Biology: Chapter 13: The Nervous System

Science 00000 with N/a at University of Texas - Austin

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By: Kathy Mostajeran
Created: 2011-06-01
Size: 97 flashcards
Views: 7

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Soma

the cell body of a neuron
contains the nucleus, ER, and ribosomes

Dendrites

connected to the soma
structures made to receive info
transmit this info to the cell body

Axon hillock

enlargement at the beginning of the axon

where information transmitted from the dendrites to the cell body are integrated
provides a connection between the cell body and the axon
important in action potential generation

Axon

a nerve fiber that is specialized to carry an electrical message

Oligodendrocytes

produce myelin in the CNS

Schwann Cells

produce myelin in the PNS

Myelin

insulate the neuron
prevents signal loss
increases the speed of conduction in axons

Nodes of Ranvier

small breaks at regular intervals along the axon membrane
exposed areas of axon membrane
critical to proper signal conduction

Synaptic Bouton

nerve terminal
enlarged and flattened to maximize neuro-transmission to the next neuron and ensure proper production of neurotransmitter

Synaptic cleft or Synapse

slight space between 2 neurons
neurotransmitter released from the axon terminal traverses the synaptic cleft and binds to receptors on the second neuron

Action Potentials

all-or-nothing messages used by neurons
relay info to and from the central and peripheral nervous systems
cause the release of neurotransmitter into the synaptic cleft

Resting Potential

potential (voltage) difference between the inside of the neuron and the extracellular space
usually about -70mV: the inside of the neuron is negative relative to the outside

Resting Potential: Set Up

neurons use selective permeability to ions and the Na⁺/K⁺ ATPase to maintain a negative internal environment
inside the neuron [K⁺] is high and [Na⁺] is low
outside the neuron [Na⁺] is high and [K⁺] is low

Resting Potential

negative resting potential is generated by both negatively charged proteins within the cell and the relatively greater permeability of the membrane to K⁺ compared to Na⁺
if K⁺ is more permeable and its concentration is higher inside it will diffuse out of the cell
since K⁺ is positively charged its movement out of the cell results in a cell interior that is negative
Na⁺ cannot readily enter at rest, so the negative potential is maintained

Na⁺/K⁺ ATPase

important for restoring this gradient after action potentials have been fired
transport 3 Na⁺ out of the cell for every 2 K⁺ into the cell at the expense of 1 ATP
active transport because Na⁺and K⁺ both move against their concentration gradient
each time the pump works: inside of cell becomes more negative as only 2 positive charges are moved in for every 3 that are moved out

Action Potential Initiation

neurons can receive excitatory or inhibitory input
excitatory input = more likely to fire action potential
as info is integrated at the axon hillock, depolarization or hyperpolarization can occur
axon hillock must be depolarized to the threshold value to trigger an action potential

Hyperpolarization

caused by inhibitory inputs
make the cell more negative

Depolarization

caused by excitatory inputs
makes the cell less negative

Execution of an Action Potential

1. Na⁺channels respond to depolarization: since concentration of Na⁺ is higher outside the cell and the inside of the cell is negative = strong electrochemical gradient for Na⁺ to move into the cell = cell potential becomes more positive
2. Na⁺ channels rapidly close when membrane potential reaches about +35mV = cell is positive on the inside

Execution of an Action Potential

3. positive cell potential triggers voltage-gated K⁺ channels to open
4. since K⁺ concentration is high inside the cell and the cell is inside positive = strong electrochemical gradient to drive K⁺ out of the cell
5. movement of positive K⁺ ions out of the cell = restoration of the negative membrane potential (this is repolarization)
6. the efflux of K⁺will cause an overshoot of the resting membrane potential = membrane becomes more negative than the resting membrane potential (hyperpolarization)

Absolute refractory period

no amount of stimulation will cause another action potential to occur

Relative refractory period

there must be greater than normal stimulation to cause an action potential because the membrane is starting from a potential more negative than the resting value

1. Threshold of excitation is reached; Na⁺ channels open; Na⁺enters the cell
2. K⁺ channels begin to open; K⁺ leaves the cell
3. Na⁺ channels close; no more Na⁺ enters the cell
4. K⁺ continues to leave the cell, causes restoration of resting membrane potential
5. K⁺channels close; Na⁺ channels reset

