Higher centres

Cerebral cortex

• Prosencephalon = telencephalon + diencephalon

• Rhin-encephalon - part of telencephalon

• varies in size between mammals

  • relatively large in domestic species and higher mammals

Structural organisation of cerebral cortex

Define each phylogenetic territory

• phyogenetic territores

  • Archicortex

  • Paleocortex

  • Neocortex

• limbic system

  • closely associated with walls of ventricles

  • 8 components

Archicortex = old memory (longterm)

• Non-olfactory rhin-encephalon

  • Hippocampus

    • Retained within diencephalon

    • Important component of limbic system

Paleocortex = smelling

• Olfactory rhin-encephalon

  • mainly the Piriform lobe

  • (note CN1 and thalamus NOT paleocortex)

Neocortex = thinking

• cognitive thinking - projection and association areas

  • Projection

    • primary sensory & motor cortices/ somatosensory or -motor

  • Association areas [5]

    • somatosensory or

    • -motor association areas

    • cognitive association = parietal cortex & perception of space

    • frontal cortex assocation

    • temporal cortex association

Limbic system - components [8]

Definition = fringe or border around the thalamus

• gut reaction part of brain

• Functions: [5]

  • memory

  • behaviour

  • motivation

  • learning

  • emotion

1. Hypothalamus

2. Hippocampus

3. Amy-g-dala

4. Fornix

5. Olfactory bulb

6. Basal ganglia

   • Governs motor output of extrapyramidal system

7. Mammillary bodies

8. Cin-gul-ate gyrus

   Hyper Hippos Are Funny, Old But Miss the Cold

• 1, 2, 3 → core parts

Specialised brain functions

• behaviour

• memory

• sleep

Seizure definition

temporary disruption of brain function

• due to excessive abnormal neuronal activity

• e.g. could begin as abnormal cellular activity on the motor cortex of the brain

  • can be sensory

• result in erratic brain waves

Epilepsy definition and types

chronic condition of repeated seizures

Types

1) focal (small→ large areas of cortex)

2) generalised

3) intracranial → e.g. brain tumour

4) extracranial → toxicity or meningitis

Anticonvulsants mechanism

→ stop neurones firing/depolarisation

1. Block excitation

   • block v-gated Na+ channels

2. Enhance inhibition

   • increase GABA neurotransmitter in the brain

   • GABA = inhibitory CNS NT

Limbic system → hippocampus

• Location: floor of temporal horn of lateral ventricles

• Forms long term (episodic) memories

  • memories stored elsewhere

• Damage → cannot convert short term memories → long term

  • Alzheimer’s

  • Certain dementia types

  • Damage does not impact emotion

• Tested PM for rabies (histopathology)

  • dumb V furious rabies → emotional area of brain disrupted causing extremes

• Rigid instinctual behaviours → genetically determined

Limbic system- amygdala

• 2 almond shaped structures rostral to hippocampus

• Analyses emotional/motivational significance of stimuli → modulates emotion

• Destruction → disinhibited behaviours

  • hypersexuality

  • loss of fear

    • rats not afraid of cats → link between emotion and memory gone

Limbic system and hypothalamus

Regulate ANS (fight and flight, rest and digest) → Produce emotional response

• regulation of sex hormones

• bonding → secretion of oxytocin and prolactin from (PG) - bonds parents and children

• linked to body temp and hunger

  • Regulate spontaneous feelings and motivation:

  • motivation

    • goal-driven, increases arousal and learning

    • drawing from previous experiences

  • spontaneous feelings

    • pleasure, sexual arousal, anger, fear

Integration and coordination of hypothalamus, limbic system, cortex

Produces different responses to environmental stimuli → creates personality

General association areas → produce cognitive assocaition

Link different lobes to create a bigger picture - Picking up a coin

• Frontal lobe (primary motor cortex)

• Parietal - conscious recognition of sensory info (reinforced by temporal)

  • (somatosensory)association

  • → premotor frontal association areas

    • texture and look - identification of of lobe

• Occipital - visual association → vision/eye

• Temporal

  • meaning of coin extracted from memories from hippocampus

  • any sensory input causes a reaction from temporal

• Analyse info, select course of action, predict consequences based on past

  • Somatosensory/Parietal association area → processing and interpreting sensory stimuli

  • Somatomotor/Frontal association area → voluntary planning and organisation of movement

Structure of association areas

• Short relay neurons → only in CNS

• Many dendrites → link between areas

Projection area brain composition

Prey mammals → 100% projection areas

Predatory mammals → fewer projection (80%) , 20% association

• assess situations to catch prey

Human → 15% projection, 85% association → lots of cognition

Parietal cortex and perception of space

• somatosensory association area

• Conscious recognition of sensory info

• Reinforced by memories and experiences → cognitive association

• Damage impacts understanding of environment and sense of self

  • disorders of body awareness

  • defects in personal and spatial perception

  • lack of visuomotor integration

Prefrontal cortex association area

• Executive control of behaviour

• Remembering and acting on intentions

• Inhibits emotional urges of hypothalamus

• Damage impacts emotional state and concentration → erratic behaviour

Temporal cortex association area

• Assess information based on previous experiences

• Learning and memory

• Dreams and hallucinations

Memory types

1. Short-term

   • ~15 secs

2. Long-term

   • retrievable and permanent

   • Implicit (unconscious) → motor and perceptual learning, skill performance

     • Cerebellum + prefrontal cortex

   • Explicit (conscious)

     • Episodic → personal/contextual knowledge

     • Semantic → factual/general knowledge

     • Various regions of neocortex involved

3. Working

   • immediate processing

   • manipulation of short term memory

Sleep

• Ascending reticular formation → wakefulness

• Sleep centre in hypothalamus → dampens asc. reticular formation

Types of sleep

• Slow wave (deep)

• Rapid eye movement (REM)

Sleep wake cycle

• 3 stages of slow wave sleep (non REM)

• Stages cycle

• N1 → N2 → N3 → N2 → REM

• 4 stages before REM

• 4-5 cycles per 1 night of sleep

• Horses have to lie down for REM sleep

Control of sleep wake cycle

• Vast species differences

• Circadian rhythm differences

• Hypocretin (orexin, type of neuropeptide)

  • promotes wakefulness

    • lack of hypocretin → narcolepsy (sudden sleeping)

• Pineal gland → melatonin production for sleep synchronisation