9.1-9.4 Notes

Nervous System Functions

• Coordinate body functions

• Maintain homeostasis

• Respond to changing conditions internally and externally

• Made of 2 parts– Neurons – Neuroglial cells

Neurons (nerve cells)

• Transmit information in the form of a nerve impulse

• Different parts of a neuron– Cell body-round area/has nucleolus– Dendrites-branches that receive the signal– Axon-sends the single to the next neuron

• Nerves-bundles of axons

Neuroglial Cells

• Provide physical support, insulation, and nutrients for the neurons

• Protection devices

Organs of nervous system are in 2 groups.

• Central Nervous System (CNS)– Made of brain and

spinal cord

• Peripheral Nervous System (PNS)– Made of neurons that

connect to CNS

Have 3 general functions:SensoryMotorIntegrative

3 general functions

• Sensory-sensory receptors are at the end of peripheral neurons– Gather information about changes in and out of

the body• Example: temperature, light, sound, oxygen levels

• Integrative-bring all the information together to create perceptions from sensations

3 general functions (cont.)

• Motor– Effectors-responsive structures that receive

impulses• Are found outside the nervous system• Example: muscle, glands

– 2 categories• Somatic-conscious control (skeletal muscles)• Autonomic-unconscious control (heart and smooth

muscle)

Neuroglial cells

• Produce myelin (fat that surrounds the axon)

• Fills space• Framework• There are different

types of neuroglial cells.

Types of neuroglial in CNS

• Microglial-support neurons– Phagocytosis of bacteria and cell debris

• Oligodendrocytes-found along nerve fibers– Provide myelin for myelin sheath (around axon within

brain and spinal cord)

• Astrocytes-between neurons and blood vessels– Support, join parts, help regulate ion and nutrient

levels, form scar tissue when injury occurs to the CNS

• Ependymal cells-cover special brain parts and close spaces between the brain and CNS

Neuroglial in the PNS

• Schwann cells-create myelin for neurons in the PNS

• Too many neuroglial cells-cause brain tumors (fast growing gliomas)

Neuron Structure

• Cell body– Cytoplasm, organelles, cell membrane– Neurofibrils-fine threads– Chromatophilic substance (Nissl bodies)-like

rough ER– Nucleolus

• Dendrites– Short, highly branched, receptors

Neuron structure (cont)• Axons

– Axon hillock-elevated portion leading into the axon from the cell body

– May have side branches– PNS axons-made of Schwann cells that make myelin– Neurilemma-covering that surrounds myelin sheath– Nodes of Ranvier-gaps in between myelin sheath of axon

• Myelinated in CNS are called white matter• Unmyelinated in CNS are called gray matter

– Axons can regenerate in PNS because of neurilemma– CNS are myelinated by oligodendrocytes-no neurilemma

so can’t regenerate

Label the picture on your notes.

Groupings-Structuraltrigger point-sensitive region of axon;where nerve

impulse begins to be sent down axon• Multipolar-one axon and

many dendrites (brain and sc)

• Bipolar-1 axon, 1 dendrite (eyes, nose, ears)

Structural Differences (cont)

• Unipolar neuron-one axon, no dendrites– Dendrite near

peripheral body– Other part connected to

brain or spinal cord– Cell bodies of these are

bunched to form ganglia

• Outside the brain or spinal cord

Functional Groupings

• Sensory (afferent)-carry impulse from peripheral into CNS– Specialized receptor ends on dendrite tips– Dendrites are closely associated with receptor cells in

skin or in sensory organs– Unipolar, some bipolar

• Interneurons-in brain and spinal cord– Transmit impulses from 1 to another by forming links

with other neurons– multipolar

Functional groupings (cont)

• Motor neurons-efferent– Multipolar– Carry impulse out of CNS to the effectors– Stimulate muscle and glands to respond