Flashcards in The nervous system and reflexes (Chapter 15) Deck (31)
What do communication systems within animals coordinate?
The activities of receptors and effectors
What do receptors detect and why?
There are receptors that detect stimuli 1) in the surrounding environment 2) in the body bc the information they receive comes from the internal and external environment
What are the two types of information transfer used in animals to coordinate the body's activities?
1) nerves that transmit information in the form of electrical impulses
2) hormones that travel in the blood
What does the endocrine system consist of?
Glands that secrete hormones
What is the mammalian nervous system made up of?
1) CNS - brain and spinal cord
2) PNS - cranial nerves (attached to the brain) and spinal nerves (attached to the spinal cord)
Where do neurones carry information to?
Directly to their target cells
What are the three types of neurone?
What do sensory neurones do?
Transmit impulses from receptors to CNS
What do relay neurones do?
Transmit impulses from sensory neurones to motor neurones
What do motor neurones do?
Transmit impulses from the CNS to effectors
Describe the structure of neurones
- Nucleus in the cell body
- Thin cytoplasmic processes (dendrites and axons) extend from the cell body
- Organelles in the cytoplasm of the axon e.g. mitochondria and small regions of rough ER
What is the difference between the axon and dendrites?
1) dendrites - very short and often have many branches
2) axon - much longer and conducts impulses over long distances
What do the ends of the branches of the axon contain?
Large numbers of mitochondria and many vesicles containing transmitter substances
Describe the structure of a motor neurone
- Cell body lies within the spinal cord or brain
- There are many highly branched dendrites to give a large surface area for the endings of other neurones
- All have a motor end plate (a connection with a muscle)
Describe the structure of a sensory neurone
- One long axon with a cell body that may be near the source of stimuli or in a swelling of a spinal nerve (ganglion)
- Dendrites receive inputs from the sensory receptor
Where are all relay neurones found?
In the CNS
How are the axons of some neurones protected?
They are surrounded by myelin and protected within nerves
What are nerves not protected by myelin called and what proportion of nerves are like this?
- Unmyelinated neurones (about 2/3 of all neurones)
What is myelin made by?
Schwann cells (specialised cells)
How is myelin made?
1) myelin is made when Schwann cells wrap themselves around the axon all along its length
2) the Schwann cells spiral around, enclosing the axon in many layers of its CSM, forming an enclosing sheath (myelin sheath)
Describe the myelin sheath
- Made largely form lipid, together with some proteins
- It affects the speed of conduction of nerve impulses
- It provides electrical insulation
What are the nodes of Ranvier?
The small, uncovered areas of axon between nodes of Ranvier
Describe the nodes of Ranvier
- They occur roughly every 1-3 mm in human neurones
- They are very small (2-3 μm)
What is a reflex arc?
The pathway along which impulses are transmitted from a receptor to an effector without involving the conscious region of the brain
What is a reflex action?
A fast, automatic response to a stimulus, that is a very useful way of responding to danger signals - the response to each specific stimulus is always the same
What is an example of a reflex arc in the brain?
Those controlling focusing and how much light enters the eye
How does a reflex arc which doesn't involve a relay neurone work?
The impulse passes directly from the sensory to the motor neurone
Describe how a reflex action happens
1) within the spinal cord, the impulse will also be passed onto other neurones which take the impulse up the cord to the brain
2) this happens at the same time as impulses are travelling along the motor neurone to the effector
3) ∴ the effector responds the the stimulus before there is any voluntary response involving the conscious region of the brain
What is a stimulus?
An external condition that is detected by the body and triggers a response