Neuroanatomy (PPT)

Neuroanatomy

Components of this lecture:

1. Neurons & Glial Cells

2. Neurotransmitters & Psychopharmacology

3. Functional Organization

Neurons, Glial Cells & Neurochemistry

Nervous System

Central Nervous Peripheral Nervous

System System

Brain Spinal Cord

ii. Structure of neurons 1. Cell body - contains nucleus

2. Nucleus – contains DNA 3. Dendrites – cell body

(receives information) 4. Receptors – receive information using a chemical signal.

5. Axons – sends information 6. Axon hillock – junction between cell body and axon

**Lowest threshold for action potential**

7. Terminal (buttons or boutons) – swelling on the surface (see

slide)

- Inside buttons are synaptic vesicles,

packaging of neurotransmitter

8. Myelin sheath – insulation for axons

- comprised of glial cells (see slide)

A. In CNS it’s Oligodendrocytes

B. In PNS it’s Schwann cells

9. Nodes of Ranvier – spaces between myelinating cells along the

axon

11. Cell membranes cover all cells - Two layers of fat molecules - Tucked inside are channels made up of

protein molecules (see slide) - Protein molecules

a. Serve as receptors for NT’s – next slide

b. Serve as channels for ions (Ca++, Na+, K+, and Cl-) - next slide

c. Location along neuron differs in the type of channel protein

d. Membranes are dynamic and alive

Two Types of Receptors (more again – soon) 1. Ionotropic Receptors fast acting

ion channel/receptor complex sameonly a few Neurotransmitter activate

them2. Metabotropic Receptors

slower actingion channel and receptor are different

most Neurotransmitters act on them

12. Cytoskeletons (Neurofilaments) inside cell

provide structural support

- Microfilaments

- Microtubules – Fairly large, play important role in transport

a. Send vesicles to the buttons where

they are filled with NT. Acts like a conveyor belt.

13. Organelles within the cell

a. Mitochondria – Convert glucose into energy we can use: ATP (energy

source for cell)

b. Endoplasmic Reticulum – Synthesis of fat molecules and protein molecules

3. Synapse - the junction between cells (neurons). - synaptic cleft - space between cells a. synapse is made of 3 parts: 1. Presynaptic cell– sending side of synapse 2. Postsynaptic – receiving side of neuron 3. Synaptic Cleft b. Purpose: promote chemical-electrical signal c. Types of Synapses: axodendritic, axosomatic

axoaxonic, dendrodendritic

4. Chemical Milieu of Cellular Spaces when the neuron is “at rest”

Intracellular space & extra cellular space (inside of cell membrane & outside of cell membrane)

a. Cl- = Chloride (more outside than inside)

b. Na+ = Sodium (more outside than inside)

c. A- = Anions (more inside than outside)

d. K+ = Potassium (more inside than outside)

Forces that maintain the chemical balance

i. Concentration gradient – lesser concentration

ii. Electrostatic pressure – attraction toward opposite charges

iii. Na & K pumps – Throws out sodium and takes in potassium to keep cell balanced

5. Four states of neuronal electrical charge (potentials)

a. Resting Membrane Potential -70 mV (transient state, constantly affected

by forces that increase or decrease charge) b. Excitatory Post-Synaptic Potential or EPSP–

Charge across the membrane becomes less negative

- depolarization of the neuron (i.e. decrease negative charge from –70mV to –65mV)

- Leads to an action potential

c. Inhibitory Postsynaptic Potential or IPSP Charge across the membrane becomes more negative

- hyperpolarization of neurons (i.e. increase in negative charge from –70mV to –90 mV)

- Reduces the likelihood of an action potential d. Action Potential or AP Charge across the membrane becomes less negative

- depolarization of neurons (i.e. decrease in negative charge from –65mV to +55 mV) - charge for the AP begins at Axon Hillock - significant shift in ions

Neurotransmitters and

Psychopharmacology

Neurotransmitters

80 plus chemical substances that provide communication between cells. Some of these are actually NTs and others are neuromodulators (i.e. they augment the activity of the NT)

Amino Acid NTs

Glutamate• Uses both ionotropic

and metabotropic receptors

• NT of the cerebral cortex

• Excitatory effect

GABA• Uses ionotropic

receptors

• Most prevalent NT in the CNS

• Inhibitory effect

Seizures disorders are the caused by overactive Glu and/or under active GABA

Not in Book

Monoamine NTs

Catecholamines

Dopamine

Norepinephrine

Epinephrine

Indolamines

Serotonin

These NTs use both reuptake and enzymes

(e.g. MAO) to terminate action

Not in Book

Acetylcholine

• Two Receptors:

nicotinic receptor – uses ionotropic receptor

muscarinic receptor – uses metabotropic receptor

Degradation is through enzyme only:

acetylcholinesterase inhibitor

Neuropeptides

• Long chains of amino acids

• Numerous categories (see appendix VII)

• One category is the ENDORPHINS– Enkephalins– Beta-endorphin

Soluble Gases

• Nitric Oxide – involved in learning and memory (more on this later)

Neurotransmitters have 7 actions 1. Synthesized2. Stored 3. Enzymatically destroyed if not stored4. Exocytosis5. Termination of release via binding with

autorecptors6. Binding of NT to receptors7. NT is inactivated

Drugs are developed that address these actions as an AGONIST (mimic the NT ) or ANTAGONIST (block the NT)

Drugs that Block Reuptake

• SSRIs (Selective Serotonin Reuptake Inhibitors)

• Cocaine

- highly addictive, both physiologically and

psychologically

(see interactive CD ROM)

Tolerance & Dependence• Tolerance – state of decreased sensitivity to the drug

as a result of exposure to it. functional tolerance (number of

binding sites is reduced – also called “down regulation” of receptors) note: opposite phenomenon: up-regulation• Physical Dependence – caused by withdrawal

symptoms (not the reason that people continue to take most drugs)

• Psycholological Dependence (now called positive-incentive theory of addiction)

e.g., intracranial self-stimulation studies & dopamine

Functional Organization

2. Brainstem medulla, pons & midbrain a. Medulla (Myelencephalon) center for vital functions decussation of the pyramids crossing over for most nerve fibers b. Pons (Metencephalon) numerous cranial nerves reticular formation raphe nucleus and sleep

c. Midbrain (Mesencephalon)

Superior Colliculus

Inferior Colliculus

Central Gray (periaqueductal gray)

Substantia Nigra

Ventral Tegmentum

Schizophrenia & Parkinson’s

disease

3. Cerebellum (Metencephalon)

smooth coordination of practiced

movements

integrates sensory & motor

cognitive functions (with frontal lobe)

4. Hypothalamus (Diencephalon)

22 sets of nuclei

homeostasis, biological rhythms

drives

5. Thalamus (Diencephalon)

Relay Station

Topographic arrangement with cortex

6. Basal Ganglia (Telencephalon)

Striatum (Caudate & Putamen)

Globus Pallidus

“Substantia Nigra”

7. Limbic System (Telencephalon)

Hippocampus

Amygdala

Nucleus Accumbens

“Prefrontal Cortex, Cingulate Cortex

& Hypothalamus”

8. Cerebral Cortex (Telencephalon)

- 6 layered structure

- Four lobes: Frontal

Parietal

Temporal

Occipital

- sulcus (i) & fissure (s) (lateral, central)

- gyrus (i)

Features of the Cerebral Cortex

note: more on this later

Somatosensory Cortex (homunculus)

Motor Cortex (homunculus)

Visual Cortex

Auditory Cortex