Week 12 - hippocampus and limbic system - finished Flashcards Preview

YEAR 3 SEMESTER 1 NEURO-ANATOMY > Week 12 - hippocampus and limbic system - finished > Flashcards

Flashcards in Week 12 - hippocampus and limbic system - finished Deck (50):
1

What % of brain mass does the hypothalamus contribute?

Less than 1%

2

What % of brain mass does the hypothalamus contribute?

3

Where is the hypothalamus located?

What else is it connected to and how?

Beneath the thalamus, in the walls of the 3rd ventricle and is connected to the pituitary by a stalk

4

What is the function of the hypothalamus?

Maintains homeostasis.

Also serves the limbic system for emotional expression
- fear
- depression
- pleasure
- rage

5

What is homeostasis and what are some examples

Maintaining consistent internal conditions within a very narrow range:
Temperature
pH
Blood volume
Blood pressure
Blood oxygen
Blood glucose
Electrolyte balance & salinity

6

What is the structure of the hypothalamus?

Each side of the hypothalamus is divided into 3 zones:
- lateral
- medial
- periventricular

7

What are the functions of the medial and lateral zones of the hypothalamus?

They connect the hypothalamus to the brainstem, spinal cord and the cortex for the expression and experience of certain emotions.

8

What does the periventricular zone of the hypothalamus do?

1) Regulated the output of the ANS
2) Influences the pituitary and endocrine regulation
3) Controls circadian rhythms via the suprachiasmatic nucleus

In order to perform these functions it has 3 functionally distinct groups of cells.

9

Where is the periventricular zone of the hypothalamus located?

Its the area directly surrounding the 3rd ventricle

10

How many groups of cells are found in the periventriular zone? What are their functions?

3

1) Suprachiasmatic nucleus
- direct retinal input
- monitors daily light/dark cycles
- synchronises circadian rhythms.

2) Cells for the control of the ANS
Connections between the periventricular zone and the autonomic preganglionic nuclei in the brainstem (PS) and spinal cord (S) are essential to autonomic control

Integrates information about body status, anticipates the body’s needs and coordinates a set of both neural and hormonal outputs

3) Neurosecretory neurons:
Axons of neurosecretory neurons project down into the pituitary stalk
Neurohormones are secreted directly into the blood stream
Posterior Pituitary = Neurohypophysis -> CNS
Anterior Pituitary = Adenohypophysis -> gland

11

What is the solitary nucleus and tract? Where are they located?

Located in the medulla and receives extensive input from the hypothalamus

It is important for the autonomic control and possibly responsible for almost normal control of some autonomic functions even in the absence of the hypothalamus

It coordinates sensory information form the internal organs and outputs to the autonomic brainstem nuclei

12

What are the functions and divisions of the ANS?

Functions:
Automatic
Involuntary
Complex and highly coordinated functions

Divisions:
Sympathetic
Parasympathetic
Enteric

13

SNS information:

Fight, Flight, Fright & Sex

Preganglionics from intermediolateral cell column in the thoracolumbar cord

Exit via the ventral root to synapse at the postganglionics
Postganglionics from sympathetic chain ganglia, out with spinal nerves via gray rami communicans

Sympathetic influence:
Increase heart rate
Peripheral vasodilation/ GIT vasoconstriction
Orgasm and ejaculation
Pupillary dilation
Increase glucose production and mobilisation
Dilation of airways
Stimulation of adrenal adrenalin & noradrenalin release

14

PSNS information:

Rest & digest

Growth, immune responses & energy storage

Preganglionics from autonomic nuclei of brainstem and sacral spinal cord, travel with various cranial & sacral spinal nerves

Parasympathetic ganglia tend to sit within/ local to their target tissues, it is from here that the postganglionic axons extend

Parasympathetic influence
Decrease heart rate
Pupillary constriction
Stimulates salivation and lacrimation
Constricts airways
Stimulates GITl vasodilation/ Peripheral vasoconstriction
Stimulates digestion & insulin release
Stimulates sexual arousal - erection not ejaculation

15

Enteric division of ANS information:

Embedded in the wall of the oesophagus, stomach, intestines, pancreas and gall bladder are two interconnected plexuses for regulation of GIT function