Impulse Propagation

all the ion movement only occurs at the axon hillock
action potential must travel down the axon and initiate neurotransmitter release for a signal to be conveyed to another neuron
propagation occurs by ordered opening and closing of voltage-gated channels

Impulse Propagation: Steps

1. As Na⁺ from the axon hillock rushes in = causes depolarization of surrounding regions = opening of Na⁺ channels along the axon in a wavelike function
2. depolarization of membrane to +35mV causes Na⁺ channels to shut as K⁺ channels begin to open; unidirectional flow of info because at this point the region of the axon is refractory immediately after firing an A.P
3. After Na⁺ depolarization wave, K⁺ channels will cause a repolarization wave that resets the axon for the next action potential

1. Na⁺ influx leads to depolarization of the bracketed area
2. Na⁺ has caused the opening of neighboring voltage-gated Na⁺ channels causing depolarization there
3. the first set of Na⁺ channels has close and K⁺ channels have opened causing repolarization

Conduction Speed of Action Potentials

longer axon = higher resistance = slower conduction
diameter has a greater effect: greater diameter = faster propagation by decreasing resistance

Saltatory Conduction

mammalian organisms
myelin is a good insulator and prevents the loss of electric signal
the membrane is only permeable to ion movement at the nodes of Ranvier
transmission in which the signal hops from node to node

Synapse

connection between 2 neurons
chemical in nature
use small molecules called neurotransmitters to send messages from one cell to the next

Presynaptic terminal

terminal before the synapse
neuron using its axon

Postsynaptic terminal

neuron receiving info through its dendrites

Effector cell

a neuron that signals to a gland or muscle

Process of synaptic transmission

1. at the nerve terminal, NTs are stored in membrane-bound vesicles
2. vesicles wait for an AP to come down the axon and depolarize the terminal membrane
3. vesicles then fuse with the presynaptic terminal and release the NT into the synaptic cleft = exocytosis that is Ca²⁺ dependent

Process of Synaptic Transmission

4. once released into the synapse, NTs diffuse across the cleft and bind to receptors on the postsynaptic membrane = allows message to be passed from 1 neuron to the next
5. binding can either result in hyperpolarization or depolarization of the post-synaptic cell

Removing NTs from the synaptic cleft

some NTs are broken down by enzymatic reactions (action of ACh-esterase on ACh)
some use reuptake carriers to be recycled into the presynaptic neuron (dopamine or serotonin)
others simply diffuse out of the area (nitric oxide)

Key concept: Electrical v. Chemical transmissions

neurons use both:
within a neuron: electricity is used to pass message in an all-or-none fashion
between neurons: chemical molecules are used to pass messages in a modulated manner that depends on how much NT is released

Afferent Neurons

sensory neurons
carry info from the periphery to the brain or spinal cord

Efferent Neurons

motor neurons
carry info from the brain or spinal cord to the periphery

Nerves

bundles of many axons together
can be sensory, motor, or mixed

Ganglia

clusters of neuron cell bodies (somas) in the peripheral nervous system

Nuclei

clusters of neuronal cell bodies in the central nervous system

Central Nervous System

brain
spinal cord

Brain

responsible for integration of sensory info
coordination of motor movement
cognition
has myelin to distinguish between gray matter and white matter

Gray matter

unmyelinated axons in the brain

White matter

myelinated axons in the brain

Forebrain

most recently acquired part of the CNS in terms of evolutionary development
breaks down into the telencephalon and diencephalon

Telencephalon

consists of right and left hemispheres
part of the forebrain
large portion is the cerebral cortex

Each hemisphere

sectioned into the frontal, parietal, occipital, and temporal lobes
independent but communicate through the corpus collosum

Cerebral cortex

region of highly convoluted gray matter that can be seen on the surface of the brain
responsible for the highest-level of functioning
integrates sensory info and controls movement

Diencephalon

nested below and inside the telencephalon
consists of the thalamus and hypothalamus

Midbrain

serves as a relay point between more peripheral structures and the forebrain
passes sensory and visual info to the forebriain
receives motor instructions from the hindbrain

