Unit 2.5: Efferent Branch of the PNS Flashcards
What are the 2 parts of the efferent branch of the PNS?
- Autonomic division
2. Somatic division
What is the autonomic division also called and what does it innervate?
Innervates smooth and cardiac muscle, glands and some adipose tissue
Sometimes called involuntary division
What is the somatic division also called and what does it innervate?
Innervates skeletal muscles
Sometimes called voluntary division
What are the branches of the autonomic division?
Sympathetic: physical activity, stress, fight or flight
parasympathetic: rest and digest
What is the structure of the autonomic division?
2 neuron chain between CNS and effector
Synapse located in cell clusters called autonomic ganglia
What are the lengths of the neurons in sympathetic ganglia?
short pre-ganglionic axons
long post-ganglionic axons
What are the lengths of the neurons in parasympathetic ganglia?
long pre-ganglionic axons
short post-ganglionic axons
ganglions are generally on the target tissue
What are the primary neurotransmitters of the autonomic system?
Sympathetic: pre - ACh & nicotinic, post - Norepinephrine & adrenergic
Parasympathetic, pre- ACh & nicotinic, post - ACh & muscarinic
What are the targets of the autonomic pathway?
Innervates smooth and cardiac muscles
Exocrine and endocrine glands
Adipose tissue
What is the synapse structure of the autonomic pathway?
Axon ends with swollen areas at distal ends called a varicosity
Varicosity contains vesicles with neurotransmitters to be released in interstitial fluid
What are the 2 types of receptors?
Adrenergic & Cholinergic
What are adrenergic receptors for and what types are there?
For epinephrine (E) and norepinephrine (NE)
a1 receptors: found on most tissues, best for NE
b1 receptors: muscles and kidneys, response NE = E
b2 receptors: blood vessels, smooth muscle, E
How do adrenergic receptors act via?
G proteins
B1 & B2 stimulate cAMP production
A1 increase Ca2+ levels in cytoplasm
What are the 2 classes of cholinergic receptors?
nicotinic & muscarinic
What are nicotinic receptors stimulated by?
ACh & Nicotine
What are muscarinic receptors stimulated by?
ACh & Muscarine
Where are nicotinic receptors found and what do they act via?
Found on motor end plates (on skeletal muscle) and sympathetic/parasympatheic ganglia
act via ion channels > Na+ goes in cell > depolarization
ALWAYS excitatory
What do muscarinic receptors target and what do they act via?
Target tissues of parasympathetic system
Act via G-protein
May close or open different ion channels
May be excitatory OR inhibitory
What do sympathetic axons release?
NE
What do parasympathetic axons release?
ACh
What are the 2 parts of the adrenal gland? What do they secrete?
Adrenal cortex: secretes steroid hormones Adrenal medulla (associated with sympathetic division, modified sympathetic ganglion): has special cells called chromaffin that secrete epinephrine, that travels in the blood
What is the structure of the somatic division?
Controls skeletal muscles
has only one neuron from CNS to effector
Causes only muscle excitation
What are the 3 components of the neuromuscular junction?
Pre-synaptic axon terminal: filled with neurotransmitter vesicles (ACh)
Synaptic Cleft
Post-synaptic membrane of skeletal muscle fiber: membrane modified into motor end plate with nicotinic ACh receptor channels
