Download Nervous System P2

Nervous System
Sodium-Potassium Pump
Resting Potential
•
The sodium potassium pump pumps
out and
into the axon in unequal
amounts
–
•
•
•
This results in an excess of
charge (Na+) outside and an excess of
charge (organic ions) inside the
axomembrane
An electrical potential difference of millivolts is generated
To maintain the resting potential of resting
neurons,
is continually needed to
supply
to the sodiumpotassium pumps as sodium ions and
potassium ions tend to
or diffuse
across the
–
potassium tends to
out faster than
the sodium
back in, and
the axoplasm contains large organic
negative
that contribute to the
negative charge inside the
Action Potential
• If nerve is stimulated by electric
, pH
change,
stimulation, a nerve
impulse is generated, and there is a
in
potential
• The action potential has three phases:
,
, and a
recovery period
Action Potential - Depolarization
• A nerve is
• The sodium
open to
allow Na+ to
into axon
through a channel so the Na+
ions rush from the outside of the
to the inside
• This changes the
across the neuron from (resting potential) to +
• The
is now
charged compared to the outside
of the neuron.
Note: during the depolarization
phase, there is
of sodium ions
Action Potential - Repolarization
• potassium gated channels
open and + ions rush to the
outside of the axomembrane
via the
• This makes the
of
the membrane positively
charged relative to the inside
once
• The
across the
membrane returns from
+40mV back to -
Note: during the
phase, there is facilitated
diffusion of
ions
Action Potential – Recovery
(Refractory) Period
• follows
• a neuron can not
an
action potential during this phase
since the sodium
cannot open
• the sodium-potassium pump is
busy
the resting
potential by pumping sodium ions
out and
ions back
in through the
• recovery period
the action potential from moving
backwards
• Resting potential is re-established
Threshold Stimulus
•
•
Action potentials occur only when the
membrane is stimulated (depolarized)
enough so that sodium channels open
completely. The minimum stimulus
needed to achieve an action potential is
called the
.
If the membrane potential reaches the
(generally 5 - 15
mV less negative than the resting
potential), the voltage-regulated sodium
channels all open. Sodium ions rapidly
diffuse inward, & depolarization occurs.
All-or-None Law - action
occur
maximally or not at all. In other words, there's
no such thing as a
or
action potential. Either the threshold potential
is reached and an action potential occurs, or it
isn't
and no
potential occurs.
Transmission of an Impulse
from Neuron to Neuron
What happens to a nerve impulse
once it reaches the end of an axon?
How does one nerve communicate
with another? The answer lies in the
specialized regions at the ends of
axons called SYNAPSES.
•
•
•
•
•
•
•
•
Synapse: the region
end of an axon and the
body
or dendrite to which it is attached.
Synaptic Endings: swollen
knobs on the ends of
axon terminal branches.
Presynaptic Membrane: the membrane of the axon synaptic ending.
Postsynaptic Membrane: the membrane of the next neuron just
beyond the axon's synaptic membrane.
Synaptic Cleft: the space between the
and the
postsynaptic membranes
Neurotransmitter Substances (
):
chemicals that transmit the nerve impulses across a synaptic cleft.
Synaptic Vesicles: contain the neurotransmitters. Contained near
surface of synaptic endings.
(Ach), Noradrenalin (NA), Serotonin,
Adrenalin (epinephrine) are some important neurotransmitters.
Sequence of Events
1.
2.
3.
4.
Nerve
(action potential) travels
along axon, and
a synaptic ending.
Arrival of the action potential causes calcium ion
gates on the
to open and
calcium ions move into the
.
The rise in
in the axon bulb
causes synaptic vesicles containing
to move towards the inner
surface of the presynaptic membrane
Synaptic vesicles merge
the presynaptic
membrane and
of neurotransmitters
(Ach) into the synaptic cleft occurs
–
Recall that endocytosis requires ATP energy. The
axon bulb contains many
to
produce
Sequence of Events
5.
6.
Neurotransmitters diffuse
synaptic
cleft to
on
membrane.
The receptors control selective ion channels;
binding of a
to its specific
receptors opens the ion channels.
The resulting ion flux changes the
of
the postsynaptic membrane. One of the following
can occur:
– an
synapse: moves the membrane
voltage closer to the ‘
voltage’
required for an action potential and the excitatory
neurotransmitters cause sodium ions to move
through receptor
depolarizing the
membrane
• nerve impulse will be
down the
dendrite of the second neuron
• Examples of excitatory neurotransmitters: ACETYLCHOLINE
(ACh),
(epinephrine)
– an
: Inhibitory neurotransmitters
do not depolarize the postsynaptic membrane
• Examples of inhibitory neurotransmitters: GABA (gamma
aminobutyric acid)
Sequence of Events
7.
