Chapter 5: The Neuron Flashcards
CNS
central nervous system- brain, spinal cord (interneurons)
no nerves, instead, analogous structures known as tracts
neural tube-> precursor
PNS
peripheral nervous system- afferent and efferent neurons
in spinal cord:
dorsal root- afferent
ventral root- efferent
afferent neurons
sensory neurons; pick up stimulus through sensory receptors, transmit to interneurons (usually) in CNS
usually have one axon with 2 branches (no dendrites from cell body):
- peripheral branch: from cell body to periphery (skin, joint, muscle)
- central branch: from cell body to spinal cord
sensory receptors/neuronal endings can be encapsulated or free
ex. pacinian corpuscle: in skin, encapsulated: detects vibration/pressure and discerns rough/smooth feeling
efferent neurons
carry response signal so that response can be carried out
ex. motor neuron (carries signals to skeletal muscle)
information processing in the nervous system
Sense, Integrate, Act (SIA)
stimulus -> (reception) afferent neurons -> (transmission) -> interneurons -> (integration) interneurons -> (transmission) efferent neurons -> (response) effectors -> action
neuron
a type of cell
anatomy:
dendrites
cell body (soma)
nucleus
axon hillock
axon
axon terminals
nerve
cordlike structure that contains many axons (fibers)
provides a common pathway for the electrochemical nerve impulses transmitted along each of the axons, (31 pairs of spinal nerves)
only found in PNS. in CNS -> tracts (analogous structures)
interneurons
integrate information, formulate a response
part of CNS
nerve
cordlike structure with many axons (fibers)
provides a common pathway for the electrochemical nerve impulses that are transmitted along each of the axons
31 pairs of spinal nerves in humans
ONLY found in PNS
ex. radial nerve: supplies the triceps brachial muscle and all 12 muscles in the posterior osteofascial compartment of the forearm, associated joints, and overlying skin
white matter
myelinated (has fatty layer to insulate electrical impulses) axons and glial cells
glial cells (neuroglia)
non-neuronal cells that provide nutrition and support to neurons
examples:
ependymal cells
microglia
astrocytes
schwann cells
oligodendrocytes
ependymal cells
glial cell, produces cerebrospinal fluid
microglia
glial cell. phagocytic cell that ingests and breaks down pathogens and waste products in the CNS
astrocytes
glial cell in CNS. cover surfaces of blood vessels (structural support)
help maintain ion concentrations in interstitial fluid surrounding them
satellite cells have similar function but work in the PNS
schwann cells
form myelin sheath in PNS
oligodendrocytes
form myelin sheath in CNS
myelin sheath
have high lipid content; serve to insulate the electrical impulse as it travels along an axon (white color)
node of ranvier
gaps in the myelin that expose the axon membrane directly to extracellular fluid
speed the rate at which electrical impulses move along axons
signal conduction in the neuron (regions/terminals)
presynaptic region/terminal- transmitting
postsynaptic region- receiving
axon hillock
emerges out from the soma of the neuron
high concentration of voltage activated Na channels
considered the “spike initiation zone” for action potentials
multiple signals (from presynaptic neuronal terminals) are generated at the dendrites and transmitted by the soma. converge at axon hillock
synapse
junction between axon terminals of a neuron and the receiving cell (another neuron, muscle fiber, gland cell)
2 types of synapses: electrical and chemical
variability of synapses
allows for modulation of transmission
axodendritic synapse: axon to dendrites
axosomatic: axon to soma/cell body
axoaxonic: axon and axon meet
electrical synapses
found in pulp of tooth, heart muscle tissue, smooth muscle
plasma membranes of pre and postsynaptic cells make direct contact through connexon proteins. ions flow through gap junctions that connect both membranes, allowing impulses to pass through
important where uniform contractile activity among a group of cells is needed (action potential transferred such that tissue acts like one cell)
faster than chemical synapse
chemical synapse
plasma membrane of presynaptic and postsynaptic cells are separated by narrow synaptic cleft. neurotransmitter molecules diffuse across cleft and bind to receptors in the postsynaptic cell. this opens channels to ion flow that may generate an impulse in the postsynaptic cell
better modulated than electrical synapse
- allow neurons to receive inputs from numerous axon terminals at same time
membrane potential
separation of positive and negative charges across a membrane
membrane pot at rest: -70mV
1. DNA/proteins are neg
2. more K+ leaves the cell than Na+ enters:
- membrane more permeable to K+ than Na+ (many more ungated K+ channels/K+ leak channels open than ungated Na+ channels)
- at rest: higher Na+ concentration outside, higher K+ inside
- Na+ passively diffuses in, K+ out (against Na+/K+ pump)
- Na+/K+ pump: 3 Na+ out, 2 K+ in (against conc gradient)
- neg charged organic molecules create electrical force that attract K+ to stay in, this balances the tendency of K+ to leak out
Electro-chemical gradient: net driving force; consists of concentration gradient and electrical/voltage gradient
resting membrane potential
equilibrium condition, no net flow of ions across the plasma membrane (cell not transmitting electrical impulse)
equilibrium potential
membrane potential at which the voltage gradient of an ion balances the concentration gradient for the ion (no net flow of ion through channel
nerst equation
predicts equilibrium potential in mV across the membrane of a cell for a singly charged positive ion (Eion)
=62mV log10([X]outside/[X]inside)
goldman equation
predicts membrane potential (Vm) when membrane is permeable to more than one ion Pion=permeability to that ion
Vm =62log10{Px[X]outside+Py[Y]outside+Pz[Z]inside/Px[X]inside+Py[Y]inside+Pz[Z]outside}
*reciprocal if ion is negatively charged
ion channels in neurons (types; 4)
- ungated channels (leak)
- voltage gated (in axon membranes) (respond to changes in Vm)
- ligand gated channels (primarily at synapses) (open when neurotransmitters bind and cause conformational change)
- mechanically gated (in sensory receptors)
in a neuron at rest, it is primarily ungated K+ channels that are open
can more than one ion pass through an ungated channel?
no
- ions form transient associations with amino acid side groups of intermembrane proteins of channel.
