The Central Nervous System

• The central nervous system (CNS) includes the brain and spinal cord.
• The CNS is involved in movement, sensory information interpretation, homeostasis maintenance, and functions related to the mind.

Overview of CNS Functions

• Nervous system functions include motor and sensory functions.
• Motor functions involve stimulating muscle cell contraction or gland secretion, which is a function of the peripheral nervous system (PNS).
• Sensory functions involve detecting sensations within and outside the body and is also a function of the PNS.
• Integrative functions are exclusive to the CNS and involve decision-making processes that include interpreting sensory information, planning and monitoring movement, maintaining homeostasis, and higher mental functions (language and learning).

Basic Structure of the Brain and Spinal Cord

• The brain is a soft, whitish-gray organ, anatomically continuous with the spinal cord and resides in the cranial cavity.
• The brain directly or indirectly controls most of the body's functions.
• The brain weighs between 1250 and 1450 grams and is made of mostly nervous tissue, as well as epithelial and connective tissues.
• The ventricles are internal cavities filled with cerebrospinal fluid.
• The brain receives about 20% of total blood flow during rest, reflecting its need for oxygen, glucose, and nutrients.
• The brain consists of four divisions: cerebrum, diencephalon, cerebellum, and brainstem. It is distinct in type of input received and where output is sent.
• The cerebrum is the enlarged superior portion of the brain and is divided into left and right cerebral hemispheres.
• Each cerebral hemisphere is further divided into five lobes and contains neurons that perform specific tasks.
• The cerebrum's key roles include higher mental function (learning, memory, personality, cognition, language, and conscience) and sensation and movement.
• The diencephalon lies deep underneath the cerebral hemispheres and forms the central core of the brain.
• The diencephalon has four distinct structural and functional parts and is responsible for: Processing/integrating/relaying information to different parts of the brain, homeostatic functions, regulating movement, and maintaining biological rhythms.
• The cerebellum is the posterior and inferior portion of the brain which is heavily involved in the planning and coordination of movement, especially complex activities
• The cerebellum is divided into left and right hemispheres.
• The brainstem connects the brain to the spinal cord and is involved in basic involuntary homeostatic functions, controlling certain reflexes, monitoring movement, and integrating and relaying information to other parts of the nervous system.
• The spinal cord is a tubular organ enclosed within the vertebral cavity that blends with the inferior portion of the brainstem and ends between the first and second lumbar vertebrae.
• The spinal cord spans 43–46 cm (17–18 inches) in length and ranges from 0.65–1.25 cm (0.25–0.5 inches) in diameter.
• The central canal is an internal cavity within the spinal cord that is contiguous with the brain's ventricles and filled with cerebrospinal fluid.
• White matter has myelinated axons which exists in the brain and spinal cord.
• Each lobe of the cerebrum contains bundles of white matter (tracts) and receives input from/sends output to clusters of cell bodies and dendrites in cerebral gray matter (nuclei).
• Spinal cord contains white matter tracts, thus shuttles information processed by nuclei in spinal gray matter.
• Gray matter, found in both the brain and spinal cord, contains neuron cell bodies, dendrites, and unmyelinated axons.
• The outer few millimeters of the cerebrum is gray matter, with deeper portions of the brain consisting mostly of white matter and gray matter scattered throughout.
• The spinal cord has mostly gray matter (in the cord center) which processes information and is surrounded by tracts of white matter (outside) for relaying information to and from the brain.
• Communication between gray and white matter connects different regions of the brain and spinal cord via myelinated axons for near instantaneous communication between locations.
• The spinal white matter is superficial, and brain white matter is deep.

Myth of Brain Differences Between the Sexes

• Humans are sexually dimorphic and have differences in physical characteristics that extend beyond the reproductive system.
• Scientists have been trying to prove existence of male and female brains.
• Men, on average, have higher visual-spatial intelligence, whereas women, on average, have higher verbal-emotional intelligence.
• The evidence suggests this is due to neuroplasticity.
• Socialization influences neural network development.
• Engaging in sports or building activities encourages development of visual-spatial skills, while participating in imaginative play fosters verbal-emotional skills.
• These sex differences in cognitive patterns become statistically insignificant when testing very young children.
• MRI studies show vastly dissimilar brain maps between sexes, but when maps are corrected for inconsistencies, differences virtually disappear.
• It has long been held that the hippocampus is larger in females relative to males, accounting for higher emotional intelligence, when recent studies suggest no significant size difference.

