The Peripheral Nervous System Flashcards
What is the PNS?
PNS is composed of nerves (cranial and spinal) and ganglia outside brain and spinal cord
What are the divisions of the peripheral nervous system?
Sensory and motor
motor=> autonomic and somatic
autonomic= para and symp
What carries information to the CNS?
Sensory (afferent) nerves carry information towards the CNS
- back of cord
What carries information away from the CNS?
Motor (efferent) nerves carry information away from the CNS
How many cranial nerves?
12 pairs of cranial nerves
How many spinal nerves?
31 pairs of spinal nerves
What are somatic nerves?
Somatic afferent nerves convey information from skin, skeletal muscle and joints
Somatic efferent nerves convey information to skeletal muscles
What is a dermatome?
An area of skin that is supplied by a single spinal nerve
- bones don’t match up with the segments
What is a myotome?
Group of muscles innervated by a single spinal nerve
What are visceral autonomic nerves?
Visceral afferent nerves carry information from the viscera (thoracic, abdominal and pelvic organs)
Visceral efferent nerves can be divided into sympathetic and parasympathetic
What is the difference between the para and symp visceral efferent autonomic nerves?
Sympathetic efferent nerves innervate the viscera (organs) and periphery (vasculature and sweat glands)
Parasympathetic efferent nerves innervate the viscera (organs) only
What is a ganglion?
A ganglion is a collection of cell bodies outside the CNS
What is a nucleus?
A nucleus is a collection of cell bodies inside the CNS
What is a plexus?
A plexus is a network of interconnecting nerves
What is the similarity between all afferent nerves (somatic and visceral)?
All afferent (somatic and visceral) fibres have their cell bodies in spinal ganglia.
Where do visceral nerves synapse?
In the peripheral ganglion
What is an overview of direction of afferent and efferent nerves and where they go in the peripheral nervous system?
How are peripheral nerves arrange?
in fasciculli
What are the layers of connective tissue in peripheral nerves?
3
External vascular layer - epineurium
Individual fascicles covered in perineurium
Individual axons covered in endoneurium
How are peripheral nerves classified?
Two classification systems
- one based on conduction velocity
- one based on axonal diameter (sensory only)
How does the conduction velocity method of classification of peripheral nerves work?
uses letters A,B, and C (A is the fastest)
- e.g., the one that is most myelinated would be the fastest so would be A
How does the axonal diameter method of classification of peripheral nerves work?
sensory only
Uses roman numerals I-IV with I being the largest diameter
How would the classification system help us see the function of nerves?
Myelinated Aa would be motor to skeletal muscle
unmyelinated C IV would be postganglionic autonomic fibres; sensory from free nerve endings for pain and temperature; smell
What do sensory receptors do?
Detect external or internal information