- there are exceptions
functional elements of ion superfamily of proteins
- ion conductance
- pore gating
- regulation
voltage gated Na+ channel
- 6 alpha helical transmembrane segments
- 4 homologous domains
key regions: - voltage sensing (4th transmembrane segment on domain I)
- pore (between 5th and 6th transmembrane segment)
- inactivation (between 6th and 1st transmembrane)
voltage gated K+ channels
variable
- inactivate fast (A type currents)
- others inactivate slowly/not at all
variability ensures they’ll always be available source of current for repolarization
properties of ion channels
- may have multiple internal gates that respond to changes in opposite ways/different rates)
- single-channel current amplitude (rate of ionic flow through channel) determined by
1. maximum channel conductance (how fast ion channel can pass ions)
2. electrochemical driving force for ion
action potential
abrupt and transient change in membrane potential that occurs when an electrically excitable cell conducts an electrical impulse
action potential series of events (in neuron):
- stimulus causes positive charges to flow into neuron
- membrane potential depolarizes (becomes less negative)
- this occurs slowly until membrane pot reaches “threshold” (10-20mV more positive than resting potential)
- activation gate of Na+ channel opens - sudden increase in membrane potential (firing) due to rapid influx of positive ions
- when potential peaks, inactivation part of protein blocks Na+ channel)
- K+ channels allow K+ to flow outward - membrane potential falls, usually below resting (hyperpolarization)
- returns to resting
*all or nothing: once threshold is reached, regardless of strength of stimulus, AP will fire
key features of AP’s in neurons
all or none
maintain size (magnitude of AP doesn’t change with propagation down axon)
propagate
intensity of stimulus is encoded by the frequency of APs (rate at which they happen)
refractory period (2 types)
absolute refractory period: time when an excitable membrane cannot generate an AP in response to any stimulus
- from beginning of AP until near end of repolarization
- sodium channels inactivated and voltage gated potassium channels open
relative refractory period: time during which excitable membrane will produce AP but only to a stimulus of greater strength than the usual threshold strength, must also outlast relative refractory period (AP will be smaller than normal)
- density and subtypes of K+ channels may differ greatly between different types of neurons, so duration is highly variable as well as threshold strength, which gets smaller as time passes
- some Na+ channels still inactivated, K+ channels open (contributes most), membrane hyperpolarized
primary afferent axons
from large diameter to small:
information they carry
1. A-alpha nerve fibers: proprioception (muscle sense)
2. A-beta nerve fibers: touch
3. A-delta nerve fibers: pain and temp
4. C-nerve nerve fibers: pain, temp, itch
*larger diameter= lower internal resistance, greater conduction velocity of APs because more myelinated
conduction velocity-basis
cable theory
- describes flow of currents within an axon
- neuron is treated as an electrically passive, perfectly cylindrical transmission cable
- local circuits of current flow, symmetrical
ohms law: Current (I)= voltage difference (delta V)/resistance (R)
cable theory
- describes flow of currents within an axon
- neuron is treated as an electrically passive, perfectly cylindrical transmission cable
- local circuits of current flow, symmetrical
ohms law: Current (I)= voltage difference (delta V)/resistance (R)
myelin inscreases conduction velocity because insulate current and bring to node of ranvier (saltatory conduction)
capacitance and resistance
capacitance: stored electrical energy
resistance:f force that counteracts flow of current
capacitance of neuronal fiber is due to electrostatic forces that act through the phospholipid bilayer
resistance (longitudinal/internal resistance) due to the cytosol (proteins/organelles)
lambda length constant
- characteristic length on which the voltage across a membrane decays
- size of an applied voltage will decline to 37% of the original size (roughly 1/3)
- larger length constant gives greater conduction velocity because can reach threshold further down axon each time AP is generated (AP doesn’t have to be regenerated as much)
equation: sqrt(rm/rl)
rm: resistance of membrane
rl: longitudinal resistance; resistance of axoplasm (internal)
therefore, larger rm=larger conduction velocity
neurotransmitter
small signal molecules secretes by the pre synaptic nerve cell to relay the signal to the postysynaptic nerve cell
- may have stimulatory or inhibitory effect
neurotransmission at a chemical synapse
- info received at post synaptic neuron is integrated
- resulting response (whether AP fires) reflects sum of the combined effects of all signals/info received
- Ap reaches axon terminal of presynaptic neuron
- Ca2+ enters axon terminal
- neurotransmitter released by exocytosis (synaptic vesicles merge with membrane on presynaptic terminal, release neurotransmitters to synapse, bind to ligand gated channels)
- when stimulus subsides: no APs generated, voltage gated Ca2+ channels close
- Ca2+ pumped outside axon terminal, vesicles no longer fuse with membrane
- any remaining neurotransmitters in cleft diffuse away/broken down, reuptake to presynaptic terminal
- ligand gated channels open on post synaptic cell membrane when neurotransmitters bind
- flow of ions can stimulate or inhibit the generation of an AP in the post synaptic cell
acetylcholine
neurotransmitter between nerves and muscle;
in brain (hippocampus) (memory, attention, learning) and in heart (binds to muscarinic receptors- parasympathetic, slows heart rate down)
Alzheimer’s: degeneration of acetylcholine releasing neurons
removal from synaptic cleft:
- unbind from receptors
- acetylcholinesterase splits acetylcholine into choline and acetic acid, which prevents it from binding to receptors again
- choline used to make new acetylcholine molecules that are packaged into synaptic vesicles in presynaptic terminal
aricept: acetylcholinesterase inhibitor (AD) (treatment for early alzheimer’s/demetia)
acetylcholine
neurotransmitter between nerves and muscle;
in brain (hippocampus) (memory, attention, learning) and in heart (binds to muscarinic receptors- parasympathetic, slows heart rate down)
Alzheimer’s: degeneration of acetylcholine releasing neurons
GABA
gamma aminobutyric acid
- inhibitor or neutrotransmission
- opens Cl- channels on post synaptic membrane (further from threshold)
glycine
neurotransmitter
- inhibitor of neutrotransmission
- can increase Cl- influx in post synaptic membrane (further from threshold)
glutamate
neurotransmitter
involved with learning and memory
generally excitatory
released when rod cell in dark
norepinephrine and epinephrine (adrenaline)
dual roles as hormones and neurotransmitters
involved in attention and mental focus
can be excitatory or inhibitory depending on receptor it binds to
plays a role in pleasure/reward pathway (addiction and thrills), memory, and motor control
derived from tyrosine
norepinephrine removal from synaptic cleft:
- unbinds from receptor and uptakes by presynaptic terminal
- repackaged into synaptic vesicles or broken down by monoamine oxidase (MAO)
dopamine
neurotransmitter/neurohormone
behavior and cognition
voluntary movement
motivation and reward
inhibition of prolactin production (lactation)
sleep, mood attention and learning
parkinsons: degeneration of dopamine releasing neurons in substantia nigra, progressive loss of muscle control
derived from tyrosine
serotonin
Neurotransmitter
derived from tryptophan
regulates intestinal movements
mood appetite sleep
neuropeptides
indirect neurotransmitters (go through second messenger pathway to open channels)
endorphins (endogenous morphines)
neuropeptide
- released during pleasurable experience,
- reduce perception of pain
work on PNS
enkephalins: subset of endorphins
work in CNS
modulate pain response
substance P
neuropeptide
released by spinal cord
increase perception of pain
carbon monoxide (dissolved?)