Auerbach’s Plexus -> Myenteric Plexus
Meissner’s Plexus -> Submucosal Plexus

Both contain autonomic motor & sensory neurons
Contains approx # neurons as entire spinal cord
Can acts to regulate homeostasis with a great deal of autonomy but not entirely

16

Overall autonomic function:

Innervates secretory glands
Innervates heart to control heart rate, BP & flow
Innervates bronchi to meet O2 demands
Regulates digestive & metabolic functions of the liver, GIT & pancreas
Regulates function of the kidney, urinary bladder, intestines & rectum
Essential to sexual responses of the genitals and reproductive organs
Interacts with the immune system

Functions of the sympathetics & parasympathetics generally oppose each other, so substantial of stimulation of both is incompatible

The two systems function in parallel to balance excitation and inhibition for coordinated and graded control of body systems

17

What are magnocellular neurons and where are they found? Where do they extend and what do they release?

Found in the hypothalamus

Extend their axons all the way down the pituitary stalk and into the neurohypophysis

They release neurohormones directly into the capillary bed

- Oxytocin: uterine contraction in final stages of child birth and milk ejection from mammary glands

- Vasopressin/ADH: regulates blood volume & salt [C], is released in response to input from cardiovascular pressure receptors & salt [C] sensitive cells in the hypothalamus. Acts directly on the kidney to increase H20 retention & decrease urine production

18

What are parvocellular neurons and where do they extend? What do they secrete and what do these secretions influence?

They extend into the base of the pituitary stalk & secrete their neurohormones into the capillary bed of the hypothalamopituitary portal system which sits in the base of the stalk and the floor of the 3rd venticle

Neurohormones travel downstream and bind at hormone specific receptors on anterior pituitary cells to exert their effects and either stop or start pituitary hormone release

19

What hormones are released from the anterior pituitary?

GH: growth hormone
TSH: thyroid stimulating hormone
ACTH: adrenocorticotropic hormone
PROLACTIN
FSH: follicle stimulating hormone
LH: leutinising hormone

20

What hormones are released from the anterior pituitary?

GH: growth hormone
TSH: thyroid stimulating hormone
ACTH: adrenocorticotropic hormone
PROLACTIN
FSH: follicle stimulating hormone
LH: leutinising hormone

21

Where is the hypothalamus located?

What else is it connected to and how?

Beneath the thalamus, in the walls of the 3rd ventricle and is connected to the pituitary by a stalk

22

What is the function of the hypothalamus?

Maintains homeostasis.

Also serves the limbic system for emotional expression
- fear
- depression
- pleasure
- rage

23

What is homeostasis and what are some examples

Maintaining consistent internal conditions within a very narrow range:
Temperature
pH
Blood volume
Blood pressure
Blood oxygen
Blood glucose
Electrolyte balance & salinity

24

Midbrain and aggression:

Hypothalamic projections to brainstem for ANS function via the medial forebrain bundle & the dorsal longitudinal fasciculus.

Lateral hypothalamus -> MFB -> ventral tegmental area -> stimulation -> predatory aggression -> lesion -> decrease predatory aggression

Interestingly: cut MFB -> can still elicit aggression -> aggression not completely reliant on hypothalamus

Medial hypothalamus -> DLF -> PAG -> stimulation -> increases affective aggression -> lesion -> decreases affective aggression

25

What are the functions of the medial and lateral zones of the hypothalamus?

They connect the hypothalamus to the brainstem, spinal cord and the cortex for the expression and experience of certain emotions.

26

What happens when the amygdala is removed?

attention / concentration

27

Where is the periventricular zone of the hypothalamus located?

Its the area directly surrounding the 3rd ventricle

28

Selective stimulation in humans: Severe narcolepsy:

Stim. -> hippocampus -> mild pleasure
Stim. -> midbrain tegmentum -> alert but unpleasant
Stim. -> septal area -> alert & pleasant
-> described as build up to orgasm
-> repeated stim. -> no orgasm
-> frustration

29

Selective stimulation in humans: Severe epilepsy

Stim. -> septal area -> pleasure/sexual feeling
Stim. -> midbrain tegmentum -> pleasure/happy drunk
Stim. -> amygdala -> mild pleasure
Stim. -> caudate nucleus -> mild pleasure
Stim. -> medial thalamus -> irritable feeling
-> about to recall a memory
-> repeated stim. -> didn’t recall
-> frustration

30

What are the functions and divisions of the ANS?