To prevent
stimulation or inhibition
of the postsynaptic membrane,
are broken down
by enzymes or are reabsorbed through the
presynaptic
by
(also requires ATP energy)
a.
b.
neurotransmitter is degraded by enzymes
e.g.,
breaks down
acetycholine
synaptic ending reabsorbs the
neurotransmitter
e.g. this is what happens to
This results in only a single stimulus and
propagation of the impulse
Divisions of the Nervous System
Divisions of the Nervous System
1. Central Nervous System: (CNS) - includes spinal cord
and brain. In the "center" of the body.
2. Peripheral Nervous System: (PNS) - the rest of the
nervous system:
The Central Nervous System
•
•
•
The central nervous system is made up of the
— The brain is protected by the
of the
column
— The brain and spinal cord are
fluid that protects the CNS
and
cord.
and the spinal cord is protected by the
by
and
The brain
— contains approximately
billion neurons (nerve cells) and
between 1.3 and 1.4 kgs in the average adult human.
— The function of the brain is to
information
from other areas
of the central nervous system and the
nervous system via the spinal
cord.
The spinal cord
– is about 45 cm long and weighs about 35-40
grams.
– The function of the spinal cord is to
from the brain to the peripheral
nerves and from peripheral
to the
brain.
– The spinal cord also
reflex arcs or
involuntary responses that
the
brain
The Peripheral Nervous System
• The peripheral nervous system is made up of the
and
(groups of cell bodies) that
are found outside of the CNS
– Recall, sensory neurons transmit impulses from the
PNS to the
and motor neurons transmit
impulses from the
to the
.
• Peripheral nerves that communicate directly with
the brain are called
(12 pairs connect sensory
in nose, eyes, ears,
tongue, etc.)
• Peripheral nerves that communicate with the brain
via the spinal cord are called
(31 pair - muscles of the body and various glands
and organs)
• The PNS is broken down into
other divisions.
–
nervous system and
nervous system.
• autonomic nervous system (ANS) is further divided into
sympathetic and parasympathetic branches.
Somatic Nervous System
•
•
•
•
peripheral
that receive and send
to skeletal
muscle, skin, and tendons
Sensory
in skin, muscle and
send information to the
CNS about body position and
conditions
The CNS relays
to motor neurons that control the
of
skeletal muscle and the movement of the body.
The somatic nerves
voluntary movements of the body such as
walking, jumping, writing, typing, etc. Somatic nerves also
reflex
actions that
skeletal muscles as the effector, such as when you touch
sharp or hot.
Autonomic Nervous System
• Controls involuntary
to stimuli by the body.
• Autonomic nerves serve
muscle, smooth muscle,
glands, and all of the
organs.
• The ANS acts on these
effectors to maintain
homeostasis within the body (parasympathetic branch
neurotransmitter) and respond to
stress (sympathetic branch neurotransmitter).
Reflex Arc
• Reflex actions are
responses to a stimulus and are
a part of the
nervous
system.
• These actions do not involve the
cortex (conscious
brain) only the
cord and
are faster than
actions
that involve the brain.
• The
of these reflex
actions often prevents
injury
Parts of the Reflex Arc
• Reflex actions are
carried out by a
path called a
arc
• Reflex arcs involve
five main parts:
–
–
–
–
–
–
sensory
Sensory
Interneurons
effectors
How a Reflex Arc Functions
1.
Sensory Receptor (e.g. in skin) –
receive a stimulus and generates a
2.
Sensory Neuron - takes message to
CNS. Impulses move along
, proceed to
(in dorsal
root ganglia) and then go from cell
body to axon in
of cord.
Interneuron - passes message to
motor neuron
Motor neuron - takes message
away from CNS to axon of spinal
nerve
Effector - receives nerve impulses
and
: glands secrete and
muscles contract
3.
4.
5.
SUMMARY:
The sensory receptors receive a stimulus
and generate a nerve impulse. The
sensory neurons then carry this impulse
to the interneurons of the spinal cord.
The interneurons then carry the impulse
directly to the motor neurons
. The motor
neurons then carry the impulse to an
effector. The effector, which is normally a
muscle or a gland, responds by
contracting or releasing a biologically
active compound. The action of the
muscle or gland often is beneficial to the
individual
Sympathetic System
• The sympathetic branch of the
prepares
the body for “
or
".
