2.1 Physiological And Pharmacological Aspects Of The CNS

Question 1

Basic functions of the nervous system are to

Answer 1

1. Recognize - identify changes in the internal and external environment. For example, a change in the external temperature (28 or 0)
2. Process and integrate - perceive the changes in the environment. For example, the body feels hot or cold.
3. React - produce a response or an action to the changes in the environment. For example, the body will sweat or shiver.

Question 2

Divisions of the nervous system

Answer 2

Central nervous system - brain, spinal cord

Peripheral nervous system - everything else

Question 3

The brain

Answer 3

• receives and processes information
• initiate a response
• stores memory
• generates thoughts and emotion

Question 4

The spinal cord

Answer 4

• carries sensory information from the skin, muscles, joints, and internal organs to the brain
• Controls motor out flow to the muscles
• Controls sensory input (pain sensations)
• Controls reflex activity (breathing)

Question 5

Three parts of the brain

Answer 5

The forebrain, the midbrain, and the hindbrain.

Question 6

The forebrain - cerebral cortex (cerebrum)

Answer 6

Largest part of the brain. Richard nerve cells. Functions are sensory and motor coordination, mental processes, intelligence, memory, vision, judgment, thought, speech, emotions, and consciousness. Can be stimulated or depressed by drugs.

Question 7

The forebrain - thalamus

Answer 7

• release centre from which impulses are transmitted to the cerebral cortex. Function is to coordinate and filter incoming signals. It is also involved in the appreciation of painful sensation.

Question 8

The forebrain- hypothalamus

Answer 8

• located near the base of the skull
• Controls the involuntary functions of the body that are necessary for living like regulation of heart, blood pressure, body temperature, and metabolism
• Controls feeding, drinking, sexual, and emotional responses
• Neurons produce substances called releasing factors which travel to the pituitary gland and modify this gland

Question 9

The forebrain - limbic system

Answer 9

• closely associated with the hypothalamus
• integrates memory, emotion and reward.
• together with the hypothalamus, controls emotion and behaviour
• contains the dopaminergic reward centers, which are targets for drugs of abuse

Question 10

The forebrain - pituitary

Answer 10

• small gland located at the base of the brain that secretes hormones
• Act on peripheral tissues, and are involved in the control of growth, behaviour, and metabolism

Question 11

The midbrain

Answer 11

• Area that links the forebrain with the hindbrain

- relay centre for visual I an auditory ear stimuli or signals

Question 12

The hindbrain

Answer 12

• consist of the pons, the medulla, and the cerebellum.

Question 13

Pons

Answer 13

• connects the midbrain to the medulla and cerebellum

- involved in conducting signals from the cerebral cortex down to the medulla and cerebellum

Question 14

Medulla (the bulb)

Answer 14

• site of origin of money cranial nerves
• where regulation of respiration, heart rate, blood pressure and some involuntary activity occurs.
• drugs which depress respiration and blood pressure will do so by depressing the medulla.

Question 15

Cerebellum

Answer 15

• responsible for coordination and posture
• does not initiate movement, but is an organizer of voluntary activity initiated elsewhere
• drugs that affect the cerebellum like alcohol will cause ataxia, loss of coordination

Question 16

The neuron

Answer 16

• functional unit of the brain
• nerve cell capable of generating in transmitting electrical signals
• differ in shape and size
• new Neurons are generated continuously and the connection between neurons is constantly being reshaped
• each nerve cell or neuron has three main parts

Question 17

The cell body or soma

Answer 17

• largest part of the neuron
• contains a nucleus and surrounding cytoplasm
• cytoplasm contains abundant vesicles which can be secreted
• two types of projections dendrites and the axon

Question 18

The dendrites

Answer 18

• short, and have highly complex branching patterns
• Function as the receiving antenna for incoming information, and except information through receptors located on the dendritic membranes
• upon receipt, an electric current is generated and directed down the neuron

Question 19

The axon

Answer 19

• Single fibre that extends from the cell body and ends at a Synapse
• continues to carry incoming information away from the dendrites and cell body by way of electrical pulses
• info then passed onto subsequent neurons
• Neurons are activated by other neurons, many neurons can activate themselves spontaneously

