Download Psych 11Nervous System Overview

Knowledge
 We need to cover
 Functions of parts of the brain
 Divisions of the NS and their interrelationships
 Autonomic and somatic, sympathetic and
parasympathetic
 Neurons
 Transmission of nerve impulse
 Components of synapse
 Impulse transmission across synapse
What makes us who we are?
 An Interesting
Question:
 Nature vs. Nurture
 Nature refers to the
role that “genetics”
plays in the
development of a
person’s behavior or
personality traits
 Nurture refers to the
role that the
“environment” plays
in the development of
a person’s behavior or
personality traits
Why does this question
have an impact on our lives?
 What determines your likes, dislikes, and personality characteristics?
 How much of an impact does he environment have on your genetic
information?
 http://ngm.nationalgeographic.com/2012/01/twins/miller-text
 The nature versus nurture question refers to the interactive role that
heredity (nature) and environment (nurture) play in human behavior.
Although no contemporary psychologist would take either a pure
nature or a pure nurture view of human behavior, the extent to which
many traits are influenced by genetics and environment is still
debated. The related fields of behavior genetics and evolutionary
psychology help psychologists explore the influence of heredity on
human behavior.
Complete Structures
Structures and Functions of
the Brain.
 Medulla Oblongata – base of the brain, top of the spinal cord.
Brain stem. Reflexive, homeostatic actions. Non-skeletal
muscles. Heart rate, breathing rate, swallowing, vomiting.
 Cerebrum – divided into R and L and connected by Corpus
Callosum. Thinking part, interprets and integrates sensory
input.
 Thalamus – sorting center or switchboard, impulses destined for
the cerebrum (cerebral cortex) are directed by the thalamus to
their correct location.
 Cerebellum - coordinates movement/balance, located at the top
of the spinal cord.
continued
 Hypothalamus (not directly associated with thalamus) – lower
portion of mid brain. Checks blood conditions and produces
chemicals to help maintain homeostasis. Works with pituitary gland.
 Pituitary Gland – attached to the hypothalamus. It is involved in
production, storage and secretion of hormones. Hormones are
chemical messengers (transmitted in blood) which allow different
parts of the body to communicate.
 Corpus Callosum – the nerve bundles which connect the two
hemispheres (sides) of the Cerebrum.
 Meninges – 3 layered membrane structure which helps protect the
brain.
 http://www.nursingassistantcentral.com/blog/2008/100-fascinatingfacts-you-never-knew-about-the-human-brain/
Cerebrum: 4 lobes
Continued
Structures
Hemispheric Specialization
 The two hemispheres of the cerebral cortex are linked
by the corpus callosum, through which they
communicate and coordinate. Nevertheless, they
appear to have some separate functions. The right
hemisphere of the cortex excels at nonverbal and
spatial tasks, whereas the left hemisphere is usually
more dominant in verbal tasks such as speaking and
writing. The right hemisphere controls the left side of
the body, and the left hemisphere controls the right
side.
PET scans Positron Emission Tomography
Comparisons
Cerebellum Divisions
Spinal Cord
 The spinal cord is a complex cable of
nerves that connects the brain to most
of the rest of the body. It is made up of
bundles of long nerve fibers and has
two basic functions: to permit some
reflex movements and to carry
messages to and from the brain.
 Control of the body systems from the
CNS follows a very ordered sequence.
The way we were created puts priority
of function at the top, with lesser
important functions at the bottom.
Why do you think this is?
Nervous System Divisions
Nervous System Divisions
 Central Nervous System: CNS made up of the spinal cord and
brain.
 Peripheral Nervous System: PNS made up of the nerves and
ganglia (groups of cell bodies) that are found outside of the CNS.
Recall, sensory neurons transmit impulses from the PNS to the
CNS and motor neurons transmit impulses from the CNS to the
PNS.
 Peripheral nerves that communicate directly with the brain are
called cranial nerves (12 pairs - connect sensory receptors in nose,
eyes, ears, tongue, etc.). Peripheral nerves that communicate with
the brain via the spinal cord are called spinal nerves (31 pairs muscles of the body and various glands and organs).
Peripheral Divisions
 The PNS is broken down into two other divisions.
These divisions are the somatic nervous system and
autonomic nervous system.
 The autonomic nervous system (ANS) is further
divided into sympathetic and parasympathetic
branches.
Somatic Vs Autonomic
 The somatic nervous system describes peripheral nerves
that receive and send signals to skeletal muscle, skin, and
tendons. Sensory receptors in skin, muscle and tendons send
information to the CNS about body position and
environmental conditions. The CNS relays signals to motor
neurons that control the contraction of skeletal muscle and