neurotransmitter
regulates the release of hormones from the hypothalamus
nitric oxide (dissolved)
learning, muscle movement, replaces smooth muscle in walls of blood vessels, causes dilation
Relaxes smooth muscles
nitric oxide (dissolved)
learning, muscle movement, replaces smooth muscle in walls of blood vessels, causes dilation
SSRIs and SSNRIs
selective serotonin reuptake inhibitors
selectice serotonin norepinephrine reuptake inhibitors (antidepressants)
inhibitory/stimulatory neurotransmitters
inhibitory neurotransmitters: cause K+ out or Cl- in (inside more negative
stimulatory neurotransmitters: open Na+ channels
direct neurotransmission
- direct:
- neurotransmitter binds directly to a ligand gated ion channel
- opens or closes; affects flow of ions in postsynaptic cell
- quick
- ionotropic receptors (proteins) form an ion channel pore (what neurotransmitters bind to)
indirect neurotransmission
- indirect:
- neurotransmitter binds to G-protein coupled receptors on postsynaptic membrane
- G protein causes second messenger pathway is activated
- ion channels opened/closed, signals propagated
- slower
- effects may last minutes to hours
- ex. metabolic receptors: indirectly linked with ion channels on the plasma membrane of the cell through signal transduction mechanisms, often G proteins
EPSP
excitatory post synaptic potential: change in membrane potential that moves neuron closer to threshold
ligand gated channels open to Na+, membrane depolarizes
- precursors to APs
IPSP
inhibitory post synaptic potential: change in membrane potential that pushes membrane farther from threshold
K+ channels open, K+ exits or Cl- comes in, membrane becomes hyperpolarized
graded potentials or receptor potential
inc or dec in membrane pot that is below threshold, so it DOES NOT trigger action potential
(ESPS and IPSPs)
- no refractory periods
- can occur in sensory cell when sensory stimulus excites it or postsynaptic cell when chemical neurotransmitter binds
-size of graded potential IS related to stimulus intensity/ amount of neurotransmitter
- decrease with distance
- rise and fall more gradual
- responses can sum:
temporal summation (single presynaptic neuron)
spatial summation: (different presynaptic neurons)
cephalization
development of an anterior head where sensory organs and nervous tissues are concentrated
nerve nets
loose mesh of neurons found in radially symmetrical animals
nerve cord
bundle of nerves which extend from the central ganglia (functional clusters of neurons) to the rest of the body
cadherins
calcium dependent adhesion molecules
- transmembrane proteins
- role in cell adhesion, ensures that cells within tissues are bound together
- dependent on Ca2+
cadherins
calcium dependent adhesion molecules
- transmembrane proteins
- role in cell adhesion, ensures that cells within tissues are bound together
- dependent on Ca2+
functions of the brain
receive
integrate
send out
store
retrieve
information
key features of brain
blood brain barrier, meninges, ventricular system
blood brain barrier
- brain highly vascularized
- seperation of circulating blood and CSF
- occurs along all capillaries; consists of tight junctions that do not exist in normal circulation
- endothelial cells restrict diffusion of microscopic objects and large/hydrophilic molecules (allow small hydrophobic ex. O2, hormones)
- other cells of the barrier actively transport metabolic products with specific proteins (ex. glucose)
- what CAN pass: glucose, alcohol, CO2, anesthetics, nicotine
meninges
layers of connective tissue (membranes) covering the brain and spinal cord
3 connective tissue layers: (PAD)
pía (deepest)
arachnoid
dura mater (2 layers) (surface)
skull
- provide structural support for blood vessels
- serve as PAD between brain and skull
CSF
clear colorless fluid produced in choroid plexus (complex of glial cells called ependymal cells)
- found in brain + spinal cord
- circulates nutrients and chemicals filtered from blood and removes waste products from the brain
- occupies subarachnoid space (between arachnoid mater and pía mater) and the ventricular system
provide buoyancy and support to brain against gravity (suspend brain) prevents from resting against cranium bc brain and CSF has same density
ventricles and ventricular system in brain
ventricles: cavities in brain filled with CSF
4 ventricles:
2 lateral
third and fourth
- cushion brain and take brunt of force
ventricular volume is significantly higher in AD patients
forebrain
forms the cerebrum
cerebrum
has left and right hemisphere as well as 4 lobes
left:
- responds to sensory signals and controls movements from right side of body (right hemisphere does opposite)
- focus on details, spoken written language, abstract reasoning, math
- wernickes and broca’s areas (language)
right:
- broad background spatial relative position
- intuitive thinking, conceptualization, music, art, etc.
