Nervous System- The Control Center of Your Body
Cell Types of Neural Tissue:
1. Neurons
a. Nerve cells
b. Respond to stimuli and signals
2. Neuroglial cells
a. Provide support, nutrition, and insulation
b. Helps with the signal transmission in the NS
Divisions of the NS
1. CNS (Central Nervous System )- ​Main Control Center
a. Brain
b. Spinal Cord
2. PNS (Peripheral Nervous System)​- allows CNS to communicate with the body
a. 2 Divisions:
i.
Sensory Division (AFFERENT- carrying TO NS)​- picks up sensory
information and delivers it to CNS
ii.
Motor Division (EFFERENT carrying AWAY from NS)​- Carries
information to muscles and glands
1. 2 Divisions:
a. Somatic​- carries information to the skeletal muscles
b. Autonomic​- carries information to smooth muscle, cardiac
muscle, and glands.
b. Made up of:
i.
Cranial Nerves
ii.
Spinal Nerves
1
Functions of the NS
1. Sensory Input (Monitor Stimuli)
a. Sensory receptors gather information
b. Information is carried to the CNS
2. Integrative Functions (Interpret Sensory Input)
a. Sensory information used to create:
i.
Sensations
ii.
Memory
iii.
Thoughts
iv.
Decisions
3. Motor Function (Response to Stimuli)
a. Decisions are acted upon
b. Impulses are carried to effectors
i.
Effectors do the work
Neuron Structure
Classification of Neurons- STRUCTURAL Difference
● Bipolar ​(rare)
○ 2 processes
■ processes= projecting part
○ Eyes, ears, and nose
● Unipolar
○ One process
○ Found in sensory receptors (Ganglia).
● Multipolar ​(99% of your neurons)
2
○
○
Many processes
Most neurons of CNS
Classification of Neurons- FUNCTIONAL Differences
● Sensory Neurons
○ Afferent
■ Transmits impulses FROM sensory receptors TOWARD the CNS
○ Most are unipolar
○ Some are bipolar
○ Ex: skin or internal organs
● Interneurons ​(Association Neurons)
○ Link neurons
○ Transmits between sensory and motor neurons
○ Most abundant
■ Found in CNS
○ Multipolar
● Motor Neurons
○ Efferent
■ Transmits impulse AWAY from CNS TO the effectors in the body
○ Multipolar
Types of Neuroglial Cells in the PNS
1. Schwann Cells​= oligodendrocytes
a. Produce myelin found on peripheral myelinated neurons
b. Speed neurotransmission
2. Satellite Cells ​=astrocyte cells
a. Surround neuron cell bodies
b. Support clusters of neuron cell bodies (ganglia)
Types fo Neuroglial Cells in the CNS
1. Astrocytes ​=satellite cells
a. Exchanges materials between neurons and capillaries
b. Support and regulates ions
c. Induce synapse formation
3
d. Connects neurons to blood vessels
e. Ex: CNS Scar tissue
2. Microglia
a. Defend and protect
i.
Immune defense against invading microorganisms
1. Phagocytic cells
3. Oligodendrocytes ​= Schwann Cells
a. Insulate and form the myelin sheath
i.
CNS myelinating cells
4. Ependyma
a. Create, secrete, and circulate cerebrospinal fluid that cushions organs
b. Ciliated
c. Lines cavities
i.
Line central canal of spinal cord
ii.
Line ventricles of the brain
APPLICATION: ​Spider crawling on your leg
1. Legs of spider activate ​unipolar ​sensory neurons in the skin of your knee
2. The signal travels up an axon wrapped in ​Schwann Cells​ and into the spinal cord
3. The signal gets passes onto several ​multipolar ​cells in the spinal cord where one of 2
things happen:
a. Some might automatically send the signal straight back down ​multipolar
neurons to your quadriceps muscle.
b. The signal gets passed up your spinal cord to your brain
i.
Your body recognizes the thing on your leg as a spider
ii.
Your brain decides what to do
4. You kick your leg to get the spider off or flick it with your hand
Regeneration of a Nerve Axon
The Synapse
● The meeting point between 2 neurons
● Nerve impulses pass from neuron to neuron at a synapse.
4
●
●
Able to change and adapt in response to neuron firing patterns
2 Types:
● Electrical Synapse
○ immediate or urgent
● Chemical Synapse
○ Used more often
○ Not as urgent
○ Controlled and more personal
○ Use NTM
■ NTM are released when impulse reaches the synaptic knob.
