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Chapter 4

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John Gibson

on 1 June 2016

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Transcript of Chapter 4

The Nervous System
Homeostasis
Ability of an organism or cell to maintain internal equilibrium
Adjusting its physiological processes to keep functions within physiological limits at rest or during exercise.
Examples:
increased body temperature
changes in acid-base balance
hypohydration
blood pressure
blood glucose
Positive Feedback
Negative Feedback
Positive Feedback
Changes in the environment cause reactions to occur at a faster and more intense rate
Increased acidity of muscles cause more blood flow to those muscles.
As acidity continues to rise, blood flow increases
Open wound
Child birth
Negative Feedback
Most common
As environment changes it diminishes or reduces the intensity of an ongoing process
Sweating
Most hormonal processes
Neurons
electrically excitable cell
initiates, receives and transmits information throughout the body
dendrites
cell body
axons
axon hillock
different shapes and sizes
different functions
Cell Body
contains nucleus, mitochondria, ribosomes, etc.
Dendrites
receive information
sends info to the cell body
Axons
transfers signal to another cell
dendrites must receive a stimulus that exceeds a threshold
once the threshold is reached the axon can pass along the stimulus
Axon Hillock
gate keeper for an action potential
location of summation of all incoming electrical signals
once threshold is reached an action potential is sent down the axon
Shapes and Sizes
Multipolar
many dendrites and one axon
motor
Pseudounipolar
axon and dendrite fuse to form a single process
sensory
bipolar
one axon and one dendrite
sensory
Different Length
a few millimeters
to more than a meter
7 foot tall athlete
Sensory
Relays information from the periphery to the central nervous system
long dendrite, short axon
Motor Neurons
Short dendrites from the spinal cord.
Long axon to the muscle fibers
Interneurons
Only found in the central nervous system
Main function is to connect sensory and motor neurons
Help fine tune motor control
Neuroglia
Only 10% of CNS is neurons
The rest are neuroglia cells or glial cells
They are their to help support the neurons
Ex. Myelin Sheath
helps conduct impulse faster
Synapses
Synapse is the point of connection and communication between two excitable cells
The process
impulse travels down nerve axon to the nerve terminal (pre-synaptic neuron)
stimulates release of neurotransmitters
neurotransmitters diffuse across a small gap (synaptic cleft) and binds to receptors on the target cell (post-synaptic neuron)
causes a reaction in the target cell
types of synapse
Target Cells
Examples
dendrites of neurons
muscle cells
secretory cells
Chemical Synapse
Neurotransmitters pass across the synaptic cleft
Bind to receptors
Opens channels allowing the movement of ions across the post-synaptic membrane
If adequate amounts of ions cross the membrane a response will occur in the post-synaptic membrane
Electrical Synapse
Not very common in mammals
heart muscle
smooth muscle
allows ions of one cell to pass directly to the adjacent cell
Common Neurotransmitters
acetylcholine (Ach)
histamine
norepinephrine
dopamine
serotonin
glutamate
gamma-aminobutyric acid (GABA)
glycine,
substance P
enkephalins
endorphins
Receptors
proteins designed to bind to specific substance (neurotransmitter, hormone, etc.)
these substances are called ligands
only one ligand per receptor and only one receptor per ligand
Organization of The Nervous System
Central Nervous System (CNS)
brain
spinal cord
Peripheral Nervous System (PNS)
Autonomic Nervous System (has its own subdivisions)
Sensory-Somatic Nervous System
Central Nervous System
Brain - Protected by the skull
Spinal Cord - Protected by the vertebrae
Bathed in cerebrospinal fluid
helps protect the tissue
keeps the environment constant
Brain
Cerebrum
Cerebellum and Medulla Oblongata
Hypothalamus
Cerebrum
largest part of the human brain
left and right hemispheres connected by the corpus callosum
covered by gray matter
Cerebellum and Medulla Oblongata
unconscious brain
includes midbrain and pons
regulates heart, breathing, blood pressure and reflexes like swallowing, hiccups, etc.
cerebellum regulates muscle coordination and balance
Hypothalamus
Most important regulatory part of the brain
Regulates
thirst
body temperature
blood pressure
water balance
endocrine function
Spinal Cord
Transmits information from the brain to periphery
site of reflex action
Reflex Action
Knee tap reflex
Reciprocal innervation (inhibition)
