1. Chapter Nine Nervous System
Part 1

2. Functions of the Nervous System
Sensory input- information gathered by sensory receptors about internal and external changes
Integration- interpretation of sensory input
Motor output- activation of effector (muscles and glands) produces a response

3. Divisions 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

4. Peripheral Nervous System Functions
Sensory (afferent) division
1 Somatic afferent fibers- convey impulses from skin, skeletal muscles, and joints
2 Visceral afferent fibers- convey impulses from visceral organs

5. Motor (efferent) division
Transmits impulses from the CNS to effector organs
Somatic (voluntary) nervous system
Conscious control of skeletal muscles
Autonomic (involuntary) nervous system (ANS)
Visceral motor nerve fibers
Regulated smooth muscle, cardiac muscle, and glands
Functional divisions
Sympathetic good pic
Parasympathetic next slide

10. Up next! The neuron! (AKA Nerve Cell)

11. Histology of nervous system
Neurons- excitable cells that transmit electrical signals
Characteristics
Long lived, amitotic, high metabolic rate, electrical signaling and cell-to-cell interactions during development

12. Parts of a neuron
Cell body- biosynthetic center of a neuron, network of neurofibrils (neurofilaments)
Axon hillock- cone shaped area where the axon arises
Clusters of cell bodies in the CNS are called nuclei, and in the PNS are called ganglia

13. Processes- bundles are classed tracts (CNS) and nerves (PNS) Dendrites
Parts of a neuron
Processes- bundles are classed tracts (CNS) and nerves (PNS)
Dendrites
Short, tapering and diffusely branched
Receptive (input) region of the neuron
Convey electrical signals toward the cell body

14. Parts of a neuron Axons One long axon per cell body
Long axons are called nerve fibers
Knoblike axon terminals
Secretory region of the neuron
Release neurotransmitters to excite or inhibit other cells
Conducting region of the neuron, generates and transmits nerve impulses away from the cell body

15. Nerve bundles
Unmyelinated axons are thin nerve fibers and one Schwann cell can incompletely enclose 15 or more unmyelinated axons

16. End of Day 1

17. Structural classifications of neurons
Multipolar- 1 axon and several dendrites (most abundant)
Bipolar- 1 axon and 1 dendrite (rare)
Unipolar (pseudounipolar)- single, short process that has two branches
Peripheral process- most distal branch
Central process- branch entering the CNS

18. Functional classification of neurons
Sensory (afferent)- transmit impulses from sensory receptors toward the CNS
Motor (efferent)- carries impulses from the CNS to effectors
Interneurons (association neurons)- Shuttle signals through CNS pathways

19. Neuroglia (glial cells)- supporting cells
Astrocytes (CNS)
Most abundant, versatile, and highly branched glial cells
Cling to neurons, synaptic endings, and capillaries
Support and brace neurons
Determine capillary permeability
Guide migration of young neurons
Control chemical environment
Information processing in the brain

20. Neuroglia (glial cells)- supporting cells

21. Neuroglia (glial cells)- supporting cells
Microglia (CNS)
Migrate toward injured neurons
Phagocytize microorganisms and neuronal debris
Ependymal cells (CNS)
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

22. Neuroglia (glial cells)- supporting cells
Oligodendrocytes (CNS)
Branched cells
Processes wrap CNS nerve fibers, forming insulating myelin sheaths
Myelin sheath- concentric layers of Schwann cell membrane
Neurilemmal- peripheral bulge of Schwann cell cytoplasm
Nodes of Ranvier-myelin sheath gaps between Schwann cells, sites where axon collaterals can emerge
CNS
Formed by processes of oligodendrocytes, Nodes of Ranvier not present, no neurolimma, thinnest fibers are unmyelinated
White matter
Dense collections of myelinated fibers
Grey matter
Mostly neuron cell bodies and unmyelinated fibers

23. Neuroglia (glial cells)- supporting cells
Satellite cells (PNS)
Surround neuron cell bodies in the PNS
Schwann cells (PNS)
Surround peripheral nerve fibers and form myelin sheaths
Vital to regeneration of damaged peripheral nerve fibers

24. Membrane potentials Role of membrane ion channels
Proteins serve as membrane ion channels
Two main types of channels
Leakage (nongated) channels- always open

25. Membrane potentials Gated channels Three types
Chemical gated (ligand-gated) channels- open with binding of a specific neurotransmitter
Voltage-gated channels- open and close in response to changes in membrane potentials
Mechanically gated channel- open and close in response to physical deformation of receptors

26. When gated channels are open
Ions diffuse quickly across the membrane along their electrochemical gradients
Chemical gradients go from high to low
Electrical gradients go from low to high
Ion flow creates an electrical current and voltage changes across the membrane

27. Resting membrane potential
Potential difference across the membrane of a resting cell
Approximately -70mV in neurons
Generated by
Differences in ICF (intracellular fluid) and ECF (extracellular fluid)
Differential permeability of the plasma membrane

28. Resting membrane potential
Differences in ionic makeup
ICF has lower concentration of Na+ and Cl- than ECF
ICF has higher concentration of K+ and negatively charged proteins (A-) than ECF
Sodium-potassium pump stabilizes the resting membrane potential by maintaining the concentration gradients for Na+ and K+

29. Membrane potentials act as signals
Changes when concentrations of ions across the membrane change and permeability of membrane to ions changes
Signals used to receive, integrate, and send information

