PNS and ANS Flashcards
nerve
a cordlike organ composed of numerous nerve fibers (axons) bound together by connective tissue
endoneurium
surrounds the axon of a single nerve fiber
perineurium
surrounds a bundle of nerve fibers
epineurium
surrounds an entire nerve
peripheral nervous system
composed of nervous system structures outside the brain and spinal cord (nerves, ganglia, sensory receptors, efferent nerve endings)
mixed nerves
nerves that contain both sensory and motor fibers (most nerves are this type)
sensory (afferent) nerves
carry impulses only toward the CNS
motor (efferent) nerves
carry impulses away from the CNS
ganglia
collections of neuron cell bodies associated with nerves in the PNS
sensory receptors
- specialized cells or multicellular structures that collect information from the environment
- stimulate neurons to send impulses along sensory fibers to the brain
- classified by stimulus modality and origin as well as the receptor distribution
thermoreceptors
respond to heat and cold (plus some pain)
photoreceptors
respond to light
nociceptors
- pain receptors that respond to tissue injury or potentially damaging situations
- Type A and Type C fibers
Type A fibers
myelinated fibers that are involved in acute, sharp, localized pain
Type C fibers
unmyelinated fibers that are involved in chronic, dull pain
chemoreceptors
respond to chemicals, including odors, tastes, and body fluid composition
mechanoreceptors
respond to mechanical pressure change
- proprioceptors, baroreceptors, tactile receptors
proprioceptors
- convey nerve impulses related to muscle tone, movement of body parts, and body position
- skeletal muscles, tendons, joints, internal ear
- Pacinian corpuscles, muscle spindles, Golgi tendon organs
baroreceptors
receptors that respond to pressures such as blood pressure
tactile receptors
include fine and crude touch and pressure receptors
exteroceptors
receptors that sense stimuli external to the body
interoceptors
receptors that detect stimuli in the internal organs
encapsulated nerve endings
nerve fibers wrapped in glial cells or connective tissue (most are mechanoreceptors for touch, pressure, and stretch)
tactile sensations
touch, pressure, vibration, itch, and tickle
crude touch
the ability to perceive that something has simply touched the skin
fine touch
the ability to perceive specific information about a touch sensation such as location, shape, size, and texture of the stimulus
pressure
- sensations that generally result from stimulation of tactile receptors in deeper tissues
- longer lasting and with less variation in intensity than touch sensations
- sustained sensation felt over a larger area than touch
vibration
- sensations resulting for rapidly repetitive sensory signals from tactile receptors
- receptors are corpuscles of touch and lamellated corpuscles, which detect low-frequency and high-frequency vibrations
free nerve endings
- bare dendrites that lack structural specializations (simplest receptors)
- common in epithelial tissues
- respond to pain, temperature, tickle, itch, and some touch
Merkel’s discs
- tonic receptors for light touch, textures, edges, and shapes
- slowly adapting touch receptors
- saucer-shaped, flattened free nerve endings
- found in fingertips, hands, lips, and external genitalia
hair root plexuses
- rapidly adapting touch receptors (we are not constantly stimulated by clothing but are very sensitive to light touch)
- free nerve endings wrapped around hair follicles
- detect movements of the skin surface that disturb hairs - fine touch
Meissner’s corpuscles
- consist of two or three nerve fibers meandering upward through a mass of flattened Schwann cells
- phasic receptors for light touch and texture; distinguish between two points on the skin (kisses)
- rapidly adapting receptors that generate impulses mainly at onset of a touch
- dermal papillae such as fingertips, hands, eyelids, tip of tongue, lips, nipples, soles, clitoris, tip of penis
Pacinian (lamellated) corpuscles
- multilayered CT capsules that enclose a dendrite
- phasic/fast adapting receptors
- deeper subcutaneous tissues, tendons and ligaments, periosteum, joint capsules, mammary glands, etc
- heavy pressure, vibrations, and stretching
Ruffini’s corpuscles
- slowly adapting touch receptors
- tonic receptors for heavy touch, pressure, skin stretching, and joint movements
- deep dermis, ligaments and tendons, hands, soles
Pacinian corpuscles
proprioceptors that detect speed of joint movement
muscle spindles
proprioceptors in skeletal muscles that monitor changes in the length of skeletal muscles and participate in stretch reflexes
Golgi tendon organs
proprioceptive stretch receptors that protect from over stretching
- located at the junction of a tendon and a muscle
referred pain
the phenomenon where pain in the viscera is often mistakenly thought to come from the skin or other superficial sites
olfactory nerve (I)
