CH. 7 - Neuroscience

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Keywords

1. General

1. Nervous system - a collective of nerve ending that enables organisms to receive and respond to stimuli from external and internal environment

2. Neurons - functional units of nervous system.  Converts stimuli into eletrochemical signals.

2. Neuron

1. Action Potential - when a threshold is reached (-50 mv), series of action causes impulse to travel down the axon and invade the nerve terminal, causing neurotransmitter to synapse

2. Axon - long cellular process that transmits impulse away from cell body to next neuron

3. Cell body - contains the nucleus and controls the metabolic activity of the neuron

4. Dendrite - cytoplasmic extensions that receives the information and transmit it to cell body

5. Depolarization - voltage-gated sodium channel opens to allow rapid depolarization, sending signal down the axon

6. Myelin - allows axons to conduct impulses faster, sheath the axon

7. Neurotransmitter - a chemical substance that transmit nerve impulse across synapse

8. Nodes of Ranvier - gaps between segments of myelin

9. Oligodendrocytes - produce myelin in the central nervous system

10. Refractory period - immediately following action potential, a period of rest

11. Repolarization - when voltage-gated potassium channel opens to return cell to negative potential after firing.

12. Resting potential - the potential difference between inside and outside of cell -70 mv

13. Schwann cells - produce the myelin in the peripheral nervous system

14. Synapse - gap between axon terminals of one cell and dendrite of the next cell

15. Synaptic terminals - swellings at the end of axon that releases neurotransmitters

3. Synapse

1. Acetylcholine - chemicals in vesicles called neurotransmitter

2. Anti-cholinesterases - inhibit activity of acetylcholinesterase enzyme, causing undegradable neurotransmitter and causing uncoordinated muscular contractions

3. Botulism toxin - prevents the release of acetylcholine, leads to paralysis

4. Curare - blocks the post-synaptic acetylcholine receptors, leads to paralysis

4. Vertebrate Nervous system

1. Afferent neurons - neurons that carry sensory information

2. Autonomic Nervous system - Involuntary.  Regulates internal environment.

3. Aqueous humor - formed by eye and exits through ducts to join the venous blood

4. Auditory canal - part of the outer ear

5. Auricle - external ear

6. Basiliar membrane - hair cells here are stimulated by cochlea and transduces pressure into action potential

7. Blindspot - the location where optic nerve exits the eye

8. Brainstem - consists of midbrain, pons, and medulla

9. Cerebellum - helps modulate motor impulses initiated by cerebral cortex (hindbrain)

10. Choroid - under the sclera layer that helps supply retina with blood, reduces reflection

11. Ciliary muscles - controls the shape and focal length of the lens

12. Cochlea - inner ear, fluid here is pressured by vibration in ossicles

13. Cones - type of photoreceptors responding to high-illumination

14. Cornea - front of eye and bends/focuses light ray

15. Diencephalon - contains the thalamus and hypothalamus (forebrain)

16. Dorsal horn - sensory information enters spinal cord here

17. Dorsal root ganglia - cell bodies of the sensory neuron

18. Efferent neurons - neurons that carry motor information

19. Forebrain - prosencephalon consists of telencephalon and diencephalon

20. Fovea - spot of cone concentration on retina for vision acuity

21. Ganglia - cluster of neuronal cell bodies in the periphery nervous system

22. Hindbrain - rhombencephalon, consists of cerebellum, the pons, and medullua

23. Hypothalamus - visceral functions and control of endocrine system (forebrain)

24. Medulla - controls autonomic functions like breathing, heart rate (hindbrain)

25. Midbrain - mesencephalon, relay center for visual and auditory impulses

26. Nuclei - cluster of neuronal cell bodies in the central nervous system

27. Olfactory bulb - center for reception and integration of olfactory input

28. Ossicles - three bones consist of malleus, incus, and stapes that amplifies the sound

29. Parasympathetic nervous system - acts to conserve energy and restore the body.  Part of the autonomic nervous system

30. Plexus - network of nerve fibers

31. Pons - relay center to allow the cortex to communicate with cerebellium (hindbrain)

32. Pupil - with help of iris, controls how much light comes through

33. Retina - innermost layer of eye that contain the photoreceptors

34. Rhodopsin - rod pigment that absorbs single wavelength

35. Rods - detects low-intensity illumination and important for night vision

36. Sclera - the thick outer opaque layer, called white of the eye

37. Sympathetic Nervous system - responsible for flight or fight response.  Uses norepinephrine as primary neurotransmitters.  In the Autonomic Nervous System.

