THE NERVOUS SYSTEM THE REFLEX ARC Reflexrapid predictable

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

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

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. 12 b

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. 16 a

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. 16 b

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