peripheral nervous system Flashcards
describe nervous system
coordinates voluntary and involuntary actions and transmits signals between different parts of the body
includes all neural tissue in body
basic functional units called neurons
supporting cells called neuroglia = seperate and protect neurons, provide supportive framework
anatomical divisions of NS I
CNS - brain and spinal cord
responsible for integrating, processing and coordinating sensory data and motor commands
responsible for higher functions such as intelligence, memory, learning and emotion
anatomical divisions of PNS
consists of all neural tissue except brain and spinal cord
PNS delivers sensory info to CNS and carries motor demands to peripheral tissues and systems
functionally divided into afferent and efferent divisions
afferent vs efferent
afferent - brings sensory info to the CNS from receptors in peripheral tissues and organs
efferent = carries motor commands from CNS to muscles and glands
functional divisions of the NS I
somatic = innervates musculoskeletal structures and sense organs of the skin.
efferent functions under voluntary control
autonomic = innervates smooth muscles and glands. maintains at constant level an internal environment of body
sympathetic vs parasympathetic NS
have opposing effects
sympathetic division - active during periods of exertion, stress or emergency (fight or flight)
parasympathetic division- under resting conditions (rest and digest)
spinal cord
spinal cord continuous with the lowermost part of the brainstem, medulla oblongata
passes down the vertebral canal and terminates as a cone shaped swelling, conus medullaris
terminates at approx level of L1-2
spinal nerves continue to branch out diagonally forming cauda equina
slender strand of fibrous tissue extends from inferior tip of spinal cord to attach to sacrum called filum terminale
gross anatomy of spinal cord I
spinal cord and brain consist of 2 types of nervous tissue:
- grey matter = contains cell bodies, dendrites and proximal parts of axons of neurons
- white matter = contains abundance of myelinated axons which run in tracts carrying signals from one part of the CNS to another
gross anatomy of spinal cord II
grey matter
butterfly or H shaped in cross section
two posterior horns = receive sensory information
two anterior horns = cell bodies of motor neurons
lateral horn only present in thoracolumbar regions as these contain cell bodies of sympathetic NS
grey mater greatest in cervical and lumbar regions, sensory and motor control of limbs is greatest giving rise to cervical and lumbar enlargements
gross anatomy of spinal cord III
white matter :
- surrounds grey matter
- contains axons that course up and down cord
- bundles arranged in 3 pairs called columns
- posterior, lateral and anterior
each column consist of subdivisions called tracts. ascending tracts conduct motor impulses down cord
components of PNS
consists of:
cranial nerves = 12 pairs, arise from brain and brainstem
spinal nerves = 31 pairs, arise from spinal cord
spinal nerves
31 pairs
first pair between skull and C1
cervical region there are 8 spinal nerves and only 7 cervical vertebrae
rest pass through intervertebral foramen so: 12 thoracic 5 lumbar 5 sacral 1 coccygeal
distribution of typical spinal nerve
dorsal ramus = to muscles and skin in region of back
ventral ramus = to anterior and lateral muscles and skin of trunk
gives rise to nerves of limbs
dermatomes and myotomes
spinal nerves have motor fibres and sensory fibres
skin area supplied by sensory fibres of a single nerve root is known as a dermatome
group of muscles primarily innervated by motor fibres of a single nerve root is known as myotome
nerve plexuses
ventral rami of adjacent spinal nerves merge, to form nerve plexuses
contain sensory as well as motor fibres
5 spinal plexuses:
- cervical plexus
- lumbar plexus
- sacral plexus
- brachial plexus
- coccygeal plexus
brachial plexus I
innervates pectoral girdle and upper limb
nerves originate from:
- roots, trunks, cords and branches
musculocutaneous nerve
spinal segments C5,6,7
penetrates the coracobrachialis muscle and passes between the biceps brachia and brachialis muscle
innervates all three flexor muscles in anterior compartment of the arm
median nerve
spinal segments C5,6,7,8 and T1
passes through arm and into forearm through cubital fossa
innervates most of muscles in anterior compartment of forearm
except: flexor carpi ulnas and medial half of flexor digitorum profundus muscle
continues to hand via carpal tunnel
radial nerve
spinal segments C5,6,7,8 ans T1
enters arm by crossing the inferior margin of the term major muscle through triangular interval
in arm passes diagonally from medial to lateral through posterior compartment
passes anteriorly through lateral inter muscular septum and enters anterior compartment of forearm
radial nerve II
bifurcates into:
deep - mostly motor
superficial
sensory
continues laterally and posteriorly to enter hand
innervates all muscles in posterior compartment of arm and forearm
sensory innervation to skin on posterior aspect of arm and forearm and dorsal lateral surface of the hand
ulnar nerve I
spinal segment C7,8 & T1
passes through arm and posterior to medial epicondyle of humerus and into anterior compartment of forearm
ulnar nerve II
passes down medial side of forearm between flexor carpi ulnas and flexor digitorum profundus
innervates these muscles
passes into hand superficial to flexor retinaculm
femoral nerve
L2,3,4
leaves abdomen under inguinal ligament to enter the anterior compartment of the thigh
innervates all muscles in anterior compartment
innervates skin over anterior thigh, anteromedial Side of knee, medial side of leg, medial side of foot
sciatic nerve I
largest nerve of body
L4 to S3
leaves pelvis through greater sciatic foramen into gluteal region
enters posterior compartment of thigh
divides into two branches
= common fibular and tibial
