CNS Anatomy & Neurotransmitter Systems

Describe the directional orientation of the CNS and apply it in distinguishing proximity of brain regions from each other

SUPERIOR (top) = Dorsal

INFERIOR (bottom) = Ventral

ANTERIOR (front) = Rostral

POSTERIOR (back) = Caudal

Identify the difference between white and gray matter

Gray matter: the location of cell bodies and dendrites

White matter: axonal fibers that project to various brain regions to transmit messages

Why is white matter white?

Caused by myeline

What are the 3 large axonal fibers that connect the two hemispheres together

Corpus Callosum [LARGEST fiber track]

Anterior Commissure (Front)

Posterior Commissure (Back)

Describe the location and function of various CNS regions

What are the 8 regions of the CNS

☼ Spinal Cord

☼ Medulla

☼ Pons

☼ Cerebellum

☼ Midbrain

☼ Diencephalon

☼ Cerebral Cortex

☼ Deep Cortical Areas

SPINAL CORD

☼ Most caudal region of the CNS, critical for all sensory & motor function

☼ Responsible for relaying and processing sensor and motor input (afferent) and output (efferent) signals)

SENSORY

temperature, touch, pressure

MOTOR

skeletal & soft (smooth) muscle

AFFERENT signals

info TOWARDS CNS, spinal cord & brain

ex: Touch something hot; you feel the heat; temperature info went in a afferent path hand → spinal cord → brain

EFFERENT signals

info from brain → spinal cord → periphery

ex: motion of moving hand away from heat source

PROCESSING

evaluates, spinal cord gets information from the periphery, decides if it wants to CHANGE importance, then sends to brain

RELAYING

PASSES ON (like baton relay) info from periphery and transfers it to the brain (NO ALTERATION)

DORSAL ROOT GANGLION

SENSORY NEURONS

Where cell bodies collect & sensory nerves are located

VENTRAL ROOT

MOTOR NEURONS

Has motor neurons, toward your chest

What is the HINDBRAIN composed of?

MEDULLA OBLONGATA

PONS

CEREBELLUM

MEDULLA OBLONGATA

☼ Most CAUDAL portion of the brain stem

☼ Responsible for the process of respiration, heart rate, blood pressure, vomiting, and salivation

PONS

☼ has neurons that project to the cerebellum

AXONS THAT CONTROL….

sleep, arousal, and dreaming

RAPHE SYSTEM (nucleus)

cell bodies for serotonin synthesizing neurons

LOCUS COERULEUS

cell bodies for norepinephrine synthesizing neurons

CEREBELLUM

connect to the pons, but not considered a part of the brain stem

• Planning, Timing & Patterning of SKELETAL MUSCLE CONTRACTS during movement

• Maintaining POSTURE and COORDINATING head & eye movements

CEREBELLUM RECEIVES INFORMATION FROM…

SPINAL CORD = Somatosensory information

CEREBRAL CORTEX = Motor information

VESTIBULAR ORGANS  OF INNER EAR = Input about balance

MIDBRAIN

SUBSTANTIA NIGRA = ☼ Cell bodies that synthesize dopamine, controls voluntary muscle movements

VENTRAL TEGMENTAL AREA (VTA) = ☼ Cell bodies that synthesize dopamine, controls sensation of pleasure

BRAIN STEM

☼ Midbrain (Substantia Nigra, VTA) + Hindbrain (pons, medulla, midbrain)

Cerebellum NOT included

DIENCEPHALON

• located between midbrain and cerebral hemispheres

• Consists of thalamus, hypothalamus & gray matter

THALAMUS

☼ Critical role in sensory and motor PROCESSING

☼ ability to modify and traffic input & output signals relating to emotions and awareness

(Can connect to any region)

HYPOTHALAMUS

☼ critical regulator of the endocrine system via the pituitary gland

☼ Link between the endocrine system and the brain, many connections to the thalamus, midbrain and cortex

☼ ability to regulate the autonomic nervous system

PITUITARY GLAND

connected to the hypothalamus by the INFUNDIBULUM (pituitary stalk)

What 2 lobes does the pituitary gland consist of?

Anterior Pituitary

Posterior Pituitary

DEEP CORTICAL AREAS

☼ Nuclei that is deep within the brain includes…

BASAL GANGLIA: Caudate, Putamen, Globus pallidus

LIMBIC SYSTEM: Hippocampus, Amygdala

BASAL GANGLIA

 involved in voluntary control of motor movements and posture

CORPUS STRIATUM: Caudate & Putamen

Globus pallidus

What is the corpus striatum composed of

Caudate & Putamen

What is the Limbic system is composed of?

