Chapter 7 Part 3 The Nervous System The

Chapter 7 - Part 3 The Nervous System

The Reflex Arc · Reflex – rapid, predictable, and involuntary responses to stimuli · Much like a one-way street – once a reflex begins, it always goes in the same direction · Reflex arc – direct route from a sensory neuron, to an interneuron, to an effector · The neural pathway where reflexes occur over

Simple Reflex Arc

Types of Reflexes and Regulation 1. Autonomic reflexes · Regulate the activity of smooth muscles, the heart, and glands. · Regulate digestion, elimination, blood pressure, and sweating. · Examples: Secretion of saliva and changes in the size of the eye pupils. 2. Somatic reflexes · Include all reflexes that stimulate the skeletal muscles. · Examples: When you pull your hand away quickly from a hot object.

CNS · During embryonic development, the CNS first appears as a simple tube, the neural tube · The neural tube becomes the brain and spinal cord · The opening of the neural tube enlarges and becomes the ventricles or chambers · Four chambers within the brain · Filled with cerebrospinal fluid

The Brain • It weighs a little over 3 lbs. • It looks wrinkled like a walnut and with the texture of cold oatmeal. • Largest and most complex mass of nervous tissue in the body.

Regions of the Brain 1. Cerebral hemispheres 2. Diencephalon 3. Brain stem 4. Cerebellum

Cerebral Hemispheres (Cerebrum) · Paired (left and right) superior parts of the brain · Include more than half of the brain mass · Encloses and obscures much of the brain stem · How a mushroom cap covers the top of the stalk

Cerebral Hemispheres (Cerebrum) · The surface is made of elevated ridges (gyri) and shallow grooves (sulci)

Lobes of the Cerebrum · Fissures (deep grooves) divide the cerebrum into lobes · Surface lobes of the cerebrum 1. Frontal lobe 2. Parietal lobe 3. Occipital lobe 4. Temporal lobe

Lobes of the Cerebrum

Specialized Areas of the Cerebrum · Somatic sensory area – receives impulses from the body’s sensory receptors · Located in the parietal lobe · Allows you to recognize pain, coldness, or a light touch · The body is represented in an upside down manner in the sensory area · The sensory pathways are crossed – the left side of the cortex receives impulses from the right side of the body

Sensory and Motor Areas of the Cerebral Cortex

Specialized Areas of the Cerebrum · Impulses from the special sense organs are interpreted in other cortical areas. · Visual area · Located in the posterior part of the occipital lobe · Olfactory area · Located deep inside the temporal lobe

Specialized Areas of the Cerebrum · Primary motor area – sends impulses to skeletal muscles · Allows us to consciously move our skeletal muscles · Located in the frontal lobe · The body is represented upside-down · Pathways are crossed · Most of the neurons in the this primary motor area control body areas having the finest motor control (face, mouth, hands)

Specialized Areas of the Cerebrum · Broca’s area – involved in our ability to speak · Damage to this area causes inability to say words properly (you know what you want to say, but you can’t vocalize the words)

Specialized Areas of the Cerebrum · Higher intellectual reasoning – believed to be in the anterior part of the frontal lobe · Complex memories – Appear to be stored in the temporal and frontal lobes · Language comprehension (word meanings) – located in the frontal lobes · Speech Area – allows one to sound out words · Located at the junction of the temporal, parietal, and occipital lobes

Layers of the Cerebrum · Gray matter · Outer layer · Composed mostly of neuron cell bodies · Cerebral cortex – the outermost gray matter of the cerebrum

Layers of the Cerebrum · White matter · The remaining, deeper cerebral hemisphere tissue · Composed of fiber tracts (bundles of nerve fibers) carrying impulses to or from the cortex · The corpus callosum (large fiber tract) connects the cerebral hemispheres · Allows the cerebral hemispheres to communicate with one another

Layers of the Cerebrum · Although most of the gray matter is in the cerebral cortex, there are several islands of gray matter buried deep within the white matter. · Basal nuclei – internal islands of gray matter · Help regulate voluntary motor activities by modifying sent instructions · Individuals who have problems with their basal nuclei are often unable to walk normally or carry out other voluntary movements. · Examples: Huntington’s disease and Parkinson’s disease

Diencephalon · Sits on top of the brain stem · Enclosed by the cerebral hemispheres · Made of three parts 1. Thalamus 2. Hypothalamus 3. Epithalamus

Diencephalon

Thalamus · Surrounds the third ventricle · The relay station for impulses · Transfers impulses to the correct part of the cortex for localization and interpretation

Hypothalamus · Under the thalamus · Important autonomic nervous system center · Helps regulate body temperature · Controls water balance · Regulates metabolism

Hypothalamus · Center for many drives and emotions · An important part of the limbic system (emotions) · Thirst, appetite, sex, pain, and pleasure centers are in the hypothalamus · Regulates the pituitary gland (endocrine organ) and produces two hormones of its own. · The pituitary gland hangs from the anterior roof of the hypothalamus by a slender stalk.

Epithalamus · Forms the roof of the third ventricle · Houses the pineal body (an endocrine gland) · Includes the choroid plexus – knots of capillaries within each ventricle that forms the cerebrospinal fluid

Brain Stem · Attaches to the spinal cord · About the size of a thumb in diameter and approximately 3 inches long · Functions: 1. Provide a pathway for ascending and descending tracts 2. Has many small gray matter areas (form cranial nerves and control many vital activities) · Parts of the brain stem: 1. Midbrain 2. Pons 3. Medulla oblongata

Brain Stem Figure 7. 15 a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 38 b

Midbrain · Mostly composed of tracts of nerve fibers · Composed primarily of two bulging fiber tracts – cerebral peduncles (literally, “little feet of the cerebrum”) · Function is to convey ascending and descending impulses · Has four rounded protrusions – corpora quadrigemina · These bulging nuclei are reflex centers involved with vision and hearing

Pons · The bulging center part of the brain stem · Mostly composed of fiber tracts · Includes nuclei involved in the control of breathing

Medulla Oblongata · · The lowest part of the brain stem Merges into the spinal cord Is an important fiber tract area Contains important control centers · Heart rate control · Blood pressure regulation · Breathing · Swallowing · Vomiting

Reticular Formation · Diffuse mass of gray matter along the brain stem · Involved in motor control of visceral organs · Reticular activating system (RAS) plays a role in awake/sleep cycles and consciousness · Damage to this area can result in permanent unconsciousness (coma)

Reticular Formation Figure 7. 15 b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7. 42 b

Cerebellum · Projects dorsally from under the occipital lobe · It has two hemispheres and a convoluted surface · Has an outer cortex made up of gray matter and an inner region of white matter

Functions of the Cerebellum · Involuntary · Provides the precise timing for skeletal muscle activity and controls our balance and equilibrium · Makes our body movements smooth and coordinated

Damage to the Cerebellum · If the cerebellum is damaged, movements become clumsy and disorganized. · Cannot keep their balance and appear to be drunk because of the loss of muscle coordination. · They are no longer able to touch their finger to their nose with their eyes shut.