Coordination and Response in Humans

What do organisms respond to

They respond to the change in environment (stimulus) in order to survive

What does a co-ordinated response require

It requires stimulus, receptor and coordinator

Nervous system

It has faster message that act for a short term. It has electrical impulses through neurons

Endocrine system

Slower messages that act for a long time. Chemical messengers via the blood stream

What does the Central Nervous System consist off

CNS- the brain and the spinal cord

Motor neuron

Transmits impulses from the brain/ spinal cord to the muscles (effectors) stimulating them into a response

Sensory Neuron

Send electrical impulses to brain/spinal cord using receptors that detect a stimuli

Relay neuron

receive impulses from sensory neurons and pass it onto the motor neuron

What is the reflex arc

The reflex arc is an automatic response to a stimulus.

• Stimulus detected by receptor

• Impulses sent along sensory neurone from receptors to the CNS

• The relay neuron receives the impulse and passes it on to the motor neuron across the synapses

• The motor neuron sends to impulse to the effectors (muscles) and they contract/ move away from the stimulus

What is the role of the synapses

The synapses is the gap between neurones- where neurotransmitters diffuse across. Synapses connect neurones.

What does the axon, the axon terminal, myelin sheath and dendrites do.

The axon is the long part of a neuron which impulses are conducted along the one cell body to other cells

The axon terminals is where the impulses are transferred to the effector

The myelin sheath insulates the cell and speeds up the impulses transmission along the cell

Dendrites receive impulses from other neurons and conduct them towards the cell body

How does the eye focus on light from a far/near object

Far object:

The ciliary muscles relax and the suspensory ligaments pull tight making the lens pull thin. The cornea refracts light by a smaller amount

Near object:
The ciliary muscles contract and the suspensory ligaments slacken making the lens rounder. The cornea refracts light by a larger amount

Iris Reflex in bright and dim light

Bright light:

The radial muscles relax and the circular muscles contracted making the pupil smaller

Dim light:

The radial muscles contracts and the circular muscles relax making the pupil larger