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chp 13
chp 13
104
Anatomy
Undergraduate 1
11/18/2010

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Term
Peripheral Nervous System (PNS)–
Definition
– all neural structures outside the brain and spinal cord
Includes sensory receptors, peripheral nerves, associated ganglia, and motor endings
Provides links to and from the external environment
Term
receptors
Definition
are structurally classified as either simple or complex
most are are simple and include encapsulated and unencapsulated varieties
Complex ones are special sense organs
Term
Sensation
Definition
is the awareness of changes in the internal and external environment
Term
Perception
Definition
is the conscious interpretation of those stimuli
Term
receptor level, circuit level and perceptual level
Definition
The three main levels of neural integration in the somatosensory system are
Term
Receptor level
Definition
the sensor receptors
Term
Circuit level –
Definition
ascending pathways
Term
Perceptual level –
Definition
neuronal circuits in the cerebral cortex
Term
Input comes from
Definition
from exteroceptors, proprioceptors, and interoceptors
Term
Processing at the Receptor Lever
Definition
The receptor must have specificity for the stimulus energy
The receptor’s receptive field must be stimulated
Term
Processing at the Receptor Lever
Definition
Stimulus energy must be converted into a graded potential
A generator potential in the associated sensory neuron must reach threshold
Term
Adaptation of Sensory Receptors
Definition
occurs when sensory receptors are subjected to an unchanging stimulus
Term
Adaptation of Sensory Receptors
Definition
Receptor membranes become less responsive
Receptor potentials decline in frequency or stop
Term
adapt quickly
Definition
Receptors responding to pressure, touch, and smell
Term
Receptors responding slowly include
Definition
Merkel’s discs, Ruffini’s corpuscles, and interoceptors that respond to chemical levels in the blood
Term
Definition
Pain receptors and proprioceptors do not exhibit adaptation. Why is this statement true?
Term
upward to the brain
Definition
Chains of three neurons conduct sensory impulses
Term
Processing at the Perceptual Level
Definition
First one modality is sent, then those considering more than one
Term
Processing at the Perceptual Level
Definition
The result is an internal, conscious image of the stimulus
Term
Perceptual detection
Definition
– detecting that a stimulus has occurred and requires summation
Term
Magnitude estimation
Definition
– how much of a stimulus is acting
Term
Spatial discrimination
Definition
– identifying the site or pattern of the stimulus
Term
Feature abstraction
Definition
– used to identify a substance that has specific texture or shape
Term
Quality discrimination
Definition
the ability to identify submodalities of a sensation (e.g., sweet or sour tastes)
Term
pattern recognition
Definition
ability to recognize patterns in stimuli (e.g., melody, familiar face)
Term
Nerve
Definition
cordlike organ of the PNS consisting of peripheral axons enclosed by connective tissue
Term
Connective tissue coverings include:
Definition
Endoneurium – loose connective tissue that surrounds axons
Perineurium – coarse connective tissue that bundles fibers into fascicles
Epineurium – tough fibrous sheath around a nerve
How do these relate to muscle coverings?
Term
Classification of Nerves
Definition
Sensory and motor divisions
Sensory (afferent) – carry impulse to the CNS
Motor (efferent) – carry impulses from CNS
Mixed – sensory and motor fibers carry impulses to and from CNS; most common type of nerve
Term
Mixed nerves
Definition
carry somatic and autonomic (visceral) impulses
Term
The four types of mixed nerves are:
Definition
Somatic afferent and somatic efferent
Visceral afferent and visceral efferent
Term
repaired
Definition
If the soma of a damaged nerve remains intact, damage can be
Term
Twelve pairs of cranial
Definition
nerves arise from the brain
Term
Cranial Nerves
Definition
They have sensory, motor, or both sensory and motor functions
Term
Four cranial nerves
Definition
carry parasympathetic fibers that serve muscles and glands
Term
Cranial Nerve III: Oculomotor
Definition
Fibers extend from the ventral midbrain, pass through the superior orbital fissure, and go to the extrinsic eye muscles
Functions in raising the eyelid, directing the eyeball, constricting the iris, and controlling lens shape
Parasympathetic cell bodies are in the ciliary ganglia
Term
Cranial Nerve IV: Trochlear
Definition
Fibers emerge from the dorsal midbrain and enter the orbits via the superior orbital fissures; innervate the superior oblique muscle
Primarily a motor nerve that directs the eyeball
The superior oblique muscle travels through a loop called the trochlea
Term
Cranial Nerve V: Trigeminal
Definition
Three divisions: ophthalmic (V1), maxillary (V2), and mandibular (V3)
Fibers run from the face to the pons via the superior orbital fissure (V1), the foramen rotundum (V2), and the foramen ovale (V3)
Conveys sensory impulses from various areas of the face (V1) and (V2), and supplies motor fibers (V3) for mastication
Term
Cranial Nerve VI: Abducens
Definition
Fibers leave the inferior pons and enter the orbit via the superior orbital fissure
Primarily a motor nerve innervating the lateral rectus muscle…helps the eye to “abduct”
If the nerve is damaged, the eye will rotate medially and lead to strabismus (crossed-eyes)
Term
Cranial Nerve VII: Facial
Definition
Fibers leave the pons, travel through the internal acoustic meatus, and emerge through the stylomastoid foramen to the lateral aspect of the face
Mixed nerve with five major branches
Motor functions include facial expression, and the transmittal of autonomic impulses to lacrimal and salivary glands. Damage leads to Bell’s palsy
Sensory function is taste from the anterior two-thirds of the tongue
Term
Cranial Nerve VIII: Vestibulocochlear
Definition
Fibers arise from the hearing and equilibrium apparatus of the inner ear, pass through the internal acoustic meatus, and enter the brainstem at the pons-medulla border
Two divisions – cochlear (hearing) and vestibular (equilibrium)
Functions are solely sensory: equilibrium and hearing
Term
Cranial Nerve IX: Glossopharyngeal
Definition
