The Autonomic Nervous and Limbic Systems (7)

September 23

Limbic system

• a collection of grey-matter nuclei connected via white matter tracts

• Responsible for memory and emotional and behavioural responses 

Deep nuclei

Consists of the basal ganglia and limbic system

Memory in the limbic system

• Hippocampal formation

• Anterior thalamus

• Hypothalamus: mammillary bodies

Emotional/behavioural response in the limbic system

• Amygdala

• Dorsomedial Thalamus

• Hypothalamus: ANS Nuclei

Limbic lobe

• used in both memory and emotional response in the limbic system

• consists of the cingulate gyrus and the parahippocampal gyrus

Mammillary bodies

• thalamic relay

• recollective memory

• appropriate behavioural reactions

Amygdala

• analyses anger and fear expressions

• assesses danger and elicits fear response 

  • memory is key here! next to hippocampus 

  • long-term memory and emotion are connected! you remember things better when they elicit a strong emotion 

• emotional memories

• output to hypothalamus —> SNS

Fornix

White matter tract

Hippocampus

• who, what, where, when

• long-term memory formation

• output to cortex via fornix 

Episodic memory

• located in the medial temporal lobe (thalamus, amygdala, hippocampus)

• i.e., event memory

  • e.g., “I got married one week ago in Australia”

Semantic memory

• Located in the neocortex (auditory, somatosensory, visual cortex)

• i.e., factual memory

  • e.g., “The sky is blue”

Procedural memory

• Located in the cerebellum and basal nuclei

• i.e., muscle memory

  • e.g., riding a bike

Papez circuit 

• creates and strengthens episodic memory

• diffused across your cortex

• damage to the papez circuit creates false memories

Connections between amygdala and hypothalamus enable an autonomic response to govern:

• Emotional Responses

  • via pituitary gland

• Behaviours

  • Feeding – differentially activate hypothalamic nuclei associated with satiety or hunger

  • Sexual – increases oxytocin (from the posterior pituitary which is part of the hypothalamus)

  • Motivation – Increases dopamine in specific areas outside of the hypothalamus

Autonomic Nervous System (ANS) 

• The branch of your nervous system that controls your glands and involuntary muscles (heart and smooth muscle).

• aka visceral motor nervous system

• There is also a sensory part of the system, but it is largely ignored

  except regarding referred pain and interoception

• Mainly controlled by the limbic system connections in the hypothalamus

To maintain homeostasis (i.e., blood pressure) 

What is the most important role of the ANS?

Ganglion

Neurons synapsing together

Pre-ganglionic neuron

Post-ganglionic neuron

Acetylcholine

Neurotransmitter between the motor nerve and —- in the ——

Epinephrine

• adrenaline

• used in sympathetic nervous system

What would happen if a sympathectomy (taking away sympathetic input) were performed on the heart (i.e., all the sympathetic input was stopped)?

Decrease in heart rate and blood pressure

If all autonomic input to the heart was stopped then what would happen to heart rate and force of contraction?

• lost both parasympathetic and sympathetic input

• took more parasympathetic than sympathetic input

Heart rate would increase, and the force of contractions would increase

If all autonomic input to the peripheral blood vessels (only has sympathetic input) were to stop what would happen?

Blood vessels would dilate, and blood pressure would drop

Miosis

Constriction of the pupil

Mydriasis

Relaxation of the pupil

Atropine blocks the muscarinic cholinergic neurons (i.e., the

postganglionic parasympathetic receptors). What would this drug do

to the pupil size?

The pupil would dilate (mydriasis)

Parasympathetic nervous system is responsible for…

SLUDD

• Salivation

• Lacrimation

• Urination

• Digestion

• Defecation

Receptors of the autonomic nervous system

cholinergic receptors and adrenergic receptors

Cholinergic receptors

• Found in the synapses of

  • the sympathetic and parasympathetic ganglia

  • the postganglionic parasympathetic effectors

Adrenergic receptors

Found only on the sympathetic postganglionic target organs (or effectors, whatever you want to call them)

Muscarinic receptors and nicotinic receptors

Two Types of Cholinergic Receptors

Muscarinic receptors

Found on all parasympathetic target organs

• Acetylcholine (or muscarine) stimulating these receptors leads to

  • Decreases heart rate

  • Increases intestinal motility

  • All parasympathetic effects