1. Ch. 7a
The nervous system

2. Functions of the Nervous System
Sensory input
Sensory receptors gather information about internal and external changes
Integration
Interpretation of sensory input
Motor output
Activation of effector organs produces a response

3. Sensory input
Integration
Motor output
Figure 7.1

4. Structural Classification of the Nervous System
Central nervous system (CNS)
Brain and spinal cord
Integration and command center
Peripheral nervous system (PNS)
Paired spinal and cranial nerves carry messages to and from the CNS

5. Functional Classification : The Peripheral Nervous System (PNS)
Two functional divisions
Sensory (afferent) division
Somatic afferent fibers - convey impulses from skin, skeletal muscles, and joints
Visceral afferent fibers -convey impulses from visceral organs
Motor (efferent) division
Transmits impulses from CNS to effector organs

6. Visceral motor (involuntary) systems during activity
Central nervous system (CNS)
Peripheral nervous system (PNS)
Sensory (afferent) division
Motor (efferent) division
Somatic NS
Autonomic NS
Skin
Somatic motor
(voluntary)
Visceral motor (involuntary)
skeletal muscles
cardiac muscles,
smooth muscles,
and glands
Sympathetic
Parasympathetic
Conserves energy
Mobilizes body
systems during activity
Promotes house-
keeping functions
during rest
Heart
Bladder

7. Motor Division of the PNS
1.Somatic (voluntary) Nervous System
Conscious control of skeletal muscles
Autonomic (involuntary) Nervous System (ANS)
Visceral motor nerve fibers
Regulates smooth muscle, cardiac muscle, and glands
Two functional subdivisions
Sympathetic
Parasympathetic

8. Nervous Tissue: Structure and Function
Two Main Cell Types
Neurons - excitable cells that transmit electrical signals
Neuroglia (glial cells) - supporting cells:
Astrocytes (CNS)
Microglia (CNS)
Ependymal cells (CNS)
Oligodendrocytes (CNS)
Satellite cells (PNS)
Schwann cells (PNS)

9. (a) Astrocytes are the most abundant CNS
Capillary
Neuron
Astrocyte
Astrocytes:
Most abundant, versatile, and highly branched glial cells
Cling to neurons, synaptic endings, and capillaries
Support and brace neurons
(a) Astrocytes are the most abundant CNS
neuroglia. Connect neuron to blood supply
Figure 7.3

10. (b) Microglial cells are defensive cells in the CNS.
Neuron
Microglial
cell
Microglia (CNS):
Small, ovoid cells with thorny processes
Migrate toward injured neurons
Phagocytize microorganisms and neuronal debris
(b) Microglial cells are defensive cells in the CNS.
Figure 7.3

11. (c) Ependymal cells line cerebrospinal fluid-filled cavities.
Fluid-filled cavity
Ependymal
cells
Brain or
spinal cord
tissue
Ependymal cells (CNS):
Range in shape from squamous to columnar
May be ciliated
Line the central cavities of the brain and spinal column
Separate the CNS interstitial fluid from the cerebrospinal fluid in the cavities
(c) Ependymal cells line cerebrospinal fluid-filled cavities.
Figure 7.3

12. Myelin sheath Process of oligodendrocyte Nerve fibers
Branched cells
Processes wrap CNS nerve fibers, forming insulating myelin sheaths
(d) Oligodendrocytes have processes that form myelin sheaths around CNS nerve fibers.
Figure 7.3

13. (forming myelin sheath)
Satellite
cells
Cell body of neuron
Schwann cells
(forming myelin sheath)
Nerve fiber
(e) Satellite cells and Schwann cells surround
neurons in the PNS. (forms myelin)
Satellite cells
Surround neuron cell bodies in the PNS
Schwann cells (neurolemmocytes)
Surround peripheral nerve fibers and form myelin sheaths
Vital to regeneration of damaged peripheral nerve fibers
Figure 7.3

14. (a) Myelination of a nerve fiber (axon)
Schwann cell
plasma membrane
Schwann cell
cytoplasm 1
Axon
Schwann cell
nucleus 2 3
Myelin sheath
(a) Myelination of a nerve fiber (axon)
Figure 7.5

15. Structure of a Typical Motor Neuron
Cell Body – contains nucleus and typical organelles
Clusters of cell bodies are called nuclei in the CNS, ganglia in the PNS
Axon hillock - cone-shaped area from which axon arises

16. Bundles of nerve fibers (processes) are called:
Dendrites
Receptive (input) region of a neuron
Convey electrical signals toward cell body
Axon
Generates & transmits nerve impulses away from cell body
Only one axon/cell arising from axon hillock
Bundles of nerve fibers (processes) are called:
Tracts in the CNS
Nerves in the PNS

17. Dendrites
(receptive regions)
Cell body
(biosynthetic center
and receptive region)
Axon
(impulse generating
and conducting region)
Impulse
direction
Nucleus
Node of Ranvier
Axon
terminals
(secretory
region)
Axon hillock
Schwann cell
(one inter-
node)
Neurilemma
Terminal
branches

18. White Matter and Gray Matter
Dense collections of myelinated fibers
Gray matter
Mostly neuron cell bodies and unmyelinated fibers

19. Structural Classification of Neurons
Three types:
Multipolar—1 axon and several dendrites
Most common type in CNS
Motor neurons and interneurons
Bipolar—1 axon and 1 dendrite
Rare, e.g., retinal neurons

20. Structural Classification of Neurons
Unipolar—single, short process that has two branches:
Peripheral process—more distal branch, often associated with a sensory receptor
Central process—branch entering the CNS

22. Functional Classification of Neurons
Three types:
Sensory (afferent)
Transmit impulses from sensory receptors toward the CNS
Motor (efferent)
Carry impulses from the CNS to effectors
Interneurons
Shuttle signals through CNS pathways; most are entirely within the CNS