1. Chp 9: Nervous tissue chp 11: autonomic nervous system chp 12: somatic senses and special senses

2. Chapter 9: Nervous Tissue Learning Objectives
Describe the organization of the nervous system.
Explain the three basic functions of the nervous system.
Contrast the histological characteristics and the functions of neuroglia and neurons.
Distinguish between gray matter and white matter.
Describe how a nerve impulse is generated and conducted.
Explain the events of synaptic transmission and the type of neurotransmitters used.

3. Structures of the Nervous System
CNS (Central Nervous System) Brain (110 billion neurons) and spinal cord (100 million neurons)
Function: processes different kinds of sensory information; source of thoughts, emotions, memories
PNS (Peripheral Nervous System) all nervous tissue outside the CNS
Nerves: bundles of 100s to 1000s of axons plus associated connective tissue and blood vessels lying outside the brain and spinal cord CLICK
CRANIAL nerves 1-12 (twelve pairs; right and left) emerge from base of brain CLICK
SPINAL nerves connect to brain encircled by bones of vertebral column CLICKed with previous
GANGLIA small masses of nervous tissue located outside the brain and spinal cord; contain cell bodies of neurons closely associated with cranial/spinal nerves CLICK
ENTERIC PLEXUSES; network of neurons in walls of organs of gastrointestinal tract; regulate digestive system
CLICK
SENSORY RECEPTORS; either in dendrites of sensory neurons (SKIN) or specialized cells (photoreceptors in the retina); monitor change in the internal/external environment CLICK

4. Organization of the Nervous System
Recall:
CNS - brain and spinal cord; integrates and correlates many different kinds of incoming sensory information; source of thoughts, emotions, and memories.
PNS – cranial nerves and their branches, spinal nerves and their branches, ganglia, and sensory receptors; functions divided into subdivisions….
Somatic nervous system (SNS)
_Sensory neurons_: convey information from somatic receptors in head, body wall, and limbs, and from receptors for special senses of vision, hearing, taste, and smell to CNS
_Motor neurons_: conduct impulses from CNS to _skeletal_ muscles only; can be consciously controlled, voluntary actions
Autonomic nervous system (ANS)
_ Sensory neurons _: convey information from autonomic sensory receptors, located in visceral organs (stomach, lungs) to CNS
_ Motor neurons _: conduct nerve impulses from CNS to _smooth_, _cardiac_ muscles and glands; cannot be consciously controlled, involuntary actions
Two divisions of ANS are: _sympathetic_ and _parasympathetic_; these divisions usually perform opposite functions
“Fight-or-flight” responses  _ sympathetic _______________
“Rest-and-digest” activities  _ parasympathetic ___________

5. SUBDIVISIONS OF PNS Somatic Nervous System (SNS)
Sensory neurons conveys information from somatic receptors in head, body wall, and limbs, and from receptors for special senses of vision, hearing, taste, and smell to CNS
Motor neurons conduct impulses from CNS to skeletal muscles only; can be consciously controlled, voluntary actions
Autonomic nervous system (ANS)
Sensory neurons convey information from autonomic sensory receptors, located in visceral organs (stomach, lungs) to CNS
Motor neurons conduct nerve impulses from CNS to smooth muscles, cardiac muscles and glands; cannot be consciously controlled, involuntary actions
Two divisions of ANS are sympathetic division and parasympathetic division; these divisions usually perform opposite functions
“Fight-or-flight” responses  emergency actions (sympathetic)
“Rest-and-digest” activities  GI tract activities (parasympathetic)

6. Enteric Nervous System (ENS)
nnGet a copy of checkpoint questions 1-3, complete them and hand them in… b
Enteric nervous system (ENS) follows a different pathway
Known as _”brain of the gut”_; operation is involuntary
Neurons found in and extend through _gastrointestinal (GI) tract______________
_ Sensory neurons _: monitor chemical changes within the GI tract and the stretching of its walls
_ Motor neurons _: govern _contraction_ of GI tract smooth muscle, _secretions_ of GI tract organs, and activity of GI tract endocrine cells.
CLICK>>>PLACE CKPOINT 1-3 on table
Get a copy of checkpoint questions 1-3,
complete them and hand them in…

7. Functions of the Nervous System
Sensory functions _ (AFFECTORS)
Sensory receptors_ detect stimuli inside and outside
the body.
- Sensory or afferent neurons carry information from cranial to
spinal nerves into brain and spinal cord or visa versa
Integrative functions _(LIKE A CONTROL CENTER)
Process sensory information by analyzing and storing
some of it and by making decisions for appropriate
responses
- Interneurons; have short axons that connect with neurons in brain,
spinal cord, and ganglion; are majority neurons in the body

