ANHB1102 Final: ANHB1102 (1)
5 Jun 2018
School
Course
Professor
ANHB 1102 – CHELSEA GRAY
The Nervous System: L1
• The nervous system is very complex → the nervous system is huge
• The nervous system is the foundation of our conscious experience, personality and
behaviour → an injured nervous system is very hard to treat due to every individual
having different experiences, personalities and behaviours, so imagine trying to
treat one person who is different to another
• Neurobiology combines the behavioral and life sciences
The Principal Divisions of the Nervous System:
• CNS (Central Nervous System) → The brain and spinal chord enclosed by the
cranium and vertebral column (bony boundaries) and protected by meninges (e.g.
the brain is found within the skull) → has both grey and white matter but it is
divided differently (e.g. spinal chord has grey matter on the inside and white matter
on the outside, but the brain has white matter on the inside and grey matter on the
outside)
• Tracts → A bundle of axons in the brain and spinal chord
• PNS (Peripheral Nervous System) → All of the nervous system except the brain
and spinal chord → composed of nerves and ganglia (projects out to different areas)
→ e.g. for doctors that have patients with a loss of sensation in their fingers to see if there is damage to that level of the
spinal chord)
• Nerves → A bundle of nerve fibers (axons) wrapped in fibrous connective tissue
• Ganglion → A knot-like swelling in a nerve where neuron cell bodies are concentrated
• Grey matter → Neuron cell bodies and glia
• White matter → Myelinated axons and glia (myelin is lipids which appear white)
Control Systems:
• The nervous system relies on control systems
• Molecular messengers → Circulate with blood, most must pass through the circulatory system, variable speed but is
generally slow → depending on the type of the chemical, amount of the chemical, etc.
• Many aspects of control → different mechanisms, remembering early experiences → not conscious experience → a
small child that cant walk but has the muscles and the ability to walk → gets better and
better at walking and eventually can walk freely → if becomes paralysed, they do not
forget how to walk, but the neurons that were responsible for that movement have been
damaged and will not allow that movement, if you havent learnt the experience on the
other hand, there is no way you will be able to efficiently execute the task
Overview of the Nervous System:
• The nervous system carries out its task in three basic steps:
1. Sense organs receive information about changes in the body and external
environment (e.g. temperature change) and transmit coded messages to the
brain and spinal cord (CNS → the central nervous system)
2. The CNS processes information, relates it to past experiences and
determines appropriate response
3. The CNS issues commands to muscles and gland cells to carry out such a
response
• Hand on the Hotplate example
• PNS → contains sensory (what we feel) and motor (what we do) divisions each with
somatic (voluntary → contraction of skeletal muscle) and visceral (involuntary
→ contraction of smooth and cardiac muscle) subdivisions
Afferent and Efferent Division:
• Sensory (afferent) division (FEELING)→ carries signals from receptors to the CNS
➢ Somatic sensory division → carries signals from receptors in the skin,
muscles, bones and joints
➢ Visceral sensory division → carries signals from the viscera (heart,
lungs, stomach and urinary bladder)
• Motor (efferent) division (DOING) → carries signals from CNS to effectors (glands
and muscles that carry out the bodys response
➢ Somatic motor division → carries signals to skeletal muscles, output
produces muscular contraction as well as somatic reflexes (involuntary
contractions)
➢ Visceral motor division (autonomic nervous system) → carries
signals to glands, cardiac and smooth muscle → involuntary responses
are visceral reflexes
1. Sympathetic division (FIGHT or FLIGHT) → tends to arouse body for action, accelerating heart beat and respiration, while
inhibiting digestive and urinary systems
2. Parasympathetic division (REST and DIGEST) → tends to have a calming effect, slows the heart rate and breathing and
stimulates the digestive and urinary systems
find more resources at oneclass.com
find more resources at oneclass.com
ANHB 1102 – CHELSEA GRAY
Transmission of Information:
• Along a single axon of a neuron → electrical transmission and is very fast
• Requires cell to cell communication → faster chemical messengers, across narrow gaps between cells
Universal Properties of Neurons:
• Excitability (irritability) → respond to environmental changes called stimuli → cell can
generate a signal (can be inhibitory also)
• Conductivity → respond to stimuli by producing electrical signals that are quickly conducted to
other cells at distant locations
• Secretion (neurotransmitter release) → when an electrical signal reaches the end of nerve
fiber, the cell secretes a chemical neurotransmitter that influences the next cell, the
neurotransmitter will bind to receptors on the next cell
Functional Classes of Neurons:
• Sensory (afferent) Neurons → detect stimuli (or change) and transmit information about them
toward the CNS (senses such as taste, touch, smell, sight, etc.) → ascending to CNS → STEP 1
• Interneurons → lie entirely within the CNS, connecting neurons and carry out the integrative
functions (to make decisions and responses) → STEP 2
• Motor (efferent) Neurons → Send signals out to the
muscles and gland cells (the effectors that cause
movement) → Descending from CNS → STEP 3
• Your motor neurons may be fine but you can have
simultaneous damage to your sensory neurons (e.g.
being able to touch something but not feel it)
The Structure of a Neuron:
• Soma (cell body) → control center of the neuron → has
a single, centrally located nucleus with large nucleolus
and cytoplasm containing organelles → cell bodies are
vital to the existence of the neuron
• Dendrites → branches that come off the soma → the
primary site for receiving signals from other neurons,
the more dendrites the neuron has, the more
information it can receive and provides precise
pathways for the reception and processing of
information → the more dendrites the more information
it can receive and the more responses it can make
• Axon (nerve fiber) → originates from a mound on the
soma called the axon hillock (signal starts), the axon is
cylindrical and relatively un-branched for most of its
length, it takes information away from the soma and the
myelin sheath may enclose the axon → transmits the
information
• Terminal part → the little swelling that forms a synapse (junction) with the next cell, contains synaptic vesicles full of neurotransmitter
What do Neurons Look Like?
