Nervous Flashcards
What are neurons
The functional unit of the nervous system. It is an elongated cell with three parts
How does the nervous system function? How does the transmission occur?
By the almost instantaneous transmission of electrochemical signals. The means of transmission are highly specialized cells knows as neurons.
What are the three major parts of the neuron
Dendrites, cell body, axon
How many dendrites does the typical neuron have
Many
What do dendrites look like
Thin branches extending from the cell body
What does the cell body of the neuron contain
Nucleus and organelles
How many times longer is the axon than the rest of the neuron
Can be thousands
What is the axon
A single, long projection extending from a cell body
What does the axon end in
Several small branches known as axon terminals
How are neurons connected/not connected
They are often connected in chains and networks, yet they never actually come in contact with one another: the axon terminals of one neuron is separated from the dendrites of an adjacent neuron
What separates the axon terminals of one neurons from the dendrites of an adjacent neuron
A small gap known as a synapse
Where does the electrical impulse moving through a neuron begin
The dendrites
Where does the electrical impulse move after the dendrites
It passes through the cell body and then along the axon
What does the impulse always do
Follow the same path from dendrite to cell body to axon
What happens when the electrical impulse reaches the synapse at the end of the axon
It causes the release of specialized chemicals known as neurotransmitters
What do the neurotransmitters do after the electrical impulse activated them
They carry the signal across the synapse to the dendrites of the next neuron, starting the process again in the next cell
What is the cell at when there is no impulse traveling through a neuron? What is the charge of the cell?
The cell is at its resting potential and the inside of the cell contains a negative charge in relation to the outside
To keep the cell negatively charged inside, what does it require
Energy: it is an active process
What protein does the cell membrane of the neuron contain
Na+/K+ ATPase
What does Na+/K+ ATPase do (the sodium potassium pump)
Uses the energy provided by one molecule of ATP to pump three positively charged sodium ions out of the cell, while simultaneously taking into the cell two positively charged potassium ions.
What does the sodium potassium pump build up outside and inside the cell
Outside: a high concentration of sodium ions
Inside: an excess of potassium ions
What is one of the special properties of phospholipid cell membranes and what does that mean for the concentrations that the sodium potassium pump created
The special property is that they bar passage to ions unless there is a special protein channel that allows a particular ion in or out. This means that all of the ions can’t diffuse across the membrane to regularize the distribution like they want
Does a special protein channel exist for the sodium that is built up
For the sodium that is built up outside the cell, there is no channel
Does a special protein channel exist for the potassium that is built up inside the cell
Yes- there are potassium leak channels that allow some of the potassium ions to flow out of the cell
What does the difference in ion concentrations create
A net potential difference across the cell membrane of approximately -70 mV or millivolts ( the value of the resting potential )
What is the value of the resting potential
-70 mV
What do most cells have
Some sort of resting potential from the movement of ions across their membranes
Neurons are among only a few types of cells in that they can also form a ____
An action potential
What is the action potential
The electrochemical impulse that can travel along the neuron
(Comprehensive) what does the neuron membrane contain
Sodium potassium pump and potassium leak channel proteins as well as voltage gated proteins
What do voltage gated proteins do
Respond to changes in the membrane potential by opening to allow for certain ions to cross that would not normally be able to do so
What channels does the neuron contain
Voltage gated sodium channels and voltage gated potassium channels that open under different circumstances
Where does the action potential begin
When chemical signals from another neuron manage to depolarize, or make less negative, the potential of the cell membrane in one localized area of the neuron cell membrane, usually in the dendrites
What happens if the neuron is stimulated enough so that the cell membrane potential in that area manages to reach as high as -50 mV (from the resting potential of -70 mV)
The voltage gated sodium channels in that region of the membrane open
What is the threshold potential
The voltage at which the voltage gated channels open
What happens when the voltage gated channels open and why
The sodium ions follow the concentration gradient and Rush into the cell because there is a large concentration of positive sodium ions just outside the cell membrane that have been pumped out by the sodium potassium pump
What happens with the flood of positive ions
The cell continues to depolarize, or become less negative
What happens when the membrane potential gets as high as +35 mV
The voltage gated sodium channels close and the voltage gated potassium channels open, letting the positive potassium ions concentrated in the cell rush out of the neuron, repolarizing the cell membrane to its negative resting potential
As the potassium ions rush out of the neuron, what happens
The membrane potential continues to drop beyond -70 mV until the voltage gated potassium channels close once again around -90 mV
With the voltage gated proteins closed what happens
The sodium potassium pump and the potassium leak channels work to restore the membrane potential to its original polarized state of -70 mV.
How long does the whole process with the pump take to occur
Approximately one millisecond
The action potential does not occur in one localized area of the neuron and then stop (t/f)
True
Describe the action potential traveling down the length of the neuron
When one portion of the neuron’s cell membrane undergoes an action potential, the entering sodium atoms not only diffuse into and out of the neuron, they also diffuse along the neuron’s length. These sodium ions depolarize the surrounding areas of the neuron’s cell membrane to the threshold potential, at which point the voltage gated sodium channels in those regions open, creating an action potential. This cycle continues to occur along the entire length of the neuron in a chain reaction
What doesn’t happen during the time it takes the neuron to polarize back from +35 mV to -70 mV and what is the result of this
The voltage gated sodium channels will not reopen. This lag prevents the action potential from moving backward to regions of the cell membrane that have already experienced an action potential.
