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26. Neurotransmitters
Definition: Chemical messengers that transmit signals across synapses.

27. Acetylcholine
Definition: A neurotransmitter involved in muscle contraction and various neural functions.

28. Cholinesterase
Definition: An enzyme that breaks down acetylcholine, terminating its action at the synapse.

29. Central Nervous System Structures

Gray Matter
Definition: Regions of the CNS containing neuron cell bodies, dendrites, and unmyelinated axons.

30. White Matter
Definition: Regions of the CNS containing myelinated axons.

31. Meninges
Definition: Protective membranes covering the brain and spinal cord.

32. Cerebellum
Definition: A brain region that coordinates movement and balance.

33. Medulla Oblongata
Definition: The base of the brainstem, controlling autonomic functions like heartbeat and breathing.

34. Pons
Definition: A brain structure involved in the regulation of breathing and other vital functions.

35. Midbrain
Definition: A region of the brain involved in sensory and motor functions.

36. Thalamus
Definition: A brain region that relays sensory signals to the cerebral cortex.

37. Hypothalamus
Definition: A brain region regulating homeostasis and basic survival functions, including hunger, thirst, and temperature.

38. Cerebrum
Definition: The largest part of the brain responsible for higher cognitive functions.

39. Blood-Brain Barrier
Definition: A protective barrier that restricts the passage of substances from the bloodstream into the brain.

40. Cerebrospinal Fluid
Definition: Fluid that cushions and nourishes the brain and spinal cord.

41. Cerebral Cortex
Definition: The outer layer of the cerebrum, responsible for conscious thought and voluntary actions.

42. Corpus Callosum
Definition: A bundle of nerve fibers connecting the two cerebral hemispheres.

43. Occipital Lobes
Definition: Brain lobes responsible for visual processing.

44. Temporal Lobes
Definition: Brain lobes involved in auditory processing and memory.

45. Parietal Lobes
Definition: Brain lobes responsible for processing sensory information from the body.

46. Frontal Lobes
Definition: Brain lobes involved in motor control, decision-making, and personality.

47. Broca’s Area
Definition: A region in the left frontal lobe responsible for speech production.

48. Wernicke’s Area
Definition: A region in the left temporal lobe involved in language comprehension.

49. Autonomic Nervous System

Somatic System
Definition: The part of the PNS that controls voluntary muscle movements.

50. Autonomic System
Definition: The part of the PNS that controls involuntary functions like heartbeat and digestion.

51. Sympathetic Nervous System
Definition: The division of the autonomic nervous system responsible for the "fight or flight" response.

52. Parasympathetic Nervous System
Definition: The division of the autonomic nervous system responsible for the "rest and digest" response.