Fibers emerge from the medulla, leave the skull via the jugular foramen, and run to the throat
Nerve IX is a mixed nerve with motor and sensory functions
Term
Cranial Nerve IX: Glossopharyngeal
Definition
functions
Motor – innervates part of the tongue and pharynx, and provides motor fibers to the parotid salivary gland
Term
Cranial Nerve IX: Glossopharyngeal
Definition
Sensory – fibers conduct taste (posterior one-third) and general sensory impulses from the tongue and pharynx
Term
Cranial Nerve X: Vagus
Definition
The only cranial nerve that extends beyond the head and neck
Fibers emerge from the medulla via the jugular foramen
is a mixed nerve
Term
Cranial Nerve X: Vagus
Definition
Motor – most motor fibers are parasympathetic fibers to the heart, lungs, and visceral organs
Term
Cranial Nerve X: Vagus
Definition
Sensory – transmitting impulses (1) from thoracic and abdominal vicera, (2) from aortic baroreceptors and chemoreceptors, (3) from taste buds
Term
Cranial Nerve XI: Accessory
Definition
Formed from a cranial root emerging from the medulla and a spinal root arising from the superior region of the spinal cord
The spinal root passes upward into the cranium via the foramen magnum
nerve leaves the cranium via the jugular foramen
Term
Cranial Nerve XI: Accessory
Definition
Primarily a motor nerve
Supplies fibers to the larynx, pharynx, and soft palate
Innervates the trapezius and sternocleidomastoid, which move the head and neck
Term
Cranial Nerve XII: Hypoglossal
Definition
Fibers arise from the medulla and exit the skull via the hypoglossal canal
Innervates both extrinsic and intrinsic muscles of the tongue, which contribute to swallowing and speech
Term
Spinal Nerves
Definition
Thirty-one pairs of mixed nerves arise from the spinal cord and supply all parts of the body except the head
Term
medial roots
Definition
Each spinal nerve connects to the spinal cord via two
Term
Each root
Definition
forms a series of rootlets that attach to the spinal cord
Term
Ventral roots
Definition
arise from the anterior horn and contain motor (efferent) fibers
Term
Dorsal roots
Definition
arise from sensory neurons in the dorsal root ganglion and contain sensory (afferent) fibers
Term
Small dorsal ramus
Larger ventral ramus
Tiny meningeal branch
Rami communicantes at the base of the ventral rami in the thoracic region
Definition
The short spinal nerves branch into three or four mixed, distal rami
Term
All ventral rami
Definition
except T2-T12 form interlacing nerve networks called plexuses
Term
Plexuses
Definition
are found in the cervical, brachial, lumbar, and sacral regions
Term
spinal nerves
Definition
Each resulting branch of a plexus contains fibers from several
Term
Nerve Plexuses
Definition
Fibers travel to the periphery via several different routes
Each muscle receives a nerve supply from more than one spinal nerve
Damage to one spinal segment cannot completely paralyze a muscle
Term
several braches
Definition
The back is innervated by dorsal rami via
Term
Intercostal nerves
Definition
supply muscles of the ribs, anterolateral thorax, and abdominal wall
Term
cervical plexus
Definition
plexus is formed by ventral rami of C1-C4
Most branches are cutaneous nerves of the neck, ear, back of head, and shoulders
The most important nerve of this plexus is the phrenic nerve
Term
phrenic nerve
Definition
is the major motor and sensory nerve of the diaphragm
Term
Brachial Plexus
Definition
Formed by C5-C8 and T1 (C4 and T2 may also contribute to this plexus)
It gives rise to the nerves that innervate the upper limb
Term
Brachial Plexus
Definition
There are four major branches of this plexus
Roots – five ventral rami (C5-T1)
Trunks – upper, middle, and lower, which form divisions
Divisions – anterior and posterior serve the front and back of the limb
Cords – lateral, medial, and posterior fiber bundles
Term
Axillary
Definition
– innervates the deltoid and teres minor
Term
Musculocutaneous –
Definition
sends fibers to the biceps brachii and brachialis
Term
Median
Definition
– branches to most of the flexor muscles of arm
Term
Ulnar
Definition
– supplies the flexor carpi ulnaris and part of the flexor digitorum profundus
Term
Radial
Definition
– innervates essentially all extensor muscles
Term
Lumbar Plexus
Definition
Arises from L1-L4 and innervates the thigh, abdominal wall, and psoas muscle
The major nerves are the femoral and the obturator and saphenous
Term
Sacral Plexus
Definition
Arises from L4-S4 and serves the buttock, lower limb, pelvic structures, and the perineum
The major nerve is the sciatic, the longest and thickest nerve of the body
Term
The sciatic
Definition
is actually composed of two nerves: the tibial and the common fibular (peroneal) nerves
Term
Dermatomes
Definition
is the area of skin innervated by the cutaneous branches of a single spinal nerve
All spinal nerves except C1 participate in
Term
Motor Endings
Definition
PNS elements that activate effectors by releasing neurotransmitters at:
Neuromuscular junctions
Varicosities at smooth muscle and glands
Term
Innervation of Visceral Muscle and Glands
Definition
Acetylcholine and norepinephrine are used as neurotransmitters
Visceral responses are slower than somatic responses
Term
The three levels of motor control are
Definition
Segmental level
Projection level
Precommand level
Term
The segmental level
Definition
is the lowest level of motor hierarchy
It consists of segmental circuits of the spinal cord
Its circuits control locomotion and specific, oft-repeated motor activity
These circuits are called central pattern generators (CPGs)
Term
The projection level consists of:
Definition
Cortical motor areas that produce the direct (pyramidal) system
Brain stem motor areas that oversee the indirect (multineuronal) system
Term
Projection Level
Definition
Helps control reflex and fixed-pattern activity and houses command neurons that modify the segmental apparatus
Term
Precommand Level
Definition
Cerebellar and basal nuclei systems that:
Regulate motor activity
Precisely start or stop movements
Coordinate movements with posture
Block unwanted movements
Monitor muscle tone
Term
There are five components of a reflex arc
Definition
Receptor
Sensory neuron
Integration center
Motor neuron
Effector
Term
Receptor
Definition
reflex arc
– site of stimulus
Term
sensory neuron
Definition
reflex arc