• Involves several
responses to a stressful
such as:
– increases in
rate (effector is cardiac muscle)
and
rate
–
of the pupils (effector is smooth muscle)
–
of blood
from the digestive organs to make
more blood
to muscles (effector is smooth
muscle of arterioles),
– the
of hormones such as
(effector is adrenal gland)
Adrenalin
• also called
• is produced in the
adrenal glands.
– located on the top of each
of the
.
• The sympathetic nervous system
the adrenal gland (an effector) to
release the hormone adrenalin or
epinephrine into the
.
• The target tissue for adrenalin is mainly
and
muscle.
• Adrenalin increases heart
and
blood
providing more to
working muscles.
– It also increases blood sugar levels
providing more
to cardiac
and
muscles
Parasympathetic System
•
•
Acts to
conditions in the body and return the body to a relaxed state.
Parasympathetic nerves also cause
responses that:
– increase
function
– decrease heart rate and
–
the pupils
The Brain
• The brain is made up of an estimated 100
billion
.
• Each of these neurons has
of
connections (synapses) with other
.
• These neurons or brain cells do not
and cannot be
if damaged.
• It has been estimated that the brain which
makes up about
of body weight uses
% of the body's energy.
• Many of the
related to the
functioning of the brain are still not well
.
• The brain receives input from sensory neurons
throughout the body,
the
information it receives (this may involve
communication between neurons in different
regions of the brain), and
an
appropriate output response using motor
.
Meninges
• Is the
of membranes
which
the central
nervous system.
• The meninges consist of three
layers:
– the
– the
– the
mater
mater
mater
• The
function of the
meninges and of
the cerebrospinal fluid is to
the central
nervous system.
Corpus Callosum
• The brain is divided into a
and a
hemisphere.
• Each hemisphere is further divided into
lobes.
• The left hemisphere of the brain controls the
side of the
body and the
hemisphere controls the
side
of the body.
• The corpus callosum is an area of nervous tissue that connects the
two
of the brain. It allows the two hemispheres to
and
information.
Cerebrum
• The cerebrum is the
part
of the human brain
• gives us
and the
ability to think, wonder, ponder, etc.
• It is highly
in structure.
• The cerebrum is responsible for
receiving
signals (ex.
touch) and
voluntary
responses by the body such as
movement.
• The billion neurons of the cerebrum
also allow for
, learned
behaviours,
of
speech, and determine personality
and
.
Thalamus
• is called the “
cerebrum.
" for the
– All information received by the cerebrum
is routed through the
(except smell).
• Like a switchboard, the thalamus
signals entering the cerebrum and sends
them to the
areas
(called sensory processing).
• The thalamus also plays a role in the
reticular activating system (
)
that makes the cerebrum aware of
important
(ex: awakening you
from sleep) and
out
stimuli (background noise).
Hypothalamus
• lies below the
.
• maintains
in the body
• Some of the bodily functions controlled by the
hypothalamus are
–
–
–
–
–
–
sleep
Thirst
water
pressure
body
(thermostat).
• The mechanism by which it controls the above
functions often involves
released
from the pituitary gland that have effects on target
organs in the body
– Ex: thyroid gland,
glands, and kidneys
Medulla Oblongata
• located in the brain stem at the
of the skull.
• It has neurons that
with both the brain and the spinal cord.
• The medulla oblongata
involuntary functions vital to life and is the
site of the
(breathing)
and cardiac (heartbeat) control centers
mentioned
in the course.
– Other reflexes controlled by the medulla
oblongata include;
, coughing,
sneezing,
, and swallowing
Cerebellum
• Lies behind the
stem.
• Responsible for
coordination and
balance.
• Receives information from the
and
related to
and
of the
body and from proprioceptors (sensory receptors
that signal the position of body parts and control
posture) in
and
.
– It is very well
birds.
in animals such as
• The cerebrum also provides the
with information about the normal position of
body parts.
• The cerebellum uses this
information
to initiate
responses that are
coordinated and balanced.
– This helps us when preventing a fall or when
learning a new motor skill such as walking or
.
Neuroendocrine Center
• Located in the
• The
control center able to
maintain
or internal
balance in the body with the help of the
system.
– It receives information about the status of
things such as
temperature,
water
, and the levels of many
hormones within the blood and acts to
keep them
• The neuroendocrine center interacts
with
the anterior and
posterior pituitary
Posterior Pituitary Gland
•
•
The pituitary gland is made up of the
pituitary and
pituitary (one lies in
front of the other).
cells (neurons that
produce hormones) in the hypothalamus
produce
hormone
(ADH) and oxytocin.
– ADH helps gauge the water level in blood and tells
kidneys to either expel or reabsorb water in urine.
