Lecture 10: PNS Flashcards
What are the four types of sensory receptors?
- Free nerve endings (exposed dendrites)
- Encapsulated nerve endings (connective tissue capsule)
- Specialized sensory cells associated with dendrites of a sensory neuron (taste receptors)
- Peripheral processes.
Functional Classifications of Sensory receptors.
- Mechanoreceptors: Touch, pressure, vibration and stretch.
- Thermoreceptors (temperature change)
- Photoreceptors (light)
- Chemoreceptors (Chemical detection, taste, chemical conc. within blood)
- Nociceptors (Perception of pain)
What is the difference between a cranial and a spinal nerve?
Cranial nerve: Attached directly to the brain (12 pairs).
Spinal nerve: Attached directly to the spinal cord (31 pairs).
What is a fascicle?
Bundles of neuron axons in a nerve.
What are the layers of protection for each nerve?
From deepest to most superficial:
1. Endoneurium (around each axon)
2. Perineurium (encloses each fascicle)
3. Epineurium (around each nerve)
Cranial nerve: Olfactory I
Transmit sensory input from olfactory receptors in nasal cavity to brain.
Cranial nerve: Optic II
Transmits sensory input from photoreceptors in eyes to brain.
Cranial nerve: Oculomotor III
Transmit motor output from brain to skeletal and smooth muscles of eyes.
Cranial nerve: Vagus X
Mixed nerves because they transmit both sensory input to the brain and motor output to cardiac muscle and smooth muscle in walls of visceral organs.
Why is the Vagus nerve vital in maintaining homeostasis?
- Transmits essential sensory info to the brain about blood pressure and chemistry.
- Contains parasympathetic motor neurons which communicate with visceral organs
(Heart rate; Swallowing; Digestive activity; Diameter of bronchioles in lungs)
What are the functional steps to any sensory pathway?
- Detection of stimulus
- Transmission of afferent impulses to appropriate sensory area in cerebral cortex.
- Perception of sensation. Integration in sensory and association areas in cerebral cortex.
Define the difference between first, second and third order neuron?
First order: Transmits from receptor to spinal cord/brainstem.
Second order: Transmits from spinal cord/brainstem to thalamus
Third order: Transmits from thalamus to sensory area in cerebral cortex.
Reasons to loss of sensation
- Compressed nerve or lack of oxygen delivered to neurons.
- Damage to neurons
- Toxins or anesthetics inhibit action potential or synaptic transmission.
Difference between somatic and visceral pain?
Somatic pain: Afferent transmissions from skin and skeletal muscle.
Visceral pain: Afferent transmissions from internal organs including the heart.
How can pain be interrupted from first order neuron?
- Local anesthetics such as lidocaine and Novocain. (Inhibit AP transmissions)
- Ibuprofen and aspirin (Inhibit enzymes required to make inflammatory chemicals)
How can pain be interrupted from second and third order neuron?
Second order: Spinal anesthesia
Third order: Opioids (Block binding of neurotransmitters in pain pathways in brain)
What is somatic motor control?
Only one motor neuron involved for each pathway.
Acetylcholine stimulates contraction.
What is autonomic motor control?
2 motor neurons involved for each pathway.
Explain the function between first and second motor neuron.
First motor neuron: Neuron has it’s cell body in CNS, axon extends into PNS where it synapses with second neuron. Acetylcholine is released at this synapse.
Second motor neuron: Axon extends to the effector organ.
Parasympathetic: Acetylcholine at synapse
Sympathetic: Norepinephrine at synapse
Which organs only have sympathetic innervation?
Adrenal medulla, sweat glands, arrector pili muscles of the skin, kidneys and most blood vessels.
Where are pre ganglionic motor neuron cell bodies located?
Brain stem or spinal cord in the sacral region only. (Parasympathetic division)
Where are sympathetic motor neurons located?
Emerge from the spinal cord in the thoracic and lumbar regions only.
Pre and Post ganglionic fibers for sympathetic and parasympathetic division
Preganglionic: Short (sympathetic); Long (Parasympathetic)
Postganglionic: Long (sympathetic)
Short (Parasympathetic)
What does adrenal medulla release?
Epinephrine and norepinephrine by exocytosis.
Blood vessels are innervated by which neurons?
Blood vessels are innervated by sympathetic neurons only.