Hindbrain

contains structures that are seen ascross wide variety of organisms and responsible for many involuntary actions
consists of cerebellum, pons, and medulla (the brainstem)
connected to the spinal cord

Cerebellum: quality control agent

part of the hindbrain
checks that motor signals sent from the cortex are in agreement with the sensory info coming from the body
if motor signals are not in agreement with the sensory info the cerebellum helps the cortex adjust to the new situation

Medulla

part of the hindbrain
mostly highly conserved part of the brain
modulates ventilation rate, heart rate, and GI tone

Spinal Cord

connected to the hindbrain
divided into cervical, thoracic, lumbar, and sacral regions
sends sensory and motor innervation to most structures below the neck
protected by/runs through the vertebral column with nerves entering and exiting at each vertebra
has grey matter deep within the white matter

Spinal Cord: White Matter

axons of motor and sensory neurons

Spinal Cord: Movement of Info

sensory (afferent) neurons being info from the periphery a on the dorsal (back) side of the spinal cord
the cell bodies of these sensory neurons are found in the dorsal root ganglia
motor (efferent) neurons exit the spinal cord ventrally

Peripheral Nervous system

has 12 pairs of cranial nerves
has 31 pairs of spinal nerves
divided between somatic and autonomic nervous system

Somatic Nervous System

responsible for voluntary movement
ACh/muscle contraction
provides us with reflexes which are automatic: do not require input or integration from the brain to function = monosynaptic and polysynaptic reflexes

Monosynaptic Reflexes

a single synapse between the sensory neuron that received info and the motor neuron that responds
example: knee-jerk reflex

Knee-jerk Reflex

when the patellar tendon is stretched: info travels up the sensory neuron to the spinal cord where it interfaces with the motor neuron to contract the quadriceps
net result: straightening of the leg to lessen the tension on the patellar tendon
this reflex helps protect us from tearing the patellar tendon or damaging the knee joint due to over-stretching it

Polysynaptic Reflex

there is at least one interneuron between the sensory and motor neuron
example: withdrawal reflex

Withdrawal Reflex

if we step on a tack our foot will be stimulated to jerk up (monosynaptic reflex) but we need our other foot to go down and plant to maintain our balance
for this to occur: motor neuron that controls the opposite (downward moving) leg must be stimulated
interneurons in the spinal cord provide the connection from the incoming sensory info on the leg being jerked up to the motor neuron for the supporting leg

Autonomic Nervous System

part of the PNS
involuntary nervous system: requires no conscious control
innervates cardiac and smooth muscle
controls blood pressure, ventilation dynamics, urination, and digestion
2 neuron system: 2 neurons work in series to transmit messages

Preganglionic neuron

the first neuron in the 2 neuron network of the ANS
soma is in the CNS
axon travels to a ganglion in the PNS where it synapses on the cell body of the postganglioncic neuron

Postganglionic neuron

the second neuron in the 2 neuron network of the ANS
soma is located in the PNS
receive info from preganglionic neuron
affects the target tissue

Sympathetic Nervous System

part of the ANS

responsible for "flight-or-fight" during a life threatening situation:

increases blood flow to the heart and skeletal muscle
decreases blood flow to the GI tract and kidneys
increases breathing rate and heart rate to ensure an adequate supply of O₂ to meet the demands of rapidly contracting skeletal muscles
dilates pupils

Sympathetic Nervous System: Preganglionic Neurons

use ACh
can also cause the release of epinephrine from the adrenal medulla

Sympathetic Nervous System: Postganglionic Neurons

use norepinephrine

Parasympathetic Nervous system

responsible for "rest-and-digest"

increased blood flow to the organs of digestion and excretion
decrease blood flow to the skeletal muscles and heart
heart rate and ventilation decrease
important: vagus nerve
uses ACh for both pre/postganglionic neurons

Vagus Nerve

cranial nerve responsible for many parasympathetic effects in the thoracic and abdominal cavities

Sensory neurons: Interoceptors

monitor internal environment parameters:

blood volume
blood pH
partial pressure of CO₂ in blood

Sensory neurons: Proprioceptors

important for out position sense
help our brains grasp the relative position of our bodies in the dark

