Download 6.5 Nerves, Hormones and Homeostasis

6.5 Nerves,
Hormones
and
Homeostasis
Assessment Statements
6.5.1 State that the nervous system consists of the central
nervous system (CNS) and peripheral nerves, and is
composed of cells called neurons that can carry rapid
electrical impulses.
6.5.2 Draw and label a diagram of the structure of a motor
neuron.
6.5.3 State that nerve impulses are conducted from receptors
to the CNS by sensory neurons, within the CNS by relay
neurons, and from the CNS to effectors by motor neurons.
6.5.4 Define resting potential and action potential
(depolarization and repolarization).
6.5.5 Explain how a nerve impulse passes along a nonmyelinated neuron.
6.5.6 Explain the principles of synaptic transmission.
Why do we need control systems?
Response to stimuli is
essential for survival
Multicellular organisms
need coordination
Nervous versus
endocrine systems
Both work together
e.g. rabbit running from
fox – what systems
involved?
Sense organs detect change (receptors)
Effectors respond
Distance between two
Every sensor and effector has at least 1 link to CNS
Spinal cord links brain to rest of body
6.5.1 State that the nervous system consists
of the central nervous system (CNS) and
peripheral nerves
6.5.1... cells called neurons that can carry
rapid electrical impulses.
6.5.2 Draw and label a diagram of the
structure of a motor neuron
Dendrites transmit
impulses to cell body
Nodes of Ranvier
Impulses
leave via axon
Myelin sheath composed
of Schwann cells
Cell body with
nucleus
direction of impulse
Axon terminal
passes signal to
effector
Neurones packed and wrapped to form nerves
May contain sensory, effector or mixture
6.5.3 State that nerve impulses are conducted
from receptors to the CNS by sensory neurons,
within the CNS by relay neurons, and from the
CNS to effectors by motor neurons.
Relay neurone
Sensory neurone
Motor neurone
Sensory neurons carry
messages from
receptors in sense
organs to CNS.
Relay neurones connect
sensory neurons to
motor neurones in the
CNS.
Motor neurons connect
the CNS to the
effector.
A Receptor in skin
B Sensory neurone
C Relay neurone
D Motor neurone
E Effector
6.5.4 Define resting potential and action
potential (depolarization and repolarization).
Neurons have an electrical potential (voltage) across the
cell membrane, i.e. membrane is polarised.
The inside of the cell is more negative than the outside
This is called the Resting Membrane Potential = 70mV
Definitions
Resting potential - the electrical potential
across the cell membrane of a cell that is not
conducting an impulse
Action potential - is the reversal
(polarisation) and restoration
(depolarisation) of the electrical potential
across the plasma membrane as an
impulse passes along a neurone
Concentration of
This results in the
Na+ is high
Sodium/potassiu
inside being more
m cation pumps outside the neuron
negative than outside
transport Na+ out
and K+ in
Difference in
Membrane is
concentration of ions
more permeable
maintained by active
This requires to K+ than Na+
transport against
ATP
C
oncentration
of
K+
concentration gradient
inside 20x greater
so K+ ions rapidly
Concentration of
diffuse out until
K+ is high inside
equilibrium reached
the neuron
6.5.5 Explain how a nerve impulse
passes along a non-myelinated
neuron.
Stimulation can reverse the charge on a neuron
(-70 to +40 mV)
Membrane becomes depolarised
If stimulus exceeds certain threshold value an
action potential results
Action potential - rapid reversal of the resting
membrane potential that travels down the
axon
The nervous impulse
6.5.6 Explain the principles of synaptic
transmission.
Synapses occur where neurons
meet
Outline the use of four method of membrane
transport in nerves and synapses (8)
Assessment Statements:
6.5.7 State that the endocrine system consists of glands that release
hormones that are transported in the blood.
6.5.8 State that homeostasis involves maintaining the internal
environment between limits, including blood pH, carbon dioxide
concentration, blood glucose concentration, body temperature and
water balance.
6.5.9 Explain that homeostasis involves monitoring levels of variables
and correcting changes in levels by negative feedback
mechanisms.
6.5.10 Explain the control of body temperature, including the transfer
of heat in blood, and the roles of the hypothalamus, sweat glands,
skin arterioles and shivering.
6.5.11 Explain the control of blood glucose concentration, including
the roles of glucagon, insulin and α and β cells in the pancreatic
islets.
6.5.12 Distinguish between type I and type II diabetes.
6.5.7 State that the endocrine system consists of glands
that release hormones that are transported in the blood.
The endocrine system consists
of glands.
Glands secrete chemicals
called hormones directly into
the blood.
Hormones travel in the blood to
a target organ (effector) and
bring about a response.
The response becomes a
feedback stimuli.
6.5.8 State that homeostasis involves maintaining the
internal environment between limits
Homeostasis literally means “same state” - refers
to the process of keeping the internal body
environment in a steady state.
Very important - a great deal of the endocrine
system and autonomic nervous system is
dedicated to homeostasis.
What needs to be controlled?
●
●
●
●
●
Blood pH 7.35 to 7.45
Blood carbon dioxide levels
Blood glucose concentration 70 - 100 mg/dL
Body temperature 37.0oC
Water balance
All of these factors are maintained between
limits within the blood and tissue fluid.
6.5.9 Explain that homeostasis involves monitoring
levels of variables and correcting changes in levels by
negative feedback mechanisms.
Negative feedback loops
All homeostatic
mechanisms use negative
feedback to maintain a
constant value (called the
set point).
