Neuroscience Unit 2

cocaine

* extracted from coca plant
* injected, snorted, smoked (crack)
* stimulant and sympathomimetic

sympathomimetic

activates sympathetic nervous system; causing increased alertness, euphoria, less appetite

rush

when cocaine is inhaled or injected, it produces a very rapid euphoria

letdown

after taking a drug like cocaine, feeling of well being lasts for 10-20min, then a mild depression follows

cocaine acts by

* blocking DA transporter
* increasing synaptic levels of DA
* stimulated reward pathway and increases the release of DA in the nucleus accumbens, leading to euphoria

coke rush

euphoria develops very quickly, results in a continuous cycle of cocaine use

for a more intense cocaine rush...

users switch from intranasal route to injection

cocaine high doses symptoms

* intense anxiety
* toxic paranoid psychosis
* stereotypes, repetitive behavior (taking apart and putting objects together)
* convulsions, strokes, lethal cardiorespiratory arrest, severe heart damage

symptom of cocaine induced psychosis

sensation of bugs crawling under the skin

addiction to cocaine can lead to

* developing psychiatric disorders
* car accidents when mixed with alcohol
* loss of gray matter

most cocaine users ...

are dependent on other drugs too (alcohol and heroin)

cocaethylene

activated by cocaine and alcohol being taken together; potentiates euphoric effects of cocaine; increases dual dependency and withdrawal effects

speedball

injecting cocaine and heroin together

why does cocaine addiction sometimes lead to purple scars

most cocaine is contaminated with levamisole (a deworming drug for lifestock) to increase potency, leading to purple scarring

sensory-motor system two parts

sensory and motor pathway

sensory pathway

carries sensory information from all parts of the body to the brain (sensory cortex)

motor pathway

brain integrates and processes sensory information and sends back messages from the motor cortex to the muscles of the body to respond to these stimuli

sensory nervous system

a part of the nervous system responsible for processing sensory information

sensory system contains

\-sensory neurons (including sensory receptor cells)

\-neural pathways

\-parts of the brain

common sensory systems are those for

vision, hearing, touch, taste, smell, and balance

what makes up sensory systems

sensory organs

receptor cells

specialized cells present in sense organs

receptor cells functions

respond to energy from stimuli and convert the energy into a change in the electrical potential across the membrane; focus on key stimuli

receptor cells structure

determines what energy they respond to

energy

can be in the form of light, sight, sound

receptor cells convert energy to

electrical signal, neural activity, AP; the language of the nervous system

stimuli

a physical event triggering sensory response

modality

a way of sensing the stimuli

labeled lines

action potentials for each sense is carried in different nerve tract

steps leading to sensory tranduction

1. stimuli energy is detected by receptors
2. causes a local change in the resting membrane potential of the receptor (receptor potential)

sensory transduction

process in which receptor cells convert energy in a stimulus into a change in the electrical potential across its membrane

somatosensory systems

regulated by receptor cells throughout the body; measure different sensory modalities

somatosensory system sensations

can be external stimuli, internal stimuli, and a sense of where the body is in space

skin receptors

discriminative touch (shape of the object), deep pressure, vibration, tickle, pain, itch, smoothness, wetness; depending on the location, density of receptors vary

types of receptor cells in the skin

* meissner's (tactile) corpuscle
* pacinian (lamellated) corpuscle
* ruffini corpuscle
* Merkel's disc
* free nerve endings

meissner's corpuscles and Merkel's discs functions

detects light touch (forms of object)

Pacinian (lamellated) corpuscles functions

detect pressure and vibration (textures)

ruffini corpuscles functions

stretching of skin

free nerve endings function

pain, temperature

pacinian corpuscle

* inner most layer of skin
* nerve ending stimulated and stretching occurs
* stretching results in opening of Na+ channels and receptor potential is generated

AP in pacinian corpuscle

travel through sensory nerves to the spinal cord and then to the brain

in pacinian corpuslce, size of receptor potential is

directly proportional to the strength of the stimulus

path of touch information

from its own pathway from the sensory surface, to the spinal cord, to the brain

reflex

mediated by spinal cord; simple, automatic, unlearned response to a specific stimuli

non-reflex

information is passed from the dorsal part of the spinal cord to the brain (ascending) via the dorsal column pathway/tract

ascending tract

information is carried upwards to the brain

dorsal column pathway to the brain

1. axons from sensory surface (starts)
2. spinal cord
3. medulla
4. midbrain
5. thalamus
6. primary somatosensory cortex (terminates)

sensory cortex regions

primary sensory cortex and nonprimary sensory cortex

primary sensory cortex includes

primary auditory cortex, primary somatosensory cortex

primary somatosensory cortex (S1 region)

located in the postcentral gyrus, gets touch information from contralateral side

central sulcus

separates frontal lobe from parietal lobe, and precentral gyrus from postcentral gyrus

