Nervous System and Blood-Brain Barrier Quiz

Functional Organisation of the Nervous System

• The nervous system has overall functions that need to be described
• Different classes of neurons make up the nervous system, requiring description
• Brain components and their major functions should be described

Divisions of the Nervous System

• Nervous System (NS) is divided into Peripheral and Central NS
• Peripheral NS is further divided into Autonomic and Somatic NS
• Autonomic NS is involuntary; somatic NS is voluntary
• Autonomic NS has sympathetic and parasympathetic branches.
• Central NS is further divided into brain and spinal cord
• The brain is further divided into forebrain, midbrain, and hindbrain.
• Forebrain is made up of telencephalon and diencephalon.
• Telencephalon consistes of cerebral cortex, basal ganglia, hippocampus & amygdala
• Diencephalon includes thalamus and hypothalamus
• The midbrain is composed of mesencephalon, with tectum and tegmentum.
• Metencephalon consist of pons & cerebellum
• Myelencephalon consists of medulla

Functional classes of Neuron

• Afferent neurons carry information from external or internal environment to the CNS.
• Efferent neurons carry instructions from CNS to effector organs (muscles/glands).
• Interneurons are entirely within CNS; integrating and formulating responses
• Higher mental function is associated with interneurons (thoughts, emotions, memory, creativity, intellect, motivation)

Glial Cells

• Glial cells form connective tissue in CNS and support interneurons physically, metabolically, and functionally
• Glial cells do not conduct nerve impulses
• Four types of glial cells:
  • Astrocytes: form blood-brain barrier (BBB), neural scar tissue, and maintain optimal ion conditions.
  • Oligodendrocytes: form myelin sheath around axons in CNS.
  • Microglia: phagocytosis (immune defense cells in the CNS) and release nerve growth factor.
  • Ependymal cells: form cerebrospinal fluid (CSF) and work as neural stem cells.

Cerebral Cortex

• The cerebrum is divided into left and right hemispheres.
• Corpus callosum connects the hemispheres
• White matter consists of myelinated axons that interconnect.
• Gray matter is the outermost layer, organized into functional columns.
• Each column coordinates distinct functions
• Differences in input/output and layering result in differing cognitive functions
• Lobes include Frontal, Parietal, Temporal, and Occipital lobes

Voluntary Motor Activities

• Frontal lobe enables voluntary motor activities, speech, and thought.
• Stimulation in primary motor cortex moves body parts.
• Parietal lobe processes somatosensory and proprioceptive input.
• Each region receives input from a specific body part (typically opposite side).
• Temporal lobe processes auditory input.
• Occipital lobe processes visual input.

Basal Nuclei

• Also known as basal ganglia, these are masses of gray matter deep within the white matter.
• They modify motor pathways, controlling muscle tone, and initiating voluntary movement.
• Damage can lead to Parkinson's disease, characterized by increased muscle tone, rigidity, tremors, and slowness of movement.

Diencephalon: Thalamus & Hypothalamus

• Thalamus is a relay station for sensory input to the cerebral cortex.
• It directs attention and integrates motor control.
• Hypothalamus is involved in homeostasis (regulating temperature, thirst, urine production, food intake), pituitary hormone secretion, uterine contractions, milk production.
• The hypothalamus also functions within the Autonomic Nervous System (ANS) and helps regulate sleep-wake cycles, emotional & behavioural patterns.

Limbic System

• Several forebrain structures function together for emotional & behavioral aspects
• These include cingulate gyrus, hippocampus, amygdala, basal nuclei, thalamus & hypothalamus
• They play roles in learning, memory and emotional states.

Cerebellum

• The cerebellum is a highly folded, posterior portion of the brain, with roles in balance, and planning/executing voluntary movement.
• Three main areas coordinate movement (cerebrocerebellum, vestibulocerebellum & spinocerebellum)
• Cerebrocerebellum plans and coordinates movements + storing procedural memories
• Vestibulocerebellum manages balance & eye movements
• Spinocerebellum coordinates muscle tone.
• Damage causes issues with movement.

Brain Stem

• The brain stem connects the rest of the brain to the spinal cord
• Cranial nerves originate from the brain stem
• Neuronal clusters control heart rate, blood vessels, respiration, swallowing, and posture
• Reticular formation integrates sensory info.
• Also involved in sleep, pain transmission & awakening.

Spinal Cord

• The spinal cord extends from the brain stem and acts as a critical connection.
• It has two vital functions: neuronal links between brain and PNS and spinal reflexes.
• 31 pairs of spinal nerves emerge, passing through spaces between vertebrae (Cervical, Thoracic, Lumbar, Sacral, & Coccygeal nerves)
• Spinal nerves are further divided into dorsal and ventral branches.

Cerebrospinal Fluid (CSF)

• CSF cushions and protects the CNS from injury.
• CSF is fluid produced by choroid plexus in the brain ventricles, circulating throughout brain and spinal cord.
• CSF is mostly water with a composition very different to blood
• CSF is then filtered and reabsorbed into venous blood
• Brain damage can arise if CSF pathways are blocked or abnormal cerebrospinal fluid build up.

Blood-Brain Barrier (BBB)

• The BBB is a protective barrier between blood and brain
• Tight junctions and capillaries prevent harmful substances from entering the brain tissue.
• Astrocytes help regulate this barrier allowing some substances to pass through actively or passively
• BBB's tight junctions regulate movement of most substances.

Brain Nourishment

• Brain cells rely on glucose as major fuel while being unable to store glucose
• Glucose transport is vital for cellular ATP
• The brain is highly dependent on blood supply for oxygen and glucose while needing consistent blood supply
• The brain switches to ketones for fuel during starvation to preserve glucose
• Lack of adequate glucose and oxygen causes severe damage.