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Neurons and Synapses Types of Neurons Sensory Motor Interneurons Sensory Neurons INPUT From sensory organs to the brain and spinal cord. Brain Drawing shows a somatosensory neuron Vision, hearing, taste and smell nerves are cranial, not spinal Sensory Neuron Spinal Cord Brain

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neurons and synapses
Neurons and Synapses

Types of Neurons

Sensory

Motor

Interneurons

sensory neurons
Sensory Neurons
  • INPUT Fromsensory organs to the brain and spinal cord.

Brain

Drawing shows a somatosensory neuron

Vision, hearing, taste and smell nerves are cranial, not spinal

Sensory

Neuron

Spinal

Cord

motor neurons

Brain

Sensory

Neuron

Spinal

Cord

Motor

Neuron

Motor Neurons
  • OUTPUTFrom the brain and spinal cord To the muscles and glands.
interneurons

Brain

Sensory

Neuron

Spinal

Cord

Motor

Neuron

Interneurons
  • Interneurons carry information between other neurons only found in the brain and spinal cord.
the cell body
The cell body
  • Round, centrally located structure
  • Contains DNA
  • Controls protein manufacturing
  • Directs metabolism
  • No role in neural signaling
  • Contains the cell’s Nucleus
dendrites
Dendrites
  • Information collectors
  • Receive inputs from neighboring neurons
  • Inputs may number in thousands
  • If enough inputs the cell’s AXON may generate an output
dendritic growth
Dendritic Growth
  • Mature neurons generally can’t divide
  • But new dendrites can grow
  • Provides room for more connections to other neurons
  • New connections are basis for learning
slide9
Axon
  • The cell’s output structure
  • One axon per cell, 2 distinct parts
    • tubelike structure branches at end that connect to dendrites of other cells
myelin sheath

Myelin Sheath

Myelin sheath
  • White fatty casing on axon
  • Acts as an electrical insulator
  • Not present on all cells
  • When present increases the speed of neural signals down the axon.
how neurons communicate
How neurons communicate
  • Neurons communicate by means of an electrical signal called the Action Potential
  • Action Potentials are based on movements of ions between the outside and inside of the cell
  • When an Action Potential occurs a molecular message is sent to neighboring neurons
ion concentrations

Outside of Cell

K+

Na+

Cl-

Cell Membrane in resting state

K+

Na+

Cl-

A-

Inside of Cell

Ion concentrations
the cell membrane is semi permeable

K+

Na+

Cl-

Outside of Cell

Cell Membrane at rest

Na+

- 70 mv

A-

K+

Cl-

Inside of Cell

Potassium (K+) can pass through to equalize its concentration

Sodium and Chlorine cannot pass through

Result - inside is negative relative to outside

The Cell Membrane is Semi-Permeable
resting potential
Resting Potential
  • At rest the inside of the cell is at -70 microvolts
  • With inputs to dendrites inside becomes more positive
  • if resting potential rises above threshold an action potential starts to travel from cell body down the axon
  • Figure shows resting axon being approached by an AP
depolarization ahead of ap
Depolarization ahead of AP
  • AP opens cell membrane to allow sodium (NA+) in
  • inside of cell rapidly becomes more positive than outside
  • this depolarization travels down the axon as leading edge of the AP
repolarization follows
Repolarization follows
  • After depolarization potassium (K+) moves out restoring the inside to a negative voltage
  • This is called repolarization
  • The rapid depolarization and repolarization produce a pattern called a spike discharge
finally hyperpolarization
Finally, Hyperpolarization
  • Repolarization leads to a voltage below the resting potential, called hyperpolarization
  • Now neuron cannot produce a new action potential
  • This is the refractory period
neuron to neuron

Dendrite

Axon

Cell

Body

Neuron to Neuron
  • Axons branch out and end near dendrites of neighboring cells
  • Axon terminals are the tips of the axon’s branches
  • A gap separates the axon terminals from dendrites
  • Gap is the Synapse
synapse

Sending

Neuron

Axon

Synapse

Terminal

Synapse
  • axon terminals contain small storage sacs called synaptic vesicles
  • vesicles contain neurotransmitter molecules
neurotransmitter release
Neurotransmitter Release
  • Action Potential causes vesicle to open
  • Neurotransmitter released into synapse
  • Locks onto receptor molecule in postsynaptic membrane
locks and keys
Locks and Keys
  • Neurotransmitter molecules have specific shapes
  • Receptor molecules have binding sites
  • When NT binds to receptor, ions enter

positive ions (NA+ ) depolarize the neuron

negative ions (CL-) hyperpolarize

some drugs work on receptors
Some Drugs work on receptors
  • Some drugs are shaped like neurotransmitters
  • Antagonists : fit the receptor but poorly and block the NT
    • e.g. beta blockers
  • Agonists : fit receptor well and act like the NT
    • e.g. nicotine.
summary
Summary
  • 3 types of neurons
  • The cell membrane
  • Ion movements
  • Action potentials
  • Synapse
  • Neurotransmitters
  • Receptors and ions
  • Agonists and antagonists