38. Thalamus - relay and integration center for spinal cord and cerebral cortex (forebrain)

39. Telencephalon - part of forebrain, major component is the cerebral cortex which processes and integrates sensory and motor. Cognitive thinking.  (forebrain)

40. Tympanic membrane - the eardrum and start of middle ear

41. Vagus nerve - parasympathetic nervous system for the gut area

42. Ventral horn - all motor information exits spinal cord here

43. Vestibular apparatus - involved in maintaining equilibrium

44. Vitreous humor - jellylike material in eye that helps maintain shape and optical properties

  

Neuron

1. Structure

1. Dendrite

1. Cytoplasmic extensions that receive information and transmit it to cell body

2. Cell Body (soma)

1. Contains the nucleus and controls the metabolic activity of neuron

3. Single Axon

1. Long cellular process that transmits impulses away from cell body

2. Sheathed by insulating substance known as myelin

1. Produced by cells known as glial cells

1. In the CNS, oligodendrocytes produces the myelin

2. In the peripheral nervous system, Schwann cells produces the myelin

2. Gaps between myelin is called nodes of the Ranvier

3. Ends in swellings known as synaptic terminals (synaptic boutons)

1. Neurotransmitters are released from these terminals into the synapse

1. Synapse - gaps between axon terminals of one cell and dendrites of the next cells

2. Function

1. Receive signals, pass them to the next neuron

2. Resting Potential

1. When neuron is at rest, the potential difference between extracellular and intracellular space is called the resting potential

2. Neuron is polarized even at rest

1. Due to unequal distribution of ions between inside and outside of cell

2. Typical resting membrane potential is -70 millivolts

1. Inside of neuron is more negative than outside

2. Due to selective ionic permeability of the neuronal cell membrane

1. Potassium can diffuse past, sodium can't

2. Concentration of potassium is higher inside neuron than outside

3. Concentration of sodium is higher outside neuron than inside

1. Maintained by the active transport of sodium potassium pump

2. Negative charged protein trapped inside cell

3. Each time action potential fires, the ionic gradient is disrupted and it must be restored by the sodium potassium pump.  Transports 3 sodium out for every 2 potassium into the cell

3. Action potentials

1. Can be impulses that travel the length of the axon and invade the nerve terminal

1. Causes the release of neurotransmitter into the synapse

2. Nerve cell receives both excitatory and inhibitory impulses

3. If cell becomes sufficiently excited or depolarized where the inside the cell becomes less negative, action potential is generated

4. The minimum threshold membrane is around -50 millivolts, after this threshold is reached, the voltage-gated sodium channel is opened

5. This causes sodium ion to flood into cell down the electrochemical gradient, causing a further depolarization and release of the neurotransmitter

6. The voltage-gated sodium channel will then close, and the voltage-gated potassium channel open to allow potassium to rush out and balance the charge.  This is known as repolarization.

7. Following repolarization, the neuron will need a resting period known as refractory period.

4. Impulse propagation

1. Information transfer from dendrite to synaptic terminal direction only (even if its capable of going in reverse)

2. Action potential propagation goes at different speed depending on the diameter of the axon.

1. Greater the diameter, the more heavily it is myelinated and faster it'd travel

2. Myelin increases the conduction velocity by insulating segments so the membrane is only permeable in the nodes of Ranvier

1. So the action potential jumps from node to node.

Synapse

1. Synapse

1. Gap between the axon terminal of one neuron and the dendrite of another neuron

1. The axon terminal of one neuron is called presynaptic neuron

2. The dendrite of another neuron is called postsynaptic neuron

2. The axon terminal contains thousands of membrane-bound vesicles full of chemical messenger known as neurotransmitter

1. When the axon action potential reaches the nerve terminal and depolarize it, the synaptic vesicles fuse with the presynaptic membrane and neurotransmitters are released

2. The neurotransmitters diffuses across the synapse and acts on receptor proteins and depolarize them until they reach threshold and consequently firing of an action potential

3. Neurotransmitter is then removed from synapse

1. Taken back up into nerve terminal via protein known as the uptake carrier

2. Degraded by enzyme located in synapse

1. Acetylcholinesterase inactivates the neurotransmitter acetylcholine

3. Simply diffuse out of the synapse

3. Drugs may have effects on the Synpase

1. Curare - blocks the post-synaptic acetylcholine receptors so acetylcholine is unable to interact with receptor leading to paralysis.