30. Graded potentials- incoming short-distance signals
Depolarization
Reduction in membrane potential
Inside of the membrane becomes less negative than the resting potential
Increases the probability of producing a nerve impulse
Hyperpolarization
An increase in membrane potential
Inside of the membrane becomes more negative than the resting potential
Reduces the probability of producing a nerve impulse
Occur when a stimulus causes gated ion channels to open
Decrease in magnitude with distance as ions flow and diffuse through leakage channels

31. Action potentials- long-distance signals of axons
Brief reversal of membrane potential with an amplitude of ~100mV
Occur in muscle cells and axons of neurons
Does not decrease in magnitude over distance

32. Nerve fiber classification
Group A fibers
Large diameter, myelinated somatic sensory and motor fibers
Group B fibers
Intermediate diameter, lightly myelinated ANS fibers
Group C fibers
Smallest diameter, unmyelinated ANS fibers

33. The synapse
A junction that mediated information transfer form one neuron to another neuron or an effector cell
Presynaptic neuron- conducts impulses toward the synapse
Postsynaptic neuron- transmits impulses away from the synapse

34. synapses Types of synapses
Axodendritic- between the axon of one neuron and the dendrite of another
Axosomatic- between the axon of one neuron and the soma of another
Less common
Axoaxonic (axon to axon)
Dendrodendritic (dendrite to dendrite)
Dendrosomatic (dendrite to soma)

35. Synapses Electrical synapses Less common than chemical synapses
Neurons are electrically coupled (joined by gap junctions)
Communication is very rapid and may be unidirectional or bidirectional
Important in embryonic nervous tissue and some brain regions

36. Synapses Chemical synapses
Specialized in the release of neurotransmitters
Composed of two parts
Axon terminal of the presynaptic neuron
Receptor region on the postsynaptic neuron

37. Synaptic cleft
Fluid-filled space separating the presynaptic and postsynaptic neurons
Prevents nerve impulses from directly passing from one neuron to the next
Transmission across the synaptic cleft
Is a chemical event that involves the release, diffusion, and binding of neurotransmitters that ensures unidirectional communication between neurons

38. Neurotransmitters and their receptors
Most neurons make two or more neurotransmitters, which are released at different stimulation frequencies
50 or more neurotransmitters have been identified

39. Classified by chemical structure and by function
Acetylcholine (Ach)
Released at neuromuscular junctions and some ANS neurons
Synthesized by enzyme choline acetyltransferase
Degraded by the enzyme acetylcholinesterase (AChE)

40. Classified by chemical structure and by function
Biogenic amines include
Catecholamines
Dopamine, norepinephrine (NE), and epinephrine
Indolamines
Serotonin and hisamine
Broadly distributed in the brain
Play roles in emotional behaviors and the biological clock

41. Classified by chemical structure and by function
Amino acids
GABA (Gamma-aminobutyric acid)
Glycine
Aspartate
Glutamate

42. Classified by chemical structure and by function
Peptides (neuropeptides)
Substance P
Mediator of pain signals
Endorphins
Act as natural opiates; reduce pain perception
Gut-brain peptides
Somatostatin and cholecystokinin

43. Classified by chemical structure and by function
Purines such as ATP
Act in both the CNS and PNS
Provoke pain sensation
Gases and lipids
Nitric oxide (NO)
Involved in learning and memory
Carbon monoxide (CO)
Regulator of cGMP in the brain
Endocannabinoids
Lipid soluble and involved in learning and memory

44. Neurotransmitters Direct action Indirect action
Neurotransmitter binds to channel-linked receptor and opens ion channels
Promotes rapid responses
Ach and amino acids
Indirect action
Neurotransmitter binds to a G-protein-linked receptor and acts through an intracellular second messenger
Promotes long –lasting effects
Biogenic amines, neuropeptides, and dissolved gases

45. Neurotransmitters Types of neurotransmitter receptors
Channel-linked receptors
G protein-linked receptors

46. Basic concepts of neural integration
Neuronal pools integrate incoming information and forward the processes information to other destinations
Simple neuronal pool
Single presynaptic fiber branches and synapses with several neurons in the pool
Discharge zone- neurons most closely associated with the incoming fiber
Facilitated zone- neurons farther away from incoming fiber

47. Types of circuits in neuronal pools
Diverging circuit
One incoming fiber stimulated an ever-increasing number of fibers, often amplifying circuits
May affect a single pathway or several
Common in both sensory and motor systems

48. Types of circuits in neuronal pools
Converging circuit
Opposite of diverging circuits; strong stimulation or inhibition
Also common in sensory and motor systems

49. Types of circuits in neuronal pools
Reverberating (oscillating) circuit
Chain of neurons containing collateral synapses with previous neurons in the chain
Parallel after-discharge circuit
Incoming fiber stimulates several neurons in parallel arrays to stimulate a common output cell

50. Neural processing Serial processing Parallel processing
Input travels along one pathway to a specific destination
Works in all-or-none manner to produce a specific response
Ex. reflexes
Parallel processing
Input travels along several pathways
Important in higher-level mental functioning
Ex. Smell reminds you of an odor and associated experience

51. Developmental aspects of neurons
Originates from the neural tube and neural crest formed from ectoderm
Neural tube becomes the CNS
Cell death
About 2/3 of neurons die before birth
Death results in cells that fail to make functional synaptic contacts
Many cells also die due to apoptosis (programmed cell death) during development

52. Multiple Sclerosis (MS)
An autoimmune disease that mainly affects young adults
Myelin sheaths in the CNS become nonfunctional scleroses
Shunting and short-circuiting of nerve impulses occurs, impulse condition slows and eventually ceases
Symptoms: visual disturbances, weakness, loss of muscular control, speech disturbances, and urinary incontinence.