M1s6 Physiological And Pharmacological Aspects Of The Central Nervous System Flashcards
Cerebral cortex (cerebrum)
Top portion of brain, lays like blanket covering it
-largest part of the brain
-rich in neurons
-function: sensory and motor coordination, mental processes, intelligence, memory, vision, judgement, thought, speech, emotions and consciousness
-neurons here can be stimulated (excited) or depressed (inhibited) by drugs
Lambic system
Towards middle of brain, kinda wraps around middle part towards inner
-integrates memory, ‘em option and rewards
-this area of brain together with hypothalamus controls emotion and behaviour
-contains the dopaminergic reward centres, which are targets for commonly misused drugs and are associated with addiction
What is the functional unit of the brain and explain it
Neuron
-is a nerve capable of generating and transmitting electrical signals
-brain contains about 90 billion neurons that differ from each other in shape and size
-new neurons generated continuously through process called neurogenesis
-connection between neurons is constantly being reshaped through what is known as neuroplasticity
Structure of the neuron
*photo in goodnotes
-made of 3 important structures
Dendrites:
-usually short
-can have highly complex branching patterns
-function as receiving antennae for incoming information and accept information through receptors located on the dendritic membranes
-upon receiving this information from another cell, an electric current this generated and directed down neuron
-little hair coming off head/cell body of neuron
Cell body:
-aka soma
-largest part of neuron
-contains a nucleus and surrounding cytoplasm
-cytoplasm contains abundant pre-packed neurotransmitters which can be secreted
-circle head like man connecting dendrites and axon
Axon:
-single fibre that extends from the cell body and ends at the synapse
-axon continues to carry incoming information away from the dendrites and cell body by way of electrical pulses
-information is then passed on to subsequent neurons
-long pieced together tail off cell body
Synapse
-electrical impulse has to be somehow communicated across the junction of one neuron to another neuron if it is to produce further effect
-junction between two neurons is called synapse, and is the area where one neuron’s axon ended and another neuron’s dendrite or cell body begins
Synaptic transmission
-the passage of a signal from one neuron to another is called synaptic transmission or neurotransmission
-synaptic transmission very rapid
-usually chemical in nature meaning a substance is quickly released that activates the next neuron
-endogenous chemicals that transit a signal between 2 neurons are called neurotransmitters
-usually one synapse connects two neurons
However a single neuron can make synaptic connections with many other neurons
Detailed synaptic transmission and termination of response
-electrical impulse will travel down the axon of neuron
-when electrical impulse reaches the end of the presynaptic neuron, it causes the vesicles, which contain neurotransmitters to fuse with the presynaptic membrane, thereby releasing the neurotransmitters into the synaptic cleft
-neurotransmitters will then diffuse across the synaptic cleft and bind with receptors on the postsynaptic membrane
-activation of these receptors cause a change in the permeability of the membrane, allowing ions such as calcium to move into the postsynaptic neuron
-change in electrical activity of the membrane thereby generating an action potential or electrical impulse, which will then travel down that neuron’s axon
-process continues until the neuronal signal reaches the target organ, causing an effect
-now continuous presence of neurotransmitter in the synaptic cleft would prevent other nerve impulses from being communicated, effectively rendering the neuron useless
-as such neurotransmitter has to be removed, which can occur by one of the three mechanisms
1. Neurotransmitters can be taken back into the presynaptic neuron through transporters. Norepinephrine is removed from the synaptic cleft in this fashion
2. The neurotransmitter can be broken down by enzymes in synaptic cleft. This is the case for acetylcholine, which is broken down by acetylcholinesterase into acetate and choline
3. Neurotransmitter can be taken up into adjacent glial cells which are cells that support neurons. This process occurs for glutamate
Once neurotransmitters have been removed from the synaptic cleft, the postsynaptic membrane is able to repolarize and prepare for the next neuronal impulse
*see goodnotes for image
Axon
Electrical impulses travel through this structure to reach the end of the presynaptic neuron
Plays a role in one of the mechanisms through which neurotransmitters can be removed from the synaptic cleft
Glial cells
Endogenous chemical messengers of the nervous system that transmit electrical signals from nerve cells to target cells
Neurotransmitters
Transport and release neurotransmitters into the synaptic cleft by fusing with the presynaptic membrane
Vesicles
Activating them causes ions to move into the postsynaptic neuron by changing the permeability of the membrane
Receptors
Drugs effect on synaptic transmission
-synapse can be a target site for many drugs
-some drugs interrupt synaptic transition where others enchance or facilitate it thereby modifying the activity of the brain
Neurotransmitters and receptors
-in human body hundred of different Ypres of receptors exist for a large number of neurotransmitters
*please look at organic CHEM structure of each on our goodnotes
Glutamate
-primary excitatory neurotransmitter in the CNS
-found in almost all neurons
-acts on a family of receptors called glutamatergic receptors
-neurons that release glutamate, termed glutamatergic neurons are very important
Serotonin
-In CNS, hyperactivity of serotonergic system is involved in anxiety and hypo-activity has been implicated in depression
-some classes of CNS stimulants act by increasing serotonin at the synapse
Catecholamines
Dopamine and norepinephrine (aka noradrenaline) are two catecholamines that are similar in structure
Dopamine: dopaminergic pathways involves in control of some hormonal systems, motor coordination and motivation and reward. Alternations in these dopamine-mediated motivation and reward systems are though to be involved in addition.
Norepinephrine: can bind to large number of receptor types but two main classes are alpha and beta. Activation of these receptors usually leads to excitation of the cell. This pathway is targeted by some of the CNS stimulants.
Acetylcholine
-Produces an excitatory response in CNS
-two types of receptors bind acetylcholine and they are termed cholinergic receptors
Nicotinic receptors: found in certain regions of brain and can be stimulated by acetylcholine or nicotine
Muscarinic receptors: found in many regions of the brain and involved in learning, memory and cognitive function. These receptors can be stimulated by acetylcholine or muscarine, drugs that block the action of acetylcholine at these receptors produce amnesia. Loss of these cholinergic neurons is though to be associated with Alzheimer’s disease
GABA
Gamma-amino butryic acid primary inhibitory neurotransmitter in CNS
-neurons that release GABA (GABAergic neurons) and GABA receptors are found in high concentrations in the cerebral cortex, among other areas. A number of CNS depressants (ex benzodiazepines) enchance GABA receptor function
Opioid Peptides
Three main classes of endogenous opioid peptides: enkephalins, endorphins, dynorphins. Have varying degrees of selectivity for the three opioid receptors: my, delta, and kappa. All opioids interact with these receptors
Receptors-neurotransmitter
Glutamatergic receptors-glutamate
GABAergic receptors-GABA
Nicotinic and muscarinic receptors-acetylcholine
Alpha and beta receptors-norepinephrine
