5). 5 Sacral (S1-S5). 1 Coccygeal (C0).
Spinal Nerves: Roots
Each spinal nerve connects to the spinal cord via two roots.
Contain motor (efferent) fibers from the ventral horn motor neurons (Fibers innervate skeletal muscles)
Contain sensory (afferent) fibers from sensory neurons in the dorsal root ganglia. Conduct impulses from peripheral receptors
Dorsal and ventral roots unite to form
spinal nerves, which then emerge from the vertebral column via the intervertebral foramina
Spinal Nerves: Rami
Each spinal nerve branches into mixed rami. Dorsal ramus, Larger ventral ramus, Meningeal branch, Rami communicantes (autonomic pathways) join to the ventral rami in the thoracic region.
All ventral rami except ______ form interlacing nerve networks called plexuses (cervical, brachial, lumbar, and sacral)
The back is innervated by
dorsal rami via several branches
Ventral rami of T2-T12 as intercostal nerves supply
muscles of the ribs, anterolateral thorax, and abdominal wall
Formed by ventral rami of C1-C4. Innervates skin and muscles of the neck, ear, back of head, and shoulders
Phrenic nerve (Cervical Plexus)
Major motor and sensory nerve of the diaphragm (receives fibers from C3-C5)
Formed by ventral rami of C5-C8 and T1 (and often C4 and T2). It gives rise to the nerves that innervate the upper limb
Roots (Major Branch of Brachial Plexus)
five ventral rami (C5-T1)
Trunks (Major Branch of Brachial Plexus)
upper, middle, and lower
Divisions (Major Branch of Brachial Plexus)
anterior and posterior
Cords (Major Branch of Brachial Plexus)
lateral, medial, and posterior
Axillary (Brachial Plexus Nerve)
innervates the deltoid, teres minor, and skin and joint capsule of the shoulder
Musculocutaneous (Brachial Plexus Nerve)
innervates the biceps brachii and brachialis and skin of lateral forearm
Median (Brachial Plexus Nerve)
innervates the skin, most flexors and pronators in the forearm, and some intrinsic muscles of the hand
Ulnar (Brachial Plexus Nerve)
supplies the flexor carpi ulnaris, part of the flexor digitorum profundus, most intrinsic muscles of the hand, and skin of medial aspect of hand
Radial (Brachial Plexus Nerve)
innervates essentially all extensor muscles, supinators, and posterior skin of limb
Arises from L1-L4. Innervates the thigh, abdominal wall, and psoas muscle
Femoral nerve (Lumbar Plexus)
innervates quadriceps and skin of anterior thigh and medial surface of leg.
Obturator nerve (Lumbar Plexus)
passes through obturator foramen to innervate adductor muscles
Arises from L4-S4. Serves the buttock, lower limb, pelvic structures, and perineum
Sciatic nerve (Sacral Plexus)
Longest and thickest nerve of the body. Innervates the hamstring muscles, adductor magnus, and most muscles in the leg and foot. Composed of two nerves: tibial and common fibular.
the area of skin innervated by the cutaneous branches of a single spinal nerve
Innervation of Skin
All spinal nerves except C1 participate in dermatomes. Most dermatomes overlap, so destruction of a single spinal nerve will not cause complete numbness
Inborn (intrinsic) reflex
a rapid, involuntary, predictable motor response to a stimulus.
Learned (acquired) reflexes
result from practice or repetition
Components of a reflex arc (neural path)
receptor, sensory neuron, integration center, motor neuron, effector.
site of stimulus action
transmits afferent impulses to the CNS
either monosynaptic or polysynaptic region within the CNS
conducts efferent impulses from the integration center to an effector organ
muscle fiber or gland cell that responds to the efferent impulses by contracting or secreting
For skeletal muscle activity to be smoothly coordinated, proprioceptor input is necessary
Muscle spindles inform the nervous system of the length of the muscle. Golgi tendon organs inform the brain as to the amount of tension in the muscle and tendons