Functions:
Automatic
Involuntary
Complex and highly coordinated functions

Divisions:
Sympathetic
Parasympathetic
Enteric

31

Serotonin and aggression:

Serotonergic neurons from raphe nuclei to hypothalamus & other limbic structures via MFB

Study of rats & mice in isolation:
No Δ in absolute serotonin levels
Decreased turnover rate
Only noted in those that became hyperactive & aggressive, no Δ in those that didn’t develop aggression
♀ typically didn’t become aggressive & showed no Δ in serotonin turnover

Drugs that decrease serotonin release or synthesis tend to increased aggressive behaviour

32

PSNS information:

Rest & digest

Growth, immune responses & energy storage

Preganglionics from autonomic nuclei of brainstem and sacral spinal cord, travel with various cranial & sacral spinal nerves

Parasympathetic ganglia tend to sit within/ local to their target tissues, it is from here that the postganglionic axons extend

Parasympathetic influence
Decrease heart rate
Pupillary constriction
Stimulates salivation and lacrimation
Constricts airways
Stimulates GITl vasodilation/ Peripheral vasoconstriction
Stimulates digestion & insulin release
Stimulates sexual arousal - erection not ejaculation

33

Enteric division of ANS information:

Embedded in the wall of the oesophagus, stomach, intestines, pancreas and gall bladder are two interconnected plexuses for regulation of GIT function

Auerbach’s Plexus -> Myenteric Plexus
Meissner’s Plexus -> Submucosal Plexus

Both contain autonomic motor & sensory neurons
Contains approx # neurons as entire spinal cord
Can acts to regulate homeostasis with a great deal of autonomy but not entirely

34

Overall autonomic function:

Innervates secretory glands
Innervates heart to control heart rate, BP & flow
Innervates bronchi to meet O2 demands
Regulates digestive & metabolic functions of the liver, GIT & pancreas
Regulates function of the kidney, urinary bladder, intestines & rectum
Essential to sexual responses of the genitals and reproductive organs
Interacts with the immune system

Functions of the sympathetics & parasympathetics generally oppose each other, so substantial of stimulation of both is incompatible

The two systems function in parallel to balance excitation and inhibition for coordinated and graded control of body systems

35

What are magnocellular neurons and where are they found? Where do they extend and what do they release?

Found in the hypothalamus

Extend their axons all the way down the pituitary stalk and into the neurohypophysis

They release neurohormones directly into the capillary bed

- Oxytocin: uterine contraction in final stages of child birth and milk ejection from mammary glands

- Vasopressin/ADH: regulates blood volume & salt [C], is released in response to input from cardiovascular pressure receptors & salt [C] sensitive cells in the hypothalamus. Acts directly on the kidney to increase H20 retention & decrease urine production

36

What are parvocellular neurons and where do they extend? What do they secrete and what do these secretions influence?

They extend into the base of the pituitary stalk & secrete their neurohormones into the capillary bed of the hypothalamopituitary portal system which sits in the base of the stalk and the floor of the 3rd venticle

Neurohormones travel downstream and bind at hormone specific receptors on anterior pituitary cells to exert their effects and either stop or start pituitary hormone release

37

What hormones are released from the hypothalamus?

TRH: thyrotropin releasing hormone
CRH: corticotropin releasing hormone
GHRH: growth hormone releasing hormone
GHIH: growth hormone inhibiting hormone
GnRH: gonadotropin releasing hormone
PIF: prolactin inhibiting factor

38

What hormones are released from the anterior pituitary?

GH: growth hormone
TSH: thyroid stimulating hormone
ACTH: adrenocorticotropic hormone
PROLACTIN
FSH: follicle stimulating hormone
LH: leutinising hormone

39

What is involved in the limbic system?

Cingulate gyrus, cortex around the corpus callosum and the hippocampal formation.

40

What does lateral hypothalamic nucleus stimulation induce

Eating

41

What is Kluver- Bucy syndrome?

Bilateral temporal lobectomy:

Psychic blindness
Oral tendencies
Hypermetamorphosis
Altered sexual behaviour
Emotional changes/flattening -> most obvious is the loss of fear

42

Where is the amygdala found? What is its function?

