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The PNS
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39
Anatomy
Undergraduate 3
10/01/2012

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Term
What does the PNS include?
Definition
nervous structures outside the brain and spinal cord=
-cranial nerves and spinal nerves
Term
What are the functional components of PNS?
Definition
Motor: categorized as somatic or visceral
Sensory inputs: classified as general or special
Term
What are somatic motor neurons of PNS?
Visceral?
Definition
somatic-go to skeletal muscle
visceral- autonomic NS
Term
Spinal Nerves have -- pairs? Containing? How are they named?
Definition
31 pairs containing thousands of nerve fibers and connect to the spinal cord
Named according to point leave from spinal cord.
Term
Pairs per section of spinal region:
Definition
8 pairs of cervical (C1-C8)
12 pairs of thoracic nerves (T1-T12)
5 pairs of Sacral (S1-S5)
1 pair of coccygeal nerves (co1)
Term
Spinal cord is --, spinal nerves leave at --
Definition
segmented
leave at regular intervals between vertebrae
Term
How do Spinal nerves connect to the spinal cord?
Definition
By the dorsal and ventral root
Term
Roots are composed of-- which are arranged--
Definition
Rootlets- arranged continuously along spinal cord
Term
Dorsal root contains --
Cell bodies are located --
Definition
sensory fibers
in the dorsal root ganglion
Term
Ventral root contains--
Definition
motor fibers arising from anterior (ventral) gray column
Term
What do the spinal roots branch into?
Definition
Dorsal ramus and ventral ramus
Term
Dorsal and ventral rami contain--
Dorsal rami innervates--
Ventral rami innervate-
Definition
both sensory and motor neurons
A horizontal strip of muscle and skin on back
Anterior torax and abdomen in a simple segmented pattern, gives off lateral and anterior cutaneuous branches
Term
What is a dermatome, what innervates it?
Definition
An area of skin innervated by cutaneous branches of a single spinal nerve
Term
What nerves supply the upper limb?
Definition
brachial plexus
Term
anterior surface of the lower limb-
posterior surface of the lower limb-
Definition
lumbar nerves
sacral nerves
Term
Functions of Peripheral sensory receptors-
Definition
Structures that pick up sensory stiumuli from inside and outside body and initiate signals in sensory axons
Term
Types of Peripheral sensory receptors-
Definition
Exteroceptors
Interoceptors (visceroceptors)
Proprioceptors
Term
What are exteroceptors
Definition
Sensitive to stimuli arising from outside body
Located at or near body surfaces
Include receptors for touch, pressure, pain, and temp
Term
What are interoceptors?
Definition
Receive stimuli from internal viscera
Monitor a variety of stimuli
Term
What are proprioceptors?
Definition
Monitor degree of stretch
Located in musculoskeletal organs
Term
How do sensory receptors in PNS exist as?
Definition
Nerve endings of sensory neurons
Receptor cells- specialized epithelial cell or small neurons; synapse with sensory neurons
-usually associated with special senses
Term
How are receptors as nerve endings divided?
Definition
2 groups:
-free nerve endings
-encapsulated nerve endings
Term
What do receptors as nerve endings of sensory neurons monitor?
Definition
touch pain pressure vibration stretch temperature and proprioception
Term
Where are free nerve endings present? Respond to:
Definition
abundant in epithelia and underlying connective tissue
Respond to pain and temperature- widely distrubuted throughout body
Term
What is a specialized type of free nerve ending?
Definition
hair follicle receptors- wrap around hair follicles, light touch.
Term
Encapsulated Nerve Endings Consist of:
enclosed in:
Examples:
Definition
consists of one or more ends of sensory neurons
Enclosed in connective tissue *
Ex: Meissner's corpuscle and Pacinian Corpuscle
Term
What are Meissner's corpuscles
Definition
spiraling nerve ending surrounded by schwann cells
occur in the dermal papillae (skin)
Discriminative touch
occur in sensitive, hairless areas of skin
Term
What are Pacinian Corpuscles?
Definition
Single nerve ending surrounded by layers of flattened Schwann cells (onion-like)
Occur in the deep dermis and hypodermis
Sensitive to deep pressure/vibration
Term
What are proprioceptors?
Definition
Monitor stretch in locomotory organs
-muscle
-tendons
-joints
Three types
Term
What are the tree types of proprioceptors?
Definition
Muscle spindles
Golgi tendon organs
join receptors
Term
What do muscle spindles do?
Definition
measure the changing length of muscle
-imbedded in perimysium between muscle fascicles
consist of intrafusal fibers *(specialized skeletal muscle cells that can still contract)
-Sensory nerve endings wrap around intrafusal fibers
-Muscle stretch causes intrafusla fibers to stretch= detected by nerve endings
Part of reflexes
Term
What do Golgi tendon organs do?
Definition
located near the muscle-tendon junction
-monitor tension w/in tendons
-prevent over contraction of muscle
Term
What do joint receptors do?
Definition
mostly synovial joints
-sensory nerve endings w/in joint capsules
monitor joint position
Term
Somatic motor neuron's cell bodies in ventral gray matter of spinal cord exit-
Definition
thru ventral root
Term
What is a motor unit?
Definition
a motor neuron and all the muscle cells it innervates
Term
How does a motor unit innervate?
Definition
1 MN innervates many skeletal muscle cells, but each muscle cell is only innervated by one motor neuron
Term
What is a neuromuscuscular junction? How many per muscle cell?
Definition
synapse between a motor neuron and a muscle fiber
One neuromuscular juntion per muscle cell
Term
What is a motor end plate?
Definition
Axon terminal plus specialized region of muscle cell membrane
Term
What is a nerve plexuses?
Ventral rami (except --) :
Definition
a network of nerves
t2-12 exceptions
branch and join w/one another
form nerve plexuses in cervical, brachial, lumbar, and sacral regions
Primarily serve the limbs
Fibers form ventral rami crisscross.
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