The Nervous System Introduction, Spinal Cord, and Spinal Nerves Chapter 10 The Nervous System Introduction, Spinal Cord, and Spinal Nerves

Introduction Control center and communication network Directs functions of body’s organs and systems Interprets external environment Determines reaction to change

Introduction (cont’d.) Homeostasis: balanced internal environment Controlled by nervous and endocrine systems

Organization

Organization (cont’d.) Central nervous system: brain and spinal cord Peripheral nervous system Afferent peripheral system Sensory neurons Efferent peripheral system Somatic Autonomic: sympathetic and parasympathetic

Organization (cont’d.)

Classification of Nerve Cells

Neuroglia Cells Astrocytes: support, connection, blood-brain barrier Oligodendroglia: support, myelin sheath formation Microglial: phagocytosis Ependymal: line the ventricles of the brain Schwann: myelin sheaths in peripheral nervous system

The Structure of a Neuron Cell body Dendrites: receptive areas Axon: extension of cell body Schwann cells Nodes of Ranvier

The Structure of a Neuron (cont’d.) Needs Fig 10-2

The Structure of a Neuron (cont’d.) Multipolar: several dendrites coming off cell body Bipolar: one dendrite and one axon Unipolar: one process extending from cell body

The Structure of a Neuron (cont’d.) Receptors: detect environmental stimuli Sensory: receive impulse from receptor site Internuncial: transmit impulse for interpretation and processing Motor: reaction to the stimulus

The Physiology of the Nerve Impulse

The Physiology of the Nerve Impulse (cont’d.) Nerve cell fiber resting potential Na+ concentration higher on outside K+ concentration higher on inside Negative charge on inside Positive charge on outside

The Physiology of the Nerve Impulse (cont’d.) Depolarization: Na+ rush inside cell Repolarization: K+ rush out to restore balance Depolarization: Repolarization moves in one direction Myelinated vs. unmyelinated All-or-none law

The Synaptic Transmission

The Synaptic Transmission (cont’d.) Synapse: axon terminal branches close to next dendrites Impulse reaches axon terminals Triggers neurotransmitter release into synaptic cleft

The Synaptic Transmission (cont’d.) Neurotransmitters Acetylcholine Most common Epinephrine Norepinephrine Serotonin Dopamine Endorphins

The Synaptic Transmission (cont’d.)

The Reflex Arc

The Reflex Arc (cont’d.) Knee-jerk reflex Maintain homeostasis Heartbeat/breathing rates Digestion Coughing Sneezing Swallowing Vomiting

The Reflex Arc (cont’d.) Involuntary reaction to external stimulus

Grouping of Neural Tissue

Grouping of Neural Tissue (cont’d.) White matter Groups of myelinated axons Forms nerve tracts in CNS Gray matter Nerve cell bodies and dendrites Unmyelinated axon bundles Cortex: gray matter on surface of brain

Grouping of Neural Tissue (cont’d.) Nerve: bundle of fibers outside CNS Ganglia: nerve cell bodies outside CNS Tract: bundle of fibers inside CNS Nucleus: nerve cell bodies and dendrites inside CNS Horns: areas of gray matter in spinal cord

The Spinal Cord

Introduction Continuation of medulla oblongata 31 segments each with a pair of spinal nerves Protected by meninges Dura mater Arachnoid Pia mater

Functions of the Spinal Cord Conveys sensory impulses to the brain Integrates reflexes Spinal nerves connect at roots Dorsal root: sensory Ventral root: motor

The Spinal Nerves

The Spinal Nerves (cont’d.) All 31 pairs arise from union of dorsal and ventral roots Mixed nerves consisting of motor and sensory fibers Most exit vertebral column between vertebrae

The Spinal Nerves (cont’d.) Named and numbered according to region and level of spinal cord Cervical: 8 pairs Thoracic: 12 pairs Lumbar: 5 pairs Sacral: 5 pairs Coccygeal: 1 pair

Summary Named the major division of the nervous system Classified neurons and neuroglial cells Discussed the physiology of the nerve impulse and transmission at synapses Named the different types of neural tissue Discussed the structure of the spinal cord Named the spinal nerves