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Semester 2 BMA 1912 > Sem 2 Module 3 - The Autonomic Nevous System & CNS Neurotransmitters > Flashcards

Sem 2 Module 3 - The Autonomic Nevous System & CNS Neurotransmitters Flashcards

1
Q

What does the somatic nervous system do?

A

Innervates skeletal muscles

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2
Q

What are impulses which lead to skeletal muscle contractions are along?

A

Pathways which descend from the brain:

  • From the motor cortex for voluntary movements
  • From other parts of the brain for involuntary movements e.g. from the respiratory centre in the brainstem.
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3
Q

What are efferent arms of reflex arcs in somatic nervous system?

A
  • In spinal nerves e.g. for deep tendon reflexes

- In some cranial nerves e.g. for head-turning reflexes

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4
Q

What is the Autonomic nervous system?

A
  • The ANS innervates smooth muscles, cardiac muscles and glands
  • Every organ includes at least of these tissues (even skeletal muscle)
  • In a skeletal muscle, striated muscle cells are innervated by somatic motor nerves,,
    - But the smooth muscle cells of arterioles are innervated by autonomic motor nerves
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5
Q

Where are impulses which modify the function of smooth, cardiac muscle and glands carried on?

A

Pathways which descend from the hypothalamus

e.g. pathways from the hypothalamus (thermostat) to sweat glands

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6
Q

What are the efferent arms of reflex arcs in the autonomic nervous system?

A
  • In spinal nerves e.g. leading to increase in heart rate when you feel sudden pain
  • In some cranial nerves e.g. leading to constriction of the iris in response to bright light
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7
Q

What does the hypothalamus control?

A

Both the endocrine system and autonomic system

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8
Q

What is the effect of autonomic nerves?

A
  • The functions of organ can be profoundly affected by changes in the activities of tissues such as smooth muscle
  • The autonomic nervous system does not turn such functions “on” or “off”, but rather modulates them —- turns them “up” or “down”
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9
Q

What are the two divisions of the autonomic nervous system?

A
  • Sympathetic

- Parasympathetic

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10
Q

What is the sympathetic division of the ANS?

A
  • In general, the sympathetic nervous system is the “up” control for organs which are more active when you are frightened (“fight or flight”, acute stress), excited, or exercising
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11
Q

What is the parasympathetic division of the ANS?

A
  • Is the “up” control for organs that are more active when you are relaxed, and promote build-up of body reserves e.g. digestive organs
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12
Q

What are autonomic effects on specific organs?

A

Major activities regulated by autonomic nervous system include:

  • Heart rate —> Strength of contraction
  • Local blood flow and blood pressure
  • Digestive activity
  • Respiratory airways resistance
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13
Q

What are the autonomic pathways?

A

In the somatic nervous system, a chain of neurons and their axons conveys signal from the motor cortex of the cerebrum to skeletal muscle.

Upper motor neuron:
- Motor cortex —> corticospinal tract —> anterior horn of grey matter

Lower motor neuron:
- Anterior horn of grey matter —> Anterior root of spinal nerve —> skeletal muscle

Thus, the pathway from the CNS to skeletal muscles consist of single neuron, the lower motor neuron and its axon

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14
Q

What are the two neurons that are in the pathway from the CNS to effector tissues?

A
  • THE FIRST NEURON - Has its cell body in the CNS, with the axon reaching out of the CNS to an autonomic ganglion.
    There it synapses with the cell body of —>
    THE SECOND NEURON - From its cell body in an autonomic ganglion, the axon reaches out to its effector tissue
               - The first neuron is therefore termed presynaptic
           - The second neurone is postsynaptic
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15
Q

Where are the cell bodies of sympathetic presynaptic neuron located?

A

In the T1 and L2 segments of the spinal cord

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16
Q

In this region they make up what horns of grey matter?

A

Lateral

Lateral horns are only found between T1 and L2

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17
Q

What happens in the Sympathetic pathways?

A

Some postganglionic fibres run up from the topmost sympathetic ganglia into the head:
- this explains how the eye receives sympathetic innervation — no sympathetic fibres in cranial nerves

In the sympathetic nevous system, a single preganglionic neuron may synapse with many postganglionic neruons —-> single impulse in a preganglinoic neuron transmitted to a large number of effector tissues
- Thus, sympathetic impusles may be “broadcast” and produce generalized effects.

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18
Q

What is the neurotransmitter between sympathetic ganglionic fibres and their effector tissues? and the transmission?

A

Neurotransmitter —> Noradrenalin

Transmission —-> Adrenergic

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19
Q

What is the exception – when a neurotransmitter between sympathetic postganglionic fibres and sweat glands?

A

It is Acetylcholine

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20
Q

What is the adrenal medulla controlled by?

A

Hypothalamus

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21
Q

What does the adrenal medulla do?

A

Its acts in some ways like a sympathetic ganglion. It receives sympathetic preganglionic fibres, which synapse with medullary cells. These cells in turn, like sympathetic postganglionic neurons, release noradrenalin

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22
Q

What is noradrenalin secreted with?

