11.1 Structures and Processes Nervous System Flashcards
What is Homeostasis?
The state of relative stability within the body
Why is homeostasis important?
Because the body can only survive within a narrow range of conditions
How does the nervous system of people in warmer climates act when encountering cold?
The nervous system constricts blood to extremities to conserve heat
How does the nervous system of people in colder climates act when encountering cold?
The nervous system fluctuates the constriction and dilation of blood vessels. This conserves heat but also allows for continual blood flow to prevent frostbite
What does the Nervous system do?
Monitors and controls most body processes
What makes up the Nervous System?
The Brain, the Spinal cord, and the Nerves
How many nerve cells does the human nervous system contain?
100 Billion
What are the two major divisions of the nervous system?
- Central Nervous System (CNS)
* Peripheral Nervous System (PNS)
How did researchers come up with CNS and PNS?
Based on where the tissue is located in the body. Centrally or away from the center of the body (peripherally)
What does the Central and Peripheral nervous system control?
- Sensory Input
- Integration
- Motor Output
What makes up the Central Nervous system?
The brain and the spinal cord
What does the Central Nervous system do?
Integrates and processes information sent by nerves
What is the Peripheral Nervous system made of?
Nerves that carry sensory messages to the central nervous system
and nerves that send info from the CNS to the muscles and glands
What is the Peripheral Nervous system further divided into?
The Somatic System and the Autonomic System
What does the Somatic System consist of?
- Sensory receptors in the head and extremities
- Nerves that carry info to the CNS
- Nerves that carry info from the CNS to the skeletal muscles
What does the Autonomic system control?
Glandular secretions and the functioning of smooth cardiac muscles
What is the Autonomic system further divided into?
The Sympathetic nervous system and the Parasympathetic nervous system
What do the Sympathetic and Parasympathetic Nervous system do?
Work in opposition to each other to regulate the involuntary processes of the body
What are some involuntary processes in the body?
- Heartbeat
* Peristalsis
What are the 2 main types of cells that make up the nervous system?
Neurons and Glial cells
What are the cells that support Neurons called?
Glial cells
What are Neurons?
The basic structural and functional unit of the Nervous system
What do Neurons do?
They respond to physical and chemical stimuli
How do Neurons respond to physical and chemical stimuli?
By conducting electrochemical signals and releasing chemicals that regulate various body processes
Where does the word Glial come from?
Greek for meaning glue
How many Glial cells are there in comparison
Glial cells outnumber neurons 10:1
What do Glial cells do?
They nourish neurons, remove their waste, and defend against infection. They also provide a supportive framework for all the nervous system tissue
How are individual neurons organized?
They are organized into tissues called Nerves
What do nerves do?
Extend Neurons throughout the peripheral nervous system
What are two jobs of nerves?
Some consist of neurons that carry information from sensory receptors
Other nerves consist of neurons that carry information to the muscles or glands
Why do neurons vary in different sizes and appearance?
Because of where they are present in the body and their function
What does the basic impulse transmission pathway depend on?
Sensory input
Integration
Motor output
What does sensory input mean?
Sensory neurons gather information from sensory receptors and transmit these impulses to the central nervous system (brain and spinal cord)
Where are interneurons found?
Within the central nervous system
What do interneurons do?
They act as a link between sensory and motor neurons
What does integration mean?
When interneurons process and integrate sensory information relay outgoing motor information
What is the function of sensory receptors?
Receive stimuli and form a nerve impulse
What is the function of sensory neurons?
Transmit impulses from the sensory receptors to the interneurons
What is the function of interneurons?
Are found in the brain and spinal cord and act as an integration center
What is the function of motor neurons?
Conduct impulses from interneurons to the effectors
What are effectors?
Muscles, glands, and other organs that respond to impulses from the motor neurons
What is motor output?
When motor neurons transmit information from the central nervous system to the muscles, glands, and other organs
What are reflexes?
Sudden unlearned, involuntary responses to stimuli
What are reflex arcs?
Simples connections of neurons that explain reflexive behaviors
Why are reflexes very rapid?
Because they use very few neurons to transmit messages
What is an example of a reflex arc?
The sensory neuron senses a stimuli and sends a message to the interneuron and which then relays the message to the motor neuron
What are the 4 common features of neurons?
Dendrites, a cell body (soma), an axon, and branching ends
What are dendrites?
Short, branching terminals that receive nerve impulses from other neurons or sensory receptors and relay the impulse to the cell body
Why are dendrites highly branched?
To increase the surface area able to receive information
What does the cell body contain and what happens in it?
It contains the cell body and is the sight of metabolic reactions. They also process input from the dendrites
What happens after the cell body receives input from the dendrites?
It relays it to the axon where an impulse is initiated
What does the axon do?
Conducts impulses away from the cell body
Why does the end of the axon branch into many fibres?
To communicate with adjacent neurons, glands, or muscles
How does the axon communicate with adjacent neurons, glands or muscles?
It releases chemical signals into the space between it and the receptors or dendrites of neighboring cells
What is the myelin sheath?
When the axons of some neurons are enclosed in a fatty insulating layer
What does the myelin sheath do?
Protects myelinated neurons and speeds the rate of nerve impulse transmission
What are Schwann cells?
A type of glial cells
How do Schwann cells form a myelin sheath?
By wrapping themselves around the axon
What forms white matter in the central nervous system?
Myelinated neurons
What forms grey matte in the central nervous system?
