Ch 13 PNS

Question 1

Purpose of Pns

Answer 1

Provides links from and to world outside body

All neutral structure outside brain
Sensory receptors
Peripheral receptors
Efferent motor ending

Question 2

What are sensory receptors?

Answer 2

Specialized to respond to changes in the environment ( stimuli )
Activation results in graded potentials that trigger nerve impulses

Sensation ( awareness of stimulus )
Perception ( interpretation of meaning of stimulus) occur in the brain

Question 3

Classifications of receptors

Answer 3

The type of stimulus they detect
Location in body
Structural complexity

Question 4

Classification of stimulus type

Answer 4

Menchanoreceptors- respond to touch, pressure, vibration and stretch

Themoreceptore- sensitive to change in temp
Photoreceptors- respond to light energy
Chemoreceptors- responds to chem ( taste , smell )
Nociceptors - sensitive to pain

Question 5

Classifications by location

Answer 5

Exteroceptors:
Respond to stimuli arising outside body
Receptors in the skin for touch, pressure, pain and temperature

Most special sense organs

Question 6

Classifications by locations

Answer 6

Interceptors ( visceoroceptors )
Sensitive to chemical changes and sometimes cause discomfort

Proprioceptors : respond to stretch in skeletal muscle , inform brain of ones movement

Question 7

Classifications by receptors structure

Answer 7

Simple receptors for general sense :
Tactile receptors ( touch pressure stretch
Modified dendritic ending of sensory neurons

Receptors for special sense :
Vision hearing equilibrium, smell and taste

Question 8

Senses : non encapsulated or encapsulated

Answer 8

Non encapsulated( free) nerve endings
Abundant in epithelial and ct
Most nonmyelinated, small diameter fibers
Respond mostly to temp and pain , and some pressure movements (itch)

Question 9

Simple receptors of general sense

Answer 9

Thermoreceporys
Cold ( 10-40) in superficial Dermis
Heat receptors ( 32-48) in deeper dermis

Outside those temperatures range- nociceptors activated pain

Question 10

Unencapsukated dentritic endings

Answer 10

Nociceptors
Player in detection-
Ion channel opened by heat , low ph chem eg

Respond to : pinching, chemicals from damage tissues, capsaicin

Other light touch receptors
Tactile ( Markell) docs
Hair follicle receptors

Question 11

Encapsulated dendritic endings

Answer 11

All mechanoreceptors in ct capsule
Tactile ( meissner’) corpuscles discriminative touch
Lamellar ( pacinian) corpuscles- deep pressure and vibration
Bulbous corpuscles ( riffini endings ) deep continuous tissue

Muscle spindles- muscle stretch
Tendon organs- stretch in tendons
Joint kinesthtic receptors- joint position and motion

Question 12

Sensory integration

Answer 12

Somatosensoru system - part of sensory system serving body wall and limb

Receives input from
Exteroceptors , proprioceptors and interceptors

Input relayed towards head, but processed along way

Question 13

Sensory integration continues

Answer 13

Levels of neural integration in sensory systems:
Receptors level - sensory receptors
Circuit level - processing in ascending pathways
Perceptual level - processing’s in cortical sensory areas

Question 14

Processing’s at receptor level

Answer 14

To produce a sensation:
Receptors have specificity for stimulus energy
Stimulus must be applied in receptive field
Transduction occurs
Stimulus change to garage potential
Generator potential or receptor potential

Grades potentials must reach threshold ap

Question 15

Continue…

Answer 15

Grades potential called generator potential
Stimulus
Generator potential in after repair neuron
Action potential

Question 16

Adaptation of sensory receptors

Answer 16

Is change in sensitivity in presence of constant stimulus

Receptors membranes become less responsive
Receptor potential risk decline I. Frequency or stop

Question 17

Professing at circuit level

Answer 17

Pathways of 3 neurons conduct sensory impulses upward to appropriate cortical regions
First order : conduct impulses from receptors level to spinal reflexes
Second order: transmit impulses to 3rd order sensory neurons

3rd order sensory : conduct impulses from thalamus to the somatosensory cortex

Question 18

Structure of a nerve

Answer 18

Cordlike organ of pns budge of myelinated and no myelinated peripheral axons enclosed by ct

Ct covering:
Endometrium - loose ct that encloses axons and their myelin sheaths
Perineurim: coarse cr that bundles fibers into fascicles
Epineurium- tough fibrous stealth around nerve

Question 19

Classifications of nerve

Most are mixed

Answer 19

Classified according to direction transmit impulses
Mixed nerves - both sensory and motor fibers : impulses both to and from cns sensory ( afferenr) nerves - impulses only towards cns
Motor ( effenent) nerves - impulses only away from cns

