The Brain and Central Nervous System

• The body's organs include the brain, spinal cord and various nerves.
• Organs can be divided into the central nervous system (CNS) and the peripheral nervous system (PNS).
• The CNS includes the brain and spinal cord.
• The PNS includes nerves.

The Brain

• The brain is one of the body's largest organs.
• The brain coordinates most bodily activities.
• Thought, memory, judgment, and emotion are controlled and based in the brain.
• Different brain portions regulate the body, such as temperature and breathing.
• The brain is contained in the skull.
• The brain weighs 1300-1400 g.
• The brain is made up of about 1000 billion neurons.
• Each neuron is surrounded by roughly 10 glial cells, also known as neuroglia.
• Neurons are not able to multiply.
• Many neurons are lost every day in life, but glial cells can multiply throughout the life.
• Meninges cover the brain like the spinal cord including outer duramater, middle arachnoidmater & inner piamater.

Brain Ventricles

• Cavities in the brain are called ventricles.
• Ventricles are filled with cerebrospinal fluid.
• There are four brain ventricles.
• Two lateral ventricles reside in two brain hemispheres.
• The third ventricle lies between the hypothalamus and thalamus.
• The fourth ventricle lies between the brain stem and cerebellum.
• The fourth ventricle is continuous with the central cavity of the spinal cord.

Brain Parts

• The brain consists of the cerebrum, cerebellum, brain stem, and diencephalon.
• The cerebrum includes right and left cerebral hemispheres.
• The brain stem includes the medulla, pons, and midbrain.
• The diencephalon includes the thalamus, hypothalamus, epithalamus, and pineal gland.

Cerebrum

• The largest section of the brain is the cerebrum.
• The cerebrum is located in the brain's upper portion.
• The cerebrum processes thoughts, judgment, memory, problem solving, language, and imaginations.
• The cerebrum's superficial layer is the gray matter called the cerebral cortex.
• The cerebral cortex is 2-4 mm thick and contains billions of neurons.
• Cortical region roles and folds upon itself during embryonic development as brain size increases rapidly and the cortex's gray matter enlarges faster than deeper white matter.
• Folds are called gyri, or convolutions
• The deepest grooves between the folds are called "fissures."
• Shallower grooves between folds are called "sulci."
• The longitudinal fissure separates the cerebrum into right and left halves called cerebral hemispheres.
• Each hemisphere has 4 lobes.
• The cerebrum is subdivided into the left and right hemispheres which are connected by a bridge of nerve fibers that relay information, called the "corpus callosum."
• The left hemisphere controls the right side of the body.
• The right hemisphere controls the body's left side.

Cerebrum Lobes

• The frontal lobe is the cerebrum's most anterior portion, under the forehead.
• The central sulcus separates the frontal and perital lobe.
• The Frontal lobe controls motor function, personality, and speech.
• The Frontal lobe is the center of reasoning, planning, some parts of speech, movement, emotions, and problem solving.
• The Frontal lobe is also called the "motor cortex".
• The parietal lobe is the cerebrum's most superior portion, which lies at the top of the head
• The Parietal lobe receives and interprets nerve impulses from sensory receptors and interprets language.
• The Parietal lobe receives sensory input from the skin regarding touch, pressure, temperature, and pain.
• The Parietal lobe is also called the "sensory cortex".
• The occipital lobe is the cerebrum's most posterior portion, located at the back of the head.
• The Occipital lobe receives input from the eyes and controls vision.
• The Occipital lobe is also called the "visual cortex".
• The temporal lobe is the left and right lateral portion of the cerebrum, located on the sides of the head above the ears.
• The Temporal lobe controls hearing and smell.
• The Temporal lobe is also called the "auditory cortex".

Cerebrum Functions

• Motor functions like control of voluntary movements
• Sensory functions like perception of pain, temperature, touch, hearing, taste, and smell
• Controls intelligence, speech, memory, and learning.

Cerebellum

• The cerebellum is the brain's second largest portion.
• The cerebellum is beneath the posterior part of the cerebrum.
• A deep groove known as a transverse fissure separates the cerebrum and cerebellum.
• The cerebellum Coordinates voluntary body movements and maintains balance and equilibrium.
• The external surface, called the cerebellar cortex, resembles a butterfly, with a constricted area called "vermis."
• The lateral wings, or lobes, are called cerebellar hemispheres; they are interconnected by a narrow portion called the vermis.
• Each hemisphere has lobes separated by deep fissures.
• The cerebellum is part of the human brain located in the posterior cranial fossa, inferior to the occipital lobes.
• The cerebellum is 10% of the entire brain's weight.
• The cerebellum contains 50% of the neurons.

Cerebellum Divisions and Layers

• Anterior lobe regulates subconscious aspects of skeletal muscle movements.
• The posterior lobe assists regulating subconscious aspects of skeletal muscle movements.
• The flocculonodular lobe, located on the inferior surface, maintains equilibrium and balance.
• The superficial layer of the cerebellum is called the "cerebellar cortex," consisting of gray matter with slender and parallel folds called "folia."
• Deep to the gray matter, the white matter is called "arbor vitae" and resembles a tree branch.
• Even deeper white matter areas include "cerebellar nuclei", which are regions of gray matter having axons that carry impulses from the cerebellum to other brain parts.

Cerebellar Peduncles

• Cerebellar peduncles attach the cerebellum to the brain stem.
• Bundles of white mater consist of axons that conduct impulses between the cerebellum and other parts of the brain.
• The superior cerebellar peduncle is a paired structure that connects the cerebellum to the midbrain.
• Middle cerebellar peduncles connect the cerebellum to the pons.
• The inferior cerebellar peduncle is a thick rope-like strand that occupies the upper part of the posterior district of the medulla oblongata.