Found: Subcortical nucleus formed from infolding of the infromedial temporal lobe cortex

All sensory systems input into the amygdala

Centre for the identification of danger or learned fear

The amygdala appears to give emotion content to memories rather than control the storage of memory

Intensely connected to the hypothalamus

43

Midbrain and aggression:

Hypothalamic projections to brainstem for ANS function via the medial forebrain bundle & the dorsal longitudinal fasciculus.

Lateral hypothalamus -> MFB -> ventral tegmental area -> stimulation -> predatory aggression -> lesion -> decrease predatory aggression

Interestingly: cut MFB -> can still elicit aggression -> aggression not completely reliant on hypothalamus

Medial hypothalamus -> DLF -> PAG -> stimulation -> increases affective aggression -> lesion -> decreases affective aggression

44

Anger and aggression:

As noted earlier the hypothalamus appears to be involved in aggression but several other factors appear to also be involved including:

The amygdala

The midbrain

The raphe nuclei of the brainstem (possibly due to their serotonin content)

45

What happens when the amygdala is removed?

attention / concentration

46

Negative reinforcement and displeasure centres:

Animals will actively avoid situations that stimulate certain areas of the brain or repeatedly perform activities which cease or decrease stimulation of these areas.

Some of these areas include:
Medial parts of the hypothalamus
Lateral midbrain tegmental area

47

Selective stimulation in humans: Severe narcolepsy:

Stim. -> hippocampus -> mild pleasure
Stim. -> midbrain tegmentum -> alert but unpleasant
Stim. -> septal area -> alert & pleasant
-> described as build up to orgasm
-> repeated stim. -> no orgasm
-> frustration

48

Neurotransmitters and emotions:

Several neurotransmitters have been implicated in emotional dysfunctions

Neurotransmitters implicated in common diseases with emotional components:

- Dopamine abnormalities are thought to be responsible for both schizophrenia and parkinson’s disease

- Noradrenalin and serotonin have both been implicated in depression

49

Serotonin and aggression:

Serotonergic neurons from raphe nuclei to hypothalamus & other limbic structures via MFB

Study of rats & mice in isolation:
No Δ in absolute serotonin levels
Decreased turnover rate
Only noted in those that became hyperactive & aggressive, no Δ in those that didn’t develop aggression
♀ typically didn’t become aggressive & showed no Δ in serotonin turnover

Drugs that decrease serotonin release or synthesis tend to increased aggressive behaviour

50

Suggested limbic system structures and their roles:

Thalamus:
lesions and stimulation can alter emotional reactivity probably because of connections to other limbic structures……… actual emotional function or just relay point to cortex ???

Fornix & Parahippocampal gyrus:
Thought to be important in connecting the limbic pathway
-> fornix connects hippocampus, septal areas and hypothalamus
-> hippocampus for laying down of memory (amygdala is thought to give emotional content to memories) hippocampus..emotional learning ???

Hypothalamus:
-> Lateral parts appears to be most active in pleasure and rage
-> Medial parts appear to be most active in displeasure and aversion. Also noted to give rise to the expression of uncontrollable laughter, is simply expression not genesis of the underlying emotion

Cingulate gyrus:
- Appears to regulate aggressive behaviour
- Co-ordinate emotional responses to pain & lesions result in indifference to pain
- Co-ordinates smells & sights with previous pleasant emotions

Locus ceruleus: is very poorly understood but has ascending inputs into all limbic structures.
- Via these diffuse connections it appears to play a role in :
Attention
Arousal
Sleep/wake cycles
Learning & memory
Anxiety
Pain
Mood
Brain metabolism

Ventral tegmentum:
As noted in human stimulation studies and notes on dopamine, appears to be involved in reinforcement & reward, some people have attached sexual qualities to the feelings experienced

Cranial nerve nuclei:
Function in the expression of emotions

Septum:
Centre for orgasm
Note: ♀ = 4 ♂ = 1
Also assoc. with other levels & forms of pleasure but most notably those related to sexual experiences

Prefrontal lobe:
Bidirectional connections to thalamus and amygdala and other limbic structures

Prefrontal damage:
Loss of social responsibility
Decrease [C]

Prefrontal lobotomy:
No signs of joy
No sadness, hope or despair
No affection