A

Adrenalin

23
Q

What is noradrenalin and adrenalin secreted into?

A

Adrenalin and noradrenalin are secreted not onto specific effector cells but into the bloodstream

24
Q

So therefore what else does the adrenal medulla act as?

A

An endocrine gland

25
Q

Where are the cell bodies of parasympathetic preganglionic neurons in the CNS located in?

A
  • Grey matter nuclei in the brainstem

- Grey matter of the spinal cord in sacral segments (S2-S4)

26
Q

What can neurons of the first type do?

A
  • Receive “instructions” from the hypothalamus in the form of descending impulses
  • Receive afferent imulses which enter the brain through cranial nerves, or which ascend through the spinal cord
  • Such impulses may serves as the afferent arms of cranial parasympathetic reflexes, with the parasympathetic preganglionic neurons serving ast he efferent arms.
27
Q

What can neurons of the sencon type, like sympathetic preganglionic neurons do?

A
  • Receive “iinstructions” from the hypothalamus in the form of descending impulses
  • Receive afferent impulses which enter the spinal cord
  • Such impulses may serve as the afferent arms of spinal parasympathetic reflexes
28
Q

What happens in parasympathetic pathways?

A
  • The axon (fibre) of a parasympathetic preganglionic neuron leaves the skin in a cranial nerve (or leaves the spinal cord in a sacral spinal nerve)
  • Axon of a parasympathetic preganglionic neruons runs all the way to it effector organ.
    - Synapses with the postganglionic neuron in a ganglion - close to or within the organ itself
    - The neurotransmitter at these synapses is acetylcholine
    - Transmission is cholinergic

The axon of the postganglionic neruon then runs a short distance to its effector tissue within that organ
- Thus, the parasympathetic preganglionic fibres are long, and postganglionic fibres are short

The neurotransmitter between parasympathetic postganglioinic fibres and their effector tissues is acetylocholiine
- and the tranmitter is cholinergic

29
Q

Which cranial nerves carry parasympathetic fibres?

A

III (Oculomotor)
VII (Facial)
IX (Glossopharyngeal)
X (Vagus)

30
Q

What are the sympathetic effects?

A
  • Exercising, excited or frightened —> more efferent impulses in sympathetic pathways (fewer in parasympathetic)
  • Sympathetic system serves as “up” control enhanced e.g. heart rate
  • “Down” control diminished e.g. blood flow through the skin
  • The overall effect is to mobilize the body for action
31
Q

What happens when sympathetic pathways are activated?

A

The effects are widespread

  • Single preganglionic neruon may synapse with many postganglionic neurons —> large number of effector tissue “broadcast”
  • The release of adrenalin and noradrenalin from the adrenal medulla into the blood —> “Sympathetic” stimulation even if no direct postganglionic neurons
    - Effects of direct sympathetic stimulation intensified and prolonged
32
Q

What are the parasympathetic effects?

A

When you are happy and relaxed, the hypothalamus sends more efferent impuses down parasympathetic pathways (and fewer down sympathetic pathways)

  • Functions for which the parasympathetic system serves as an “up” control will be enhanged e.g. digestive activities
  • Functions for which it is a “down” contorl will be diminished e.g. heart rate
  • The overall effect is to build up your resources such as nutrient storage
33
Q

What is one specific parasympathetic pathways?

A

Via vagus nerve (X)

  • Heart —> Reduced rate of contraction
  • Lungs —> Bronchoconstriction
  • Digestive tract —> Increased digestive functions
34
Q

What is another specific parasympathetic pathway?

A

Via oculomotor nerve (III)

- Eye —> Pupil constriction, lens thickening for near vision

35
Q

What is another specific parasympathetic pathway?

A

Via facial nerve (VII) & Glossopharyngeal (IX)

- Salivary glands —-> increased secretion of saliva

36
Q

What is another specific parasympathetic pathway?

A

Via nerves from sacral segments of spinal cord

  • Bladder —-> Urination
  • Rectum —-> defecation
  • Genitals —-> Erection of clitoris, penis (increased blood flow in erectile tissue)
37
Q

What are the autonomic transmitters and receptors?

A
  • There are multiple types of receptors in the autonomic nervous system
  • Pharmacologists produce drugs - selective for only one type of receptor
    - Selectively affect one organ while leaving others alone
    - Drugs that stimulate receptors - Agonist
    - Drugs that inhibit recptors - Antagonists
38
Q

What about the neurotransmitter at all autonomic ganglia is acetylocholine?

A
  • All postganglionic neurons have nicotinic recptors for acetylocholine
  • Such receptors are named after nicotine, a drug which act as an agonist at these recptors (activates them)

The parasympathetic system uses acetylocholine as its tranmitter at effector tissues

  • Muscarinic receptors for acetycholine
  • Named after muscarine, a drug which acts as an agonist at these receptors
39
Q

What are examples of different receptors that account for different actions of transmitters and drugs?

