Lecture 6 Flashcards
Diencephalon
Diencephalon is deep within the brain, it composes the
walls of third ventricle
Diencephalon consists of
thalamus, hypothalamus, pituitary gland and pineal gland
Thalamus
Gateway to sensation
“Relay station and integrating centre” for preliminary processing of sensory afferent signals (what gets through, what doesn’t)
All sensory input (spinal cord, optic tract, cochlear tract) synapses here, are screened out and routed accordingly to cortex
Helps to direct attention to stimuli of interest (aircon noise, street noise etc filtered out)
Crude awareness of sensations (without location or intensity)
Positively reinforcing voluntary motor control
Hypothalamus
Collection of specific nuclei and associated fibers (less than 1% of total brain volume)
Integrating centre for homeostasis
Hypothalamus input
from reticular formation, cerebrum, sensory receptors
hypothalamus output
thalamus, multiple effector pathways
Hypothalamus links
autonomic nervous system with endocrine system
Hypothalamus controls
- body temperature
- Thirst and urine output
- Food intake/hunger
- Controls anterior pituitary hormone secretion
- Produces posterior pituitary hormones
- Directly regulating internal environment (eg shivering, vasoconstriction for heat homeostasis) Controls uterine contraction and milk ejection
- Autonomic nervous system: Smooth muscle, cardiac muscle, exocrine glands
- Emotion and behaviour
- Sleep/wake cycle
Upstream endocrine control
Upstream endocrine control: example cortisol
Thirst: Δ osmolarity and volume
Vasopressin/ADH (antidiuretic hormone)
Generated in N supraopticus: increases aquaporins in renal distal tubule and collecting duct
Damage in nucleus: Diabetes insipidus
20 l of urine loss per day
Feeding center
Hypophysis tumour infiltrating hypothalamus: affecting hunger/food intake homeostasis (60kg increase in 2 years)
Neurohypophysis/posterior pituitary:
downgrowth of hypothalamus
Adenohypohysis/anterior pituitary:
true endocrine gland
Portal System
A vascular channel that begins in one set of capillaries and runs to another without coursing through the heart in between
Hypothalamus controls pituitary hormone secretion
Hypothalamus synthesises pituitary hormones
Pineal gland
Suprachiasmic nucleus (SCN) neurons in hypothalamus: establish circadian rhythms of neuronal activities
Retinohypothalamic tract –> SCN–> pineal gland –> Δ Melatonin synthesis
Melatonin (“hormone of darkness) synthesis increases 10x at night
Chemical messenger for light dark cycle and biological clock
Powerful antioxidant, decreasing reactive oxygen species
Jetlag-treatment (taken as pill it also induces sleep)
Other functions: effect on ovulation and spermatogenesis
Basal ganglia
Orientation, proximity to III ventricle
Basal nuclei/basal ganglia
1 of 3 grey matter structures in cerebrum (cortex, limbic system)
Complex role in controlling movement:
Inhibiting muscle tone
Maintaining purposeful motor activity, supressing unwanted patterns
Monitor and coordinate slow and sustained contractions (posture) eg erector spinae
No direct effect on efferent motorneurons, but modifying pathway activity
Tremendous nr of fibers
Strategic interconnections between: basal nuclei, thalamus, cortex
Thalamus: positive reinforcement of voluntary movements, basal nuclei inhibit it
PD
Destruction of dopaminergic neurons projecting into the basal ganglia –> 3 types of motor disturbance:
1. rigidity (increased muscle tone)
2. involuntary, unwanted movements (resting tremor)
3. slowness in initiating, changing and terminating motor behaviour