The Cerebrum

• The cerebrum is responsible for higher mental functions.
• Cerebrum's gross anatomical features include sulci which are shallow grooves on the surface of the cerebrum, and gyri which are elevated ridges found between sulci
• Sulci and gyri together increase surface area of the brain to maximize limited space within the confines of the skull.
• Fissures are deep grooves on the surface of the cerebrum.
• The longitudinal fissure is a long, deep groove that separates the left and right cerebral hemispheres.
• A cavity exists deep within each cerebral hemisphere, whereby the right hemisphere surrounds the right lateral ventricle, with the left hemisphere similarly surrounding the left lateral ventricle.
• Five lobes are found in each hemisphere of the cerebrum.
• Frontal lobes are most anterior and responsible for planning and executing movement and complex mental functions such as behavior, conscience, and personality.
• Parietal lobes are just posterior to frontal lobes. Neurons within are responsible for processing and integrating sensory information/function in attention.
• Temporal lobes are lateral surfaces of each cerebral hemisphere and involved in hearing, language, memory, and emotions.
• Occipital lobes are the posterior aspect of each cerebral hemisphere; neurons are for processing everything related to vision.
• Insulas are located deep underneath lateral fissures. Neurons there are currently thought to be involved in functions related to taste and viscera (internal organs)
• The cerebral cortex consisting of gray matter is functionally the most complex part of the brain, covers the underlying cerebral hemispheres, and is known as neocortex.
• Neocortex is the most recently evolved region and has a huge surface area.
• The cortex is composed of six layers (of neurons and neuroglia) of variable widths and are all interneurons.
• Neocortex functions revolve around conscious processes like planning movement, interpreting sensory information, and complex higher functions.
• Neocortex is divided into three areas: primary motor cortex, primary sensory cortices, and association areas.
• The primary motor cortex plans and executes movement.
• Primary sensory cortices are the first regions to receive and process sensory input.
• Association areas integrate different types of information that include unimodal and multimodal integrations.
• Unimodal areas integrate one specific type of information.
• Multimodal areas integrate information from multiple different sources to carry out many higher mental functions.
• Multimodal association areas perform complex mental functions.
• Two areas process language: Broca's area & Wernicke's area
• Broca's area is a pre-motor area in the anterolateral frontal lobe with the ability to produce speech sounds.
• Wernicke's area is an integrative speech area in the temporal and parietal lobes with the ability to understand language.
• The prefrontal cortex occupies most of the frontal lobe and communicates with the diencephalon, other regions of cerebral gray matter, and association areas located in other lobes.
• Its functions include modulating behavior, personality, learning, memory, and an individual's personality state.
• Parietal and temporal association areas occupy most of their respective lobes with multiple functions including integration of sensory information, language, maintaining attention, recognition, and spatial awareness.
• Basal nuclei are deep within each cerebral hemisphere and are clusters of neuron cell bodies that function to control movement which is separated from the diencephalon by a region known as the internal capsule.
• The basal nuclei include caudate nuclei, putamen, and globus pallidus.
• Caudate nuclei are C-shaped rings of gray matter and lateral to the lateral ventricle of each hemisphere with an anteriorly oriented tail.
• The putamen is posterior and inferior to the caudate nucleus and connected to the caudate nucleus by small bridges of gray matter whose combination is called the corpus striatum.
• The globus pallidus is medial to the putamen.
• Cerebral white matter connects the right and left hemispheres and is classified as commissural fibers with the largest category being corpus callosum which is in the middle of the brain and at the base of the longitudinal fissure.
• Projection fibers connect the cerebral cortex of one hemisphere with other areas of the same hemisphere, other parts of the brain, and the spinal cord.
• Corona radiata fibers spread out in a radiating pattern and condense around the diencephalon to form two V-shaped bands (internal capsules).
• Association fibers are restricted to a single hemisphere and connect gray matter of cortical gyri with one another.

The Cerebrum and Limbic System

• Information is transferred by the conduction of action potential from one region of the brain to another.
• First, action potential originates in gray matter.
• Second, the potential is sent to another area of gray matter by projection fibers.
• Third, a new action potential is generated by gray matter that spreads to neighboring gray matter by association fibers.
• Fourth, the action potential can be sent to the other cerebral hemisphere by commissural fibers.
• The limbic system is an important functional brain system that includes the limbic lobe (region of medial cerebrum), hippocampus, amygdala, and pathways where each region of gray matter connects with the rest of the brain.
• The limbic system is found only within mammalian brains and is involved in memory, learning, emotion, and behavior.
• The limbic lobe (and associated structures) form a ring on the medial side of the cerebral hemisphere that contains two main gyri: cingulate gyrus and parahippocampal gyrus.