8. Functions…continued Respond the integrative decisions
Motor functions _(EFFECTORS)
Respond the integrative decisions
- Motor of efferent neurons carry information from brain
toward spinal cord or out of brain to spinal cord into cranial or
spinal nerves
Sensory (afferent/affector) neuron-follow green, interneuron -follow red, and motor (efferent/effector)- follow blue, communicate via synapses in spinal cord

9. HISTOLOGY OF NERVOUS TISSUE
Two types of cells
Neurons
unique functions of the nervous system; sensing, thinking, remembering, controlling muscle activity, and regulating glandular secretions
Neuroglia
support, nourish, and protect neurons and maintain homeostasis in the intestinal fluid that baths neurons

10. Neurons Three parts: Processes or extensions: Cell Body
nucleus surrounded by cytoplasm; includes RER, lysosomes, mitochondria, Golgi
synthesizes cellular molecules needed for a neuron’s operation
Processes or extensions:
Dendrites (“little trees”)
multiple per single axon
combined with cell body receiving and input parts of a neuron
short, tapering, and highly branched, tree-branch array emerging from cell body
Axons_
conducts nerve impulses toward another neuron, muscle fiber, or gland cell
long, thin, cylindrical projection that joins cell body at a cone-shaped elevation
Axon hillock: cone-shaped elevation where axon joins cell body
Axon collaterals: side branches of some axons
Axon terminals: many fine processes that denote the ends of axon collaterals and axons
Synapse is site where two neurons or a neuron and an effector cell can communicate, can you find it in the picture??? Click>>
Synaptic end bulbs tips of most axon terminals CLICK>>>
Synaptic vesicles are tiny sacs that store chemicals
Neurotransmitters synaptic vesicle chemicals/molecules that are a means of communication at a synapse

11. nn

12. Classification of Neurons
STRUCTURAL CLASSIFICATION
Multipolar neurons: have several dendrites and one axon; most in brain and spinal cord
Bipolar neurons: have one main dendrite and one axon; retina of the eye, inner ear, olfactory area of brain
Unipolar neurons: dendrites and one axon fused together forming a continuous process that emerges from cell body; begin in embryo as bipolar neurons; most function as sensory receptors for touch, pressure, pain, or thermal stimuli. Cell bodies of most of this type located in ganglia of spinal and cranial nerves.

13. Classification of Neurons
FUNCTIONAL CLASSIFICATION
Sensory or afferent neurons: once sensory receptor activated, these form an action potential in their axon that is conveyed into the CNS through spinal and cranial nerves
contain sensory receptors at their distal ends or are located just after sensory receptors that are separate cells; most unipolar in structure
Motor or efferent neurons: convey action potential away from CNS to effectors (muscles and glands) in PNS through cranial and spinal nerves
Most are multipolar in structure
Interneurons or association neurons: integrate incoming sensory information from sensory neurons and then elicit a motor response by activating appropriate motor neurons
Located within CNS between sensory and motor neurons; most multipolar in structure

14. Neuroglia Smaller than neurons 5-50 times more numerous
”glue” that holds nervous tissue together
do not generate or conduct nerve impulses
can multiply and divide in mature nervous system
in case of injury or disease multiply to fill in spaces formerly occupied by neurons
Gliomas: brain tumors derived from glia called gliomas; very malignant and grow rapidly
6 types of neuroglia: point out in picture
4 in CNS astrocytes, oligodendrocytes, microglia, ependymal cells (not shown)
2 in PNS Schwann cells and satellite cells (not shown)

15. Myelination
Myelin sheath, many-layered covering composed of lipids and protein, surround the axons of most of our neurons.
Two Functions:
(1) insulates the axon
(2) increases the speed of nerve impulse conduction
The amount of myelin increases from birth to maturity
gaps in myelin sheath: nodes of Ranvier
Define myelinated: _axon with a myelin sheath______________________________________
Define unmyelinated: _axon without a myelin sheath_________________________________
What two diseases are known to destroy myelin sheaths? _multiple sclerosis, Tay-Sachs disease

16. Collections of Nervous Tissue
Clusters of Neuronal Cell Bodies
Ganglion: cluster of neuronal cell bodies located in PNS
Nucleus: cluster of neuronal cell bodies in CNS
Bundles of Axons
Nerve: bundle of axons located in PNS; cranial nerves connect brain to periphery and spinal nerves connect spinal cord to periphery
Tract: bundle of axons located in CNS; tracts interconnect neurons in spinal cord and brain

17. Gray and White Matter
White matter: myelinated and unmyelinated axons of many neurons which is white in color; also has blood vessels
Gray matter: neuronal cell bodies, dendrites, unmyelinated axons, axon terminals, and neuroglia white is grayish pink in color; also has blood vessels
Seen in spinal cord and brain…show next slide before handout…

18. ACTION POTENTIALS AKA  nerve impulses
Two features of plasma membrane needed for action potentials in muscle fibers and in neurons
existence of resting membrane potential
presence of specific types of ion channels
Membrane potential difference in the amount
of electrical charge inside and outside plasma
membrane.
membrane that has potential is polarized
Resting membrane potential  voltage difference between the inside and outside of a plasma membrane when not responding to a stimulus, in muscle fibers and neurons
voltage created by flow of ions

19. Ion Channels Two types of ion channels:
Leakage channels allow small but steady stream of ions to leak across the membrane
Gated channels  open and close on command
Voltage-gated channels are used to generate and conduct action potentials; open in response to a change in membrane potential
specific ions move from areas of high concentration to areas of low concentration, or from positively charged areas to negatively charged areas or vice versa to equalize differences in charges or concentration.

