NEU 201 Lecture 6: Dendritic Intergration

How many muscle fibers are connected to a motor neuron

one muscle fiber per motor neuron

Why does the Nerve-Muscle Synapse always fire?

huge synapse

alot of vesicles ~200

many postsynaptic receptors

How many inputs does a CNS receive?

thousands

How many outputs are made by most CNS neurons

one (excitatory or inhibitory PSP)

How do CNS neurons receive multiple inputs

with multiple neurotransmitters (1 vesicle per AP)

ionotropic and metabotropic receptors

diverse ion flow

What is dendritic intergration?

the spatial and temporal summation of inputs

What effects the size of PSP

the number of channels open during dendritic integration

What is at a dendrite synapse?

neurotransmitter molecules

vesicles

postsynaptic receptors

Types of dendritic input summation

1. single channel currents become EPSP or IPSP

2. EPSP and ISPS are integrated

3. Spatial summation

What determines if an action potential threshold is crossed in Dendritic integration

number, amplitude (stronger vs weaker) , and timing (did they fire close to each other) of EPSP and IPSP

location of axon inputs

Spatial Summation

inputs that arrive at different synapses can sum to a larger EPSP or IPSP

How does EPSP and IPSP spread in Dendrites?

passively but voltage-gated channels can boost signals

How does location affect Spatial Summation

inputs closer to axon initial segment are more effective to trigger AP

Temporal Summation

when 2 inputs at the same synapse sum within 1-15 miliseconds

What happens to EPSP and IPSP over time

they spread out as they trave; which helps temporal integration

What affects Action Potential Propogation Speed?

time constant and length constant

What is time constant?

time to charge membrane

What is the relationship between time constant and charging speed?

smaller time constant = faster charging speed

What is length constant?

distance where graded potential decays to 37% of original amplitude

What is the relationship between length constant and propagation of action potentials?

larger length constant = more effective propagation

What are the two types of resistance that oppose current spread?

membrane resistance and axial (internal) resistance

What is membrane resistance (Rm)?

the opposition to ion flow across the membrane

subject to change

What causes membrane resistance?

less open channels (less conductance)

constant in mature neurons

What is Axial( (internal) resistance?

opposition to the flow of ions down the inside of neurites

What affects Axial resistance?

larger axons =less resistance

What is the length constant formula?

Length constant depends on what?

axon diameter , internal resistance, membrane resistance

How can you reduce axial resistance?

widen the axon and close channels

How are length constant and membrane resistance related?

increased membrane resistance = increased length constant= faster conduction = higher time constant (slow conduction)

What is the relationship between Myelin and Conduction

Myelin increase specific membrane resistance and decreases membrane capacitance

What effect does Myelination have on the time constant?

no effect

what effect does myelination have on the length constant

myelination increases the length constant

Impact of Length constant on spatial summation

larger length constant: action potential travels farther

smaller length constant: decays fast

same for EPSP and IPSP

affects how much inputs is need to make postsynaptic cell fire

What does Lidocaine do to Voltage-gated Sodium Channels?

it blocks open, inactivated channel ONLY

Why are small axons like pain fibers sensitive to Lidocaine?

smaller axons have high internal resistance and low length constant so they require more depolarization and are more sensitive to lidocaine

What is the relationship between Neuromodulators and Length constant?

neuromodulators regulate the efficiency of distant synapse through length constant because less current leaks during transmission

How can length constant change?

locally (neuromodulators)

rapidly

Shunting Inhibition

lowering of the length constant to prevent action potentials

How do ions affect shunting inhibition?

Inhibitory Cl- influx holds membrane potential at 65mV

Open channels reduce the membrane resistance and length constant because depolarization is leaking out

What is counterbalance excitation in Spatial Summation

inhibitory neurons can influence which EPSP trigger action potential

What is Microcephaly

to have reduced brain size (~400cm)

average adult ~1200-1600cm

What is cerebral rubicon

human behavior result of human brain organization rather than brain size

Common features of the Nervous system

the neuron

the synapse

neural circuits

Similarities in rat and human brain

two cerebral hemispheres

relative locations of brain regions ventricles

complexity of cerebellum

Ipsilateral

from brain to tail

Contralateral

from side to midline

Superior

Above

Posterior

behind

Anterior

in front of (toward the eyes)

Inferior

below (toward spine)

Rostral

toward eyes on longitudinal axes

Caudal

toward back of brain on longitudinal axis

Coronal

cut the brain like a guillotine

Horizonal Slice

like a pencil held horizontally

Sagittal Slice

like a cut forward and back

What are the two types of nervous systems

Central and Peripheral Nervous System

What makes up the central nervous system

brain and spinal cord

Which neurons cross the midline

most sensory and motor neurons

Which brain regions are in all mammals?

cerebrum, cerebellum, brainstem (CNS)

Which layers protect the brain?

Dura mater, Arachnoid Membrane, Pia mater

What is Dura Mater?

the most external covering of the brain under the skull

What is the arachnoid membrane?

series of spiderweb like connects that connect the dura mater to the pia mater

What is the pia mater?

the layer that directly covers the brain

Ventricular System

CSF is made in ventricles

flows to subarachnoid

leaves via blood vessels

What happens when the CSF flow is disrupted

the CSF continues to flow in but cannot flow out, so it presses on the brain and causes swelling

What makes up white matter

mylination

What makes up gray matter

neurons

Anatomy of cerebral hemisphere

Frontal Lobe

Parietal Lobe

Occipital Lobe

Temporal Lobe

Frontal Lobe

reasoning, speech, problem solving, movement, emotions

Parietal Lobe

movement, orientation, perception of stimuli

Occipital Lobe

visual processing

Temporal Lobe

perception and recognition of audio, memory, speech

Spinal Cord

get signals to and from body

has white and gray matter

Somatic PNS

spinal nerves that control voluntary behaviors

Dorsal Roots

incoming sensory

Ventral Roots

outgoing motor

Somatic Motor Neurons are in which nervous systems

cell bodies : CNS (spinal cord)

axons: in PNS

Visceral PNS (autonomic nervous system)

involuntary reactions (organs, blood, rate of heart)

How many cranial nerves?

12

How to define a brain area

lesions studies

stimulate and monitor responses

image cytoarchitecture

trace connections

record responses properties

wiring diagram/ map

Which staining technique absorbs light?

lipids replaced by water-soluble gel

Types of brain imaging

CT , MRI, fMRI, PET

What do fMRI and PET measure?

blood flow

good spatial bad temporal resolution

shows activity

What does MRI measure?

changes in the H atom energy state in response to magnetic fields

Common organization of cerebral cortex

outer layer (layer I) no neuronal cell bodies

1 or more layer of pyramidal neurons with large dendrites in layer 1

Does the amygdala is made of layers or nuclei?

nuclei

How to identify receptive fields

with single unit electrophysiological recording from cortical pyramidal neuron

Which cortex are organized into maps

sensory and motor cortices

What is the sensory map called

somatosensory map

What does the homunculus tell us about brain organization

more area dedicated to finer precepting body movement and regions