Peripheral nerves Flashcards
Draw a motor neuron, sensory neuron and multi-polar interneurones
Motor- cell body is at the end, mylinated, mucles attached to axon terminal
Sensory- cell body is at the middle, mylinated, receptor attached to top dendritic cells
Multi-polar neurons- Unmylinated, dendritic cells are long
Labels- Axon, Axon hillock, axon terminal, cell body, dendritic cells, nodes of ranvier
What are the receptors located on hairy skin? What does it respond to?
Hair follicle receptors
Hair displacement
What do free nerve endings respond to? What are they called?
Chemical stimuli
Chemoreceptors
What are the parent nerve fibers to chemo-receptors?
A delta and C receptors- axons with bare nerve endings
What is the name for non-hairy skin?
Glabrous skin
What type of receptor will you find in non hairy skin?
free nerve endings
Nerve endings with connective tissue capsules: Meissner’s corpuscles, Ruffini corpuscles and Pacinian corpuscles.
What causes the formation of capsules in capsulated nerve fibers?
When nerve fiber first grows into tissue it is bare, no caspule. Cytokines from the bare end causes local connective tissue to form a capsule around it, the type of capsule is dictated by the cytokine
List the different types of encapsulated tissues and what they respond to?
Pacinian corpuscle - makes the nerve ending selectively sensitive to high frequency (>50 Hz) vibration.
Ruffini ending makes the nerve fibre sensitive to pressure on the skin.
What is a receptive field/ dermatome?
area of skin innervated by a single nerve fibre
Where are receptive fields largest?
proximal limbs, back and abdomen, areas not used for tactile discrimination.
What is found in the node of ranvier?
Na+/K+ ATPases
Na+/Ca2+ exchangers
Voltage-gated Na+ channels
How are encapsulated axons activated?
- Physical distortion of terminal membrane
- Sodium enters cell through mechnically sensitive sodium channels
- Cell becomes depolarised
- This is called a receptor potential
- This triggers an action potential or a train of action potentials
What are rapidly and slowly adapting receptors? Which receptor types fit into each?
Rapidly adapting-only respond at the beginning of a stimulus: they ‘fatigue’ after a second or so to a sustained steady stimulus
Pacinian corpuscles
Meissner’s corpuscles
Slowly adapting- continue firing to a sustained stimulus but at a gradually reducing rate.
Ruffini endings
Merkel’s disks
How is the speed of receptor conduction calculated? What is the maximum?
velocity is 6 times the fiber diameter
120m/sec.
What are the symptoms of a peripheral nerve injury?
LOSS of reflexes Hyposensitivity (anaesthesia) Muscle weakness (paralysis) Atrophy Hyporeflexia (areflexia) Possibly neuropathic pain
