1. The Nervous System

2. The Nervous System Overall Function COMMUNICATION
Works with the endocrine system in regulating body functioning, but the nervous system is specialized for SPEED

3. Neurons A neuron is the functional unit of the nervous system
Neurons are specialized for transmitting signals from one location in the body to another
Neurons consist of a large cell body (contain a nucleus and other organelles), and neuronal processes
Axons
Conduct messages AWAY from cell body
Dendrites
Conducts messages TOWARD cell body

4. Neuron Structure

5. Communication Lines Stimulus (input) Receptors (sensory neurons)
Integrators
(interneurons)
motor neurons
Effectors
(muscles, glands)
Response
(output)
Figure 34.1 Page 579

6. Major Nervous System Processes
Input
The conduction of signals from sensory receptors to integration centers in the nervous system
Integration
The process by which the information from the environmental stimulation of the sensory receptors is interpreted and associated with appropriate responses of the body
Motor Output
The conduction of signals from the processing center to the muscle cells or gland cells that actually carry out the body’s responses to stimuli

7. Central and Peripheral Nervous Systems
The central nervous system consists of the brain and spinal cord
This is where integration occurs
Made of interneurons
The peripheral nervous system consists of the nerve cells that communicate signals between the CNS and the rest of the body
Sensory neurons
Carry info from the sensory receptors to the brain
Motor neurons
Carry info from the brain to effector cells (to do whatever the brain said!)
Central and Peripheral Nervous Systems

8. Action Potentials
In order to actually TRANSMIT a signal, the voltage (charge) across the membrane has to change
A signal will cause the ion channels to open, letting some of the ions (Na+, K+) through, trying to achieve EQUILIBRIUM
This depolarizes the membrane
This causes the signal to be passed along the neuron, which is known as an ACTION POTENTIAL (like a wave of electricity)

9. Action Potentials Action potentials are either ALL or NONE
Either there is enough change in the voltage to pass the message along, or there isn’t
The neuron either “fires” or it doesn’t fire
If your hand is on a 100˚C stove, the action potentials aren’t STRONGER than if you were on a 50˚C stove; they just happen MORE OFTEN

10. Structure of a Neuron dendrites INPUT ZONE cell body axon OUPUT ZONE
TRIGGER ZONE
CONDUCTING ZONE
axon endings
Figure 34.2
Page 580

11. Resting Potential
Charge difference across the plasma membrane of a neuron
Fluid just outside cell is more positively charged than fluid inside because of larged negatively charged proteins in the cytoplasm
Potassium (K+): Higher inside than outside
Sodium (Na+): Higher outside than inside
Potential is measured in millivolts
Resting potential is usually about -70mv

12. Action Potential A transitory reversal in membrane potential
Voltage change causes voltage-gated channels in the membrane to open
Na+ leaks in (depolarization): Inside of neuron briefly becomes more positive than outside
K+ leaks out (repolarization): Inside goes back to being negatively charged compared to outside.
Na+ / K+ pumps the Na+ and K+ back to original positions (refractory period)

13. Action Potential 1 2 3 4 Figure 34.5d Page 583 Na+ Na+ Na+ K+ K+ K+ K+

14. All or Nothing All action potentials are the same size
If stimulation is below threshold level, no action potential occurs
If it is above threshold level, cell is always depolarized to the same level

15. Recording of Action Potential
+20
-20
Membrane potential (millivolts)
threshold
-40
resting membrane potential
-70 1 2 3 4 5
Figure 34.6b Page 583
Time (milliseconds)

16. Chemical Synapse
Gap between axon of one neuron and dendrite of adjacent neuron
Action potential in axon ending of presynaptic cell causes voltage-gated calcium channels to open
Flow of calcium into presynaptic cell causes release of neurotransmitter into synaptic cleft
plasma membrane of axon ending of presynapic cell
plasma membrane of postsynapic cell
synaptic vesicle
synaptic cleft
membrane receptor
Figure 34.7a Page 584