• Neurons are types of cells
• Pre-synaptic neuron → becomes before the synapse, doing the connecting
• Post- synaptic neuron → The neuron that it is being connected to
• Action potentials → the communication between neurons
• Neurons are unique and contain:
o Cell body: Soma containing nucleus and structures vital for keeping neuron alive
o Dendrites: Short extensions of cytoplasm of cell body (soma), highly branched to carry nerve impulses to cell
body, unique to neurons and serve as an input to neurons, receive messages to determine whether it will make
its own action potential
o Axon: Single long extension of cytoplasm, conducts electrical impulses away from cell body to other neurons,
muscles, or glands, only has one, unique to neurons, serve as an output from neurons, has only one output even
though there are many inputs, these send very basic messages, but when combined together, allows for a lot of
productivity and ability
find more resources at oneclass.com
find more resources at oneclass.com
ANHB 1102 – CHELSEA GRAY
Nervous Impulse → Fundamentals:
• Action Potential → momentary reversal of membrane potential (electrical signaling
within neurons) → the change in potential is what makes it excite
• Resting membrane potential → membrane contains a lot of ions (sodium, potassium, etc.)
• More negatively charged inside than the outside
• Neurons will sit at around -70 mV (depolarization)
• Potassium/Sodium Pump
• Makes it more positive on the inside → allowing sodium ions inside
• Once the action potential is at its peak, sodium channels shut and potassium
channels open to bring the excitement down
How do Neurons Talk?
• You can get a lot of messages but nothing will happen unless the neurons can talk
and are active to send messages to each other
• Step 1 → Neurons sit in cerebral spinal fluid (lots of ions), but are made of fat
themselves, so they can keep this fluid out and regulate the flow to create a resting
membrane potential → a voltage difference between the inside and the outside of
the neuron (-70 millivolts) → Can generate a current, at rest, it has potential energy
and when it wants to be used it creates an action potential
• Step 2 → Neuron receives excitatory and inhibitory messages from other neurons
(via dendrites) and changes the resting potential, (can make more negative or more
neutral), if there is enough excitatory message received, resting potential will exceed
a threshold which gives it enough to create an action potential
• Step 3 → this initiates a rapid depolarisation at the axon hillock (just before the axon) which creates a current that moves down
the axon (creates a charge), this current is called an action potential
• Step 4 → there is a problem sometimes: sometimes the energy isnt enough to send the message down the end of the axon, for a
number of reasons, the charge sent down the axon wouldnt travel far enough or fast enough if not for some help, there are
solutions!
o Part 1: one for of help comes from the oilgodendrocytes (a type of glial cell) that form the myelin sheath → a
layer of fatty cells that keep the ions inside the axon (the axon is permeable to ions allowing them to escape
and dissipating charge), myelin sheath acts like duct tape to the axon to form an inescapable barrier to
ions, most of our axons mylanate until we are in our 20s and it is believes that the emotional senses mylanate
before the others, so our bad teenage behaviour may be caused by the lack of structure where the neurons do not
inhibit bad behaviour as well as they could, but even with this, it might still not be enough to create an action
potential
o Part 2: the Nodes of Ranvier act like amplifiers that re-generate the action potential, acts as a booster or activates
another action potential
• Step 5 → ultimately, the current reaches the end of the axon, while communication within the neuron is purely electrical, this is
not how it goes between neurons as there is a tiny gap between neurons, they arent completely connected, arrival of action
potential at pre-synaptic axon terminal triggers release of chemicals (neurotransmitters → a chemical process)
• Step 6 → neurotransmitters enter the synaptic cleft and float through cerebrospinal fluid, some then bind with receptors on
dendrites of adjacent neurons (rubber ducks float away in all different places)
• Step 7 → depending on the neurotransmitter and the dendrite, two things can happen:
o Excitatory post-synaptic potential (EPSP) → depolarises post-synaptic
neuron
o Inhibitory post-synaptic potential (IPSP) → hyper polarises post-
synaptic neuron
What is an Action Potential?
• X-Axis = time in milliseconds → very quick changes in potential
• Y-Axis = Membrane voltage
• If it gets enough messages = the orange parabola
• Depolarisation and repolarisation occurs in less than 0.002 seconds → neurons talk to
each other very quickly
• Reaction times = can be quite quick despite such a long process
• Depolarisation overshoots (past the neutral point) and repolarisation undershoots (becomes more
negative than it was before)
• This slows down the action potential and leads to a refractory period (hyperpolarization) of about
0.0015 seconds → there is a limit to how quickly we can generate an action potential and then the
mV returns to normal resting potential
• Potential changes from -70 to -50/55
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
The nervous system is very complex the nervous system is huge. Tracts a bundle of axons in the brain and spinal chord. Pns (peripheral nervous system) all of the nervous system except the brain and spinal chord composed of nerves and ganglia (projects out to different areas) E. g. for doctors that have patients with a loss of sensation in their fingers to see if there is damage to that level of the spinal chord) Nerves a bundle of nerve fibers (axons) wrapped in fibrous connective tissue. Ganglion a knot-like swelling in a nerve where neuron cell bodies are concentrated. Grey matter neuron cell bodies and glia: white matter myelinated axons and glia (myelin is lipids which appear white) The nervous system carries out its task in three basic steps: Pns contains sensory (what we feel) and motor (what we do) divisions each with somatic (voluntary contraction of skeletal muscle) and visceral (involuntary. Contraction of smooth and cardiac muscle) subdivisions.
