Psychoactive Substances CH 3

Neuraxis

an imaginary line draw through the center of the length of the central nervous system, from the bottom of the spinal cord to the front of the forebrain

Anterior

Near/towards the head

Posterior

Near/towards the tail/feet

Rostral

• another word for anterior

• toward the front of the face

  • “toward the beak”

Caudal

• another word for posterior

• away from the front of the face

  • “toward the tail”

Dorsal

toward the back or top of the head

Ventral

• toward the belly

  • toward the bottom of the skull of the front surface of the body

lateral

• away from the middle

• toward the side of the body

medial

• closer to the middle

• toward the middle of the body

ipsilateral

refers to structures on the same side of the body

contralateral

refers to structures on opposite sides of the body

Cross section

with respect to the CNS, a slice taken at right angles to the neuraxis

Frontal/coronal section

a slice through the brain parallel to the forehead

Horizontal/transverse section

a slice through the brain parallel to the ground

sagittal section

• a slice through the brain parallel to the neuraxis and perpendicular to the ground

• divides the brain into left and right sections

midsagittal plane

• the plane through the neuraxis perpendicular to the ground

• divides the brain into 2 symmetrical halves

Describe the essential blood supply in the brain

• brain gets 20% of blood flow

• brain cannot store energy

• needs oxygen to extract energy

• disruption of blood flow results in unconsciousness in 6 seconds

What makes up the central nervous system (CNS)?

Brain and spinal cord

What makes up the peripheral nervous system (PNS)?

Nerves and peripheral ganglia

describe the meninges in the PNS

• dura mater and pia mater fuse

  • no arachnoid membrane space

meninges

the 3 layers of tissue that encase the CNS:

• dura mater

• arachnoid mater

• pia mater

dura mater

• outermost layer of meninges

• tough and flexible

arachnoid membrane

• the middle layer of the meninges

  • located between the dura mater and pia mater

pia mater

• the inner most later of meninges that clings to the surface of the brain

• thin and delicate

subarachnoid space

• the fluid-filled space that cushions the brain

• located between the arachnoid membrane and the pia mater

cerebrospinal fluid (CSF)

• a clear fluid, similar to blood plasma

• fills the ventricular system of the brain and the subarachnoid space surrounding the brain and spinal cord

ventricle

• one of the hollow spaces within the brain

• filled with cerebrospinal fluid

lateral ventricle

one of the 2 ventricles located in the center of the telencephalon

third ventricle

the ventricle located in the center of the diencephalon

massa intermedia

bridge of neural tissue through the 3rd ventricle

cerebral aqueduct

• a narrow tube interconnecting the third and fourth ventricles of the brain

• located in the center of the mesencephalon

fourth ventricle

the ventricle within the center of the metencephalon (between the cerebellum and the dorsal pons)

choroid plexus

• the highly vascular tissue that protrudes into the ventricles

• produces cerebrospinal fluid

  • about 125 mL with a ½ life of 3 hours

  • reabsorbes CSF into the blood stream

What ventricle(s) make up the forebrain?

lateral and third ventricles

What makes up the telencephalon subdivision of the lateral ventricle?

• cerebral cortex

• basal ganglia

• limbic system

What makes up the diencephalon subdivision of the third ventricle?

thalamus and hypothalamus

What ventricle(s) make up the midbrain?

cerebral aqueduct

What makes up the mesencephalon subdivision of the cerebral aqueduct?

tectum and tegmentum

What ventricle(s) make up the hindbrain?

fourth ventricle

What makes up the metencephalon subdivision of the fourth ventricle?

cerebellum and pons

What makes up the myelenceohalon subdivision of the hindbrain?

medulla oblongata

cerebral cortex

• the outermost layer of gray matter of the cerebral hemispheres

• 3 mm thick

• corrected for body size

  • it is largest in humans than any other species

• develops from the inside out

apoptosis

death of a cell caused by a chemical signal that activates a genetic mechanism inside the cell

neurogenesis

• the production of new neurons

• occurs in the adult brain

• demonstrated in the olfactory bulb and hippocampus

sulci

• small grooves

• the valley between mountains

fissure

large groove/sulci

gyri

• raised ridges

• the mountains between valleys

longitudinal fissure

divides the left and right hemispheres

central sulcus

separates the frontal and parietal lobes

lateral sulcus/fissure (AKA Sylvian fissure)

divides the frontal and parietal lobes superiorly from the temporal lobe inferiorly

parieto-occupital sulcus

separates the parietal and occipital lobe

Describe the geography of the frontal lobe

• largest of all lobes

• ends at the coronal sulcus

What is within the frontal lobe?