the movement of the body. The somatic nerves control
voluntary movements of the body such as walking,
jumping, writing, typing, etc. Somatic nerves also facilitate
reflex actions that involve skeletal muscles as the effector,
such as when you touch something sharp or hot.
Continued
 The autonomic nervous system controls involuntary
responses to stimuli by the body. Autonomic nerves
serve cardiac muscle, smooth muscle, glands, and all of
the internal organs. The ANS acts on these various
effectors to maintain homeostasis within the body.
 ANS is further divided into parasympathetic branch
and sympathetic branch
Sympathetic and
Parasympathetic
 The sympathetic branch of the ANS prepares the body for "fight
or flight". This involves several involuntary responses to a stressful
situation such as increases in heart rate (effector is cardiac muscle)
and respiratory rate, dilation of the pupils (effector is smooth
muscle), shunting of blood away from the digestive organs to
make more blood available to muscles (effector is smooth muscle
of arterioles), and the release of hormones such as
adrenalin/epinephrine (effector is adrenal gland).
 The parasympathetic branch of the ANS acts to normalize
conditions in the body and return the body to a relaxed state.
Parasympathetic nerves also cause involuntary responses that
increase digestive function, decrease heart rate and respiration,
and constrict the pupils.
Summary
Notes on Effectors and
contractile proteins:
 Effectors are muscles or glands that receive input from
the nervous system and ‘do something’ with that
information. It can be a muscle contraction or a release
of hormones.
 A contractile protein is a protein (can be muscle or
cellular) which has the ability to contract or change
shape. This causes movement.
Adrenalin
 Adrenalin (also called epinephrine) is produced in the
medulla (middle) of the adrenal glands. The adrenal glands
are located on the top of each kidney. The sympathetic
nervous system stimulates the adrenal gland (an effector)
to release the hormone adrenalin or epinephrine into the
bloodstream. Adrenalin is a modified amino acid hormone.
The target tissue for adrenalin is mainly cardiac and skeletal
muscle. Adrenalin increases heart rate and blood pressure
providing more oxygen to working muscles. It also increases
blood sugar levels providing more energy to cardiac and
skeletal muscles
Reflex Arc: Somatic
Reflex Arc
 a simple neurologic unit of a sensory neuron that
carries a stimulus impulse to the spinal cord, where it
connects with a motor neuron that carries the reflex
impulse back to an appropriate muscle or gland
BFF Hypothalamus and
Pituitary Gland
 Explain how hypothalamus and pituitary gland
interact as the neuroendocrine control center.
 Endocrine (refers to hormones released directly into the
blood stream)
 Hypothalamus is the ‘brain’ in this relationship. It
monitors blood and directs the hypothalamus with
respect to the release of chemicals.
Continued
 The neuroendocrine control center is able to maintain
homeostasis or internal balance in the body with the help of
the autonomic nervous system. It receives information
about the status of things such as body temperature, water
balance, and the levels of many hormones within the blood
and acts to keep them constant.
 The neuroendocrine control center is composed of the
hypothalamus and pituitary gland. The pituitary gland is
made up of the anterior pituitary and posterior pituitary
(one lies in front of the other). The interaction between the
hypothalamus and the two portions of the pituitary are
quite different.
Neurons: Functional Unit
of our Nervous System
Structure and Function of
Neuron
 The neuron is the main communication structure of
the body, it consists of:
 Dendrite (receiving), cell body (summation of
impluse), axon (conduct impulse), axoplasm and
axomembrane. As well as schwann’s Cells (make
myelin), nodes of Ranvier (gaps in myelin), myelin
sheath (speeds up transmission)
 Be able to label and give a function of these basic parts.
Summary of a
Afferent or Sensory Neuron
Notes
 In the nervous system, afferent neurons (otherwise known
as sensory neurons), carry nerve impulses from receptors or
sense organs towards the central nervous system.
 A touch or painful stimulus, for example, creates a sensation
in the brain only after information about the stimulus travels
there via afferent nerve pathways.
 Afferent neurons have a single long dendrite and a short
axon. The dendrite is structurally and functionally similar to
an axon, and is myelinated;
Efferent or Motor Neuron
Notes.
 In the nervous system, efferent nerves – also known as
motor neurons – carry nerve impulses away from the
central nervous system to effectors such as muscles or
glands. The opposite activity of direction or flow is
afferent.
 The motor nerves are efferent nerves involved in
muscular control. The cell body of the efferent neuron
is connected to a single, long axon and several shorter
dendrites projecting out of the cell body itself
Nerve Impulses