20. Resting Membrane Potential
Charge of the resting neuron outside surface of the plasma membrane is positive; on the inside its negative
Potential energy in cells is measured in millivolts; mV.
Resting membrane potential in neurons is -70mV; negative value because inside of the membrane is negative relative to the outside
Interstitial fluid is rich in Na+ ions and Cl- ions; cytosol is rich in K+ ions.
Sodium-potassium pump offsets the small inward leak of Na+ and outward leak of K+
DO QUESTION 8; ON YOUR OWN…
Resting membrane potential arises due to an unequal distribution of ions on either side of the plasma membrane and a higher membrane permeability to K+ than to Na+. The level of K+ is higher inside and the level of Na+ is higher outside, a situation that is maintained by sodium-potassium pumps.

21. Generation of Action Potential
Action potential (AP) or impulse generates rapidly occurring events that decrease and increase the membrane potential and eventually restore it to its resting state
Ability of muscle fibers and neurons to convert stimuli into action potential is called electrical excitability.
Stimulus in cell’s environment changes resting membrane potential; if stimulus causes cell to depolarize to a critical level; called a threshold (about -55mV) then an action potential arises
Two main phases:
Depolarizing phase- rapidly occurring events that decrease and eventually reverse polarization of membrane, makes inside more positive than outside; Na+ ions move into cell
Repolarizing phase- membrane polarization is restored to resting state; Na+ ions move back out cell restoring charge to original state

22. Explain the process of action potential from threshold state to depolarization to after-hyperpolarization phase. _Action potential depend on the existence of a resting membrane potential and the presence of voltage-gated channels for Na+ and K+. At resting membrane potential of -70mV, cell is polarized. Stimulus of muscle fibers or neurons convert action potential into excitability. During an action potential, voltage-gated Na+ and K+ channels open in sequence. Opening of voltage-gated Na+ channels results in depolarization, the loss and then reversal of membrane polarization (from -70mV to +30 mV). Then, opening of voltage-gated K+ channels allows repolarization, recovery of the membrane potential to the resting level.

23. All-or-None Principle
What is the all-or none principle? If a stimulus is strong enough to generate an action potential; the impulse generated is of a constant size (causes depolarization to threshold, voltage-gated Na+ and K+ channels open and action potential occurs). A very strong stimulus cannot cause a larger action potential because the size of an action potential is always the same, a weak stimulus that fails to cause a threshold-level depolarization does not elicit an action potential
What type of stimuli elicit an action potential? Strong
What is a refractory period? a period during which action potential cannot be generated

24. Depolarizing phase
Repolarizing phase
Reversal of polarization
Threshold
7.Resting membrane potential
Stimulus
6After-hyperpolarizing phase

25. Conduction of Nerve Impulses
Also called propagation
Way cells communicate information from one part of body to another
Nerve impulses travel from where they arise, usually axon hillock, along axon to axon terminal
Positive feedback process

26. Continuous & Saltatory Conduction
Continuous conduction
Step-by-step process; impulses travel a short distance in 10 milliseconds
Occurs in unmyelinated axons (muscle fibers)
Have smallest diameter
Saltatory conduction
Impulses leap from one node of Ranvier to the next
Occurs in myelinated axons
Have largest diameter
What type of factors influence the speed of nerve impulse conduction? _warmth (conducted at higher speeds), coolness (conduct at lower speeds); large diameters impulse moves faster, smaller diameter impulse moves slower; myelinated axons conduct impulses faster than unmyelinated

27. Synaptic Transmission
How synapses neurons communicate with other neurons or with effectors through a series of events
neuron sending the signal is called the presynaptic neuron
neuron receiving the signal called the postsynaptic neuron
A synaptic cleft separates the presynaptic and postsynaptic neurons
Neurotransmitters
Different neurotransmitters are found in synaptic vesicles. These different neurotransmitters have different effects.
GO TO NEXT SLIDE>>>>

28. Postsynaptic: Deactivating Neurotransmitters
Essential neurotransmitters are removed in order to restore normal synaptic function
Three ways:
Diffuse away from synaptic cleft (out of reach of receptors)
Destroyed by enzymes
Actively transported back into neuron (reuptake)
NEED TO ADD THIS TO NOTES!!!!!!
Complete synaptic transmission worksheet now….