Peripheral Nervous System - Lecture Notes - A&P 2

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Peripheral Nervous System (PNS) properties
* All neural structures outside the brain & spinal cord
* Sensory receptors
* Peripheral nerves & associated ganglia
* Motor nerve endings
* Provides links to & from external environment
How the nervous systems "branch out"
CNS
|
PNS
/ \
Sensory Motor
/ \
Autonomic Somatic
/ \
Sympathetic Parasympathetic
What is the Somatic Nervous System for?
Skeletal muscle
What is the Autonomic Nervous System for?
* Glands
* Smooth muscle
Sensory receptor properties
* Specialized to respond to stimuli
* Activation results in depolarization that trigger impulses to the CNS
* Realization, sensation, & perception of them occur in brain
The 5 stimulus types of receptors
* Mechanoreceptors
* Thermoreceptors
* Photoreceptors
* Chemoreceptors
* Nociceptors
What are mechanoreceptors?
Responds to:
* Touch
* Pressure
* Vibration
* Itch
* Stretch
What are thermoreceptors?
Responds to change in temperature (hot & cold receptors)
What are photoreceptors?
* Responds to changes in light energy
* Only found in Retina
What are chemoreceptors?
Responds to chemicals:
* Smell
* Taste
* Blood pH changes
What are Nociceptors?
Pain receptors
Properties of an Exteroreceptor
* Responds to stimuli outside of body
* Found near body surface
* Sensitive to: pain, touch, pressure, pain, & temperature
* Includes special sense organs
Properties of an Interoceptor
* Responds to stimuli within the body
* Found in viscera & blood vessels
* Sensitive to: chemical, stretch, & temperature changes
Properties of Proprioceptors
* Responds to degree of stretch of the organs they occupy
* Found in: skeletal muscle, tendons, joints, ligaments, & connective tissue coverings of muscle & bone
* Advise the brain of one's movements
Complex Receptors
Special sense organs
Unencapsulated Simple Receptors
* Free dendritic nerve endings
* Respond primarily to temperature & pain
* Merkel discs
* Hair follicle receptors
Encapsulated Simple Receptors
* Meissner's corpuscles
* Pacinian corpuscles
* Muscle spindles
* Golgi tendon organs
* Ruffini's corpuscles
* Joint kinesthetic receptors
What is sensation?
The awareness of changes in the internal & external environment
What is perception?
The conscious interpretation of sensation stimuli
Somatosensory System organization
* Input comes from: exteroceptors, proprioceptors, & interoceptors
* Three main levels of neural integration: receptor level, circuit level, & perceptual level
Receptor level processing
* The sensory receptors
* Must have specificity for the stimulus energy
* The receptor's receptive field must be stimulated
* Stimulus energy must be converted to a grated potential
* Generator potential in sensory neuron must reach threshold
Sensory receptor adaptation
* Occurs when sensory receptors are subjected to unchanging stimulus
* Receptor membrane becomes less responsive
* Receptor potentials decline in frequency or stop
Which sensory receptors adapt quickly?
The receptors that respond to pressure, touch, & smell
Which sensory receptors adapt slowly?
The receptors resonding to Merkel's discs, Ruffini's corpuscles, & interoceptors that respond to chemical blood changes
Which sensory receptors do NOT adapt?
