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 hemi- spheres 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 Slide 7.38b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 7.15a

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 Slide 7.42b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 7.15b

Cerebellum  Projects dorsally from under the occipital lobe  It has two hemi- spheres 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.