Negative feedback means that
whenever a change occurs in a
system, the change automatically
causes a corrective mechanism
to start, which reverses the
original change and brings the
system back to normal.
The bigger the change the bigger the corrective
mechanism.
Applies to electronic circuits and central heating
systems as well as to biological systems.
In a system controlled by negative feedback the
level is never maintained perfectly, but
constantly oscillates about the set point.
An efficient homeostatic system minimises the
size of the oscillations.
6.5.10 Explain the control of body temperature, including the
transfer of heat in blood, and the roles of the hypothalamus,
sweat glands, skin arterioles and shivering.
Homeotherms - animals that maintain a
fairly constant body temperature (birds
and mammals)
Animals with variable body temperature
(all others) are called poikilotherms
Homeotherms maintain body
temperature at around 37°C (warmblooded)
Poikilothermic animals can also have very
warm blood during the day by basking
in the sun.
In humans temperature is controlled by the
thermoregulatory centre in the hypothalamus.
Receives input from two sets of thermoreceptors
Receptors in the skin
monitor the external
temperature.
Receptors in the hypothalamus
monitor the temperature of the
blood as it passes through the
brain
(core body temperature)
The thermoregulatory centre
sends impulses to several
different effectors to adjust body
temperature.
The skin and temperature control
Temperature homeostasis
Behavioural control of temperature
6.5.11 Explain the control of blood glucose
concentration, including the roles of glucagon, insulin and
α and β cells in the pancreatic islets.
Glucose is the transport carbohydrate in
animals, and its concentration in the
blood affects every cell in the body.
Concentration is therefore strictly
controlled within a range of 80-100 mg
100cm-3
Very low levels (hypoglycaemia) or very
high levels (hyperglycaemia) are both
serious and can lead to death.
Controlled by the pancreas.
Glucose receptor cells monitor the
concentration of glucose in the blood.
Endocrine cells (called the islets of
Langerhans), which secrete
hormones.
α cells secrete glucagon
β cells secrete insulin.
The two hormones are antagonistic,
and have opposite effects on blood
glucose.
promotes
insulin
release
High blood
sugar
Increase in
blood sugar
stimulates
breakdown of
glycogen
Glucagon
α cells
glycogen
glucose
stimulates
formation of
glycogen
Decrease in
blood sugar
Insulin
β cells
Stimulates
uptake of
glucose by
cells
Low blood
sugar
promotes
glucagon
release
Control of blood glucose concentration
6.5.12 Distinguish between type I and type II diabetes.
Diabetes is a disease caused by a failure of glucose
homeostasis.
Insulin-dependent diabetes (type 1 or early onset diabetes) a severe insulin deficiency due to autoimmune killing of β
cells (possibly due to a virus).
Non insulin-dependent diabetes (type 2 or late-onset
diabetes) - insulin is produced, but the insulin receptors in
the target cells don’t work, so insulin has no effect.
In both cases:
- high blood glucose concentration after a meal,
- not reabsorbed by kidneys
- much of the glucose is excreted in urine
- osmosis causes water to follow producing large quantities
of dilute urine
- less glucose for cells means that proteins are metabolised
in respiration
- organ damage follows
Diabetes mellitus means “sweet fountain”) - doctors
used to test for diabetes by tasting urine!
Diabetes can be treated by
injections with insulin or by
careful diet.
It can be monitored using clinistix
or blood/urine analysis
Until the discovery of insulin in
1922 by Banting and Best,
diabetes was an untreatable,
fatal disease.
What are causes of type I and type II diabetes?
Type I
Type II
A.
autoimmune disease leading
to reduced insulin secretion
decreased responsiveness of
the body to insulin
B.
decreased responsiveness of
the body to insulin
autoimmune disease leading
to reduced insulin secretion
C.
increased responsiveness of
the body to insulin
autoimmune disease leading
to increased insulin secretion
D.
autoimmune disease leading
to increased insulin secretion
increased responsiveness of
the body to insulin
What is a role of the hypothalamus in homeostasis?
A.
B.
C.
D.
Monitoring body temperature
Monitoring blood glucose concentration
Secretion of glucagon
Secretion of sweat
Outline how the human body prevents blood glucose
concentration from rising excessively (5 marks)
blood glucose concentration monitored by
pancreas/islets/beta cells;
(more) insulin secreted in response to high blood glucose /
glucose
above threshold level;
insulin stimulates cells to absorb glucose;
glucose used in cell respiration (rather than lipids);
glucose converted to glycogen;
by liver/muscle cells;
glucose converted to fatty acids / triglycerides / fat;
negative feedback process;
Accept these points if clearly made in an annotated diagram.
Explain the principle of homeostasis with reference
to the control of body temperature (9 marks)
homeostasis involves maintaining a constant internal environment;
involves the concept of negative feedback;
a deviation from the norm is the stimulus to trigger the mechanisms
to restore the norm / OWTTE;
body temperature in mammals must be maintained at a constant
level for enzymes;
controlled by the hypothalamus / hypothalamus as a thermostat;
too hot causes vasodilation so more heat is lost from skin;
too hot causes sweating as evaporation of sweat leads to cooling;
too cold causes shivering/muscle contraction as (increased
metabolic rate) generates heat;
too cold causes vasoconstriction so less heat lost from skin;
liver/muscles can generate heat which is distributed around the
body by blood;
hair can trap air which insulates against heat loss (goose bumps);
behavioural example of heat retention;
(e.g. adding layers of clothes, jumping up and down,huddling in groups)