Autonomic & Limbic Systems Flashcards
What is the autonomic nervous system responsible for?
Control of involuntary bodily functions
Where are the autonomic nuclei found in the brain?
Forebrain and brainstem (pons, medulla & hypothalamus)
What systems does the hypothalamus integrate autonomic response with?
Limbic (behaviour/emotion/motivations), endocrine (hormonal response), somatic nervous system (motor behaviour to maintain homeostasis)
What are the three vegetative functions regulated by the hypothalamus?
Body temperature, fluid/electrolyte volume and blood pressure and feelings of hunger/satiety
What do the sympathetic and parasympathetic nervous systems innervate?
Cardiac and smooth muscle, glandular tissue and visceral reflexes
What does the enteric system innervate?
Digestive reflexes in the gastrointestinal tract
In the somatic & autonomic nervous systems, upper motor neurons in the brain innervate lower motor neurons.
Where are the lower motor neurons located in each system?
Somatic: CNS (spinal cord)
Autonomic: Autonomic ganglion
How many synapses occur in the somatic motor pathway and what neurotransmitter is used?
One, ACh
Describe the structure of the sympathetic neural pathway
- Sympathetic ganglia located close to the spinal cord
- Short preganglionic fibres, long postganglionic fibres
- Mainly adrenergic fibres (preganglionic)
Describe the structure of the parasympathetic neural pathway
- Parasympathetic ganglia located close to the effector tissues
- Long preganglionic fibres, short postganglionic fibres
- Mainly cholinergic fibres
What neurotransmitters are used by the sympathetic and parasympathetic neural pathways and where?
Both preganglionic: ACh
Sympathetic postganglionic: Norepinephrine & ACh
Parasympathetic postganglionic: ACh
What does the second synapse in the ANS neural pathways allow for?
Divergence (stimulating multiple organs/tissues at once)
Describe the relationship between sympathetic and parasympathetic preganglionic axons
Anatomically complimentary, target the same organs (antagonistic)
Where are the three points at which the preganglionic fibres synapse in the sympathetic nervous system?
- Ganglia of sympathetic chain it enters
- Ganglia of sympathetic chain higher or lower
- Peripheral sympathetic ganglia (e.g. deep digestive organs)
What root/ramus do the sympathetic preganglionic nerve fibres exit the spinal cord through?
Vemtral root, white ramus
75% of parasympathetic nerves leave the CNS through which nerve?
Vagus nerve (cranial nerve X)
Where are parasympathetic postganglionic nerve fibres located?
In the walls of organs, containing very short axonal fibres
Neural cells that release norepinephrine are said to be what?
Adrenergic neurons
Neural cells that release ACh are said to be what?
Cholinergic neurons
What type of neurons are all autonomic preganglionic neurons?
Cholinergic neurons
What postganglionic neurons of the sympathetic system are cholinergic?
Sweat glands, hair cell muscles & some blood vessels
What are the two major classes of receptors ACh binds to?
Muscarinic and nicotinic
Where are muscarinic receptors found?
Effector cells
Where are nicotinic receptors found?
At synapses between all pre and post ganglionic neurons of the ANS
What is the adrenal medulla regulated by?
Sympathetic nervous system
What is the adrenal cortex regulated by?
Pituitary gland secretions
What does the adrenal medulla secrete?
Epinephrine and norepinephrine
Why does the adrenal medulla secrete hormones into the bloodstream?
To generate a whole-system response rather than an organ-specific response
True or false: Secretions of the adrenal medulla have the same effect on organs as direct sympathetic innervation, except the effect lasts 5-10 times longer
True
By what two means are organs simultaneously stimulated?
Direct sympathetic neural innervation and indirect sympathetic innervation (medulla)
What effects do the sympathetic and parasympathetic systems have on the visual system?
Sympathetic: Maximum pupillary dilation
Parasympathetic: Pupillary constriction/dilation, contraction of ciliary muscles to induce accommodation
What is the name of the PNS hub for occulomotor activity?
Edinger-Westphal nucleus
What is the pathway for accommodation and pupil constriction?