Question 20

Synapse

Answer 20

• junction between two neurons
• The area ever one neurons axon ends and another neurons dendrite or cell body begins
• can be a target site for many drugs
• Some drugs interrupting snap dick transmission, others enhance or facilitate it, modifying the activity of the brain

Question 21

Synaptic transmission

Answer 21

• passage of a signal from one neuron to another
• very rapid and usually chemical in nature, meeting at the release of a substance is required in order to activate the other neuron
  Usually, one synapse connects two Neurons
• however, a single neuron can make synaptic connections with many other neurons
• Endo genius chemicals that transmit a signal between two neurons are called neurotransmitters

Question 22

Synaptic transmission steps

Answer 22

• an electrical impulse will travel down the axon of the neuron
  -When the electrical impulse reaches the end of the pre synaptic neuron it causes the vesicles which contain neurotransmitters to fuse with the pre synaptic membrane, releasing the neurotransmitters into the synaptic cleft
  -The neurotransmitters will then diffuse across the synaptic cleft and bind with receptors on the post synaptic membrane
  -Activation of these receptors will cause a change in the permeability of the membrane allowing ions such as calcium to move into the post synaptic neuron
  -This changes the electrical activity of the membrane thereby generating an electrical impulse which will then travel down that neurons axon this process continues until the neuronal signal reaches the target organ causing an effect
  -the continuous presence of neurotransmitter in the synaptic cleft would prevent other nerve impulses from being communicated effectively rendering the neuron so the neurotransmitter has to be removed
  -Can occur by 1 of 3 mechanisms
  -The first is that the neurotransmitters can be taken back up into the pre synaptic neuron through transporters
  -Norapanefron Is removed from the synaptic cleft in this fashion
  -Alternatively (2) the neurotransmitter can be broken down by enzymes in the synaptic cleft this is the case for acetyl choline which is broken down by acetyl cholinesterase into acetate and choline
  -The final mechanism (3) is that the the neurotransmitter can be taken up into adjacent glial cells which are cells that support neurons this process occurs for glutamine
  -Once the neurotransmitters have been removed from the synaptic cleft the post synaptic membrane is able to repolarize
  And prepare for the next neuronal impulse

Question 23

Neurotransmitters and receptors

Answer 23

• hundreds of different types of receptors exist for a large number of neurotransmitters

Question 24

Glutamate

Answer 24

• primary excitatory neurotransmitter in the CNS and is found in almost all neurons
• acts on a family of receptors called the glutamatergic receptors
• important for learning

Question 25

Gamma-aminobutyric acid (GABA)

Answer 25

• primary inhibitory neurotransmitter in the CNS
• found in high concentrations in the cerebral cortex, hippocampus, and cerebellum
• Number of CNS depressants (benzodiazepines) enhance GABA receptor function

Question 26

Acetylcholine

Answer 26

• produces an excitatory response in CNS

- receptors that bind acetylcholine are termed cholinergic receptors two types exist nicotinic and muscarinic

Question 27

Nicotinic receptors

Answer 27

• found in certain regions of the brain

- can be stimulated by acetylcholine or nicotine

Question 28

Muscarinic receptors

Answer 28

• found in many regions of the brain
• involved in learning, memory and cognitive function
• 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 thought to be associated with Alzheimer’s disease

Question 29

Catecholamines

Answer 29

• dopamine and norepinephrine are two catecholamines similar in structure

Question 30

Dopamine

Answer 30

• dopaminergic pathways involved in control of some hormonal systems, motor coordination, and motivation and reward
• Disturbances associated with Parkinson’s disease and schizophrenia, depending on the location of the affected neurons

Question 31

Norepinephrine

Answer 31

• bind to a large number of receptor types, two main classes are alpha and beta
• activation predominantly leads to excitation of the cell.
• pathways targeted by some of the CNS stimulants

Question 32

Serotonin

Answer 32

• in the CNS hyperactivity of the 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

Question 33

Opioid peptides

Answer 33

• three main classes of endogenous opioid peptides exist
• enkephalins, endorphins, and dynorphins
• have varying degrees of selectivity for these 3 opioid receptors: mu, delta and happy
• all options interact with these receptors