Hippocamus & Amygdala

HIPPOCAMPUS

☼ intimately involved in LEARNING & MEMORY

AMYGDALA

☼ almond shaped region just ROSTRAL to hippocampus

☼ range of emotions, defensive behaviors (fear & rage)

☼ learning and memory of emotional experiences

☼ RETRIEVAL OF EMOTIONAL EXPERIENCES

CEREBRAL CORTEX

important for perception of sensory and motor inputs and initiator of outputs

Larger surface area due to extensive series of folds (gyri) and grooves (sulci)

FOLDS

gyri

GROOVES

sulci

FRONTAL LOBE

☼ executive function, language, primary motor cortex 

☼ decision making, managing emotions, higher order things

PARIETAL LOBE

☼ sensory integration, proprioception

☼ primary sensory cortex

TEMPORAL LOBE

☼ hearing, visual memories

☼ comprehension of language

OCCIPITAL LOBE

☼ visual processing

☼ identification of shapes and colors

Describe the different neurotransmitter classes and explain their synthetic pathways

CATEGORIES OF NEUROTRANSMITTERS

Amines Transmitters

☼ Acetylcholine 

☼ Serotonin

CATECHOLAMINES

• Dopamine

• Epinephrine

• Norepinephrine

Amino Acid Neurotransmitters

☼ Gamma-Amino Butyric Acid (GABA)

☼ Glutamate (Glu)

Peptide Transmitters

HOW TO DETERMINE IF A MOLECULE IS A NEUROTRANSMITTER [MUST HAVE ALL THREE]

#1 ☼ Molecule must be synthesized in the neuron and stored in the PRESYNAPTIC TERMINAL

#2 ☼ Upon action potential occurrence / stimulation, the molecule must be released from the presynaptic terminal and lead to an action / effect on the postsynaptic terminal

#3 ☼ If given EXOGENOUSLY the molecule must produce a response in the postsynaptic membrane that is identical to that of its natural release from the presynaptic terminal

ACETYLCHOLINE SYSTEM

SYNTHESIZED FROM COMBINATION OF

Choline

Acetyl Coenzyme A

☼ CHLOLINESTERASES (Acetyl & Butyryl): breaks down acetylcholine into choline and acetate

WHAT ARE THE 2 TYPES OF CHOLINERGIC RECEPTORS

MUSCARINIC

☼ M1 - M5

Odd: Excitatory (1,3,5) 

Even: Inhibitory (2,4)

☼ GPCR

NICOTINIC

☼ Muscle & Neuronal Type

☼ Consists of Various Subunits

☼ Ion Channel Receptors

☼ Excitatory Receptor: net effect of activating →

depolarization of membrane potential (+)

• DEPOLARIZATION = easier for cell to fire action potential

☼ Inhibitory Receptor: net effect of activating →

hyperpolarization of membrane potential (-)

• HYPERPOLARIZATION = harder for cell to fire action potential

CATECHOLAMINES

neurotransmitters that are derived from tyrosine and possess a catechol group: C₆H₄ (OH)₂

Derived from TYROSINE

Has CATECHOL group

CATECHOLAMINES INCLUDES

Dopamine

Norepinephrine

Epinephrine

CATECHOLAMINES BROKEN DOWN BY

MONOAMINE OXIDASES (MAO)	CATECHOL-O-METHYL TRANSFERASE (COMT)
Presynaptic terminal	synapse

SYNTHETIC PATHWAY

1) TYROSINE

↓ Tyrosine Hydroxylase (TH)

2) L-DIHYDROXY-PHENYLALALINE (DOPA)

↓ Dopa decarboxylase

3) DOPAMINE (DA)

↓ Dopamine β-hydroxylase (DBH)

4) NOREPINEPHRINE (NE)

↓ Phenotolamine N-methyltransferase (PNMT)

5) EPINEPHRINE

Employ the properties of each neurotransmitter class

DOPAMINE

mainly synthesized in the ventral tegmental area, substantia nigra and arcuate nucleus of the hypothalamus

DOPAMINE FUNCTIONS

☼ Involved in many functions in the CNS & PNS

MODULATION OF

Motor Activity & Reward

DOPAMINE DEACTIVATED BY

COMT & MAO

DOPAMINE RECEPTOR FAMILIES

D1-LIKE (D1 & D5)

Postsynaptic Receptors

Excitatory

D2-LIKE (D2, D3 & D4)

Pre & Postsynaptic Receptors

Inhibitory

NOEPINEPHRINE / EPINEPHRINE

☼ Largely synthesized in the locus coeruleus nucleus of the pons, and peripheral organs (adrenal glands)