hemispheres connected by thick axon bundles (corpus callosum) which enables exchange of info between them
4 lobes:
1. frontal: executive function (thinking, organizing, planning, problem solving, memory, attention, movement)
2. parietal lobe: perception and integration of stimuli from the senses
3. occipital: vision
4. temporal: senses of smell, sound, and formation and storage of memories
laterization
difference in function between left and right hemisphere
cerebral cortex (outermost layer)
outermost thin layer of grey matter (comprised of 6 layers of neurons, 2-4mm thick in humans) covering a core of white matter
grey matter: neuron cell bodies and dendrites
white matter: axons (myelin sheaths)
convoluted folds to increase surface area
- regulates cognitive functions (thinking, learning, speaking, remembering, making decisions)
areas:
primary somatosensory area: recieve and integrate sensory information
primary motor area: involved in planning control, and execution of voluntary movements
association areas: integrate sensory information, formulate responses, relay responses to motor area (broca’s wernicke’s)
cerebellum
- coordinates/refines body movements by information integration and comparison
- compares sensory input with signals from cerebrum that control voluntary body movement
receives sensory input from: receptors in muscles/joints, balance receptors in inner ear, touch, vision and hearing receptors (info about body position, directions)
brain stem
connects forebrain with spinal cord
3 structures:
1. medulla
2. pons
3. midbrain
vital functions:
heart + resp rate, blood pressure, blood vessel dilation, digestive system reflexes (vomiting)
midbrain
smallest region of brain
- acts as relay station for auditory and visual info, controls eye movement
VTA (ventral tegmental area) and substantia nigra
pons
secondary respiration center
cardiac acceleration and vasoconstriction
medulla
respiratory center
cardiac slowing
medulla
respiratory center
cardiac slowing
VTA
ventral tegmental area
- part of midbrain
- has dopamine and serotonin producing neurons
- involved in pleasure pathway/reward circuit
substantia nigra
part of midbrain
- involved in control of body movement
- contains large number of dopamine producing neurons
- degeneration of neurons in substantia nigra is associated with parkinson’s
reticular formation
network of neurons in brain stem that connect thalamus to spinal cord
- integrate incoming sensory information
- filter info
consists of 100+ neural networks with varied functions
2 divisions:
1. ascending: sends stimulatory signals to thalamus to activate cerebral cortex
- produces levels of alertness/conciousness
- filters incoming stimuli to discriminate background stimuli
- abnormalities result in coma
2. descending: recieve info from hypothalamus
- connects with interneurons of spinal cord that control skeletal muscle contraction
thalamus
between cerebral cortex and midbrain
- relays signals from special senses and motor signals to cerebral cortex
- regulates conciousness, sleep and alertness
- “relay station”
hypothalamus
below thalamus, above brain stem
- synthesizes and secretes hormones (neurohormones) (ex. ADH)
- links nervous system to endocrine system via pituitary gland
- controls body temp, hunger, thirst, fatigue, circadian cycles, etc
- triggers sweating, shivering
- monitors osmotic balance of blood (urine output)
basal nuclei (basal ganglia)
group on nuclei or varied origin in brain that act as a cohesive unit (substantia nigra is component of basal ganglia)
- surround thalamus
- involved with voluntary movement
- damage or loss of dopaminergic neurons in substantia nigra can lead to muscle rigidity, tremors, inability to start/stop movements (parkinson’s)
limbic system
functional network with number of components
- parts of thalamus, hypothalamus, basal nuclei
- amygdala (emotion, fear)
- hippocampus (memory)
- olfactory bulbs (smell)
- some basal nuclei
“emotional brain” involved with emotional behavior
hippocampus
part of limbic system
-important roles in consolidation of info from short to long term memory and spatial navigation
- in alzheimer’s, hippocampus one of the first regions to suffer damage
- resemblance to sea horse
reward pathway brain circuit
- VTA releases dopamine
- nucleus accumbens has dopamine sensitive cells
- causes feelings of pleasure
- amygdala and hippocampus plays a role in memory and whether experience is desireable
- prefrontal cortex coordinates all the info and determines behavior of individual
- pathway same for opiates, methamphetamines, and nicotine
efferent system
2 divisions:
somatic: skeletal muscles (mostly conciousness movements)
motor neurons
carries efferent signals from CNS to skeletal muscles
autonomic: smooth muscles, glands (involuntary)
collections motor neurons (ganglia) situated in head, neck, thorax, abdomen, and pelvis + axonal connections of these neurons
- visceral (organs of gut) functions
- heart rate, digestion, respiratory rate, salivation, perspiration, diameter of pupils, micturition (urination), arousal
autonomic nervous system
- sympathetic
- fight or flight
- inc BP, force and rate of heart beat, constricts blood vessels, dilates bronchioles, suppress digestion - parasympathetic
- rest and digest
- nerves of parasympathetic division (optic, cranial, spinal) are located around sympathetic nerves
work in tandem: upregulate one, downregulate other
vagus nerve
- cranial nerve 10
- extends below head to neck chest and abdomen, where contributes to the innervation of the viscera (organs in abdominal region)
- output to various organs in the body, conveys sensory info about state of the body’s organs to CNS
- 80-90% nerve fibers in vagus nerve are afferent (sensory nerves of viscera to brain
- responsible for. heart rate, gastrointestinal peristalsis, sweating, muscle movements in mouth
spinal cord
carries impulses between brain and PNS
- contains inter neuron circuits that control motor reflexes
- each pair of spinal nerves (31) have
dorsal root: afferent - dorsal rot ganglion (lump) (cluster of nerves)
ventral root: efferent
“DAVE”
primary somatosensory area
- located in parietal lobes of each hemisphere
- integrates info regarding touch/pressure, temp, pain
- if portions are stimulated, causes tingling in related body parts on opposite side of body
primary motor area
- anterior to primary somatosensory area
- stimulation of portions cause movements of body parts n opposite sides of the body
association areas: integration
- areas surround sensory and motor areas
- integrate info from sensory areas
- formulate responses
- transmit the responses to motor cortex
ex. wernickes (understanding language) broca’s (expressing language)
PET scan
positron emission tomography
- reveals function
- ingest radioactively labeled material (glucose)
- active cells in brain take up glucose
brocas aphasia
- expressive aphasia
- characterized by hesitant and distorted speech
- can comprehend written and spoken words
brocas aphasia
- expressive aphasia
- characterized by hesitant and distorted speech
- can comprehend written and spoken words
wernickes aphasia
wernickes: understanding and formulating coherent speech
- coordinates input from auditory and visual areas
- fluent language with made up or unnesessary word with little to no meaning, difficulty understanding others speech, unawareness of own mistakes
wernickes aphasia
wernickes: understanding and formulating coherent speech
- coordinates input from auditory and visual areas
- fluent language with made up or unnesessary word with little to no meaning, difficulty understanding others speech, unawareness of own mistakes
memory
storage and retrieval of sensory/motor experience
memory
storage and retrieval of sensory/motor experience
short term: depends on transient changes in neurons (membrane pot EPSP, IPSP) and/or reversible changes in ion transport caused by indirect neurotransmitters
