Peripheral Nervous System Flashcards
Composition of PNS
Cranial and Spinal nerves and ganglia outside brain and spinal chord
Sensory Afferent
Motor Efferent division: Somatic NS + Autonomic NS (sympathetic and parasympathetic division)
Where do sensory and motor nerves carry info with regards to CNS?
Sensory nerves carry info towards the CNS
Motor nerves carry info away from the CNS
Number of nerves in brain and spine
12 pairs of cranial nerves
31 pairs of spinal nerves
Where do somatic afferent nerves convey info from?
Skin
Skeletal muscles
Joints
Where do somatic efferent nerves convey information to?
Skeletal muscles
Dermatome
Area or skin that is supplied by a single spinal nerve
Myotome
Group of muscles innervated by a single spinal nerve
Describe the types Visceral nerves
Visceral afferent nerves:
Carry info from the viscera (thoracic/ abdominal/ pelvic organs)
Visceral efferent nerves:
Divided into sympathetic and parasympathetic efferent nerves
Sympathetic - innervate the viscera (organs) and periphery (vasculature+sweat glands)
Parasympathetic - innervate the viscera (organs) only
Ganglion vs Nucleus vs Plexus
Ganglion: collection of cell bodies outside CNS
Nucleus: collection of cell bodies inside CNS
Plexus: network of interconnecting nerves
Where are the cell bodies of afferent fibres located?
Spinal ganglia
Where do visceral efferent nerves synapse?
In a peripheral ganglion
Describe the structure of peripheral nerves
Arranged in fasciculi
Three layers of connective tissue present:
External vascular layer - epineurium
Individual fascicles covered in perineurium
Individual axons covered in endoneurium
Classification of peripheral nerves
Two classification systems:
- Based on Conduction velocity (uses ABC) - A is the fastest
- Based on Axonal diameter sensory only (uses I-IV) - I is largest diameter
Sensory receptors
Detect external/internal info Can be classified by source of stimulus or by mode of detection External: exteroceptors Internal: proprioceptors/enteroceptors Chemo/Photo/Thermo/Mechanoreceptors
Nociceptors
Detect tissue damage, interpreted as pain
Proprioceptors
Found in joints, muscles + golgi tendon organs
Muscle spindle - detect change in muscle length
Golgi tendon organs - detect changes in tension in tendons
Join receptors - found in joint capsule and detect start and end of movement
Neuromuscular junction
Specialised synapse between a motor neurone and a muscle fibre
Motor unit
Single motor neurone together with all the muscle fibres that it innervates
Smallest functional until with which to produce force
Stimulation of one motor until causes contraction of all the muscle fibres in that unit
Reflex action
Involuntary coordinated pattern of muscle contraction and relaxation elicited by peripheral stimuli
Eg: (hammer on knee)
Stretching stimulates sensory receptor (muscles spindle)
Sensory neurone activated
Sensory neurone activates motor neurone within Integrating Centre (spinal chord)
Motor neurone activated
Effector contracts and relieves stretching
ANS
Where are sympathetic and parasympathetic neurones situated on spinal chord
Parasympathetic - from brain stem, cranial nerves III VII IX X down to S2-S4 spinal segments
Sympathetic - T1 to L2 spinal segments
ANS
Visceral Sensory Neurones
Relay sensory info from the core
Detect pain, fullness, BP
situated T1-L2, S2-S4 and cranial nerves IX and X
ANS
Visceral Motor Neurones
Outflow to core and body wall
Controls pupils, sweat glands, salivary glands, heart muscle, airways
T1-L2 (thoracolumbar) and cranial nerves III VII IX X (craniosacral outflow)