Sensory neurons: Exteroceptors

responsible for monitoring the external environment:
light, sound, touch, taste, pain, and temperature

Sensory neurons: Exteroceptors: Nociceptors

sense pain and relay that info to the brain
nociceptors sense pain and have their cell bodies in the dorsal root ganglion of the spinal cord→ generate impulses that convey word of trouble to nerve cells in the dorsal horn region of the spinal cord → info is then passes to the brain who interprets it as pain

The Eye

detects light in the form of photon
filled with fluid to simplify transmission of light to the retina
aqueous humor is secreted near the iris at the base of the eye → then travels to the anterior chamber→ eventually exits and enters the venous blood

Sclera

thick layer that covers the exposed portion of the eye
the white of the eye
doe not cover the cornea

Choroid

supplies the eye with nutrients and oxygen
directly beneath the sclera

Retina

inner most layer of the eye
contains actual cells (photoreceptors) that transduce the light into electrical info the brain can process

Cornea

light first passes through here
transparent structure that bends and focuses light

Pupil

light ray move through the pupil
muscular, pigmented iris can adjust the amount of light entering the eye by altering the diameter of the pupil
the more light available = the more constriction

Lens

receives light that has passed through the pupil
does final focusing
thickness can be adjusted by ciliary muscles to focus the image on the retina

Rods

transmit black and white images
respond to low-intensity illumination
good for night vision
only have one pigment: rhodopsin

Cones

come in three varities: each absorbs a different wavelength because each contains a different pigment: colors = red, green, and blue
color images

Bipolar cells

receive info from photoreceptors
relay info to retinal ganglion cells

Retinal ganglion cells

receive info from bipolar cells
bundle to form the optic nerve

Optic Nerve

bundle of ganglion cells
exits the back of the eye
displaces photoreceptors at the back of the eye to form a blind spot at the site of exit (each eye compensates for the other eye's blind spot)

The Ear

tranduces sound wave (mechanical disturbances of pressure) into electrical signals that can be interpreted by the brain
houses certain nerves that help coordinate balance

Outer Ear

consists of the auricle and auditory canal
collects the waves and channels them to the tympanic membrane

Tympanic memebrane

receives sound waves from the outer ear
beginning of the middle ear
vibrates due to sound waves pushing on it and ossicles move back and forth

Middle Ear

includes the ossicles:

malleus

incus
stapes
transmit info through the oval window

Oval Window

receives info from ossicles
fluid filled inner ear
made up of the cochlea and semicircular canals
movement of the ossicles on the oval window creates fluid waves in the inner ear that depolarizes hair cells of the cochlea = generates an electrical signal

Hair cells

located in the inner ear
part of the cochlea
generate action potential that travel along the auditory nerve to the brain

Semicicular canals

3 per ear; one oriented in each plane

filled with a fluid called endolymph: endolymph movement puts pressure on the hair cells inside
because there is a can oriented in each direction: brain can integrate the signal from each canal and maintain balance + interpret sudden acceleration/deceleration

Movement of sounds

outer ear → tympanic membrane (start of the middle ear) → ossicles → oval window → cochlea → hair cells → auditory nerve → brain

Gustatation: Taste Receptors

taste receptors are located on the tongue, soft palate, and epiglottis
consist of 40 epithelial cells
outer surface contains a taste pore from which microvilli (taste hairs/receptors) protrude
around taste receptors = network of nerve fibers they stimulate that transmit gustatatory info to the brainstem via 3 cranial nerves
respond preferentially

Olfaction

receptor are found in the olfactory membrane which lies in the upper part
receptors are specialized neuron from which olfactory hairs (cilia) project
cilia form a dense mat in the upper nasal mucosa
odor enters nasal cavity and bind to receptors in the cilia to depolarize olfactory receptors
axons from receptors join to form olfactory nerve which projects directly to the olfactory bulbs in the base of the brain

About this deck

By: Kathy Mostajeran
Created: 2011-06-01
Size: 97 flashcards
Views: 7

About StudyBlue

“Simply amazing. The flash cards are smooth, there are many different types of studying tools, and there is a great search engine. I praise you on the awesomeness.”
Dennis