long term: permanent biochemical, molecular, or structural changes that establish signal pathways that cannot be easily terminated
LTP
- memory based on this theory
long term potentiation - caused by short bursts of repetitive firing in presynaptic neurons such that when there is single AP later, evokes greatly enhanced response in post synaptic cells
- occurs when presynaptic cell fires at a time when the post synaptic membrane is strongly depolarized (due to recent repetitive firing of the same presynaptic cell or other means)
molecular basis: (early LTP)
- hippocampus: presynaptic cell releases glutamate, binds to AMPA receptor on postsynaptic cell
- Na+ depolarizes cell
- NMDA receptor (which is usually blocked by Mg2+ ion) Na+ removes block, opens and calcium fluxes in
- increased Ca2+ in cytosol induces postsynaptic cell to insert new AMPA receptor in plasma membrane, increasing cells sensitivity to glutamate
late LTP
permanent alterations in
- number and area of synaptic connections
- number and branching of dendrites
- gene transcription
- protein synthesis
- repeated stimulation of presynaptic cell reaches threshold such that dopamine is release
- dopamine acts on a GPCR that is coupled to an adenyl cyclase
- inc lvl of cyclic AMP (cAMP), activates protein kinase
- this activates CREB (cAMP response element binding protein) which is a transcription factor,
- turns on genes that make proteins involved in generating new synaptic connections
EEG
electroencephalography
recording of electrical activity along the scalp produced by the firing of neurons within the brain
special senses
have receptors strategically placed in unique organs
sensory receptors
2 main types:
1. formed by terminals (dendrites) of afferent neurons or
2. specialized cells that synapse with afferent neurons
- dunction: gather info abt the external and internal environment
- respond to stimuli by changing their conductance to ions
- results in change in membrane potential
sensory transduction: conversion of a stimulus to a change in membrane potential
types of receptors (5)
mechanoreceptors: changes in body pos, pressure, acceleration
photoreceptors: detect light, located in eye (absorb energy of light photon, generate change in membrane potential)
chemoreceptors: detect specific molecules/conditions such as acidity (taste buds)
thermoreceptors: temp (free nerve endings)
nocireceptors: detect tissue damage/noxious chemicals, activity leads to pain
- axons that transmit pain:
glutamate releasing: sharp localized pain
substance P: dull, aching, not well localized (endorphins can bind to receptors on substance P releasing neurons and dec amt released)
mechanoreceptors (skin)
free nerve endings: not encapsulated, light touch
pacinian corpuscle: lower part of dermis,, deep pressure and vibrations (tool use)
ruffini endings: deep pressure (detection of hand shape/finger position)
meissners corpuscle: light touch, surface vibrations (grip control)
all other are encapsulated
proprioception
sense of relative position of neighboring parts of the body
sense is composed of:
- info from sensory neurons located in inner ear
- stretch receptors (type of mechanoreceptors/propioceptor) located in muscles and joint-supporting ligaments (stance)
proprioceptors
detect stimuli used by CNS to monitor and maintain body and limb positions
- mechanoreceptors in muscles, tendons, joints detect changes in pressure/tension of body parts
stretch receptor
type of proprioceptor
- found in muscles and tendons (called golgi tendon organs GTO- nerve fiber with collagen strands that connect muscle to tendon)
- in muscle: detect position and movement by detecting how much and how fast a muscle is stretched
- when muscle generates force: sensory terminals compressed, open stretch sensitive cation channels on an afferent axon, depolarizes and fires APS that propagate to spinal cord
vestibular apparatus
- 3 semicircular canals: filled with endolymph (rich in K+), oriented perpendicular, detects rotational motion. perilymph fluid (ricch in Na+) found between membrane and bone of canal
- 2 fluid filled chambers
urticle
saccule - perceives position and motion of head using mechanoreceptors
ampulla of semicircular canal
ampulla: region at the base of a semicircular canal with sensory hair cells
- detects rot motion and causes movement of endolymph which displaces cúpula and bends sensory hair cell-> mechanoreceptors
- generates AP in afferent neurons that synapse with hair cells (gelatinous membrane)
ampulla of semicircular canal
ampulla: region at the base of a semicircular canal with sensory hair cells
- detects rot motion and causes movement of endolymph which displaces cúpula and bends sensory hair cell-> mechanoreceptors
- generates AP in afferent neurons that synapse with hair cells (gelatinous membrane)
depending how hair bends, inc (towards longest) or dec (away from longest) nerve AP rate (hyper/de polarization)
urticle and saccule
- fluid filled chambers
- 30 degrees to each other
- info abt:
head position (up/down)
changes in rate of linear motion of body
contain sensory hair cells with stereocilia: have membrane that contains otoliths (calcium carbonate crystals)-> otolithic membrane (similar to cupula)
vestibular system (in sum)
- otolith organs
urticle/saccule
- linear acceleration, gravity
- acceleration forward, backward, up down left right
- upside down right side up - semicircular canals
- angular motion
sound waves
exist as variations of pressure in a medium such as air
created by vibration of an object, which causes the air surrounding it to vibrate
volume/loudness: function of wave amplitude
pitch: function of wave frequency
ossciles
next to timpanic membrane/eardrum
malleus (hammer),
incus (anvil),
stapes (stirrup) - contacts oval window (first part of cochlea)
eustachian tube
leads to throat, when we swallow, tube opens, air flows in or out of ear to equalize pressure
cochlea
spiraled, hollow, conical chamber of bone
structures:
- scala vestíbuli (contains perilymph Na+) superior to cochlear duct; abuts the oval window (outer side of cochlea
- scala media/cochlear duct (contains endolymph K+) membranous cochlear duct containing organ of Corti
- scala tympani (perilymph Na+) lies inferior to scala media terminates at round window (outer side of cochlea)
sterocilia of hair cells sandwiched in between basilar membrane and tectorial membrane (vibrate to bend stereocilia)
basilar membrane
forms part of floor of cochlear duct
- anchors sensory hair cells in organ of cortisol
- vibrates in response to vibrations transmitted through inner ear
>15000 hair cells located along
- synapse to afferent neurons=auditory nerve-> auditory center in temporal lobe of brain
- basilar membrane is narrow and stiff near oval window, wider at outer end of cochlear duct
organ of corti (spiral organ)
located in cochlear duct and contains sensory hair cells that detect sound vibrations transmitted to the inner ear
- sensory organ of hearing
- distributed along partition separating fluid chambers in the coiled tapered tube of the cochlea
- is sensory epithelium, a cellular layer on the basilar membrane
- hair cells arranged in rows of inner hair cells (hearing) and outer ( regulate tension on basilar membrane)
tiplink (gating spring), open K+ channels as bend (mechanically gated ion channels) (releases glumate on afferent neurons)
- hair cells are tuned to certain sound frequencies by way of their location in the cochlea due t the degree of stiffness in the basilar membrane
high pitched sounds vibrate at beginning of basilar membrane
low pitched vibrate near wider farther end, travel down tube
blind spot
area where optic nerve passes through optic disc, has no light detecting photoreceptive cells
cornea
transparent, admits and refracts light; covers the iris, pupil and anterior chamber
iris
eye color
- behind cornea, around pupil
- controls diameter of pupil.