Cerebellum Functions

• Coordinates contractions of skeletal muscles
• Regulates posture & balance
• May play a role in cognition, learning from experiences and language processing

Brain Stem

• Consists of the midbrain, pons, and medulla oblongata.
• It is superiorly continuous with the diencephalon.
• The brain stem is inferiorly continuous with the spinal cord.
• Posteriorly, the pons and medulla are separated by the fourth ventricle.
• The midbrain, pons, and medulla are connected to the cerebellum by superior, middle, and inferior cerebellar peduncles.

Midbrain

• Extends from the pons to the diencephalon and is about 2.5 cm long.
• It acts as a pathway for impulses to be conducted between the brain and the spinal cord.
• It is associated with vision, hearing, motor control, sleep/wake, arousal, and temperature regulation.
• The midbrain serves to screen information before it reaches the high brain structure.
• The midbrain has an anterior part called 'cerebral peduncles'.
• The midbrain has a posterior part called Tectum, containing four rounded elevations/swellings.
• The motor neurons relay inhibitory signals for unwanted body movements.

Midbrain Portions

• The superior colliculi receive input from the retina and the visual cortex and participate in a variety of visual reflexes, particularly the tracking of objects in the visual field.
• The inferior colliculi receive auditory fibers and relay the nucleus of the thalamus.

Midbrain Functions

• The midbrain serves important functions in motor movement, particularly movements of the eye, and in auditory and visual processing.
• Dopamine produced in the substantia nigra and ventral tegmental area plays a role in excitation and motivation.
• The midbrain relays information for vision and hearing.

Pons

• Means bridge and connects the cerebellum to the rest of the brain.
• Located between the midbrain above and the medulla below, in front of the cerebellum.
• Like the medulla, it is also a sensory and motor tract.
• Contains nuclei that deal with respiration, swallowing, bladder control, hearing, equilibrium, eyeball movements, facial expressions, etc.

Medulla Oblongata

• The lowermost part of the brain stem is the continuation of the spinal cord's superior portion.
• Situated at the base of the skull, starting from the foramen magnum and extending to the inferior border of the pons, a distance of about 3 cm.
• The ascending and descending sensory and motor white mater tracts, or nerves, connecting the brain to the spinal cord pass through the medulla oblongata.
• Regulatory centers reside in the medulla oblongata.
• The cardiovascular center regulates heart rate, heartbeat force, and blood vessel diameter.
• The medullary rhythmicity center is responsible for maintaining the basic rhythm of breathing.
• The vasomotor center regulates blood pressure.
• Vomiting, swallowing, cough, hiccups, and sneezing regulatory centers located in the medulla oblongata.
• Five pairs of cranial nerves originate from the nuclei located in the medulla oblongata.

The Diencephalon

• It is the posterior part of the forebrain that connects the midbrain with the cerebral hemispheres
• It encloses the third ventricle
• Includes the Thalamus, Hypothalamus & Epithalamus.

Thalamus

• Composed of a mass of nerve cells.
• The term Thalamus means "inner room" in Greek.
• Located deep in the brain at the top of the brainstem
• Serves as the gateway to the cerebral cortex
• Almost all sensory inputs pass through it to get to the higher levels of the brain.
• The thalamus makes up 80% of the diencephalon.
• It is an important relay station for sensory nerves, which convey pain, temperature, touch, and pressure, from the periphery and/orspinal cord that are first conveyed to thalamus before going to the cerebrum.
• Information is relayed from the thalamus to the cerebrum through thalamic nuclei.
• The median geniculate nucleus is related to hearing
• The lateral geniculate nucleus-related to vision
• The ventral posterior nucleus is related to taste & somatic sensations like touch, pain, pressure, cold, heat, and vibrations.

Hypothalamus

• Sits under the thalamus at the top of the brainstem.
• Although it's small, it controls many critical bodily functions

Hypothalamus Functions

• Controls the autonomic nervous system
• Center for emotional response and behavior
• Regulates body temperature
• Regulates food intake (appetite)
• Regulates water balance and thirst
• Controls sleep-wake cycles
• Controls the endocrine system
• Controls cardiovascular system regulation via heart rate and blood pressure.

Epithalamus and Pineal Gland

• The epithalamus is a small region superior and posterior to the thalamus.
• The epithalamus consists of the pineal gland.
• The pineal gland is pea-sized and protrudes from the posterior midline of the third ventricle.
• It is an endocrine gland that secretes the hormone melatonin.
• Darkness stimulates the pineal gland to secrete melatonin, which promotes sleepiness.

Cranial Nerves

• There are 12 pairs of cranial nerves.
• They are named because they pass through the cranium bones and arise from the brain inside the cranial cavity.
• Nerves may be sensory, carrying impulses to the brain
• Nerves can also be motor, carrying impulses from the brain to the periphery.
• Nerves may also be mixed, i.e., containing both sensory and motor fibers.

Cranial Nerve Functions

• I Olfactory : smell
• II Optic : Sight
• III Oculomotor: moves eye, pupil
• IV Trochlear: moves eye
• V Trigeminal: face sensation
• VI Abducens: moves eye
• VII Facial: moves face, salivate
• VIII Vestibulocochlear: hearing, balance
• IX Glossopharyngeal: taste, swallow
• X Vagus: heart rate, digestion
• XI Accessary: moves head
• XII Hypoglossal: moves tongue