W15 - Autonomic Physiology Flashcards
What is the autonomic nervous system?
- part of the peripheral nervous system (all connections BUT the brain and spine)
- involuntary system
- the sympathetic and parasympathetic work together in reciprocal/complementary manner to maintain homeostasis
- SYM: controls stress response & energy consumption associated with fight or flight reactions
- PSYM: regulates many functions, some of them are restorative + energy conserving ‘rest & digest’
Appreciate that the autonomic nervous system (ANS) is essential to life due its fundamental roles in homeostasis
- homeostasis: -ve feedback loop; 3 parts: a sensor, comparator/integrator and effector
- skin: thermoregulation by controlling contraction/relaxation of smooth muscle in the vasculature
- liver/pancreas: metabolism of glucose and lipids
- lungs: ventilation to control partial pressures and pH
- heart & vasculature: blood pressure by contraction and relaxation of smooth muscle in the vasculature
- kidneys: fluid balance
Describe the structure of an axon
- Head: Cell body, dendrite
- Neck: Axon hillock
- Body: Axons, covered in Myelin sheath (some but not all neurons of the ANS)
- Legs: Axon terminal
Describe the functional anatomy of the motor ANS utilising the terms, pre- and post-ganglionic fibre, ganglia, paravertebral ganglia and prevertebral gangli
- Ganglia/on: collection of neuronal bodies
- Can be though of as synaptic relay stations
- Information enters the ganglia → excites neurons in ganglia → exits
- 2-types of sympathetic ganglia: paravertebral ganglia & prevertebral ganglia
- Prevertebral ganglia: made of celiac, superior and inferior ganglia
- Paravertebral ganglia:
- Parallel to spine
- Serve primarily as a relay
- Can be though of as synaptic relay stations
- Pre-ganglionic fibre/neurons: Fibres that connect from the central nervous system to the ganglion
- Post-ganglionic fibre/neurons: fibres that connect from the ganglion to effector organs
Compare and contract sympathetic and parasympathetic nervous system
- sympathetic
- myelinated pre ganglion if fibres (neurons) - short
- pre-ganglionic fibres synapse in paravertebral or prevertebral ganglia (make a stop)
- unmyelinated post-ganglionic fibres (neurons) - long
- parasympathetic
- myelinated pre-ganglionic fibres (neurons) - long
- pre-ganglionic fibres synapse in or on target tissues/organs
- unmyelinated post-ganglionic fibres (neurons) - short
Explain neurotransmission in the ANS (sympathetic)
Preganglionic neurons:
- Neurotransmitter: ACh (cholinergic)
- Post synaptic receptor: Nicotinic acetylcholine receptor (cholinoreceptor)
Post ganglionic neurons
- Neurotransmitter: ACh (cholinergic)
- Post synaptic receptor: Muscarinic acetylcholine receptor (cholinoreceptor)
AND
- Neurotransmitter: Noradrenaline (adrenergic)
- Post synaptic receptor: α1/ α2 adrenoreceptor; β1/β2 adrenoreceptor
Explain neurotransmission in the ANS (parasympathetic)
Preganglionic neurons:
- Neurotransmitter: ACh (cholinergic)
- Post synaptic receptor: Nicotinic acetylcholine receptor
(cholinoreceptor)
Post ganglionic neurons
- Neurotransmitter: ACh (cholinergic)
- Post synaptic receptor: Muscarinic acetylcholine receptor (cholinoreceptor)
Explain NANC transmission
- Non-adrenergic, non cholinergic transmission
- i.e. not a result of ACh or NA (noradrenaline)
- could be the result of a NANC co-transmitter
- Parasympathetic NS:
ACh (Classic): rapid response
Nitric Oxide (NO) : intermediate (medium) response
Vasoactive intestinal peptide (VIP): slow response - Sympathetic NS:
Adenosine triphosphate (ATP): rapid response
NA (Classic): intermediate response
Neuropeptide Y (NPY): slow reponse
Explain the regulation of vascular smooth muscles tone
- Electrical stimulation of postganglionic parasympathetic fibre to vessel
- ACh and NO -> rapid relaxation
- Vasoactive intestinal peptide can produce a slow, delayed response
- Electrical stimulation of postganglionic sympathetic fibre to vessel
- ATP => produces fast contraction of smooth muscle
- Noradrenaline => moderately fast response
- Neuropeptide Y => Slow response
Describe cholinoreceptors
- ACh: endogenous (naturally produced by body) agonist for nicotinic or muscarinic (cholinoceptors)
- Nicotinic acetylcholine receptors (nAChR)
- Present in ganglia
- Ligand-gated ion channels
- Muscarinic acetylcholine receptors (mAChR)
