The Nervous System

The Reflex Arc Reflex – rapid, predictable, and involuntary responses to stimuli Reflex arc – direct route from a sensory neuron, to an interneuron, to an effector All reflex arcs have 5 elements (#ed below) Figure 7.11a

Simple Reflex Arc Figure 7.11b–c

Types of Reflexes and Regulation Autonomic reflexes Smooth muscle regulation Heart and blood pressure regulation Regulation of glands Digestive system regulation Somatic reflexes Activation of skeletal muscles

Central Nervous System (CNS) CNS develops from the embryonic neural tube The neural tube becomes the brain and spinal cord The opening of the neural tube becomes the ventricles Four chambers within the brain Filled with cerebrospinal fluid

Regions of the Brain Cerebral hemispheres Diencephalon Brain stem Cerebellum Adult brain weighs a little over 3 pounds Figure 7.12b

Cerebral Hemispheres (Cerebrum) Paired (left and right) superior parts of the brain Include more than half of the brain mass Figure 7.13a

Cerebral Hemispheres (Cerebrum) The surface is made of ridges (gyri) and grooves (sulci) Figure 7.13a

Lobes of the Cerebrum Fissures (deep grooves) divide the cerebrum into lobes Single deep fissure (longitudinal fissure) separates the cerebral hemispheres Surface lobes of the cerebrum named for the cranial bones that lie over them Frontal lobe Parietal lobe Occipital lobe Temporal lobe

Lobes of the Cerebrum Figure 7.13b

Specialized Areas of the Cerebrum Figure 7.13c

Specialized Areas of the Cerebrum Somatic sensory area – receives impulses from the body’s sensory receptors (pain, coldness, light touch) Located in the parietal lobe posterior to central sulcus Left side of the sensory cortex receives impulses from the right side of the body

Specialized Areas of the Cerebrum Primary motor area – sends impulses to skeletal muscles Located in the frontal lobe anterior to the central sulcus Axons of these motor neurons form the corticospinal or pyramidal tract, which descends to the cord

Specialized Areas of the Cerebrum Broca’s area – involved in our ability to speak Located at the base of the precentral gyrus Located in only one hemisphere (usually the left) Damage to this area causes inability to say words properly – know what you want to say but can’t vocalize

Sensory and Motor Areas of the Cerebral Cortex Figure 7.14

Specialized Areas of the Cerebrum Cerebral areas involved in special senses Gustatory area (taste) Parietal lobe – corner of the central & lateral sulcus Visual area Posterior part of the occipital lobe

Specialized Areas of the Cerebrum Auditory area In the temporal lobe bordering the lateral sulcus Olfactory area Deep inside the temporal lobe

Specialized Areas of the Cerebrum Interpretation areas of the cerebrum Speech/language region Junction of the temporal, parietal, & occipital lobes Allows one to sound out words Usually in only one cerebral hemisphere

Specialized Areas of the Cerebrum Language comprehension region Frontal lobes Word meanings General interpretation area Temporal, parietal, & occipital lobes

Specialized Areas of the Cerebrum Figure 7.13c

Layers of the Cerebrum Gray matter Outer layer (cerebral cortex) Composed mostly of neuron cell bodies Highly ridged (convoluted) – gives more surface area for neurons Figure 7.13a

Layers of the Cerebrum White matter Fiber tracts (bundles of nerve fibers) inside the gray matter Carry impulses to & from cerebral cortex Figure 7.13a

Layers of the Cerebrum Example: corpus callosum connects cerebral hemispheres allowing for communication *Important because some of the critical functional areas are in only one hemisphere

Layers of the Cerebrum Basal nuclei (basal ganglia) – internal islands of gray matter Help regulate voluntary motor activities by modifying instructions sent to the skeletal muscles by the primary motor cortex Figure 7.13a

Diencephalon Sits on top of the brain stem Enclosed by the cerebral hemispheres Made of three parts Thalamus Hypothalamus Epithalamus

Diencephalon Figure 7.15

Thalamus Surrounds the third ventricle The relay station for sensory impulses upward to the sensory cortex Transfers impulses to the correct part of the cortex for localization and interpretation by the neurons

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

Hypothalamus An important part of the limbic system (emotions) The pituitary gland hangs from the anterior floor of the hypothalamus by a slender stalk Regulates the pituitary gland Produces 2 of its own hormones

Epithalamus Forms the roof of the third ventricle Houses the pineal body (an endocrine gland) Includes the choroid plexus – forms cerebrospinal fluid

Brain Stem (size of a thumb) Attaches to the spinal cord Parts of the brain stem Midbrain Pons Medulla oblongata Provides pathway for ascending & descending tracts Basal nuclei of brain stem control breathing & blood pressure

Brain Stem Figure 7.15a

Midbrain Mostly composed of tracts of nerve fibers Has two bulging fiber tracts – cerebral peduncles – convey ascending & descending impulses Has four rounded protrusions – corpora quadrigemina Reflex centers for vision and hearing

Pons (“bridge”) 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 Includes important fiber tracts 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 plays a role in awake/sleep cycles and consciousness *Damage to this area can result in permanent unconsciousness (coma)

Reticular Formation Figure 7.15b