Download Nervous System Function

Nervous System Function

Neurons


Base unit that has very simple function – “decide” whether to
transmit signal or not
Organization





Billions of Neurons (estimates of 100 billion)
Very complex interconnections
Create systems/circuits that can function independently (parallel
processing)
“Simple decisions” passed to “higher” levels for that add
additional information to create generate more complex
decisions (hierarchical processing)
Very expensive - less than 2% of weight but uses 20% of
energy
Neuron Structure

Cell Body


Dendrites


Receive information
Axon



Nucleus – genetic information
Carry information “long” distances
Myelin (Multiple Sclerosis)
Axon Terminals

Transmit information
Neuron - Structure
Neuron Function

Electrical Activity


Used to transmit signal within neuron
Chemical Activity


Used to transmit signal between neurons
Synapse – small gap that physically separates
neurons

Neurotransmitters – special “chemicals” that
neurons use to transmit message across the
synapse
Neuron Function

Electrical Activity

Resting Potential




Inside negative (-70 mV) compared to outside
Inside has high K+ (negativity comes from proteins
& other negative ions)
Outside has high Na+
Forces at work
 Electrical
 Diffusion
Neuron Function

Electrical Activity

Graded Potential



Depolarization – Inside less negative (e.g., Na+ enters)
Hyperpolarization – Inside more negative (e.g., Cl- enters)
Action Potential



When graded reaches approximately -55mV
Electrical impulse that travels down cell – axon to axon
terminals
Axon terminals release neurotransmitter
Neuron Function

Electrical Activity

Restoring Resting Potential


Sodium-Potassium Pump – moves Na+ out of cell
and K+ into cell
This requires cell to use energy
Neuron Function

Chemical (Neurotransmitter) Activity

Leads to graded potentials in neuron


Excitatory NTs – causes depolarization in neuron
Initiatory NTs – causes hyperpolarization in
neuron
Neuron – Excitation & Inhibition
Neuron - Synapse
Synapse Types

Multiple ways of connecting

Examples



Axon to Dendrite – excite or inhibit neuron
Axon to Axon Terminal – moderate NT release
Axon to Extracellular Space or blood – potential
for diffuse effects
Synapse Types
Synapse Function

Neurotransmitter cycle in Axon Terminals







Synthesis
Storage
Release
Inactivation
Reuptake
Degradation
Neural transmission problems if cycle disrupted
(e.g., drugs) at any step
Synapse Function
Synapse Function
Neurotransmitter Types

Small Molecules


Nine – Acetylcholine (ACh), dopamine (DA),
norepinephrine (NE), epinephrine (adrenaline), serotonin
(5-HT), histamine, GABA, glycine, glutamate
Simple (or no) alterations to basic food components




Glutamate & glycine are amino acids
DA and NE from tyrosine & 5-HT made from tryptophan
Manufactured in axon terminals
Large quantity and have short duration
Neurotransmitter Types

Peptides

50+ and grouped into families depending on function



2 or more amino acids and made in cell body (ribosomes)
from DNA instruction



Opoids (enkephalins, dynorphin) – pain
Gastrins (gastrin, cholocystokinin) – food digestion
Slower to manufacture & transport
Small concentrations and longer durations
Gases


At least 2 – nitric oxide (NO) & carbon monoxide (CO)
Can work on releasing cell
Neurotransmitter Function

No one to one relation between type and
function

Same NT can be used in different places with
very different effects

Acetylcholine – contracts muscles, used in
autonomic nervous system, and brain
Neurotransmitter Receptor Proteins

Channel Proteins



NT binding site and channel trough membrane
NT opens a channel to allow chemical flow (Na+) across
membrane
Second Messengers


NT binding site – NT activates a “second messenger” (1st
is the NT) inside the cell
Change function of cell (e.g., change protein production to
permanently alter cell function for learning)
Neurotransmitter Receptor Proteins
Neurotransmitter Receptor Proteins

Usually multiple receptors for a given NT

Acetylcholine




Nicotinic receptor – found a junction between
neuron and muscle
Muscarinic receptor – more prevalent in brain
Acetylcholine affects both
Drugs can have more specific effects (or not
depending on the drug)
 Nicotine & curare –affect nicotinic but not muscarinic
Neurotransmitter Receptor Proteins

Usually multiple receptors for a given NT

Serotonin (5-HT)


13 known receptors grouped into 6 families
People with schizophrenia have an excess of one
type
 Demonstrates how genetic differences can influence
motivational temperaments

Dopamine

5 known receptors grouped into 2 families
Psychoactive Drug Overview

Two Broad effects on NT function



Facilitate or increase function of a specific NT
Inhibit or Decrease function of a specific NT
2 Broad effects accomplished by altering
any of the 7 synapse functions (previous
slide)

Acetylcholine
Psychoactive Drug Overview

Acetylcohine Example

Axon Release



Synapse Stimulation



Black widow spider venom – released from axon terminals
Botulinum toxin (Botox) – blocks release from axon
terminals
Nicotine – mimics ACh
Curare – blocks ACh from getting to terminals
Inactivation

Physostigmine – blocks effect of enzyme that destroys ACh
Psychoactive Drug Overview
Psychoactive Drug Overview

Nervous System adapts drug presence



Inhibitory drug – may create more protein
receptors to detect smaller amounts of NTs that
are getting to postsynaptic cell
Excitatory drug – may remove protein receptors
NS now requires drug for functioning


Inhibitory drug – “normal” signals are too strong
Excitatory drug – “normal” signals not strong
enough
Nervous System Organization
Nervous System Organization

Central Nervous System (CNS)



Spinal Cord – simple decisions & information transmission
Brain – “complex” decisions
Peripheral Nervous System (PNS)


Somatic – sensory information & voluntary movement
Autonomic



Sympathetic – increases support increased physical activity
Parasympathetic – increases support decreased physical
activity
Enteric – gastrointestinal system
Autonomic Nervous System
Nervous System Organization

Neuron Groups

Peripheral NS



Central NS



Nerve – collection of axons in PNS
Ganglia – collection of cell bodies & dendrites
Tract – collection of axons in CNS (White Matter)
Nuclei – collection of cell bodies (Grey Matter)
Glial Cells

Support and assist neurons (many types)

Produce myelin, nourishment, repair, waist disposal, etc.
Spinal Cord


31 segments with pairs (left & right) nerves
carrying sensory and efferent information
Functions


Ascending and descending neural tracts
Interneurons responsible for spinal reflexes
(relatively simple decisions)

Link sensory information (e.g., pain) with motor
response (e.g., muscle contraction)
Brain

Structure

Very Complex


Many different ways of describing brain
structures (location, function, etc.)
General Principles
Layered
 Lateralized

Brain

Neural Systems

Brain circuits responsible for brain function


E.g., - vision, hearing, movement, reward
System could be
 Localized (vision) or diffuse (arousal)
 General (vision) or specific (color vision)

Broad Divisions



Sensory
Motor
Association
Brain

Complex behaviors (fear/defensive learning)
depend on many systems





Sensory
Learning
Memory
Output
Differences in a function (e.g., motivation) might
be due to different reasons (e.g., sensory,
learning, etc.)
Studying Brain Function



Gross lesions
Structural assessments
Selective lesions



Local functioning




specific neurotoxins
transient lesions
Single-cell recording
Neurotransmitter measurement & manipulation
Gene expressions
Non-invasive measures


Functional MRI
EEG & ERP