– Oxytocin is released during childbirth to stimulate
uterine contractions and during breastfeeding to
stimulate milk letdown
•
•
These hormones travel along axons to terminal
bulbs in the posterior pituitary where the
hormones are
.
The posterior pituitary does not produce these
hormones but does act as a
gland.
Anterior Pituitary
• The anterior pituitary contains cells that
produce many
hormones.
• The anterior pituitary or "master gland"
produces hormones that
the
following:
–
–
–
–
–
(thyroid stimulating hormone
or TSH)
adrenal
(adrenal cortex
stimulating hormone or ACTH)
glands (prolactin - for milk
production)
bones and
(growth
hormone or GH)
ovaries and
(follicle stimulating
hormone or FSH and luteinizing
hormone or LH).
Anterior Pituitary and the
Hypothalamus
•
•
•
•
•
•
Neurosecretory cells (neurons that produce
hormones) in the hypothalamus produce
hormones
These hormones are transported directly to the
pituitary.
When they reach the anterior pituitary, they cause
the
of a specific anterior pituitary
hormone into the blood which is transported to a
specific
organ or gland (ex:
TSH which stimulates the
)
When
pituitary hormones reach the
target
, target organs produce
hormones that perform a
within
the body (ex: Thyroxin – the hormone
by the thyroid gland which increases
metabolic rate)
These hormones, produced by target organs, inhibit
the
of their own
releasing hormones in the hypothalamus and their
own stimulating hormones in the anterior pituitary
This is
to keep hormone levels
relatively
Mandatory Vocabulary
acetylcholine (ACh), acetylcholinesterase (AChE), action potential,
adrenal medulla, adrenalin, “all-ornone” response, autonomic nervous
system, axomembrane, axon, axoplasm, calcium ion, cell body, central
nervous system, cerebellum, cerebrum, contractile protein, corpus
callosum, dendrite, depolarization, effector, excitatory
neurotransmitter, hypothalamus, impulse, inhibitory neurotransmitter,
interneuron, medulla oblongata, meninges, motor neuron, myelin
sheath, myelinated nerve fibre, neuroendocrine control centre,
neuron, neurotransmitters, node of Ranvier, norepinephrine,
parasympathetic division, peripheral nervous system, pituitary gland,
polarity, postsynaptic membrane, potassium gate, presynaptic
membrane, receptor, reflex arc, refractory period, repolarization,
resting potential, saltatory transmission, Schwann cell, sensory neuron,
sodium gate, sodium-potassium pump, somatic nervous system,
sympathetic division, synapse, synaptic cleft, synaptic ending, synaptic
vesicle, thalamus, threshold value
By the end of this section, you should
be able to:
•
•
•
identify and give functions for each of the following: dendrite, cell body, axon,
axoplasm, and axomembrane
differentiate among sensory, motor, and interneurons with respect to structure
and function
explain the transmission of a nerve impulse through a neuron, using the following
terms:
– resting and action potential
– depolarization and repolarization
– refractory period
– sodium and potassium gates
– sodium-potassium pump
– threshold value
– “all-or-none” response
– polarity
•
q relate the structure of a myelinated nerve fibre to the speed of impulse
conduction, with reference to myelin sheath, Schwann cell, node of Ranvier, and
saltatory transmission
• identify the major components of a synapse, including
– synaptic ending
– presynaptic and postsynaptic membranes
– synaptic cleft
– synaptic vesicle
– calcium ions and contractile proteins
– excitatory and inhibitory neurotransmitters (e.g.,
norepinephrine, acetylcholine – ACh)
– receptor
– acetylcholinesterase (AChE)
• explain the process by which impulses travel across a synapse
• describe how neurotransmitters are broken down in the synaptic cleft
• describe the structure of a reflex arc (receptor, sensory neuron,
interneuron, motor neuron, and effector) and relate its structure to how it
functions
• compare the locations and functions of the central and peripheral
nervous systems
• identify and give functions for each of the following parts of the brain:
– medulla oblongata
– cerebrum
– thalamus
– cerebellum
– hypothalamus
– pituitary gland
– corpus callosum
– meninges
• explain how the hypothalamus and pituitary gland interact as the
neuroendocrine control centre
• differentiate between the functions of the autonomic and somatic
nervous systems
• describe the inter-related functions of the
sympathetic and parasympathetic divisions of the
autonomic nervous system, with reference to
– effect on body functions including heart rate, breathing rate,
pupil size, digestion
– neurotransmitters involved
– overall response (“fight or flight” or relaxed state)
• identify the source gland for adrenalin (adrenal
medulla) and explain its role in the “fight or
flight” response