- origin in olfactory mucosa of nasal cavity, termination in olfactory bulb
- detect impulses associated with smell
- if damaged: sense of small is impaired
optic nerve (II)
- origin formed by ganglia cells in retina, passes through optic foramen, termination in thalamus and midbrain
- transmits impulses associated with vision
- if damaged: blindness in part or all of the visual field
oculomotor nerve (III)
- origin in the midbrain, termination in somatic fibers to muscles of the eye
- motor impulses to muscles that move eyeball up, down, and medially, as well as those that control iris, lens, and raise upper eyelid (levator palpebrae)
- focuses lens and adjusts light entering eye
- some sensory proprioceptors
- if damaged: drooping eyelid, dilated pupil, inability to move eye in some directions, tendency of eye to move laterally at rest, double vision, and/or difficulty focusing
trochlear nerve (IV)
- origin in the midbrain, termination in the superior oblique muscle
- controls superior oblique muscle that rotates eyeball laterally and slightly depresses it when the head turns
- if damaged: double vision, inability to rotate eye inferolaterally, eye pointing superolaterally
trigeminal nerve (V)
- largest and most important sensory nerve of the face
- sensation of the face and motor control of chewing muscles
- ophthalmic, maxillary, and mandibular divisions
ophthalmic division (CN V)
- origin in superior region of face, surface of eyeball, lacrimal gland, superior nasal mucosa, frontal and ethmoid sinuses, termination in pons
- touch, temperature, and pain from eyes, tear glands, scalp, forehead, and upper eyelids
- if damaged: loss of sensation from upper face
maxillary division (CN V)
- origin in middle region of the face, nasal mucosa, maxillary sinus, palate, upper teeth and gums, termination in pons
- touch, temperature, and pain from middle of face
- if damaged: loss of sensation from middle face
mandibular division (CN V)
- sensory origin in inferior region of face, anterior 2/3 of tongue but not taste buds, lower teeth and gums, floor of mouth, dura mater, sensory termination in pons
- motor origin in pons, motor termination in anterior belly of digastric, masseter, temporalis, mylohyoid, and pterygoid muscles and tensor tympani muscle of middle ear
- sensory from scalp, skin of saw, lower teeth, lower gum, lower lip
- motor to muscles of mastication and muscles in floor of mouth
- if damaged: loss of sensation and impaired chewing
abducens nerve (VI)
- origin in inferior pons, termination in lateral rectus of eye
- motor impulses to lateral rectus of eye
- some sensory proprioceptors
- if damaged: inability to turn eye laterally, at rest eye turns medially
facial nerve (VII)
- sensory origin in taste buds of anterior 2/3 of tongue, sensory termination in thalamus
- motor origin in pons, motor termination in muscles of jaw, middle ear, and facial muscles
- major motor nerve of movement of muscles creating facial expression
- sensory function in taste
- if damaged: inability to control facial muscles and facial sagging due to loss of muscle tone, plus a distorted sense of taste, especially for sweet flavor
vestibulocochlear nerve (VIII)
- acoustic/auditory nerve
- responsible for hearing and balance
- vestibular and cochlear branches
- motor origin in pons, motor termination in outer hair cells of cochlea
- sensory origins and terminations differ between the branches
- if damaged: nerve deafness, dizziness, nausea, loss of balance, and nystagmus (involuntary oscillation of eyes side to side)
vestibular brach (CN VIII)
- begins in pons
- sensory origin in vestibule and semicircular ducts of the inner ear equilibrium receptors, sensory termination in fibers for hearing ending in medulla and for equilibrium ending at the medulla-pons junction
- vertigo (feeling of rotation) and ataxia (lack of coordination)
cochlear branch (CN VIII)
- begins in medulla
- sensory origin in cochlea hearing receptors, sensory termination same as vestibular branch
- hearing
glossopharyngeal nerve (IX)
- primarily controls tongue and pharynx
- sensory origins in pharynx, middle and outer ear, posterior 1/3 of tongue including taste buds, internal carotid artery, sensory termination in medulla oblongata
- motor origin in medulla oblongata, motor terminations in parotid (salivary) gland, glands of posterior tongue, stylopharyngeal muscle to lift throat during swallowing
- if damaged: impaired swallowing and loss of bitter and sour tastes
vagus nerve (X)
- parasympathetic nerve
- most extensive distribution of any cranial nerve, supplying organs in the head, neck, and most viscera of the thoracic and abdominopelvic cavities
- sensory origin in thoracic and abdominopelvic viscera, root of tongue, pharynx, larynx, epiglottic, outer ear, dura mater, sensory termination in medulla oblongata