Unmyelinated neurons
How are neurons able to create an electrical impulse?
By using the voltage difference from the inside and outside of the neuron
How is nerve conduction different from a wire?
Nerve conduction is considerably slower and more complex. It depends on the movement of ions across the membrane of the axon
Which side of a resting neuron is negative?
The cytoplasmic side of the membrane
What is a form of potential energy or membrane potential in a neuron?
The charge separation of the inside and the outside of the neuron
What is the resting membrane potential?
the potential difference across the membrane of a resting neuron
What is the resting membrane potential of most unstimulated neurons?
-70mV
What is polarization?
The process of generating a resting membrane potential of -70mV
What causes resting neurons to be negative on the inside?
Large protein molecules that are negative are present in the inside of the neuron. they are too large so they are unable to pass the membrane
What is the most important contributor to the separation charge and the resulting electrical potential difference?
The sodium-potassium exchange pump
What does the sodium potassium exchange pump do?
Uses the energy of ATP to transport sodium ions out of the cell and potassium ions into the cell
What is the result of the sodium potassium exchange pump?
Positive charge accumulates outside the cell
What are the steps in the sodium potassium exchange pump?
A carrier protein allow 3 Na+. The ATP splits and the Na+ is allowed to exit the cell.
The carrier protein then takes in 2K+, the phosphate group then removes itself from the carrier protein and the 2K+ are allowed to enter the cell
Where do action potentials occur in myelinated neurons?
At the nodes of Ranvier
When is neuronal membrane said to be depolarized?
If the transmembrane potential is reduced to less than the resting potential of -70mV
What occurs if the membrane at the node of Ranvier become depolarized to -55mV?
A dramatic change in the membrane called action potential
Why is action potential called an all or none event?
Because depolarization to between -70mV and -55mV has no effect
What is threshold potential?
-55mV because that is when an event occurs
What happens when the transmembrane potential at the node of ranvier reaches threshold?
Special structures in the membrane called voltage -gated sodium channels open and make the membrane permeable to sodium ions.
why do sodium ions rush into the axon when the voltage gated sodium channels open?
Because of the concentration gradient and potential difference
What is the result of the sodium ions rushing into the axon?
The potential difference in the node of ranvier reached +35
What happens when the potential difference in the node of ranvier reaches +35?
The sodium channels close and the voltage gated potassium ions open and the potassium ions move down their concentration gradient (towards the outside of the axon)
What happens as the potassium ions move outside the axon?
The positive charge is carried out of the neuron and the axon become repolarized
What is the refractory period?
When the brief period after the action potential when the neuron cannot be stimulated again
What does nerve pulse consist of?
A series of action potentials
How does one action potential stimulate another?
At the end of an action potential when sodium ions diffuse out, the neighboring nodes receive these sodium ions and reduce the net negative charge inside the axonal membrane. This causes depolarization to occur
What is saltatory conduction?
The conduction of an impulse along a myelinated neuron
What is multiple sclerosis caused by?
The breakdown of the myelin sheath surrounding the axons of the central nervous system
What happens as a result of the breakdown of the myelin sheath in multiple sclerosis?
The neurons can no longer efficiently carry electrochemical signals between the brain and the body
What is a synapse?
The connection between 2 neurons or a neuron and and an effector
What is neuromuscular junction?
A synapse between a motor neuron and a muscle cell
What is the gap between neurons called?
A synaptic cleft
What does the presynaptic neuron do?
Sends out information
What does the postsynaptic neuron do?
Receives information
What do neurotransmitters do?
Carry the neural signal from one neuron to another
What is the first step in an impulse moving across a synapse?
When an action potential arrives at the end of a presynaptic neuron, the impulse causes sacs that contain neurotransmitters to fuse with the membrane of the axon
What are synaptic vessels?
The vessels that contain neurotransmitter molecules
What happens when the synaptic vessels fuse with the membrane of the axon?
The sacs release their contents into the synaptic cleft by exocytosis and diffuse across the synapse to reach the dendrites of the postsynaptic neuron. Or the cell membrane of the effector
What happens once the neurotransmitters reach the postsynaptic membrane?
They ind to specific receptor proteins in the membrane and trigger ion specific channels to open. This depolarizes the postsynaptic membrane and if the threshold potential is reached initiates an action potential
What are the two effects that neurotransmitters have on the postsynaptic membrane?
Excitatory or inhibitory
What does it mean for the effects to be excitatory?
The neurotransmitters cause the receptor proteins to trigger the ion channels that open to allow positive ions, such as sodium to flow into the postsynaptic neuron. As a result becoming slightly depolarized
What does it mean for the effects of neurotransmitters to be inhibitory?
The receptor will trigger potassium channels to open, allowing the potassium ions to flow out
What is the result of potassium ions flowing out of a neuron?
A more negative transmembrane potential resulting in hyperpolarization
What happens after a neurotransmitter has had its effect?
Enzymes break it down and inactivate it so that its components can be reabsorbed by the presynaptic cell
What is Acetylcholine?
A neurotransmitter that crosses a neuromuscular junction
What does Acetylcholine do?
Excites the muscle cell membrane, causing depolarization and contraction of the muscle fibre
What is Cholinesterase?
An enzyme released in the synapse to breakdown Acetylcholine
How does Cholinesterase work?
It breaks down acetylcholine so that it can be removed from the protein receptors, thus allowing ion channels to close and the membrane to repolarize
