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

TYPES OF REFLEXES AND REGULATION Somatic reflexes Activation of skeletal muscles Example : When you move your hand away from a hot stove

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 Four chambers within the brain Filled with cerebrospinal fluid

CEREBRUM Figure 7.14

Layers of the cerebrum Gray matter— White matter— Corpus callosum – Basal nuclei—islands of gray matter buried within the white matter

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

DIENCEPHALON Hypothalamus Under the thalamus Important autonomic nervous system center

DIENCEPHALON Hypothalamus (continued) An important part of the limbic system (emotions)

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

THOUGHT QUESTIONS 1.If the right side of the pons is injured which side of the body will be affected? 2.If you sustain an injury to the very lowest, right side of the medulla oblongata, which side of the body will be affected?

PROTECTION OF THE CENTRAL NERVOUS SYSTEM Scalp and skin Skull and vertebral column Meninges Cerebrospinal fluid (CSF) Blood-brain barrier

PROTECTION OF THE CENTRAL NERVOUS SYSTEM

DURA MATER Double-layered external covering Periosteum— Meningeal layer—

DURA MATER

CEREBROSPINAL FLUID (CSF) Similar to blood plasma Forms a watery cushion to protect the brain

CEREBROSPINAL FLUID (CSF)

HYDROCEPHALUS CSF accumulates and exerts pressure on the brain if not allowed to drain