The Diencephalon

• The diencephalon exist at the physical center of the brain with four components, each with its own nuclei that receives specific input/send output to other regions.
• The diencephalon includes the Thalamus, Hypothalamus, Epithalamus, and Subthalamus.
• The thalamus is the main entry route of sensory data into the cerebral cortex
• Consists of two egg-shaped regions of gray matter and constitutes 80% of diecephalon.
• The third ventricle is between these two thalamic regions.
• Thalamic nuclei receive afferent fibers from many other regions of the nervous system, excluding the sense of smell.
• The thalamus regulates cortical activity by controlling which input should continue to the cerebral cortex.
• Each half of the thalamus has three main groups of nuclei separated by thin layers of white matter: Specific nuclei, Association nuclei, and Nonspecific nuclei
• The hypothalamus is a collection of nuclei anterior and inferior to the larger thalamus.
• Neurons perform several vital functions critical to survival like the regulation of the autonomic nervous system, sleep/wake cycle, thirst & hunger, and body temperature.
• The inferior hypothalamus is anatomically and functionally linked to the pituitary gland by the infundibulum and is made up of posterior endocrine tissue.
• The hypothalamus secretes releasing and inhibiting hormones to affect pituitary gland causing it to affect activities of other endocrine glands throughout body.
• The hypothalamus releases antidiuretic hormone (for water balance) and oxytocin (for stimulation of uterine contraction during childbirth)
• Input to the hypothalamus arrives from many sources including the cortex and basal nuclei.
• Mammillary bodies connect the hypothalamus with the limbic system and receive input from the hippocampus for memory regulation and behavior.
• Input from outside the nervous system along with that from the endocrine system provides the hypothalamus with information from receptors that detect body temperature and osmotic concentration of blood.
• The epithalamus is superior to the thalamus and mostly includes the pineal gland (endocrine gland) which secretes melatonin, a hormone involved in the sleep/wake cycle.
• The subthalamus is inferior to the thalamus and functionally connected with basal nuclei which together control movement.

Cerebellum

• The cerebellum is the posterior and inferior portion of the brain that is functionally connected with the cerebral cortex, basal nuclei, brainstem, and spinal cord to coordinate movement.
• The Cerebellum divides anatomically into two cerebellar hemispheres which are connected by the vermis.
• Ridges (folia) cover the exterior cerebellar surface and are separated by shallow sulci that increase surface area of the region.
• The cerebellum has three lobes: anterior, posterior, and flocculonodular.
• The cerebellar cortex is the outer layer of gray matter that is extremely folded and with branching white matter (arbor vitae) for branches.
• White matter contains clusters of gray matter scattered throughout, and it converges into three large tracts (cerebellar peduncles) as the main connection between the cerebellum and the brainstem.

The Brainstem

• The brainstem serves as one of the oldest components of the brain, and is essential to immediate survival.
• Nuclei control basic homeostatic functions, reflexes (automatic responses to stimuli) in movement, sensation, and maintaining alertness
• The location of brainstem is inferior to the diencephalon, anterior to the cerebellum, and superior to spinal cord.
• There are three subdivisions: superior midbrain, middle pons, and inferior medulla oblongata.
• Fibers of the cerebellum and related nuclei travel through portions of the brainstem.
• Nuclei of the reticular formation are a group of connected nuclei that are scattered throughout the brainstem.
• The nuclei carry out many functions including the regulation of respiration, blood pressure, sleep/wake cycle, pain perception, and consciousness.
• The white matter tracts are those that carry impulses between the spinal cord and brain.
• Cranial nerve nuclei are in the brainstem involved in many cranial nerves with sensory, motor, and autonomic responsibilities.

Midbrain

• The midbrain is inferior to the diencephalon and surrounds the cerebral aqueduct (which connects the third and fourth ventricles).
• Also known as the mesencephalon, which is recognized as the shortest and most superior brainstem region.

Pons

• The Pons are inferior to the midbrain.
• The prominent anterior surface contains descending motor tracts to spinal cord.
• Other tracts enter the cerebellum by way of the middle cerebellar peduncle.
• The reticular formation and cranial nerve nuclei are posterior to these tracts.

Medulla Oblongata

• The Medulla Oblongata is inferior to the pons.
• It is also most inferior structure of the brainstem, continuous with the spinal cord at the foramen magnum.
• The reticular formation is one of the most complex regions of the brain and consists of 100 nuclei in the central core of three brainstem subdivisions.
• Input is received from multiple sources including the cerebral cortex, limbic system, and sensory stimuli
• Output is sent throughout the entire brain and spinal cord