17. Neurotransmitters
Neurotransmitters are substances that carry the “message” across the synapse
Important neurotransmitters:
Acetylcholine (bridges gaps between motor neurons & muscle cells),
norepinephrine, dopamine, serotonin work in CNS

18. Synaptic Transmission
Neurotransmitter diffuses across cleft and binds to receptors on membrane of postsynaptic cell
Binding of neurotransmitter to receptors opens ion channels in the membrane of postsynaptic cell

19. Ion Gates Open neurotransmitter ions receptor for neurotransmitter
gated channel protein
Figure 34.7c Page 584

20. Synaptic Transmission
Enzymes in synaptic cleft will degrade neurotransmitters after action potential is initiated on the post-synaptic cell. The neurotransmitters are recycled after they are broken down.
Example: Acetylcholine is broken down by the enzyme cholinesterase

21. Nerve A bundle of axons enclosed within a connective tissue sheath
myelin sheath
nerve
fascicle
A bundle of axons enclosed within a connective tissue sheath
Figure Page 586

22. Myelin Sheath A series of Schwann cells Sheath blocks ion movements
Action potential must “jump” from node to node; CREATES RAPID MOVEMENT OF ELECTRICAL IMPULSE
Figure 34.11a Page 586

23. Multiple Sclerosis A condition in which nerve fibers lose their myelin
Slows conduction
Symptoms include visual problems, numbness, muscle weakness, and fatigue

24. Reflexes Automatic movements made in response to stimuli
In the simplest reflex arcs, sensory neurons synapse directly on motor neurons; interneurons in CNS aren’t involved.
Most reflexes involve an interneuron

25. Stretch Reflex Figure 34.12b Page 587 STIMULUS Biceps stretches.
sensory neuron
motor neuron
Response
Biceps contracts.
Figure 34.12b Page 587

26. Central and Peripheral Nervous Systems
Central nervous system (CNS)
Brain
Spinal cord
Peripheral nervous system
Nerves that thread through the body

27. Peripheral Nervous System
Somatic nerves
Controls skeletal muscle (voluntary)
(Shown in green)
Autonomic nerves
_ Controls certain organs, smooth muscle & cardiac muscle (involuntary)
(Shown in red)
Figure Page 591

28. Two Divisions of Autonomic Nervous System
Sympathetic: “speeds up” heart, breathing, release of sugar into blood; fight or flight response
Parasympathetic: slows heart, breathing rate; causes secretion of digestive enzymes, etc.
Most organs receive input from both
Usually have opposite effects on organ

29. Structure of the Spinal Cord
ganglion
nerve
meninges
(protective
coverings)
vertebra
Figure 34.19a Page 593

30. Divisions of Brain Division Main Parts Forebrain Cerebrum
Olfactory lobes
Thalamus
Hypothalamus
Limbic system
Pituitary gland
Pineal gland
Midbrain
Tectum
Hindbrain
Pons
Cerebellum
Medulla oblongata
anterior end of the
spiral cord
Figure Page 594

31. Cerebrospinal Fluid Surrounds the spinal cord
Fills ventricles within the brain
Blood-brain barrier controls which solutes enter the cerebrospinal fluid
Figure Page 595

32. Anatomy of the Cerebrum
Largest and most complex part of human brain (Responsible for thinking & higher level functions)
Outer layer (cerebral cortex) is highly folded
A longitudinal fissure divides cerebrum into left and right hemispheres
Corpus collosum connects the two hemispheres

33. Lobes of the Cerebrum Parietal Frontal Occipital Temporal
Primary somatosensory cortex
Primary motor cortex
Parietal
Frontal
Occipital
Temporal
Figure 34.25a Page 597

34. Limbic System Controls emotions and has role in memory
(olfactory tract)
cingulate gyrus
thalamus
amygdala
hypothalamus
Figure Page 597
hippocampus

35. Other Parts of the Brain
Cerebellum - Controls muscle coordination and posture
Medulla oblongata- Controls heart rate & breathing rate

36. Variations in Nervous Systems Among Animals