CH 10 Functions of the Nervous System The master controlling and communicating system of the body Functions 1.Sensory input: detects external and internal stimuli 2.Integration: processes and responds to sensory input 3.Control of Muscles and Glands 4.Homeostasis is maintained by regulating other systems 5. Center for Mental Activities

Fig. 10.1

Parts of the Nervous System Two anatomical divisions –Central Nervous System (CNS) Brain and spinal cord Encased in bone –Peripheral Nervous System (PNS) Nervous tissue outside of the CNS Consists of sensory receptors and nerves The anatomical divisions perform different functions –PNS detects stimuli and transmits information to the CNS and receives information from the CNS –CNS processes, integrates, stores, and responds to information from the PNS

Parts of the Nervous System PNS has two divisions –Sensory division transmits action potentials from sensory receptors to the CNS –Motor division carries action potentials away from the CNS in cranial or spinal nerves (two subdivisions) Somatic nervous system innervates skeletal muscle Autonomic nervous system (ANS) innervates cardiac muscle, smooth muscle, and glands (three subdivisions) –Sympathetic division is most active during physical activity (fight or flight division) –Parasympathetic division regulates resting functions (rest and digest division) –Enteric nervous system controls the digestive system

Central Nervous System (CNS) Brain and Spinal Cord Peripheral Nervous System (PNS) Nervous tissue outside the CNS Sensory receptors and nerves Sensory Division Transmits action potentials from sensory receptors to the CNS Motor Division Carries action potentials away from the CNS in cranial nerves or spinal nerves Sympathetic Division Most active during physical activity Somatic Nervous System Innervates skeletal muscle Autonomic Nervous System (ANS) Innervates cardiac muscle, smooth muscle, and glands Parasympathetic Division Regulates resting functions Enteric Nervous System Controls the Digestive System Parts of the Nervous System

Fig. 10.2

Cells of the Nervous System The two principal cell types of the nervous system are: –Neurons: excitable cells that transmit electrical signals –Glial cells: cells that surround neurons. Account for over half of the brain’s weight Less than 20% is extracellular space

Neurons Receive stimuli and transmit action potentials Have three components: –Cell body (soma) is the primary site of protein synthesis –Dendrites are short, branched extensions of the cell body that conduct electric signals toward the cell body –An axon is a cytoplasmic extension of the cell body that transmits action potentials to other cells

Fig. 10.3

Neuron Structure Cell Body (Soma) Fig. 10.3

Neuron Axon HillockSomaNucleus AxonDendritesNucleolus Nissl substance

Neuron Structure –Usually, there is only one unbranched axon per neuron Rare branches, if present, are called collateral axons –Presynaptic terminal: branched end of an axon (10,000 or more) –Synapse: junction between a nerve cell and another cell Fig Axons (Nerve Fibers) Takes action potential away from the cell body

Glial Cells Glial Cells of the CNS –Oligodendrocytes Glial Cells of the PNS –Schwann cells Glial Cells (Supporting Cells): –Provide a supportive scaffolding for neurons –Segregate and insulate neurons –Guide young neurons to the proper connections –Promote health and growth

Glial Cells of the CNS Oligodendrocytes: form myelin sheaths around the axons of several CNS neurons Fig. 10.8

Glial Cells of the PNS Schwann cells: form a myelin sheath around part of the axon of a PNS neuron –Can help to repair severed nerves – lc/n-reading30.htmlhttp:// lc/n-reading30.html Fig. 10.9

Myelinated and Unmyelinated Axons Myelinated axons –Plasma membrane of Schwann cells or Oligodendrocytes repeatedly wraps around a segment of an axon to form the myelin sheath –Myelin is a whitish, fatty (protein-lipid), segmented sheath around most long axons –It functions to: Protect the axon Electrically insulate fibers from one another Increase the speed of nerve impulse transmission Node of Ranvier –Gaps in the myelin sheath Fig

Myelinated and Unmyelinated Axons Unmyelinated axons –Rest in invaginations of Schwann cell (PNS) or Oligodendrocytes (CNS) –Conduct action potentials slowly Fig

Organization of Nervous Tissue Nervous tissue can be grouped into white matter and gray matter –White matter (outermost) Consists of myelinated axons Propagates action potentials Forms nerve tracts in the CNS and nerves in the PNS –Gray Matter (innermost) Collections of neuron cell bodies or unmyelinated axons Forms cortex and nuclei in the CNS and ganglia in the PNS

Spinal Cord Gray matterWhite matter

Brain Gray Matter and White Matter