2.10.6 The Human Nervous System Flashcards
Central nervous system (CNS) consists of what?
The brain and spinal cord
Peripheral nervous system (PNS) consists of what?
All of the nerves in the body
Information is sent through the nervous system as what?
Electrical impulses
These are electrical signals that pass along nerve cells known as what?
Neurones
A bundle of neurones is known as what?
A nerve
The nerves spread out from the central nervous system to where?
To all other regions of the body and importantly, to all of the sense organs
The CNS, therefore, acts as a central coordinating centre for what?
The impulses that come in from (or are sent out to) any part of the body
Neurones have a cell body (where the nucleus and main organelles are found) and cytoplasmic extensions from this body are called what?
Axons and Dendrites
The Axon is the main what?
Long fibre of the neurone
Some human neurones have axons of what length?
Over a metre in length (but only 1 – 4 micrometres wide)
why is it more efficient than having multiple neurones to convey information from the CNS to effectors?
Less time is wasted transferring electrical impulses from one cell to another
The axon is insulated by what?
A fatty myelin sheath with small uninsulated sections along its length (called nodes)
The electrical impulse does not travel down the whole axon, what does it do?
It jumps from one node to the next
Many extensions called dendrites extend out from where?
From the cell body of the neurone and at the far end of the axon
This means neurones can connect to many other neurones and what?
Receive impulses from them, forming a network for easy communication
Name the three main types of Neurones
Sensory neurones, relay neurones and motor neurones
Sensory neurones carry impulses from where?
Sense organs to the CNS (brain or spinal cord)
Relay neurones are found inside where?
The CNS and connect sensory and motor neurones
Motor neurones carry impulses from where?
The CNS to effectors (muscles or glands)
What is the structure of sensory neurones?
They are long and have a cell body branching off the middle of the axon
What is the structure of relay neurones?
They are short and have a small cell body at one end with many dendrites branching off it
What is the structure of motor neurones?
They are long and have a large cell body at one end with long dendrites branching off it
The pathway through the nervous system is…
stimulus →
sensory neurone → relay neurone →
motor neurone → effector →
response
First, a stimulus is received by what?
A sensory (receptor) neurone
Most receptors are specialised to detect what?
Particular stimuli
When a receptor is stimulated, it produces what?
Electrical impulses
These impulses then travel along a sensory neurone to where?
Central nervous system (the coordinator is either the brain or the spinal cord)
In the CNS, the impulses are passed on to what?
A relay neurone
The relay neurone links to a motor neurone, along which the impulses travel until they reach what?
The effector
What is the role of the effector?
It carries out the response (the effector may be a muscle or gland)