NOEPINEPHRINE / EPINEPHRINE FUNCTIONS

☼ Involved in many functions in the CNS & PNS

NOEPINEPHRINE / EPINEPHRINE DEACTIVATED BY

COMT & MAO

NOEPINEPHRINE / EPINEPHRINE RECEPTOR FAMILIES

ALPHA

Alpha-1 & Alpha-2

BETA

Beta 1-3

SEROTONIN (5-HT) IS SYNTHESIZED FROM

TRYPTOPHAN - NOT A CATECHOLAMINE]

SEROTONIN (5-HT) PROCESS

1) TYRPTOPHAN

↓ Tryptophan Hydroxylase

2) 5-Hydroxytryptophan (5-HTP)

↓ 5-HTP Decarboxylase

3) 5-HydroxytryptAMINE 

(Serotonin, 5-HT)

SEROTONIN (5-HT) SYNTHESIZED IN..

Raphe Nucleus (Pons) & Peripheral Organs (GI tract, intestines)

SEROTONIN (5-HT) FUNCTIONS

☼ Involved in many functions in the CNS & PNS

FUNCTIONS: Mood, Perception, Cognition

SEROTONIN (5-HT) BROKEN DOWN BY

MAO

☼ Main mechanism of terminating synaptic transmission via reuptake of neurotransmitter into presynaptic terminal

• MAO breaks down 5-HT

SEROTONIN (5-HT) RECEPTOR

Pre or Post Synaptic, GPCRs, Ligand Gated Ion Channels

AMINO ACID NEUROTRANSMITTERS

GLUTAMATE (excitatory) ☼ most powerful and predominant EXICITATORY in the brain

GABA (inhibitory) ☼ most predominant INHIBITORY in the brain

WHAT IS THE PREDOMINANT EXCITATORY NEUROTRANSMITTER IN CNS?

GLUTAMATE

GLUTAMATE FUNCTIONS

☼ Excess amounts of glutamate has been linked to excitotoxicity of neurons

Learning & Memory, Reward Systems, Pain, Vision

GLUTAMATE CLASSES

NMDA, AMPA, Kainate Receptors

What binding sites does NMDA receptor have?

Glutamate, Glycine, Zinc, PCP, Magnesium

STEPS TO ACTIVATE NMDA RECEPTOR  [NEED TO KNOW]

1. Magnesium plug has to be removed

2. At least TWO binding sites of receptor must be occupied (not counting Mg²⁺)

3. Out of the 2 occupied, 1 of them MUST BE GLYCINE

What binding sites does Kainate receptor have?

Glutamate

STEPS TO ACTIVATE KAINATE RECEPTOR  

1. Bind glutamate to Kainate receptor

What binding sites does AMPA receptor have?

Glutamate and zinc

STEPS TO ACTIVATE AMPA RECEPTOR  

1. Bind glutamate and zinc to AMPA receptor

2. As long as one of them is active you can open the channel

WHAT IS THE PREDOMINANT INHIBITORY NEUROTRANSMITTER IN CNS?

GAMMA-AMINO BUTYRIC ACID (GABA)

GAMMA-AMINO BUTYRIC ACID (GABA)

☼ Derived from glutamate via glutamic acid decarboxylase (GAD)

glutamate

↓ GAD carboxylases

GABA

GAMMA-AMINO BUTYRIC ACID (GABA) TYPES

GABA_A

GABA_B

GABA_C

GABA_A RECEPTORS BINDING SITES

GABA

Neurosteroids

Barbiturates

Benzodiazepines

Ethanol

How to activate GABA_A Receptor?

Binding or activating any one of their sites is sufficient to activate the receptor

GABA_A are _____. Why?

Inhibitory; B/c when ion channel opens theres an influx of Cl- into the cell → cell membrane hyperpolarizes (becomes more (-))

PEPTIDE TRANSMITTERS FUNCTION

☼ Peptide transmitters are involved in just about every physiological function in the CNS, PNS, and periphery

2 Examples

• Opioid Peptides

• Substance P

OPIOID PEPTIDES

Endorphin, Enkephalin, Dynorphin

WHAT OPIOID PEPTIDES ARE FOUND IN CNS & PNS

Endorphin, Enkephalin, Dynorphin

OPIOID PEPTIDES MODULATION OF…

Reward, Pain, Respiration, GI motility

WHERE IS SUBSTANCE P FOUND?

☼ found in CNS and PNS

SUBSTANCE P MODULATION OF…

mood, pain, nausea, vomiting