- regulates amount of light that strikes the lens
sclera
white outer layer of the eyeball
protective layer
choroid
vascular layer of eye between sclera and retina
lens
focuses image on retina
retina
layer of neural cells that lines the back of the eye
- has photoreceptor cells that are sensitive to light and neurons that integrate information detected by photoreceptors
macula
pigmented area in the retina, contains fovea
involved in high acuity vision
fovea
region of the macula in the retina, has a high density of cone cells (photoreceptive cell for color) also needed for sharp vision (detail)
chambers of the eye
anterior chamber: between cornea (front of eye) and iris
- filled with aqueous humor
posterior chamber: located behind the iris and in front of the lens
- filled with aqueous humor
vitreous chamber: located behind the lens
- filled with vitreous humor
aqueous humor
thin watery fluid found both the anterior and posterior chambers of the eye
- maintains intraocular pressure
- supplies nutrients to avascular parts of the eye
- removes wastes
vitreous humor
thick, viscous fluid (gel like) helps maintain the shape of the eye and absorb shocks
- occupies space behind lens and in front of the retina at the back of the eye
ciliary body
[art of eye that includes ciliary muscle (controls shape of the lens) and the ciliary epithelium (produces aqueous humor)
suspensory ligaments connect ciliary muscle to the lens
accommodation
change in shape of lens when focusing on an object (distant or near)
distant: ciliary muscle relaxes, ligaments support eye tighten, lens flattens
near: ciliary muscles contract, loosening ligaments and lens becomes rounded
vision pathway
direct pathway: photoreceptors (cones/rods) -> bipolar + horizontal + amacrine cells -> ganglion cells
direction of light is opposite to direction of retinal visual processing
horizontal modulate synapse between photoreceptive cells and bipolar cells
amacrine work to modulate synapse between bipolar cells and ganglion cells
amacrine cells
group of dopamine secreting neurons located in retina of eye
- release dopamine into extracellular medium, actoive during daylight silent at night
- enhances activity of cone cells in the retina while suppressing rod cells -> increases sensitivity to color and contrast during bright conditions
amacrine cells
group of dopamine secreting neurons located in retina of eye
- release dopamine into extracellular medium, actoive during daylight silent at night
- enhances activity of cone cells in the retina while suppressing rod cells -> increases sensitivity to color and contrast during bright conditions
horizontal cells
allow eyes to adjust to see well under both bright and dim light conditions (involved with lateral inhibition, edges of objects))
rods
photoreceptor cell of retina
- specialized for detection of low intensity light
- light absorbing photopigment/photoreceptive molecule on disc -> rhodopsin
cones
3 types of cones for humans
photopigment on disc on outer segment -> iodopsin (rhodopsin analog)
iodopsins contain protein complexes: photopsin I, II, or III (blue, red and green light)
- specialized for detecting light of different wavelengths of different wavelengths (color) (400-700nm)
- numerous in fovea and macula lutes, fewer over rest of retina
photopigment molecules
found in discs of photoreceptor cells
- consist of retinal combined with an opsin protein
rhodopsin: retinal (form of vitamin A) + opsin, found in rods, is a GPCR (7 transmembrane regions coupled with G protein which uses GTP not ATP to carry out function)
rhodopsin function
sits on rod cell membrane (6 transmembrane regions), associated with retinal
- in cis conformation when dark (inactivated)
rod cell depolarized, releases glutamate
- trans conformation when photon hits (activated)
activates G protein transducin -> activates phosphodiesterase -> cuts cGMP to 5’GMP, this closes Na+ channel
hyperpolarized, glutamate release is diminished
bipolar cell no longer inhibited can now stimulate ganglion cells to produce APs, send signal to brain
receptive fields
- group of photoreceptor cells a bipolar cell receives signals from (circular area of the retina)
far more photoreceptor cells than ganglion cells - smaller receptive fields = sharper images
2 parts:
1. center: provides direct input from photoreceptors to bipolar cells
2. surround: provides indirect input from the photoreceptors to the bipolar cells via horizontal cells
bipolar cell
on center and off center (receptive fields and this help id changes in contrast/brightness)
exhibit graded potentials
- photoreceptor synapses and on center and an off center bipolar cell
- each on center bipolar cell synapses with an on center ganglion cell and each off center bipolar cell synapses with an off center ganglion cell -> optic nerve -> brain
when receptive field center is in dark, photoreceptor cells depolarized and release glutamate constantly
on center pathway:
- glutamate stimulates metabotropic glutamate receptors, K+ channels opened, hyperpolarized, decreased release of transmitter, decrease in firing of on center ganglion cells
off center pathway:
- glutamate stimulates ionotropic glutamate receptors Na+ channels opened, depolarized, release of transmitter inc, inc in firing of off center ganglion cells
one bipolar cell can synapse with set of photoreceptive cells
horizontal cell can synapse with many photoreceptive cells
light and dark adaptation
rods: in bright light, more rhodopsin broken down, less sensitive to light (opposite for darker conditions)
pupils: constrict in bright light, dilate in dim light
how is location of visual stimulus encoded in nervous system?
