The Nervous System

The Reflex Arc Reflex—rapid, predictable, and involuntary response to a stimulus Occurs over pathways called reflex arcs Reflex arc—direct route from a sensory neuron, to an interneuron, to an effector

The Reflex Arc Stimulus at distal end of neuron Skin Spinal cord (in cross section) Interneuron Receptor Effector Sensory neuron Motor neuron Integration center (a)

Simple Reflex Arc Sensory receptors (stretch receptors in the quadriceps muscle) Sensory (afferent) neuron Sensory receptors (pain receptors in the skin) Spinal cord Sensory (afferent) neuron Synapse in ventral horn gray matter Inter- neuron Motor (efferent) neuron Motor (efferent) neuron Effector (quadriceps muscle of thigh) Effector (biceps brachii muscle) (b) (c)

Types of Reflexes and Regulation Somatic reflexes

Types of Reflexes and Regulation Autonomic reflexes

Types of Reflexes and Regulation Patellar, or knee-jerk, reflex is an example of a two-neuron reflex arc

Central Nervous System (CNS) Ventricles

Cerebrum Figure 7.14

Layers of the cerebrum Corpus callosum – Gray matter— White matter— Basal nuclei-

White Matter

Cerebrum

Diencephalon Figure 7.12b

Diencephalon (Interbrain) On top of the brain stem Enclosed by the cerebral hemispheres Made of three parts:

Regions of the Brain: Diencephalon Figure 7.16

Diencephalon Thalamus The relay station for sensory impulses Crude:

Diencephalon Hypothalamus Under the thalamus Important autonomic nervous system center

Diencephalon Hypothalamus (continued)

Diencephalon Epithalamus Houses the pineal body (an endocrine gland)

Brain Stem Attaches to the spinal cord Parts of the brain stem:

Brain Stem Figure 7.16a

Brain Stem Midbrain Mostly composed of tracts of nerve fibers Has two bulging fiber tracts— cerebral peduncles

Brain Stem Pons The bulging center part of the brain stem Mostly composed of fiber tracts

Brain Stem Medulla Oblongata The lowest part of the brain stem - Merges into the spinal cord Contains important control centers:

Medulla Oblongata Projection fiber tracts cross here - right to left

Regions of the Brain: Brain Stem Reticular Formation Diffuse mass of gray matter along the brain stem Involved in motor control of visceral organs

Reticular Formation of the Brain Stem Figure 7.16b