Coordination Response And Homeostasis

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Notes

Mammalian Nervous System

The nervous system consists of the **central nervous system (CNS)** (brain and spinal cord) and the **peripheral nervous system (PNS)** (all nerves).
It allows us to sense and respond to the environment and coordinate body functions.
Information is transmitted as **nerve impulses** (electrical signals) along **neurones**; a bundle of neurones is a **nerve**.

Types of Neurones

**Sensory neurones** carry impulses from sense organs to the CNS.
**Relay neurones** (in the CNS) connect sensory and motor neurones.
**Motor neurones** carry impulses from the CNS to effectors (muscles or glands).
Neurones have a long **axon** insulated by a **myelin sheath** with **nodes of Ranvier**; impulses jump between nodes for rapid transmission.
Cell bodies have **dendrites** that connect to many other neurones.

The Reflex Arc

A **reflex action** is an automatic, rapid, protective response that does not involve the brain.
Pathway: **stimulus** → **receptor** → **sensory neurone** → **relay neurone** (in spinal cord) → **motor neurone** → **effector** → **response**.
Example: touching a sharp object causes pain receptors to send impulses via sensory neurone to spinal cord; relay neurone passes impulse to motor neurone; muscle contracts to withdraw foot.

Sense Organs

**Receptors** are groups of specialised cells that detect stimuli and generate electrical impulses.
**Sense organs** contain receptors that respond to specific stimuli (e.g., eyes to light, ears to sound).
Impulses from sense organs travel via sensory neurones to the CNS, which coordinates a response via motor neurones to effectors.

Hormones in Humans

A **hormone** is a chemical substance produced by a **gland**, carried by the blood, that alters the activity of **target organs**.
The **endocrine system** consists of glands that secrete hormones directly into the bloodstream.
**Insulin** (from pancreas) lowers blood glucose by converting glucose to **glycogen** in liver and muscles.
**Glucagon** (from pancreas) raises blood glucose by converting glycogen to glucose.
**Adrenaline** (from adrenal glands) prepares the body for 'fight or flight': increases blood glucose, heart rate, breathing rate, diverts blood to muscles, dilates pupils.

Homeostasis

**Homeostasis** is the maintenance of a constant internal environment.
**Negative feedback** reverses changes from the set point: if a level rises, mechanisms reduce it; if it falls, mechanisms raise it.
Blood glucose is controlled by negative feedback involving insulin and glucagon.

Homeostasis & Temperature Control

Body temperature is maintained at about **37°C** by the skin and brain.
The brain contains receptors sensitive to blood temperature; skin has temperature receptors that send impulses to the brain.
When hot: **vasodilation** of skin arterioles increases heat loss; **sweating** cools the body via evaporation.
When cold: **vasoconstriction** reduces heat loss; **shivering** generates heat; **erector pili** muscles raise hairs (ineffective in humans).
Fatty tissue under the dermis provides insulation.

Structure of a myelinated motor neurone showing dendrites, cell body, axon, myelin sheath, and nodes of Ranvier.

The reflex arc pathway: stimulus → receptor → sensory neurone → relay neurone → motor neurone → effector.

Practice questions

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1.Complete the sentence.
Easy
The human nervous system consists of the central nervous system (CNS) and $the ____$ nervous system.
2.Which type of neurone carries impulses from sense organs to the central nervous system?
Medium
- ASensory neurone
- BRelay neurone
- CMotor neurone
- DInterneurone
3.Name the part of a neurone that is insulated by a fatty sheath and carries electrical impulses.
Medium
4.A reflex action involves the brain as the coordinator.
Easy
True or false?
5.Place the following events in a reflex arc in the correct order.
Hard
- Impulse travels along sensory neurone to spinal cord
- Stimulus detected by receptor
- Effector produces response
- Impulse passes to relay neurone then motor neurone
6.Name the hormone produced by the pancreas that lowers blood glucose concentration.
Medium
7.What is the optimum temperature for human enzyme activity in degrees Celsius?
Easy
- A41
- B45
- C33
- D37
8.Which of the following is NOT an effect of adrenaline?
Hard
- AIncreased blood glucose concentration
- BDecreased pulse rate
- CDilated pupils
- DDiverted blood flow to muscles

Slides

The Mammalian Nervous System

The nervous system is divided into the central nervous system (CNS) – brain and spinal cord – and the peripheral nervous system (PNS) – all other nerves.
It allows us to sense our surroundings and respond, and to coordinate body functions.
Information travels as electrical impulses along nerve cells called neurones.