Continuous practice trains the reflexes to automatically respond to sensory stimuli
Peripheral Nervous System
Autonomic Nervous System
Sympathetic Nervous System
Parasympathetic Nervous System
Thought to be unconscious (but there may be some conscious control)-bear and surgery
Sensory-Somatic Nervous System
Sensory (afferent)
Motor (efferent)
Sympathetic Nervous System
Division of autonomic nervous system
Freeze, Flight or Fight
Stimulates physiological systems of survival and stress
Examples
increased heart rate and blood pressure
more blood flow to skeletal muscles
release of glucose by the liver
breakdown of glycogen in muscles
Parasympathetic Nervous System
controls body's homeostatic state
rest and digest
brings body back to resting levels
ability to return to resting levels is trainable
Sensory-Somatic Nervous System
Sensory
receives signals from the periphery
Motor
controls muscle contraction
Motor Unit
contains alpha motor neuron and all muscle fibers stimulated by that neuron
motor units fall into one of three categories
slow motor units
fast fatigue resistant motor units
fast fatigable motor units
different number of fibers
different amounts of force development occurs by stimulation of varying amounts of motor units
Slow Motor Unit
slow action potential
time to twitch or peak force is slow
small axon
associated with Type I
Fast Fatigue Resistant Motor Units
FFR
larger axon
increase rate of propagation
type IIA
Fast-Fatigable Motor Units
FF
large axon
very quick action potential
high levels of force production
very rapid twitch rate
Fiber Amount
fine control will have fewer muscle fibers
5-10 fibers per motor unit
less control will have more muscle fibers
up to 1000 fibers per motor unit
Action Potential
Propagation of an electrical impulse
aka nervous impulse
resting membrane potential
the impulse
neurotransmitter release
Resting Membrane Potential
impermeable membrane separates ions
Na+ outside the cell
K+ inside the cell
net negative charge inside the cell due to negatively charged ions (e.g., phosphate groups)
-65 to -70 mV
Impulse
As an impulse travels it makes the membrane become permeable to Na+
Na+ enters the cell and stimulates K+ permeability
Causes depolarization
Na+ and K+ channels close
Na+ and K+ exchange pumps push Na+ out and pull K+ in
Neurotransmitter release
Action potential stimulates the release of secretory vesicles
Neurotransmitters are either excitatory or inhibitory
excitatory neurotransmitters increase permeability to Na+
inhibitory neurotransmitters increase permeability to K+ and Cl-
Myelination
myelinated nerves conduct an impulse up to 100m/s
unmyelinated nerves conduct an impulse from .5 to 10 m/s
saltatory conduction
Saltatory Conduction
Nodes of Ranvier
Size Principle
Impulse travels faster through a larger diameter neuron
Larger neurons are harder to recruit than smaller neurons
Small (type I) fibers will be recruited first
Amount of force produced is dependent on the number and type of motor units recruited
Asynchronous Recruitment
Asynchronous Recruitment
During endurance activity, Type I motor units have the ability to alternate contraction between motor units
Cycling motor units to allow some to rest while others contract
The greater the force requirement, the less asynchronous recruitment occurs
All-or-None Law
When threshold is achieved in the axon of a motor unit all muscle fibers of that motor unit will contract
When threshold isn't achieved none of the muscle fibers of that motor unit will contract
Gradations of Force Production
We achieve different levels of force production based on the number of motor units recruited
The is called multiple motor unit summation
Wave summation
how rapidly action potentials are generated to stimulate a motor unit
Rate Coding - Ability of neurons to vary the rate of generating action potentials
Neural Adaptations
Neural drive - measure of motor unit recruitment and rate coding
Measured through electromyography (EMG)
Weight training produces same force with lower EMG activity
Strength increases due to hypertrophy don't show up for a couple weeks
Neural Adaptations
30% increase in strength can be attributed to 9% from hypertrophy
Strength increases could be due to
increased neural drive
increased motor unit firing
greater synchronization between different motor units
increased excitability of motor neurons
Sports Specific Neural Adaptations
Rowers learn how to alternate muscle recruitment
NMJ Adaptations
Endurance Training
increase acetylcholine
increase post-synaptic receptors
Resistance Training
increase the size of NMJ
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