2. Botulism toxin - prevents release of acetylcholine from presynaptic membrane, leads to paralysis

3. Anti-cholinesterases - inhibits the activity of acetycholinesterase enzyme and acetylcholine is not degraded in the synapse.  This continues to affect the post-synaptic membrane and no coordinated muscular contractions can take place.

Invertebrate Nervous System

1. Protozoa

1. Single cell organisms possess no organized nervous system.

2. May respond to stimuli like touch, heat, light, and chemicals

2. Cnidaria

1. Have simple nervous system called nerve net.

2. Limited centralization

3. Jellyfish have clusters of cells and pathways that coordinate complex swimming movement

3. Annelida

1. Earthworms posses primitive central nervous system consisting of

1. Defined ventral nerve cord

2. Anterior "brain" of fused ganglia

3. Definite nerve pathways leading from receptors to effectors

4. Arthropoda

1. Brain similar to annelida but with more specialized sense organs

Vertebrate Nervous System

1. General

1. Afferent neurons - neurons that carry sensory information about external or internal environment to the brain

2. Efferent neurons - neurons that carry moter information to the brain or spinal cord

3. Interneurons - local circuits, linking sensory and motor neurons in the brain

4. Division of the nervous system

1. Nerves are essentially bundles of axons covered with connective tissues

2. A network of nerves is called a plexus

3. Cluster of plexus is called ganglia in periphery, nuclei in central nervous system

4. Nervous system

1. Central Nervous System

1. Brain and Spinal Cord

2. Peripheral Nervous System

1. Sensory

2. Motor

1. Somatic

2. Autonomic

1. Sympathetic

2. Parasympathetic

2. Central Nervous System

1. Brain

1. Mass of neurons that resides in the skull

2. Interprets sensory information, forming motor plans, and cognitive thinking

3. Consists of

1. outer portion called gray matter

2. Inner portion called inner white matter (myelianated axons)

4. Divided into three parts

5. Forebrain (Prosencephalon)

1. Telencephalon

1. Cerebral cortex

1. Highly convoluted gray matter on surface of brain

2. Processes and integrates sensory input and motor responses

3. Important for memory and creative thoughts

2. Olfactory bulb

1. Center for reception and integration of olfactory input

2. Diencephalon

1. Contains the thalamus and hypothalamus

2. Thalamus

1. Relay and integration center for spinal cord and cerebral cortex

3. Hypothalamus

1. Controls visceral functions

2. Hunger, thirst, sex drive, water balance, blood pressure, temperature regulation

3. Control of endocrine system

6. Midbrain (mesencephalon)

1. Relay center for auditory impulses

2. Role in motor control

7. Hindbrain (rhombencephalon)

1. Posterior part of the brain

2. Cerebellum

1. Helps modulate motor impulses initiated by cerebral cortex

2. Important in the maintenance of balance

3. Hand eye cordination

4. Timing of rapid movement

3. Pons

1. Relay center to allow cortex to communicate with the cerebellum

4. Medulla (medulla oblongata)

1. Controls vital functions such as breathing, heart rate, and gastrointestinal activity

8. Both midbrain and hindbrain together forms the brainstem

2. Spinal Cord

1. Elongate extension of the brain

2. Acts as conduit for sensory information to the brain and motor information from the brain

3. Can integrate simple motor responses (reflexes) by itself

4. Cross section of spinal cord

1. Outer white matter area

1. Motor and sensory axons

2. Inner gray matter area

1. Nerve cell bodies

5. Sensory information enters the spinal cord through dorsal horn

1. The cell bodies are located in the dorsal root ganglia

6. All motor information exits the spinal cord through the ventral horn

7. For simple reflexes, sensory fibers synapse directly on ventral horn motor fibers

3. Peripheral Nervous System

1. Somatic Nervous System

1. Nerves inside skeletal muscles and responsible for voluntary movement

2. Autonomic Nervous System

1. Involuntary nervous system

1. Because it regulates body's internal environment without conscious control

2. Includes

1. Cardiac

2. smooth muscles

1. Blood vessels, digestive tract, bladder, bronchi

3. Motor fibers

4. Sensory fibers

3. Sympathetic

1. Responsible for "flight or fight" response

2. Increases the blood pressure and heart rate

3. Increases blood flow to skeletal muscle and decreases gut motility

4. Dilates the bronchioles to increase gas exchange

5. Uses norepinephrine as primary neurotransmitter

4. Parasympathetic

1. Acts to conserve energy and restore body to resting activity levels after exertion

2. Lower heart rate and increase gut motility

Most important nerve is the vagus nerve, this innervates many of the thoracic and abdominal viscera