APPLICATION​: Drug Addiction
● occurs because of the complex interaction of neurons, drugs, and individual behaviors
understanding how neurotransmitters fit receptors can help explain the actions of certain drugs.
● Drugs have different mechanisms of action several questions remain about the biological
effects of addiction, such as why some individuals become addicted and others do not.
Resting Membrane Potential
● More negative on the inside than outside
● Na+/ K+ pump (straddles the neural membrane)
○ For every 2 K+ ions it brings in, it pumps 3 Na+ ions out that create a gradient.
● Resting State= -70mV
● If a membrane is more negative it is ​polarized.
● If membrane potential becomes less negative, it is​ depolarized.
● Graded- ​a little sodium gets through making a small change in membrane potential
○ The​ summation ​can lead to ​threshold stimuli​ that start an action potential.
Action Potential
● Brief reversal of ​membrane potential​ (-70mV to +40mv)
● Self-propagating
● All-or-none response
○ If it doesn’t meet -55mV it won’t happen (false alarm)
● All impulses carried on same strength, but different frequency.
● Na+ surround membrane
● K+ are on inside
● -proteins on inside
○ More proteins than K+ giving the inside a negative charge
States of Neurons
● Resting-State​: -70mV (polarized)
● Initial Threshold​: -55mV
● Peak Depolarization​: +40mV
Gates (evens out concentrates):
Ion channels provide gateway across the cell when gates are open
1. Voltage-gated Channel
5
a. Open and close in response to changes in membrane potential
2. Ligand-Gated Channel
a. Open when an NTM latches to its receptor
b.
3. Mechanically-Gated Channel
a. Opens in response to the physical stretching of a membrane
Steps of Action Potential
1. The membrane is in ​resting state​ (-70mV)
2. Environmental stimulus occurs
a. Temperature change, light, or pressure
i.
Affects the membrane by opening gated ion channels
3. Triggers sodium channels to open
4. MUST CROSS THRESHOLD OF -55mV (​all-or-none/ initial threshold​)
5. Voltage-gated Na+ channels open allowing Na+ to get through
6. Na+ ions rush in, depolarizing the membrane
7. Reaches +40mV (​peak depolarization​)
8. Repolarization starts
9. Voltage-gated K+ channels open in an attempt to rebalance the charges.
10. Hyperpolarization​ occurs and voltage drops to ​-75mV
11. Na+/K+ pump takes over and brings membrane back to ​resting state​ (-70mV)
6
Refractory Period
● Absolute
○ The time when a threshold stimulus does not start another action potential.
● Relative
○ The time when a stronger threshold stimulus can start another action potential.
Synaptic Transmission
An AP in one neuron will generate an AP in other cells across the synapse
1. The ​electrical synapse​ sends an ion current directly from the cytoplasm through ​gap
junctions.
2. The ​presynaptic neuron​ sends the signal
3. The signal transmits through the ​presynaptic terminal (axon terminal).
4. The ​postsynaptic neuron​ receives the signal, accepts ​NTW​ in the​ receptor region
(usually on the dendrite or cell body)
5. The chance of the synapse continuing the AP to the next neuron depends on the sum of
all the inhibitions in that area.
Synaptic Potentials
Depends on which NTM binds to which receptor
● EPSP
○ Excitatory Postsynaptic Potential
○ Graded
○ Depolarizes (makes inside more positive) and brings it closer to AP
● IPSP
○ Inhibitory Postsynaptic Potential
○ Graded
○ Hyperpolarizes (makes inside more negative) and AP becomes less likely.
Summation of EPSP and IPSP
● EPSPs and IPSPs are added together in a process called ​summation.
● More EPSPs lead to a greater probability of action potential.
Impulse Processing
The way the NS processes nerve impulses and acts upon them.
1. Neuronal Pools
a. Groups of interneurons that make synaptic connections with each other.
7
b. Interneurons work together to perform a common function
c. Each pool receives input from other neurons
d. Each pool generates output to other neurons.
2. Convergence
a. A neuron receives input from several neurons
b. Incoming impulses represent information from different types of sensory
receptors.
c. It allows the NS to collect, process, and respond to information.
d. It makes it possible for a neuron to sum impulses from different sources.
3. Divergence
a. One neuron sends impulses to several neurons
b. Can amplify an impulse.
c. The impulse from a single neuron in CNS may be amplified to activate enough
motor units’ needs for muscle contraction.
8