Chapter 6: Neuronal Signaling (Part 3)

Purine Neurotransmitters

ATP and adenosine which act as neuromodulators

Brainstem

All the nerve fibers that relay signals between the forebrain, cerebellum, and spinal cord. Consisting of loosely arranged neuron cell bodies intermingled with bundles of axons

Amino acid neurotransmitters at excitatory synapses

Aspartate, Glutamate

Norepinephrine is found in

CNS and PNS but epi is found in PNS

Histamine

CNS neurotransmitter, hypothalamus, paracrine actions, peripheral system. Involved in allergic reactions, nerve sensitization, acid production in stomach

Serotonin

CNS neurotransmitter, made by enterochromaffin cells in gut and collected by platelets, in brain stem (1-2%)

ionotropic receptor increases

Cl- flux into the cell, resulting in hyperpolarization of the postsynaptic membrane.

Alzheimer's Disease

Degeneration of cholinergic neurons is associated with decreased amount of ACh in certain areas of brain and loss of postsynaptic neurons

Neuropeptides

Endogenous opioids, Substance P

Adrenergic Receptors

G protein coupled that are generally linked to second messenger signal transduction pathways, utilized by neurotransmitters Norepinphrine and Epinephrine

Amino acid neurotransmitters at inhibitory synapses

Glycine, GABA

Acetylcholine (ACh) is found in

PNS and CNS. Neurons that use ACh as primary neurotransmitter are cholinergic neurons

Functions of Serotonin

Regulating sleep, Emotions, Excessive serotonin release by gut increases motility causing diarrhea, Regulates cell growth, Vascular smooth muscle cell contraction

Substance P

Released by afferent neurons that relay sensory info into CNS. Known for pain sensation

Somatic

Single neuron between CNS and skeletal muscle cells, innervates skeletal muscle cells, lead only to muscle cell excitation

Blood-Brain Barrier

Substances in brain's capillaries are separated from extracellular space by continuous endothelium of capillary walls and thick basal lamina, least permeable ones in the body. Very selective, things that are highly lipid-soluble cross easily

Autonomic

Two neuron chain between CNS and effector organ. Innervates smooth and cardiac muscle, glands, GI neurons, not skeletal muscle cells, either inhibitory or excitatory

Hydrocephalus

accumulation of CSF in brain often caused by tumors, In newborns it results in enlargement of the head. In adults, it puts pressure on the brain and causes brain damage

excessive stimulation of AMPA and NMDA receptors causes

accumulation of toxic levels of intracellular Ca2+, this kills those neurons and causes them to rupture, the wave of damage progressively spreads

In cerebral cortex

basic afferent information is collected and processed into meaningful perceptual images, and control over systems that govern movement of skeletal muscles

hypothalamus

below the thalamus; contain cell groups and pathways that form master command center for neural and endocrine coordination; eating and drinking, reproduction

ischemic stroke

caused by the occlusion of cerebral arteries, usually by a blood clot that blocks an artery or by the rupture of an atherosclerotic plaque

pia mater

clings to the brain and contains a network of blood vessels

thalamus

collection of several large nuclei that serve as synaptic relay stations and important integrating centers for most inputs to cortex, and play a key role in general arousal, involved in focusing attention

limbic system

consisting of both gray and white matter, associated with learning, emotional experience and behavior, and wide variety of visceral and endocrine functions

Diencephalon

divided by narrow third cerebral ventricle, contains thalamus, hypothalamus, and epithalamus

Cerebrospinal Fluid (CSF)

extracellular fluid of the CNS and it is secreted by ependymal cells of choroid plexus. It circulates through subarachnoid space and ventricles, reabsorbed by arachnoidvilli

subarachnoid space

filled with CSF and contains the largest blood vessels serving the brain

pyramidal cells

form major output cells of the cortex, sending their axons to other parts of the cortex and other parts of CNS

subcortical nuclei

heterogeneous groups of gray matter that lie deep within the cerebral hemispheres, contain basal nuclei

Cerebellum

important center for coordinating movements and for controlling posture and balance, implicated in some forms of learning.