• motor cortex (most posterior part) → controls voluntary movement

• anterior cingulate cortex - default mode network (DMN) - posterior cingulate cortex

What are the functions of the frontal lobe?

• decision making

• future-planning

• personality

• judgement

• motor movement

• impulse control

Describe the default mode network (DMN)

• where your personality is stored

• this area lights up when you describe yourself as an addict

• when you are hallucinating, you imagine who you are and start to build new connections (neural plasticity)

  • when you exit this state, you are a new person

What are the functions of the parietal lobe?

Spacial awareness, etc.

What are the functions of the temporal lobe?

auditory processing, memory formation, etc.

What are the functions of the occipital lobe?

visual processing

What are the structures of the limbic system?

• limbic cortex

• hippocampus

• amygdala

• fornix

• mammillary bodies

What is the function of the limbic system?

Emotion processing

Describe the Basal Ganglia

• subcortical nuclei involved in movement

  • responsible for involuntary movements/reflexes

    • develop reflexes from habitual voluntary movement to free up space in the motor cortex

  • compulsive behaviors live here

Define compulsive

consistent habitual habits without control

Describe the thalamus

• relays all senses EXCEPT olfactory

• psychedelics can disrupt this, causing hallucinations

What are the functions of the hypothalamus?

• regulate autonomic nervous system

• regulates endocrine system by releasing hormones

• biological drive structure

  • feeding, fighting, fleeing, fornicating

  • regulates food/water intake

  • temperature regulation

  • sex drive

How does MDMA/ecstasy affect the hypothalamus?

• tells the brain region that you’re super hot

• makes one super horny

• makes one feel super thirsty

How does THC affect the hypothalamus?

increases appetite

How does cocaine/amphetamines/methamphetamines affect the hypothalamus?

appetite suppresent

All substances that have abuse potential activates which area?

The tegmentum of the hindbrain

Describe the ventral tegmental area (VTA)

• a cluster of nuclei that projects to the nucleus accumbens

• this area is very active when one is abusing substances and dopamine neurons are activated

• reinforces the removal of pain (negative reinforcement)

What would happen if you were to lesion/ablation the VTA in a rat study were they are addicted to some drug?

• the rat would no longer eat, drink, have sex, etc. because there is no reward

  • no motivation without reward

Nucleus accumbens

reward center

What are the functions of the cerebellum?

• standing

• walking

• coordinated movements

• balance

• refinement center

• equilibrium

What is an example of a drug disrupting the neural activity of the cerebellum?

Stumbling on alcohol

How does IPSP drugs affect motor movement?

It causes a breakdown, leading to decreased motor control

How does EPSP drugs affect motor movement?

It causes an enhancement, leading to increased motor control

Describe the function of the pons

• involved in alertness/enrichment

• controls the circadian rhythm (sleep and arousal)

• controls light sensitivity

What happens to the pons while on a psychoactive substance (specifically amphetamines for example0?

• disregulates norepinephrine response

  • norepinephrine release in the dense nuclei increases indirectly

Describe the functions of the medulla oblongata

• regulates the autonomic nervous system and skeletal muscle

• controls vital functions such as breathing, heart rate, blood pressure, digestion, etc

• where the declaration of death is determined

What happens when you take 2 drugs of the same class (ex: sleeping pills and alcohol [2 CNS depressants])?

• the synergistic affects will enhance each other

• shuts down the medulla oblongata

  • doesn’t matter if it is an EPSP drug and an IPSP drug