1. Chapter 45
Nervous Regulation

2. Nervous Systems Contains Contains : Subdivided into Brain Spinal Cord
Peripheral Nervous System
(PNS)
Central Nervous System
(CNS)
Contains :
Sensory Receptors
Sensory Neurons
Stimulus detection
Effectors
Muscles and Glands
Motor Neurons
Respond to stimuli
Subdivided into
Autonomic System
Involuntary regulation
Somatic System
Voluntary regulation
Contains
Brain
Control and coordination of responses to stimuli
Spinal Cord
Interneurons – relay information
Interneurons are located in both the brain and spinal cord
Nervous Systems

3. I) Impulse Pathways Impulses move in one-way pathways along neurons
Receptor (sensory structures)
Sensory Neurons
Interneurons (brain and/or spinal cord)
Motor Neurons
Effectors (response structures)
ReceptorSensory NeuronInterneuronMotor NeuronEffector

4. II) Neurons Neurons are nerve cells with specialized structures
Cell body (cyton) – contains nucleus and organelles to regulate cell processes
Dendrites – cytoplasmic extensions that contain receptors for sensory stimuli
Temperature, touch, pressure, chemicals
Axon – long extension of cytosol that carries impulses
Myelin Sheath – lipid layer that insulates axons
Myelin is formed by Schwann cells growing on the axon
Schwann cells are a support cell known as a glial cell
Terminal Branches – end branches of neuron
Synaptic Knobs – end of the neuron that contain neurotransmitters

5. III) Nerve Impulses Neurons are electrically excitable
Impulses are the result of depolarizations along the neuron
Neurons maintain a resting potential using the sodium- potassium pump
Ions move across the membrane through ion channels
Voltage gated channels open at a specific charge
Sodium – open at -55mV and close at +35 mV
Potassium – open at +35 mV and close at -70 mV
Calcium – located at synaptic knobs only - open at +35mV
Resting Potential
Internal charge is -70mV (lower than the outside)
Sodium is in a higher concentration outside the cell
Polarized membrane has potential for activity to occur
Depolarization
Occurs when ions move across a membrane and the charge difference changes
Becomes less polarized

6. Threshold Potential (-55mV)
Local Potential – some Na+ ions enter the cell in response to a stimulus (-70mv to -56V)
Results in a depolarization as more Na+ enters the cell reducing the charge difference across the membrane
Interior of neuron gradually increases in electrical charge
Ligand-gated Na+ channels open
Threshold Potential (-55mV)
The point at which an impulse “fires”
All-or-nothing event – must achieve -55mV voltage
When threshold is reached ALL voltage gated Na+ ion channels open and Na+ ions rush into the cell
Action Potential (Impulse)
Moment when all Na+ channels open and the cell interior becomes positively charged to +35mV
Repolarization – return to resting potential (-70mV)
All voltage gated Na+ channels close and voltage-gated K+ channels open to let potassium exit the cell
The Na+ / K+ pump moves Na+ out of the cell
Remember the Na+ / K+ pump operates the entire time
During repolarization Na+ and K+ exit the neuron to return the interior to a negative (-70mV) charge animation

7. F. Impulse Propagation Nerve impulses travel at very high rates
Approximately 100 meters/second
Two Factors Affect Impulse Speed
Diameter of Axon
Large diameter reduces internal resistance
Myelination of Neurons
Myelin sheath insulates nerves and promotes “jumping” impulses
Saltatory Conduction – impulses “jump” from node to node animation
Fewer depolarizations are required -
Depolarization only occurs at exposed areas on Nodes of Ranvier

8. IV) Synapses Microscopic gaps between neurons
Synaptic cleft (synapse) is 20 nm wide
Two components to a synapse
Presynaptic Membrane (synaptic knob of terminal branch)
Contains synaptic vesicles filled with neurotransmitter
Calcium ions enter the presynaptic membrane in response to the influx of sodium from an action potential
This causes the vesicles to fuse with cell membrane and release neurotransmitters into synaptic cleft
Post Synaptic Membrane (dendrites of another nerve cell)
Contains ligand-gated sodium ion channels
Ligand-gated channels open only when a neurotransmitter (ligand) binds to the receptor site
This causes an influx of sodium ions and starts an action potential in the post-synaptic membrane
animation

9. V) Human Nervous System
Central Nervous System
Brain
2 hemispheres (sides) separated by a large furrow
Connected by nerves called corpus callosum
Provides integration between 2 hemispheres
3 Major parts of the brain
Cerebrum – thought, senses, memory, conscious activity
Cerebellum – coordination of movements
Medulla Oblongata – involuntary actions, reflexes, heart rate, breathing, blood pressure
Other structures
Hypothalamus – body temperature, control of pituitary gland, hunger, thirst
Thalamus – integration of sensory impulses to cerebral cortex

10. Peripheral Nervous System
Spinal Cord
Relay of impulses from peripheral nervous system
Reflex regulation
Reduces reaction time
Does not require thought and cerebral processing
Peripheral Nervous System
Contains sensory and motor neurons
Two Subdivisions
Autonomic System – involuntary actions
Heart rate
Blood pressure
Hormone secretion
Secretion of digestive enzymes

11. Subdivisions of Autonomic System
Sympathetic Nervous
System
Parasympathetic Nervous System
Stimulation
Increases the following:
Heart rate
Blood pressure
Adrenaline release
Glucose released into blood
Dilates iris
Inhibits digestion
Dry mouth
Conserve Energy
Decreases the following:
Heart rate
Blood pressure
Glucose release
Increased salivation
Increased digestion
“rest and rumination”
Subdivisions of Autonomic System

12. Somatic Nervous System
Control of voluntary activities
Skeletal muscles
Diaphragm
Blinking