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84 Cards in this Set

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Peripheral Nervous System (PNS) includes what?
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
Sensory Receptors
Structures specialized to respond to stimuli

The realization of these stimuli, sensation and perception, occur in the brain
The activation of sensory receptors results in:
depolarizations that trigger impulses to the CNS
Receptor Classification by Stimulus TYPE
Mechanoreceptors
Thermoreceptors
Photoreceptors
Chemoreceptors
Nociceptors
Mechanoreceptors
respond to touch, pressure, vibration, stretch, and itch
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
Receptor Class by Location: Exteroceptors
-Respond to stimuli arising outside the body
-Found near the body surface
-Sensitive to touch, pressure, pain, and temperature
-Include the special sense organs
Receptor Class by Location: Interoceptors
Respond to stimuli arising within the body

Found in internal viscera and blood vessels

Sensitive to chemical changes, stretch, and temperature changes
Receptor Class by Location: Proprioceptors
Respond to degree of stretch of the organs they occupy

Found in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and
muscles

Constantly “advise” the brain of one’s movements
Receptor Classification by Structural Complexity
Receptors are structurally classified as either simple or complex

Most receptors are simple and include encapsulated and unencapsulated varieties

Complex receptors are special sense organs
Free dendritic nerve endings
Simple Receptors: Unencapsulated

Respond chiefly to temperature and pain
Merkel (tactile) discs
Simple Receptors: Unencapsulated
Hair follicle receptors
Simple Receptors: Unencapsulated
Meissner’s corpuscles (tactile corpuscles)
Simple Receptors: Encapsulated
Pacinian corpuscles (lamellated corpuscles)
Simple Receptors: Encapsulated
Ruffini’s corpuscles
Simple Receptors: Encapsulated
Sensation & Perception
Survival depends on both
Sensation is:
the awareness of changes in the internal and external environment
Perception is:
the conscious interpretation of those stimuli
Organization of the Somatosensory System
Input comes from exteroceptors, proprioceptors, and interoceptors

outside, inside or where your body is in space
The three main levels of neural integration in the somatosensory system are:
Receptor level – the sensory receptors

Circuit level – ascending pathways

Perceptual level – neuronal circuits in the cerebral cortex
Processing at the Receptor Lever
The receptor must have specificity for the stimulus energy

The receptor’s receptive field must be stimulated

Stimulus energy must be converted into a graded potential

A generator potential in the associated sensory neuron must reach threshold
Adaptation of Sensory Receptors
Adaptation occurs when sensory receptors are subjected to an unchanging stimulus-

*Receptor membranes become less responsive

*Receptor potentials decline in frequency or stop
Adaptation of Sensory Receptors
Receptors responding to pressure, touch, and smell adapt quickly

Receptors responding slowly include Merkel’s discs, Ruffini’s corpuscles, and interoceptors that respond to chemical levels in the blood

Pain receptors and proprioceptors do not exhibit adaptation
Processing at the Circuit Level
Chains of three neurons conduct sensory impulses upward to the brain
First-order neurons
conduct impulses from the skin to the spinal cord or brain stem
Second-order neurons
transmit impulses to the thalamus or cerebellum
Third-order neurons
conduct impulses to the somatosensory cortex of the cerebrum
Main Aspects of Sensory Perception:
Perceptual detection
detecting that a stimulus has occurred from several receptors
Main Aspects of Sensory Perception:
Magnitude estimation
how intense the stimulus is
Main Aspects of Sensory Perception:
Spatial discrimination
identifying the site or pattern of the stimulus (two point discrimination)
Main Aspects of Sensory Perception:
Feature abstraction
used to identify a substance that has specific texture or shape
Main Aspects of Sensory Perception:
Quality discrimination
the ability to identify submodalities of a sensation (e.g., sweet or sour tastes)
Main Aspects of Sensory Perception:
Pattern recognition
ability to recognize patterns in stimuli (e.g., melody, familiar face)
Classification of Nerves
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
Number of Cranial Nerves?
12 pairs arise from the brain
Characteristics of cranial nerves:
They have sensory, motor, or both sensory and motor functions

Each nerve is identified by a number (I through XII) and a name

Four cranial nerves carry parasympathetic fibers that serve muscles and glands
Cranial Nerve I
Olfactory- SMELL

carrying afferent impulses for the sense of smell
Cranial Nerve II
Optic- VISION

carrying afferent impulses for vision

Arises from the retina of the eye
Cranial Nerve III
Oculomotor

Functions in raising the eyelid, directing the eyeball, constricting the iris, and controlling lens shape

