Lecture 24- The Peripheral Nervous Sytem Flashcards
What is the PNS?
Peripheral nervous system
All neural structures outside the brain and spinal cord
Sensory receptors
Peripheral nerves
Efferent motor endings
Sensory receptors
Specialized receptors that respond to changes in environment called stimuli
Non encapsulated dendritic endings
Free nerve endings that detect temp., pain, itch, light touch or are located at base of hair follicles.
Encapsulated dendritic endings
Consist of dendrite enclosed in a connective tissue capsule and detect discriminatory touch,initial, continuous and deep pressure and stretch of muscle , tendons and joint. Capsules
What can graded receptor potentials trigger?
Action potentials that travel along the axon to the CNS
Mechanoreceptors
Stimulated by mechanical force, such as touch,pressure, vibration and stretch
Thermoreceptors
Detect changes in temperature
Photoreceptors
Detect light
Generally in the eyes
Chemoreceptors
Stimulated by chemicals such as odours,tastes or chemical components of body fluids
Nolcireceptors
Respond to painful stimuli
Where exteroceptors located?
Near the body surface
And detect stimuli from outside body- touch, pressure, pain
Where are interceptors located?
Associated with internal organs and vessels
Monitor chemical changes, stretch or temperature
Where are proprioreceptors located?
Within skeletal muscles, joints and associated connective tissues
Relay information about body movements
Sensation
Awareness of changes in internal and external environment
Perception
The conscious interpretation of sensation stimuli
First order sensory neurons
Carry impulses from receptors
Second order neurons
Transmit to the cerebellum
Third order neurons
Carry impulses to postfrontal gyrus
Perception of Pain
Protects body from damage
Stimulate by extremes of pressure and temperature as well as chemicals releases from damaged tissues
Pain threshold
Stimulus intensity at which we begin to perceive pain
Same for most people
Pain tolerance
Genetically determined trait with learned aspects that varies from person to person
Perceived pain can be affected by environment
Visceral pain
Results from stimulation of receptors within internL organs from stimuli such as extreme stretch, ischemia, chemical irritation and muscle spasms
What does visceral pain travel along?
The same fibre tracts as somatic pain impulses, giving rise to reffered pain
Reffered pain
Pain that feels as though it is located in an area different from the affected body region
Mixed nerves
Contain both sensory and motor fibres
Most nerves are mixed nerves
Sensory/ afferent nerves
Carry impulses only toward CNS
Motor/ efferent nerves
Carry impulses away from CNS
Endoneurium
Thin layer of loose connective tissue Around each axon
Around axon
Perineurium
Connective tissue wrapping that bundles groups of fibres into fascicles
Around fascicle
Epimeurium
Bundles all fascicles into a nerve
Around nerve
Nerve plexus
Interlacing networks formed by all vertebral brances EXCEPT T2 - T12
What is in each nerve plexus? And what does it do?
Fibres crisscross so each branch contain fibres from multiple spinal nerves
Each limb muscle is innervated by more than one spinal nerve and damage to one does NOT cause paralysis
Dermatomes
Areas of skin innervated by cutaneous branches of single spinal nerve
Most overlap so destruction of single spinal nerve will NOT cause complete numbness
What forms neuromuscular junctions?
Terminals of somatic motor fibres that innervate voluntary muscles
Release acetylcholine
What forms synapses en passant?
Junctions between autonomic motor endings and visceral effectors
Release acetylcholine or epinephrine
Varicosities… what are they? What do they do?
Bulge of neurotransmitter
Autonomic nerve fibres that innervate most smooth muscle
These contractions tend to be slower than skeletal
Vesicles release neurotransmitter into synaptic cleft
Ganglia
Collection of neuron cell bodies associated with nerves in PNS
Do damaged CNS nerve fibres regenerate?
Almost ever.
Do PNS nerve fibres regenerate?
If cell body remains intact, yes
What cell help regeneration of PNS axons?
Schwann cells
What cells in CNS do not supporter regrowth of axons?
Oligodendrocytes
Chromatolysis
Breakdown of nissl bodies after nerve damage
Wallerian degeneration
Breakdown of the distal portion. Of axon and myelin sheath
How fast do nerves with regeneration tube grow?
A rate of 1mm per day
