Unit 7: The Peripheral Nervous System (Efferent Division) Flashcards
What are the 2 Efferent Pathway’s of the PNS?
The Autonomic system (involuntary) and the Somatic System (voluntary)
Describe the Autonomic Nervous Pathway
- Each autonomic nerve pathway is made out of a 2 chain neuron (pre synpatic and post synaptic).
- > The postsynpatic neuron innervates the effector organ.
What are the 2 divisions of the Autonomic Nervous System?
The Sympathetic nervous system (fight or flight) and Parasympathetic systems (rest and digest)
What are the features of the Parasympathetic system ?
- Preganglionic fibres arise from the cranial and sacral areas of the CNS
- LONG postganglionic fibres- end on effector organs
What are the features of the Sympathetic system?
- Sympathetic nerve fibres originate in the thoracic and lumbar regions of the spinal cord.
- Preganglionic fibres are short, and synapse with cell bodies of postganglionic cells within the sympathetic ganglion chain.
- ->Some preganglionic cells bipass synapsing
- ->Instead, they end up in sympathetic collateral ganglia, with postganglionic cells going the rest of the distance to effector organs.
What neurotransmitter do the preganglionic Sympathetic and Parasympathetic release?
Acetylcholine (ACh)
What neurotransmitter do the postganglionic Parasympathetic cells release?
Release Acelylcholine, known as Cholinergic fibres.
What neurotransmitter do the postganglionic Sympathetic cells release?
Release Noradrenaline (Norepinepherine), called Adrenergic fibres.
What are the swellings of terminal branches on autonomic nerve fibres called?
–>Varicosities
What is Parasympathetic/ Sympathetic tone (tonic activity) ?
–>Both systems working together
What is the Adrenal Medulla?
- Lie above the kidneys
- ENDOCRINE GLANDS
- Secretes hormones into the blood on preganglionic fibre stimulation
What is the ratio of medulla hormones?
1:5 Norepinepherine (20%) to Acetylcholine (80%)
What are the two types of Acetylcholine receptors?
- Nictonic -activated by Nictoine
2. Muscarnic- activated by Muscarine.
What are the two types of Adrenergic receptors?
- Alpha receptors
- Beta receptors
* Influence secondary messengers which influence metabolic processes.
What is an Agonist?
-Bind the same receptor as the neurotransmitter and mimics the effect of it.
What is an Antagonist?
-Bind with the receptor and block neurotransmitter response.
Where in the brain is Autonomic response governed?
- The brain stem contains the medulla, where the autonomic nervous system is controlled.
- The hypothalamus integrates emotional and behavioral states
- ->The prefrontal cortex can affect personality and expression
The Somatic Nervous System mechanisms
- Innervate skeletal muscle by motor neurons
- The axon of motor neurons are continuous from its origin in the CNS to their ending.
What neurotransmitter do motor neurons release?
Acetylcholine, which brings about excitation and contraction of skeletal muscle cells.
*Only way to activate skeletal muscles.
What is a neuromusclar junction?
- An action potential in a motor neuron rapidly propagates along the cell body within the CNS to skeletal muscle along a large myelinated axon.
- ->As the axon approaches a muscle, it divides into terminal branches and looses its myelin sheath–> this forms a neuromuscular junction.
Where does the Specialized End Plate sit?
Below the terminal button
Events of a neuromuscular junction
- Action potential is sent to the terminal button (TB)
- Triggers the opening of Ca2+ into the TB
- Ca2+ leads to the release of ACh
- ACh binds receptor sites on the motor end plate
- This binding leads to an influx of Na+ and not alot of K+
- Results in an End Plate Potential (EPP). Local current flows between the depolarized end plate & membrane
- Local flow opens Na+ channels
- Local Na+ reduces the potential to threshold, initiating an action potential through the muscle fibre
- Acetylcholine is broken down by aceytlcholinesterase, terminating muscular response
