Unit 1: The Nervous System Flashcards
Overview (The function of the nervous system):
•The nervous system works in conjunction with the endocrine system to respond to both internal and external environmental change, thereby maintaining homeostasis within the body.
-the nervous system responds via electrochemical messages relayed from the brain.
-the endocrine system responds via chemical messengers relayed through the bloodstream (hormones).
Nerves:
•two main types of nerve cells found in the nervous system:
1. Glial cells
-used for structural and nutritional support.
2. Neurons
-conduct nerve impulses throughout the body.
-supported by glial cells.
Neurons are:
The basic unit of the nervous system.
Neuron structure (dendrites):
-branches which accept nerve impulses from other neurons and carry them towards the cell body.
Neuron structure (axons):
-longer branches which carry nerve impulses away from the cell body.
Neuron structure (myelin sheath):
-a fatty myelin sheath surrounds each axon, insulating the neuron and speeding up the rate of impulse transmission.
Neuron structure (schwann cells):
-a type of glial cell, are responsible for producing the myelin around each axon.
Neuron structure (nodes of ranvier):
-gaps between Schwann cells are referred to as the nodes of ranvier. Electrical impulses “jump” from node to node (saltatory conduction).
Neuron structure (axon terminal):
-once the electrical signal reaches the axon terminal, it is passed on to the dendrites of an adjoining neuron.
Myelination:
-the myelination of neurons is vital for proper signal transduction within the nervous systems.
Saltatory conduction:
-action potentials travelling down the axon “jump” from node to node.
Myelinated neurons:
-make up the white matter of your brain, which is responsible for conducting nerve impulses.
-can regenerate after injury.
Unmyelinated neurons:
-make up the grey matter of your brain, which is responsible for processing information and generating nerve impulses.
-cannot regenerate after injury.
Types of neurons:
-three main types of neurons carry signals to and from the brain (sensory neurons, interneurons, motor neurons).
Types of neurons (sensory neurons):
-afferent- moving towards CNS.
-gather information from sensory receptors (i.e. touch/sight/sound/taste receptors) and transmit these impulses to the brain.
Types of neurons (interneurons):
-process and integrate incoming sensory info from sensory neurons and relay outgoing information to motor neurons.
Types of neurons (motor neurons):
-efferent- moving away from CNS.
-transmit information from the brain to muscles (effectors), glands, and other organs.
Reflex arc:
•a neural circuit that passes through interneurons in the spinal cord for immediate response.
-simplest nerve pathway.
-neural circuit through the spinal cord.
-reflexes are involuntary & unconscious (no brain coordination).
5 essential components for a reflex arc:
- Receptor.
- Sensory neuron.
- Interneuron (in spinal cord).
- Motor neuron.
- Effector.
The speed of an impulse:
-the speed of an impulse along the nerve fiber is dependent on 2 things:
1. Myelin: myelinated axons send impulses faster than non-myelinated axons because the impulse jumps from node to node all along the axon.
2. Diameter of axon: bigger = faster.
Conduction of nerve impulses (electrical event):
-a nerve impulse or action potential has both a chemical and electrical component (hence the term electrochemical impulse).
Four stages of a nerve impulse:
- Polarized/resting state.
- Depolarization.
- Repolarization.
- Refractory period.
Four stages of a nerve impulse
(1. Resting state):
•the difference in charge across the membrane of a resting neuron is called resting membrane potential.
-the inside of a neuron has a slight negative charge at rest, whereas the outside has a slight positive charge.
-this results in a resting potential of -70mV.
Four stages of a nerve impulse
(Resting state & the Sodium-Potassium pump):
•A) at rest Na+ ions are found mostly outside the axon membrane and K+ ions are found mostly within the axon, along with larger negatively charged ions that cannot pass through the membrane.
•B) membrane is impermeable to Na+ ions.
•C) membrane is slightly permeable to K+ ions so some K+ ions leak out (leaky K+ ion channels).
•D) as a result, slightly more positive ions are outside the membrane, making the inside relatively negative.
•E) the sodium-potassium pump along the membrane surface maintains the electrical potential difference by transporting 3 Na+ ions out of the cell and 2 K+ ions inside the cell.
•F) as a result, an excess of positive charge accumulates outside of the cell membrane. A constant membrane potential of -70mV is maintained.