- comparing input
- left/right location, distance (depth) - map-like projection from retina to cortex
- relays “coordinates”
- info in a visual field is processed in the opposite side of the brain
- processed signal is sent via the optic nerve through the lateral geniculate nuclei to the visual cortex
papillae
specialized regions on tounge
types:
- filiform: filament shaped, provide rough surface for food manipulation
vallate: largest, least numerous. 8-12 in V along border between anterior and posterior parts of the tounge. have taste buds
fungi form: mushroom shaped.scattered irregularly over the superior surface of tounge. look like small red dots interspersed among filiform. have taste buds
foliate: leaf shaped. in folds on the sides of the tounge. contain most sensitive taste buds. decrease in number with age
taste bud
includes supporting cells surrounding taste cells
sensory structures that detect taste
- taste cells have microvilli (gustatory hairs) extending into taste pores
- replaced about every 10 days
taste receptors
detect molecules from food/other that come into direct contact with receptor
- used primarily to ID foods
tastebuds contain sensory receptor cells specific for 5 taste types
- sweet, salty, bitter, sour, umami (savoriness)
tastants
substances dissolved in saliva
- enter taste pores
- by various mechanisms, tastants cause taste cells to depolarize
tastants
substances dissolved in saliva
- enter taste pores
- by various mechanisms, tastants cause taste cells to depolarize
- texture, temp and olfaction affect taste perception
taste types (where found, sensitivity, what causes sensation)
sour: most sensitive receptors on lateral aspects of tounge H+ ion of acids cause depolarization
salty: tip of tounge. lowest sensitivity along with sweet. Na+ causes depolarization
bittter: posterior aspect. highest sensitivity. sensation produced by alkaloids, (toxic)
sweet: tip of tounge. lowest sensitivity. sugars, some carbs, some proteins (G protein coupled receptor)
umami: scattered sensitivity. caused by amino acids such as glutamate binding to receptors
neuronal pathways of taste
axons of sensory neurons synapse with taste receptors, pass through cranial nerves VI, IX, and X and through ganglion of each nerve
enter brain stem -> thalamus -> taste area of cortex
olfactory tract
axons of afferent neurons from cells (mitral and tufted) of olfactory bulb that connect to several target regions in brain (amygdala)
olfactory bulb
multilayered structure that has axons from olfactory neurons organized in clusters (glomeruli); functions to help discriminate odors, filter out background odors to enhance sensitivity to odor detection
olfactory receptive neurons
bipolar neurons that have dendrites with cilia that protrude into the mucus covering the olfactory epithelium and axons that synapse with mitral cells in the olfactory bulb
olfaction key points
- 4000 different recognizable odors
- dendrites of olfactory neurons have enlarged ends (olfactory vesicles)
- cilia (olfactory hairs) of olfactory neuron are embedded in mucus, odorants dissolve in mucus
- odorants attached to to receptors, cilia depolarize and initiate APs in olfactory neurons, one receptor may respond to more than one type of odor
- olfactory epithelium is replaced as wears down. olfactory neurons are replaced by basal cells every 2 months (this is unique)
olfactory receptors
used for:
food ID
detection of predator/prey
ID of family/known
location of territories
communication
also connect to limbic system
GPCRs
neuronal pathways of olfaction
info goes to olfactory cortex of frontal lobe without going through thalamus first! (only major sense that does this)
3 regions in frontal lobe affect conscious perception of smell and interact with limbic system
lateral olfactory area: conscious perception of smell (olfactory cortex)
medial olfactory area: visceral and emotional reactions to odors
intermediate olfactory area: effect modification of incoming information
general properties of muscle
contractility: ability to shorten with force
excitability: capacity to respond to a stimulus (from nerves)
extensibility: muscle can be stretched to its normal resting length and beyond to a limited degree
elasticity: ability of muscle to recoil to original resting length after stretched
3 types of muscle tissue
skeletal muscle (striated)
cardiac (branched w/ interpolated discs)
smooth muscle (tapered)
skeletal muscles
many attached to bones via tendons (connective tissue)
appear striated due to thick (myelin protein) and thin (actin protein) filaments (light and dark banding)
cells multi-nucleated
under voluntary control
humans > 600 muscles
body movements
- complete organs
- composed of muscle cells (fibers), connective tissue, blood vessels, nerves
- fibers are long, cylindrical, multinucleated
fasiculus
sarcolema:
sarcoplasm:
myofibril:
sacromere
smooth muscle
found in walls of hollow organs, blood vessels, eye, glands, skin
- propel urine, mix food in digestive tract, dilating/constricting pupils, regulating blood flow
- involuntary (endocrine and autonomic nervous system)
- visceral smooth muscle has many gap junctions (sheets of smooth muscle function as a unit)
- sometimes autorythmic
- can be mechanically coupled to one another such that one contraction of one cell invokes some degree of contraction in adjoining cell
- gap junctions coupled adjacent cells chemically and electrically, facilitating spread of chemicals/APs
thick and thin filaments, but slanted (easier to be round) use sliding filament mechanism for contraction
dense bodies: anchor thin filaments,
- shortens more than skeletal (more distance between thin and thick)
cardiac muscle
- heart major source of movement of blood
autorythmic (SA node) - controlled by endocrine/autonomic nervous system
cardiac muscle
- heart major source of movement of blood
autorythmic (SA node) - controlled by endocrine/autonomic nervous system
- fasiculus
bundle of muscle fibers, held together and in parallel by connective tissue
sarcolema
sarcolema: plasma membrane of muscle fiber/cell
sarcoplasm
sarcoplasm: cytoplasm of muscle cell
myofibril
contractile elements found in muscle cells, made of sacromeres
composed of thick and thin filaments
thick: myosin head and tail
thin: actin, troponin, tropomyosin (long skinny)
sarcomere
basic unit of contraction in myofibril, region between 2 Z lines
Z disk: filamentous network of protein, serves as attachment for actin filaments
striated appearance
I bands: between thick filaments (light)
A bands: length of thick filaments (dark)
H zone: region in A band where actin and myosin do not overlap
