Peripherla Nervius Systme Flashcards
PNS divides into
Somatic and autonomic
Sensory(afferent) carries info towards CNS
motor (efferent) carry info away from CNS
How many pairs of cranial and spinal nerves are there
12 cranial
31 spinal
What do somatic afferent and efferent nerves convey info from and to?
- Somatic afferent nerves convey info from skin, skeletal muscle and joints
- Somatic efferent nerves convey info to skeletal muscles
Dermatomes
An area of skin supplied by single spinal nerve
Myotome
A group of muscles innervated by a single spinal nerve
- What do visceral (autonomic) nerves convey info from and to?
- Visceral afferent nerves carry info from viscera (thoracic, abdominal and pelvic organs)
- Visceral efferent nerves can be divided into sympathetic and parasympathetic
What do sympathetic efferent nerves innervate
The viscera and periphery
What do parasympathetic efferent nerves innervate
Viscera only
Where do all afferent (somatic and visceral) fibres have their cell bodies?
Spinal ganglia (same as dorsal root ganglion)
Where do visceral efferent nerves synapse
Peripheral ganglion
Ganglion
Collection of neuronal cell bodies outside of the CNS
Nucleus
Collection of cell bodies inside the CNS
Plexus
Network of interconnecting nerves
How are peripheral nerves arranged at spinal vertebrae
3 layers
1) individual axons have the endoneurium around them
2)the axons bundle together to form a fascicle which is covered in perineurium
3)fascicles bundle together to form the spinal nerve with the epineurium around it
How can peripheral nerves be classified
- One based on conduction velocity → uses letters A, B and C (A the fastest)
- One based on axonal diameter (sensory nerves only) → uses Roman numerals I-IV (I the largest diameter)
What two properties do faster conducting peripheral nerves have
Myelination
Larger diameter
How can sensory receptors be classified
Exteroreceptors respond to external stimuli like pain temp touch and pressure
Propioreceptors and enteroreceptors respond to internal stimuli
Chemoreceptors
Detect molecules which bind to receptor in olfactory
Photoreceptors
Detect light in retina
Thermoreceptors
Temp in skin
Mechanoreceptors
Mechanical opening of ion channels eg touch receptors in skin
Nociceptors
Tissue damage interpreted as pain
Where are proprioreceptors located
Muscle spindles are small sensory organs that detect whether muscle has been stretched
Golgi tendon organs detect changes in tension in tendons
Joint receptors found in joint capsules and detect start and end of movement
Neuromuscular joints
Specialized synapse between a motor neurone and muscle fibre
Motor units
A single motor neurone with all muscle fibres it innervates
Humans have 420k motor neurone and 259 mil skeletal muscle fibres
Reflex action
An involuntary coordinated pattern of muscle contraction and relaxation elicited by peripheral stimuli
Reflex action when tendon hammer hits patella ligament
- Stretching stimulates sensory receptor (muscle spindle)
- Sensory neurone activated
- Sensory neurone activates motor neurone within the spinal cord (integrating centre)
- Motor neurone is activated
- ## Effector (quadricep muscle of thigh) contracts
Which cranial nerves do visceral sensory neurones run into
IX - Glossopharyngeal Nerve
X - Vagus Nerve
Relay painn fullness and bp
What do the visceral motor neurones control?
Pupils, sweat glands, salivary glands, heart muscle, airways
-thoracolumbar and craniosacral outflow
Cranial nerves 3,7,9,10
Where is the sympathetic system said to have its outflow and what is this outflow known as?
Thoracolumbar region of spinal cord
So cells only emerge from T1 to L2
Thoracolumbar outflow
Where is the parasympathetic system said to have its outflow and what this outflow also known as?
Pre-ganglionic neurones emerge from the brain stem and sacral portion of spinal cord
Craniosacral outflow
Where does visceral motor synapse
For sympathetic if going to head or skin it synapses in sympathetic chain and elsewhere it synapses to pre aortic ganglia
For parasympathetic it synapses in ganglia
Sympathetic outflow to periphery
Sympathetic nerves arise from thoracic and lumbar region forming sympathetic chain
Form the symmetric chain post ganglionic fibres project to target tissues in periphery
Controls blood vessel diameter and pilo erection
Anatomy of sympathetic outflow to heart
Sympathetic nerves innervate cardiac plexus . Post ganglionic fibres release noradrenaline onto cardiac plexus
Sympathetic outflow to heart
Cervical chord have no preganglionic neurons s they have no lateral horn
T1-T4 have preganglionic neurones which go into sympathetic chain which synapse or go into another chain and synapse
Sympathetic nerves going to heart have preganglionic chord which go into chain synapses at the same level or else where
Sympathetic outflow to viscer
To the heart synapse in sympathetic chain
To skin synapse in sympathetic chain
Other organs synapses at other gangli at the front of the aorta
All start in preganglionic neurons of throacolumbar chord. They synapse at pre aortic ganglia synapse