transmit the afferent impulse to the CNS
Term
integration center
Definition
reflex arc

either monosynaptic or polysynaptic region within the CNS
Term
motor neuron
Definition
reflex arc

conducts efferent impulses from the integration center to an effector
Term
effector
Definition
reflex arc

muscle fiber or gland that responds to the efferent impulse
Term
For skeletal muscles to perform normally:
Definition
The Golgi tendon organs (proprioceptors) must constantly inform the brain as to the state of the muscle
Stretch reflexes initiated by muscle spindles must maintain healthy muscle tone
Term
Muscle Spindles
Definition
Are composed of 3-10 intrafusal muscle fibers that lack myofilaments in their central regions, are noncontractile, and serve as receptive surfaces
Term
Muscle Spindles
Definition
are wrapped with two types of afferent endings: primary sensory endings of type Ia fibers and secondary sensory endings of type II fibers
Term
Muscle Spindles
Definition
These regions are innervated by gamma () efferent fibers
Note: contractile muscle fibers are extrafusal fibers and are innervated by alpha () efferent fibers
Term
Stretching the muscles activates the muscle spindle
Definition
There is an increased rate of action potential in Ia fibers
Term
Contracting the muscle reduces tension on the muscle spindle
Definition
There is a decreased rate of action potential on Ia fibers
Term
Stretch Reflex
Definition
Stretching the muscle activates the muscle spindle
Excited  motor neurons of the spindle cause the stretched muscle to contract
Afferent impulses from the spindle result in inhibition of the antagonist
Term
Stretch Reflex
Definition
Example: patellar reflex
Tapping the patellar tendon stretches the quadriceps and starts the reflex action
The quadriceps contract and the antagonistic hamstrings relax
Term
Golgi Tendon Reflex
Definition
The opposite of the stretch reflex
Contracting the muscle activates the Golgi tendon organs
Term
golgi tendon reflex
Definition
Afferent Golgi tendon neurons are stimulated, neurons inhibit the contracting muscle, and the antagonistic muscle is activated
Term
contracts
Definition
As a result, the contracting muscle relaxes and the antagonist
Term
The flexor reflex
Definition
is initiated by a painful stimulus (actual or perceived) that causes automatic withdrawal of the threatened body part
Term
The crossed extensor reflex has two parts
Definition
The stimulated side is withdrawn
The contralateral side is extended
Term
Superficial Reflexes
Definition
Initiated by gentle cutaneous stimulation
Example:
Plantar reflex is initiated by stimulating the lateral aspect of the sole of the foot
The response is downward flexion of the toes
Indirectly tests for proper corticospinal tract functioning
Term
Babinski’s sign:
Definition
abnormal plantar reflex indicating corticospinal damage where the great toe dorsiflexes and the smaller toes fan laterally
Term
head
Definition
Cranial nerves innervate muscles of the
Term
Developmental Aspects of the PNS
Definition
Distribution and growth of spinal nerves correlate with the segmented body plan
Sensory receptors atrophy with age and muscle tone lessens
Peripheral nerves remain viable throughout life unless subjected to trauma
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