Lecture 8: Peripheral Nervous System Flashcards
What is the peripheral nervous system composed of?
nerves (cranial and spinal) and ganglia outside the brain and spinal cord
What can the PNS be divided into?
somatic and autonomic nervous system
Which nerves carry information towards the CNS?
sensory afferent nerves
Which nerves carry information away from the CNS?
motor efferent nerves
What are the peripheral nerves?
- 12 pairs of cranial nerves
- 31 pairs of spinal nerves
What do somatic afferent nerves convey information from?
- skin
- skeletal muscle
- joints
What do somatic efferent nerves convey information to?
skeletal muscles
What is a dermatome?
an area of skin that is supplied by a single spinal nerve
What is a myotome?
group of muscles innervated by a single spinal nerve
Where do visceral afferent nerves carry information from?
the viscera (thoracic, abdominal and pelvic organs)
What can visceral efferent nerves be divided into?
sympathetic and parasympathetic
What do sympathetic efferent nerves innervate?
the viscera (organs) and periphery (vasculature and sweat glands)
What do parasympathetic efferent nerves innervate?
the viscera (organs) only
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
All afferent (somatic and visceral) fibres have their cell bodies…?
In spinal ganglia
Where do visceral efferent nerves synapse?
In a peripheral ganglion
How are peripheral nerves arranged?
In fasciculi: 3 layers of connective tissue
- external vascular layer = epineurium
- individual fascicles covered in perineurium
- individual axons covered in endoneurium
What are the 2 ways in which peripheral nerves can be classified?
- conduction velocity (A,B and C, A= fastest)
- axonal diameter (sensory only, uses roman numeral I-IV - with I as largest diameter)
What can sensory receptors detect?
external or internal information
How can sensory receptors be classified?
By source of stimulus or by mode of detection
Name some external and internal sensory receptors.
EXTERNAL: exteroceptors = pain, temp, touch, pressure
INTERNAL:
- proprioceptors = movement, joint position
- enteroceptors = movement through gut, blood pH
Name some receptors classified by mode of detection.
- chemoreceptors
- photoreceptors
- thermoreceptors
- mechanoreceptors
- nociceptors
What are chemoreceptors?
detector molecules which bind to receptor e.g. 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 e.g. touch receptors in skin
What are nociceptors?
detect tissue damage, interpreted as pain (nut not interchangeable with pain)
What do proprioceptors detect?
- muscle spindles: detect changes in muscles length
- Golgi tendon organs: detect changes in tension in tendons
- joint receptors: found in joint capsules - detect start and end of movement
What is a neuromuscular junction?
specialised synapse between a motor neuron and a muscle fibre
What is a motor unit?
a single motor neuron together with all the muscle fibres that it innervates - smallest functional unit with which to produce force
What happens when you stimulate one motor unit?
all the muscle fibres in that unit contract
What is a reflex action?
an involuntary coordinated pattern of muscle contraction and relaxation elicited by peripheral stimuli
What do visceral sensory nerves do?
- relay sensory info from core
- pain, fullness, blood pressure
- T1-L2, S2-S4 and cranial nerves IX and X
What do visceral motor nerves do?
- outflow to core and body wall
- controls pupils, sweat glands, salivary glands, heart muscle, airways
- thoracolumbar (T1-L2) and craniosacral outflow (cranial nerves III, VII, IX and X)
Where does sympathetic outflow go to?
the organs and to the skin
Where are the pre-ganglionic neurons of the sympathetic system?
in the spinal cord
What path generally do the pre-ganglionic neurons take?
They come out and go into the sympathetic trunks
What are the sympathetic trunks?
Trunks that run alongside the spinal cord but are outside the vertebral column, within the chest
Why do the sympathetic trunks have enlargements?
Due to the post-ganglionic neurons
What do white ramus communicans do?
carry preganglionic sympathetic fibres from spinal nerves to sympathetic ganglia
What do gray ramus communicans do?
carry postganglionic sympathetic fibres from the sympathetic ganglia to the spinal nerves
What are communicans?
small branches containing myelinated or unmyelinated nerves
Where do pre-ganglionic neurons going to the heart or skin synapse?
in sympathetic trunk
What is the function of the sympathetic trunk?
to send post-ganglionic nerves up to the head or arms or down into limbs
What is the cardiac plexus?
The cardiac plexus is a plexus of nerves situated at the base of the heart. It is formed by cardiac branches derived from both the sympathetic and parasympathetic nervous systems.
Where does the pre-ganglionic nerve synapse if it is going to the viscera?
in the pre-aortic ganglia (synapse occurs on front of aorta)
What is different between the sympathetic and parasympathetic nervous system in terms of what they innervate?
parasympathetic only innervates core but sympathetic innervates core and periphery