The dendrites and axons of a neuron are basically tubes constructed of cell
membrane, called axomembrane, that are filled with cytoplasmic fluid called
axoplasm. The electrochemical signal or impulse that allows neurons to
communicate travels along the axomembrane.

This section describes how a nervous impulse travels along the axomembrane
of a dendrite or axon. When the dendrite of a neuron receives sufficient
excitatory stimulation, called threshold, an action potential results. This
action potential is an "all or none response". If stimulation exceeds the
threshold, an impulse will be generated. Sub-threshold stimulation will not
elicit an action potential.

The stimulation that initiates an action potential usually will be generated by
sensory receptors for sensory neurons and at a synapse for interneurons and
motor neurons.
Resting Potential
Resting Potential
 A neuron in the resting state is polarized. Its ready to go.
 There is a potential difference across the axomembrane of -65
millivolts (mV).
 This negative reading means the inside of the neuron (axoplasm)
is negatively charged compared to the outside of the
axomembrane. This potential difference is produced by the action
of the sodium-potassium pump.
 Sodium-potassium pumps are membrane proteins that actively
transport:
 sodium ions to the outside of the membrane. (+)
 potassium ions to the inside of the membrane. (-)
Action Potential
 The Action Potential: When the dendrite of a neuron receives stimulation
exceeding threshold, an action potential is generated in the axomembrane of the neuron
and quickly moves along the dendrite to the cell body and axon.

An action potential is produced by the action of gated channel proteins embedded in the
axomembrane. There are gated protein channels for both sodium ions and potassium
ions. The action potential has three phases; depolarization, repolarization, and a
recovery period. Each of these phases is associated with the action of a membrane
protein as summarized below.
 Depolarization (facilitated diffusion of sodium ions)

Following an above threshold stimulus, sodium gated channel proteins open and sodium
ions rush from the outside of the axomembrane to the inside. This changes the polarity
across the neuron from -65mV (resting potential) to +40mV. The axoplasm is now
positively charged compared to the outside of the neuron.
Repolarization and
Recovery
 Repolarization (facilitated diffusion of potassium ions)

Following the movement of sodium into the axoplasm, potassium gated channels
open and potassium ions rush to the outside of the axomembrane. This makes the
outside of the membrane positively charged relative to the inside once again. The
potential across the membrane returns from +40mV back to -65mV.
 Recovery/Refractory Period (active transport of sodium and
potassium ions)

During the recovery period following repolarization the membrane experiences
hyperpolarization or refractory period during this time a neuron can not generate
an action potential.