M line: middle of H zone, delicate filaments holding myosin in place
actin (thin filaments)
can polymerize to create filament
beta plated sheets, alpha helices, binding for ATP, and polarity
proteins associated:
troponin: found between ends of the tropomyosin molecules in the groove between actin strands
- 3 subunits:
1. binds to actin
2. binds to tropomyosin
3. binds to calcium ions
tropomyosin: elongated protein that winds along the groove of the actin double helix
- troponin/tropomyosin complex regulates the interaction between active sites on actin and myosin
myosin motor proteins (thick filaments)
myosin II: motor protein found in skeletal muscle
- generates force for muscle contraction
- formed from 2 heavy chains, 2 copies each of 2 light chains
head: binds and hydrolyzes ATP, generates force for movement
tail: formed from coiled-coil interaction 2 alpha helices of heavy chains
- large bipolar filaments formed from tail-tail interactions between myosin filaments
- contain several hundred myosin heads oriented in opposite directions
- thick filaments can slide oppositely oriented pairs of actin filaments past each other (I band and H zone bands decrease when muscle shortens)
cross bridge: when myosin head is bound to actin filament
muscle innervation
motor neurons stimulate muscle fibers to contract
neuromuscular junction (NMJ) contact point between axon and muscle
- postsynaptic membrane (sarcolema) or motor-end plate
function of neuromuscular junction
synaptic vesicles contain:
neurotransmitter-> acetylcholine
acetylcholinesterase: degrading enzyme in synaptic cleft. prevents accumulation of ACh
ACh receptor site-> nAChR (nicotinic)
t tubule
transverse tubule
deep invagination of sarcolema only found in skeletal and cardiac muscle cells
- allow depolarization of the membrane to quickly penetrate to the interior of the cell
muscle contraction
AP arrives at NMJ, causing release of acetylcholine -> triggers AP in muscle fiber that spreads over its plasma membrane into t tubules -> AP triggers Ca++ release from Sarcoplasmic reticulum, releases into cytosol -> Ca++ binds troponin, exposes myosin binding sites -> myosin head acquires high energy config (ATP to ADP + P) -> binds and moves actin filaments -> tropomyosin block myosin sites, contraction ends -> Ca++ reuptake to SR through pump (uses ATP)
cross bridge cycle
- myosin head has atp bound, not in contact with actin
- myosin binding site on actin becomes available
- ATP -> ADP+P and myosin head attaches to actin and initiates “power stroke” (bending of myosin head and movement of actin filament) releasing ADP
- myosin head binds a new ATP and detaches from actin
rigor mortis
Ca2+ leaks into cytoplasm causing myocin head to attach to actin -> muscle contraction
no ATP, so myosin head can’t be released from actin
in humans: starts 3-4 hrs, reaches max at 12 hrs, dissipates until 48-60 hrs
muscle twitch
contraction in response to stimulus that causes AP in 1 + muscle fibers
phases:
lag/latent
contraction
relaxation
restimulation of muscle fiber before it relaxes can cause 2nd twitch which can sum
peak lvl of contraction: tetanus
tetanus
sustained muscle contraction evoked when the motor nerva that innervates a skeletal muscle emits APs at a very high rate
tupes of muscle fibers
differ in # of mitochondria and capacity to produce ATP
1. slow muscle fibers (SO: slow oxidative)
2. fast aerobic (fast oxidative glycolytic fibers FOG)
3. fast anaerobic fibers (fast glycolytic FG)
slow muscle fibers
small
- weak contractions, resist fatigue
- contract slowly
- intensity is low bc ATP on myosin head is hydrolyzed slowly
- do not fatigue rapidly (postural muscles)
- high concentration of myoglobin (O2 storing protein), good supply of O2
fast aerobic fibers
intermediate size + strength, some fatigue
- contract relatively quickly + powerfully
- fatigue more quickly than slow fibers
- used in endurance activities
fast anaerobic fibers
large, strong, fatigue quickly
- few mitochondria, little myoglobin, depend on anaerobic glycolysis to generate ATP
- larger fibers, so more force
- used for rapid movements of short duration
energy sources for muscle contraction
ATP provides immediate energy
produced from 3 sources:
1. creatine phosphate
- accumulates in muscle tissue, used up quickly
- ADP + creatine phosphate -> (kinase) creatine + ATP
2. anaerobic respiration
- breakdown of glucose to yield ATP + lactic acid
3. aerobic respiration
- req oxygen
- glucose + 6O2 + 36 ADP + 36 Pi -> 6 CO2 + 6H2O + 36 ATP
muscle conversion
endurance training: convert fast from anaerobic to aerobic
weight lifting: converts fast from aerobic to anaerobic
motor unit
single motor neuron + all muscle cells innervated by it
larger muscle = more muscle fibers
motor unit
single motor neuron + all muscle cells innervated by it
larger muscle = more muscle fibers
optimal length of muscle
have maximal # of cross bridges available for contraction, good overlap between thick and thin filaments, thin filaments not getting int e/os way
more stretch = losing thick and thin filament overlap, tension can’t be generated
less stretch/length = thin filaments start to get into each others way, less tension, myosin binding sites not available to bind with myosin heads
- not a mechanism in animals: we aren’t capable of changing length that much
types of muscle contractions
isomeric
isotonic
isomeric muscle contractions
muscle same length
- only exerts force/tension doesn’t shorten
ex. holding object up
- muscular force precisely matched the load
isotonic contraction
muscle length changes
tension in muscle remains constant despite a change in muscle length
2 types:
concentric: causes muscle to shorten, generating force
eccentric: causes muscles to elongate in response to greater opposing force
smooth muscle excitation
neural input from autonomic nervous system can induce or inhibit contraction
hormonal input: hormone will stimulate a second messenger molecule which will lead to calcium release
- in smooth muscle, no t tubules, calcium can come from sarcoplasmic reticulum or can enter from outside via voltage or ligand gated channels
calcium binds calmodulin (not troponin) -> activates enzyme that can phosphorylation cross bridges -> cross bridges can bind and pull on thin filaments
smooth muscle contractions
tend to be slower
fatigue slower
Order light passes through eye
Cornea aqueous humor pupil lens VH retina optic nerve occipital lobe
Muscle contraction
H and I def in length
Ca binds troponin, moving tromomyosin
SR releases calcium
ADP + Pi bound to myosin head (releases from actin)
Order of electrical activity of heart
SA AV BOH P