What are axons of many neurons surrounded by
A structure known as the myelin sheath
What does the myelin sheath do
Helps to speed up the movement of action potentials along the axon
What is the sheath made of
Schwann cells
What do Schwann cells do
They wrap themselves around the axon of the neuron
What are the small gaps between the Schwann cells known as
Nodes of Ranvier
Why does the action potential not have to occur along the entire length of the axon
Because the sodium and potassium ions that caused the action potential are only able to cross the cell membrane at the nodes of Ranvier
What happens when the action potential is triggered at one node
The sodium ions that enter the neuron will trigger an action potential at the next node -> causes action potential to jump from node to node, greatly increasing its speed
What is the jumping of the action potential called
Saltatory conduction
What does multiple sclerosis do
Damages the myelin sheaths, greatly impeding conduction of impulses along the neurons
How is a stronger signal generated when needed
Firing action potentials more rapidly -no such thing as stronger or weaker action potential
What happens when an action potential reaches a synapse
Neurotransmitter vessels are released; they diffuse across gap and bind to receptors
What is an excitatory neurotransmitter
Cause target neuron to allow positive ions to enter it
What is an inhibitory neurotransmitter
Cause target neuron to allow negative ions to enter i
What are ganglia and what organisms have just the ganglia
Simple, organized clusters of neurons. Annelids and mollusks.
Which organisms have ganglia and sensory organs and describe them
Arthropods - more complex with antennae and compound eyes
What does the vertebrate nervous system include
A brain and numerous specialized sensory organs
What is the CNS and what does it do
central nervous system: central command. Receives sensory input from all of the body, integrates info, creates response. Controls most basic functions necessary for survival and complex behavior and consciousness
What is the PNS and what does it do
Peripheral nervous system - refers to the pathways through which the central nervous system communicates with the rest of the organism
What type of systems have three types of neural building blocks
Highly evolved systems
What are the three types of neural building blocks
Sensory motor and interneurons
Describe sensory neurons
After an organism’s sense organs receive a stimulus from the environment, sensory neurons send that info to the CNS
Describe motor neurons
In response to some stimulus or as a voluntary action, motor neurons carry information away from the CNS to an organ or muscle
What do interneurons do
Provide the connection between sensory and motor neurons
What does the CNS consist of
Brain and spinal cord
Describe the spinal cord
A long cylinder of nervous tissue that extends along the vertebral column from the head to lower back
What is the brain made up of
Almost entirely interneurons
Describe the cerebrum
Largest portion of the brain
What does the cerebrum control
Voluntary movement, sensory perception, speech, memory, creative thought
What does the cerebellum do
Fine tunes voluntary movement; coordination and balance
What does the brain stem (medulla specifically) do
Involuntary functions. Medulla processes info and maintains alertness
What does the hypothalamus control
Homeostasis, temperature, hunger and thirst, water balance, emotion
What types of neurons does the spinal cord have
All three types of neurons: the spinal cord is a link between the body and the brain and also regulates simple reflexes.
What are the brain and spinal cord bathed in
A fluid known as the cerebrospinal fluid that acts as a cushion and is maintained by the glial cells
What does the PNS consist of
A sensory system and a motor system (which further splits into the somatic system and the autonomic system)
What does the sensory system of the PNS do
Carries info from senses to CNS
What does the motor system do
Branches out from CNS to targeted organs and muscles
What does the somatic system (division of motor system of PNS) control
Voluntary movement
What is acetylcholine
An excitatory neurotransmitter that causes contraction of skeletal muscles
All somatic system neurotransmitters are ___
Excitatory
What does the autonomic system do (subdivision of motor system of PNS)
Controls tissues other than from skeletal muscles
What is the sympathetic division of the autonomic system of the motor system of the PNS
Prepares body for emergency situations
What does the parasympathetic division of the autonomic system of the motor system of the PNS do
During sleep, it slows breathing, speeds up digestion, and slows heartbeat
Sense organs transmit signals from the environment through the what to the what
Through the PNS to the CNS
What can the eyes sense
Intensity and frequency of light
What are two photoreceptors
Rods and cones
What do rods do
Respond to low illumination levels
What do cones do
Color vision and brighter lights
What is the path of action potential impulses
From neurons to the occipital lobe of the brain
What is the retina
What light is focused on
What do the lens do
Maintain focus by changing shape
What do the pupils do
Regulate amt of light able to pass to lens
What does the cornea do
Bends light through pupil
What is another name for the ears
Tympanic membrane
What do the ears do
Sense frequency of air molecules
What do auditory ossicles do
Amplify vibrations and direct them to the cochlea
What does the cochlea do
Converts vibrations to action potentials
What is the auditory nerve
What transmits action potentials to brain
What do taste buds/chemoreceptors do
Create action potentials that travel to the brain
What are the four main taste sensations
Sour salty bitter sweet
What is the olfactory epithelium
Where smell originates
What do the somatic senses include
Touch pressure posture movement temperature pain