The sodium-potassium pump is busy re-establishing the resting potential by pumping
sodium ions out and potassium ions back in through the axomembrane. This recovery
period also prevents the action potential from moving backwards.
Saltatory Conduction
 Myelin sheaths (neuron wraps) are formed by Schwann
Cells. Schwann cells form multiple layers of membrane
around the neuron and insulate it. In between the areas of
myelin sheath, Nodes of Ranvier or bare patches exist. The
nerve impulse or action potential will jump form node to
node greatly increasing the speed of nerve transmission.
 This node to node transmission, called saltatory
conduction, can produce transmission speeds of up to 200
meters per second and explains the speed at which we can
react to potentially harmful stimuli.
Synapse Structure
 A synapse describes the region at which the axon bulb of a
neuron is positioned very near the dendrite or cell body of a
second neuron.
 Neurons communicate with other neurons at the synapse.
 A synapse is composed of a presynaptic membrane on the
axon bulb of the first neuron and a postsynaptic membrane
on the dendrite or cell body of the second neuron. A very
small gap, called the synaptic cleft, lies between the
presynaptic and postsynaptic membranes.
Neurotransmitters

Molecules called neurotransmitters relay messages across the synaptic cleft between the
two neurons.

The communication between neurons is chemical in nature.

Synaptic vesicles, located in the axon bulb, contain neurotransmitters, produced by the
neuron, that are released by exocytosis into the synaptic cleft. These neurotransmitters
diffuse quickly across the short distance between the presynaptic and postsynaptic
membranes.

Neurotransmitters (there are about 25 different ones and probably others yet to be found)
can cause excitation or inhibition at the postsynaptic membrane. A single neuron will
have many dendrites and many synapses with other neurons.

Generally, many excitatory signals will depolarize the neuron and cause an action
potential, while inhibitory signals super polarize the neuron and prevent an impulse
being generated. If both excitatory and inhibitory signals are sent to the same neuron,
the signals will add together. Many more excitatory signals than inhibitory signals
results in an impulse, while similar numbers of both types of signals will have no net
effect on the membrane potential. This adding together of signals from many neurons is
called synaptic integration.
Excitatory and Inhibitory
 A common excitatory neurotransmitter is norepinephrine
or adrenalin and a common inhibitory neurotransmitter is
acetylcholine.
 If sufficient excitation is caused by neurotransmitters, an
action potential may be initiated in the postsynaptic
membrane and move along the second neuron.
 Neurotransmitters are broken down by enzymes (ex.
acetylcholinesterase breaks down acetylcholine) or are
reabsorbed into the presynaptic bulb to prevent continued
stimulation or inhibition. The steps involved in synaptic
transmission are outlined below.
Neurotransmitters
Synaptic Transmission: in 6 easy steps!
 Step 1: The action potential reaches an axon bulb and
causes calcium ion gates to open and calcium ions move
into the axon bulb.
 Step 2: The rise in calcium ions in the axon bulb causes
synaptic vesicles containing neurotransmitter to move
towards the presynaptic membrane.
 Step 3: Synaptic vesicles merge with the presynaptic
membrane and exocytosis of neurotransmitters into the
synaptic cleft occurs. Recall that endocytosis requires ATP
energy. The axon bulb contains many mitochondria to
produce ATP.
Continued
 Step 4: Neurotransmitters diffuse across the synaptic cleft (a very
short distance) and bind to receptor proteins on the postsynaptic
membrane. Excitatory neurotransmitters cause sodium ions to move
through receptor proteins depolarizing the membrane. Inhibitory
neurotransmitters do not depolarize the postsynaptic membrane.
 Step 5: If sufficient excitatory neurotransmitter binds to receptors, an
action potential is produced in the postsynaptic membrane and travels
along the length of the second neuron.
 Step 6: To prevent continuous stimulation or inhibition of the
postsynaptic membrane, neurotransmitters are broken down by
enzymes or are reabsorbed through the presynaptic membrane by
endocytosis (also requires ATP energy).
Digital Sources

http://outreach.mcb.harvard.edu/animations/actionpotential.swf


http://www.youtube.com/watch?v=DJe3_3XsBOg&feature=related


Khan Academy Action Potential
http://www.youtube.com/watch?v=Tbq-KZaXiL4&feature=mfu_in_order&list=UL


Myelinated vs Unmyelinated.
http://www.youtube.com/watch?v=gkQtRec2464&feature=mfu_in_order&list=UL


Interactive Video
Khan Academy: Synapse
http://www.youtube.com/watch?v=90cj4NX87Yk

Synapse and AP