THE FUNCTIONS OF THE NERVOUS SYSTEM The Central Nervous System

THE CENTRAL NERVOUS SYSTEM The nervous system is divided into two subunits Central nervous system (CNS) –Brain –spinal cord. Peripheral nervous system –Any part of nervous system outside of CNS –Afferent and efferent.

THE Cells of the CENTRAL NERVOUS SYSTEM Contains neurons: obviously single neural cells. Nucleus –A group of cell bodies (somas) in the CNS and a Ganglion –Group of cell bodies in the peripheral nervous system.

THE Cells of the CENTRAL NERVOUS SYSTEM Contains neurons: obviously single neural cells. Nerve : –is a bundle of axons running together –like a multi-wire cable. –Nerve is used only in the peripheral nervous system. Tracts. –Bundles of neurons –Inside the CNS –Tracts = nerves

Divisions of the CNS Forebrain –Cerebral hemispheres Frontal lobe Parietal lobe Occipital lobe Temporal lobe –Thalamus and hypothalamus –Corpus callosum –Ventricles Midbrain and Hindbrain –Superior colliculi –Thalamus –Pineal gland –Hindbrain Pons; Medulla; Reticular activating system Spinal Cord

Let’s start at the top! The Forebrain!

THE Forebrain Forebrain –two cerebral hemispheres, –the thalamus, –the hypothalamus. The large, wrinkled cerebral hemispheres dominate the brain’s appearance. The longitudinal fissure –that runs the length of the brain –separates the two cerebral hemispheres, –Two cerebral hemispheres are mirror images of each other in appearance. Remember: –Left hemisphere brain controls right side of body –Right brain hemisphere controls left side of body

Gyri and sulci The brain’s surface has many ridges and grooves that give it a very wrinkled appearance. Several geographic landmarks: –gyrus. Each ridge –a sulcus The groove or space between two –Fissure: large sulcus

Gyrus Sulcus

convolutions of the cortex The outer surface is the cortex, which is made up mostly of the cell bodies of neurons. –Because cell bodies are not myelinated, the cortex looks grayish in color, –Thus referred to as gray matter. The cortex is only 1.5 – 4 mm thick, Convolutions (folds) increase the amount of cortex by tripling the surface area. –Also provides axons easier access to cell bodies –Axons come together at central core of each gyrus –Here the brain appears white

Organization of the CENTRAL NERVOUS SYSTEM The central nervous system is arranged in a hierarchy. As you ascend from the spinal cord through the hindbrain and midbrain to the forebrain, the neural structures become more complex and so do the behaviors they control. The hemispheres are divided into four lobes – –frontal –parietal, –occipital –temporal –each named after the bone of the skull above it.

Is size important? Relation of brain size to body size versus intelligence –Brain size more related to body size –Brains of elephants and sperm whales 5-6x larger than human brain What is important? –Convolutions are the important variable! –Greater number of gyri = more cortex –Also; more gyri in cerebral hemispheres than lower brain parts –More surface area = more connections

THE frontal lobe Frontal lobe –anterior to (in front of) the central sulcus –superior to (above) the lateral fissure. Precentral gyrus, –extends the length of the central sulcus –Contains primary motor cortex, which controls voluntary (nonreflexive) movement. –The parts of the body are “mapped onto” the motor area of each hemisphere –Can be illustrated in the form of a homunculus, which means “little man.” The secondary motor areas are located just anterior to the primary area.

THE motor homunculus More brain area is devoted to parts of body with greater/finer motor movement Fingers Hands Lips Legs Arms Little brain area devoted to motor movement of back, toes, etc.

broca’s area Broca’s area is located anterior to the motor area and along the lateral fissure. Broca’s area controls speech production contributes the movements involved in speech and grammatical structure.

THE prefrontal cortex Prefrontal Cortex – –The most anterior part of the frontal lobes –largest region in the human brain, – Twice as large as in chimpanzees, –Accounts for 29% of the total cortex. The prefrontal cortex is involved in –Planning and organization, –Impulse control, –Adjusting behavior in response to rewards and punishments, –Some forms of decision making.

THE prefrontal cortex Prefrontal Cortex

THE prefrontal cortex How know the effects of the Prefrontal cortex? –During the 1940s and 1950s surgeons performed tens of thousands of lobotomies, a surgical procedure that disconnected the prefrontal area from the rest of the brain. –Initially the surgeries were performed on very disordered schizophrenics, but many overly enthusiastic doctors lobotomized patients with much milder problems. Effects? –The surgery calmed agitated patients, –Benefits came at a high price in that patients often became: emotionally blunted distractible childlike in behavior. Psychosurgery rarely used today to treat psychiatric problems

THE parietal lobes Parietal lobes –located superior to the lateral fissure –between the central sulcus and the occipital lobe. Primary somatosensory cortex –located on the postcentral gyrus, –processes the skin senses (touch, warmth, cold, and pain), –Also senses that inform us about body position and movement.

THE somatosensory homunculus The somatosensory cortex also is organized as a homunculus, –size of each area depends on the sensitivity in that part of the body.

THE parietal association areas Association areas –Contained in each of the lobes –carry out further processing beyond what the primary area does –often combine information from other senses. Parietal lobe association areas : –receive input from the body senses and from vision. –Help a person identify objects by touch –help determine the location of the limbs –Help locate objects in space. Damage to the posterior parietal cortex may produce sensory neglect: a disorder in which the person ignores –objects, –people, –activity on the side opposite the damage. –Why the opposite side of the damage?

THE temporal lobe Temporal lobes Separated from the frontal and parietal lobe by the lateral fissure Three important areas: –Auditory projection area, –visual and auditory association areas –Additional language area: Wernicke’s Area.

THE auditory or temporal cortex Auditory cortex: –receives sound information from the ears –lies on the superior (uppermost) gyrus of the temporal lobe. Wernicke’s area –Just posterior to the auditory cortex –interprets language input arriving from the nearby auditory and visual areas. –also generates spoken language through Broca’s area and written language by the way of the motor cortex. Inferior temporal cortex –lower part of the lobe (as the name implies) –plays a major role in the visual identification of objects.

THE occipital cortex Occipital lobes –location of the visual cortex, –visual information is processed. contains a map of visual space because adjacent receptors in the back of the eye send neurons to adjacent cells in the visual cortex.