7.Coordination, Response & Homeostasis

What is the nervous system?

A system that coordinates and regulates body responses to stimuli

Name the two parts of the human nervous system

Central nervous system and peripheral nervous system

What does the central nervous system consist of?

Brain and spinal cord

What does the peripheral nervous system consist of?

All nerves outside the CNS

What is a nerve impulse?

An electrical signal that travels along neurones

What is a neurone?

A specialised nerve cell

What is a nerve?

A bundle of neurones

Name the three types of neurone

Sensory relay motor

What is the function of sensory neurones?

Carry impulses from receptors to the CNS

What is the function of relay neurones?

Connect sensory and motor neurones in the CNS

What is the function of motor neurones?

Carry impulses from the CNS to effectors

What is an effector?

A muscle or gland that produces a response

What is an axon?

A long fibre that carries nerve impulses

Why are neurones long?

To reduce time taken for impulses to travel

What is the role of myelin sheath?

Insulates the axon and speeds up impulse transmission

What are nodes of Ranvier?

Gaps in the myelin sheath where impulses jump

What are dendrites?

Extensions that receive impulses from other neurones

Describe a sensory neurone

Long with cell body in the middle

Describe a relay neurone

Short with many dendrites

Describe a motor neurone

Long with large cell body at one end

What is a voluntary response?

A conscious response controlled by the brain

Give an example of a voluntary response

Picking up a cup

What is a reflex response?

An automatic rapid response not involving the brain

Why are reflexes fast?

They bypass the brain

State one advantage of reflex responses

Minimises damage to the body

Define a stimulus

A change in the environment

Define a response

An action produced by an effector

What is a reflex arc?

The pathway followed by a nerve impulse in a reflex

List the stages of a reflex arc

Receptor sensory neurone relay neurone motor neurone effector

Where is the coordinator in a reflex?

Spinal cord

What is a receptor?

A group of specialised cells detecting stimuli

What happens at the effector in a reflex?

A muscle contracts or gland secretes

What is a synapse?

A junction between two neurones

Why do neurones not touch?

To control direction of impulses

What is a neurotransmitter?

A chemical messenger released at a synapse

How is an impulse transmitted across a synapse?

By diffusion of neurotransmitters

Why do impulses travel in one direction across synapses?

Neurotransmitters are released from presynaptic neurone only

What happens to neurotransmitters after transmission?

They are destroyed

Why do drugs affect synapses?

Because synapses use chemicals

What are receptors?

Cells that detect stimuli

What do sense organs contain?

Groups of receptors

What happens when a receptor is stimulated?

An electrical impulse is generated

Name the main parts of the eye

Cornea iris lens retina optic nerve

What is the function of the cornea?

Refracts light

What is the function of the iris?

Controls pupil size

What is the function of the lens?

Focuses light onto the retina

What is the function of the retina?

Contains light receptors

What is the function of the optic nerve?

Carries impulses to the brain

What is the fovea?

Area of retina with many cones

What is the pupil reflex?

Control of pupil size in response to light

What happens to the pupil in dim light?

It dilates

What happens to the pupil in bright light?

It constricts

What muscles control the pupil?

Circular and radial muscles

What does antagonistic mean?

Muscles working in opposition

What happens to iris muscles in dim light?

Radial contract circular relax

What happens to iris muscles in bright light?

Circular muscles contract radial muscles relax in bright light

Define accommodation

Adjustment of lens shape to focus light

What happens to the lens for near objects?

Becomes thicker

What happens to the lens for distant objects?

Becomes thinner

What do ciliary muscles do when viewing near objects?

Contract

What happens to suspensory ligaments when viewing near objects?

Loosen

What are rod cells?

Receptors sensitive to low light

What are cone cells?

Receptors sensitive to colour

Where are cone cells concentrated?

Fovea

Where are rod cells found?

Throughout the retina except blind spot

What is a hormone?

A chemical messenger transported in the blood

What system produces hormones?

Endocrine system

Why do endocrine glands have good blood supply?

To transport hormones quickly

What is a target organ?

Organ affected by a hormone

How does the liver affect hormones?

Breaks down excess hormones

State one difference between nervous and hormonal control

Nervous is fast hormonal is slow

What is homeostasis?

Maintenance of a constant internal environment

Give one example of a controlled condition

Body temperature

What is negative feedback?

A system that returns conditions to a set point

What happens when blood glucose rises?

Insulin is released

What does insulin do?

Converts glucose to glycogen

What happens when blood glucose falls?

Glucagon is released

What does glucagon do?

Converts glycogen to glucose

Where are insulin and glucagon produced?

Pancreas

What is glycogen?

Stored form of glucose

What is adrenaline?

Fight or flight hormone

Where is adrenaline produced?

Adrenal glands

Give one effect of adrenaline

Increased heart rate

Why does adrenaline increase blood glucose?

To provide energy for muscles

Define Type 1 diabetes

Inability to produce insulin

How is Type 1 diabetes treated?

Insulin injections

State one symptom of diabetes

Extreme thirst

Why must diabetics monitor blood glucose?

To control insulin dosage

What is temperature regulation?

Control of body temperature

What is the normal human body temperature?

37 degrees Celsius

Why is temperature regulation important?

Enzymes denature at high temperatures

Name three skin structures involved in temperature control

Sweat glands capillaries hairs

What happens when the body is too hot?

Sweating vasodilation

What happens when the body is too cold?

Shivering vasoconstriction

Define vasodilation

Widening of blood vessels

Define vasoconstriction

Narrowing of blood vessels

What is the effect of vasodilation?

Increased heat loss

What is the effect of vasoconstriction?

Reduced heat loss

What is a tropism?

A growth response to a stimulus

What is phototropism?

Response to light