Chapter 10 The Nervous System Introduction Spinal Cord

Chapter 10 The Nervous System Introduction, Spinal Cord, and Spinal Nerves 2

Introduction • Control center and communication network – Directs functions of body’s organs and systems – Interprets external environment – Determines reaction to change 3

Introduction (cont’d. ) • Homeostasis: balanced internal environment – Controlled by nervous and endocrine systems 4

Organization 5

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 6

Organization (cont’d. ) 7

Classification of Nerve Cells 8

Neuroglia Cells • Astrocytes: support, connection, bloodbrain barrier • Oligodendroglia: support, myelin sheath formation • Microglial: phagocytosis • Ependymal: line the ventricles of the brain • Schwann: myelin sheaths in peripheral nervous system 9

The Structure of a Neuron • Cell body • Dendrites: receptive areas • Axon: extension of cell body – Schwann cells – Nodes of Ranvier 10

The Structure of a Neuron (cont’d. ) 11

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 12

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 13

The Physiology of the Nerve Impulse 14

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 15

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 16

The Synaptic Transmission 17

The Synaptic Transmission (cont’d. ) • Synapse: axon terminal branches close to next dendrites • Impulse reaches axon terminals • Triggers neurotransmitter release into synaptic cleft 18

The Synaptic Transmission (cont’d. ) • Neurotransmitters – Acetylcholine • Most common – Epinephrine – Norepinephrine – Serotonin – Dopamine – Endorphins 19

The Synaptic Transmission (cont’d. ) 20

The Reflex Arc 21

The Reflex Arc (cont’d. ) • Knee-jerk reflex • Maintain homeostasis – Heartbeat/breathing rates – Digestion – Coughing – Sneezing – Swallowing – Vomiting 22

The Reflex Arc (cont’d. ) • Involuntary reaction to external stimulus 23

Grouping of Neural Tissue 24

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 25

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 26

The Spinal Cord 27

Introduction • Continuation of medulla oblongata • 31 segments each with a pair of spinal nerves • Protected by meninges – Dura mater – Arachnoid – Pia mater 28

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Functions of the Spinal Cord • Conveys sensory impulses to the brain • Integrates reflexes • Spinal nerves connect at roots – Dorsal root: sensory – Ventral root: motor 30

The Spinal Nerves 31

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 32

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 33

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 34