Nicotinic receptors in brain are

important in cognitive functions and behavior. Presence of nicotinic receptors in reward pathways of brain explains why tobacco are among most highly addictive substances

Meningitis

inflammation of meninges and is serious threat to brain since bacterial or viral meningitis can spread to the CNS

Drugs act by

interfering with or stimulating normal processes involved in neurotransmitter synthesis, storage, and release, and receptor activation

Nonpyramidal cells

involved in receiving inputs into cortex and in local processing of information

Receptors for neurotransmitters affect

ion channels that directly affect excitation or inhibition of postsynaptic cell, this operates within milliseconds

If Cl- channels open

it moves into cell

If K+ channels open

it moves out of cell

Parkinson's Disease

loss of dopamine-releasing neurons in the substantia nigra. Symptoms include persistent tremors, head nodding, forward bent walking posture, shuffling gait, stiff facial expressions, slow in initiating movement

Normal function of glycinergic neurons essential for

maintaining a balance of excitatory and inhibitory activity in spinal cord integrating centers that regulate skeletal muscle contraction

GABA

major inhibitory neurotransmitter, modified form of glutamate

Glycine

major neurotransmitter released from inhibitory interneurons in the spinal cord and brainstem. It binds to ionotropic receptors on postsynaptic cells that allow Cl- to enter

NMDA Receptors

mediate excitotoxicity, injury or death of some brain cells (ex. blocked or ruptured blood vessels) rapidly spreads to adjacent regions

Receptors for neuromodulators can change

metabolic processes in neurons, alterations in enzyme activity, DNA transcription, protein synthesis. Tend to be associated with slower events such as learning, development, motivational states, and some sensory or motor activities

ACh acts as

muscarinic (G protein coupled) or nicotinic (ion channels) receptors found at neuromuscular junctions of skeletal muscles

cerebellum receives information from

muscles and joints, skin, eyes and ears, viscera, and the parts of the brain involved in control of movement

parasympathetic division

neurotransmitter is ACh at long preganglionic and short postganglionic synapses, "rest-or-digest"

Sympathetic division

neurotransmitters are ACh at short preganglionic synapse and NE and Epi at long postganglionic synapse, "fight-or-flight"

Biogenic amine

neurotransmitters made from amino acids; catecholamines, dopamine, norepinephrine, epinephrine (made from tyrosine)

Basal nuclei

play an important role in controlling movement and posture and in more complex aspects of behavior.

Neuromodulators modify

presynaptic and the postsynaptic cell's response to specific neurotransmitters, amplifying or dampening effectiveness of synaptic activity

ACh is produced in

presynaptic axon by the enzyme choline acetyl transferase (CAT)

Glutamate

primary neurotransmitter at 50 percent of excitatory synapses in the CNS. Two types: Metabotropic glutamate receptors (G protein coupled receptors), Ionotropic glutamate receptors

Gas Neurotransmitters

produced by enzymes in axon terminals (in response to Ca2+ entry), diffuse from their sites of origin into intracellular fluid of other neurons or effector cells where they bind to and activate proteins (ex. Nitric oxide)

cerebral cortex are composed of

pyramidal cells and nonpyramidal cells. integrating area of nervous system.

Functions of Brainstem

receives and integrates input from all regions of CNS; involved in motor functions, cardiovascular and respiratory control, and mechanisms that regulate sleep and wakefulness and focus of attention.

GABA neurons in brain are

small interneurons that dampen activity within neural circuits. Postsynaptically, GABA may bind to ionotropic or metabotropic receptors

epithalamus

small mass of tissue that includes the pineal gland, which has role in regulating biological rhythms

Cerebrovascular Accidents

stroke, can be caused by decreased blood supply or hemorrhage

When glutamate-containing cells die

their membranes rupture, flood of glutamate excessively stimulates AMPA and NMDA receptors on nearby neurons

Peripheral Nervous System

transmit signals between CNS and receptors and effectors; has 43 pairs of nerves: 12 pairs of cranial nerves and 31 pairs that connect with spinal cord

Overstimulation of ACh receptors causes

uncontrolled muscle contractions, ultimately leading to receptor desensitization and paralysis

hemorrhagic stroke

where blood vessel has ruptured

General factors that determine synaptic strength

• Area of synaptic contact • Enzymatic destruction of neurotransmitter • Geometry of diffusion path • Neurotransmitter reuptake

Presynaptic Factors that determine Synaptic Strength

• Availability of neurotransmitter • Axon terminal membrane potential • Axon terminal calcium ion concentration • Activation of membrane receptors on presynaptic terminal • Drugs and diseases

Postsynaptic factors that determine Synaptic Strength

• Immediate past history of electrical state of postsynaptic membrane • effects of other neurotansmitters/neuromodulators • Up-/down-regulation and desensitization of receptors • Drugs and diseases

Excitatory Synapses and EPSPs

• Neurotransmitter binding opens chemically gated channels • Na+ influx greater than K+ efflux net depolarization called EPSP • EPSP help trigger AP if EPSP is of threshold strength

Inhibitory Synapses and IPSPs

• Reduces postsynaptic neuron's ability to produce action potential - Makes membrane more permeable to K+ or Cl- - neurotransmitter hyperpolarizes cell • Inner surface of membrane becomes more negative • AP less likely to be generated