Transcript Homeostasis 1

Homeostasis 1:
What is Homeostasis?
Structures and Processes of the Nervous
System
Homeostasis
Your body is always working to maintain your
internal temperature near a set point of
37°C, blood glucose level at 100mg/mL and
blood pH of 7.4.
The tendency of your body to remain around
the same conditions is called homeostasis
Feedback Systems
 Changes in the external environment or within your
body can disturb homeostasis, so body systems are
constantly monitoring changes.
 Feedback systems consist of 3 parts:
 A sensor, that detects the change and sends a signal to a
control centre
 A control centre, receives information and sends signals to
the effectors when needed
 An effector, that receives signals form the control centre
and responds, resulting in a change to an internal variable.
 The body has two different types of feedback
systems to regulate its internal environment:
negative and positive feedback systems.
Negative Feedback
 Body works to reverse whatever change is detected
in the body, and is brought back within normal range
(set point).
 i.e. body temperature:
 You start to work out, your muscles gets warmer
 Your body senses that you are warmer, and signals the
control centre, which sends a signal to your sweat glands
and to the blood vessels
 Your sweat glands release sweat, blood vessels dilate. This
continues until you return to the optimal temperature.
 The opposite is true with cold and shivering.
Positive feedback
 Positive feedback is when the body wants to increase
or strengthen the change.
 I.e. blood clotting: when you have a cut, you release
platelets, those will stimulate more platelets to be
released in the area until bleeding stops.
 I.e. childbirth: uterus contracts, signals brain to
release oxytocin (hormone that causes the uterine
walls to contract more) from the pituitary gland,
uterus contracts, and keeps going on this cycle until
birth occurs.
The Nervous System
Cells of the Nervous System
Composed of only 2 main types: neurons and
glial cells.
Neurons are specialized to receive and conduct
chemical stimuli. Neuron cells are organized into
tissues called nerves.
Glial cells nourish the neurons, remove wastes and
defend against infections. They also provide a
supporting framework for the nervous system
tissue.
Structure of a Neuron
 Dendrites: are short, branching terminals that receive
nerve impulses from other neurons or sensory
receptors and relay the impulse into the cell body.
 Cell Body: has the nucleus and is the site of the
metabolic reactions, process input form dendrites.
 The axon: conducts impulses away from the cell
body. The terminal end branches into many fibres
and releases chemicals into the space between it and
the receptors or dendrites of neighbouring cells.
 Myelin Sheath: a fatty, insulating glial layer that
encloses some of the neurons. It is there for
protection and speeds the rate of nerve impulse
transmission.
Neuron
3 Types of Neurons
 Functionally, neurons are classified into:
 Sensory input: sensory receptors (like in the skin) receive
stimuli and form a nerve impulse that is sent to the central
nervous system.
 Integration: interneurons are found in the CNS that act as a
link between sensory and motor neurons. They process
incoming sensory information and relay outgoing motor
information.
 Motor Output: motor neurons transmit information form the
CNS to the effectors (muscles, glands, organs) that respond
to impulses from the motor neurons.
Reflex Arc
 Some neurons are organized so that they allow your
body to react very quickly in times of danger even
before you are aware of the threat consciously.
 Called reflexes
 Examples: moving hand from hot objects, blinking
when something moves towards your eye.
 Usually use only 3 neurons to transmit messages
Practice:
Try the Inquiry Investigation on page 374
P.348 # 5, 8, 9, 10.
P.354 # 7, 9, 10