Fibers supply the extrinsic eye muscles
Cranial Nerve IV
Trochlear

Fibers innervate the superior oblique muscle

Primarily a motor nerve that directs the eyeball
Cranial Nerve V
Trigeminal

Conveys sensory impulses from various areas of the face (V1) and (V2), and supplies motor fibers (V3) for mastication
3 divisions of Cranial Nerve V: Trigeminal
ophthalmic (V1),
maxillary (V2),
mandibular (V3)
Cranial Nerve VI
Abducuens- ABducts the eye

Primarily a motor nerve innervating the lateral rectus muscle (abducts the eye)
Cranial Nerve VII
Facial

Mixed nerve with five major branches

Motor functions include facial expression, and the transmittal of autonomic impulses to lacrimal and salivary glands

Sensory function is taste from the anterior two-thirds of the tongue
Cranial Nerve VIII
Vestibulocochlear

*Functions are solely sensory – equilibrium and hearing

Fibers arise from the hearing and equilibrium apparatus of the inner ear

Two divisions – cochlear (hearing) and vestibular (balance)
Cranial Nerve IX
Glossopharyngeal

Fibers run to the throat

Nerve IX is a mixed nerve with motor and sensory functions
Motor function of Cranial Nerve IX
innervates part of the tongue and pharynx, and provides motor fibers to the parotid salivary gland
Sensory function of Cranial Nerve IX
fibers conduct taste and general sensory impulses from the tongue and pharynx
Cranial Nerve X
Vagus

The only cranial nerve that extends beyond the head and neck

The vagus is a mixed nerve
Motor function of Cranial Nerve X
Most motor fibers are parasympathetic fibers to the heart, lungs, and visceral organs
Sensory function of Cranial Nerve X
Its sensory function is in taste
Cranial Nerve XI
Accessory

Primarily a motor nerve

-Supplies fibers to the larynx, pharynx, and soft palate

-Innervates the trapezius and sternocleidomastoid, which move the head and neck
Cranial Nerve XII
Hypoglossal

Innervates both extrinsic and intrinsic muscles of the tongue, which contribute to swallowing and speech
Spinal Nerves
Thirty-one pairs of mixed nerves arise from the spinal cord and supply all parts of the body except the head

They are named according to their point of issue
Cervical Spinal Nerves
8 cervical (C1-C8)
Thoracic Spinal Nerves
12 thoracic (T1-T12)
Lumbar Spinal Nerves
5 Lumbar (L1-L5)
Sacral Spinal Nerves
5 Sacral (S1-S5)
Coccygeal Spinal Nerves
1 Coccygeal (C0)
Spinal Nerves: Roots
Each spinal nerve connects to the spinal cord via two medial roots
Ventral roots contain:
motor (efferent) fibers
Dorsal roots contain:
sensory (afferent) fibers
Dermatomes
A dermatome is the area of skin innervated by the cutaneous branches of a single spinal nerve

All spinal nerves except C1 participate in dermatomes
Reflexes
A reflex is a rapid, predictable motor response to a stimulus
Reflexes may:
Be inborn (intrinsic) or learned (acquired)

Involve only peripheral nerves and the spinal cord

Involve higher brain centers as well
Reflex Arc
There are five components of a reflex arc:
-Receptor
-Sensory neuron
-Integration center
-Motor neuron
-Effector
Reflex Arc:
Receptor
site of stimulus
Reflex Arc:
Sensory neuron
transmits the afferent impulse to the CNS
Reflex Arc:
Integration center
either monosynaptic or polysynaptic region within the CNS
Reflex Arc:
Motor neuron
conducts efferent impulses from the integration center to an effector
Reflex Arc:
Effector
muscle fiber or gland that responds to the efferent impulse
For skeletal muscles to perform normally:
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
Muscle Spindles are wrapped with 2 types of Afferent endings:
primary sensory endings of type Ia fibers and secondary sensory endings of type II fibers

These regions are innervated by gamma (γ) efferent fibers
Stretching the muscles activates the muscle spindle
There is an INCREASED rate of action potential in Ia fibers
Contracting the muscle reduces tension on the muscle spindle
There is a DECREASED rate of action potential on Ia fibers
Excited γ motor neurons of the spindle cause the stretched muscle to ____
contract
Afferent impulses from the spindle result in
inhibition of the antagonist
(ex: tapping patellar tendon)
What is the Golgi Tendon Reflex?
The opposite of the stretch reflex

Contracting the muscle activates the Golgi tendon organs

Afferent Golgi tendon neurons are stimulated, neurons inhibit the contracting muscle, and the antagonistic muscle is activated

As a result, the contracting muscle relaxes and the antagonist contracts
The flexor reflex is:
initiated by a painful stimulus (actual or perceived) that causes automatic withdrawal of the threatened body part
The crossed extensor reflex has two parts
The stimulated side is withdrawn

The contralateral side is extended