Overview
This lecture covers the structure and functions of the diencephalon and cerebrum, highlighting their regions, major roles, and key anatomical features.
Diencephalon Structure and Functions
- The diencephalon is a central brain region acting as a relay center between the brain stem and cerebrum.
- It includes four regions: thalamus, epithalamus, hypothalamus, and subthalamus.
Thalamus
- The thalamus consists of paired gray matter masses beside the third ventricle.
- It relays all sensory info except smell and directs signals to proper brain areas.
- Functions include sensory processing, arousal, and consciousness.
Epithalamus
- The epithalamus is part of the diencephalon's roof and controls the pineal gland.
- The pineal gland releases melatonin, which regulates sleep-wake cycles.
Hypothalamus
- Located anteriorly and inferiorly, the hypothalamus maintains homeostasis and regulates hormone release.
- It controls the endocrine system by secreting hormones that regulate the anterior pituitary.
- The HPA axis: stress triggers CRH release, stimulating ACTH release, which prompts the adrenal cortex to produce cortisol.
- Produces antidiuretic hormone (reduces water loss) and oxytocin (social bonding, labor contractions).
- Regulates the autonomic nervous system (heart rate, blood pressure, digestion, respiration).
- Controls body temperature via shivering and sweating.
- Responsible for hunger and thirst sensations.
- Regulates sleep-wake cycles through melatonin release.
- Links the limbic system (emotions/memories) to physical responses.
Subthalamus
- The subthalamus, between thalamus and midbrain, is part of the basal nuclei involved in movement regulation.
Cerebrum Structure and Functions
- The cerebrum is the largest brain region, managing voluntary movement, intelligence, reasoning, memory, and sensory perception.
- The cerebral cortex is the outer gray matter with neuron cell bodies, dendrites, and unmyelinated axons.
- Gyri (folds) and sulci (grooves) increase cortical surface area for more processing power.
- The cerebrum has left and right hemispheres, each controlling the opposite side of the body.
- Hemispheres show lateralization, with some functions (e.g., speech) more dominant on one side.
- Hemispheres are divided by the longitudinal fissure and separated further by central and lateral sulci.
Lobes of the Cerebral Hemisphere
- Frontal lobe: voluntary movement, concentration, speech, planning, memory, personality.
- Parietal lobe: general sensation, object shape/texture evaluation.
- Occipital lobe: visual processing and memory.
- Temporal lobe: hearing and smell processing.
- Insula: deep lobe involved in self-awareness, perception, and cognition.
Key Terms & Definitions
- Diencephalon — central brain region acting as a relay for sensory and motor signals.
- Thalamus — relay station for most sensory information.
- Epithalamus — contains pineal gland, regulates melatonin.
- Hypothalamus — regulates hormones, homeostasis, and links emotions to physiological responses.
- Subthalamus — part of basal nuclei, involved in movement.
- Cerebrum — largest brain part, responsible for higher brain functions.
- Cerebral Cortex — outer layer of cerebrum with gray matter.
- Gyrus (gyri) — folds of the cerebral cortex.
- Sulcus (sulci) — grooves between gyri.
- Longitudinal Fissure — deep groove separating cerebral hemispheres.
- Central Sulcus/Lateral Sulcus — grooves separating brain lobes.
- Lateralization — functional differences between the two cerebral hemispheres.
Action Items / Next Steps
- Review brain region diagrams and label the diencephalon and cerebrum lobes.
- Prepare for upcoming lecture on hormones and the endocrine system.
- Read about the autonomic nervous system for more detail.