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• Chapter 14 delves into the grey matter of the spinal cord and brain, the structures of the brain.

Objectives:

• Describe the anatomical and physiological differences between white and grey matter.
• List and describe the components of the midbrain and hindbrain.
• Describe the types of tracts in cerebral white matter.
• Describe the composition and organization of the cerebral cortex.
• Describe the functions of the limbic system.
• Explain the process of memory processing and storage.
• Describe the properties behind EEGs and their significance.

Grey Matter vs. White Matter

• Grey matter comprises neurosomas, dendrites, synapses, and the cortex, which is an integration center.
• White matter consists of tracts of axons, myelinated axons, and relays signals.

Cerebral Cortex

• The cerebral cortex is the brain's surface layer and grey matter of the telencephalon.
• Stellate cells are spherical with short dendrites and axons and receive input from afferent fibers.
• Pyramidal cells synapse with other cortical neurons and output neurons. Some axons leave the cortex.
• The thickness of the cerebral cortex varies based on the function of the area.

Cerebral White Matter

• Cerebral white matter takes up the largest brain volume.
• Glia and myelinated fibers transmit signals between and within areas.
• Projection tracts are vertical tracts.
• Commissural tracts bridge between hemispheres, including the corpus callosum.
• Association tracts connect regions within the same hemisphere.

Hindbrain

• The medulla oblongata is part of the myelencephalon.
• The medulla oblongata includes pyramids.
• Axons of gracile and cuneate fasciculi (nuclei) are sensory. These decussate to the medial lemniscus and then to the thalamus and cortex.
• Corticospinal tracts are motor (anterior).
• The inferior olivary nucleus acts as a relay center, sending signals from the brain and spinal cord to the cerebellum.
• Pons are part of the metencephalon.
• Cerebellar peduncles connect the pons and mesencephalon to the cerebellum.
• Transverse and longitudinal tracts run from the cerebellum to the cerebellum, carrying sensory information up.
• The pons facilitates hearing, equilibrium, facial sensation, chewing, salivation, urination.
• Cranial nerves 5-8 are associated with the pons, enabling facial sensation, motor functions, taste, equilibrium, and hearing.
• Trigeminal enables facial sensory and mastication abilities.
• Abducens enables eye abduction..
• Facial nerve enables taste and expressions.
• Vestibulocochlear nerve mediates hearing and equilibrium.

Midbrain

• The midbrain is also known as the mesencephalon.
• It contains the corpora quadrigemina and the tectum, circled by grey matter.
• Cerebral peduncles are present in the midbrain.
• The oculomotor nucleus is located in the midbrain, relating to cranial nerves III and IV.
• Reticulospinal tracts related to pain are found in the midbrain, as well as the red nucleus and blood vessels.
• Tracts with the cerebellum are found in the midbrain, involved with fine motor control.
• Substantial Nigra inhibits motor movement to the thalamus
• Cerebral crus contains corticospinal tracts.

Reticular Formation (RF)

• The reticular formation is found in the brainstem, specifically in the midbrain, pons, and medulla oblongata.
• It controls somatic motor functions through reticulospinal tracts.
• It regulates posture and balance during movement.
• It contains networks of central pattern generators (CPGs) for breathing and throat muscles.
• It controls pain by using pain signals and inhibitory neurons.
• The reticular formation projects into the thalamus, controlling signals reaching the cerebrum.
• It helps regulate alertness and affecting sleep and consciousness.
• Damage to the reticular formation can lead to irreversible coma.
• The reticular formation is involved in habituation, i.e. learning which signals are important.

Cerebellum

• The cerebellum comprises 10% of the brain's mass but possesses 60% of its surface area and over 50% of all brain neurons.
• It is crucial for muscle coordination and evaluates sensory input with muscle movement.
• The cerebellum contributes to equilibrium and balance.
• It also contributes to tactile exploration and understanding the 3D aspects of objects, time coordination, and sound interpretation & language output.

Thalamus

• The thalamus is part of the diencephalon.
• It serves as a gateway to the cerebral cortex.
• Input to the cerebrum, including smell, vision, taste, touch, pressure, and temperature, passes through the thalamus.
• The thalamus filters out unimportant information.
• It receives information from basal nuclei and refines and modulates signals.
• The Thalmus sends information to the cortex and controls descending motor pathways.
• The thalamus contributes to memory functions.

Hypothalamus

• The hypothalamus is part of the diencephalon and is located beneath the thalamus.
• It serves as the endocrine control center.
• The Hypothalamus regulates homeostasis, secretes hormones (controlling the anterior pituitary), integrates with autonomic regions, and is involves in thermoregulation, regulating hunger and thirst, and part of memory pathways.
• The paraventricular nucleus produces oxytocin.
• The supraoptic nucleus prodices ADH.
• The anterior nucleus regulates thirst.
• The ventromedial nucleus regulates hunger.
• The preoptic nucleus controls reproductive function and hormones.
• The suprachiasmatic nucleus functions as a biological clock and controls reproductive cycles.
• The mammillary nucleus regulates long-term memory.
• Optogenetics uses light-gated ion channels to control the activity of genetically modified neurons in living animals.

Limbic System

• The limbic system is paired.
• It includes a loop of fiber tracts and feedback loops.
• It is implicated in emotion, learning and memory.

Memory

• The hippocampus integrates sensory and cognitive experiences.
• It learns from sensory input during an experience and processes short-term memories.
• Memory is relayed repeatedly during sleep.
• It also sends long term memories to the cortex for memory consolidation.
• Memory storage includes vocabulary and memory of faces and objects, stored in the superior temporal lobe.
• Memory related to plans and social roles is stored prefrontal lobe.
• Lesions to the hippocampus result in anterograde amnesia.
• Surgical removal of hippocampi impairs the the the ability to form new memories, but does not effect old memories or intelligence.

Electroencephalogram (EEG)

• An electroencephalogram (EEG) measures rhythmic voltage changes, including postsynaptic potentials in the superficial cortex layer.
• It helps study brain function during sleep and wakefulness.
• It helps diagnose brain diseases, tumors, and trauma.
• It measures voltage fluctuations and determines normal from abnormal brain activity.
• Alpha waves are present when awake and resting, particularly in the parietal-occipital region.
• Beta waves show mental activity and sensory stimulation, mainly in the frontal-parietal regions.
• Theta waves are seen in children and tired adults. Abnormal amounts in adults indicates stress or disorder.
• Delta waves occur during deep sleep in adults and indicate major brain damage if dominant when awake.