- present in effector cells (organs; post ganglionic)
- G-coupled protein receptors
Describe adrenoreceptors
- NA and adrenaline: endogenous (naturally produced by body) agonists of a family of adrenoreceptors (GPCRs)
- α-adrenoceptor: noradrenaline > adrenaline > isoprenaline
- β-adrenoceptor: isoprenaline > adrenaline > noradrenaline
Describe the overall organisation of the somatic motor system
- somatic = voluntary
- the other branch of the peripheral nervous system, along with autonomic
- consists of skeletal muscle + their neutral component elements
Describe the structure of the “arm”
- Biceps brachii + brachialis work together (i.e. helps the muscle perform the function well)
- work as flexors; i.e. oppose triceps brachii and anconeus (as extensors) -> oppose each other
- axial muscles control movements of the trunk proximal muscles are found in the shoulder, elbow, pelvis and knee (mediate locomotion) and distal muscles move the hands, feet and digits
Describe the overall organisation of the somatic motor system
2 types of motor neurons
1. Upper motor neurons
- arise from cerebral cortex
- use glutamate as neurotransmitter
2. Lower motor neurons
- arise from spinal cord
- use ACh as neurotransmitter
Describe the segmental organisation of lower motor neurons (LMNs)
- exits the spinal cord in spinal nerves
- provides both motor and sensory supply to skeletal muscle
- and sensory input from skin, visceral receptors too
- 30 spinal nerves which innervate muscles roughly at that spinal segment
Distiguish between a motor unit and motor pool
- Motor unit = α motor neuron + all of the skeletal muscle it innervates
- Motor pool = single muscle innervated by group of α motor neurons
Explain the factors that contribute to force of contraction
- Motor unit recruitment
- ↑motor units = ↑force of contraction produced by muscle
- size principles = fixed order of recruitment => ↑ activity of LMNs stimulating the muscle (the motor pool)
- Slow motor units
- Fast fatigue-resistant units
- Fast fatiguable units
- Frequency of action potentials generated
- Frequency (temporal) summation of muscle fibre contraction
- Active motor unit = shrinking skeletal muscle
Describe the features of motor units
- they vary in size
- smaller motor units control finer movements
- inervated by smaller α motor neurons
- i.e. extraocular muscles of the eye
- larger motor units control postural muscles
- inervated by smaller α motor neurons
- smaller motor units control finer movements
- there are fast and slow types
- pectoralis and erector spinae
State the types of skeletal muscle fibre types
- Synonyms: red (slow); white (fast) (ans. respectively)
- Myosin ATPase activity: slow, fast
- Fatigue resistance: high, low
- Oxidative capacity: high, low
- Myoglobin: high, low
- Glycolytic capacity: low, high
State the types of motor units and their traits
- Fast fatiguing
- Very high tension
- large α-MN; high threshold
- type IIx fibres (?)
- Fatigue resistant
- high tension
- slow fatiguing
- intermediate α-MN and threshold
- type IIa fibres (?)
- Slow
- low tension
- fatigue resistant
- small α-MN; low threshold
- Type I fibres
State the two types of muscle fibres
- Extrafusal
- bulk of skeletal muscle fibres (force generation)
- innervated by α motoneuron
- Intrafusal
- remaining specialised fibres (muscle spindles)
- innervated by γ motoneuron and sensoryafferents
Explain how muscle spindles are innervated (???)
- sensory innervation: either the group la afferents or ll afferents
- motor innervation
Explain muscle spindles in action
- they can sense change and respond to changes in muscle length to return skeletal muscles to resting state
- abdominus rector: contracts; sitting -> standing
- extrafusal/intrafusal fibres shorten
- sensory afferents (group la and ll fibres) in the the intrafusal fibres relay info to the α motorneuron
- activation of α motoneuron stimulates abdominus rectus to relax
- when α motoneuron is stimulated, the γ motoneuron is activated at the same time
State what reflex arcs for stretch (myotatic) reflex consist of !!!!!!!!!
- sensory receptors
- sensory afferents (group la or ll)
- interneurons in spinal chord
- motor efferents (α motoneurons)
- ex. knee jerk
1. muscle stretched -> group la afferents fibres in muscle spindle start firing -> synapse on α motoneurons
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