A

Beta blockers –> inhibit receptors in both the heart and lung bronchioles

  • Heart has beta 1 receptors: beta blockers lower blood pressure by slowing the heart
  • Lung has beta 2 receptors: beta blockers constrict the bronchioles, making it harder to breathe

Propranolol —> blocks both types of beta receptor and hsould not be used to lower blood pressure in a person who is asthmatic

Metoprolol —> can be used to slow the heart without endangering asthmatic because it is specific for beta 1 and does not cause constriction of the bronchioles

40
Q

What are neurotransmitters?

A

Neurotransmitters - Chemicals that allow one neve cell to talk to another nerve cell - can also be found in the brain and spinal cord —- the central nervous system

41
Q

What are CNS neurotransmitters?

A
  • Our whole brain consists of about 40 different types of CNS neurons (classified by the type of neurotransmitter)
42
Q

What is the classification of neurotransmitters?

A

Amino Acids
- Excitatory: Glutamine (Glu), aspartate, cysteic acid, homocysteic acid
- Inhibitory: Glycine, Y-aminobutyric acid (GABA), alanine, taurine, serine
Monoamines
- Noradrenalin (NA), adrenalin (Adr), dopamine (DA), serotonin, histamine

43
Q

More classification of neurotransmitters:

A

Acetylcholine (Ach)

Neuroactive Peptides

44
Q

What are Amino Acid Peptides?

A

Inhibitory transmitter – e.g. GABA

  • Important in interneurons of spinal cord, cerebellum & hippocampus
  • Involved in motor control, spasticity & sleep/wakefulness
  • We need inhibitory control to avoid excessive excitation (e.g. seizures & epilepsy)
45
Q

What are Monoamines?

A 
Monoamines are a class of related chemicals 
   - Noradrenalin
   - Adrenalin
   - Dopamine
   - Serotonin 
Diverse neural circuits 
   - Autonomic arousal 
   - Cardiorespiratory control
   - "Reward"
   - Affect 
   - Motor control 
   - 5-HT involved in cognition, behaviour, sleep/wake cycles, mood, vomiting and pain (migraine) 
Implicated in mental illness e.g. Schizophrenia & depression
46
Q

What is Acetylcholine (Ach)?

A

Ach is widespread in the PNS

In CNS

  • Reticular formaiton
  • Basal forebrain
  • Basal Ganglia
  • Anterior Spinal Roots
47
Q

What are the roles of Ach in the PNS?

A
  • Cognition
  • Memory
  • Consciousness
  • Motor control
    Low levels in Huntington’s Disease and Denentias such as Alzheimer’s disease
    Muscarinic and Nicotonic receptors in the CNS
48
Q

What are neuropeptides?

A

E.g. Vasopressin, oxytocin, encephalon’s and endorphins (opioids)

  • Formed into he cell body
  • May cause excitation or inhibition of target neurons
  • May have potent behavioural effects when injected parenteral or intracerebrally
  • Difficult to identify their functions

B Endorphins
Neuropeptide Y
Vasoactive intestinal peptide (VIP)
Substance P

49
Q

What are the behavioural effects of Neuropeptides?

A

Huge range of behavioural effects:

  • Hunger/satiety
  • Sleep/wake cycle
  • Temperature regulation
  • Pain modulation
  • Reward circuits
50
Q

What are neurotransmitter imbalances in disease state?

A

In many CNS disorders appears to be imbalances the levels of neurotransmitters in particular areas of the brain

51
Q

How do we know this?

A

From post-mortems - tracts and neurons have degenerated in particular areas
- Effects of monoamines “balance” Ach
- Motor control
- Mood (affect)
- Thought process
Simplistic - highly complex and not well understood

52
Q

What are neurotransmitter imbalances in disease state examples?

A

Depression - deficiency of NA and 5-HT in areas of the brain related to mood and an excess of Ach
- Antidepressant drugs - SSRIs, TCAs & MAOIs increase the levels of monoamines

Parkinson’s disease - damage to the DA-containing neurons and a deficiency of DA or excess of Ach
- Drugs raise levels of DA or block actions of Ach (atropine drugs)

Schizophrenia - Ach levels = low, DA levels = High

Mania - Ach levels = low, Glu, NA & DA = high

Dementia - Ach levels = low, Monoamines levels = high

53
Q

What are the social drugs that work on the CNS?

A

Drugs acting on the CNS are used more than any other type of agent
In addition to their therapeutic uses, drugs such as
- Caffeine (stimulate)
- Alcohol (depressant)
- Nicotine (stimulate)
- Are used socially to provide a sense of wellbeing

Central drugs of produce dependence with continued use, and many are subject to strict legal controls

54
Q

What are clinical drugs that work on the CNS?

A

Anaesthetics
E.g. halothane, propofol, ketamine, thiopentone

Analgesics
E.g. Codeine, morphine, oxycodone, pethidine

Antianxiety, sedative and hypnotic
E.g. Diazepam, phenobarbitone, Chloral hydrate

Psychotropic agents
E.g. imipramine, lithium

Semester 2 BMA 1912 (5 decks)

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