Biology 115, Lecture12:
Neurons and the Nervous System II
T. Irving 1/21/99; Revised A.Howard 2/21/00
Goals of this section:
- Describe general anatomy of the brain giving functions
for each part
- Name the lobes of the cerebrum and give a function
for each
- Describe the effects of drug action in general and
discuss the effects of alcohol, marijuana, cocaine and heroin in this context.
Central Nervous System
- Nerves in the CNS are protected by three layers of membranes called
meninges (hence meningitis)
- Spaces between membranes filled with cerebrospinal fluid which protects
neuron from physical shocks
- Spaces in brain called ventricles also contain cerebrospinal fluid
Spinal cord
- central canal: contains cerebrospinal fluid
- "gray matter" consists of unmyelinated fibers and cell bodies:
centrally located
- White matter consists of long fibers of myelinated interneurons running
up and down the spinal cord connecting the spinal cord to the brain.
- Axons of sensory neurons in dorsal "horns"
- Dendrites and cell bodies of motor neurons found in the ventral "horns"
of gray matter
- Dorsal tracts (white matter) carry information to the brain
- Ventral tracts (white matter) carry information from the brain
- These tracts cross over so that right side of brain controls left side
of body & vice versa.
- functions:
- handles reflex actions: center for many reflex arcs
- connects brain and spinal nerves
- two-way conduction path for nerve impulses
Brain: the divisions
- brain stem
- medulla oblongata
- contains "vital centers" for controlling heartbeat, breathing
vasoconstriction
- reflexes such as vomiting, coughing, sneezing, hiccoughing, and swallowing.
- pons
- Bridge between cerebellum and rest of CNS
- aids medulla in controlling breathing rate, reflex head movements
- midbrain
- reflex centers for vision, hearing and feeling
- connects lower brain stem, cerebrum
- cerebellum
- Surface gray matter, interior white
- Muscle coordination, muscle tone & posture
- Receives input from inner ear (body position)
- and stimulates muscle to maintain balance
- diencephalon
- hypothalamus
- control center for maintaining homeostasis
- hunger, sleep, thirst, body temperature, water balance and blood pressure
- Controls pituitary gland
- Connection between nervous and endocrine systems
- thalamus: routing center for all sensory input except smell
- cerebrum
- Responsible for consciousness
- Cerebral cortex is gray matter containing cell bodies and unmyelinated
short fibers
- Left and right cerebral hemispheres
- Each hemisphere contains frontal, parietal, temporal and occipital
lobes
- Various areas of the brain have been associate with various functions.
- Basal ganglia made up of gray matter between the cerebrum and thalamus
Implicated in voluntary muscle actions
- Left half of brain "verbal". right half "visual"
- Two halves connected by corpus collosum
EEG
- electrical activity in the brain can be picked up by electrodes attached
to the scalp
- Can be used as a diagnostic tool for cerebral activity
- Irregularities associated with epilepsy, brain tumors
- Lack of electrical activity = "brain death"
Limbic System
- Neural pathways lying just below the cerebral cortex, connecting frontal
& temporal lobes, thalamus, hypothalamus and basal ganglia.
- Sensations of pain, pleasure rage, affection, sex drive (libido), fear,
sorrow.
- Also involved in learning and memory
Higher Mental Functions
- Memory
- may involve increasing the number of synapses and forgetting decreasing
- Short term memory: mostly occurs in prefrontal lobe
- Long term memories involve ACh stimulating sensory areas where memories
are stored: semantic, episodic, skill memory
- Hippocampus (structure in temporal lobe) and amygdala involved
- Long-term potentiation:
enhanced response of synapses; can lead to excitotoxicty via glutamate
- Alzheimer Disease: gradual loss of memory, culminating in inability
to function
- Language and Speech
- depends on semantic memory
- Broca's area involved in speech; Wernicke's area involved in comprehension
- left hemisphere only
Neurological Drugs
- Generally affect the limbic system
- Usually promote or decrease the effect of a particular neurotransmitter
- Any of these may be abused
Drug abuse:
- Psychological & physical dependence
- In physical dependence, person becomes tolerant
- Withdrawal symptoms when drug is not available: e.g. Nicotine
- Stimulative effects comes from mimicking ACh
- addictive, carcinogen, respiratory problems
Specific drugs of abuse:
Alcohol
- Alcohol probably produces feeling of euphoria by affecting gamma-aminobutyric
acid (a neurotransmitter) receptors so that GABA's inhibitory effect is
enhanced.
- Alcohol is a depressant
- 20% absorbed in stomach,rest in intestines
- Bad health effects in young people mainly accidents
- Liver damage begins immediately and continues with heavy alcohol use
- Disrupts Krebs cycle, acetyl CoA accumulates causing fatty deposits
in liver which later turns to scar tissue
- Final stage liver cells die and turn orange - Cirrhosis of the liver
- Heavy drinking can increase incidence of throat cancer or high blood
pressure
- Short Term Effects of Alcohol
- Effects of drinking occurs in stages as blood alcohol concentration
increases
- 005% relaxed state, judgment slightly impaired (mainly effects frontal
lobe)
- 0.08% everyday stress lessened
- 0.1% Movements and speech become clumsy( speech, vision coordination
centers)
- 0.2% very drunk, loud emotionally unstable (control of large muscle
s goes)
- 0.4% passed out
- 0.5% coma and or death
Nicotine
- Causes neurons to release dopamine (neurotransmitter)
- Has acetylcholine-like activity in PNS
- Gives rise to physical and psychological dependence
- Many non-CNS-related effects
Tetrahydrocannabinol
- Marijuana, hashish, variants
- hallucinogen
- psychological dependence may occur with heavy use
- cannabis intoxication may result from very heavy use
- hallucinations, anxiety depression, paranoia, other psychotic symptoms
- Smoke contains carcinogens--same problems as tobacco smoking.
- Effects may involve interaction with serotonin receptors much like
LSD, peyote and mescaline; serotonin is an excitatory neurotransmitter
in the brain
Cocaine
- Heavy doses cause massive release of NE & and inhibits reuptake
of dopamine in sympathetic system
- causes "rush"
- Followed by depression in extreme form a "crash"
- Overdoses can result in seizures and cardiac arrest
- Tolerance and addiction
Heroin & other opiates
- Most are alkaloids derive from opium poppy
- Bind to endorphin receptors - prevents releasing of neurotransmitters
responsible for pain
- Promotes tranquil feeling by binding to neurons that join spinal cord
to limbic system
Methamphetamine ("ice")
- Variant of amphetamine can be synthesized in rudimentary laboratories
- Effects similar to cocaine but longer lasting