HOMEOSTASIS & RESPONSE
omeostasis
H
Homeostasis is the maintenance of a constant internal environment
Homeostasis is really important for humans because. . .
● Whilst the external environment changes around your body the internal
environment of the body must be kept steady.
● You need the right conditions for your cells to function properly and for
enzyme action
onditions in the body are automatically controlled by nervous or chemical
C
responses:
● Blinking
● Vasodilation
Automatic control systems:
● Receptorsdetect the stimulus (if a level is too highor low) for negative
feedback
● Thecoordination centrereceives and processes theinformation before
organising a response
● Effectorsproduces a response which counteracts thechange and restores
the optimum level
ervous System
N
The nervous system controls how humans react to their surroundings and
coordinate their behaviour
How information is passed through the nervous system:
- Receptores are the cells that detect stimuli
- There are many types (such as sound for the ears and taste for the
tongue).
- Receptors often form part of a larger, complex organ
- Effectors respond to nervous impulses and bring the change
- There are different types of effectors (physical - muscles contract and chemical -
glands secrete hormones)
he nervous pathway is:
T
[stimulus] → receptor → sensory neuron → CNS → motor neurons → effector → [response]
Synapses:
● The connection between two neurones is called a synapse
● The nerve signal is transferred by chemicals that diffuse across the gap
, ● These chemicals then set off a new electrical signal in the next neurone
Reflexes:
● rapid automatic responses to certain stimuli that don’t need the conscious
part of the brain
○ Can help prevent injuries
○ Eg. pupils getting smaller in bright lights to let the light in and
prevent eye damage
○ The passage of information in a reflex (from receptor to effector) is
called a reflex arc
Reflex arc:
1. The neurons in the reflex arc go through the spinal cord or the unconscious
part of the brain
2. When a stimulus is detected (by receptors) impulses are sent along sensory
neurons to relay neurons in the CNS
3. When the impulse reaches synapses they trigger chemicals to be released.
This causes further impulses to be sent through the relay neuron
4. The impulse reaches another synapse and the same thing happens. The
chemicals are released and cause impulses to be sent along the motor
neuron
5. The impulses travel along the motor neuron to the effector
6. The body reacts (eg. flinching)
ecause you don’t have to think about the response it’s quicker than normal
B
responses
Required Practical #7 (investigating reaction time)
1 . W ork with a partner.
2. Person A holds out their hand with a gap between their thumb and first
finger.
3. Person B holds the ruler with the zero at the top of person A's thumb.
4. Person B drops the ruler without telling Person A and Person A must catch
it.
5. The distance on the ruler level with the top of person A's thumb is recorded
in a suitable table.
6. Repeat this ten times.
7. Swap places, and record another ten attempts.
8. Record the catch distance in cm.
omeostasis
H
Homeostasis is the maintenance of a constant internal environment
Homeostasis is really important for humans because. . .
● Whilst the external environment changes around your body the internal
environment of the body must be kept steady.
● You need the right conditions for your cells to function properly and for
enzyme action
onditions in the body are automatically controlled by nervous or chemical
C
responses:
● Blinking
● Vasodilation
Automatic control systems:
● Receptorsdetect the stimulus (if a level is too highor low) for negative
feedback
● Thecoordination centrereceives and processes theinformation before
organising a response
● Effectorsproduces a response which counteracts thechange and restores
the optimum level
ervous System
N
The nervous system controls how humans react to their surroundings and
coordinate their behaviour
How information is passed through the nervous system:
- Receptores are the cells that detect stimuli
- There are many types (such as sound for the ears and taste for the
tongue).
- Receptors often form part of a larger, complex organ
- Effectors respond to nervous impulses and bring the change
- There are different types of effectors (physical - muscles contract and chemical -
glands secrete hormones)
he nervous pathway is:
T
[stimulus] → receptor → sensory neuron → CNS → motor neurons → effector → [response]
Synapses:
● The connection between two neurones is called a synapse
● The nerve signal is transferred by chemicals that diffuse across the gap
, ● These chemicals then set off a new electrical signal in the next neurone
Reflexes:
● rapid automatic responses to certain stimuli that don’t need the conscious
part of the brain
○ Can help prevent injuries
○ Eg. pupils getting smaller in bright lights to let the light in and
prevent eye damage
○ The passage of information in a reflex (from receptor to effector) is
called a reflex arc
Reflex arc:
1. The neurons in the reflex arc go through the spinal cord or the unconscious
part of the brain
2. When a stimulus is detected (by receptors) impulses are sent along sensory
neurons to relay neurons in the CNS
3. When the impulse reaches synapses they trigger chemicals to be released.
This causes further impulses to be sent through the relay neuron
4. The impulse reaches another synapse and the same thing happens. The
chemicals are released and cause impulses to be sent along the motor
neuron
5. The impulses travel along the motor neuron to the effector
6. The body reacts (eg. flinching)
ecause you don’t have to think about the response it’s quicker than normal
B
responses
Required Practical #7 (investigating reaction time)
1 . W ork with a partner.
2. Person A holds out their hand with a gap between their thumb and first
finger.
3. Person B holds the ruler with the zero at the top of person A's thumb.
4. Person B drops the ruler without telling Person A and Person A must catch
it.
5. The distance on the ruler level with the top of person A's thumb is recorded
in a suitable table.
6. Repeat this ten times.
7. Swap places, and record another ten attempts.
8. Record the catch distance in cm.
