peripheral nervous system Flashcards
what is the PNS
peripheral nervous system
nerves (cranial and spinal) and ganglia (collection of cell bodies) outside the brain and spinal cord
what 2 nerves are not known as peripheral nerves
cranial nerves 1 and 2
what can the PNS be divided into
the somatic and autonomic nervous system
what does the sensory division do
composed of sensory neurons
conducts signals from receptors to CNS
afferent nerves - info to CNS
what does the motor division do
composed of motor neurones
conducts signals from CNS to effectors
efferent nerves away from CNS
how many pairs of cranial nerves are there
12 pairs
how many pairs of spinal nerves are there
31 pairs (emerge from spinal cord through intervertebral foramina)
what do somatic afferent nerves do
convey info from skin, skeletal muscles and joints
what do somatic efferent nerves do
convey info to skeletal muscles
what does somatic mean
under voluntary control
what is dermatome
an area of skin that is supplied by a single spinal nerve
what is myotome
a group of muscles innervated by a single spinal nerve
what do visceral afferent nerves do
carry info from viscera (thoracic, abdominal and pelvic organs)
what can visceral efferent nerves be divided into
sympathetic and parasympathetic
what do visceral sympathetic efferent nerves innervate
the viscera (organs) and periphery (sweat glands and vasculature)
what do visceral parasympathetic efferent nerves innervate
viscera only
what does autonomic mean
involuntary responses
what is a ganglion
a collection of cell bodies outside the CNS
what is a nucleus
a collection of cell bodies inside the CNS
what is a plexus
a network of interconnecting nerves
where do visceral efferent nerves synapse
in a peripheral ganglion
where do all afferent (somatic and visceral) fibres have their cell bodies
in spinal ganglia
what does visceral mean
not under voluntary control
structure of peripheral nerves, how are they arranged, how many layers of connective tissue is around the nerve and name them
arranged in fasciculi
3 layers of connective tissue around entire nerve
external vascular layer = epineurium
individual fascicles are covered in perineurium
individual axons are covered in endoneurium
how are peripheral nerves classified (2 ways)
based on conduction velocity (uses A/B/C where A is the fastest)
based on axonal diameter (sensory only - using roman numerals I-IV with I being largest diameter)
sensory receptors can direct either..
external or internal info
how can sensory receptors be classified
by source of stimulus or
by mode of detection
external sensory receptors are called.. and they detect… (source of stimulus)
exteroceptors pain temp touch pressure
two types of internal sensory receptors (source of stimulus)
proprioceptors - movement and joint position
enteroceptors - movement through gut and blood pH
receptors by mode of detection
- chemoreceptors
- photoreceptors
- thermoreceptors
- mechanoreceptors
- nociceptors
what are chemoreceptors
detector molecules which bind to receptor eg in olfactory bulb
what are photoreceptors
detect light in retina
what are thermoreceptors
detect temp in skin
what are mechanoreceptors
mechanical opening of ion channels eg touch receptors in skin
what are nociceptors
detect tissue damage - interpreted as pain
what are 3 types of proprioceptors
muscle spindles - detect changes in muscle length
golgi tendon organs - detect changes in tension in tendons
joint receptors - found in joint capsules - detect start and end of movement
where are motor neurones found
neuromuscular junction - specialised synapse between a motor neurone and a muscle fibre
what is a motor unit
a single motor neurone together with all the muscle fibres that it innervates
the smallest functional unit with which to produce force
in humans how many motor neurones are there
approx 420,000 motor neurones
how many skeletal muscle fibres in humans are there
approx 250 million
how many muscle fibres does each motor neurone supply
approx 600 muscle fibres
what happens upon stimulation of one motor unit
contraction of all muscle fibres in that unit
what is a reflex action
an involuntary coordinated pattern of muscle contraction and relaxation elicited by peripheral stimuli
STEPS for the reflex action arc
1) stretching stimulates sensory receptor (muscle spindle)
2) sensory neurone activated
3) within integrating centre (spinal cord) sensory neuron activates motor neuron
4) motor neuron activated
5) effector (same muscle) contracts and relieves the stretching
describe the autonomic nervous system
has visceral afferent and efferent parts
efferent has sympathetic and parasympathetic nervous systems
which have opposing actions
have pre and post ganglionic neurons
release ACh at preganglionic synapses
releases NA (sympathetic) - exceptions being sweat glands where ACh is released or acetylcholine (parasympathetic) at post ganglionic neurons
what is the visceral sensory NS
relays sensory info from the core
pain, fullness, BP
what is the visceral motor NS
outflow to core and body wall
controls pupils, sweat glands, salivary glands, heart muscle and airways
thoracolumbar and craniosacral outflow
actions of the parasympathetic NS
eyes - constricts pupils salivary glands - stimulates salivation heart - slows heartbeat lungs - constrict bronchi stomach - stimulates digestion liver - stimulates bile release intestines - stimulates peristalsis and secretion bladder - contracts bladder
actions of the sympathetic NS
eyes - dilates pupils salivary glands - inhibits salivation heart - accelerates heartbeat lungs - dilates bronchi stomach - inhibits digestion liver - stimulates glucose release kidneys - stimulates epinephrine and norepinephrine release intestines - inhibits peristalsis and secretion bladder - relaxes bladder
