Lecture 12

Question 1

ANP

Answer 1

Controls CM, SM, adipose tissue, glands divided into sympathetic and parasympathetic

Question 2

Autonomic reflexes

Answer 2

Stimulus acts on receptor, sensory neuron sends signal to CNS where it is integrated. Signal is sent through preganglionic neuron which signals the target cells for response.

Question 3

integration of autonomic function

Answer 3

Sensory input sends signals to hypothalamus and somatic and visceral neurons. Then, signals are sent to various parts of the brain (brain stem, limbic system and cerebral cortex) to coordinate all responses associated with the ANS, generating an autonomic response that can incl. hormone secretion and behavioural response.

Question 4

homeostasis and antagonistic control

Answer 4

important for maintaining homeostasis. Branches are often antagonistic. Balancing the 2 helps maintain homeostasis. Exceptions incl. sweat glands (can only be turned on) and vascular SM (only has sympathetic input). Type of neurotransmitter generating responses will determine response types.

Question 5

Rule of thumb

Answer 5

All ANP have 2 neurons in series, therefore ALWAYS polysynaptic

Preganglionic neuron: CNS to autonomic ganglia
Postganglionic ceurin: Autonomic ganglionic to target tissue

Question 6

Sympathetic vs parasympathetic NS

Answer 6

Site of Origin in CNS: Sympathetic have lumbar and thoracic regions in spinal cord while para is in sacral region and brain stem

Site of autonomic ganglia: Symp is close to spinal cord while para is close to target organs.

Question 7

Sympathetic vs parasympathetic RESPONSES

Answer 7

Symp utilises andregenic receptors that have multiple subunits while Para responses use Ach acting on muscarinic receptors at target organ.

Question 8

Neurotransmission in ANS

Answer 8

Within autonomic ganglion, always Ach released from CNS neuron to autonomic ganglion acting on nicotinic receptors (excitatory). For both. Then, in symp, autonomic ganglion release noradrenaline acting on adrenergic receptors on target tissue to initiate response whereas para ganglia utilise ACh again to act on muscarinic receptors for a response. Both androgenic and muscarinic receptors are GPCR.

Question 9

Neuroeffector junctions

Answer 9

At target organ, neurotransmission differs to the CNS and somatic NS. Differs as post ganglionic axons contain varicosities which release neurotransmitters onto the tissue. You may have multiple. Neurotransmitter is synthesised in axons before travelling to varicosities. At NMJ and synapses with CNS, there is a cluster of receptors at the post-synaptic membrane that is directly opposite to release site. At the neuroeffector junctions, there’s no clustering. The neurotransmitter is released into the environment and it will diffuse until it makes contact with receptor, impacting more cells. Though less precise and lower [neurotransmitter] reveived. Receptors have high affinity for ligands as they are exposed to lower concs that aren’t dynamically regulated.

Question 10

Noradrenergic neuroeffector junction

Answer 10

1. action potential arrives at varicosity
2. Ca2+ influx due to opening of voltage-gated Ca2+ channels
3. Vesicles fuse with the membrane and exocytose neurotransmitter
4. Neurotransmitters activate GPCR on target cell, generating response
5. Neurotransmitter diffuses away, or, is taken up by the varicosity for repackaged into synaptic vesicle or metabolised

**noradrenaline is metabolised by monoamine oxidase which is associated with the mitochondria

Question 11

Neurotransmitter receptors in the ANS

Answer 11

There’s alpha and beta adrenergic receptors. Alpha is most common and strongly responds to noradrenaline, B has three subtypes which have different sensitivities to noradrenaline vs adrenaline. All GPCR, but, A and B trigger different 2ndary messenger receptors. For muscarinic, ACh receptors, there 5 subtypes (all GPCR)

Question 12

Role of adrenal medulla

Answer 12

Part of ANS. Neuroendocrine tissue associated with sym NS called ‘modified sympathetic ganglion’. Receives preganglionic neuronal imput, but, there’s no projecting axons to tissue. Chromaffin secretes adrenaline instead.

Question 13

Salbutamol

Answer 13

Ventolin. Asthma. Agonist of B2 adrenergic receptors on brochioles. Mimics sympathetic activity causing them to dilate (increases air flow)

Question 14

B Blockers

Answer 14

used to treat abnormal heart rate, hypertension, antagonist of B Adrenergic receptors. Blocks sympathetic activity.