The receptors responding to pain & proprioceptors
First-Order Neurons
* Soma reside in dorsal root or cranial ganglia
* Conduct impulses from the skin to the spinal cord or brain stem
Second-Order Neurons
* Somas reside in dorsal horn of spinal cord or medullary nuclei
* Transmit impulses to thalamus or cerebellum
Third-Order Neurons
* Located in thalamus
* Conduct impulses to the somatosensory cortex of the cerebrum
How occurs at the perceptual level
Thalamus projects fibers to the somatosensory cortex & sensory association areas
Perceptual Detection
Detecting a stimulus has occurred & requires summation
Magnitude Estimation
How much of a stimulus is acting
Spatial Discrimination
Identifying the site or pattern of the stimulus
Feature Abstraction
Used to identify a substance that has specific texture or shape
Quality Discrimination
Ability to identify submodalities of a sensation (like sweet or sour)
Pattern Recognition
Ability to recognize patterns in stimuli (like a melody or a familiar face)
Main aspects of sensory perception
* Perceptual detection
* Magnitude estimation
* Spatial discrimination
* Feature abstraction
* Quality discrimination
* Pattern recognition
Nerve
* Cordlike organ of the PNS
* Consists of peripheral axons enclosed by connective tissue
Endoneurium
Loose connective tissue that surround the individual axons
Perineurium
Coarse connective tissue that surrounds a bunch of axons, forming a fascicle
Epineurium
Tough fibrous sheath that surrounds the nerve
How nerves are classified
* Sensory
* Motor
* Mixed
Sensory Nerves
* Afferent
* Carries impulses to the CNS
Motor Nerves
* Efferent
* Carries impulses from CNS
Mixed Nerves
* Sensory & motor fibers that carry impulses to and from CNS
* Most common type of nerve
Peripheral Nerve properties
* Mixed nerves
* Carries somatic & autonomic impulses
* 4 different types
* Originate from brain or spinal column
The 4 Different Types of peripheral nerves
* Somatic Afferent
* Somatic Efferent
* Visceral Afferent
* Visceral Efferent
The reason nerve tissue is serious if damaged
They are amitotic
When can a damaged be repaired?
If the soma remains intact
Macrophages, in regards to nerve repair
Remove debris
Schwann's Cells , in regards to nerve repair
Form generation tube, & secrete growth factors
Axons, in regards to nerve repair
regenerate damaged part
Reflex vs. Purposeful action
* Reflex = same action every time
* Purposeful = not the same action every time
Hilton's Law
Any nerve serving a muscle that produces movements at a joint also innervates the joint itself, and the skin over the joint .
Properties of a reflex
* It's a rapid, predictable motor response to a stimulus
* May be intrinsic
* May be learned
* Only involve peripheral nerves & spinal cord
* Involve higher brain centers
Monosynaptic vs. Polysynaptic
* Mono = fastest synapse
* Poly = slowest synapse
Interneuron
* Located between sensory & motor neuron
* Integrates spinal cord
Which neuron is ventral?
Motor
Which neuron is dorsal?
Sensory
Reflex Arc properties
* Receptor
* Sensory neuron
* Integration center
* Motor neuron
* Effector
Reflex Arc Receptor
Site of stimulus
Reflex Arc Sensory Neuron
Transmits afferent impulse to CNS
Reflex Arc Integration Center
Either monosynaptic or polysynaptic region w/in the CNS
Reflex Arc Motor Neuron
Conducts efferent impulses from the integration center to an effector
Effector
Muscle fiber or gland that responds to the efferent impulse
Needed for stretch & Deep tendon reflexes to perform normally?
* 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 tone
Muscle Spindle operation
* Stretching muscle activates muscle spindle
* Increased rate of action potential in the fibers
* Contracting muscle reduces tension on spindle
* Decreased rate of action potential on the fibers
Properties of Stretch Reflex
* Stretching muscle activates muscle spindle
* Excited motor neurons of spindle cause the stretched muscle to contract
Example of Stretch Reflex
* Patellar Reflex
~How it works: Tapping patella tendon stretches quadriceps & starts the reflex action; the quadriceps contract & the antagonistic hamstrings relax
Golgi Tendon Reflex Properties
* Opposite of stretch reflex
* Contracting muscle activates Golgi tendon organs
* Afferent Golgi tendon neurons stimulated
* Neurons inhibit contracting muscle
* Antagonistic muscle activated
* As a result of previous happenings, contracting muscle relaxes & antagonistic muscle contracts
Superficial Reflexes & Example
* Initiated by gentle cutaneous stimulation
* Example: Plantar Reflex
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