Question 20

Classifications of nerve

Answer 20

Purse sensory ( afferent) or motor ( efferent) nerves are rare ; most mixed

Types of fibers in mixed nerves
Somatic afferent /efferent
Visceral afferent / efferent

Peripheral nerves classified as cranial or spinal nerve

Question 21

Ganglia

Answer 21

Contain neuron call bodies associated with nerves in pns

Associated with afferent nerve fibers contain cell bodies of sensory neurons
Dorsal root ganglia ( sensory , somatic )

Ganglia associated wirh efferent nerve fibers contain autonomic motor neurons 
  Automatic ganglia ( motor, visceral)

Question 22

Regeneration of nerve fibers

Answer 22

Mature neurons are amitotic but if soma of damage nerve is intact, peripheral axon may regenerate

If peripheral axon damaged
Axon fragments ( wallerian degeneration) spreads distally from injury
Macrophages clean dear axon; myelin sheath intact
Axon filaments grow through regeneration tube
Axon regenerates: née myelin sheath forms
Greater distance between severed ends-less chance of regeneration

Question 23

Nerve fiber

Answer 23

Most cns fibers never regenerate
Cns oligodendrocytes bear growth inhibiting proteins that prevents cns fiber regeneration
Astrocytes at injury site from scar tissue containing chondroitin sulfate that blocks axonak regrowth
Treatment
Newuteuzinf growth inhibitors, blocking receptors for inhibitory proteins, destroying chondroitin sulfate promising

Question 24

Cranial nerve

Answer 24

12 park of nerves that arise from brain and exit through foramina leading to muscles, glands and sense organs in head and neck

Input and output reminds ipsilatreal except vn ( 2,4)

Question 25

Cranial nerve

Answer 25

Olfactory : smell /sensory only Optic nerves vision / sensory only Oculomotor nerve : motor eyelid movement Trickle at nerve muscle for eye rotation/motor Trigeminal nerve : both face nerve , motor for mastification Abducens nerve : rotate laterally, motor

Question 26

Cranial nerve

Answer 26

Vestibulocochlear nerve : sensory only hearing sense of balance Glossopharyngeal nerve : mixed : motor for salvation and sensory for Tate’s Vagus nerve: major motor , allows muscle to swallow and speech Accessory nerve : motor , head neck and shoulder movement Hypoglossal nerve : motor provides tongue movement

Question 27

Spinal nerves

Answer 27

31 Paris of mixed nerves named for point of issue from spinal cord Supply all body parts but head and part of neck 8- cervical 12 throacic 5 lumbar 5 sacral 1 coccygeal

Question 28

Spinal nerve roots

Answer 28

Each spinal nerve connects to spinal cord via two roots Ventral roots Contains motor efferent fibers from central horn motor neurons Fibers inner age skeletal muscles Dorsal roots Contains sensory afferent fibers from sensory neurons in dorsal root ganglia and conduct impulses from peripheral receptors Dorsal and ventral roots unite to form the spinal nerves ,

Question 29

Soinak nerves : rami

Answer 29

Spinal nerves quite short ( 1-2 vn) Each branches into mixed rami Dorsal Ramus Ventral ramus - larger Meninges branch - find reeters vertebral canal, innervates meninges and blood vessels Rami communicantes: ( autonomic pathways) Join ventral rami in thoracic region

Question 30

Spinal nerves plexuses

Answer 30

Within plexus fibers criss cross Each branch contains fibers from several spinal nerves Fibers from ventral ramus go to body periphery via several routes Each limb muscle innervates by more than spinal nerve Damage to one does not paralysis

Question 31

Innnervation of the skin: dermatomes

Answer 31

Area of skin innervates by cutaneous branches of single spinal nerve All spinal nerves except C1 participate in dematomes Extent of spinal cord injuries ascertained by affected dermatomes Most overlap. So desctrution won’t cause compete numbness

Question 32

Stretch and tendon reflexes

Answer 32

To smoothly coordinate skeletal muscle nervous system must receive proprioceptor input regarding Length of muscle : from muscle spindles Amount of tension in muckraker From tendon organs

Question 33

Muscle spindles ( proprioceptors )

Answer 33

Sense organs that monitor the length of the skeletal muscle

Question 34

The stretch myotatic reflex

Answer 34

When muscle is stretched, it contracts and maintain increase tonus Help maintain equilibrium and posture Stabilize joint by balancing tension in extensors and flexors smoothing muscles actions Very sudden muscle stretch =tendon reflex Reciprocal inhibition