What does the nervous system include?
brain, spinal cord, nerves
What are the functions of the nervous system?
overall function - coordinate the body’s systems by receiving and sending information, maintaining homeostasis
Sensory Input
gathering information from receptors in the body
to monitor changes occurring inside and outside the body
changes = stimuli
Integration
to process and interpret sensory input and decide if action is needed and where the action will occur
Motor Output
a response to integrated stimuli
the response activates muscles or glands to maintain homeostasis
What are the two divisions of the nervous system?
Central Nervous System (CNS), Peripheral Nervous System (PNS)
Central Nervous System (CNS)
brain and spinal cord
Peripheral Nervous System (PNS)
nerves throughout the body
31 pairs of spinal nerves
12 pairs of cranial nerves
What are the functional classification of the peripheral nervous system?
sensory (afferent) division, motor (efferent) division
Sensory (Afferent) Division
nerve fibers that carry information to the central nervous system
Motor (Efferent) Division
nerve fibers that carry impulses away from the central nervous system, two subdivisions (somatic nervous system, autonomic nervous system)
Somatic Nervous System
voluntary; ex. skeletal muscles
Autonomic Nervous System
involuntary; ex. smooth and cardiac muscles, glands
What are the nervous tissues (support cells)?
support cells in the CNS are grouped together as “neuroglia"; functions: to support, insulate, and protect neurons
What are the types of support cells?
microglia
oligodendrocytes
astrocytes
ependymal cells
schwann cells'
satellite cells
Microglia Cells
immune function; spider-like phagocytes that digest debris and kill bacteria
Oligodendrocytes
make myelin sheath that provides insulation around the axons in the central nervous system
Astrocytes
abundant; star-shaped cells; brace neurons; connect blood vessels to neurons; form barrier between capillaries and neurons; control the chemical environment of the brain
Ependymal Cells
forms membranes around tissue; lines cavities of the brain and spinal cord; circulates cerebrospinal fluid
Schwann Cells
form the insulating myelin sheath around the neurons in the PNS (same function as oligodendrocytes, which are found only in the CNS)
Myelin Sheaths
insulate axons; schwann cells supply the myelin for peripheral neurons; oligodendrocytes myelinated the axons of the central nervous system
What are the gaps in the sheath are called?
nodes of ranvier
Satellite Cells
protect neuron cell bodies
Neurons
masses of nerve cells that transmit information (functional unit of the system); major regions are cell body and processes (dendrites and axons)
Cell Body
contains the nucleus and other cell organelles
Dendrites
shorter, more numerous, receive information, conducts information toward the cell body
Axons
single long fibers, conducts information away from the cell body
Where do axons ends?
in axonal terminals
What do axonal terminals contain?
vesicles with neurotransmitters (different neurotransmitters for different muscles)
What are axonal terminals separated from?
separated from the next neuron by a gap or a synapse
Chromatophilic Substance (Rough ER)
transport system
Myelin
insulation surrounding axons (white, fatty material)
Nodes of Ranvier
gaps in the insulation
Neurofibrils
fibers within the axon
Sensory (Afferent) Neurons
carry impulses from the sensory receptors to the CNS
What are the sensory receptors?
cutaneous sense organs; proprioceptors; other sensory organs (eyes, ears, nose, mouth)
Cutaneous Sense Organs
naked nerve endings (temperature and pain); Meissner’s Corpuscle (light touch); Pacinian Corpuscle (deep touch)
Proprioceptors
detect stretch or tension in tendons, ligaments, or muscles
Motor (Efferent) Neurons
carry impulses from the CNS to viscera, muscles, or glands
Interneurons (Association Neurons)
found in neuro pathways in the CNS; connect sensory and motor neurons
Myelinated
white matter
Unmyelinated
grey matter
What are the functional parts of a neuron?
sensory, motor, interneurons
What are the structural parts of the neuron?
bipolar, unipolar, multipolar
FUN FACTS!!! :)
longevity - can live and function for lifetime
do not divide - fetal neurons lose their ability to under go mitosis; neural stem cells are an exception
high metabolic rate - require abundant oxygen and glucose
the nerve fibers of newborns are unmyelinated - this causes their responses to stimuli to be cause and sometimes involve the whole body
What are some cell membrane potentials?
resting potential, threshold potential, action potential
Nerve Impulse
weak electric current, like a wave
How does Voltage-gated Na+ Channels work?
