3 Functions of the Nervous System (SIM)

1. Sensory input—gathering information– monitor changes inside and outside the body– changes = stimuli– sensory receptors responsible for input

2. Integration – decide if and what action is needed

3. Motor Output– a response– activates muscles or glands (effectors)

Functions of the Nervous System

Figure 7.1

Organization of the Nervous System

Structural Classification of the Nervous System

2 Main Divisions1. Central nervous system

(CNS)– Brain– Spinal cord

2. Peripheral nervous system (PNS)

• Spinal nerves (to and from spinal cord)

• Cranial nerves (to and from brain)

Functional Classification of the Peripheral Nervous System

• Sensory (afferent) division– carry information to the central nervous system– Keep the body informed of internal and external

environment• Motor (efferent) division– carry impulses away from the central nervous

system– Cause some sort of effect

Functional Classification ofthe Peripheral Nervous System

– Two subdivisions of the Motor (efferent) division1. Somatic nervous system = voluntary

Skeletal muscles (except reflexes)

2. Autonomic nervous system = involuntarysmooth muscle, cardiac muscle, glands

Functional Classification ofthe Peripheral Nervous System

Two subdivisions of the Autonomic nervous system 1. Sympathetic

Concerned with processes involving expending energy. Active during times of extreme stress, emotion, and

exercise.2. Parasympathetic

Concerned with conservation of energy Can dominate sympathetic system.

Books says antagonistic, but they are more complimentary

Nervous Tissue:

2 Main Types of Cells 1. Neurons

carry messages (impulses)2. Supporting cells or neuroglia

Nervous Tissue: Neuronsspecialized to transmit messages– structures may differ, but all neurons have:

PARTS:1. Cell body–contains transparent nucleus– large conspicuous nucleolus–metabolic center of the cell

Nervous Tissue: Neurons2 Types of Processes• fibers that extend from the cell body– Dendrites—conduct impulses toward the cell body– Axons—conduct impulses away from the cell body

Nervous Tissue: Neurons

Figure 7.4

Axon Terminals- axon ends• contain vesicles with neurotransmitters• do not touch dendrite of next neuron OR

muscle– Synaptic cleft—gap between adjacent neurons– Synapse—junction between nerves

Nervous Tissue: Neurons• Myelin sheath—whitish, fatty

material covering axons

• Schwann cells—produce myelin sheaths in jelly roll–like fashion

• Nodes of Ranvier—gaps in myelin sheath along the axon

Neurons

Figure 7.4

Functional Classification of Neurons

• Sensory (afferent) neurons– Carry impulses from the sensory receptors to the

CNS• Cutaneous sense organs

– Heat, cold, pressure, pain• Proprioceptors—detect stretch or tension (found in

muscles, tendons and joints)

• Motor (efferent) neurons– Carry impulses from the central nervous system to

viscera, muscles, or glands

Functional Classification of Neurons• Interneurons (association neurons)– Found in neural pathways in the central nervous

system– Connect sensory and motor neurons

• Receptors– Specialized dendritic endings• Simple: cutaneous receptors (pain, touch)• Complex: special sense organs (eye, nose)

Figure 7.6

6 Types of Support Cells1. Astrocytes (CNS)– star-shaped cells–Most abundant of the glial cellsMainly function between neurons and capillaries• Bridging the two• Communication between the two• Barrier between the two

– Control the chemical environment of the brain (taking in extra K+ or neurotransmitters)

Nervous Tissue: Support Cells2. Microglia (CNS)–Spiderlike phagocytes (phago- eat)

–Dispose of debris (dead brain cells and bacteria)

Nervous Tissue: Support Cells3. Ependymal cells (CNS)–Line cavities of the brain and spinal cord–Ciliated cuboidal epithelial cells–Circulate cerebrospinal fluid–Help in production of cerebrospinal fluid

Nervous Tissue: Support Cells4. Oligodendrocytes (CNS)

– Wrap around nerve fibers in the central nervous system– Produce myelin sheaths in CNS

5. Schwann cells (PNS)– Form myelin sheath in the PNS

Nervous Tissue: Support Cells6. Satellite cells (PNS)–Protect neuron cell bodies by providing cushion

Regions of a Typical Neuron

VocabularyTract- bundles of nerve fibers running through the CNS.Nerves-bundles of nerve fibers running through the PNSWhite matter- Consists of dense collections of myelinated fibersGray matter- Consists of mostly unmyelinated fibers and cell bodies