Physiology + pharmacology Parasympathetic Flashcards
-Outline the effects of the rest and digest response on the body -Describe the effects of stimulating the parasympathetic nervous system and different muscarinic receptor subtypes involved in the heart, GI tract, eye, lungs, secretory glands, and male genitalia -Describe chemical transmission at cholinergic synapses, and how drugs may alter the synthesis, release, and termination of acetylcholine -Outline different cholinergic receptor subtypes and their associated intracellular pathways, and de
Where are parasympathetic pre-ganglionic fibres found in the spinal cord?
- Brainstem, cranial nerves
- Cervical region
- Sacral region
Outline the effect of the rest and digest response (parasympathetic) on the body
- Slows heart rate
- Pupils constrict
- Bronchoconstriction
- Increased GI motility, sphincter relaxation, increase gland secretion
- Bladder sphincter relaxation
- Increased salivation
- Increased pancreatic activity
Where are the M3 receptors in the parasympathetic nervous system?
- Pupils
- Lungs
- GI tract
- Urinary tract
- Glands (these also have M1)
Where are the M2 receptors in the parasympathetic nervous system?
- Heart
Where are the nicotinic receptors of the parasympathetic system?
- At the NMJ of skeletal muscle
Describe the effect of stimulating the parasympathetic on the heart
- Stimulation of vagus nerve releases Ach, which acts at M2 receptors
- Decreases frequency of electrical activity generated at SAN, leads to reduction in heart rate
- This leads to decrease in cardiac output and blood pressure
- Parasympathetic nerves innervate ventricles and most blood vessels BUT do not affect heart contractility or TPR
Describe the effect of stimulating the parasympathetic on the eye
- Stimulation of M3 receptors leads to contraction of circular smooth muscle of iris (constrictor papillae)
- Constriction of pupil (mitosis)
- Constriction of pupil (M3) has secondary action of opening cancel of Schlemm at back of pupil, drains aqueous humour from eye, reduces intraocular pressure within eye
How do parasympathetic nerves control accommodation of the eye?
In distance vision:
- Light waves in parallel
- Long thin lens can refract light so it reaches retina at focused point
- Ciliary muscle relaxed
- Suspensory ligaments taut, this causes lens to become long +thin, so we can refract light from parallel rays.
- Long focal length
In close vision:
- Light rays divergent
- Causes stimulation of parasympathetic nerves
- Ciliary muscle contracted
- Suspensory ligaments relaxed
- Bulged lens shape
- Refracts the divergent lens rays, and get a focused image at a reduced focal length
Describe the effect of the parasympathetic and sympathetic on the bladder
- Bladder voiding requires interactions between parasympathetic, sympathetic, motor and sensory nerves:
- Bladder made of detrusor muscle (smooth muscle0
- On entrance of bladder = internal sphincter, can be opened + closed. Further down = external sphincter, can be opened + closed - this is the sphincter mediating urine being released from the urethra
- Parasympathetic releases Ach, acts at M3 receptors on smooth muscle producing contraction
- Sympathetic releases NA at B2, causing smooth muscle relaxation
- Sympathetic also controls contraction of internal sphincter, alpha 1 adrenoceptor, when sympathetic active, smooth muscle relaxes, sphincter muscle contracts
- External sphincter controlled by skeletal muscle - voluntary control, contract = hold urine, relax = release urine
- Smooth muscle contains sensory nerves, indicate when bladder full, when full bladder stretches, more pressure on smooth muscle, stimulates sensory nerves
- At rest, bladder filling, sympathetic system working, smooth muscle relaxes, bladder opens. Also contracts internal sphincter, so no need to urinate, as bladder fills, sensory nerves stimulated, this stimulation relays information to CNS, in brainstem, in area called micturition centre, tells brain bladder’s full
- This sends 2 signals, one to sympathetic in lumbar region of spinal cord to switch off, no need to relax smooth muscle or contract internal sphincters AND to parasympathetic to switch on, sends into to sacral region of spinal cord, stimulates pre-ganglionic nerves, contract smooth muscle, internal sphincter opens, bladder voids
- Once urination complete, bladder is empty, sensory nerves no longer stimulated, brainstem no longer being signalled that bladder full, parasympathetic switches off, sympathetic switches back on
Describe the effect of stimulating the parasympathetic on the GI tract
- Stimulation of vagus nerve released Ach, acts on M3 receptors
- Allows PIP2 to be converted into IP3 and DAG by PLC, binds to Gq protein
- IP3 binds to IP3 receptors on SR, which then open ion channels, allows influx of Ca2+
- DAG activates PKC, increasing Ca2+ influx
- This increases membrane excitability as it can phosphorylate the protein ion channel, opening Na channels, causing an influx of Na, leading to depolarisation, which opens the VGCC, leading to influx of Ca2+
- Ca2+ ions bind to calmodulin and this complex activates the myosin light chain kinase (MLCK)
- MLCK phosphorylate light chains in myosin heads, increases myosin ATPase activity
- Active myosin crossbridges slide along actin, create muscle tension
- Contraction of circular and longitudinal smooth muscle in GI tract - causes it to work more- increases motility
- Vagus also contains afferent (sensory fibres) - peristaltic reflex control
Describe the effect of stimulating the parasympathetic on the salivary glands
- VII (facial nerve) and IX (glossopharyngeal nerve)
- Stimulate acing cells
- Increases amylase/mucins
Describe the effect of stimulating the parasympathetic on the gastric glands
- X (vagus nerve)
- Stimulate parietal cells - parietal cells contain HCL
- Increases gastric acid
Describe the effect of stimulating the parasympathetic on the pancreatic glands
- X (vagus nerve)
- Stimulate acinar + islet cells (secret insulin, glucagon, somatostatin)
- Increase pancreatic secretions
Describe the effect of stimulating the parasympathetic on the pancreas
- X (vagus nerve)
- Increase insulin secretion from beta cells
Describe the effect of stimulating the parasympathetic at the lungs
- Stimulation of M3 receptors contracts bronchi smooth muscle cells, causes bronchoconstriction