neuron membrane maintains resting potential
threshold stimulus is received
sodium channels open
sodium ions diffuse inward, depolarizing the membrane
potassium channels open
potassium ions diffuse outward, repolarizing the membrane
the resulting action potential causes a local bioelectric current that stimulates the membrane
wave of action potentials travel the length of the axon as a nerve impulse
Depolarization
is the loss of the difference in charge between the inside and outside of the plasma membrane of a muscle or nerve cell due to a change in permeability and migration of sodium ions to the interior
Repolarization
is when potassium ions rush out of the neuron after sodium ions rush in
the sodium-potassium pump, using ATP, restores the original configuration
potassium ions diffuse out of the cell as the membrane permeability changes again restoring the negative charge on the inside of the membrane and the positive charge on the outside surface
Nerve Impulse
speed is proportional to the size of the axon (a greater diameter = faster impulse); myelinated axons conduct impulses faster than unmyelinated ones
What is the synapse?
is the junction between two communicating neurons; a nerve pathway is the path from which nerve impulses travels from neuron to neuron
What is the synapse’s nerve pathway follow (in order)?
dendrite, cell body, along axon, synapse, dendrite
What happens when electrical impulses are not able to cross the synapse to another nerve?
a neurotransmitter is released from a nerve’s axon terminal; he dendrite of the next neuron has receptors that are stimulated by the neurotransmitter; an action potential is started in the dendrite
How are transmission of a signal at the synapses completed?
a neurotransmitter is released at the gap to signal the next neuron; receptors on the dendrite receive this chemical message
Anatomy of the Synapse
A: Neuron (axon)
B: Neuron (dendrite)
mitochondria
vesicles
receptor
synapse
receptor
calcium channel
release neurotransmitter
re-uptake
What are the types of neurotransmitter?
excitatory, inhibitory
Excitatory
increase membrane permeability, increases chance for threshold to be achieved
Inhibitory
decrease membrane permeability, decrease chance for threshold to be achieved
What are several examples of neurotransmitters?
acetylcholine
dopamine
serotonin
endorphins
gaba (common)
Acetylcholine
stimulates muscles contraction
Dopamine
mood, makes happiness or some other emotion
Serotonin
sleepiness; mood
Endorphins
pain reduction; mood
GABA (gamma-aminobutyric acid)
reduces the activity of the neurons to which it binds (inhibitory); most common type of receptor; 40% of all synapses work with GABA; GABA has a tranquilising effect; low levels of GABA associated with anxiety and phobia
Agonist
molecule that has the same effect on the postsynaptic neuron as the neurotransmitter itself does
Antagonist
molecule that blocks the effect that the neurotransmitter normally has on the postsynaptic neuron
Neuronal Pool
groups of neurons that make hundred of synaptic connections and work together to perform a common function; these “pools” help us remember sequential tasks (ex. tying a shoe, riding a bike)
Reflex
rapid, predictable, and involuntary response to a stimulus; occurs over pathways called reflex arcs
Reflex Arc
direct route from a receptor, to a sensory neuron, to a interneuron, to a motor neuron, to an effector
What are the types of reflexes and regulations?
somatic reflexes
patellar, or knee-jerk, reflex
autonomic reflexes
Somatic Reflexes
activation of skeletal muscles (ex. when you move your hand away from a hot stove)
Patellar Reflex
is an example of a two-neuron reflex arc
Autonomic Reflexes
smooth muscle regulation; heart and blood pressure regulation; regulation of glands; digestive system regulation
Central Nervous System (CNS)
CNS develops from the embryonic neural tube
What does the neural tube become?
the brain and spinal cord
What does the opening of the neural tube become?
the ventricles
What are the four chambers within the brain?
cerebral hemispheres (cerebrum)
diencephalon
brain stem
cerebellum
What is the brain filled with?
cerebrospinal fluid
Cerebrum
inky large part of the brain (cerebral cortex); includes more than half of the brain’s mass; higher mental function, solving problems
What parts of the neuron are afferent?
dendrites, axon, axon terminal, cell body
What parts of the neuron are efferent?
motor neuron,
What are the two types of neurotransmitters, and what are they? Why does the body need it?
Excitatory and inhibitory; excitatory: increase membrane permeability, increases chance for threshold to be achieved; inhibitory: decrease membrane permeability, decrease chance for threshold to be achieved; why the body needs it: both are necessary for you to not be overstimulated (by too much excitatory) or have dulled senses (by too much inhibitory), Mr Ronnie says you need to have them, instead of not having any at all, because if you had none you “wouldn’t be able to feel anything.”