S1 region is arranged as a

body map

Homunculus

shows body surface with each area drawn in proportion to the size of its representation in the S1 region

how can S1 regions change/show plasticity

with experience or due to the amputation of limbs

how is S1 region changed when a limb is amputated

other cortical areas take over the area of the missing limb

musicians ex of changed S1 region

have larger cortical representations of left fingers

pain

an unpleasant and emotional experience associated with tissue damage

how do we respond to pain

act to minimize risk to our bodies or socially communicate (ex. scream) our pain to get help or warn others

nociceptor

pain receptor, sensitive to both pain and temperature

nociceptors located in

skin, cornea, joints, muscles, internal organs

types of nociceptors

vanilloid receptor 1, TRPM3 receptor

vanilloid receptor 1

located on unmyelinated c fibers, detects rising temperature by eating capsaicin; dull pain following burning

TRPM3 receptor

located on A delta fibers (myelinated) detects even higher temperature and initial sharp pain following burning

what stimulates nociceptors

tissue injuries releases serotonin, histamine, substance P; stimulation can also cause local inflammation

spinothalamic pathway

information about pain is transmitted to the brain via sensory neurons in the spinal cord

pain fibers within the spinal cord...

* cross over, go to the opposite side
* release glutamate and substance P which enhance pain signals
* axons then ascent upwards to the brain

spinothalamic pathway to the brain

1. spinal cord (crossing over)
2. medulla
3. pons
4. midbrain (periaqueductal gray)
5. thalamus
6. S1
7. cingulate cortex

types of pain

short term, long term/chronic, neuropathic pain

short term pain

withdrawal from source (reflex action) preventing further tissue damage; biologically useful

long term or chronic pain

lasts more than 3 months; we sleep, restrict movement, try to recuperate (ex. back pain, arthritis)

neuropathic pain

sensations of pain felt after healing of the injury (ex. phantom limb)

congenital insensitivity to pain (CIP)

condition where people do not feel pain

CIP cause

a mutation of the gene SCN9A leads to absence of sodium channels on nocicpetors; sensory information about pain is not transmitted to the brain

different ways to control pain

analgesic drugs, electrical stimulation, placebos, acupuncture

morphine

* opiate drug extracted from poppy plant
* reduces pain by binding to existing mu receptors in the brain
* taken orally, injected, inhaled, or directly injected into the spinal cord (epidural)

peptides/opioids

\-endorphins

\-enkephalin, dynorphin (delata, kappa, mu)

\-anandamide (CB1 and CB2)

which parts of the brain have a lot of delta, kappa, or mu receptors

periaqueductal gray region (PAG) of midbrain and spinal cord

narcan or naloxone

antagonist at mu receptors used to reverse the effects of morphine

gate control theory

spinal nerves act as gates allowing or preventing pain to reach the brain; consistently open gates cause chronic pain

analgesics

pain relievers; shut the gates

exogenous painkillers

\-opiates

\-morphine, fetanyl, codeine (mu)

\-cannabis (CB1)

acetaminophen

tylenol; does not bind to receptors but reduces pain by blocking 2 enzymes: COX-1 and COX-2; inhibits postaglandin synthesis

COX enzymes

make prostaglandins (PG) from arachidonic acid

prostaglandins

cause pain

primary sensory cortex

receives and integrates information, then sends it to the primary motor cortex

primary motor cortex

receive messages from primary sensory cortex and other associated regions, converts them into responses sent via motor neurons in descending tracts to the spinal cord

motor cortex is in the

frontal lobe

motor system

information goes from spinal cord to different muscles; muscles contract and cause movements

muscles of the head

directly controlled by the brain via cranial nerves; does not involve the spinal cord

neuromuscular junction

the junction between a muscle fiber and the motor unit it supplies

muscle cell is also called a

fiber

an axon terminal branches to

one muscle fiber

motor unit

all the connections of the motor axon terminals with the muscle fibers

muscle movements

* Ach is released at NMJ
* binds to nicotinic receptors
* causes muscle contractions and muscle movements

types of behavioral changes

reflex, movement, act

movements

simple, single relocation of a body part due to a brief muscle contraction

acts

complex behavior such as walking, speaking in a sentence, getting dressed; due to a series of muscle contractions; need a motor plan

motor plan

plan for a series of muscle contractions established in the nervous system before the act happens; motor nerves are involved in preparation and execution of motor plan

electromyography

measures muscle activity

neuromuscular system hierarchy

\-skeletal system (bones and muscles)

\-spinal cord

\-cerebellum, basal ganglia

\-MI region

\-nonprimary motor cortex