- motor origin in medulla oblongata, motor terminations in tongue, pharynx, larynx, lungs, heart, liver, spleen, digestive tract, kidney, and ureter
- if damaged: hoarseness, loss of voice, impaired swallowing and gastrointestinal motility, or even death if both vagus nerves are damaged
accessory nerve (XI)
- primarily motor nerve involved in head, neck, and shoulder actions
- does not arise entirely from brain but in part from the cervical spinal cord
- cranial and spinal branches
- some sensory proprioceptors
- if damaged: impaired movement of head, neck, and shoulders, difficulty shrugging on affected side, and paralysis of sternocleidomastoid causing the head to turn toward injured side
cranial branch (CN XI)
- origin in medulla
- motor termination at muscles of soft palate, pharynx, and larynx
spinal branch (CN XI)
- arises in cervical spinal cord segments C1-C6
- motor termination at muscles of neck and back: sternocleidomastoid and trapezius
hypoglossal nerve (XII)
- origin in medulla oblongata
- motor termination at muscles of tongue when speaking and swallowing
- some sensory proprioceptors
- if damaged: impaired speech and swallowing with deviation of tongue toward injured side, atrophy, or an inability to protrude tongue if both left and right nerves are damaged
somatic fibers of spinal nerves
connect to skin and skeletal muscles
autonomic fibers of spinal nerves
connect to viscera
spinal nerves
- all are mixed nerves (except the first pair)
- arise from spinal cord and serve entire body except head and neck
- 8 cranial pairs, 12 thoracic pairs, 5 lumbar pairs, 5 sacral pairs, 1 coccygeal pair
numbering of spinal nerves
- cervical nerves: numbered same as the vertebra BELOW them (nerve C5 is superior to vertebra C5)
- all other spinal nerves: numbered same as vertebra ABOVE them (nerve L3 is inferior to vertebra L3)
dorsal root
contains sensory nerve fibers and conducts nerve impulses from the periphery into the spinal cord
dorsal root ganglion
contains the cell bodies of the sensory neurons from the periphery
ventral root
contains motor neuron axons and conducts impulses from the spinal cord to the periphery
- cell bodies of motor neurons are located in gray matter of the cord
rami
branches that a spinal nerve divides into shortly after passing through its intervertebral foramen
meningeal branch
branch of a spinal nerve that reenters the vertebral canal and innervates the meninges, vertebrae, and spinal ligaments
dorsal (posterior) rami
branches of a spinal nerve that supply the deep back muscles and skin of the posterior aspect of the thorax
ventral (anterior) rami
branches of a spinal nerve that innervate the anterior and lateral skin and muscles of the back and give rise to nerves of the limbs
- except for in T2-T12, ventral rami of spinal nerves form networks of nerves called plexuses
- ventral rami of T2-T12 are the intercostal/thoracic nerves
communicating rami
a pair of branches that emerges from a ventral ramus and connects with a string of sympathetic chain ganglia in spinal nerves T1-L2
nerve plexi
weblike networks of nerves that branch off from the ventral rami
- everywhere except in thoracic region
cervical plexus
- formed by ventral rami of first four cervical nerves (C1-C5)
- supplies the skin and muscles of the head, neck, and upper part of the shoulders
- connects with some cranial nerves
- supplies the diaphragm
phrenic nerve
supply the diaphragm
brachial plexus
- C4-T1
- situated in neck and axilla and gives rise to virtually all the nerves that innervate the upper limb as well as the neck and shoulder
musculocutaneous nerve
innervates the brachialis, biceps brachii, and skin of forearms
axillary nerve
innervates the deltoid, teres minor, and skin of anterior, lateral, and posterior arms
radial nerve
innervates the posterior muscles of the arms (triceps brachii, extensor carpi radialis longus) and skin of forearms and hands
ulnar and median nerves
innervate the muscles of the forearms (flexor carpi ulnaris) and skin of hands
lumbar plexus
- L1-L5
- supplies the anterolateral abdominal wall, external genitals, and part of the lower extremities
- femoral and obturator nerves
femoral nerve
- largest nerve that arises from the lumbar plexus
- sends motor impulses to muscles of the anterior thigh (quadriceps) and sensory impulses from skin of thighs and legs
- if damaged: inability to extend leg and loss of sensation in thigh
obturator nerves
- arise from the lumbar plexus
- motor impulses to adductors of thighs
- if damaged: paralysis of thigh adductors
sacral plexus
- L4-L5 and S1-S4, anterior to the sacrum
- supplies the buttocks, perineum, and part of the lower extremities
- sciatic nerve and its branches
sciatic nerve
- largest nerve in the body
- arises from the sacral plexus
- L4-S3 supplies posterior thigh and all of lower leg
- muscles and skin of thighs, legs, and feet
- if damaged: pain from buttock to foot
causes of sciatic nerve injury
- herniated (slipped) disc