Which part of the nervous system includes the brain and spinal cord?

Peripheral nervous system
Central nervous system
Autonomic nervous system
Somatic nervous system

Types of Neurones

Sensory neurones carry impulses from sense organs to the CNS.
Relay neurones are inside the CNS and connect sensory to motor neurones.
Motor neurones carry impulses from the CNS to effectors (muscles or glands).
Neurones have a long axon insulated by a fatty sheath with nodes of Ranvier, allowing impulses to jump and travel faster.

Which of these are true about neurones?

Sensory neurones carry impulses from the CNS to effectors.
Relay neurones are found only in the CNS.
Motor neurones carry impulses from the CNS to effectors.

The Reflex Arc

A reflex action is an involuntary, rapid, protective response to a stimulus.
It does not involve the brain; the spinal cord acts as the coordinator.
The reflex arc: stimulus → receptor → sensory neurone → relay neurone → motor neurone → effector → response.

In a reflex arc, $the ____$ detects the stimulus and sends an impulse along $a ____$ neurone to the spinal cord. $A ____$ neurone then passes the impulse to $a ____$ neurone, which carries it to an effector.

Sense Organs as Receptors

Receptors are groups of specialised cells that detect changes in the environment (stimuli).
Sense organs contain receptors that respond to specific stimuli (e.g., light, sound, touch).
When stimulated, a receptor generates an electrical impulse that passes to a sensory neurone and then to the CNS.

What is the role of a receptor in a sense organ?

To carry impulses to the CNS
To detect a stimulus and generate an electrical impulse
To carry out the response
To connect sensory and motor neurones

Hormones in Humans

A hormone is a chemical substance produced by a gland and carried in the blood to target organs.
Hormones alter the activity of specific target organs that have complementary receptors.
The endocrine system consists of all hormone-producing glands.

Which of these are true about hormones?

Hormones are transported in the blood plasma.
Hormones affect all cells in the body.
Hormones are produced by glands.

Blood Glucose Control (Extended)

Blood glucose levels are controlled by negative feedback involving insulin and glucagon, both produced in the pancreas.
When blood glucose rises, insulin is secreted; it stimulates liver and muscle cells to store glucose as glycogen.
When blood glucose falls, glucagon is secreted; it stimulates liver and muscle cells to convert glycogen back to glucose.

When blood glucose concentration is too high, the pancreas secretes ____, which causes the liver to store glucose $as ____$ .

Adrenaline – The Fight or Flight Hormone

Adrenaline is produced in situations of danger or stress.
It increases blood glucose concentration, heart rate, and breathing rate.
It diverts blood to muscles and dilates pupils to improve awareness.

Which of the following is NOT an effect of adrenaline?

Increased heart rate
Decreased blood glucose concentration
Dilated pupils
Increased breathing rate

Homeostasis and Negative Feedback (Extended)

Homeostasis is the maintenance of a constant internal environment.
Negative feedback mechanisms reverse any change from the set point.
If a level rises, control systems reduce it; if it falls, they raise it.

Which statements about negative feedback are true?

It amplifies changes from the set point.
It helps maintain a stable internal environment.
It involves detecting a change and then reversing it.

Temperature Regulation (Extended)

Body temperature is controlled by the brain, which has receptors sensitive to blood temperature.
The skin also has temperature receptors that send impulses to the brain.
Responses include sweating, shivering, vasodilation, and vasoconstriction to maintain around 37°C.

What happens to blood vessels in the skin when body temperature rises?

They constrict (vasoconstriction)
They dilate (vasodilation)
They remain unchanged
They become more permeable

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