1) Information exists eye via optic nerve and splits - half goes to visual cortex (accommodation), half goes to pretectal region (pupil size)
2) Information rejoined in Edinger-Westphal nucleus
3) Preganglionic neuron releases Ach onto nicotinic receptor on postganglionic neuron (ciliary nerve) at parasympathetic ganglion
4) Postganglionic neuron releases ACh onto muscarinic receptor that causes accommodation and pupil constriction
How does the parasympathetic system stimulate overall GI activity?
By promoting peristalsis and sphincter relaxation
What response does sympathetic and parasympathetic stimulation evoke from the pupil?
Sympathetic: Dilation
Parasympathetic: Constriction
What response does sympathetic and parasympathetic stimulation evoke from the ciliary muscle?
Sympathetic: Slight relaxation
Parasympathetic: Constriction
What response does sympathetic and parasympathetic stimulation evoke from the glands?
Sympathetic: Vasoconstriction/slight secretion
Parasympathetic: Copious secretions
What response does sympathetic and parasympathetic stimulation evoke from the sweat glands?
Sympathetic: Copious sweating
Parasympathetic: Sweating palms and hands
What response does sympathetic and parasympathetic stimulation evoke from the blood vessels?
Sympathetic: Constriction
Parasympathetic: Little effect
What response does sympathetic and parasympathetic stimulation evoke from the heart?
Sympathetic: Increased rate/force
Parasympathetic: Decreased rate/force
What response does sympathetic and parasympathetic stimulation evoke from the lungs (bronchi)?
Sympathetic: Dilated
Parasympathetic: Constricted
What response does sympathetic and parasympathetic stimulation evoke from the gut (lumen)?
Sympathetic: Decreased peristalsis
Parasympathetic: Increased peristalsis
Where are baroreceptors located and what do they detect?
Carotid artery and aortic arch, changes in blood pressure
What is the pathway for decreasing blood pressure?
1) Baroreceptors in carotid artery and aortic arch detect stretch
2) Stretch causes Na+ gates to open, initiates AP
3) AP causes increased frequency of firing of baroreceptors
4) Info goes from baroreceptors along glossopharangeal/vagus nerve to medulla
5) Cardioaccelatory and vasomotor areas of medulla are inhibited, cardioinhibitory area is stimulated
6) Information goes to brainstem via vagus nerve
7) Preganglionic neuron exits along vagus nerve and binds to postganglionic neuron
8) Postganglionic neuron releases ACh onto nicotinic receptor, innervates heart
9) Heart releases Ach onto muscarinic receptor in sinoatrial node
10) SA node is hyper polarised by opening ligand-gated K+ channels
11) Decreased heart rate/blood pressure
What does the limbic system include?
Areas of the neural circuitry that control emotional behaviour and motivational drive
What systems is the limbic system involved in modulating through integration at the hypothalamus?
Autonomic nervous system, endocrine system and vegetative functions
What is the difference between an emotion and a feeling?
Emotion: Physiological, unconscious response e.g. increased heart rate, sweating
Feeling: Conscious awareness of the emotional response
What structures form the limbic system?
Hypothalamus, cingulate gyrus, amygdala and basal ganglia
What is the general order of an emotional response and how is each element coordinated?
1) Unconscious detection of a sensory stimulus: Occurs within prefrontal cortex and cingulate gyrus
2) Peripheral response: Coordinated by hypothalamus and brainstem through modulation of autonomic & endocrine systems
3) Conscious experience (feeling): Coordinated by the amygdala
What is the function of the amygdala?
- Coordinates the conscious experience and peripheral expression of emotion based on memory and previous sensory experience
- Fine tunes the hypothalamus
- Helps pattern appropriate behaviour
- Strong fear responses
Where are the reward and punishment centres of the limbic system located?
Reward: Medial forebrain bundle
Punishment: Midbrain, hypothalamus and thalamus
What takes precedence, reward or punishment?
Punishment
What happens if a sensory experience neither rewards or punishes and the stimulus is repeated?
Complete extinction of the cortex response, i.e. no memory tract is formed
What happens if a sensory experience either rewards or punishes and the stimulus is repeated?
Cortex response becomes increasingly intense, i.e. memory tract is formed
What is the function of the hippocampus?
Involved in decision-making, conscious memory and conversion of short term (implicit) memories into long term (explicit) memories
What is the function of the cingulate gyrus?
Transitional zone between the cortex and limbic system, may be an association are for control of behaviour
