Ch 13 PNS Flashcards
Purpose of Pns
Provides links from and to world outside body
All neutral structure outside brain
Sensory receptors
Peripheral receptors
Efferent motor ending
What are sensory receptors?
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
Classifications of receptors
The type of stimulus they detect
Location in body
Structural complexity
Classification of stimulus type
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
Classifications by location
Exteroceptors:
Respond to stimuli arising outside body
Receptors in the skin for touch, pressure, pain and temperature
Most special sense organs
Classifications by locations
Interceptors ( visceoroceptors )
Sensitive to chemical changes and sometimes cause discomfort
Proprioceptors : respond to stretch in skeletal muscle , inform brain of ones movement
Classifications by receptors structure
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
Senses : non encapsulated or encapsulated
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)
Simple receptors of general sense
Thermoreceporys
Cold ( 10-40) in superficial Dermis
Heat receptors ( 32-48) in deeper dermis
Outside those temperatures range- nociceptors activated pain
Unencapsukated dentritic endings
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
Encapsulated dendritic endings
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
Sensory integration
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
Sensory integration continues
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
Processing’s at receptor level
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
Continue…
Grades potential called generator potential
Stimulus
Generator potential in after repair neuron
Action potential
Adaptation of sensory receptors
Is change in sensitivity in presence of constant stimulus
Receptors membranes become less responsive
Receptor potential risk decline I. Frequency or stop
Professing at circuit level
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
Structure of a nerve
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
Classifications of nerve
Most are mixed
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
Classifications of nerve
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
Ganglia
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)
Regeneration of nerve fibers
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
Nerve fiber
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
Cranial nerve
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)
Cranial nerve
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
Cranial nerve
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
Spinal nerves
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
Spinal nerve roots
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 ,
Soinak nerves : rami
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
Spinal nerves plexuses
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
Innnervation of the skin: dermatomes
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
Stretch and tendon reflexes
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
Muscle spindles ( proprioceptors )
Sense organs that monitor the length of the skeletal muscle
The stretch myotatic reflex
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
