Neuropsychology: Brain Structure and Cells

• The information provided relates to neuropsychology, specifically, the cellular and basic structure of the human brain.

Neurons

• Nerve cells are not capable of replenishing themselves.
• Sprouting, the growth of nerve fibers to make new connections, can still occur in remaining portions of neurons or other neurons.
• A structure of a typical neuron includes: Dendrites, Cell body, Nucleus, Axon, Myelin Sheath, Node of Ranvier, Schwann cells, Axon Terminals, Synapse.
• Dendrites transmit impulses to the cell.
• The axon transmits impulses from the cell.
• Axon terminals contain neurotransmitters, which influence the activity of other cells when released.
• A synapse is the point of interaction between two cells.
• The estimated total possible connectivity among neurons in the human brain is approximately 10^15, more than the known stars.

Glial Cells

• Glial cells outnumber neurons 10 to 1, but are smaller.
• Neurons and glial cells each account for 50% of the volume of the nervous system.
• Glial cells serve as "nerve glue."
• Glial cells supply nutrients and oxygen to neurons.
• Glial cells remove neurons destroyed by injury or disease.
• Some glial cells are thought to direct and regulate neuronal behavior.
• Most tumors that invade the brain arise from glial cells and are termed 'gliomas'.

Color of the Nervous System

• Grey matter contains capillary blood vessels and cell bodies of neurons.
• White matter contains axons, which are covered in insulating glial cells composed of a fatty substance that makes them look white.
• A nervous system rich in axons has a white appearance.
• Reticular matter consists of cell bodies and axons mixed together, resulting in a mottled grey and white color. Reticular is from the Latin "rete" meaning "net".
• Nucleus is a large number of cell bodies grouped together.
• Tract is a large collection of axons.

Anatomical Terms

• Central Nerves are located in the brain and spinal cord.
• Cranial nerves go from your brain to your eyes, mouth, ears, and other parts of your head.
• Peripheral nerves go from your spinal cord to your arms, hands, legs, and feet.
• The Central Nervous System (CNS) and the Peripheral Nervous System (PNS) are differentiated based on the location of nerves.
• There are 12 pairs of cranial nerves and 30 pairs of spinal nerves.
• The Voluntary Nervous System/Somatic is part of physiologic function; nerves connect the CNS with muscles and skin.
• Also part of physiologic function is the Autonomic Nervous System, whose nerves connect the CNS with smooth muscles, heart muscles, and glands.
• ANS (Autonomic Nervous System) = Sympathetic NS (alerts body and preps for action) and Parasympathetic NS (relaxes body, slows down functions).
• Anatomical Direction terms include: Rostral, Caudal, Dorsal, Ventral, Anterior or Frontal, Posterior, Lateral, and Medial.
• Rostral, Caudal, Dorsal, and Ventral are relative to body parts.
• Anterior or Frontal, Posterior, Lateral, and Medial are relative to location.
• Brain section terms include: Coronal, Horizontal, and Sagittal.

Directional Terms

• Ipsilateral: same side.
• Contralateral: opposite sides.
• Bilateral: both sides.
• Proximal: close to each other.
• Distal: far from each other.
• Afferent: approaching center.

Meninges

• Meninges are membranes covering the brain and spinal cord.
• The layers of the meninges are: the Dura mater (2 layers), Arachnoid, and Pia mater.
• The Dura Mater has tentorium, which separates the cerebellum from the overlying cerebrum.
• The Dura Mater has falx cerebri, which protrudes down through dorsal parts of two cerebral hemispheres.
• The Arachnoid layer has a cobweb-like appearance and is delicate and soft. It is separated from the subdural space and pia mater.
• The Pia Mater is thin and delicate.

CSF and Ventricles

• CSF, or Cerebrospinal Fluid, is in the subarachnoid space.
• CSF immerses the brain in liquid, reducing the nett weight from 1.4kg to 80 grams.
• The Ventricles are hollow, interconnected chambers filled with CSF.
• CSF is manufactured from blood plasma in the choroid plexus (vascular structures which protrude into each ventricle).
• CSF is produced continuously, with a total volume of about 125ml.
• The continuous production of CSF necessitates a mechanism for its removal.

Blood Supply and Drainage

• Vertebral Arteries supply blood to the posterior portion of the brain.
• Internal Carotid arteries supply blood to the anterior part of the brain.
• Venous drainage from the brain occurs via the large internal jugular veins.
• There is a need for continuous supply of blood to brain as it cannot store fuel, nor extract energy without oxygen.
• A few minutes without blood to brain will result in permanent brain damage.

Spinal Cord

• Spinal Cord segments are linked with organs and muscles of a specific body segment.
• There are 30 segments: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral.
• Types of spinal cord activity: Spinal reflex (withdrawal in response to heat, pain, pressure) and channeling of information between the periphery.

Brain Organization

• Forebrain includes the Diencephalon (Thalamus, hypothalamus), Telencephalon (Limbic system, basal ganglia, cerebrum/neocortex).
• Midbrain includes the Tectum (roof) and Tegmentum (floor).
• Hindbrain includes the Medulla Oblongata, Reticular Formation, Pons, and Cerebellum.

Forebrain

• The outer layer, or cerebrum/neocortex, consists of four to six layers of cells and their synaptic connections (grey matter), beneath which are axon pathways (white matter).
• Cortex labeling should only be used for the outer layer of cells.
• Fissures are labeled if they are deep enough to dent ventricles.
• Sulcus are shallower clefts.
• Gyri are ridges.
• Parietal Lobe functions include intelligence, language, sensation, and reading.
• Occipital Lobe function is vision.
• Cerebellum functions include balance and coordination.
• Brain stem functions include breathing, blood pressure, heartbeat, swallowing, and consciousness.
• Frontal Lobe functions include movement, intelligence, behavior, and memory.
• Temporal Lobe functions include speech, behavior, memory, hearing, and vision.