The Brain

The brain is composed of the cerebrum, cerebellum, and brainstem.

The cerebrum is the largest part of the brain and is composed of right and left cerebral hemispheres. It performs higher functions like interpreting touch, vision and hearing, as well as speech, reasoning, emotions, learning, and fine control of movement.

cerebrum

The outer 4 mm surface of the cerebrum is called the cerebral cortex. The cortex contains about 70 - 75% of the 100 billion neurons of the brain. The neuron cell bodies, or gray matter, is at the surface and it has a folded structure. Beneath the gray matter are long, myelinated axons, which make up the white matter of the cortex.

The folding of the cortex increases the brain’s surface area allowing more neurons to fit inside the skull and enabling higher functions. Each fold is called a convolution or gyrus, and each groove between folds is called a sulcus.

Lobes of the Cerebrum

The cerebral hemispheres have distinct fissures, which divide each hemisphere has four lobes: frontal, temporal, parietal, and occipital.

Each lobe may be divided into areas that serve very specific functions. It’s important to understand that each lobe of the brain does not function alone. There are very complex relationships between the lobes of the brain and between the right and left hemispheres.

Frontal lobe•Personality, behavior, emotions •Judgment, planning, problem solving •Speech: speaking and writing (Broca’s area) •Body movement (motor strip) •Intelligence, concentration, self awareness

Parietal lobe

•Interprets language, words •Sense of touch, pain, temperature (sensory strip) •Interprets signals from vision, hearing, motor, sensory and memory •Spatial and visual perception

Occipital lobe •Interprets vision (color, light, movement)

Temporal lobe

•Understanding language (Wernicke’s area) •Memory •Hearing •Sequencing and organization

The cerebellum is located under the cerebrum. Its function is to coordinate voluntary muscle movements and to maintain posture and balance.

cerebellum

The brainstem includes the midbrain, pons, and medulla oblongata. Some texts include the diencephalon as a brain stem structure, but others include it in the forebrain. The brain stem acts as a relay center connecting the cerebrum and cerebellum to the spinal cord and performs many of the body’s automatic functions.

diencephalon

midbrain

pons

medulla oblongata

The medulla oblongata lies between the pons and the spinal cord. It contains centers which control key, autonomic body functions and it relays nerve signals between the brain and spinal cord. Important control centers include:•The respiratory center – controls the rate, rhythm, and depth of breathing•The cardiac center – regulates heartbeat•The vasomotor center – controls blood pressure•Reflex centers – reflex arc centers for vomiting, coughing, sneezing, hiccupping and swallowing

The Pons is an enlarged structure located just below midbrain and above the medulla oblongata. The word “pons” is the Latin word for “bridge” and indicates the function of the pons. It acts as a relay station between the lower centers and the higher centers of the brain. The 5th through the 8th cranial nerves connect directly to the pons.

The midbrain (also called the mesencephalon) is located between the diencephalon and the pons. It also acts as a relay station between the lower centers and the higher centers of the brain, but also contains important visual and auditory reflex centers, as well as motor pathways that connect the cerebrum to the cerebellum.

The diencephalon lies at the top of the brain stem, under and between the cerebral hemispheres and includes the thalamus, hypothalamus, optic tracts, optic chiasma, infundibulum, Ventricle III, mammillary bodies, posterior pituitary gland and the pineal gland.

Hypothalamus - is the master control of the autonomic system. It maintains homeostasis by regulating such things as:1.Hunger and body weight 2.Water and electrolytes through controlling thirst 3.Sleep and wakefulness4.body temperature5.blood pressure and heart rate 6.sexual response7.secretion of hormones from the pituitary gland.

Thalamus - serves as a central relay station for all sensory information (except smell) that goes into and comes out of the cerebral cortex. It plays a key role in pain, touch, and temperature sensation, as well as in attention, alertness and memory.

Thalamus

The corpus callosum connects the left and right cerebral hemispheres and facilitates communication between the hemispheres. It is the largest white matter structure in the brain, consisting of 200–250 million myelinated axons.

3. The brain and spinal cord are covered and protected by three layers of tough, connective tissue called meninges. From the outermost layer inward they are: the dura mater, arachnoid mater, and pia mater.

2. The brain has hollow fluid-filled cavities called ventricles. A clear, colorless fluid called cerebrospinal fluid flows within the ventricles and around the brain and spinal cord to help cushion them from injury.

1. The brain and spinal cord are covered and protected by the bones of the cranium and the vertebral column.

Protection of the Central Nervous System

Cranial nervesThe brain communicates with the body through the spinal cord and twelve pairs of cranial nerves. Ten of the twelve pairs of cranial nerves that control hearing, eye movement, facial sensations, taste, swallowing and movement of the face, neck, shoulder and tongue muscles originate in the brainstem. The cranial nerves for smell and vision originate in the cerebrum.

Cranial nervesNumber Name Function

I olfactory smellII optic SightIII 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 accessory moves head XII hypoglossal moves tongue