- dislocated hip
- osteoarthritis of the lumbosacral spine
- pressure from the uterus during pregnancy
- improperly administered gluteal injection
common peroneal (fibular) nerve
- branches from the sciatic nerve
- innervates biceps femoris
- if damaged: foot drop or numbness
tibial nerve
- branches from the sciatic nerve
- innervates hamstrings, gastrocnemius, flexor digitorum longus
- if damaged: calcaneovalgus (loss of function of anterior leg and dorsum of foot)
autonomic nervous system (ANS)
- a system of motor neurons that innervate the smooth muscle, cardiac muscle, and glands of the body
- division of the visceral motor division of the PNS
- depends on continual flow of sensory afferent input from receptors in organs and efferent motor output to the same effector organs
regulators of the ANS
mainly the hypothalamus and medulla oblongata
- receive input from the limbic system and other regions of the cerebrum
dual innervation
the term for when both the sympathetic and parasympathetic divisions of the nervous system innervate the same target organs and have cooperative or contrasting effects
sympathetic division of the ANS
fight or flight
- increases alertness, heart rate, blood pressure, pulmonary air flow, blood glucose concentration, and blood flow to muscles
- reduces blood flow to the skin and digestive tract
parasympathetic division of the ANS
rest and digest
- calming effect on many body functions
- reduces energy expenditure and normal body maintenance
somatic motor pathways
a motor neuron in the brainstem or spinal cord extends a myelinated axon all the way to a skeletal muscle
autonomic motor pathways
a signal must travel across two neurons to reach the target (gland or smooth muscle) and must cross a synapse where the neurons meet in an autonomic ganglion
preganglionic neuron
first neuron in autonomic motor pathway with its cell body in the brain stem or spinal cord and a myelinated axon that passes out of the CNS as part of a cranial or spinal nerve
postganglionic neuron
second neuron in autonomic motor pathway, lies entirely outside the CNS; cell body and dendrites are located in an autonomic ganglion; unmyelinated
sympathetic preganglionic neurons
- cell bodies in the lateral gray horns of 12 thoracic and first 2 or 3 lumbar (thoracolumbar division)
- leave spinal nerves through white communicating rami and enter sympathetic chain/paravertebral ganglia
sympathetic postganglionic fibers
- unmyelinated
- leave ganglion by way of gray communicating rami and extend to the target
Does sympathetic or parasympathetic stimulation cause more widespread effects?
sympathetic, because a single sympathetic preganglionic fiber may synapse with 20+ postganglionic neurons
sympathetic and parasympathetic: pupils
sympathetic: dilates pupils
parasympathetic: constricts pupils
sympathetic and parasympathetic: heart rate and blood pressure
sympathetic: increases HR and BP
parasympathetic: decreases HR and BP
sympathetic and parasympathetic: airways
sympathetic: dilates airways
parasympathetic: constricts airways
sympathetic and parasympathetic: blood vessels
sympathetic: constricts blood vessels for kidneys and GI, increases blood supply to skeletal muscle, cardiac muscle, liver, adipose tissue
parasympathetic: dilates blood vessels for kidneys and GI, decreases blood supply to skeletal muscle, cardiac muscle, liver, adipose tissue
sympathetic and parasympathetic: blood glucose
sympathetic: increases glycogenolysis from liver, which increases blood glucose
parasympathetic: decreases glycogenolysis from liver, which decreases blood glucose
sympathetic and parasympathetic: lipolysis
sympathetic: increases lipolysis from fat cells to increase available energy
parasympathetic: decreases lipolysis
sympathetic and parasympathetic: genitals
sympathetic: orgasm (shoot)
parasympathetic: genital engorgement (point)
parasympathetic preganglionic neurons
- cell bodies found in cranial nerve nuclei (III, VII, IX, X), midbrain, pons, medulla, and lateral gray horns of 2-4 sacral segments (craniosacral division)
- long, end in terminal ganglia in or near target organ
- vagus nerve carries about 90% of parasympathetic preganglionic fibers
parasympathetic postganglionic neurons
- short, continue to specific muscles or glands
visceral sensory neurons
monitor stretch, temperature, chemical changes, and irritation within visceral organs
autonomic (visceral) reflexes
defecation, micturition, erection, ejaculation
- integrated in the spinal cord
- brain can inhibit defecation and urination consciously
control of ANS by cerebral cortex
primarily during emotional stress such as anger, fear, desire, etc
control of ANS by limbic system
involved in many emotional responses and has extensive connections with hypothalamus
- connects sensory and mental experiences
control of ANS by medulla oblongata
regulates HT signals regarding cardiac, vasomotor, and respiratory activities
