Biology IGCSE - Coordination and Response

Electrical impulses travel along neurones

Central nervous system (CNS)

Brain and spinal cord

Peripheral nervous system (PNS)

nerves outside of the brain + spinal cord

Role of nervous system

coordinates + regulates body functions by detecting stimuli + sending electrical impulses to bring a response

Sensory neurones

Relay neurones

Motor neurones

Simple reflex arc

Our bodies detect changes in environment → change in environment is called a stimulus → e.g. light or temperature → sense organs → e.g. eyes help to detect stimuli using specialised cells → called receptor cells → receptor cells create electrical signal called a nerve impulse → travels down a neurone → pass the nerve impulse to each other until reaches effector → e.g. muscle or gland carries out response

Common reflex arc diagram

Reflex action

means of automatically (unconsciously) + rapidly integrating + coordinating stimuli wit responses of effectors → e.g. muscles + glands

Response of effectors

1. Muscles contract

2. Gands secrete chemicals

Sense organs

groups of receptor cells responding to specific stimuli → e.g. light, sound, touch, temperature + chemicals

Hormone

chemical substance → produced by a gland → carried by the blood → alters the activity of one or more specific target organs

Hormones VS nervous system

Hormones can act very rapidly, but compared to nervous system → effects are slower, but longer lasting

adrenal glands → adrenaline

pancreas → insulin

testes → testosterone

ovaries → oestrogen

Adrenaline

Hormones secreted in ‘fight or flight’ situations

Adrenaline effects

• Increased heart rate

• Increased breathing rate

• Pupils dilate

• Causes liver to convert glycogen → glucose → increases blood glucose concentration → ready for more respiration for fighting or running away

Glucagon is secreted by the pancreas

Homeostasis

maintenance of a constant internal environment

Homeostatic control by negative feedback

Negative feedback → process that returns a system to its set point if it moves too far from it

How negative feedback works

1. Change is detected → e.g. too hot/too much glucose

2. Body responds to counteract the change

3. Internal environment returns to normal

Control of blood glucose concentrations by the liver

Regulated by the pancreas + liver

Control of blood glucose concentrations → insulin

Insulin → secreted when blood glucose high) → produced by pancreas → tells the liver to convert glucose into glycogen for storage → lowers blood glucose

Insulin

Insulin helps cells absorb glucose → lowers blood glucose

Control of blood glucose concentrations → glucagon

Glucagon → secreted when blood glucose is low → produced by pancreas → tells the liver to convert glycogen into glucose → Raises blood glucose

Glucagon

When glucose is gone, you release glucaGON → tells liver to release glucose into blood → raises blood sugar

Diagram of skin

Maintenance of a constant internal body temperature → insulation

When body temperature low → hair erector muscles contract → makes hairs stand upright → traps layer of air close to skin → acts as insulation

Maintenance of a constant internal body temperature → sweating

Body temperature high → sweat glands release more sweat → as sweat evaporates from skin → thermal energy is lost → cools the body

Maintenance of a constant internal body temperature → shivering

Shivering → rapid contraction + relaxation of muscles → increases respiration in muscle cells → releases heat to warm body

Maintenance of a constant internal body temperature → role of the brain

Hypothalamus in brain → detects changes in blood temperature → triggers responses → e.g. sweating or shivering to maintain a stable internal temperature

Maintenance of a constant internal body temperature → vasodilation

Vasodilation → widening of arterioles near skin surface → increases blood flow to skin → allows more heat to escape

Maintenance of a constant internal body temperature → vasoconstriction

Vasoconstriction → narrowing of arterioles near skin surface → reduces blood flow → less heat is lost from body

Vasodilation

Vasodilation = ventilation → opening windows to let heat out

Vasoconstriction

Vasoconstriction = wearing a tight jacket → keeps warmth in