The Nervous System PDF

# The Nervous System ## Neuron from rat midbrain (THALAMUS) An image of a neuron from a rat midbrain is shown. ## Human Cortical Neurons Differentiated from iPSCs - Two images of human cortical neurons differentiated from iPSC (induced pluripotent stem cell) showing two states. - **DIV 28...

# The Nervous System ## Neuron from rat midbrain (THALAMUS) An image of a neuron from a rat midbrain is shown. ## Human Cortical Neurons Differentiated from iPSCs - Two images of human cortical neurons differentiated from iPSC (induced pluripotent stem cell) showing two states. - **DIV 28 WT**: Wild type (normal). - **DIV 28 Mutavnt**: Mutant type. - Each image contains three colors. - **Tuj1**: (green) - is a neuronal marker that stains for microtubule associated protein 2 (MAP2). - **Cleaved-Caspase**: (red) - is a marker for apoptosis. - **DAPI**: (blue) - stains the DNA in nuclei. - Scale bar: 50μm. ## Nervous System in Action - A video showing nervous system function is located at the following address: - [https://www.youtube.com/watch?v=IZCZV5-v3S4](https://www.youtube.com/watch?v=IZCZV5-v3S4) ## Autonomic Neurons in the myenteric plexus of the digestive tract An image of autonomic neurons in the myenteric plexus of the digestive tract. ## Regulation - **Homeostasis:** The maintenance of a stable internal environment. ### Two Systems Contribute to Homeostasis: - **Endocrine System:** Regulates the body by releasing hormones (chemical messengers), slow process. - **Nervous System:** Regulates quickly using action potentials (electro-chemical signals) which transmit through neurons (nerve cells). ## Functions of the Nervous System - **Sensory Functions:** Monitors internal and external environments by picking up information using sensory receptors. - **Integrative Functions:** Processing and interpreting sensory input to make decisions. - **Motor Functions:** Initiating and carrying out actions. - Muscle contraction and glandular secretion. ## Organization of the Nervous System - **Central Nervous System (CNS):** Includes the brain and spinal cord. The processing center, integrating sensory input and generating motor output. - **Peripheral Nervous System (PNS):** Includes all neural tissue outside the CNS. Responsible for sensory input and motor output. ### Types of Neurons: - **Sensory Neurons:** Conduct signals from receptors to the CNS. - **Motor Neurons:** Conduct signals from the CNS to effectors (muscles and glands). - **Interneurons:** (Association neurons) confined to the CNS, and are used for processing signals and communicating within the CNS. - An analogy is made between the nervous system and a computer motherboard circuit organization. ## Peripheral Nervous System - **Sensory Receptors:** Receive information from the external environment. - **Motor Endings:** Transmit signals from the CNS to muscles and glands. - **Nerves:** Bundles of neurons and their associated tissues. - **Ganglia:** Clusters of neuron cell bodies located outside the CNS. ## The Peripheral Nervous System (PNS) is Divided into: - **Somatic Nervous System (SNS):** Controls voluntary muscle movement, including the skeletal muscles. - **Autonomic Nervous System (ANS):** Controls involuntary functions, like heart rate, digestion, breathing, and body temperature. - **Enteric Nervous System (ENS):** Located in the digestive tract, controls digestive processes. ### The ANS Has Two Divisions: - **Sympathetic Division:** Prepares the body for "fight or flight" responses to stressful situations, such as increased heart rate and blood pressure. - **Parasympathetic Division:** Returns the body to a resting state ("rest and digest"), slowing heart rate and decreasing blood pressure. ## Autonomic Motor - **Somatic Nervous System (SNS):** One single synapse, at the neuromuscular junction. - **Autonomic Nervous System (ANS):** Two synapses, with a preganglionic neuron in the CNS and a postganglionic neuron in a ganglion. ### Neurotransmitters: - **Somatic:** Acetylcholine (Ach) - **Autonomic:** Acetylcholine (Ach) or Norepinephrine (NE) ### Speed: - **Somatic:** 70-120 meters per second, this is the speed of a race car. - **Autonomic:** 0.5-2.0 meters per second, the speed of a walk. ## Parasympathetic vs. Sympathetic - **Parasympathetic Nervous System:** - Constrict pupils - Stimulates exocrine glands (salivation). - Slows heart. - Constrictes bronchi. - Stimulates stomach, pancreas, and gallbladder activity. - Contracts bladder - Causes erection of genitals. - **Sympathetic Nervous System:** - Dilates pupils. - Inhibits exocrine glands (salivation). - Accelerates heart. - Relaxes bronchi. - Inhibits stomach activity. - Stimulates glucose release by liver. - Relaxes bladder. - Promotes ejaculation. ## Autonomic Motor: Sympathetic - **Neurotransmitters:** - **Preganglionic neurons:** Acetylcholine (Ach) - **Postganglionic neurons:** Mostly norepinephrine (NE), but some Ach is used. ### The majority of sympathetic effects are due to NE: - **Alpha receptors** are responsible for vasoconstriction and pupil dilation. - **Beta receptors** - **Beta-1:** For increasing heart rate and contractility. - **Beta-2:** for airway dilation and muscle relaxation. - **Nicotinic Receptors** found on postganglionic neurons and cause excitation but the action is always brief. - **Muscarinic Receptors** are found on target cells and cause longer lasting excitation. - **Adrenergic Receptors** are found in target cells and cause excitation but have a variable effect, depending on the receptor subtype. - **Emergency situations** activate the sympathetic nervous system. ## Autonomic Motor: Parasympathetic - **Neurotransmitters:** - **Preganglionic neurons:** Acetylcholine (Ach) - **Postganglionic neurons:** Acetylcholine (Ach) - **Nicotinic Receptors:** Are found on postganglionic neurons. - **Muscarinic Receptors:** are found on target cells, and responses are slower and longer lasting. - **Homeostasis:** The parasympathetic nervous system is responsible for maintaining homeostasis, when the body is in a resting state. ## Specificity - *See image.* ### The iris of the eye can be controlled by both the sympathetic and parasympathetic NS: - **Sympathetic:** Dilates the pupils (radial muscles). - **Parasympathetic:** Constricts the pupils (circular muscles). **Key:** - **Parasympathetic:** Cholinergic (Ach) - **Sympathetic:** Adrenergic (NE)